Do Orbits around Mun change over time?

[BR00NER]

Hi Folks 

Attempted an Apollo type Mun landing. Basically had a command mod in a very low orbit and had a small lander undock and head for the surface, thinking a very low orbit would mean an easier meet up later. The lander landed 7k from target so had to EVA BoB to his new craft, as this was a rescue mission (nightmare!). By this time it was dark and the lander had no power so I time accelerated. When the sun rose the future didn't look so bright as the command mod was missing. Do lunar orbits change over the course of a Kerbin day and if so can someone explain how it happens as I don't want to get a station up there for it to take a bath in a lunar crater?. 

P.s bob made it off the mun and is now in a very awkward orbit around Kerbin, with no fuel and in a lander can that can't re-enter ha

thanks in advance 

[bewing]

Just how low was your very low orbit? The mountains on the Mun can be a little over 7km high. I'm guessing that your command module got taken out by a mountain -- because the answer to your question is "no". Once you leave a craft, its orbit is "on rails" and will not change unless it runs into something rocky and immovable.

[Chaos_Klaus]

If the orbit was really low, it is possible to hit mountains. If the orbit was inclined, it is also possible that the orbit was ok one day, but the planet rotated below and a mountain moved into the trajectory.

[Magzimum]

If the craft no longer shows up in the Tracking Station, then I agree with the above comments: it probably encountered a mountain.

However, if the orbit simply no longer passes over the landing site, then this is because of the eliptical orbit: the Mun rotates under the orbit.

[LN400]

Just to eliminate a possibility no matter how unlikely.

You say the command craft was missing. Did you verify that all the filters on the slide-down menu on the map/tracking station light up or was any of them dark?

 

Other than that, inclination as mentioned above can cause problems if the altitude is low enough.

[IWanttobeEVA]

The command module ran into a mountain; it's gone. RIP your brave crew. I try to stay above 15km orbiting Mun for a little margin of safety. The rescue mission needs a rescue mission now. 

[Pecan]

Kerbin Examiner: Top 5 reasons vehicles go missing:

1. Joy riders
2. Towed-away (no parking zone)
3. Lithobraking
4. Kraken
5. 'Because'

[Kerbart]

8 hours ago, bewing said:

Just how low was your very low orbit? The mountains on the Mun can be a little over 7km high. I'm guessing that your command module got taken out by a mountain -- because the answer to your question is "no". Once you leave a craft, its orbit is "on rails" and will not change unless it runs into something rocky and immovable.

If I recall correctly, there's a "mininum altitude" requirement when on rails. For Kerbin that's around 25 km, for the Mun it's 6-7km depending on inclination (higher inclination = higher minimum altitude).

Go on rails and you don't have to actually hit a mountain; being on rails below minimum altitude is enough to be have your vessel destroyed.

[BR00NER]

Ah cheers guys! It was unmanned so wasn't a massive issue and (dont laugh to much) the orbit was just below 9km lol

However 

I now need to rescu Bob yet again from a really awkward Kerbin orbit lol any tips? 

[LN400]

1 minute ago, BR00NER said:

I now need to rescu Bob yet again from a really awkward Kerbin orbit lol any tips? 

What's the awkward bit? A pic from map view/tracking station, a few numbers (inclination, apoapsis, periapsis, eccentricity) would help a lot.

[eddiew]

I recently had a kerbal hopping out of her pod to reset an orbital science experiment for each biome, and whenever she was on the ladder, phantom forces changed the AP/PE by a tens of metres per second she was on it, and eventually she crashed down from 10x10km orbit because I didn't notice   Thankfully the magic of F9 saved her.

I've not had the problem with vessels that were on-rails however... 

TLDR: orbits shouldn't change, but bugs can make it happen.

Edited August 16, 2016 by eddiew

[Spricigo]

4 hours ago, BR00NER said:

Ah cheers guys! It was unmanned so wasn't a massive issue and (dont laugh to much) the orbit was just below 9km lol

However 

I now need to rescu Bob yet again from a really awkward Kerbin orbit lol any tips? 

How good you are at rendezvous?  Your problem now it's exactly to rendezvous with Bob. In case of doubt this tutorial  may help you. 

Also if you did the mistake of using all EVA monopropelant try put something near the hatch for Bob to grab. 

 

[dire]

Good news about rescue from orbit is that it takes something like 1500 dV less than a rescue on the munar surface; if you pack an identical ship to the one you just sent (for example) you'll have loads and loads of fuel to make rendezvous. Don't forget the heat shield and chutes, though.

It might be tempting to say you've got so much fuel left over that you can do another mission, like boots and flag on Minmus for example; but since if you're like me it's hard to guestimate just how much fuel a rescue will take, you would run the risk of running out of fuel and needing yet a third rescue. A rescue to rescue the rescue you sent to rescue the original rescue mission.

It is news to me that rails by the mun will eat a ship; I'd read elsewhere on the forum that the critical height was 1% atmosphere, which the mun doesn't have atmosphere.

Edited August 16, 2016 by dire

[Spricigo]

5 hours ago, dire said:

It is news to me that rails by the mun will eat a ship; I'd read elsewhere on the forum that the critical height was 1% atmosphere, which the mun doesn't have atmosphere.

I guess you are referring to what @Snark said it There

Also there was some mention of people observing phantom forces action on vessels on low orbit around airless bodies,  so maybe it was a bug eat you ship. 

[dire]

Maybe the Mun has an atmosphere at sea level (or even lower) and that atmosphere hits 1% at 7 km. Has anyone taken any barometer readings from below sea level on the Mun?

[Harry Rhodan]

4 hours ago, dire said:

Maybe the Mun has an atmosphere at sea level

No, and even if it had one it wouldn't affect ships on rails.