Low on fuel, need to rendezvous w/ transit vehicle in Munar orbit

[geek180]

I have a lander with low fuel, but lots of mono, and a 3rd stage rocket in orbit around the Mun @ 11km. I can get the lander high enough to intersect with the rocket's orbit with my current fuel level, but nowhere near a full orbit. Is it possible to dock like this? I've tried many times but can't seem to get the timing right and the intersection is pretty brief. I'm about ready to give up on the mission, unfortunately the only mission objective was to return to kerbin with the Science Jr. module. Any tips would be appreciated.

[DBT85]

If you burn all your fuel in your main rocket to get to the right height and start burning to make orbit, what happens if you then use all your mono as well to get the orbit? Not enough Mono to make the orbit? Or are you saying that with ALL your fuel, main and Mono, you can't get orbit?

I assume you know this, but just in case, pressing H will burn your mono to move you forward, and N will go backward.

EDIT: No idea if it's possible but try uploading the save. I'll be home in a little over 90 mins so can have a shot myself!

[Akalaël]

I'm sorry, from what I can tell, if you can't match the velocities of the two craft you just can't dock.

And if you say you can't have a full orbit, then it seems you won't be able to dock.

What is your speed when tou burn all your fuel ? And what is the speed of your target ?

One tip will be to continue the burn with the monopropellant, but if you have a hundred of delta-V to make, it will take time !

EDIT : yes, give us the file or pics to see what we've got as a situation

There is NOTHING KSP's community can't do (at least give some help)

[Renegrade]

I'm sorry, from what I can tell, if you can't match the velocities of the two craft you just can't dock.

^ this. When you match velocities, you're actually entering the same orbit as the target vehicle. So if you can't make it to that orbit at all, you definitely can't match velocities and dock.

[Cerberus738]

Save your fuel and use rcs to make your intercept (if you can?) Then when you do the rendezvous use your main engine. The reason you can't make a proper rendezvous is because you're velocities can't be matched. It's not enough to just build up your orbit on one side and get an encounter. You have to build up both sides of your orbit so it matches your target. In Munar orbit rcs should be enough to get around. Also if you can build just a low orbit with your Lander you can try and make contact using your transfer vehicle instead.

[Russoft]

this will probably fail, but you could have your CSM (3rd stage rocket / transit stage) match speed with your lander once you've spent all your fuel+mono on the lander. That's assuming you can control it. Of course, if your lander is on a sub-orbital trajectory, not sure you'll have time to match velocities and rendezvous then re-establish an orbit. I've never tried.

Another option is to lower your orbit on the transit stage so your zipping along very close to the surface. Then burn parallel the ground with your lander to get into orbit. Make sure your orbit is above any mountains though before trying to rendezvous.

Edited July 29, 2014 by Russoft

[Tsynique]

If nothing works what's been suggested here and your return-to-Kerbin stage has a control pod you can try a slightly dangerous maneuver.

Switch to the stage in orbit and slow it's orbit as much as you can but make sure you will still have enough fuel to speed up again after docking (increased mass!) and for the return burn. The dangerous part of course is that if you slow it down enough it will be on impact trajectory to the Mun, so you must be able to rendezvous quickly before it hits the surface. Once the upper stage is in slower orbit your lander will require less dV to catch up and it may just be enough.

Blue skies!

[Master Tao]

First try to establish a 5+ km orbit:

• Burn up and quickly pitchover using the main engine for a long, low hop (AP 4-5 km)
  
• Use most of your monopropellant to get your PE as high as possible
  
• Then use the main engine to raise your PE, hopefully above 5 km
  
• If you don't have enough fuel to do that, get out and push
  
  • Aim prograde
    
  • Turn on SAS
    
  • Push using the EVA pack from behind the engine bell
    
  • Return to the capsule to restore the EVA
    

I've performed rendezvous-via-get-out-and-push, so it's possible, but the key is to buy yourself enough time with the monopropellant and LF/OX with that long, low hop. Also, plan the rendezvous several orbits ahead. In my case, I had a fairly large lander (3 Kerbal command pod and lots of experiments), so it took as many as three full pushes to make maneuvers.

