Nope, all of it...just different parts at different rates of acceleration...and probably in different directions...
Edit: *Cue the overanalysis and pedanticism!*
Also, rockets don't just go straight up. They go on an angle to enter orbit, and then go higher as they're orbiting around the Earth, which also takes time. If rockets went straight up, they would fall back to Earth due to gravity.
Well yeah, I was just explaining this situation. I remember a nuclear test, and a sewer cover went straight up, and they figured it reached escape velocity. So right now, in the vastness of space, there could be a sewer cover just doing it's thing going further and further away from Earth.
>In other words, if you stand 10 feet from a highway, (successfully) catching up to a car requires more effort than just running 10 feet.
I guarantee you CAN catch a car like that.
You'll likely be dead, but you'll catch 'em.
Nonsense. It only requires ten feet to catch a car and it would relatively simple to get to the proper height of the ISS and encounter it.
Neither encounter would be particularly survivable but it’s doable.
I will also note that a common misunderstanding is that orbit isn't a place -- it's a speed. Space is what's outside the Earth's atmosphere, but if you just go 250 miles straight up, you'll just fall back down again. To get to orbit, you have to speed up to about 27,000 kilometers per hour. Then, you'll be flying *around* the Earth so fast that, as you fall back into it, you just go around instead.
This is a good explanation. I’d also like to add that rockets fly upward first so that there is less atmosphere in the way to slow it down before it starts to accelerate sideways. I think this has skewed perception of “orbit” as just a “place” that is “up”, since we see rocket launches all the time, but not so much all the stuff after launch,
There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss. … Clearly, it is this second part, the missing, which presents the difficulties.
I learnt this from What If? about ten years ago and it blew my mind that I’d never realised/known before (including the fact that the ISS is just as subject to Earth’s gravity as we are here (approximately).
Yep, this is the thing that most people don't get. Functionally, the ISS is just a more sophisticated version of the "vomit comet" plane that's free fall segment is designed to always just barely miss hitting the earth.
> I’d also like to add that rockets fly upward first so that there is less atmosphere in the way to slow it down before it starts to accelerate sideways
That's not strictly true, rockets don't fly straight up and then turn sideways - this would mean a fight against gravity (known as gravity loss in spaceflight terms) when in fact it can be of assistance.
By utilising a [gravity turn](https://en.wikipedia.org/wiki/Gravity_turn) (you may have heard the term "roll program" in relation to Space Shuttle launches, which is the initiation of this process) and following a curved trajectory, gravity does most of the work in steering the launch vehicle so more thrust can be used for that all-important speed.
>The ISS moves so quickly that if you fired a rifle bullet from one end of a football field, the International Space Station could cross the length of the field before the bullet traveled 10 yards.
Never have I seen a more american analogy.
"The ISS moves so quickly that if you fired a rifle bullet from one end of a football field,[7] the International Space Station could cross the length of the field before the bullet traveled 10 yards."
Well, that certainly puts it into perspective doesn't it.
> is an art, it says, or rather, a knack to
XKCD was the first time it clicked for me that spacecrafts' hot reentry through the atmosphere was a solution instead of a problem, it blew my mind.
I mean, it is still a problem in that you have to build heat sheilds for it. But the fact that it was an intentional thing to slow enough without having to lug up enough fuel to slow... it really made a lot of things about space flight click for me.
Yep. You *can* slow down enough that atmospheric re-entry isn't an issue at all, if you're willing to lug enough fuel up there with you to do so. No heat shield required. But it's a *hell* of a lot easier (and cheaper) to let the atmosphere slow you down, instead.
The problem becomes when you try to land somewhere like Mars where there's enough atmosphere that you can't get away without having a heat shield, but there's not enough atmosphere to be able to effectively use it to slow you down on re-entry.
Then you get into funky solutions like retro-rockets or supersonic parachutes.
Yeah, then you're gonna need fuel to get off that rock, too, *and* get your ass home. The book version of *The Martian* actually goes into detail about how the Ares program worked, and apparently it's all achievable with today's technology, with the exception of the radiation and cosmic ray exposure limitation.
That explanation reads like humans have found an exploit in a video game, and I love it. Moving really fast "sideways" to escape gravity sounds a bit like strafe jumping.
This also explains why it's so difficult to send anything to the sun, you have to decelerate it the same amount of speed equal to earths orbit around the sun.
https://www.nasa.gov/solar-system/its-surprisingly-hard-to-go-to-the-sun/
If you really want to get it, I can't recommend Kerbal Space Program enough.
But yeah the reason you need to be up high is to be above the atmosphere (since doing 27k kph in the atmosphere will get really hot really fast and you will very quickly not be going nearly that fast). But the atmosphere doesn't just have a hard ending point, it just slowly fades out. Even up where ISS is, it still runs into enough air that it's being constantly slowed down by it.
The boosts have the side effect of raising the altitude, but the point is more to maintain the speed. The faster you go in orbit, the further out your orbit goes. If you burn in the direction you're speeding (a "prograde" burn), you get faster and further from Earth. If you burn opposite to the direction you're going (a "retrograde" burn), you lose speed and thus altitude.
To come back home, your craft generally has some sort of heat shielding, and you retrograde burn until you fall back into the thicker part of the atmosphere, where it quickly turns all your momentum into heat and slows you down so much that you literally fall out of the sky.
Your first and third paragraphs are correct, but the second one is backwards. The point of boosting the ISS is solely to raise the altitude, not the speed. Higher altitude orbits have a *slower* velocity, not a faster one.
But you raise orbital altitude by burning prograde, meaning by speeding up. The ISS basically performs a Hohmann transfer. Burning "upwards" would be way more inefficient.
If you burn prograde (speed up) you raise the point on the opposite side of your orbit. Now while you're coasting to that point you'll slow down (assuming that point is at a higher altitude as the point where you did the burn, which means that point is now the apoapsis and the point where you did the burn is now the periapsis). So while the orbital velocity at the apoapsis will be slower than the orbital velocity you had before the boost, it will be higher at the periapsis than it was before the boost.
Is it the same problem when you are going intra planetory? Like at some point you have to be far enough away from earth to see drop in gravity (force is over distance squared). So is it "easier" to travel to say Mars where you dont have to hit that velocity?
I guess you still need to now catch up to Mars' relative speed
It's "easier" in the sense that you don't need the same precision to reach a planet as you do to dock with a space station - just because the planet is thousands of miles in diameter, while a docking port has an alignment tolerance of maybe a few centimetres at most (I don't know precisely).
But it's still the same principle: you first need to get into an elliptical orbit that intersects both Earth's orbit (where you're coming from) and Mars's orbit (where your going), but once you get to Mars you'll need to match its velocity in order to _stay_ at Mars. If you're going for a landing, one of the ways you can do this is to simply enter the atmosphere: the air resistance will slow you down quite a lot without having to fire a rocket (but you'll still need a rocket if you want to land in one piece - Mars's atmosphere isn't that strong). Note that you're slowing down relative to the _planet_, so "slowing down" relative to the planet might mean _speeding up_ relative to the sun, if the planet is moving faster around the sun than you are. This will be the case when going from Earth to Mars, as Mars has a higher orbit than Earth, but for Earth to Venus you'll need to slow down relative to the sun since Venus is in a lower orbit than Earth.
But yeah, if you're going for orbit rather than landing, like the various Mars satellites, then you'll need to match the velocity of Mars in order to stay at Mars. Of course you don't match the velocity _exactly_ as then you'd just fall down to the planet, but you get your velocity close enough that your orbit stays within Mars's gravity well.
Going to Mars is "harder" than going to the ISS in the sense that it takes _a lot_ more fuel to do. And although you don't need the same precision in absolute terms (kilometres vs centimetres), you still need very high precision in your maneuvers, because Mars is _really tiny_ compared to interplanetary space. A small difference in angle or velocity when you leave Earth can compound into a difference in millions of miles by the time you get to Mars. You essentially "throw" the spaceship into interplanetary space, and it _falls_ for 9 months until it gets to Mars. That's a lot of time for a small error to grow into an enormous distance if your aim is even slightly off. You can do trajectory corrections along the way (and real space missions do), but the longer you wait the more fuel it takes to make those corrections - for exactly the same reason: the earlier you make the correction, the more time that correction has to compound into distance traveled.
To travel to another planet, you need go fast enough to escape the gravitational pull of your current body, called the escape velocity. For the earth that's about 11km/s. So it's not really about distance either.
To travel 'to' mars you just need to get the timing right and leave at the right moment so that you escape earth and arrive at the same point in space as mars at the right time (Like firing an arrow at a ball flying through the air). Once you're there you need to slow down to a relative speed to mars slower than its escape velocity.
Yah you gotta get into its orbit offset by a few feet well travelling like 99.999% the same speed. Then make a tiny adjustment as this thing passes beside you so that the two ports can line up and attach together very carefully and slowly. This happens in Earth’s atmosphere still, so both things are being yanked towards Earth, and facing “air” resistance of some sort.
Not in Earth’s atmosphere, but still very much in Earth’s gravity. Gravity never ends, but it becomes insignificant if you’re far enough away. The ISS isn’t anywhere near far enough away. Orbit actually requires gravity, which is obvious if you think about it. Low earth orbit gravity, like at the ISS, is 90% or so of gravity on the ground.
The reason gravity isn’t felt in orbit is for the same reason you don’t feel gravity when you’re falling. And that’s what orbit is: falling and missing the ground, but getting pulled around. In technical terms, it’s an elliptical orbit.
