Anyone do this kind of Mun orbit?

[rodion_herrera]

In the Apollo days, it was known as a "free return trajectory" kind of orbit. Since the LM had to land near terminator, so that the commander can judge terrain by long shadows, the LM had to orbit the moon retrograde, and thus explains the "figure-8" approach. I mention this because based off screenshots and YouTube videos I've seen, looks like what most people do is a "brute force" encounter with Mun, and I haven't seen anyone doing the figure 8...

Refining the path when under influence of Mun gravity...

Just curious how many do it this way.

-RODION

Edited May 22, 2013 by rodion_herrera

[Caelib]

I have done it that way once. This is the same way they are doing the Mars mission in 2018.

[rodion_herrera]

I have done it that way once. This is the same way they are doing the Mars mission in 2018.

Did you figure out the escape/burn angle "by chance", by guesstimation? Or did you use some formula/device to figure it out? I figure that most people just do an arbitrary estimate, and use ANY encounter with Mun, to get there, which is perhaps why most screenshots I see of encounters are "brute force" (i.e some I think deliberately aim directly AT Mun). To do the figure-8, I have to do a lot of estimating, then redo the path, just to get the proper "tMi burn" angle and DeltaV needed to produce the fig-8. Can anyone else who does this regularly, tell me of a more precise method of determining angle? Thanks.

-RODION

[PakledHostage]

There was a challenge to do just that about a year and a half ago. The challenge required that players jettison everything but the command pod after completing their TMI burn and then coast around the Mun and return to a safe landing on Kerbin.

Timing your TMI burn off Mun rise is actually a very accurate method if you put some thought into it. That is how I timed the burn for my entry in the free-return trajectory challenge I mentioned above. Such rudimentary celestial navigation was all we had back then; we didn't have MechJeb, Protractor or manoeuvre nodes.

You can easily calculate the angle to Kerbin's horizon from any given orbital altitude, so you can also readily pick a parking orbit altitude that results in the Mun, while just cresting the horizon, to be at the perfect location for you to start your burn.

Edited May 22, 2013 by PakledHostage

[rodion_herrera]

There was a challenge to do just that about a year and a half ago. The challenge required that players jettison everything but the command pod after completing their TMI burn and then coast around the Mun and return to a safe landing on Kerbin.

Timing your TMI burn off Mun rise is actually a very accurate method if you put some thought into it. That is how I timed the burn for my entry in the free-return trajectory challenge I mentioned above. Such rudimentary celestial navigation was all we had back then; we didn't have MechJeb, Protractor or manoeuvre nodes.

You can easily calculate the angle to Kerbin's horizon from any given orbital altitude, so you can also readily pick a parking orbit altitude that results in the Mun, while just cresting the horizon, to be at the perfect location for you to start your burn.

I do like the fact that the maneuver nodes can now "draw" the projected orbital path--in Orbiter SFS we have something called a Transfer MFD, or there's a fancier version in the form of an addon called TransX, and it's invaluable if you want to do a precision free-return trajectory burn to the moon. I'm glad that KSP added the nodes as a feature, makes a lot of sense. Eyeballing is nice, in fact I find myself more of an eyeballer than a compute-that kind of person, but I like the nodes as they work now.

-RODION

[Flixxbeatz]

I've actually done something like it before, on my Mobile Munbase. Single insertion burn only, no corrections on the way. Should I've just only made a flyby, I would go back to Kerbin without expending fuel at all

Edited May 22, 2013 by Flixxbeatz

[rodion_herrera]

Your inclination is skewed, Cap'n But yeah, nice to know some people like that sort of finesse.

-RODION

[PakledHostage]

Such rudimentary celestial navigation was all we had back then; we didn't have MechJeb, Protractor or manoeuvre nodes.

Oh, and did I mention we also had to walk uphill through the snow to get to and from school? You kids don't know how good you've got it!

[Fel]

Oh, and did I mention we also had to walk uphill through the snow to get to and from school? You kids don't know how good you've got it!

Wait, it snowed when you were a kid? All we have now is slush!

[Flixxbeatz]

Your inclination is skewed, Cap'n But yeah, nice to know some people like that sort of finesse.

-RODION

Didn't bothered about it, just winged it without minding about the inclination

[Giggleplex777]

Wait, it snowed when you were a kid? All we have now is slush!

Where I live, it snowed until May... and on the next day, it's 31 degrees Celsius out!

[rodion_herrera]

Where I live, it snowed until May.

I haven't seen snow nor slush in my entire life. Maybe that's a good thing. And thanks for derailing the thread with ice

-RODION

[Fel]

XD

On the other note, I'm not exactly sure what the "free return" looks like in ksp; I mean is Kalawang's an actual free return, I know it is suppose to have the figure 8, which is why I indicate the confusion.