[Akalaël]

Scott has made a kind of a rescue in almost the same situation.

(the rescue itself starts near 7 minutes)

[Jebadiah Kerban]

Hmmmm opinion use ur mono in docking mode to like decent or what ever cos now mono is becoming strong so yeah.

[NecroBones]

^ this. When you match velocities, you're actually entering the same orbit as the target vehicle. So if you can't make it to that orbit at all, you definitely can't match velocities and dock.

While true, technically you can still rescue this sort of mission, if the orbiter has enough fuel & thrust to come down and pick up the lander, and re-orbit again before crashing.

The rendezvous can be performed by the orbiter and not just the lander (if the vehicle is robust enough for it, and has a control pod, etc).

[cantab]

The first thing to test would be your ascent profile. When launching from an airless body you can pitchover to near horizontal very quickly, especially if you have a high thrust engine.

The next thing I'd try is getting as close to orbit as possible with the lander, then EVAing the Kerbals out to circularise. It's tricky with more than one Kerbal though. Don't forget to take the science data! Without mods EVA Kerbals have limited instruments, but you can get map view by hitting M.

[Tsynique]

First try to establish a 5+ km orbit:

• Burn up and quickly pitchover using the main engine for a long, low hop (AP 4-5 km)
  
• Use most of your monopropellant to get your PE as high as possible
  
• Then use the main engine to raise your PE, hopefully above 5 km
  
• If you don't have enough fuel to do that, get out and push
  
  • Aim prograde
    
  • Turn on SAS
    
  • Push using the EVA pack from behind the engine bell
    
  • Return to the capsule to restore the EVA
    

I've performed rendezvous-via-get-out-and-push, so it's possible, but the key is to buy yourself enough time with the monopropellant and LF/OX with that long, low hop. Also, plan the rendezvous several orbits ahead. In my case, I had a fairly large lander (3 Kerbal command pod and lots of experiments), so it took as many as three full pushes to make maneuvers.

OR you could enable infinite fuel and problem solved. Either way is cheating and unrealistic except one is harder the other is easier.

[NecroBones]

OR you could enable infinite fuel and problem solved. Either way is cheating and unrealistic except one is harder the other is easier.

The rest of that advice was pretty solid, so I assume you mean the "get out and push". Yeah, it's cheaty, but less so because the default game-play mechanics permit it, IMHO.

[Tsynique]

The rest of that advice was pretty solid, so I assume you mean the "get out and push". Yeah, it's cheaty, but less so because the default game-play mechanics permit it, IMHO.

Yeah, it's either cheating the game or the realism of physics Although in essence, in both cases what you get is infinite fuel. Only "get out and push" method takes a bit of work sometimes

Personally, since I'm a realism junkie after 100 failed attempts I would launch a rescue mission from Kerbin

P.S. Yeah, I know saving/reloading is against realism but I'm planning on dropping that too

[geek180]

Wow can't believe all the responses! What a great community! I've been at work all day, so obviously I haven't been able to tinker with this any further. I will try a few more things when I get home, but I truthfully don't expect to have success (my lander is really low on fuel, and too heavy for the RCS to have a significant effect). It's fine if I can't succeed because my next goal is to get a mobile processing lab/refueling station in Munar orbit and research all the biomes like that. This was all an unmanned mission, and will serve as a good lesson in lander design for me.

[Tsynique]

This was all an unmanned mission, and will serve as a good lesson in lander design for me.

Get a plugin that calculates dV (I use Kerbal Engineer Redux), google a "KSP deltaV map" and never make fuel underestimations again. From my experience, I always put too much fuel when relying on the deltaV map, so after every mission I write down the exact deltaV used for a specific maneuver and use that for future missions