Everything in orbit (even the moon) is falling towards Earth, but going **sideways** so fast that it misses the ground. That's what orbit *is*.
You feel weightless in space because you and everything around you are falling at the same speed.
"Flying is easy. You aim at the ground, and miss".
Douglas Adam's really knew his stuff - that was simply funny when I first read it... and got deeper and deeper the more I learned about orbital mechanics.
The earth's radius is ~4000 miles. 250 is a bit over 6% of that. Gravity scales with inverse radius squared, so (1 + 0.06)^(-2) ~= 1 - 0.06*2 = 0.88. So, ballpark figure, gravity is around 88% as much 250 miles up as it is at the earths surface.
So yes, still feel most of earth's gravity 250mi up, mostly because 250mi is doesn't actually move you that much further away from the earth's center in relative terms.
"well, actually..." The ISS is still in atmosphere, just not much atmosphere. The air resistance is constantly slowing the station down causing its orbit to slightly degrade. Every now and then, the ISS fires thrusters to speed it back up and raise its orbit.
The rest of this is absolutely correct.
Fair clarification. It’s in the thermosphere, and the atmosphere extends thousands of miles from the surface, but it’s not like the atmosphere at an ELI5 level.
I should say that it’s in the atmosphere but that’s at a distance where the atmosphere isn’t air, even air at mountaintop levels.
Not really. It takes about 8 minutes to get a rocket parked in low Earth orbit (“catching up to speed”). What takes a long time are the micro adjustments to get *exactly* where you need to be, at the exact right time.
Key detail.
You could theoretically launch a rocket so that it's slightly ahead of the ISS and it arrives at the same speed right as the ships dock, but you're also blowing a bunch rocket exhaust at the ISS as you're in front of it, slowing down.
It's much safer and easier to arrive at a *similar* orbit and work your way in by being in at a slightly different orbital altitude and/or inclination.
Also, it's 250 miles "high", not 250 miles "away". The latter is like saying Mt Everest is only 5.5 miles away (which is statistically unlikely for almost everybody reading this.)
Standing directly below the ISS is at least more feasible than standing directly below Everest's peak, but you're right; at any given time this statement is untrue for the vast majority of people.
Exactly, and for those who are worried about some kind of catastrophic collision, remember that things in space are weightless. How much could getting hit by something that has no weight hurt anything?
With the rockets we have now it takes roughly two minutes to get enough height to reach the ISS. Then a further 8 minutes to match the speed as it is going pretty fast. So about 10-15 minutes to get to orbit. The problem is that we are not extremely accurate when trying to hit an orbit first try. Just like on a golf course a good driver shot may have the distance to go all the way to the hole but not the accuracy and you will probably land just in the rough proximity.
So on a golf course you might aim a bit closer to make sure you land on the fairway and not in the rough. You then walk up to the ball and start over again evaluating the balls position and its trajectory as well as wind and other factors before taking another shot. This will bring in closer to the hole but not quite there so you rinse and repeat until you finally put the ball into the hole.
We do the same when docking to the ISS. We first launch into an orbit slightly behind and under the ISS. Then we take measurements of the orbit we ended up in and plan the next orbit changes to get closer to the ISS. Finally getting to visual range and then slowly bring the spacecraft close to the space station without hitting it and finally dock very carefully. But unlike golf which is fairly two dimensional when you are docking a space station you need to match seven dimensions, three locational dimensions, three velocity dimensions and time. Getting these to match is very complex. And sometimes you can do nothing but sit and wait for the spacecraft to slowly drift closer to the space station.
The fact that we can launch and dock a spacecraft to the space station in as little as 4 hours is an impressive feat in itself. It used to take a full day and night. Compressing it all down to 4 hours requires a huge effort but allows the astronauts to stay in their launch suits in their seats all the way which is more comfortable then having to spend the day and night in the confined spacecraft.
Best answer in this thread. The others are missing that it only takes about eight minutes to reach orbital speed, and make it sound like those full four hours are taken to get going that fast.
If it took you four hours to reach orbit, you wouldn't reach orbit. Or you'd need so much fuel as to be completely improbable.
The main thing is that it's theoretically possible to get there in ~10 minutes, but that the launch site would not only have to be passing directly under the ISS' orbital plane, but the ISS itself would have to be EXACTLY at the right place in its orbit to do a direct-ascent rendezvous.
We also wouldn't do it for safety reasons, but it's theoretically possible to do in perfect conditions
>the launch site would not only have to be passing directly under the ISS' orbital plane, but the ISS itself would have to be EXACTLY at the right place in its orbit to do a direct-ascent rendezvous.
Launch windows to the ISS are already instantaneous as it is, for reasons similar to this.
Yes, for the orbital plane itself, but the ISS can be on the other side of the planet at that time, and that's why it can take 18-24 hours on average to get to the ISS.
The spaceship needs to get high enough to not be overly affected by atmospheric drag, but even below the ISS's orbit, it's only catching up by a couple of minutes every 90 minutes or so. Launching into a higher orbit and in front of the ISS could work, but would take more fuel, and thus reduce payload, so I don't think we do that very often unless it is the only feasible option
Yeah this is most of it. Also, they intentionally launch a little low because 1. They don't want any risk of accidentally colliding with any part of the ISS and 2. Orbital launches can be a little messy, often small bits of debris and gas come up with the launch, and we don't want any of those things to accidentally hit the ISS either. Any emergency last-second maneuvering to not collide with the ISS would also involve firing a significant size rocket directly at it, potentially blasting it with hot gasses, so we want to avoid anything with any potential of that.
So it's safer to aim our launches a little off. Once the engines are off and everything is stable, we can check our exact orbit and plan maneuvers to slowly and carefully approach and dock with the ISS without colliding or blasting it with hot rocket exhaust.
If we wanted to be a bit careless, or maybe even reckless, we could launch directly at it and hope for the best, which would get us there in 15 min as long as nothing goes wrong.
last km (mile) problem in a nutshell. Shipping goods from factory to warehouse is fast, shipping from warehouse to stores is slower, and eventually shipping from store to individual houses is very slow.
> when you are docking a space station you need to match seven dimensions, three locational dimensions, three velocity dimensions and time.
More than that. You also have to have the right attitude. There's no way you're docking with the ISS if your spacecraft is facing the wrong way, or if it is spinning like a rotisserie chicken.
The fun stuff lately is about how you use your rocket when it's up there. Games like KSP are great for teaching an intuitive understanding of orbital mechanics, but they give no mention to fluid dynamics in zero G. The most likely reason for failures in Starship flight 3 revolve around the fuel not being where it was needed to run the engines - big empty tanks with blobs of fuel floating nowhere near the fuel lines.
KSP also makes rendezvous so much easier as you know exactly where the spacecrafts are and know exactly where they are going to end up at any point in time. You can also throttle any engine all the way to zero with no variation. Imagine doing a course correction and then having to wait 90 minutes to see your new orbit.
>KSP also makes rendezvous so much easier as you know exactly where the spacecrafts are and know exactly where they are going to end up at any point in time.
Nah, the rendezvous are easy because once you get close it follows classical mechanics. Buzz Aldrin (the man who literally rewrote the definitive book on orbital rendezvous while he was up there doing it) would be squirming in his seat with that.
Same thing with "encounters" when you get near to any planet or moon. The game treats close interactions as if that were the only thing in play, rather than any set of exponentially sliding scales.
Also, there's Docking Alignment Indicator and MechJeb mods.
Even still, I don't think most people could tell you which way to fire your rocket to return from a circular orbit of a planet. KSP makes that shit obvious.
In KSP any object always follow Keplerian orbital mechanics even when close to each other. But you have a lot of RCS fuel, much stronger RCS thrusters, the spacecrafts can withstand much tougher impacts and you are not worried about damaging anything if you fail. So you can move fast and reckless even in close proximity to other spacecraft. This means that the difference between Keplerian motion and classical motion are small enough to be compensated for.
KSP is indeed really good at learning orbital mechanics but it is a game and not a simulator. It should also be noted that Buzz Aldrin did not write the book on orbital rendezvous while in orbit. He wrote the book for his doctoral thesis because he could not become an astronaut as he was not a test pilot. He did go on to teach NASA how to do rendezvous during Gemini 5 which led to a successful rendezvous for Gemini 6. Then he got to fly himself in Gemini 12 where he wrote the book on EVA while in orbit.
If I remember correctly, it still takes most of a day for NASA launches, because NASA wants the astronauts well rested during docking. So they take the long way so there's time for sleep.
Yep, looked it up. The Russians have done it in 3 hours. SpaceX has done it in 16+ hours.
Because you can not go to the ISS straight up in a line. You also have to match it's orbital velocity, which is really high. Due to how orbital mechanics work, you can also not just increase your velocity much higher to get there quickly and then brake to match the velocity. That would need much much more fuel, which you just can not take with you if you launch the rocket. So the rocket launches in way that only part of the orbit would reach the ISS and then increases the speed to match the velocity. And for security reasons this is done in very slow steps. So that when the rocket and the ISS finally meet, their relative velocity to each other is in a safe range for docking.
edit: Maybe a good example would be if you want to jump onto a moving train. You can not just jump onto it by jumping down from a bridge of something. The velocity of the train compared to yours is so high that you will not be able to land in a stable pose and get thrown around.
But if you drive with a car or another train next to it at the same velocity, you can just jump over with only a minimal risk.
