Space Plane Closed Cycle dV to LKO

[ajburges]

Many apologies if this has been answered, but I did not know the right terms to search for.

What is a ballpark figure for the closed cycle dV needed to get a spaceplane to LKO from the end of the air-breathing envelope? Multiple reference points and values would be nice, but I think a point of of 1 Km/s (10-30 deg above horizon) at 18K would be the most useful reference transition point. (if that's not a good reference point, please provide a better one with rationale)

I know that 3-3.5 is the commonly cited vacuum dV for a ballistic launch to LKO, but I can never find citation for dV of a rocket launch with initial speed and altitude.

[Reddeyfish]

orbital speed for LKO is 2200 m/s, plus a few more m/s to reach orbital height.

if you're moving at 1000 m/s, it would be about 1,400 m/s of delta v.

the amount of drag you have on the ssto could add some more delta v, since there is still some air at 20k.

[Destroyer713]

Since bare minimum Delta-V to reach a 70x70 Kerbin orbit is 3200 m/s, and you would be moving at 1000 m/s already, the amount of Delta-V you'd need would be about 2200 more.

Granted, I don't know how atmospheric drag would factor into it, and you'd probably want a higher orbit than 70x70, so more would be better, I imagine.

Edited May 10, 2015 by Destroyer713

[cybersol]

It would of course depend on your timing and ascent profile, et cetera. However, I would guesstimate around 1500-1600 additional vacuum dV to reach LKO after air-breathing rapiers give out.

[ajburges]

Well drat.

3 different answers and 2 of them ignore drag in different ways. Maybe I just need to note before and after mass once I develop a new SSTO fleet and calculate closed cycle dV myself. Too bad I'm such an inconsistent pilot.

[GoSlash27]

Well drat.

3 different answers and 2 of them ignore drag in different ways. Maybe I just need to note before and after mass once I develop a new SSTO fleet and calculate closed cycle dV myself. Too bad I'm such an inconsistent pilot.

That's pretty much what you have to do because the requirements vary so much from one plane to the next.

Note the mass at the moment you go closed cycle and at the moment you shut down in orbit.

I just ran one of my typical designs to check. 1,625 m/sec. Of course, you want a few hundred m/sec for orbital maneuvers and deorbit, so you should really bump it up to 2 km/sec DV budget.

Best,

-Slashy

Edited May 13, 2015 by GoSlash27