space rocket launching from aircraft, how to make aircraft survive?

[orangesherbet0]

I am having a problem where I want to launch rockets from a high-altitude airplane to lower costs. The airplane has a detachable rocket with enough delta-V to get to orbit from high altitude, but not enough to get to orbit from the ground. Currently I am doing my best to put the airplane in level flight, hit stability control, switch control to the rocket, then launch, but I find that in the time it takes to put the rocket in stable orbit, the airplane eventually hits the ground destructively. I'm not even sure if I can switch back to the aircraft from the space control center if it survived (anyone know?). Perhaps this type of project is not even possible in KSP?

Does anyone have any ideas to allow the airplane to survive with low cost, or implement some career-mode-allowable autopilot functionality without mods, or mods that enable this functionality via coding or otherwise without seeming like complete cheating (mechjeb)?

Edited June 13, 2016 by orangesherbet0

[volcanicshrimp]

It sounds like your plane is despawning (which happens if craft in an atmosphere get ~22.5km away from the currently controlled craft. The only ways to get around it that I know of are to put the rocket on a suborbital trajectory which it will stay in space on until you've landed the plane then circularize after landing (more complicated and inefficient) or use mods such as FMRS.

[Thalamask]

EASY WAY   --->   I haven't actually tested this in person, but it should work. Get the mod "Stage Recovery" installed and slap parachutes on your plane. When it gets out of physics range, it should despawn, with Stage Recovery giving you a refund for the parts recovered.

HARD WAY   --->   As noted above, you'd need to launch your rocket to an apoapsis that'll give you time to land and recover your plane before switching back to the rocket to circularise. Inefficient and tricky at best, a nightmare at worst.

[Snark]

Yeah, basically the mission profile you describe doesn't work in KSP, because of a limitation of the way the game works.  Only the currently controlled craft, and other craft inside the "physics bubble", is actually physically simulated.  In atmosphere, the physics bubble goes out to 22.5km.  When the airplane goes outside of that, it switches to "on rails" ... which equates to "instantly destroyed" if it's below 23 km altitude.

You can work around that with mods such as Stage Recovery, as described above.

I played around a bit with "two stage to orbit, recover the first stage" without mods.  It's doable, but requires a kind of odd mission profile that's designed more around the game's limitations than what I'd prefer to design.  The key point to remember is that it's okay to be outside the "physics bubble" while in atmosphere, without getting destroyed, as long as your altitude is above the 1%-atmospheric-pressure-line (which on Kerbin is around 23 km).

My bottom "launcher" stage wasn't an airplane, though.  It was a turbojet-powered booster; the rocket was vertical takeoff.

So the mission profile looks like this:  Bottom stage is a whole bunch of turbojets, arranged radially around a rocket-powered core for that last bit of oomph.  It has enough power to lob the whole ship into a trajectory that peaks pretty high up (in the 50 km range).  The bottom stage conks out while the craft is still rising fast-- and, crucially, is above the magic 23km altitude limit.  Stage away the top stage and apply enough thrust to lob it to a higher Ap, leaving the bottom stage behind.

What happens next depends on how high an orbit I'm targeting for the upper stage.

If it's a low orbit, I coast up to Ap and circularize, then immediately switch back to the bottom stage, which has coasted up past its Ap and started to fall back, but hasn't fallen below 23km yet and therefore hasn't been destroyed.  I control it as it falls, and land it with parachutes in the ocean east of KSC.

If it's a high orbit, then I don't have time to wait for it to get to Ap (the lower stage would get destroyed).  So in that case, I do enough burn to boost the Ap up to where I want it, and then switch back to the bottom stage and land it, and then switch back again to the 2nd stage (which hasn't reached Ap yet).  Coast up to Ap and circularize.

It works pretty well, and was interesting to play with.  However, I soon got bored with it (babysitting the booster stage back to earth is just really tedious, at least for me).  I'd rather just fly a traditional rocket and deal with money another way.

[the_Demongod]

Sounds like you're looking for FMRS, "Flight Manager for Reusable Stages." It basically freezes the stage you ditch (in your case, an aircraft, but could also be the Falcon 9 first stage for example), and then you fly the second stage to space as usual, and then you can return to the first stage afterwards to manually fly it back to base.

It hasn't been updated for 1.1.2 yet though, so YMMV with its current state.

Edited June 16, 2016 by the_Demongod

[Van Disaster]

FMRS does not seem reliable at the moment. StageRecovery works if your stages manage to live until they despawn - unfortunately launching from pure atmospheric carrier craft has usually meant the carrier crashing before it despawns when I've tried. A long time ago I managed it with a plane that could zoom climb almost to the edge of the atmosphere, that was enough time to throw the payload out & boost it out of the atmosphere & switch back to my plane and land it.