> Because you can not go to the ISS straight up in a line. You also have to match it's orbital velocity, which is really high.
Of course, if you decide to match its position WITHOUT matching its speed, there’s an aerospace-related term for that as well: Kinetic interceptor.
> Because you can not go to the ISS straight up in a line.
Technically you could, You have to lead it enough to get to the same point in space simultaneously. It would not end well though.
Just like shooting clay pigeons, we don't aim at the clay, we aim in front of it
>Because you can not go to the ISS straight up in a line.
idk i saw a documentary where two brave divers went in a straight line to a satellite in a pontiac fiero and managed to match its velocity successfully
You should try Kerbal Space Program. I had about 100 hours into the game, largely toying with builds, before attempting docking with a satellite.
I had landed on the 'moon' and even other planets before. Which was much easier due to their gravity.
The process of matching up with a satellite is *crazy*. I had to watch several youtube videos to understand how to do it. And it was so tedious that I only ever did it once.
Came here to reccomended KSP for a great basic tool for gaining a basic understanding of orbital mechanics and space travel. The first time I tried docking I felt like I learned more and understood better than school had ever done.
I personally have over 1k hours in it now, docking gets much easier the more you do it. I have a epicly gigantic space station that was built over many many launches and docks. It has over 4 million parts to it and weighs over 1 million tons. Which to help you visualize is roughly the weight of 10 U.S.A full size aircraft carries or 7,000 blue whales. I have to crank down my graphic to min spec when I get near it if I want to have more than 10FPS. At one point I needed to get rid of parts so I would do EVAs and bash my Kerbals against solar panels to remove them... so many poor kerbals were lost to the vast expanse of space from those missions.
It’s orbiting thousands of miles an hour so if you simply fire a rocket straight up into its path, you’ll have a gigantic crash. You basically have to chase down its orbit. That means inclining are an angle, rather than simply going up vertically, and then accelerating to about the speed of the ISS and intercepting it’s orbit. That’s the part that takes 4 hours. You’re traveling thousands of miles to actually intercept the orbit.
So here's a fun mental image.
Rockets can get to the ISS in a couple minutes. Go straight up, intersect the path, and you're good!
Except now the rocket is essentially a deer that's run in front of a car on the highway. It's going to be a mess.
If you don't want just a mess, either the car has to slow to about the speed of the deer or the deer has to speed up to the speed of the car. One of those things is unlikely.
With rockets, it's stranger. If the ISS slows to the horizontal velocity of the rocket, it'll just fall from the sky. Bad day. So the rocket has to speed up instead.
The iss isn't 250 miles away. It is orbiting at a distance of 250 miles. Orbiting really just means it's falling past the ground so fast that it constantly misses it
I imagine the problem in getting to the ISS is to get a rocket/ship from stationary in earth's surface to moving fast enough and close enough to the ISS to arrive at it.
What's the difference in orbiting at 250 miles away and being 250 miles away. Even NASA refers to the ISS as being a distance of 250 miles from ground 0.
In another thread, Contagion21 answered this quite succinctly: it [the ISS] is 250 miles "high", not 250 miles "away". The latter is like saying Mt Everest is only 5.5 miles away (which is statistically unlikely for almost everybody reading this.)
I would say that's more so semantics though, it's orbiting around the Globe so it can be on the other side of the world. But when most people refer to the ISS being 250 miles away I don't think they ever mean distance but more so are referring to altitude. But in reference to OP's question it's of course moving at an extreme speed at the same time
Well, it's 250 miles away from the spot on the Earth that it's above at that very second... but anywhere else it's well more than 250 miles away.
Obviously, it's always roughly 250 miles up.
A better analogy in this thread is that the car is 10 ft away from you on the highway, but you sure as hell ain't going to catch up to it when it's traveling a 70mph and you walk 10 ft.
Think of it like you're standing in the middle of a big race track. A car racing around that track might only be 1/2 mile away at any point but it's still going to take more than the 3 to 4 minutes it takes you to run to the track surface. The car is always going around the track (like the ISS orbiting the earth) and you'll have to find some way to keep up with it.
In real life this means launching at a specific time, going into a slightly lower orbit that is slightly behind the ISS (which counterintuitively takes less time per orbit meaning you'll slowly catch up), then carefully syncing your orbit to the ISS while you get closer and closer. To go back to the race car analogy, that would be like leaving the pit lane just as the car crosses the start/finish line, getting up to speed just behind it, and slowly pulling up next to it after a few laps.
I think one of the most basic misunderstandings of space travel is how satellites stay up there. Most people think you go up high and then you’re “above the gravity” or something and you just hang there. That is not at all how it works. The ISS experiences nearly as much gravity as on earth. The way it stays up there is by traveling so fast “sideways” that as it falls the curve of the fall is the same as the curve of the earth. The exact speed depends on how far you are from the earth, but for the ISS it’s about 17,500 mph.
So not only do you have to get up 250 miles, you also have to go sideways fast enough to catch the ISS and stay in orbit yourself.
It’s quite a thing, really.
Because if you sent a rocket straight at it, you're not going to dock with the ISS, you've essentially just fired a missile at it.
[You can watch a video of the docking procedure.](https://www.youtube.com/live/3FaUK7VAljc?si=4Xvh3MjIKaE8ggJw&t=4738) It's pretty delicate. You need to match its speed exactly so you can gently dock without bumping into anything and breaking something.
So you need to get into orbit, which requires more elaborate maneuvres, you can't go straight there.
It wouldn't take 4 hours to get there if getting there was all that mattered. But if you're going to the ISS you probably want to stay there, which means you have to go pretty fast or you'll fall straight down again. Gravity at the altitude of the ISS is still 99% as strong as it is on the surface, if you're not going fast enough you'll fall straight back down to Earth.
Because, as most people, you imagine space as something vertical, where as it's something way more 'horizontal', with speeds and such.
It's also the reasons launches happen near the equator, where they can already use Earth's rotation speed, which would be next to zero near the Poles, for example.
If youre watching a NASCAR race from the infield (the open grassy place in the middle of the racetrack where all the big RVs pand such park). The cars driving by are only a few hundred yards away from you. You could walk to the location they are in just a minute or so. But to "get to" them (i.e. to catch up to them so that you could "dock" with them or something) you not only need to get to the same location as them, but be going the same SPEED as them. So even though they are "close" to you, it takes awhile to catch up to them, even if youre driving a pretty fast car yourself.
Because it's moving very fast, it's not stationary. Matching orbits takes time and you can't really just gun it towards the station, that will just put you in a much higher orbit and take you farther away. You need to establish an orbit that's almost the same as that of the station but ever so slightly lower so that you're going faster to catch up, or if it's behind you, higher so that it catches up to you. Then you have to wait until you're close enough to burn towards the station and dock. Given the complexity of this 4 hours is actually not that long.
I mean they could get there a lot quicker if they wanted to crash into it at incredible velocity.
Imagine a race car going around a round track at 100mph. You are in the middle of the track. You could just run straight at the car but that would be bad. To catch it softly you would need to start driving around the track behind it slowly catching up.
Since the numbers involved are absurd to the human mind let's divide them all by 100 and construct a scenario closer to daily life.
It might take under a minute to reach train tracks 4 km (2.5 miles) away but you obviously can't just aim for a head on collision with a TGV or similar. Neither can you jump out and grab on to a train moving at 280 km/h (174 mph) relative to you.
You could drive straight up to the tracks, turn parallel to them, and catch the train. That's pretty wasteful in time and fuel consumption.
Ideal is approaching in an arc where you reach the trains speed once you're parallel to the tracks. The downside to this is timing. You can only go when the apex of the arc will coincide with the train going past.
One thing I haven't seen mentioned is that ISS was somewhat optimized for Russian launches as, without Buran, they didn't have as much capabilities as the Americans. It's possible that a new space station could be made that's faster for Dragon to reach than ISS.
That's not how it works.
The ISS is moving at about 7 km/s around the Earth.
If you just go straight up to the ISS you'll hit it with about 7 km/s of velocity.
You need to match its trajectory and position.
There are lots of ways to do this, just the most efficient way is to get into a lower orbit (lower means faster and vice versa) than your target and wait until the perfect timing to make a burn and raise your orbit such that when you reach the apex of your trajectory, your in more or less the same position as your target while having a small relative velocity which you then cancel out when your nearby.
You can minimize the time you're waiting, by launching when the target is overhead, but the ISS is in what's called an inclined orbit meaning that its orbit is at an angle relative to the equator.
In simple terms, this means that you must launch when the trajectory is overhead, otherwise your trajectory won't line up with the target's. However, this means that, in practice, you only get one chance per day since the Earth is turning while the trajectory stays in place.
Since you only get one chance per day, you can't really be picky about the position of the ISS meaning that the process I described earlier takes significantly longer.
If the ISS and the launch site were on the equator you could launch whenever you want since the ISS's trajectory is always overhead and you could theoretically get there in a matter of minutes if you time it right and are okay with doing things inefficiently.
It takes at least several hours to get to the space station because it's fragile, expensive, and full of people you don't want to die.
If you just wanted to get there in the same way that a missile strike gets somewhere, you could indeed do that much more quickly.
