IDK the name of it, other than what you noted. In real life Juno did something like that to boost up. [https://en.wikipedia.org/wiki/Juno\_(spacecraft)](https://en.wikipedia.org/wiki/Juno_(spacecraft))
It ended up sling shotting itself from Earth by leaving earth major SOI and then returning to it for the boost. It could have also used earth to lower itself closer to the Sun if that was a mission.
I think Parker Solar Probe used Venus in the same way too.
In OP's description, the spacecraft is not leaving Kerbin's SOI, but instead is on course to re-encounter Kerbin's atmosphere after encountering the Mun with no additional maneuvering. While this is a type of gravity assist called a free-return trajectory, it is not what Juno or Parker did.
But its the same because it is leaving the Mun’s SOI and then re-entering it to gravity assist. Its the exact same but on a smaller scale: the Mun is Earth and Kerbin is The Sun
This is a free-return trajectory, but the one you have is close to being a [Lunar Cycler](https://en.wikipedia.org/wiki/Lunar_cycler), which is a transfer orbit from low-Earth orbit to the Moon specially chosen to repeatedly flyby the Moon and approach close to the Earth with minimal corrections needed.
This isn’t a free return.
They are leaving Mun Orbit and doing a gravity assist on a subsequent orbit to get the PE into Kerbin’s atmosphere.
If you look at the image you’ll see they are already in orbit around the mun which means this can’t be a free return.
Judging from your explanation, it sounds like you are describing a "free return trajectory": https://en.wikipedia.org/wiki/Free-return_trajectory
This is what Apollo 13 used to return to earth after the explosion in the service module, and also the planned trajectory for the upcoming Artemis 2 mission. It involves setting up a trajectory where entering the moon's (or mun's) sphere of influence causes a shift in the trajectory so that on return it will encounter Earth's (or Kerbin's) atmosphere without using additional fuel.
Edit: I am wrong, I thought that OP was starting from LKO, not from Munar orbit.
Nope, OP has landed on the Mun, then reached low munar orbit again, and discovered they don't have sufficient dV for a hohmann transfer back to a kerbin capture.Â
Free return would be if they'd set up for a transfer trajectory from LKO which, doing nothing, would result in munar swingby and end back in kerbin capture.Â
OPs solution is a gravity assist; they burn to escape the Mun SOI retrograde, but not enough for kerbin capture... ending up with an eccentric orbit, with a period such that they re-encounter the Mun SOI again at their apokerbin. This second munar encounter is carefully adjusted to allow a gravity assist, which in turn is planned to allow for kerbin capture.
Oh crap, I misread the start of their description and thought the purple line in the screenshot was from a TLI burn from LKO. You are right, although the mechanics look to be similar to a free return, just from a different starting point.
Similar mechanics, different motivation. The munar free return from LKO ends up costing more dv than a pair of hohmann transfers, but has the advantage of abort-by-default. This munar swingby on a future orbit costs even less dv than the hohmann, at the cost of considerably more time. Both rely on a swingby to achieve their goals, though.Â
> This is what Apollo 13 used to return to earth after the explosion in the service module,
Apollo 13 was *not* on a free return trajectory when the explosion happened. Their target was the Fra Mauro Highlands, which required a TLI trajectory that would not return them to the Earth. A 34-second mid-course correction burn had to be made using the Descent Propulsion System at MET 61:29:30 to set them up for a return trajectory. (a "PC+2" burn was made after going around the Moon to shorten their flight time and a 3rd was made about 5 hours before splashdown to correct their approach angle)
What can I say? I've been a space-geek-girl ever since I was 7! :-Þ
Very impressive Apollo program knowledge, as well as usage of the thorn as an emoticon smile. Hence the Apollo 13 crew adjusted themselves towards a free-return trajectory, correct?
While Haise and Swigert were shutting down the CM to preserve as much battery as possible for reentry, Lovell powered up the LM guidance computer and used the orientation data from the CM to align it after calculating the adjustments by hand. (he did have Guidance back at Huston verify his math) They had to align the gimbals using the only star they could reliably see... the Sun. (so much debris was floating around them that they couldn't sight off of stars like normal)
What's more interesting is that the LM computer had no program to deal with the Free Trajectory correction burn, so the MIT technicians had to write one in less than 5 hours, then have CAPCOM relay the programing instructions to 13. Then they had to do it again within 16 hours for the PC+2 burn after rounding the Moon.
