Southwest Research Institute (SwRI) News

SwRI^® engineers activate Deep Space One instrument

Plasma experiment for planetary exploration instrument performing well

San Antonio -- December 11, 1998 -- The plasma experiment for planetary exploration (PEPE) instrument, one of the most advanced plasma sensors ever to fly, was activated December 10 from a distance of more than 4.5 million miles. The instrument is riding aboard the Deep Space 1 (DS1) spacecraft, which will fly by asteroid 1992 KD and Comets Wilson-Harrington and Borrelly. Southwest Research Institute™ (SwRI) designed and built the instrument in cooperation with Los Alamos National Laboratory.

“So far PEPE is operating perfectly and we’re seeing the things you expect to see in space -- no surprises yet,” says Dr. David T. Young, PEPE principal investigator and an Institute scientist in the SwRI Instrumentation and Space Research Division. Young and SwRI Senior Research Engineer John Hanley turned on PEPE from the control center at the Jet Propulsion Laboratory of the California Institute of Technology. “DS1 is testing 12 new technologies in deep space, including PEPE which has several new technologies of its own, to help lower the costs and risks of future NASA missions.” Other SwRI scientists and researchers from elsewhere in the U.S. and Europe will help analyze the data collected during the encounters.

DS1 is using an ion propulsion system -- essential for exploring deep space because it’s more efficient and can propel spacecraft further out than typical chemical rockets. PEPE will help determine whether space physics measurements can be made from spacecraft using such propulsion systems without affecting the scientific data and results. In addition, the instrument’s high mass resolution will enable it to make scientifically interesting measurements of asteroid and cometary environments and to easily distinguish between the two major species emitted by the ion propulsion system, xenon and molybdenum. The instrument’s other goals onboard the spacecraft are to validate the PEPE design and technologies, which includes multiple plasma physics capabilities in a single 6-kilogram package.

“There’s a possibility that the propulsion system could damage PEPE because the current coming out of the ion thruster is so intense -- far more intense than anything you’d normally find in space,” Young continues. “I’m beginning to think it’s a very small chance, but we’ll have our finger on PEPE’s off switch in case anything goes wrong.”

This is the first ion drive that’s ever been used to propel a spacecraft. Previous missions have avoided using ion propulsion systems as the primary system because the technology, and its interaction with other instruments, has yet to be proven in space. “We’ll know soon whether or not we have to take future precautions with instruments in this environment,” Young says.

PEPE is based on a miniaturized optimized smart sensor, an ultracompact sensor developed at SwRI to analyze the plasmas -- ionized gases -- that are found in the interplanetary medium and the space environments of most solar system bodies. PEPE’s performance compares roughly to that of the Cassini plasma spectrometer (CAPS), also developed at SwRI, yet it requires less than 30 percent of the mass and 50 percent of the power at a fraction of the cost. The dramatic reduction in mass and power was achieved through innovative ion and electron optics, the use of electroplated plastics, novel electronics architecture and packaging, and more efficient high voltage power supplies. CAPS is flying aboard the Cassini spacecraft, launched in October 1997, as it makes its way to Saturn.

The DS1 mission is the first of NASA’s New Millennium Program, which focuses on developing and validating promising technologies for use on future space missions. Three other deep space and two earth orbiting missions are in the development or planning stages. DS1 was launched from Cape Canaveral, Florida, on October 24.

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