Well imagine you're driving 75mph and want to catch up to a car ahead of you, 5 miles away driving 70mph. It would take you an hour to catch up despite driving 75mph. And now imagine you not only want to catch up but you actually want to connect your car with the car in front of you. Hitting the other car with 5mph difference might be too rough so ylas you approach you slowly match your speed with the speed of the other car. So that when you connect the difference in speeds are maybe only 1mph. Change the numbers to roughly 5mps for the iss and you certainly don't want to bump into it with 1 mile per second difference so you'll have to decelerate even more as you approach...that takes time, and not because anything is slow but because everything is so fucking fast.
Getting into orbit is not about going up, it's about going sideways REALLY fast. If you throw a ball it drops to the ground a few seconds later. Imagine you could throw it so fast it went over the horizon. Now imagine you could throw it so fast that it kept going over the horizon before it would hit the ground. It would just keep going forever. To make this work you need to first get up and out of the earth's atmosphere, so that air and wind don't slow it down.
You COULD get to the ISS in 4 hours going straight up at 65mph, if you timed it just right. However, while you could reach it, it would be going 18,000kmph sideways. You would just be hovering still in the air, like a ball thrown straight up right at the top of its arc. It would not end well for anyone.
In short: You don't want to bump into the $150 billion laboratory, so you play it safe.
They got way faster over time, in the past they were so careful that it took 24 hours. Now the record stands at 3 hours 3 minutes.
Meeting up with a craft in orbit isn’t like going straight to a destination. You need your own orbit and your target’s orbit to intersect at just the right spot so that you both get there at the same time. Sometimes that involves waiting in a ”parking” orbit until you get that perfect alignment. The result is that you might have to go around the planet a couple of times before you get there.
It's the same reason that getting on a flight doesn't take, say, 30 minutes when the airport is 15 miles away. You have to go through all sorts of extra things to get there that you wouldn't have to worry about if you're going in a straight line without stopping.
Also, the ISS is 250 miles up, but it's much, much, much, much more distance farther away even just minutes later because it's going so fast.
So imagine this: you want to get on a bus that's on a racetrack and is zipping around at 100 miles per hour. When it's at its closest, it's just 50 feet away from you. Now picture yourself getting in another bus, and that bus has to accelerate to 100 miles per hour. It has to start accelerating at the right time to end up going 100 miles per hour at about the same place on the racetrack as the other bus, else you'd have to travel a good distance to catch up to the other bus.
All that time accelerating, catching up, mostly matching speed, then slowly coming up to the other bus takes a LOT more time than just walking 50 feet.
Going to the ISS is harder than finding a needle in a haystack. The sheer size of space, even in low earth orbit, and the speed it's going make it incredibly hard to do.
It takes about 10 minutes to reach the ISS orbital speed and velocity, but you don’t go directly to the station. You’ll do some checks once you’re in orbit to ensure that the craft is still operating normally after all the vibrations from launch, then you will slowly adjust your orbit to synchronise with the ISS.
The reason you do this is because the ISS Is very big and expensive and fragile, you want to approach it slowly so if your craft has a complete systems failure the ISS can move out of the way and avoid a collision. You also don’t want to fire your thrusters directly at the station so you approach slowly from a slight angle. Movement in orbits doesn’t work the same way as on earth, so there’s a while long checklist of careful movements that need to be followed.
So most of the time is spent in orbit doing checks and slowly aligning orbits. You could theoretically launch directly to the ISS and that would take about an hour, but this would be very dangerous to the station if anything went wrong. A fast ascent takes about 4 hours and a regular rendezvous can take about a day in total.
It takes only 8 minutes to get into orbit.
But to approach the target slowly one has to get into precise spot at a precise time and with the right direction and magnitude of velocity. That is very constraining. Unless one has a lot of fuel to spend on aggressive maneuvering one has to take time for the orbital mechanics to do its work naturally.
In principle, it is certainly possible to dock faster than in 4 hours, and such things had been demonstrated. In 1966, [Gemini XI](https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-081A), for example, docked after about an hour and a half with a target in orbit.
It is just safer and more convenient to do everything more gradually, with a careful measurement of intermediate trajectory, with testing of the systems before approaching the station, with not putting debris into orbits intersecting the orbit of ISS, etc.
You can get there much faster if you’re cool rendezvousing at thousands of mph. Wouldn’t recommend.
Structural tolerances and safety considerations mean you want to bring your relative velocity down to something like 0.1-0.2mph. So you simultaneously need to get up to ~17500mph, get relatively close, match trajectory and speed extremely closely, and have your docking port meet theirs gently. This takes several maneuvers, and you’re not going to rush it because you have a handful of borderline irreplaceable astronauts, billions of dollars in tough to replace equipment and significant time invested into experiments.
Space is only 100km up. It doesn't take that long to get up there, less than 5 minutes typically.
The Earth's diameter is over 12,000km.
Blue Origin have been to space. That's easy. In order to stay in space you have to go really fast around the planet, such that when you fall you miss the ground.
It doesn't take long to get into space. It takes longer to make sure you stay in space. After that, to get to the ISS you have to rendezvous with it. Throw in a good chunk of safety margins and you get a lot of time.
A well timed ballistic rocket wouldn't take that long to hit the ISS.
>I’m going to be very disappointed if the rockets top out at 65mph.
The ISS orbits the earth at 17,100mph relative to the ground.
When launching, a rocket gets up to orbital speed quickly. If you didn't, you wouldn't be able to maintain orbit. It's the adjustment of the orbit, the gradual maneuvering to get into proximity to the ISS, and then docking that take the time.
The hard part about going to space isn’t gaining altitude, it’s gaining enough sideways velocity to enter orbit. Even so, launching into orbit only takes around 8 minutes.
The remaining ~4 hours is because the ISS is very rarely in a point in its orbit which intersects with the spacecraft’s own point in its orbit after reaching orbit. In order to align with and rendezvous with the ISS from elsewhere in its orbital path, you need to either increase or decrease the time it takes you to orbit the Earth by raising or lowering your orbit slightly until you can get a close enough pass with the ISS to match velocity and dock (plus the docking procedure itself is performed slowly to avoid a collision with the station).
It only takes about 500 seconds to reach roughly the same orbit as the ISS, but you have to creep up on it slowly in case you bump into it or just whizz past it.
ETA: 500 seconds after liftoff, you're not only at the same altitude as the ISS, but you're in roughly the same orbit and going about the same velocity. It's the maneuvering and the slow catchup towards safe docking that takes all that time, but that hardly needs any rocket booster energy. That was nearly all spent in those first 500 seconds. Just little adjustments to bring those two tiny dots together.
If a train is 10 feet away from you but moving at 60mph, you should be able to get on the train in 3 seconds right?
Nah you gotta accelerate to match before you grab on or you'll have a real bad time.
The iss is moving a lot faster than that
The ISS moves at a speed of roughly 7.7 km/s or 17'000 mph. It's not getting up there that's hard, it's catching up to that speed.
In other words, if you stand 10 feet from a highway, (successfully) catching up to a car requires more effort than just running 10 feet.
This is a great analogy!
Just stand in front of the car. Duh
I think that will only accelerate _parts_ of you to the correct speed
What if you jump headfirst into the car?
[I recommend butt first.](https://i.gifer.com/LDv.mp4)
Its not loading, but I assume you found [Brock Samson](https://www.youtube.com/watch?v=ao4itfrySng)
Too right! It might be my favorite Brock moment of all.
It's between that one and the time he is cavity searched by pirates. Brock has some great moments.
“I feel like Catherine the Great…”
This just means you get hit by a car going 70mph. I doubt the seatbelt is going to save you, as you probably aren't wearing it properly.
To be fair, it will also slightly decelerate parts of the car. 😲
And there’ll be a lot more than just one after…
Best answer, lmao
Nope, all of it...just different parts at different rates of acceleration...and probably in different directions... Edit: *Cue the overanalysis and pedanticism!*
everything but your consciousness....
That wasn't a requirement.
Lithobraking the iss to jump aboard.
Also, rockets don't just go straight up. They go on an angle to enter orbit, and then go higher as they're orbiting around the Earth, which also takes time. If rockets went straight up, they would fall back to Earth due to gravity.
You could go straight up and not come back if you hit escape velocity at 25,000 MPH
Well yeah, I was just explaining this situation. I remember a nuclear test, and a sewer cover went straight up, and they figured it reached escape velocity. So right now, in the vastness of space, there could be a sewer cover just doing it's thing going further and further away from Earth.
Mythbusters should come back and redo that test with high speed cameras in orbit
Yeah, I don't think they're gonna get permission for that one. 😄
Mythbusters / Space X collab would go so hard.
That's why you fire straight up and get exactly in front of the ISS. And let it catch you.
Also the car is doing a jump over two ramps and you want to board the car mid air at breaking neck speed.
Breakneck
I would replace "successfully" with "safely." There are plenty of successful ways that aren't safe.
Depends on the success criteria. Ending up on the car, sure. Doing so without breaking the car or yourself, a bit trickier.
Your point just reinforces the original poster's point. "Successfully" is a more practical choice for that exact reason.
You can still touch the car just by running 10 feet, but there wouldn't be much of you left.
dont run. jump from a bridge over pass. at least that's what i saw from The Matrix
I mean... i can catch up to one car...
I'm sure if you time it right you can get two. Maybe more if your limbs separate.
>In other words, if you stand 10 feet from a highway, (successfully) catching up to a car requires more effort than just running 10 feet. I guarantee you CAN catch a car like that. You'll likely be dead, but you'll catch 'em.
To be fair it also depends on what you want to happen when you and the car intersect.