[rodion_herrera]

XD

On the other note, I'm not exactly sure what the "free return" looks like in ksp; I mean is Kalawang's an actual free return, I know it is suppose to have the figure 8, which is why I indicate the confusion.

Actually, his screenshot is more accurate in the "free return" aspect, because his original ellipse does intersect back with Kerbin's. My figure-8 's usually end up not being a true free return because my fine tuning upon Mun approach actually messes up the ellipse and if I allowed the craft to continue past Mun, it will NOT really get that close to Kerbin. But by fine tuning CORRECTLY, it will let you do a nice, perfect figure-8 and free return, eventually, it just takes practice I guess.

-RODION

[CalculusWarrior]

I managed to do it once, but it was by accident. I mostly don't bother with setting up complex orbits like that; simple Munar transfers are enough for me

[SkyRender]

I've actually managed a free return orbit on accident before. It's generally not as good a method to use if you plan to be doing anything long-term (it ups the cost of landing slightly too; not a ton, fortunately, as the moon and Mun both rotate VERY slowly), but for a fly-by there's no better way.

[rodion_herrera]

I've actually managed a free return orbit on accident before. It's generally not as good a method to use if you plan to be doing anything long-term (it ups the cost of landing slightly too; not a ton, fortunately, as the moon and Mun both rotate VERY slowly), but for a fly-by there's no better way.

There was a specific reason why Apollo had to opt for it. First, is the shadows issue, which I mentioned in my first post. Now, you might say, "Well, you can have shadows too, if you orbit prograde." Yes, true, but think--those shadows / that terminator appears on the FAR SIDE of the moon...So here lies the second reason--in the case of Apollo, how will the astronauts talk to Houston, let alone show to the world LIVE, that they have indeed landed, if theres' no light-of-sight for comms, or TV broadcasts? So the figure-8 retrograde lunar orbit had a specific purpose, in the case of Apollo. I guess there's no harm done if that is not done in KSP So I'm betting that most terminator landings with prograde approaches to the moon, lands the lander on the far side

-RODION

[SkyRender]

There was a specific reason why Apollo had to opt for it. First, is the shadows issue, which I mentioned in my first post. Now, you might say, "Well, you can have shadows too, if you orbit prograde." Yes, true, but think--those shadows / that terminator appears on the FAR SIDE of the moon...So here lies the second reason--in the case of Apollo, how will the astronauts talk to Houston, let alone show to the world LIVE, that they have indeed landed, if theres' no light-of-sight for comms, or TV broadcasts? So the figure-8 retrograde lunar orbit had a specific purpose, in the case of Apollo. I guess there's no harm done if that is not done in KSP So I'm betting that most terminator landings with prograde approaches to the moon, lands the lander on the far side

Actually, the way I do landings, I almost always come down on the Kerbin side. My approach is basically: circularize, orbit to the far side, lower periapsis to 5KM, land on the near side.

[rodion_herrera]

Actually, the way I do landings, I almost always come down on the Kerbin side. My approach is basically: circularize, orbit to the far side, lower periapsis to 5KM, land on the near side.

No problem with that, but you don't take shadows into account, I bet, because it doesn't have any practical value in KSP.

-RODION

[AmpsterMan]

Doing a free return used tio be my standard Mun mission at some point. I eventually stopped however because I preferred to leave my debris in Solar Orbit or just crash it into the Moon

[Specialist290]

My Mun station is in a prograde orbit around the Mun, so I try to send most of my traffic the "brute force" way just to get it on the proper inclination for rendezvous. If I'm sending a lander directly to the surface, though, I'll typically aim for a free return trajectory, because I think it's a little easier on the delta-v to get.

[Superluminaut]

I use the free return with my tourism craft. At 80km orbit it takes about 872 ÃŽâ€V to initiate the full round trip. I use the hitchhiker thing which gives an amazing reentry show at that velocity. I've been thinking about doing a video on it because it's a great ride.

872 ÃŽâ€V is not the cheapest way to Mun so I don't use it if I want to get orbit around Mun.

[rodion_herrera]

So based off what I've read here so far, the reason why some people simply don't it is because of ÃŽâ€V budget. I still wish someone would come up with a detailed, computational explanation of when (along a Kerbin orbit altitude of say, X) EXACTLY to burn TMi (and what Y ÃŽâ€V) to establish a near-perfect FRT figure-8 around Mun. In Orbiter's TransX MFD, this was determined by two buttons called EJ+ and EJ- ...so I was hoping for a KSP equivalent of these two buttons

-RODION

[mootavic]

just use your maneuver nodes...

get to 100km orbit...

place a new one on a point where you will absolutely not enter Mun's SOI...

raise AP to around 12,000km...

drag node around till you see your figure 8...

job jobbed...

[rodion_herrera]

drag node around

*slaps forehead* You can actually DO THAT??? LOL thanks, that phrase was all I ever needed.

-RODION