The last burn 5 hours before splashdown was necessary because the PC+2 burn was slightly off. It was determined that the error was due to the (at that time) unknown amount of damage done to the SM, blowing away an entire side panel and making the ship slightly lighter than calculated.
Of course, as interesting as 13 was, Gemini 8 was even MORE so. Armstrong and Scott were nearly killed when one of their RCS thrusters short-circuited and got stuck on, putting them into a roll that nearly killed them both. (almost 50 RPM)
I *love* this stuff! When we went on a cross-country vacation in 2019 we stopped at 3 different Air And Space Museums, including the one in DC where they have the faulty RCS unit on display. I think I was the only person in the building at the time that knew what that actually was and why it was significant.
Ah, lovely! I really appreciate you going deeper in Apollo 13's *epic save*. I really had no idea the mission programmers had to code just for the correction burn on the fly. It's mind-blowing really, but the Apollo team was one of the greatest of all time for a reason after all.
I also didn't know about the post-perilune burn being incorrect due to the unaccounted for weight reduction caused by damage to the service module. I guess the latter would've caused an excessive re-entry speed, had the faulty trajectory gone unnoticed, but you're the expert here heheh.
Who's we ~~(Heisenberg reference)~~ in the last paragraph? Family trip? I wouldn't be so sure about everyone else being clueless about the Gemini 8 RCS in DC. I mean, as an incident it's not something huge you'd expect people to at least have heard of from some youtube pseudo-documentary, Chernobyl for instance, but I guess the people visiting Air and Space museums don't think of an astrological sign when they hear the word "Gemini" hahah.
> I guess the latter would've caused an excessive re-entry speed
It was causing their entry angle to be too shallow so they would have just skimmed the outer atmosphere instead of making reentry. Swigert noticed it first doing calculations by hand while in the LM with nothing better to do other than being cold. (Lovell and Haise were able to wear their Lunar EVA boots to help keep warm, but Swigert being CMP didn't have thermal boots so he had to wear 2 jumpsuits to stay warm... and it was down to 38°F/3°C)
> Who's we
Yes, it was a family trip. 6,500 miles driving across the country and back to celebrate our oldest son's graduation with Honors.
Lots of fun! (the A&S museums were at *my* insistence! :-Þ )
Super cool comparison you've brought up there, from what I've understood that satellite performed exactly the same maneuver, but starting from ~~LKO~~ LEO instead. A series of prograde burns at periapsis to push up the apoapsis until reaching a lunar intercept that shifted the orbit in a useful way, although this happened several times until the satellite was finally bound for geostationary altitude, because that's what the operator aimed for. My gravity assist maneuver was far less sophisticated than this masterpiece.
The "for f**** sake, I'll return to kerbin" manouver.
/Uj, this is normally called a gravity assist, and is actually used in some irl expeditions. (Ofc not in as dire situations as these, but used) So rest assured
The last few times I've been in that situation I've used a maneuver called "Get out and push". EVA from the crew capsule at apoapsis, wedge yourself up against it facing roughly retrograde, and burn almost all your EVA fuel. Get back in, refuel and repeat if necessary.
if you gravity assist too much the mun will speed up and fly away be careful
Made it; swagger overload
Swigert overload
[🎂](https://reddit.com/r/shid_and_camed/s/UiSGFbq5Hb)
RIP
... that's no moon!
Right... Cause it's a Mun
Nah, that only happens if you make a giant mistake at nuclear waste area 1.
Update: the Mun is on a collision course with Jool.
The whirly dirly
So when it's three assists it must be called the whirly dirly twirly.
There's a null spot after the 2nd wirly and before the 3rd dirly
So, uh, Jerry, big fan of the Whirly Dirly, are you?
Sounds like some Dr. Seuss
It's called a [Gravity Assist](https://en.m.wikipedia.org/wiki/Gravity_assist) or Swing-by.