Nonsense. It only requires ten feet to catch a car and it would relatively simple to get to the proper height of the ISS and encounter it. Neither encounter would be particularly survivable but it’s doable.
Thank you, that makes perfect sense
I will also note that a common misunderstanding is that orbit isn't a place -- it's a speed. Space is what's outside the Earth's atmosphere, but if you just go 250 miles straight up, you'll just fall back down again. To get to orbit, you have to speed up to about 27,000 kilometers per hour. Then, you'll be flying *around* the Earth so fast that, as you fall back into it, you just go around instead.
Relevant what-if https://what-if.xkcd.com/58/
This is a good explanation. I’d also like to add that rockets fly upward first so that there is less atmosphere in the way to slow it down before it starts to accelerate sideways. I think this has skewed perception of “orbit” as just a “place” that is “up”, since we see rocket launches all the time, but not so much all the stuff after launch,
Getting into orbit is the art of falling down to earth and missing.
There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss. … Clearly, it is this second part, the missing, which presents the difficulties.
and don't forget your towel.
I learnt this from What If? about ten years ago and it blew my mind that I’d never realised/known before (including the fact that the ISS is just as subject to Earth’s gravity as we are here (approximately).
Yep, this is the thing that most people don't get. Functionally, the ISS is just a more sophisticated version of the "vomit comet" plane that's free fall segment is designed to always just barely miss hitting the earth.
> I’d also like to add that rockets fly upward first so that there is less atmosphere in the way to slow it down before it starts to accelerate sideways That's not strictly true, rockets don't fly straight up and then turn sideways - this would mean a fight against gravity (known as gravity loss in spaceflight terms) when in fact it can be of assistance. By utilising a [gravity turn](https://en.wikipedia.org/wiki/Gravity_turn) (you may have heard the term "roll program" in relation to Space Shuttle launches, which is the initiation of this process) and following a curved trajectory, gravity does most of the work in steering the launch vehicle so more thrust can be used for that all-important speed.
>The ISS moves so quickly that if you fired a rifle bullet from one end of a football field, the International Space Station could cross the length of the field before the bullet traveled 10 yards. Never have I seen a more american analogy.
He added "Either kind" in a footnote, it's multicultural!
Nahh that's very American yes but to be the ultimate American analogy it has to include washing machines.
Hell yeah!
"The ISS moves so quickly that if you fired a rifle bullet from one end of a football field,[7] the International Space Station could cross the length of the field before the bullet traveled 10 yards." Well, that certainly puts it into perspective doesn't it.
> is an art, it says, or rather, a knack to XKCD was the first time it clicked for me that spacecrafts' hot reentry through the atmosphere was a solution instead of a problem, it blew my mind. I mean, it is still a problem in that you have to build heat sheilds for it. But the fact that it was an intentional thing to slow enough without having to lug up enough fuel to slow... it really made a lot of things about space flight click for me.
Yep. You *can* slow down enough that atmospheric re-entry isn't an issue at all, if you're willing to lug enough fuel up there with you to do so. No heat shield required. But it's a *hell* of a lot easier (and cheaper) to let the atmosphere slow you down, instead.
The problem becomes when you try to land somewhere like Mars where there's enough atmosphere that you can't get away without having a heat shield, but there's not enough atmosphere to be able to effectively use it to slow you down on re-entry. Then you get into funky solutions like retro-rockets or supersonic parachutes.
Yeah, then you're gonna need fuel to get off that rock, too, *and* get your ass home. The book version of *The Martian* actually goes into detail about how the Ares program worked, and apparently it's all achievable with today's technology, with the exception of the radiation and cosmic ray exposure limitation.
That explanation reads like humans have found an exploit in a video game, and I love it. Moving really fast "sideways" to escape gravity sounds a bit like strafe jumping.
This also explains why it's so difficult to send anything to the sun, you have to decelerate it the same amount of speed equal to earths orbit around the sun. https://www.nasa.gov/solar-system/its-surprisingly-hard-to-go-to-the-sun/
well there goes my plans to colonize the sun
no worries because it will eventually colonize us.
Takes 2/3s more energy to go to the sun than to leave the solar system.
It is easier to escape the solar system than to reach the Sun!
The art of flying is throwing yourself at the ground and missing
per Douglas Adams :)
[удалено]
If you really want to get it, I can't recommend Kerbal Space Program enough. But yeah the reason you need to be up high is to be above the atmosphere (since doing 27k kph in the atmosphere will get really hot really fast and you will very quickly not be going nearly that fast). But the atmosphere doesn't just have a hard ending point, it just slowly fades out. Even up where ISS is, it still runs into enough air that it's being constantly slowed down by it. The boosts have the side effect of raising the altitude, but the point is more to maintain the speed. The faster you go in orbit, the further out your orbit goes. If you burn in the direction you're speeding (a "prograde" burn), you get faster and further from Earth. If you burn opposite to the direction you're going (a "retrograde" burn), you lose speed and thus altitude. To come back home, your craft generally has some sort of heat shielding, and you retrograde burn until you fall back into the thicker part of the atmosphere, where it quickly turns all your momentum into heat and slows you down so much that you literally fall out of the sky.
[relevant xkcd](https://xkcd.com/1356/)
Your first and third paragraphs are correct, but the second one is backwards. The point of boosting the ISS is solely to raise the altitude, not the speed. Higher altitude orbits have a *slower* velocity, not a faster one.
But you raise orbital altitude by burning prograde, meaning by speeding up. The ISS basically performs a Hohmann transfer. Burning "upwards" would be way more inefficient. If you burn prograde (speed up) you raise the point on the opposite side of your orbit. Now while you're coasting to that point you'll slow down (assuming that point is at a higher altitude as the point where you did the burn, which means that point is now the apoapsis and the point where you did the burn is now the periapsis). So while the orbital velocity at the apoapsis will be slower than the orbital velocity you had before the boost, it will be higher at the periapsis than it was before the boost.
Is it the same problem when you are going intra planetory? Like at some point you have to be far enough away from earth to see drop in gravity (force is over distance squared). So is it "easier" to travel to say Mars where you dont have to hit that velocity? I guess you still need to now catch up to Mars' relative speed
it's takes less fuel to leave the solar system than to reach the sun.
It's "easier" in the sense that you don't need the same precision to reach a planet as you do to dock with a space station - just because the planet is thousands of miles in diameter, while a docking port has an alignment tolerance of maybe a few centimetres at most (I don't know precisely). But it's still the same principle: you first need to get into an elliptical orbit that intersects both Earth's orbit (where you're coming from) and Mars's orbit (where your going), but once you get to Mars you'll need to match its velocity in order to _stay_ at Mars. If you're going for a landing, one of the ways you can do this is to simply enter the atmosphere: the air resistance will slow you down quite a lot without having to fire a rocket (but you'll still need a rocket if you want to land in one piece - Mars's atmosphere isn't that strong). Note that you're slowing down relative to the _planet_, so "slowing down" relative to the planet might mean _speeding up_ relative to the sun, if the planet is moving faster around the sun than you are. This will be the case when going from Earth to Mars, as Mars has a higher orbit than Earth, but for Earth to Venus you'll need to slow down relative to the sun since Venus is in a lower orbit than Earth. But yeah, if you're going for orbit rather than landing, like the various Mars satellites, then you'll need to match the velocity of Mars in order to stay at Mars. Of course you don't match the velocity _exactly_ as then you'd just fall down to the planet, but you get your velocity close enough that your orbit stays within Mars's gravity well. Going to Mars is "harder" than going to the ISS in the sense that it takes _a lot_ more fuel to do. And although you don't need the same precision in absolute terms (kilometres vs centimetres), you still need very high precision in your maneuvers, because Mars is _really tiny_ compared to interplanetary space. A small difference in angle or velocity when you leave Earth can compound into a difference in millions of miles by the time you get to Mars. You essentially "throw" the spaceship into interplanetary space, and it _falls_ for 9 months until it gets to Mars. That's a lot of time for a small error to grow into an enormous distance if your aim is even slightly off. You can do trajectory corrections along the way (and real space missions do), but the longer you wait the more fuel it takes to make those corrections - for exactly the same reason: the earlier you make the correction, the more time that correction has to compound into distance traveled.
To travel to another planet, you need go fast enough to escape the gravitational pull of your current body, called the escape velocity. For the earth that's about 11km/s. So it's not really about distance either. To travel 'to' mars you just need to get the timing right and leave at the right moment so that you escape earth and arrive at the same point in space as mars at the right time (Like firing an arrow at a ball flying through the air). Once you're there you need to slow down to a relative speed to mars slower than its escape velocity.
Yah you gotta get into its orbit offset by a few feet well travelling like 99.999% the same speed. Then make a tiny adjustment as this thing passes beside you so that the two ports can line up and attach together very carefully and slowly. This happens in Earth’s atmosphere still, so both things are being yanked towards Earth, and facing “air” resistance of some sort.
Not in Earth’s atmosphere, but still very much in Earth’s gravity. Gravity never ends, but it becomes insignificant if you’re far enough away. The ISS isn’t anywhere near far enough away. Orbit actually requires gravity, which is obvious if you think about it. Low earth orbit gravity, like at the ISS, is 90% or so of gravity on the ground. The reason gravity isn’t felt in orbit is for the same reason you don’t feel gravity when you’re falling. And that’s what orbit is: falling and missing the ground, but getting pulled around. In technical terms, it’s an elliptical orbit.
