Permanent Mun-Kerbin Orbit

[Radsoc]

The idea is to have a permanent space station in an orbit around both Mun and Kerbin, that transports people from Kerbin to Mun and vice versa. Other local space craft would have to handle the transport to and from the station.

It should definitely be possible, but a condition is to minimize the minimum distances to the Mun and Kerbin form the station orbit. How close can you get while maintaining a stable orbit? What would it look like? Ellipse-shaped? An eight?

[Cykyrios]

I must say I\'m not sure whether this is possible with the current 'most relevant only' gravity, because each time you change SOI you might be thrown off course (I may be mistaken, though).

[mukut1994]

i think its possible but you wouldnt see as stated above the orbit on both

can someone do some calculations to see how speed and other stuff needs to be??

[Radsoc]

I guess that all celestial bodies affect the space craft gravitation-wise (within some numerical limits). The displayed trajectory likely takes all bodies into account, while being limited (in plot) to the surroundings of the dominant body.

Maybe they just don\'t show non-local trajectory plots to keep a limit on line clutter? It shouldn\'t take that much extra computational power to compute a little bit more of it. But of course, right now, with the current limited trajectories, the challenge likely relies more on math than on testing.

One very basic solution is to position the craft very very far away from both bodies, at a distance where Mun+Kerbin would behave more or less like one body. Then it would orbit both bodies. But it doesn\'t fulfill the minimization requirement on the other side. In addition to that the station should follow the rotation of the moon around Kerbin, i.e. the average angular velocity around Kerbin has to be the same.

[RedDwarfIV]

Screw maths! Break out the SPIROGRAPHS.

Potential solution to trans-Kerbin/Munar station orbital path.

[AlexanderB]

I guess that all celestial bodies affect the space craft gravitation-wise

No, they don\'t, thats exactly the point. you only experience gravity to 1 body at a time in the game, which makes this challenge impossible.

[Xazas]

Even when you were affectect by all bodys, such a space staion is impossible, even in real life. The Problem is, that the mun is moving around kerbin, but your apoapsis doesnt. A huge burn would be needed every time you pass the Periapsis to move your apoapsis along with the muns movement. By the way, i can remember that the orbit you need (free return trajectory) is rather 8 shaped then egg shaped.

Please correct me if i am wrong.

The closest aproach to this is in my oppinion a circular orbit around kerbin at the heigh of the mun, but enough before or behind it so that you stay outside mun SOI.

[rkman]

I\'m not claiming victory, but i think so far it\'s an interesting result:

I first tried an orbit with approximately the same Orbital period as Mun:

Pe ~5,000,000m

Ap ~18,000,000m

That did not last long.

Then an orbital period of about 1/2 that of Mun:

Pe 75,000m

Ap 13,8000m

That did not last long either.

To minimize gravitational influence of Mun on the station i tried a Kerbin polar orbit:

Kerbin polar orbit:

Pe ~90km

Ap ~14,000km

orb period 19:38 ( ~1/2 mun orbit)

Coincidentally Mun passed through the orbit at the same time when the station was at Ap, the orbit seems unaffected. Ap can probably be lowered while maintaining stable orbit.

Current min distance between Ap and Mun ~2600km

[silent_prtoagonist]

I\'m not sure this is completely impossible, I know in Orbiter I managed once to do a double free return, but it fell apart after that. I think in theory it\'s possible, but it would be very unstable. But with all the simplifications is KSP it might be possible to cheat your orbit to exactly the right values and keep it there (assuming it\'s still possible with KSP\'s patched conic approximation, which I think it would be)

I may load up good ol\' Transx and play around with this for a while...

[Xazas]

A double free return sounds very interessting. Perhaps it is possible when you are very low at the munar retrograde point of your orbit and rather high at the prograde part, so the mun 'pulls' you with it... but its just a guess, maybe i\'m completely wrong.

But even when its possible, how on kerbin do you get in such an orbit, which still hast to be a free return trajectory!! The manouvers must be extremly complex and highly accurate.

Was your double free return flight in orbiter intentionally or a radom result?

EDIT: Ok, i correct my last post completely, it is possible, but highly non-trivial! ???

