JPL's Advanced Propulsion Technology Group, Section 353, is doing its part to help the Lab stay in the forefront of spacecraft technology while at the same time assisting other organizations in doing the same.
The group last month completed tests of an advanced spacecraft thruster that will benefit the Lab, industry partner Space Systems/Loral and the Pentagon's Ballistic Missile Defense Organization (BMDO).
"This is a good example of cooperation between government and private industry," said John Brophy, group supervisor. "We provide the test expertise and facility for Loral and BMDO, and at the same time, JPL gets first-hand knowledge of the capabilities of these thrusters, which helps maintain our expertise in that area."
Loral provided to JPL the Russian-made Stationary Plasma Thruster (SPT-100) and its supporting electronics for the tests, performed under a JPL Affiliates Program agreement.
BMDO, which is interested in the thruster's efficient capabilities for its Brilliant Eyes satellites, sponsored JPL to perform a 5,000-hour test with 6,000 "on-off" cycles, which started in June 1993.
Loral is interested in using the thrusters on its commercial communications satellites and the stated goals of the BMDO- sponsored test are sufficient, Brophy said, to demonstrate 15 years of on-orbit satellite operations.
The success of the initial testing, which easily exceeded the 5,000-hour and 6,000 on-off cycle goals, prompted Loral to extend the test program. The company wanted to further demonstrate the thruster's reliability to its potential commercial spacecraft customers by demonstrating that the thruster could operate for 150 percent of the required mission duration with using only one of the thruster's two cathodes.
Brophy and his team extended the test for about a month, resulting in a total accumulated operating time of 5,700 hours and 6,900 on-off cycles, successfully meeting Loral's test objectives. Loral reimbursed the Lab for this test extension, he said.
The test substantially exceeded the Russian experience with this thruster, and a representative of Fakel Design Bureau, the Russian manufacturer of the thruster, came to JPL in November to inspect the device.
Loral and Fakel, along with Atlantic Research Corporation, SEP (a French aerospace company), and the Moscow Aviation Institute, have formed a joint venture to market the SPT-100 thruster for use on western spacecraft, Brophy said.
The SPT-100 thrusters are more fuel efficient than the electrothermal arcjet thrusters that are currently used in the most advanced propulsion systems on commercial communications satellites.
Brophy said the Lab is also performing tests on an advanced version of the stationary plasma thruster called the T-100, built by the Scientific Research Institute of Thermal Processes in Moscow.
Tests of this thruster are currently under way at JPL under a cooperative program that includes Space Power Inc., a small aerospace company in San Jose, and the BMDO. The tests involve "trying to verify the company's claim that the thruster has improved life characteristics and a smaller beam divergence, making it easier to put on a spacecraft," Brophy said.
A third Russian thruster has also been tested at JPL. This device, called a "thruster with anode layer" (TAL), may be the most relevant to planetary missions, Brophy noted. The version tested at JPL "runs at the same power and thrust level as the SPT- 100," he said, "but it is physically smaller and it has a lower wear rate than the SPT. Most importantly, we believe it can be made to operate with a higher exhaust velocity, making it more fuel-efficient than either the SPT-100 or T-100 thrusters."
Six-hundred hours of tests on the TAL have been completed, he noted, adding that the other partners in the venture are Russia's Central Research Institute of Machine Building (comparable to a NASA center) and an American aerospace company.
"Because of its compact design, it could be a very attractive thruster for smaller spacecraft," Brophy said, "especially for small planetary spacecraft to be developed around the turn of the century."
Brophy's group does work beyond testing Russian-made thrusters. They are currently advancing ion propulsion technology through the development of erosion-resistant, carbon- carbon electrodes in a joint effort with BF Goodrich Aerospace.
As part of NASA's Small Business Innovative Research Program, JPL is working with Space Power Inc. on the power electronics hardware required to operate the JPL-developed segmented ion engine, which incorporates the latest in ion engine technologies.
Other current projects for the group include validation of 30- centimeter ion thruster technology on JPL spacecraft for the Lab's NASA Solar Electric Propulsion Technology Applications Readiness (NSTAR) Preproject.
The group will perform an 8,000-hour test of the NASA 30-cm thruster in the same vacuum test facility used to test the Russian thrusters. To meet the needs of the NSTAR program, however, the facility, located on the west end of building 148, will be lengthened by 3 meters and its pumping speed will be doubled. These changes will make this facility one of the best chambers in the world for extended testing of electric thrusters, Brophy said.
"The ion engine is more fuel efficient than any of the Russian thrusters, but is physically larger and more complex," Brophy said. "For planetary missions where fuel efficiency is critical, the ion engine makes the most sense."
Technology advances being pursued by Brophy's group will lead to
smaller, less complex ion propulsion systems, without sacrificing
performance, he said.