Is there a way to quantify how much you would gain by air-launching a rocket compared to a ground launch?
I came across a fairly detailed comparison made by the team that worked on Interim HOTOL.
Delta-v required for a vertical launch SSTO (e.g. Delta Clipper) to LEO: 9361 m/s
For Interim Hotol:
- speed supplied by launch aircraft (An-225), launching at Mach 0.8 at 9 km altitude: - 235 m/s
- drag loss: + 67 m/s
- gravity losses: - 670 m/s
- Isp underexpansion losses at low altitude: - 180 m/s
- Thrust vectoring demands: + 10 m/s
- Improved engine Isp due to altitude start: - 214 m/s
for a total reduction in delta-V of 1222 m/s, or 13%, translating into a 24% reduction in propellant requirement.
From the book 'Spaceflight in the era of aero-space planes' (R. Hannigan, Krieger publishing, 1994).