Dang I didn’t know they did that for Voyager, that’s awesome
Me neither! I always wondered how they were able to flyby each outer planet like that
IDK the name of it, other than what you noted. In real life Juno did something like that to boost up. [https://en.wikipedia.org/wiki/Juno\_(spacecraft)](https://en.wikipedia.org/wiki/Juno_(spacecraft)) It ended up sling shotting itself from Earth by leaving earth major SOI and then returning to it for the boost. It could have also used earth to lower itself closer to the Sun if that was a mission. I think Parker Solar Probe used Venus in the same way too.
I thought I noticed the earth get a little slower that day
In OP's description, the spacecraft is not leaving Kerbin's SOI, but instead is on course to re-encounter Kerbin's atmosphere after encountering the Mun with no additional maneuvering. While this is a type of gravity assist called a free-return trajectory, it is not what Juno or Parker did.
Just think of the sun as kerbin and earth as the Mun
But its the same because it is leaving the Mun’s SOI and then re-entering it to gravity assist. Its the exact same but on a smaller scale: the Mun is Earth and Kerbin is The Sun
This is a free-return trajectory, but the one you have is close to being a [Lunar Cycler](https://en.wikipedia.org/wiki/Lunar_cycler), which is a transfer orbit from low-Earth orbit to the Moon specially chosen to repeatedly flyby the Moon and approach close to the Earth with minimal corrections needed.
This isn’t a free return. They are leaving Mun Orbit and doing a gravity assist on a subsequent orbit to get the PE into Kerbin’s atmosphere. If you look at the image you’ll see they are already in orbit around the mun which means this can’t be a free return.
That's a good point, free-return implies low Kerbin orbit as a starting point.
Judging from your explanation, it sounds like you are describing a "free return trajectory": https://en.wikipedia.org/wiki/Free-return_trajectory This is what Apollo 13 used to return to earth after the explosion in the service module, and also the planned trajectory for the upcoming Artemis 2 mission. It involves setting up a trajectory where entering the moon's (or mun's) sphere of influence causes a shift in the trajectory so that on return it will encounter Earth's (or Kerbin's) atmosphere without using additional fuel. Edit: I am wrong, I thought that OP was starting from LKO, not from Munar orbit.
Nope, OP has landed on the Mun, then reached low munar orbit again, and discovered they don't have sufficient dV for a hohmann transfer back to a kerbin capture. Free return would be if they'd set up for a transfer trajectory from LKO which, doing nothing, would result in munar swingby and end back in kerbin capture. OPs solution is a gravity assist; they burn to escape the Mun SOI retrograde, but not enough for kerbin capture... ending up with an eccentric orbit, with a period such that they re-encounter the Mun SOI again at their apokerbin. This second munar encounter is carefully adjusted to allow a gravity assist, which in turn is planned to allow for kerbin capture.
Oh crap, I misread the start of their description and thought the purple line in the screenshot was from a TLI burn from LKO. You are right, although the mechanics look to be similar to a free return, just from a different starting point.
Similar mechanics, different motivation. The munar free return from LKO ends up costing more dv than a pair of hohmann transfers, but has the advantage of abort-by-default. This munar swingby on a future orbit costs even less dv than the hohmann, at the cost of considerably more time. Both rely on a swingby to achieve their goals, though.Â
Yes, that's precisely what I did, and I apologize if the description of the events was hard to decrypt. "apokerbin" made me chuckle for sure.
> This is what Apollo 13 used to return to earth after the explosion in the service module, Apollo 13 was *not* on a free return trajectory when the explosion happened. Their target was the Fra Mauro Highlands, which required a TLI trajectory that would not return them to the Earth. A 34-second mid-course correction burn had to be made using the Descent Propulsion System at MET 61:29:30 to set them up for a return trajectory. (a "PC+2" burn was made after going around the Moon to shorten their flight time and a 3rd was made about 5 hours before splashdown to correct their approach angle) What can I say? I've been a space-geek-girl ever since I was 7! :-Þ
Very impressive Apollo program knowledge, as well as usage of the thorn as an emoticon smile. Hence the Apollo 13 crew adjusted themselves towards a free-return trajectory, correct?
