The U.S. Defense Advanced Research Projects Agency (DARPA) is paying two teams to spend the rest of 2008 preparing for a winner-take-all ground demonstration of satellite propulsion systems that harness the heat of the sun.


SpaceDev and Pratt & Whitney Rocketdyne received $3.7 million and $4.9 million respectively from DARPA in
September under the High Delta-V Experiment (HiDVE) satellite program. The funding was intended to help them complete the initial design of a 15-kilogram satellite platform equipped with a solar thermal propulsion system that would allow
the spacecraft to raise and lower its orbit and even change orbital planes, something the smallest satellites historically have not been able to do.


U.S. Air Force Lt. Col. Fred Kennedy, DARPA’s HiDVE program manager, said both teams successfully completed their critical design reviews earlier this spring and have since been directed to proceed toward late 2008 ground demonstrations of their rival propulsion systems.


“They both have very interesting approaches to the problem and we determined it would be useful to let them both proceed forward to the ground demonstration,” Kennedy said May 27.


In contrast to solar electric propulsion systems such as the ion drive engine currently powering NASA’s Dawn spacecraft toward a 2011 encounter with the asteroid Vesta, solar thermal propulsion systems have no onboard electrical generators. Instead, they rely
on the heat of the sun to warm a propellant, then
channel the heated gas through a rocket nozzle to create the desired thrust. Both the SpaceDev and Pratt & Whitney Rocketdyne teams are working on systems that would use ammonia as the propellant, according to Kennedy.


“These teams are now going to be very hardware focused,” Kennedy said. “Until now, what I’ve asked them to do is verify you could put a system like this on a small satellite.”


Only one team will be selected to continue past the current six-month phase toward an in-space flight demonstration, Kennedy said. And that will happen only if DARPA can find a suitable mission partner, such as Air Force Space Command or the National Reconnaissance Office, that would be interested enough in the technology to underwrite the cost of building a
demonstration satellite and putting it in orbit.


Kennedy said solar thermal propulsion has the potential to bring a new degree of utility to nanosatellites that, because they are usually constructed without propulsive capability and launched as secondary payloads, typically have to make the best of less-than-optimal orbits.


And whereas more conventional satellite propulsion systems, such as hydrazine or other cold gas thrusters, are not a good fit for tiny satellites because of their size, cost and/or tendency to be too low performance to deliver a sufficient change of velocity, or Delta V, Kennedy said solar thermal systems can offer “close to cryogenic performance” in a stunningly small package.


If HiDVE delivers on its promise of demonstrating an effective, low-cost propulsion system for nanosatellites, it will open
up a world of new possibilities for this class of traditionally propulsion-challenged spacecraft, said Mark Sirangelo, chairman and chief executive officer of Poway, Calif.-based SpaceDev.


“This program has the potential to transform small satellite design and how propulsion is accomplished on orbit,” Sirangelo said in a statement. “It could bring this class of space technologies development to another level while showing the significant value of government-
commercial collaboration for this type of operational effort.”


SpaceDev and its two partners on the HiDVE project – General Atomics and BAE Systems – expect to be ready to conduct the required ground demonstration of the complete system in late November or early December, Sirangelo said in a follow-up e-mail.


Patrick Frye, Pratt & Whitney Rocketdyne’s HiDVE program manager, said May 28 that his team aims to conduct its ground demo in September or October. The Canoga Park, Calif.-based propulsion company is getting help with its notional satellite design from Boeing IDS Advanced Networks and Space Systems group. Frye said the second phase of the contract is valued at $2.2 million.


Frye said HiDVE has the potential to revolutionize small satellites and on-orbit propulsion.


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