While Paul Allen and Burt Rutan plan to air-launch Elon Musk's Falcon 9 booster from a six-engined, 385ft-span mothership, DARPA is looking at the other end of the scale with its new Airborne Launch Assist Space Access (ALASA) program. This aims to air-launch 100lb satellites into low Earth orbit from an essentially unmodified aircraft, such as a business jet.Concepts: DARPA
The objective is to reduce the cost of launching small satellites at least three-fold, to less than $10,000/lb - or a total including range costs of less than $1 million to launch a 100lb payload. The belief is that, as a launch platform, an aircraft will provide higher performance, more frequent flights and greater flexibility in launch site and orbit.
DARPA plans for multiple teams to each conduct 12 launches in the first half of 2015 under the $164 million ALASA program. Demonstration goals include launching a payload within 24hr of call-up; selecting the orbit after take-off of the launch aircraft; and rapidly departing a threatened airport to launch from a remote site within 12hr.
One advantage claimed for air launch is improved performance. DARPA says the "launch assist" from a moving aircraft provides up to 800ft/sec of delta-v; ignition at altitude reduces back-pressure on the booster nozzle; and drag is less at altitude.
A DARPA/NASA horizontal launch study
preceding ALASA calculated an air-launched version of SpaceX's Falcon 1 would have a 25% greater LEO payload than the basic ground-launched booster, increasing to almost 60% with the addition of a "high-expansion" altitude nozzle.
In addition to a range of potential launch-assist platforms, including UAVs (above), ALASA will look at technologies for the air-launched booster, including advanced solid and liquid rockets and the ability to increase payload by manufacturing propellant in flight through extracting liquid oxygen from the air.
One thing I am not clear on, however, and that is where the demand for frequent launches of small satellites will come from. DARPA's $1 million average cost bogey must be reached over 36 successful launches and its ALASA industry-day presentation
highlights the cost reductions that would come with flight rates of up to 24 a year.
But while there is a lot of work going on with smallsats, microsats and nanosats. they have not broken into the market for major military space programs yet. ALASA could lead to a future 10,000lb-to-LEO air-launched medium booster but, for now, Paul Allen's 13,500lb-payload Stratolaunch
may be closer to what the market wants.