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.(Darpa) has awarded , and 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.”
.'s Pegasus was the first air-launched rocket to put a satellite into orbit, in 1990, and launched '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.
Boeing, Lockheed Martin and Virgin Galactic have been funded to explore different Alasa system concepts., Space Information Laboratories and Ventions are working on enabling technologies that could be used by any or all of the system teams. The launch platform is to be a “fundamentally unmodified” aircraft. “We do not want an aircraft dedicated to the mission. That is key to the affordability of Alasa,” he says. Apart from software, Darpa's goal is that the aircraft “does not have any modifications preventing it from performing its primary mission.”
Boeing declines to detail its initial “point of departure” system concept, but Lockheed Martin says its design “uses a tactical aircraft to provide a high energy-state, reusable first stage, enabling launches from bases worldwide.” Lockheed's team includes Alliant Techsystems Operations and Defense Propulsion System. “All three have different approaches to the basic problem,” says Burnside Clapp, indicating that Virgin Galatic's Alasa concept is “what you might expect” given the company's plan to air-launch the SpaceShip2 suborbital passenger vehicle from the WhiteKnight2 carrier aircraft.
Darpa's goal is not only an air-launch system that can place a 100-lb. satellite in low Earth orbit for $1 million, but one that requires just 24 hr. from call-up to integrate and launch the payload, with the ability to replan the launch in flight and relocate the aircraft to a different airport on short notice. The aircraft must be able to operate from civil as well as military airfields, anywhere in the world, in a crisis.
“One million dollars to LEO including range costs is very aggressive. We will need lower range costs as well as [enabling] affordable manufacture of the launch vehicle,” Burnside Clapp says. Instead of ground-based radar tracking, Alasa will use onboard GPS/inertial position reporting via satellite. And instead of completely separate flight-termination hardware, the launch vehicle will continuously compute its impact point and make its own decision when to self-destruct. Some of this technology could spin off to update current ranges, he believes.
Darpa has budgeted $46 million for the 18-month first phase through September 2013, when it plans another competition to select at least one team to conduct up to 36 launches in 2015 “to demonstrate [the Alasa system] at a persuasive scale,” he says.
Alasa supports Darpa's System F6 fractionated satellite program, under which the functionality of a large, monolithic satellite will be provided by a networked cluster of smaller spacecraft flying in formation. “System F6 is disaggregating big satellites into their components to improve resilience. Alasa will do the same on the launch side,” Burnside Clapp says. “We will be able to launch spacecraft constellations incrementally at lower cost and be less exposed to a launch catastrophe.”