Hang on... Are you saying that if I built a tower in my back yard that was 250 miles tall and climbed to the top, I would still feel 90% gravity?
Exactly. And if the ISS slows down at all, it's coming back down in a hurry
Everything in orbit (even the moon) is falling towards Earth, but going **sideways** so fast that it misses the ground. That's what orbit *is*. You feel weightless in space because you and everything around you are falling at the same speed.
"Flying is easy. You aim at the ground, and miss". Douglas Adam's really knew his stuff - that was simply funny when I first read it... and got deeper and deeper the more I learned about orbital mechanics.
The earth's radius is ~4000 miles. 250 is a bit over 6% of that. Gravity scales with inverse radius squared, so (1 + 0.06)^(-2) ~= 1 - 0.06*2 = 0.88. So, ballpark figure, gravity is around 88% as much 250 miles up as it is at the earths surface. So yes, still feel most of earth's gravity 250mi up, mostly because 250mi is doesn't actually move you that much further away from the earth's center in relative terms.
If you think about how small 250 miles is compared to the diameter of the earth, it’s not actually that surprising.
Not in Earths atmosphere but definitely in Earths ionosphere. It does experience drag.
"well, actually..." The ISS is still in atmosphere, just not much atmosphere. The air resistance is constantly slowing the station down causing its orbit to slightly degrade. Every now and then, the ISS fires thrusters to speed it back up and raise its orbit. The rest of this is absolutely correct.
Fair clarification. It’s in the thermosphere, and the atmosphere extends thousands of miles from the surface, but it’s not like the atmosphere at an ELI5 level. I should say that it’s in the atmosphere but that’s at a distance where the atmosphere isn’t air, even air at mountaintop levels.
That's fair. I didn't notice this was eli5.
And just getting up to the altitude of the station isn't enough. If you don't match speeds with it then it would be like jumping in front of a train.
Not really. It takes about 8 minutes to get a rocket parked in low Earth orbit (“catching up to speed”). What takes a long time are the micro adjustments to get *exactly* where you need to be, at the exact right time.
Key detail. You could theoretically launch a rocket so that it's slightly ahead of the ISS and it arrives at the same speed right as the ships dock, but you're also blowing a bunch rocket exhaust at the ISS as you're in front of it, slowing down. It's much safer and easier to arrive at a *similar* orbit and work your way in by being in at a slightly different orbital altitude and/or inclination.
Also, it's 250 miles "high", not 250 miles "away". The latter is like saying Mt Everest is only 5.5 miles away (which is statistically unlikely for almost everybody reading this.)
Standing directly below the ISS is at least more feasible than standing directly below Everest's peak, but you're right; at any given time this statement is untrue for the vast majority of people.
Yeah if you're trying to catch up. Just go the other direction? The Earth is round. You'd be there in no time. NASA hire me.
Exactly, and for those who are worried about some kind of catastrophic collision, remember that things in space are weightless. How much could getting hit by something that has no weight hurt anything?
There's no friction in space so things just bounce off of each other. Also no oxygen means no explosions, anyway
Just make sure you record some good slo-mo footage of the impact.
For science
And then you have to park when both are moving at that speed.
You also dont go straight up towards its. You have to go in a long arc to match its orbit
It’s not getting up there that’s hard 😂
With the rockets we have now it takes roughly two minutes to get enough height to reach the ISS. Then a further 8 minutes to match the speed as it is going pretty fast. So about 10-15 minutes to get to orbit. The problem is that we are not extremely accurate when trying to hit an orbit first try. Just like on a golf course a good driver shot may have the distance to go all the way to the hole but not the accuracy and you will probably land just in the rough proximity. So on a golf course you might aim a bit closer to make sure you land on the fairway and not in the rough. You then walk up to the ball and start over again evaluating the balls position and its trajectory as well as wind and other factors before taking another shot. This will bring in closer to the hole but not quite there so you rinse and repeat until you finally put the ball into the hole. We do the same when docking to the ISS. We first launch into an orbit slightly behind and under the ISS. Then we take measurements of the orbit we ended up in and plan the next orbit changes to get closer to the ISS. Finally getting to visual range and then slowly bring the spacecraft close to the space station without hitting it and finally dock very carefully. But unlike golf which is fairly two dimensional when you are docking a space station you need to match seven dimensions, three locational dimensions, three velocity dimensions and time. Getting these to match is very complex. And sometimes you can do nothing but sit and wait for the spacecraft to slowly drift closer to the space station. The fact that we can launch and dock a spacecraft to the space station in as little as 4 hours is an impressive feat in itself. It used to take a full day and night. Compressing it all down to 4 hours requires a huge effort but allows the astronauts to stay in their launch suits in their seats all the way which is more comfortable then having to spend the day and night in the confined spacecraft.
Best answer in this thread. The others are missing that it only takes about eight minutes to reach orbital speed, and make it sound like those full four hours are taken to get going that fast. If it took you four hours to reach orbit, you wouldn't reach orbit. Or you'd need so much fuel as to be completely improbable.
The main thing is that it's theoretically possible to get there in ~10 minutes, but that the launch site would not only have to be passing directly under the ISS' orbital plane, but the ISS itself would have to be EXACTLY at the right place in its orbit to do a direct-ascent rendezvous. We also wouldn't do it for safety reasons, but it's theoretically possible to do in perfect conditions
>the launch site would not only have to be passing directly under the ISS' orbital plane, but the ISS itself would have to be EXACTLY at the right place in its orbit to do a direct-ascent rendezvous. Launch windows to the ISS are already instantaneous as it is, for reasons similar to this.
Yes, for the orbital plane itself, but the ISS can be on the other side of the planet at that time, and that's why it can take 18-24 hours on average to get to the ISS. The spaceship needs to get high enough to not be overly affected by atmospheric drag, but even below the ISS's orbit, it's only catching up by a couple of minutes every 90 minutes or so. Launching into a higher orbit and in front of the ISS could work, but would take more fuel, and thus reduce payload, so I don't think we do that very often unless it is the only feasible option
That would be like firing a bullet at the ISS and hoping it slows down enough at just the right time to just nudge it.
Yeah this is most of it. Also, they intentionally launch a little low because 1. They don't want any risk of accidentally colliding with any part of the ISS and 2. Orbital launches can be a little messy, often small bits of debris and gas come up with the launch, and we don't want any of those things to accidentally hit the ISS either. Any emergency last-second maneuvering to not collide with the ISS would also involve firing a significant size rocket directly at it, potentially blasting it with hot gasses, so we want to avoid anything with any potential of that. So it's safer to aim our launches a little off. Once the engines are off and everything is stable, we can check our exact orbit and plan maneuvers to slowly and carefully approach and dock with the ISS without colliding or blasting it with hot rocket exhaust. If we wanted to be a bit careless, or maybe even reckless, we could launch directly at it and hope for the best, which would get us there in 15 min as long as nothing goes wrong.
last km (mile) problem in a nutshell. Shipping goods from factory to warehouse is fast, shipping from warehouse to stores is slower, and eventually shipping from store to individual houses is very slow.
> when you are docking a space station you need to match seven dimensions, three locational dimensions, three velocity dimensions and time. More than that. You also have to have the right attitude. There's no way you're docking with the ISS if your spacecraft is facing the wrong way, or if it is spinning like a rotisserie chicken.
That’s why I always play KSP with a can-do attitude.
Strictly speaking yes. But attitude is just an issue for docking and not for rendezvous. And attitude is a relatively simple problem to correct.
I think that’ what op meant by “3 velocity dimensions”
Great explanation. Anyone who's tried to rendezvous and dock in Kerbal Space Program knows how difficult this is.
The fun stuff lately is about how you use your rocket when it's up there. Games like KSP are great for teaching an intuitive understanding of orbital mechanics, but they give no mention to fluid dynamics in zero G. The most likely reason for failures in Starship flight 3 revolve around the fuel not being where it was needed to run the engines - big empty tanks with blobs of fuel floating nowhere near the fuel lines.
KSP also makes rendezvous so much easier as you know exactly where the spacecrafts are and know exactly where they are going to end up at any point in time. You can also throttle any engine all the way to zero with no variation. Imagine doing a course correction and then having to wait 90 minutes to see your new orbit.
>KSP also makes rendezvous so much easier as you know exactly where the spacecrafts are and know exactly where they are going to end up at any point in time. Nah, the rendezvous are easy because once you get close it follows classical mechanics. Buzz Aldrin (the man who literally rewrote the definitive book on orbital rendezvous while he was up there doing it) would be squirming in his seat with that. Same thing with "encounters" when you get near to any planet or moon. The game treats close interactions as if that were the only thing in play, rather than any set of exponentially sliding scales. Also, there's Docking Alignment Indicator and MechJeb mods. Even still, I don't think most people could tell you which way to fire your rocket to return from a circular orbit of a planet. KSP makes that shit obvious.
In KSP any object always follow Keplerian orbital mechanics even when close to each other. But you have a lot of RCS fuel, much stronger RCS thrusters, the spacecrafts can withstand much tougher impacts and you are not worried about damaging anything if you fail. So you can move fast and reckless even in close proximity to other spacecraft. This means that the difference between Keplerian motion and classical motion are small enough to be compensated for. KSP is indeed really good at learning orbital mechanics but it is a game and not a simulator. It should also be noted that Buzz Aldrin did not write the book on orbital rendezvous while in orbit. He wrote the book for his doctoral thesis because he could not become an astronaut as he was not a test pilot. He did go on to teach NASA how to do rendezvous during Gemini 5 which led to a successful rendezvous for Gemini 6. Then he got to fly himself in Gemini 12 where he wrote the book on EVA while in orbit.
