Beating the Rocket Equation: Air Launch With Advanced Chemical Propulsion

Performance figures are presented for reusable, winged rocket stages launched from several large transport aircraft, including the Boeing 747, the Russian Anotonov An-226, a large supersonic aircraft comparable to the XB-70 aircraft, which achieved Mach 3.1 flight with conventional turbojet propulsion in 1964, and a Mach 6 conceptual aircraft based on the MA145-XAB ramjet demonstrated in 1968. Advantages of air launch include a reduced ascent-to-orbit delta-velocity, reduced drag, the capability to launch at any latitude, and simplified abort modes. Launch from the XB-70 flight condition would allow a 22% reduction in delta-velocity required of the rocket and a significant reduction in drag incurred by rocket flight beginning at an atmospheric density 1/20th that of sea level. Launch from a Mach 6, 85,000-ft altitude condition would allow a 33% reduction in delta-velocity; ar eusable rocket of 262,000 lb launched at this condition could deliver a 23,500-lb payload to orbit utilizing a 523-s vacuum specific impulse advanced rocket engine. Fluorine/lithium‐hydrogen engines achieved 523 s in U.S. Air Force and NASA development programs of the 1960s and 1970s. Comparisons to ground-launched, all-rocket vehicles delivering equivalent payloads to orbit are presented. Fluorine propellant reactivity and engine development history are also discussed.