What we are looking for is a so called: PLANETARY MOON CYCLER TRAJECTORIE

Just found a NASA publication about the topic:

http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/40318/1/07-0390.pdf

Lets see if i have enough time tomorrow and enough english(not my native language) an math skills to understand at least a the main things. :-X ???

EDIT2: and again i am wrong... :\'( i realy should read things first before posting.

The Document is not about our challange, but a simmilar one.

A cycler trajectory is a periodic trajectory around two celestial bodys orbiting the same reference body, such as two moons around a planet or two planets aourd the sun. So this going to be (theoreticly) possible in future updates when we have more celestial bodys in our system.

But i still think a multiple free return around mun might be possible.

[rkman]

The station orbit is not stable with Ap at 13,000km.

It\'s questionable if in reality this arrangement would be energy efficient: a shuttle that would put passengers on the Kerbin-Mun station would have to match the high orbital velocity of the station at Pe (~3100m/s), that\'s a lot faster than normal velocity at 90km orbit altitude. And to traverse from the station at Ap to Mun you\'d need to get up to ~550m/s to match Mun\'s orbital velocity.

edit:

With Pe at ~90km the orbit is so elliptical that Ap is not the closest point to Mun\'s orbit, to be safe i raised Pe to 650km. Ap is at ~14,000km.

I feel confident this polar orbit is stable and can not be improved much, so to fit the criteria of the challenge i hereby submit

a elliptical polar orbit with a min distance to Kerbin of 650km and a min distance to Mun of about 2650km.

[silent_prtoagonist]

It was intentional, but this was a couple of years ago so I don\'t remember many details.

I do seem to recall though that the orbit had a very high perigee, a couple thousand km I think, and periselene was pretty high too, neither of which would be optimal for a transfer shuttle. And of course your crew module/whatever still has to make up all the delta V to get to the moon, it just gets to travel along docked to a big station instead of by itself. Basically all this would do is give you a big hotel to stay in on the trip there and back, which wouldn\'t be a huge advantage for the couple of days it takes to get to the moon, but might be if you could set up a similar orbit between two planets. (I remember a discussion somewhere about the possibility of doing this between Earth and Mars)

[Xazas]

(I remember a discussion somewhere about the possibility of doing this between Earth and Mars)

See the first edit of my last post^^

Any chance you remember how you did it?

Sorry for the stupid question but what means 'periselene'?

[Radsoc]

No, they don\'t, thats exactly the point. you only experience gravity to 1 body at a time in the game, which makes this challenge impossible.

No tidal effects in other words. They may be using such an approximation for some reason, but that alone wouldn\'t make things impossible, just maybe less accurate and prone to growing errors, because you can still just pass the station from one body to another.

Coincidentally Mun passed through the orbit at the same time when the station was at Ap, the orbit seems unaffected. Ap can probably be lowered while maintaining stable orbit.

I think that\'s a first step. The difficulty arises when we want the Ap to rotate around Kerbin at the same angular velocity as the moon. The polar orbit is intuitively a great idea (at least makes thinking easier). Initially it could be in orbit at a distance where the Moon doesn\'t affect the station.

I\'m more or less assuming a space station on the Moon here, but it doesn\'t really matter. The problem is interesting enough in itself as it is

Earth and Moon is a good start in any case.

[Xazas]

Just found this in orbiter forum:

http://orbiter-forum.com/showthread.php?t=26499

So it is possible, it has been done in orbiter 2 weeks ago (see last post on the page), and it should be recreatable in KSP.

They talked about 50-100m/s deltaV correction burns per period, that is not much for our ksp rockets.

Any chance to get that 'transx' program? sounds interresting, is it free?

[silent_prtoagonist]

See the first edit of my last post^^

Any chance you remember how you did it?

Sorry for the stupid question but what means 'periselene'?

Periselene (or perilune) is just periapsis with respect to the moon, as opposed to perigee for earth or perihelion for the sun, etc. It\'s kind of an archaic terminology that seems to be going out of style, somewhat, but I like to use them sometimes

As for how I did the double free return, I think I just loaded up IMFD (a navigation suite for Orbiter if you\'re not familiar with it) and played around with the variables until I got something that worked. I never tried an Earth-Mars free return, but I imagine I\'d use the same method. I suppose I could figure out the maths to do it right, but so far I haven\'t felt motivated to do that much work

EDIT: Transx is another navigation suite for Orbiter. Unfortunately it wont work outside of Orbiter, but there are similar programs that are stand-alone, although I don\'t have much experience with them.

