DARPA Developing Operational Pathfinder for ALASA Air Launch System

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LOS ANGELES — A U.S. Defense Advanced Research Projects Agency program to develop a small air launch system is also working on an even smaller vehicle as an “icebreaker” to learn operational lessons that can be applied to the larger system.

The Small Air Launch Vehicle to Orbit (SALVO) is a two-stage rocket being developed by San Francisco-based Ventions Inc. for DARPA as part of the Airborne Launch Assist Space Access (ALASA) program. The rocket, which uses liquid oxygen and RP-1 propellants, will launch from an F-15 aircraft and be able to place a three-unit cubesat, weighing a few kilograms, into orbit.

SALVO will demonstrate some new technologies, such as battery-powered pumps for its rocket engines. However, the ALASA program manager at DARPA said the main purpose of the program is to teach how to operate an air launch system effectively.

“It’s meant to be an icebreaker,” said Mitchell Burnside Clapp in a presentation about the ALASA program at the International Space Development Conference here May 16. 

SALVO, he said, will give the team experience with range approvals and other processes. 

“It makes sure everyone is comfortable so that when ALASA itself flies it will all be familiar to the people doing the work,” Clapp said.

He said the current schedule for SALVO calls for integrated tests of the rocket in August, followed by captive carry flights, where the rocket is flown on the F-15 but not released, in November. The first of up to three SALVO launches is planned for the spring of 2015, about six to nine months before the first ALASA launch.

The ALASA rocket itself is being built by Boeing Defense, Space & Security of Huntington Beach, California, under a $30.6 million contract awarded in March. The rocket features an unconventional design with four engines mounted just below the payload fairing that serve as both the first and second stages of the rocket. Propellant tanks mounted below the engines are dropped away during the rocket’s ascent to orbit.

The engines are powered by an unusual mixture of nitrous oxide and acetylene. That combination, Clapp explained, makes for a simpler design while still providing performance similar to that of liquid oxygen and RP-1. “In general, it’s a dramatic simplification of the complexity of a rocket vehicle,” he said.

Another key aspect of ALASA is that it will use F-15 planes that do not require modifications to carry out launches, a decision Clapp said was a lesson learned from previous air launch projects like Orbital Sciences Corp.’s Pegasus, the modified Lockheed L-1011-deployed rocket that first took wing 24 years ago with the help of a six-launch DARPA contract. “What you want to do is avoid using an aircraft that is specialized for the launch assist application,” he said. “Then you can use that aircraft at its marginal cost.”

Clapp noted that, as one example, ALASA will use the same communications protocols as those for weapons mounted on the F-15. “There are no software changes needed for the F-15. That is a huge advantage,” he said.

That approach is designed to meet the program’s goal of a launch cost of $1 million. DARPA chose that goal, Clapp said, because that price is comparable to the cost of using tactical weapons on fighter aircraft, and thus could have implications for how space is used by the military. “It makes space tactical,” he said.

The first launch of ALASA is planned for late 2015, with 12 launches planned through mid-2016. Those missions will use F-15 aircraft based at Eglin Air Force Base in northwestern Florida, with the launches taking place off the east coast of Florida, on the Eastern Range. After that, DARPA will seek to hand over ALASA to an operational customer, although Clapp said who would take it over, and how they would use it, remains unclear.

One challenge the program is facing is finding payloads for ALASA, which can place up to 45 kilograms, or 100 pounds, into low Earth orbit. “Finding an abundant array of worthwhile 100-pound payloads is actually kind of hard,” Clapp said. As one solution, the program is developing a cubesat dispenser that can accommodate up to six three-unit cubesats on an ALASA launch.

Clapp anticipates more potential payloads becoming available in the next few years as ALASA completes its test flights and as technological advancements make small satellites increasingly capable.

“Right now 100 pounds is right at the low end of what’s militarily useful,” he said. “Give me five years and I might surprise you.”