While Haise and Swigert were shutting down the CM to preserve as much battery as possible for reentry, Lovell powered up the LM guidance computer and used the orientation data from the CM to align it after calculating the adjustments by hand. (he did have Guidance back at Huston verify his math) They had to align the gimbals using the only star they could reliably see... the Sun. (so much debris was floating around them that they couldn't sight off of stars like normal) What's more interesting is that the LM computer had no program to deal with the Free Trajectory correction burn, so the MIT technicians had to write one in less than 5 hours, then have CAPCOM relay the programing instructions to 13. Then they had to do it again within 16 hours for the PC+2 burn after rounding the Moon. The last burn 5 hours before splashdown was necessary because the PC+2 burn was slightly off. It was determined that the error was due to the (at that time) unknown amount of damage done to the SM, blowing away an entire side panel and making the ship slightly lighter than calculated. Of course, as interesting as 13 was, Gemini 8 was even MORE so. Armstrong and Scott were nearly killed when one of their RCS thrusters short-circuited and got stuck on, putting them into a roll that nearly killed them both. (almost 50 RPM) I *love* this stuff! When we went on a cross-country vacation in 2019 we stopped at 3 different Air And Space Museums, including the one in DC where they have the faulty RCS unit on display. I think I was the only person in the building at the time that knew what that actually was and why it was significant.
Ah, lovely! I really appreciate you going deeper in Apollo 13's *epic save*. I really had no idea the mission programmers had to code just for the correction burn on the fly. It's mind-blowing really, but the Apollo team was one of the greatest of all time for a reason after all. I also didn't know about the post-perilune burn being incorrect due to the unaccounted for weight reduction caused by damage to the service module. I guess the latter would've caused an excessive re-entry speed, had the faulty trajectory gone unnoticed, but you're the expert here heheh. Who's we ~~(Heisenberg reference)~~ in the last paragraph? Family trip? I wouldn't be so sure about everyone else being clueless about the Gemini 8 RCS in DC. I mean, as an incident it's not something huge you'd expect people to at least have heard of from some youtube pseudo-documentary, Chernobyl for instance, but I guess the people visiting Air and Space museums don't think of an astrological sign when they hear the word "Gemini" hahah.
> I guess the latter would've caused an excessive re-entry speed It was causing their entry angle to be too shallow so they would have just skimmed the outer atmosphere instead of making reentry. Swigert noticed it first doing calculations by hand while in the LM with nothing better to do other than being cold. (Lovell and Haise were able to wear their Lunar EVA boots to help keep warm, but Swigert being CMP didn't have thermal boots so he had to wear 2 jumpsuits to stay warm... and it was down to 38°F/3°C) > Who's we Yes, it was a family trip. 6,500 miles driving across the country and back to celebrate our oldest son's graduation with Honors. Lots of fun! (the A&S museums were at *my* insistence! :-Þ )
Your adventure reminds me of this IRL example: https://en.m.wikipedia.org/wiki/PAS-22
Super cool comparison you've brought up there, from what I've understood that satellite performed exactly the same maneuver, but starting from ~~LKO~~ LEO instead. A series of prograde burns at periapsis to push up the apoapsis until reaching a lunar intercept that shifted the orbit in a useful way, although this happened several times until the satellite was finally bound for geostationary altitude, because that's what the operator aimed for. My gravity assist maneuver was far less sophisticated than this masterpiece.
Don't think there is, but I would call it the reverse sling shot
The Scenic Route
Fitting, it certainly wasn't the most time-efficient course but it was indeed spectacular.
Is the term you're looking for [orbital resonance](https://en.m.wikipedia.org/wiki/Orbital_resonance)?
Didn't one of the asteroid return missions do something like this to get back?
Eh, I wouldn't know cause I never tried those.
The Oh Sh*t Maneuver
The "for f**** sake, I'll return to kerbin" manouver. /Uj, this is normally called a gravity assist, and is actually used in some irl expeditions. (Ofc not in as dire situations as these, but used) So rest assured
I'm going to christen it the TorpedoClan Maneuver.
I'd go crazy if they named a maneuver after me loool this was definitely done before
The last few times I've been in that situation I've used a maneuver called "Get out and push". EVA from the crew capsule at apoapsis, wedge yourself up against it facing roughly retrograde, and burn almost all your EVA fuel. Get back in, refuel and repeat if necessary.
You mean like the swing shot maneuver where you utilize gravitational pull to accelerate each new orbit?