The US Defence Advanced Research Projects Agency (DARPA) has scrapped development of its fast response, low cost Airborne Launch Assist Space Access (ALASA) launch vehicle after two subsystem test explosions. The ALASA system used an air-launched 7.3m rocket dropped from an F-15E fighter jet at 40,000feet. The aim was to launch a 45kg payload to low Earth orbit for less than US$1 million. The ALASA rocket’s propulsion system was to use pre-mixed acetelyne fuel and nitrous oxide oxidiser as a “monopropellant” held in the same tanks. This would be burned by a single set of four canted engines in a forward mounted arrangement, with empty tankage being discarded during the flight. However, after two explosions during subsystem testing, the decision was made to terminate the programme before the first flight had even taken place. The ALASA system was to have been used primarily for military launches.
Comment by David Todd: The Seradata/CST World Launcher Review noted the riskiness of the fuel arrangement in its comment on ALASA: “The mono-propellant system uses an explosive mixture in its tankage resulting in a high risk of loss of vehicle and carrier aircraft.”