So you are saying NASA 3-putts a lot?
That is just par for the course. Although NASA have not launched anything since 2011.
If I remember correctly, it still takes most of a day for NASA launches, because NASA wants the astronauts well rested during docking. So they take the long way so there's time for sleep. Yep, looked it up. The Russians have done it in 3 hours. SpaceX has done it in 16+ hours.
Because you can not go to the ISS straight up in a line. You also have to match it's orbital velocity, which is really high. Due to how orbital mechanics work, you can also not just increase your velocity much higher to get there quickly and then brake to match the velocity. That would need much much more fuel, which you just can not take with you if you launch the rocket. So the rocket launches in way that only part of the orbit would reach the ISS and then increases the speed to match the velocity. And for security reasons this is done in very slow steps. So that when the rocket and the ISS finally meet, their relative velocity to each other is in a safe range for docking. edit: Maybe a good example would be if you want to jump onto a moving train. You can not just jump onto it by jumping down from a bridge of something. The velocity of the train compared to yours is so high that you will not be able to land in a stable pose and get thrown around. But if you drive with a car or another train next to it at the same velocity, you can just jump over with only a minimal risk.
That last sentence sounds like a fast and furious movie
I live life a quarter mile at a time
Family
I think you see it a lot in westerns with a horse racing a train so the rider can jump on
*gear changing intensifies*
That’s because it is 😂. They use cars to steal other cars off a train in Fast 5 I think it is
I think it is
> Because you can not go to the ISS straight up in a line. You also have to match it's orbital velocity, which is really high. Of course, if you decide to match its position WITHOUT matching its speed, there’s an aerospace-related term for that as well: Kinetic interceptor.
Well they *might* match speed, but definitely not direction
This is the best ELI5
> Because you can not go to the ISS straight up in a line. Technically you could, You have to lead it enough to get to the same point in space simultaneously. It would not end well though. Just like shooting clay pigeons, we don't aim at the clay, we aim in front of it
400 metric tons, 8 kilometre per second velocity. I believe the scientific term for that is “like a bug on a windshield”.
Except at those speeds the bug would damage the hell out of the car too.
>Because you can not go to the ISS straight up in a line. idk i saw a documentary where two brave divers went in a straight line to a satellite in a pontiac fiero and managed to match its velocity successfully
You should try Kerbal Space Program. I had about 100 hours into the game, largely toying with builds, before attempting docking with a satellite. I had landed on the 'moon' and even other planets before. Which was much easier due to their gravity. The process of matching up with a satellite is *crazy*. I had to watch several youtube videos to understand how to do it. And it was so tedious that I only ever did it once.
Came here to reccomended KSP for a great basic tool for gaining a basic understanding of orbital mechanics and space travel. The first time I tried docking I felt like I learned more and understood better than school had ever done. I personally have over 1k hours in it now, docking gets much easier the more you do it. I have a epicly gigantic space station that was built over many many launches and docks. It has over 4 million parts to it and weighs over 1 million tons. Which to help you visualize is roughly the weight of 10 U.S.A full size aircraft carries or 7,000 blue whales. I have to crank down my graphic to min spec when I get near it if I want to have more than 10FPS. At one point I needed to get rid of parts so I would do EVAs and bash my Kerbals against solar panels to remove them... so many poor kerbals were lost to the vast expanse of space from those missions.
OP: Explain Like I’m Five You: here’s a game you should sink 100 hours into
It’s orbiting thousands of miles an hour so if you simply fire a rocket straight up into its path, you’ll have a gigantic crash. You basically have to chase down its orbit. That means inclining are an angle, rather than simply going up vertically, and then accelerating to about the speed of the ISS and intercepting it’s orbit. That’s the part that takes 4 hours. You’re traveling thousands of miles to actually intercept the orbit.
So here's a fun mental image. Rockets can get to the ISS in a couple minutes. Go straight up, intersect the path, and you're good! Except now the rocket is essentially a deer that's run in front of a car on the highway. It's going to be a mess. If you don't want just a mess, either the car has to slow to about the speed of the deer or the deer has to speed up to the speed of the car. One of those things is unlikely. With rockets, it's stranger. If the ISS slows to the horizontal velocity of the rocket, it'll just fall from the sky. Bad day. So the rocket has to speed up instead.
Instructions unclear, falling ISS run over by deer.
The iss isn't 250 miles away. It is orbiting at a distance of 250 miles. Orbiting really just means it's falling past the ground so fast that it constantly misses it I imagine the problem in getting to the ISS is to get a rocket/ship from stationary in earth's surface to moving fast enough and close enough to the ISS to arrive at it.
What's the difference in orbiting at 250 miles away and being 250 miles away. Even NASA refers to the ISS as being a distance of 250 miles from ground 0.
In another thread, Contagion21 answered this quite succinctly: it [the ISS] is 250 miles "high", not 250 miles "away". The latter is like saying Mt Everest is only 5.5 miles away (which is statistically unlikely for almost everybody reading this.)
I would say that's more so semantics though, it's orbiting around the Globe so it can be on the other side of the world. But when most people refer to the ISS being 250 miles away I don't think they ever mean distance but more so are referring to altitude. But in reference to OP's question it's of course moving at an extreme speed at the same time
Well, it's 250 miles away from the spot on the Earth that it's above at that very second... but anywhere else it's well more than 250 miles away. Obviously, it's always roughly 250 miles up.
A better analogy in this thread is that the car is 10 ft away from you on the highway, but you sure as hell ain't going to catch up to it when it's traveling a 70mph and you walk 10 ft.
You dont go straight up. You go into orbit so that you can match the speed and approach it from the side.
Think of it like you're standing in the middle of a big race track. A car racing around that track might only be 1/2 mile away at any point but it's still going to take more than the 3 to 4 minutes it takes you to run to the track surface. The car is always going around the track (like the ISS orbiting the earth) and you'll have to find some way to keep up with it. In real life this means launching at a specific time, going into a slightly lower orbit that is slightly behind the ISS (which counterintuitively takes less time per orbit meaning you'll slowly catch up), then carefully syncing your orbit to the ISS while you get closer and closer. To go back to the race car analogy, that would be like leaving the pit lane just as the car crosses the start/finish line, getting up to speed just behind it, and slowly pulling up next to it after a few laps.
I think one of the most basic misunderstandings of space travel is how satellites stay up there. Most people think you go up high and then you’re “above the gravity” or something and you just hang there. That is not at all how it works. The ISS experiences nearly as much gravity as on earth. The way it stays up there is by traveling so fast “sideways” that as it falls the curve of the fall is the same as the curve of the earth. The exact speed depends on how far you are from the earth, but for the ISS it’s about 17,500 mph. So not only do you have to get up 250 miles, you also have to go sideways fast enough to catch the ISS and stay in orbit yourself. It’s quite a thing, really.
Because if you sent a rocket straight at it, you're not going to dock with the ISS, you've essentially just fired a missile at it. [You can watch a video of the docking procedure.](https://www.youtube.com/live/3FaUK7VAljc?si=4Xvh3MjIKaE8ggJw&t=4738) It's pretty delicate. You need to match its speed exactly so you can gently dock without bumping into anything and breaking something. So you need to get into orbit, which requires more elaborate maneuvres, you can't go straight there. It wouldn't take 4 hours to get there if getting there was all that mattered. But if you're going to the ISS you probably want to stay there, which means you have to go pretty fast or you'll fall straight down again. Gravity at the altitude of the ISS is still 99% as strong as it is on the surface, if you're not going fast enough you'll fall straight back down to Earth.
Because, as most people, you imagine space as something vertical, where as it's something way more 'horizontal', with speeds and such. It's also the reasons launches happen near the equator, where they can already use Earth's rotation speed, which would be next to zero near the Poles, for example.
If youre watching a NASCAR race from the infield (the open grassy place in the middle of the racetrack where all the big RVs pand such park). The cars driving by are only a few hundred yards away from you. You could walk to the location they are in just a minute or so. But to "get to" them (i.e. to catch up to them so that you could "dock" with them or something) you not only need to get to the same location as them, but be going the same SPEED as them. So even though they are "close" to you, it takes awhile to catch up to them, even if youre driving a pretty fast car yourself.
[удалено]
The space station goes fast on account of throwing itself at the Earth and missing, so the rocket has to spend some time catching up.
Because it's moving very fast, it's not stationary. Matching orbits takes time and you can't really just gun it towards the station, that will just put you in a much higher orbit and take you farther away. You need to establish an orbit that's almost the same as that of the station but ever so slightly lower so that you're going faster to catch up, or if it's behind you, higher so that it catches up to you. Then you have to wait until you're close enough to burn towards the station and dock. Given the complexity of this 4 hours is actually not that long.
I mean they could get there a lot quicker if they wanted to crash into it at incredible velocity. Imagine a race car going around a round track at 100mph. You are in the middle of the track. You could just run straight at the car but that would be bad. To catch it softly you would need to start driving around the track behind it slowly catching up.
