An emergency rescue for troubled Hubble?

WASHINGTON - NASA is considering an emergency shuttle flight to save the Hubble Space Telescope from a possible loss of control, because of flexing solar panels, unexplained failures in two of its six gyroscopes and a hint of trouble last Friday in a third, according to informed sources.

The space agency already was planning a repair mission for late 1993 to correct the effects of a serious flaw built into the telescope's 94.5-inch primary mirror. Astronauts are to replace or apply corrective optics on at least one and possibly four of five main instruments aboard the orbiting observatory.

Officials said Tuesday that the gyroscope problem may be too severe to wait until the 1993 flight but that the complex hardware and intricate planning required to fix the telescope's flawed vision would not be ready in time for an earlier emergency flight, which could occur in late 1992.

The officials said they may have to choose between the two repairs because their budget will not allow for two flights.

The telescope's gyroscopes are used to control the device's pitch, roll and yaw so the telescope can point to any part of the sky.

The gyroscope problem comes on top of concerns among some structural engineers that a continuing jitter in the telescope's European-built solar arrays could cause metal fatigue in the long booms that support the panels, resulting in breakage and loss of the spacecraft's power supply, officials said.

The European Space Agency may not be able to provide a replacement set of solar arrays in time for an earlier servicing flight, officials said. However, they emphasized, initial tests indicate the panels are not likely to break before a 1993 flight.

The observatory was expected to revolutionize astronomy by using its vantage point above Earth's distorting atmosphere to see much finer detail than ground-based telescopes, perhaps even bringing objects at the edges of the universe into focus.

A decision on when to send shuttle astronauts to work on the Hubble is at least a month away.

Friday, as the telescope was making observations, "another gyro hiccuped," according to John Campbell, deputy associate director for telescope operations at Goddard Space Flight Center in Greenbelt, Md. The telescope continued working.

The "signature" of the brief glitch was different from the two that failed earlier, he said, possibly indicating a piece of dirt around a motor that keeps the gyroscope spinning.

When the telescope was launched 15 months ago, engineers said that "only four" of the six gyroscopes were needed to provide adequate control for the telescope's uniquely precise pointing requirements. The pointing system, which includes sensors that update the gyros with new information every second, was supposed to hold the telescope so precisely on target that if it were a laser mounted on the U.S. Capitol, it could hit a dime on the top of a New York City skyscraper for hours at a time. But because of the solar panel-induced jitters, instead of a dime, officials have often measured the precision in terms of sizes of "cookies" and "pizzas."