Deep Space Network

The cost of tracking NASA satellites in low-Earth orbit may be significantly reduced using a fully automated and commercially available satellite tracking terminal recently demonstrated at the Jet Propulsion Laboratory.

The automated terminal was able to acquire and process telemetry completely on its own from the SAMPEX spacecraft, a NASA Small Explorer Program mission in orbit around Earth. The mission is operated by NASA's Goddard Space Flight Center in Greenbelt, Md.

"The importance of this technology demonstration is that it provides a new tool for ground-tracking, which can significantly reduce mission operations costs for near-Earth satellites and, generally, enable lower cost access to space in the future," said Dr. Chad Edwards, manager of the Systems Development Program in JPL's Telecommunications and Mission Operations Directorate, which sponsored the work.

Development of the tracking terminal was carried out by a JPL team of telecommunications experts led by Drs. William Rafferty and Nasser Golshan.

"JPL defined the upgrade requirements to a commercially available weather satellite tracking terminal and worked with SeaSpace Inc., a terminal manufacturer in San Diego, Calif., to implement the hardware specifications," Rafferty explained.

The low-Earth-orbiting terminal was constructed using a SPARC 10 workstation with weather satellite tracking software and a special interface for monitoring and control of the terminal subsystems, he said. A 3-meter (10-foot) aluminum mesh antenna was enclosed in a fiberglass shell -called a radome -- to protect it from rain, winds and other environmental conditions and set up to track the satellite.

The new tracking system can be easily adapted to a variety of antenna apertures, however, and receiver data rates can be upgraded to speed telemetry readouts. Recurring costs for the system would fall in the range of $250,000 to $300,000, depending on antenna and receiver options. That cost does not include site preparation, installation or any additional software required for a specific mission, Edwards said, but it is still significantly lower than the tracking systems currently used.

The tracking system is suitable for a large percentage of NASA's near-Earth missions and compatible with the S-band radio frequency used to monitor many low-Earth-orbiting satellites, such as NASA's Extreme Ultraviolet Explorer and the TOPEX/Poseidon satellite. JPL plans to demonstrate the system's capabilities again this fall using telemetry from the Extreme Ultraviolet Explorer spacecraft.

In addition to its greatly reduced cost, the terminal also features a high level of automation, Edwards said. After initial setup, the terminal requires no user intervention. Once per day, the terminal automatically dials up an electronic bulletin board and retrieves orbital elements supplied by the North American Air Defense in Colorado Springs, Colo., for the spacecraft it will track.

Based on these orbital elements, satellite view periods, antenna-pointing predicts and receiver frequency predicts are automatically generated. If multiple spacecraft are being supported, priorities can be assigned to allow the terminal to automatically resolve scheduling conflicts.

"About a minute before a target spacecraft rises above the horizon, the terminal automatically configures itself for that spacecraft's telemetry mode and slews the antenna into position," Edwards said. "Data acquisition takes place completely unattended by human operators, although the system can be monitored locally or remotely using a personal computer running windows software."

Another innovative feature of the terminal system is its use of data lines that are available from commercial telephone companies. These lines provide a high-quality, low-cost alternative bandwidth link for ground communications support of many NASA missions.

"This approach allows the use of high quality, commercially available services and hardware to interconnect the remote, unattended terminal, the terminal administrator and the science investigator sites together at low installation and usage costs," Rafferty said. "Authorized remote users of the terminal have easy access to the system."

In addition to the JPL development team, participants in the demonstration included Dr. Robert Bernstein of SeaSpace Inc., in San Diego, Calif., which upgraded the weather satellite tracking terminal; Dr. Glenn Mason, SAMPEX principal investigator at the University of Maryland; and Jim Williamson, SAMPEX project operations director at NASA's Goddard Space Flight Center.

The demonstration was conducted by JPL's Deep Space Network Technology and Science Office for NASA's Office of Space Communications.

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