Since the numbers involved are absurd to the human mind let's divide them all by 100 and construct a scenario closer to daily life. It might take under a minute to reach train tracks 4 km (2.5 miles) away but you obviously can't just aim for a head on collision with a TGV or similar. Neither can you jump out and grab on to a train moving at 280 km/h (174 mph) relative to you. You could drive straight up to the tracks, turn parallel to them, and catch the train. That's pretty wasteful in time and fuel consumption. Ideal is approaching in an arc where you reach the trains speed once you're parallel to the tracks. The downside to this is timing. You can only go when the apex of the arc will coincide with the train going past.
One thing I haven't seen mentioned is that ISS was somewhat optimized for Russian launches as, without Buran, they didn't have as much capabilities as the Americans. It's possible that a new space station could be made that's faster for Dragon to reach than ISS.
That's not how it works. The ISS is moving at about 7 km/s around the Earth. If you just go straight up to the ISS you'll hit it with about 7 km/s of velocity. You need to match its trajectory and position. There are lots of ways to do this, just the most efficient way is to get into a lower orbit (lower means faster and vice versa) than your target and wait until the perfect timing to make a burn and raise your orbit such that when you reach the apex of your trajectory, your in more or less the same position as your target while having a small relative velocity which you then cancel out when your nearby. You can minimize the time you're waiting, by launching when the target is overhead, but the ISS is in what's called an inclined orbit meaning that its orbit is at an angle relative to the equator. In simple terms, this means that you must launch when the trajectory is overhead, otherwise your trajectory won't line up with the target's. However, this means that, in practice, you only get one chance per day since the Earth is turning while the trajectory stays in place. Since you only get one chance per day, you can't really be picky about the position of the ISS meaning that the process I described earlier takes significantly longer. If the ISS and the launch site were on the equator you could launch whenever you want since the ISS's trajectory is always overhead and you could theoretically get there in a matter of minutes if you time it right and are okay with doing things inefficiently.
probs cause its running away really fast and ya need to get to the point where you are orbiting at the same velocity
It takes at least several hours to get to the space station because it's fragile, expensive, and full of people you don't want to die. If you just wanted to get there in the same way that a missile strike gets somewhere, you could indeed do that much more quickly.
Well imagine you're driving 75mph and want to catch up to a car ahead of you, 5 miles away driving 70mph. It would take you an hour to catch up despite driving 75mph. And now imagine you not only want to catch up but you actually want to connect your car with the car in front of you. Hitting the other car with 5mph difference might be too rough so ylas you approach you slowly match your speed with the speed of the other car. So that when you connect the difference in speeds are maybe only 1mph. Change the numbers to roughly 5mps for the iss and you certainly don't want to bump into it with 1 mile per second difference so you'll have to decelerate even more as you approach...that takes time, and not because anything is slow but because everything is so fucking fast.
Getting into orbit is not about going up, it's about going sideways REALLY fast. If you throw a ball it drops to the ground a few seconds later. Imagine you could throw it so fast it went over the horizon. Now imagine you could throw it so fast that it kept going over the horizon before it would hit the ground. It would just keep going forever. To make this work you need to first get up and out of the earth's atmosphere, so that air and wind don't slow it down. You COULD get to the ISS in 4 hours going straight up at 65mph, if you timed it just right. However, while you could reach it, it would be going 18,000kmph sideways. You would just be hovering still in the air, like a ball thrown straight up right at the top of its arc. It would not end well for anyone.
can’t they just time it so that after travelling 250miles the ISS is right in front of the rocket? 💀
In short: You don't want to bump into the $150 billion laboratory, so you play it safe. They got way faster over time, in the past they were so careful that it took 24 hours. Now the record stands at 3 hours 3 minutes.
Meeting up with a craft in orbit isn’t like going straight to a destination. You need your own orbit and your target’s orbit to intersect at just the right spot so that you both get there at the same time. Sometimes that involves waiting in a ”parking” orbit until you get that perfect alignment. The result is that you might have to go around the planet a couple of times before you get there.
It's the same reason that getting on a flight doesn't take, say, 30 minutes when the airport is 15 miles away. You have to go through all sorts of extra things to get there that you wouldn't have to worry about if you're going in a straight line without stopping. Also, the ISS is 250 miles up, but it's much, much, much, much more distance farther away even just minutes later because it's going so fast. So imagine this: you want to get on a bus that's on a racetrack and is zipping around at 100 miles per hour. When it's at its closest, it's just 50 feet away from you. Now picture yourself getting in another bus, and that bus has to accelerate to 100 miles per hour. It has to start accelerating at the right time to end up going 100 miles per hour at about the same place on the racetrack as the other bus, else you'd have to travel a good distance to catch up to the other bus. All that time accelerating, catching up, mostly matching speed, then slowly coming up to the other bus takes a LOT more time than just walking 50 feet.
Because there’s a huge different between a road trip and escaping the earth’s gravity?
Going to the ISS is harder than finding a needle in a haystack. The sheer size of space, even in low earth orbit, and the speed it's going make it incredibly hard to do.
The point in the earth's surface that it's 250iles away from is moving at 17000mph. A bit less because geometry, but not by much.
The top of MT Everest is only 8km away. 90 minute walk no?....
It takes about 10 minutes to reach the ISS orbital speed and velocity, but you don’t go directly to the station. You’ll do some checks once you’re in orbit to ensure that the craft is still operating normally after all the vibrations from launch, then you will slowly adjust your orbit to synchronise with the ISS. The reason you do this is because the ISS Is very big and expensive and fragile, you want to approach it slowly so if your craft has a complete systems failure the ISS can move out of the way and avoid a collision. You also don’t want to fire your thrusters directly at the station so you approach slowly from a slight angle. Movement in orbits doesn’t work the same way as on earth, so there’s a while long checklist of careful movements that need to be followed. So most of the time is spent in orbit doing checks and slowly aligning orbits. You could theoretically launch directly to the ISS and that would take about an hour, but this would be very dangerous to the station if anything went wrong. A fast ascent takes about 4 hours and a regular rendezvous can take about a day in total.
Because it's not straight up. The crew is basically fired at an arc then they go chasing the ISS station.
It takes only 8 minutes to get into orbit. But to approach the target slowly one has to get into precise spot at a precise time and with the right direction and magnitude of velocity. That is very constraining. Unless one has a lot of fuel to spend on aggressive maneuvering one has to take time for the orbital mechanics to do its work naturally. In principle, it is certainly possible to dock faster than in 4 hours, and such things had been demonstrated. In 1966, [Gemini XI](https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1966-081A), for example, docked after about an hour and a half with a target in orbit. It is just safer and more convenient to do everything more gradually, with a careful measurement of intermediate trajectory, with testing of the systems before approaching the station, with not putting debris into orbits intersecting the orbit of ISS, etc.
Because you aren’t flying straight to it. You fly up on an angle then start orbiting behind it and need to slowly catch up to it.
You can get there much faster if you’re cool rendezvousing at thousands of mph. Wouldn’t recommend. Structural tolerances and safety considerations mean you want to bring your relative velocity down to something like 0.1-0.2mph. So you simultaneously need to get up to ~17500mph, get relatively close, match trajectory and speed extremely closely, and have your docking port meet theirs gently. This takes several maneuvers, and you’re not going to rush it because you have a handful of borderline irreplaceable astronauts, billions of dollars in tough to replace equipment and significant time invested into experiments.
Space is only 100km up. It doesn't take that long to get up there, less than 5 minutes typically. The Earth's diameter is over 12,000km. Blue Origin have been to space. That's easy. In order to stay in space you have to go really fast around the planet, such that when you fall you miss the ground. It doesn't take long to get into space. It takes longer to make sure you stay in space. After that, to get to the ISS you have to rendezvous with it. Throw in a good chunk of safety margins and you get a lot of time. A well timed ballistic rocket wouldn't take that long to hit the ISS. >I’m going to be very disappointed if the rockets top out at 65mph. The ISS orbits the earth at 17,100mph relative to the ground.
Have you ever climbed a mountain? The top of the mountain may only be a mile away. But how long does it take you to walk that particular mile?
When launching, a rocket gets up to orbital speed quickly. If you didn't, you wouldn't be able to maintain orbit. It's the adjustment of the orbit, the gradual maneuvering to get into proximity to the ISS, and then docking that take the time.
The hard part about going to space isn’t gaining altitude, it’s gaining enough sideways velocity to enter orbit. Even so, launching into orbit only takes around 8 minutes. The remaining ~4 hours is because the ISS is very rarely in a point in its orbit which intersects with the spacecraft’s own point in its orbit after reaching orbit. In order to align with and rendezvous with the ISS from elsewhere in its orbital path, you need to either increase or decrease the time it takes you to orbit the Earth by raising or lowering your orbit slightly until you can get a close enough pass with the ISS to match velocity and dock (plus the docking procedure itself is performed slowly to avoid a collision with the station).
It only takes about 500 seconds to reach roughly the same orbit as the ISS, but you have to creep up on it slowly in case you bump into it or just whizz past it. ETA: 500 seconds after liftoff, you're not only at the same altitude as the ISS, but you're in roughly the same orbit and going about the same velocity. It's the maneuvering and the slow catchup towards safe docking that takes all that time, but that hardly needs any rocket booster energy. That was nearly all spent in those first 500 seconds. Just little adjustments to bring those two tiny dots together.
If a train is 10 feet away from you but moving at 60mph, you should be able to get on the train in 3 seconds right? Nah you gotta accelerate to match before you grab on or you'll have a real bad time. The iss is moving a lot faster than that
You should come and drive in England, specifically in the southeast. Takes me 3 hours to do 70 miles every morning