DARPA has released a broad area announcement (BAA) calling for information about launching small satellites from aircraft as a low-cost alternative to expensive vertical rocket launches. The programme, called airborne launch assist space access (ALASA), calls for a range of modified carrier aircraft and custom-built rockets. A computer-generated picture accompanying the BAA features a heavily modified Bombardier regional jet, providing an example of what may be to come.
BAAs do not necessarily lead to any action beyond information-gathering, but presentations accompanying the announcement request proposals for placing a 45.3kg (100lb) payload into orbit, using a 2,268kg (5,000lb) air-launched rocket. Such a vehicle would allow greater flexibility in payloads and launch conditions, and could lower launch costs significantly. The first successful air-launched satellite was orbited in 1980 by Orbital Sciences using a Pegasus rocket and a B-52 launch platform. The company now offers regular launches using a modified Lockheed L-1011 airliner. More frequent are concepts, released with some regularity by companies stirring up interest, featuring aircraft ranging from MiG-21s to massive Antonov-225s.
A DARPA/NASA report from June, 2011, examining a variety of aircraft and launch configurations, concluded that modifying an off-the-shelf aircraft could result in costs as low as $3,000/lb, or around one-third the price of a large conventional rocket.
The significant limitations associated with air launch have restricted the practice from widespread use. In particular, rocket and satellite weight and performance are greatly restricted by limited aircraft payload capacity, performance and safety issues associated with highly explosive chemicals.
The air-launch concept, which has been studied since the first satellites proposals, has become increasingly attractive as the necessary size and weight of satellites for a given mission have shrunk dramatically in recent decades. Advances in aircraft reliability and operating cost gives added incentive.