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Deep space flight ends, but exploration continues

DOE/Los Alamos National Laboratory : 18 December, 2001  (Technical Article)
NASA's Deep Space 1 carrying PEPE, or plasma experiment for planetary exploration, an instrument designed and built at the Department of Energy's Los Alamos National Laboratory, will be put to rest today after a successful and event-filled mission in space.
Deep Space 1, launched from Cape Canaveral, successfully tested 12 new technologies and flew by asteroid Braille. It extended its mission and flew by Comet Borrelly in September 2001 and gathered data that scientists are using to gain a better understanding of the origins of the solar system.

'The data we got from PEPE is fabulous,' said Beth Nordholt of Los Alamos and co-principal investigator of PEPE. 'From PEPE's data we are getting a compelling first look at a new class of comets similar to Borrelly. We are finding out more about what elements a comet is made of; what the plasma, dust and gas of the comet do to their local environment; and how the comet survives and interacts with the solar system. This was only the second time a spacecraft measured the plasma composition around a comet the first time was Comet Halley,' she said.

Deep Space 1's communication link with Earth will be turned off today, but the spacecraft will remain in orbit around the sun. According to NASA, Deep Space 1 is an ambassador of Earthlings' good will to space, carrying with it a compact disc of children's drawings and engineers' thoughts. Deep Space 1 was the first in a series of deep space and Earth-orbiting missions that NASA's New Millennium Program is conducting to demonstrate cutting-edge technologies and concepts in the environment of space. The technologies aboard Deep Space 1 will help make future science spacecraft smaller, less expensive, more autonomous and capable of more independent decision-making so that they rely less on tracking and intervention by ground controllers.

After exceeding the requirements for testing the technologies, including the ion propulsion system, during the first few months of flight, Deep Space 1 began focusing its instruments on gathering scientific information. PEPE combines multiple instruments, mass, electron and ion energy spectrometers, into one compact package and was designed to examine the plasma environments associated with comets and asteroids. It also was designed to make detailed measurements of the solar wind, the continuous flow of charged particles from the sun.

'PEPE has shown how to operate instruments on spacecraft with ion propulsion systems,' said Nordholt. 'The IPS was designed to get spacecraft to their targets much faster than chemical propulsion systems, but an experimental spacecraft was needed to be sure that IPS would not interfere with science measurements on future missions. PEPE measured the 'exhaust' of the IPS and tracked the operation of the engine and what it did to the spacecraft environment.'

PEPE also measured charged particles in space, both electrons and charged atoms, or ions, and made detailed measurements of the solar wind.

'We checked the operation and calibration of PEPE in the solar wind, and we had the opportunity to look for ions coming from asteroid Braille,' said Nordholt. 'Unfortunately asteroids do not emit much material, so we were excited to get to fly by Comet Borrelly where there was a great deal of matter coming off.'

According to scientists, comets are thought to contain pristine examples of the building blocks from our solar system's birth 4.5 billion year ago. 'Some of the data from PEPE's flyby of Comet Borrelly is surprising,' said Nordholt. 'We expected the solar wind wake to be directly behind the comet like the wake of a moving boat, but it's not, it's to the side. Our best guess as to why this is happening is that there must be a lot of gas being jetted out to the side.

'PEPE detected a high abundance of water and water-like molecules streaming out from the comet. Methane-like ions were also seen, which we expected, but not in the abundances detected,' Nordholt said. 'We also are using the electron spectrometer data from PEPE in models to say what is happening in the physics of space. We want to understand the physics of space or how space is really working, like the fact that the sun is continually spewing ions and electrons that make up the solar wind,' she added.

PEPE was developed jointly by Los Alamos' Space Plasma Physics team and the Southwest Research Institute of San Antonio, Texas. Scientists and engineers at Los Alamos came up with the concept of the linear electric field three dimension, or LEF3D, mass spectrometer that gives the highest resolution for the unruly plasmas in space that come in at a wide range of energies and directions. Los Alamos also developed the numerical codes for designing the system and designed and engineered each piece for its part of PEPE. Los Alamos' portion of PEPE was then built and tested at the Laboratory and then integrated with the part from San Antonio. Data returned from PEPE are archived on a Web site maintained by the Los Alamos.
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