Ham operators will get to help NASA with space experiment

Last flight for veteran instruments will boost new propulsion concept

Nov. 4, 1999: Some veteran space instruments are ready for a final trip into space to help demonstrate new measuring techniques for an advanced space propulsion concept. If all goes well, the project will let amateur radio operators contribute to the program by recording the data.

It's also an example of doing things "faster, better, cheaper."

"When we were first invited to participate in this mission, we had only 11 months to get ready to fly," said Dr. Nobie Stone, the project scientist for the Plasma Experiment Satellite Test (PEST) at NASA's Marshall Space Flight Center. "By the time we obtained funding and authority to proceed, we had only nine months to design, fabricate, test and calibrate the flight instrumentation. So, compared to a typical space experiment, PEST has been developed very fast and on a very low budget. This is an opportunity to fly almost for free on an orbital flight vehicle and test a new instrument concept."

PEST will ride on the Joint Air Force-Weber State University Satellite, or JAWSAT, scheduled for launch no earlier than November 19. JAWSAT will be launched by a surplus U.S. Air Force Minuteman II missile with Pegasus upper stages and avionics added (code named Minotaur). The primary payload will be the U.S. Air Force Academy's Falconsat. JAWSAT will serve as a bus for several deployable payloads and the attached PEST experiment.

Deployable payloads are the Orbiting Picosat Automatic Launcher (OPAL) provided by Stanford University, the ASUSAT provided by Arizona State University, and the Optical Calibration Sphere (OCS) experiment provided by the Air Force Research Laboratory and L'Garde, Inc. For JAWSAT, Weber State University is providing the spacecraft power, attitude control package, imaging system, and telemetry downlink.

Schematic depicts how ProSEDS will use the spacecraft's motion and the Earth's magnetic field to generate an electromotive force that will decelerate the spent rocket stage. Credit: NASA/Marshall. Full size image available through contact

The centerpiece of PEST is the new Deflection Plate Analyzer (DPA), developed by the Space Science Department of MSFC's Science Directorate. The lineage of the DPA dates back to the mid-1970s when instrumentation was developed to diagnose the complex behavior of ion streams in the wakes of bodies in flowing plasmas. The laboratory instrument was upgraded to a flight version, called the Differential Ion Flux Probe (DIFP), which flew successfully on several shuttle missions.

The present DPA is an enhanced version of the previous DIFP flight instrument in that the complete 3-D velocity and the mass of each ion stream can be resolved.

"Before, we could single out an ion stream and determine its intensity and temperature," Stone explained. "With the DPA, laboratory tests show that we can now also determine the ionic mass." However, because of the short development time, the electronics to perform the mass analysis are not included on the PEST/DPA. Instead, operation will focus on the angular and energy distribution of the plasma ion population.

Whenever a new instrument is introduced, it's best to see how it compares with older, proven methods. That is where the leftover hardware comes into play. PEST includes two additional plasma detectors, a Retarding Potential Analyzer (RPA) flown on the third Space Shuttle mission (STS-3, 1982) and Spacelab 2 (STS 51-F, 1985), and the back-up flight unit of the Soft Particle Energy Spectrometer (SPES) from the flight instrumentation for the Tethered Satellite System carried by the Shuttle (TSS-1 on STS-46 in 1992 and TSS-1R on STS-75 in 1996). The original DIFP was also carried on all of the above missions.

"Using the flight data from PEST together with laboratory test data will give us a very good idea of how the DPA will function for the ProSEDS mission," said Dr. Ken Wright, PEST co-investigator at the University of Alabama in Huntsville, referring to the Propulsive Small Expendable Deployment System (ProSEDS) being developed for flight in August 2000.

"Another reason for our interest in this project is to create a working relationship with the Air Force for future launches," explained Fred Berry, the PEST project manager. "This has gone very well. We have shown that we can build small payloads in a short period of time and stay on their schedule."

After JAWSAT reaches its desired polar orbit at 700 km (420 mi.) altitude, it will be about two weeks before PEST is first powered on, allowing sufficient time for the satellite to vent completely and eliminate the chance of electrical arcing in high voltage circuits. PEST will acquire data for at least a two-month period.

TA UAH engineer attaches part of the PEST electronics to the grid frame that forms the skeleton of JAWSAT. Credit: NASA/Marshall. Full size image available through contact

"We think that flying a new generation of instruments at this altitude (700 km) over the Earth's poles will provide a good data set that can be used to improve our ability to model that part of the magnetosphere," Stone said. "It's an important area because the polar regions are very active, including the aurora borealis, energetic particle streams, and out-flowing plasma that escapes from the Earth." The outflow of plasma from the Earth's polar regions is a research area of particular interest to the Space Science Department.

The telemetry stream from JAWSAT (which includes data from PEST) will be broadcast on frequencies in the amateur radio band. In addition to ground receiver sites at Weber State University and MSFC, ham operators can receive the downlink telemetry signal with a special kind of modem.

"Hams will be able to obtain data that characterizes certain aspects of the ionosphere above the D, E, and F layers where most of their signals are reflected," said Berry, who is a ham operator himself. "We're going to publish the data format in terms that everyone can understand."

Data from PEST will be broadcast on frequencies that amateur radio operators can receive with either a G3RUH modem or a GMSK modem. Data rates should be as high as 38.4 kb/s. Data will be broadcast on 437.175 MHz or 2403.2 MHz.

NASA will also publish instructions for sending in data so the PEST team can use it.

"We'll use it for our purposes and hopefully they'll use it in ways that we don't know yet," Berry said. "It's an experiment. We're hoping that high school and college kids will get involved and learn something about the ionosphere and radio propagation."

The RM400 coating to be tested during PEST. Credit: NASA/Marshall. Full size image available through contact

The ionosphere is the outermost layer of the Earth's atmosphere where solar ultraviolet light knocks electrons off of atoms of oxygen and nitrogen. This effectively turns the ionosphere into a mirror of varying shape and reflectivity in parts of the radio spectrum. This is why radio reception changes at night, and why some stations can be heard far outside their normal broadcast areas, even halfway around the world.

Another part of the PEST experiment will be checking out an oddity noted during the second Tethered Satellite System flight. "We noticed something strange in the characteristics of the RM400 conducting thermal coating used on the tethered satellite," Stone explained. "The data suggested tremendous emissions of secondary electrons due to particle bombardment or solar ultraviolet or both. We had no reason to suppose that the RM400 coating would behave in this way before the TSS mission."

To find out what happened, PEST will include a test panel coated with alternating stripes of gold-which has well known characteristics-and stripes of RM400. Stone hopes that data from the DPA and SPES instruments will help him and other scientists sort through the effects caused by the RM400 coating on the tethered satellite experiment.

"It's important because there aren't many thermal coatings that are electrically conducting," he added.

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