NASA Jet Propulsion Laboratory, California Institute of Technology

JPL researchers are conducting the first in series of technology-related tests expected to play major role in the development of mobile satellite communications system for the 1990s.

Scientists and engineers of the Mobile Satellite Experiment (MSAT-X), conducted by JPL for NASA, are in Erie, Colorado, March 23-26 testing antennas and other hardware that will pave the way for an eventual satellite system.

A mobile satellite communications system would extend mobile telephone service -- comparable to that currently provided in urban areas by cellular systems -- to more remote areas throughout the country.

As envisioned, the system would consist of one or more satellites in geosynchronous orbit and network management centers on the ground. Each of the satellites, to be deployed beginning in the mid-1990s, would serve as relay station for up to 1,800 mobile users communicating by voice and data links.

In the Colorado field tests, researchers are using van outfitted as mobile laboratory to test mechanically steered antennas designed to be mounted on the rooftops of user vehicles. In addition, the tests -- involving digital data transfer at 4,800 bits per second in 5-kiloHertz channel -- will be used to measure modem performance over the communication link and to gather data on modulation technique to combat multipath fading conditions.

During the tests, frequency translator mounted on top of 1,000-foot meteorological tower owned by the National Oceanic and Atmospheric Administration will simulate the role of an MSAT satellite. The translator, operating in the microwave band, will relay data communication between the mobile laboratory and stationary base station.

"This test is our first venture into the field," said Dr. William Rafferty, MSAT-X task manager at JPL. All of the hardware being tested, he noted, was developed at JPL.

Satellite tests scheduled later this year and in 1988 will be used to evaluate other equipment provided by MSAT-X subcontractors. That includes electronically steered, vehicle-borne antennas, vocoders used to digitize human speech for high-quality transmission and other system hardware.

Rafferty said JPL's role is strictly to develop new technologies required for mobile satellite system. NASA plans to seek cooperative agreements with the commercial operator of first-generation satellite system whereby the space agency will conduct technology validation experiments using small percentage of the satellite's capacity for the first two years of operation.

In addition, JPL-developed technologies would enter the public domain for use by commercial enterprises in other applications.

Besides vehicle drivers in remote areas, mobile satellite communications could serve potential users such as forestry personnel, ships at sea and planes in flight, and is projected to become billion-dollar industry. It is expected to complement, rather than compete with, existing cellular technology.

At JPL, Dr. William J. Weber III is MSAT-X program manager and Richard F. Emerson is systems subtask manager. George H. Knouse and Elisabeth J. Dutzi are responsible for MSAT-X at NASA Headquarters.

The program is funded by the Communications Division of NASA's Office of Space Science and Applications.

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