[Xazas]

unfortunately i have not much experience with orbiter :-[

do you know any good stand alone orbital calculation program that can do such a thing?

By the way: does anyone know what a 'moon to moon backflip orbit' means? It seems to be neccesary for the challange.

[Radsoc]

With Pe at ~90km the orbit is so elliptical that Ap is not the closest point to Mun\'s orbit, to be safe i raised Pe to 650km. Ap is at ~14,000km.

I feel confident this polar orbit is stable and can not be improved much, so to fit the criteria of the challenge i hereby submit

a elliptical polar orbit with a min distance to Kerbin of 650km and a min distance to Mun of about 2650km.

If you can make it follow the moon around Kerbin you have a solution, i.e. to have the moon permanently inside the orbit.

But that might not be possible.

[Ydoow]

This should be possible.

Maybe it won\'t meet with the Mun every revolution, but I think it\'s possible.

[Xazas]

thorfinn found the right paper for our station:

http://cbboff.org/UCBoulderCourse/documents/LunarCyclerPaper.pdf

I hope i can understand it. I defenitly going to try it on the weekend!

[Rascal Nag]

Well, I\'m pretty sure it\'s theoretically possible. I\'m thinking that it would be beneficial to know the range of Kerbin-Mun orbits we\'ll be dealing with per munar orbit. The Mun, IIRC, usually travels about 80 degrees of its orbit for the usual trip to it. And since we\'d have to go back to Kerbin each time, we\'d get around 2 Kerbin-Mun orbits per munar orbit.

Also, while not the same, I thought of a similar challenge while making a little diagram of this one.

Basically, you would go to the Mun and escape it in such a way that, without approaching Kerbin closely like in this challenge, you intersect with the Mun again. You would be set for escape of the Kerbin-Mun system, but then the Mun catches you and shoots you back inwards again, and this repeats. Kind of useless science wise, but a neat thing to thing about in my opinion.

[gabyalufix]

I\'m fairly sure it is possible, but I\'m similarly sure that it is also highly unstable.

In other words, any slight deviation in your initial course would be magnified with each lunar cycle. It\'s fairly likely that even if you found the exact solution and inputted it directly into the .sfs file, floating point errors / time-dilation screwyness would eventually knock you off cycle.

I would love to see someone math it out. Such math is doable, but well beyond the limits of the vector calc I am willing to dedicate to this game.

[Xazas]

So here is my first attempt. The primary objective for the first misson was to get in the moon to moon backflip orbit.

I calculated that, for a 45° inclination(needed according to the paper above) you have to leave Muns SOI in a angle of 67° retrograde to muns orbit with a speed of 383,5 m/s relative to mun surface. The MechJeb did a great job helping with the navigation.

I know i did it in a very ineficcient method, but my first goal was to make the backflip in general, fuel optimization comes later.

So far i can count this as a success. I was able to catch the mun half a relevation later, unfortunately a litte bit to late so i was behind it and got slingshoted out of Kerbins SOI.

but now i come closer in undestanding how this should finally work. If you end the backflip on the prograde site of the mun, you should be slingshoted back to Kerbin.

I have to dig in deeper on the math... does anynone know a good orbital calculator like transx? still doing this by hand and my brain is starting to hurt by all those relative velocities...need more sleep, i will give it another try tomorrow.

Pictures below: Look who is the pilot

1 Backflip probe (with second stage still atached) over the mun

2 Munar polar orbit

3 67° escape course

4 doing the backflip

5 meeting up again

6 goodbye litte probe...

[Radsoc]

I\'m also working on this, however, I\'m pretty sure it won\'t be possible for the orbit to follow the moon unless thrusters are applied. Maybe it\'s possible to make the 'rendezvous' occur relatively frequently (in periods), which in theory could be supplemented by addtional stations to make it possible to make transfers every month or so.

[NovaSilisko]

The issue I have with this is that, if you rendezvous with the station in this trajectory, you\'re -already- on a free return trajectory, so there\'s no point in having an entire station there, since leaving the station to land on the mun would require the same amount of delta-v as sending a smaller (and therefore lighter) craft there from the same trajectory.