June 25, 2012
Credit: Credit: Darpa
Moore's Law may ensure small satellites will be increasingly capable, but the rule of thumb has not reduced the size and cost of the vehicles available to launch such miniaturized spacecraft into orbit.
So the U.S. Defense Advanced Research Projects Agency (Darpa) has awarded Boeing, Lockheed Martin and Virgin Galactic contracts to design air-launch systems that can place sub-100-lb. payloads into low Earth orbit for $1 million, including range costs.
“Today the sub-100-lb. payload class is mostly rideshares, which impose constraints,” says Mitchell Burnside Clapp, Darpa's Airborne Launch Assist Space Access (Alasa) program manager. Smallsats normally are carried into space as piggyback payloads on launches of much larger spacecraft, usually headed for geostationary orbit.
“They do not permit any propulsion, and the spacecraft is dropped off in an orbit of the primary payload's choosing,” he says. The sub-100-lb. market, now around 10-12 payloads a year, “might be significantly greater if we could get into space affordably and without constraints.”
While small payloads have increased in capability since air launch was last considered seriously in the 1950s and '60s, allowing cheaper spacecraft to complete bigger missions, range costs have escalated as the ground-based infrastructure has aged, Burnside Clapp says. Range services now account for up to 35% of launch costs, he says.
There have been many previous studies of air launch, including Darpa's own Falcon prompt global strike program of the early 2000s, which proposed using an aircraft to launch a booster carrying a long-range hypersonic glider. “Previous attempts at air launch did not focus enough on the rocket side,” he says. “They over-invested in an aircraft that could only do one thing—support the launch.”
Orbital Sciences Corp.'s Pegasus was the first air-launched rocket to put a satellite into orbit, in 1990, and launched NASA's NuStar X-ray telescope on June 13, but the heavily modified Lockheed L-1011 airliner is one of most expensive ways to launch small payloads. Alasa is focused on driving down the expense of manufacturing and operating the launch vehicle, including range costs, “while incurring only marginal cost to modify an existing aircraft,” he says.