Docking Sub-orbital craft

[Jod]

Has anyone done this? The idea is to get a craft into sub-orbit(as in, high enough that it is in space but not fast enough to stay in orbit), then dock a tug to it and push it into a stable orbit.

I am guessing it would require an extremely precise and fast rendezvous and docking operation, how hard exactly is that?

Edited June 12, 2013 by Jod

[Markus Reese]

Well, I guess it depends on how unstable of orbit it is. Definitely need to be fast and precise. Best way would be if your tug was in orbit and would need to launch a precise intercept to it. Your dug would need to fast break, then accelerate back up again. Good and really only possible way would be a fairly high orbit to allow enough time for this to happen. I haven't heard of anybody doing it, but is theoretically possible. I have had interception with highly eccentric orbits before, just need to time your burns right to get matching speeds and be close enough.

[Vonar]

I think the lowest docking I've done was a mission where I sent a payload to a 63 km by 63 km orbit, and then had a tug bring up the cargo to a space station in a higher orbit. The problem with a sub-orbital flight is that chances are quick travel and the intercept burn will result in the craft that is on a sub-orbital path falling back down to Kerban. My general policy is to design rockets that can launch various cargo's in the 20 to 50 tons range into a 80 by 80 km orbit, and then have a tug refuel at a fuel depot, dock with a lander, and then meet the payload for missions to the Mun and beyond.

Edited June 12, 2013 by Vonar

[Jod]

I'm asking this because I'm still considering an Eve single stage lift-off mission. Math says I have enough delta-v to get into sub-orbit but not enough to circularize. I don't throw away any stages in my playthrough but using tugs is ok.

[Nibb31]

You'd have to be quick, and the tug will need enough delta-v to brake into the suborbital trajectory, push the rocket, plus its own mass, to orbit. You will gain nothing in terms of energy, because you still need to get the mass of propellant for the tug to go up, down and up again, plus the tug itself into orbit.

[Jod]

Ok, so I guess it is possible then. I will keep trying.

[magnemoe]

I'm asking this because I'm still considering an Eve single stage lift-off mission. Math says I have enough delta-v to get into sub-orbit but not enough to circularize. I don't throw away any stages in my playthrough but using tugs is ok.

One option is to not dock but capture, easiest is probably to intercept the orbit eva the kerbal and take him to the target, another option is to use an sort of box of the new panels and catch the pod in, use landing legs to close the opening.

You can dock but this capture methods will be far simpler unless you are real good at docking.

[Sephta]

I think, it really depends on your trajectory: if you have enough time to catch up with your tug, everything should be fine. It should be high enough to get you in an area, where drag is not relevant any more, it should stay there at least for 5 to 10 minutes. Your Tug should have it's peripasis there with a proper Apoapsis to catch your craft and get the orbit stable enough afterwards. Quite a challenge

Some things, I'd consider:

Your tug should have a big enough TWR to get everthing in a proper orbit.

I'd use KAS (so you don't have to dock - only capture your craft, which should be much faster.)

Starting phase angle is quite difficult to judge or calculate live in an atmosphere - i'd use mechjeb for that.

Prepare your tug before you launch. Safes time for docking or catching

[Rickenbacker]

I've done this around Minmus, where the orbital velocities are lower. I launched a lander straight up, into the path of a bigger mothership. The mothership then slowed down, docked with the lander, everyone transferred to the mothership which then accelerated back up to orbital speed again. This lets you have some very small and light landers, but really only works on small moons. Not sure how effective it is.

It SHOULD be doable around Kerbin too, but would require you to intercept the tug with some precision, and probably in a high orbit so you don't have to slow down and speed up as much to catch it.

[Jod]

This lets you have some very small and light landers, but really only works on small moons. Not sure how effective it is.

A very small and light lander is the only thing that can get through Eve atmosphere up to sub-orbit. I don't care if I'll have to build the USS Enterprise and burn mainsails to catch it.