Free-flying Spartan platform offers a cheap way to study space. Unit replaces out-of-date sounding rockets used in small-scale research

Besides its commercial cargo of communications satellites, the space shuttle Discovery is carrying a novel robot payload. The free-flying platform is designed to open a new era in low-cost shuttle-based space research.

National Aeronautics and Space Administration (NASA) officials expect such robot observatories to offer space scientists the kind of easy, inexpensive access to space that they have enjoyed with old-fashioned sounding rockets. Moreover, it will greatly extend the time their instruments are in space.

This should relieve some of the frustration felt especially by university scientists and their graduate students as the sounding-rocket program is phased out, says NASA chief scientist Frank B. McDonald. The demise of that program had seemed to shut the door to space for those who couldn't afford the cost or delays of experiments on board the Spacelab laboratory, which fits in the shuttle payload bay.

The robot platform is the first of a series of Spartans, which stands for Shuttle Pointed Autonomous Research Tool for Astronomy, in NASA jargon. But the name also refers to the spartan-like economy of these little observatories.

Spartan 1 on board Discovery is typical. It has X-ray detectors to study hot gases in distant galaxies and to record emissions coming from the center of our Milky Way galaxy. Housed in a 1.1-ton box measuring 101/2 feet by 4 feet by 31/2 feet, this instrument pack will be on its own when released by Discovery's robot arm on the fourth day of the mission.

Computer-controlled pointing and data-handling equipment will manage Spartan and its instruments until it is picked up by Discovery some 45 hours after its release. Project scientist Ray Cruddace of the US Naval Research Laboratory and his colleagues won't know how well the mission has gone or what has been detected until they receive the tape-recorded data.

This is part of the economy of the Spartan system. It requires little astronaut attention or special arrangements for interfacing with the shuttle.

Spartans also are economical in that they can be reused. Thus the $2.5 million cost of the basic Spartan instrument carrier is a capital investment to be amortized over a number of missions.

Future Spartans now are scheduled to observe Halley's Comet in ultraviolet ``light'' this January, to study the sun in October 1986, and to map selected star fields a year from December.

Together with another low-cost option called a Hitchiker module to be carried in the shuttle payload bay, this could be a significant new way of doing space research.

Meanwhile, Spartan 1 mission manager David J. Shrewsberry says he will be looking for the grapple fixture when Discovery tries to retrieve the space robot later this week. If the complex maneuvering programmed into Spartan 1 has been performed correctly, that fixture should end up in a convenient orientation to be grabbed by the manipulator arm. If it is in the correct position, Dr. Shrewsberry says, it will be a good indication that Spartan 1 did its job.