TacSat-2 Provides Military Testbed for Hall Thrusters

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BOSTON A small Massachusetts firm is hoping that an experimental satellite launched for the U.S. Air Force last month will open the doors to widespread adoption of their thruster technology and a change in the way the military designs and operates its satellites.

Busek Co. of Natick, Mass., designed the hall thrusters that are used on TacSat-2, which was launched from Wallops IslandVa. in December aboard an Orbital Sciences Minotaur 1 rocket. While the primary intent of TacSat-2, and the other TacSats that are expected to follow, is to give commanders in the field the chance to experiment with the concept of directly controlling a satellite, Busek believes that the thrusters could provide other significant benefits to the military as well.

Hall thrusters rely on electricity to drive their motors, enabling them to operate more efficiently without requiring the storage of a large supply of chemical fuel that is typically needed to power conventional thrusters, which can give the military several options, according to Vlad Hruby, founder and president of Busek.

The military today rarely moves its satellites due to the amount of fuel required for a maneuver, Hruby said. Senior approval is generally needed to move a satellite because of the limited chances the military will have to move the satellites due to the constraints of fuel availability, he said during a Dec. 19 interview at the company’s headquarters.

More efficient thrusters could make maneuvers more routine, Hruby said. This could give the Air Force the opportunity to optimize satellite orbits, or help a spacecraft avoid collision with another object in space, without needing a senior official to sign off, he said.

The efficiency could also be a key technology for efficient, highly maneuverable future orbital rendezvous satellites that can take pictures of other satellites or service them, according to Bruce Pote, director of hall thruster propulsion programs at Busek.

Busek began working on the thrusters that were used on TacSat-2 under a Defense Department Small Business Innovative Research contract in 1995. As the company matured the technology under subsequent contracts, it prepared to build thrusters for the Air Force Research Laboratory’s TechSat21 flight experiment, which was intended to demonstrate the ability for several small satellites to fly together in formation.

However, the TechSat21 experiment was canceled in 2003, and the thruster design, along with some other elements of the design for the spacecraft platform, was eventually incorporated on TacSat-2. Busek, which has been working on the technology for more than a decade, had already built and flight qualified the thrusters for TechSat21, but modified and re-qualified them for TacSat-2 because it required a longer lifetime than the formation flying experiment, Pote said.

Busek also is looking forward to the first launch of the Air Force’s Advanced Extremely High Frequency (EHF) communications satellites in 2008 as another demonstration on-orbit of its hall thrusters. Busek licensed its hall thruster design to Aerojet, which built the thrusters for the new communications satellites as a subcontractor to Lockheed Martin Space Systems of Sunnyvale, Calif.

Busek chose to license its hall thruster design to Aerojet in 1997 at a time when Teledesic was interested in using the thrusters for its planned constellation of dozens of low Earth orbiting telecommunications satellites.

Busek elected to license its design to Aerojet because it did not believe it could have met the production rates desired by Teledesic because of Busek’s small size, Hruby said. Busek’s work force, which numbered less than 20 at the time, as well as its manufacturing infrastructure, could not have met Teledesic’s needs at the time, though it has since grown sufficiently in both areas that it could handle a large satellite constellation today, Pote said.

Busek has doubled its work force and sales every five years since licensing its design to Aerojet, said Hruby. The company currently has 40 employees, and had sales in 2006 of $8 million, he said. At this point it is still too early to forecast how successful operations of the thrusters on TacSat-2 and the Advanced EHF satellites would affect the company’s sales, Hruby said.

The company is eying future opportunities for its hall thrusters including the Transformational Satellite (T-Sat) Communications System and later versions of the TacSats, Pote said. The inability of a U.S. firm to manufacture hall thrusters inside the United States in the past may have made the Pentagon reluctant to use the hardware, he said.

While hall thrusters are not widely used on designs for military satellites, they have been used in the commercial satellite communications arena by companies like Space Systems/Loral, which uses thrusters that were developed as part of a joint venture with the Russian firm Fakel. Wendy Lewis, a spokeswoman for Space Systems/Loral, said that while space technology is frequently developed and demonstrated under government contracts, Space Systems/Loral’s work with hall thrusters is an example of industry leading the way.

Space Systems/Loral takes advantage of the weight savings associated with the need to carry less fuel, which can take up as much as a third of a spacecraft’s mass, by adding more transponders to its satellites, Lewis said. This helps to generate more money by enabling the satellites to handle more communications capacity, she said.