Satellite Big as a Bus Could Fall From Sky

An 11-ton research satellite the size of a bus could plunge through the atmosphere and send large chunks of debris crashing to the Earth unless it is rescued by the space shuttle within the next year or two, officials said Thursday.

“We do know there will be some fairly big chunks of metal that will survive re-entry” if the satellite is not retrieved, said Robert L. James Jr., chief of the projects division at NASA’s Langley Research Center in Virginia. James hopes to rescue the satellite next year.

The $14-million satellite has no on-board propulsion or control system, so if the time comes for it to tumble out of the sky, engineers on the ground will have no control over it. Most of the debris would probably land in the ocean.

Research data collected by the satellite for the last four years also would be lost.

The Long Duration Exposure Facility was launched from the space shuttle Challenger in 1984 and was to have remained in orbit for about a year, collecting data through 57 different experiments about the effects of long-term exposure to space. The following year, however, the National Aeronautics and Space Administration delayed retrieval of the satellite because of other pressing commitments for the space shuttle.

The explosion of the Challenger in 1986 grounded all the space shuttles, robbing NASA of the capability to retrieve the satellite. And although shuttle operations are to resume later this year, the satellite is so large--measuring 30 feet long by nearly 15 feet wide--that it is not possible to retrieve it during most shuttle missions.

The shuttle’s cargo bay would have to be empty in order to rescue the satellite, and that usually is not the case. Some hardware, such as that used to launch other satellites, normally remains in the cargo area even after the payload has been delivered to space.

Time Could Be Running Out

Meanwhile, time could be running out for the satellite, experts said Thursday--partly because of the old axiom that everything that goes up must come down, and partly because of unusually strong atmospheric forces that are eroding the satellite’s orbit.

Experts said that last September the sun entered a period of high solar activity and that has raised the density of the Earth’s upper atmosphere.

“Essentially, the solar output increases, heating the atmosphere,” said Rick Chappell, chief scientist at NASA’s Marshall Space Flight Center in Huntsville, Ala.

“That causes the atmosphere to expand, increasing the density,” even at upper elevations where spacecraft orbit the Earth, Chappell said.

That increases the atmospheric drag on a spacecraft, slowing it down and gradually moving it into a lower orbit where it is subject to even greater drag, said Volis Buckelew, an aerospace engineer at the Huntsville center.

Rescue Could Be Impractical

At some point, rescue could become impractical.

“Once it gets down to a certain point, the stability will go” and the craft will begin to tumble, Langley’s James said. “You can’t retrieve a tumbling satellite because of the danger to the shuttle.”

The high level of solar activity blamed for the predicament occurs in roughly 11-year cycles. It hit earlier than NASA scientists had expected, and it will continue to increase through next year. It should peak in 1990, Buckelew said, but it is “quite a bit higher now” than had been anticipated.

Meanwhile, “the density is rising very rapidly,” he added.

The satellite is now orbiting about 250 miles above the Earth, and that is only about 10 miles lower than when it was launched in April of 1984, but the orbit could degrade very rapidly in the coming months, experts said.

Wrestling With Problem

“We’ve been looking at the data and wrestling with it,” said James, whose division includes the satellite.

“It might re-enter in the 1990-91 time frame, but we’re not that confident about our figures,” he added.

James said the matter “has been elevated to NASA headquarters.”

Retrieval has been tentatively scheduled for the middle of next year, “but that’s not an officially manifested mission yet,” James said. A source at NASA headquarters said the agency seems to have recognized the urgency of the matter, but at this point no one is sure what is likely to happen over the next couple of years.

If the satellite cannot be retrieved, the work of at least 100 scientists will be lost when the spacecraft breaks up as it passes through the atmosphere. James said the satellite and its experiments “are all passive” in that they were designed to collect, but not transmit, data--such as the effects of different types of radiation.

Thus none of the data collected during the four-year flight has been sent back to the Earth.

“The data all comes from post-flight analysis,” James said. “It’s either that or nothing.”

Data Considered Vital

The information aboard the spacecraft is considered vital to NASA’s plans to build a permanent space station because it would be the only record the nation has of the effects of long-term exposure to space. The satellite itself has presumably been hit many times by various particles, and even that should give engineers valuable information about the potential problems of space debris.

Recovering that data, James said, is the primary reason NASA wants to retrieve the satellite.

If it should plunge to Earth, most of the spacecraft probably would break up, but the craft is a fairly sturdy piece of equipment that was designed to support a wide range of instruments.

Thus some of it should survive re-entry, and pieces could be large enough to pose a danger to life and property on the ground, James said.

That prospect is no stranger to NASA.

NASA once had a space station, a 75-ton orbiting laboratory that was supposed to be the nation’s first step toward maintaining a permanent presence in space. Skylab, which was built out of the modified third stage of a Saturn V rocket, was launched into orbit May 14, 1973.

Set Endurance Record

Three crews carried out research aboard Skylab for periods ranging up to 84 days--still an endurance record for U.S. astronauts. But a year later, Skylab began to drift closer to the Earth and its ultimate fate.

NASA assured a sometimes-concerned public that the decaying orbit posed no danger. Unlike the Long Duration Exposure Facility, Skylab had a propulsion system, which permitted ground controllers to guide it into an orbit where it would break up. No pieces of any size were supposed to hit the Earth.

But debris from the spacecraft proved much more durable than NASA engineers had expected. In 1979, parts of Skylab plunged into the Indian Ocean and across Australia.

No one was reported injured by the falling debris, but the fireball was spectacular.