Space Telescope Is Still Shaky Project : Astronomy: $1.5-billion instrument is plagued by vibrations, ‘confusion’ over where to focus. Chief engineer believes the problems will be solved.

The problems plaguing the Hubble Space Telescope are far more complex than the nagging troubles it initially suffered and if not resolved will undermine the effectiveness of the $1.5-billion instrument, engineers said Thursday.

In a frank discussion with scientists attending the American Astronomical Society meeting here, the telescope’s chief engineer, Gene Oliver, said that one of the most vexing problems is an unacceptable level of vibration caused by the changes in heat and cold as the telescope orbits the Earth. He warned that “without resolution” of that “we do not have a space telescope.”

In addition, the telescope at times appears “confused” over which stars to focus on.

He quickly added, however, that he believes even the most serious problems will be solved, although they are proving more difficult than had been expected.

Taking care of complex problems with the fickle observatory is particularly difficult because it is orbiting the Earth, where it is expected to give scientists the clearest pictures they have ever had of some of the darkest objects in the universe.

“You can’t just reach over and twist a knob” when something goes wrong because the instrument is 380 miles above the Earth, noted James Westphal of Caltech, one of the telescope’s principal scientists.

Westphal and other scientists noted that it takes months to get the bugs out of a new ground-based telescope, so it should not be surprising if it takes at least that long to fix the space telescope, which was launched in April.

Engineers also have to be careful not to damage the telescope while trying to make improvements. “It’s kind of like changing a spark plug while you are driving down the road,” Oliver said. “You’ve got to be careful.”

All of the principal scientists working on the telescope were asked specifically during a press conference if they were concerned that the telescope’s problems might degrade the quality of the data they expect to get. All insisted that they believe the engineers will solve the problems and the telescope will eventually work as advertised.

“I’m not a very optimistic person,” said a normally taciturn John Brandt of the University of Colorado. But he said he is “very optimistic” that the problems will be solved.

However, Oliver, who is now the deputy project manager for the Hubble Space Telescope, made it clear that engineers will have their hands full as they try to work out at least four major bugs.

The vibration problem occurs every 90 minutes when the telescope passes from “night” to “day” as it orbits the Earth. The sudden change in temperature causes the long solar panels on each side of the spacecraft to vibrate, and that makes the entire vehicle “jitter” for up to 20 minutes.

That kind of movement is unacceptable for an instrument that must remain locked on a distant star for hours at a time, and Oliver warned that it must be solved if the telescope is to function as designed.

Engineers believe the solar panel problem stems from the fact that they vibrate a little more than had been expected, and the control system aboard the craft that is designed to dampen the vibration is overreacting. If that is the case, it should be possible to resolve the problem by changing the computer commands in the craft’s software, Oliver said.

“It’s a little like learning how to drive a car,” said William Jefferys, the principal investigator on the telescope’s fine guidance system. A new driver who senses the car veering to one side will tend to turn the steering wheel too much and then must make adjustments for the overcompensation, he said.

Engineers hope that they will learn how to reprogram the telescope’s computers to keep its jitters down.

Oliver said another frustrating problem with the telescope is that it has proven very difficult to lock the instrument on the right targets, and sometimes it just drifts in confusion.

The pointing of the telescope is controlled by a series of smaller scopes that serve as “star trackers.” These small instruments are designed to recognize certain stars that are catalogued in a huge inventory of stars, and that in turn tells the telescope where it is pointing and what adjustments to make.

Unfortunately, the “star trackers” have turned out to be more sensitive than had been expected, and quite often they lock on the wrong star or become confused because of light from other stars, and “you may go several hours just drifting,” Oliver said.

“We’re really fighting this one,” he added. “We’re just beginning to understand it.”

He said engineers believe the problem can be solved through improvements in the computerized star catalogue that gives the telescope its frame of reference, as well as improvements in the craft’s software.

Another problem involves a strange phenomenon in the Earth’s upper atmosphere that causes the telescope to do some “squirrelly, strange things,” Oliver said.

There is a “non-uniformity” in the Earth’s magnetic field over the Atlantic Ocean, called the South Atlantic anomaly, that has caused problems with other spacecraft and is giving the telescope occasional fits.

“Sometimes, we just all sit there and cuss a little bit,” after the telescope passes through the area, Oliver said.

The Earth’s magnetic field helps protect spacecraft from charged particles from space and other forms of radiation striking the Earth. But the protection is less whenever a spacecraft passes through the South Atlantic anomaly, and it has frequently caused the telescope’s fine guidance sensors to fail.

Oliver said the temporary solution seems to be to turn the sensors off as the craft approaches the area, and then turn them back on after it emerges from the other side. In time, he said, a permanent solution should be found by changing the telescope’s computer software.

Some problems that gave the engineers nightmares in the early days have already been solved, Oliver said. For example, one of the telescope’s main antennas kept hitting some kind of obstruction, causing the telescope to shut down all of its systems and assume a “safe mode” which would protect it from drifting out of control.

It turned out that the obstruction was an electrical cable that had not been lashed down properly, and the antenna hit it as it tracked stations on the ground. Engineers have now programmed the antenna to stop moving before it hits the cable, and that problem has been pretty well laid to rest, Oliver said.

“We’re making progress,” he added. “But it’s slower than we had expected.”

Meanwhile, all five of the major scientific instruments have gone through their preliminary checkouts, and all are performing well, scientists told the astronomy meeting here Thursday.

Within a couple of months, scientists hope to produce a few more photographs that should be a bit more exciting than the engineering photo released late last month. However, it still will be several months before the telescope is able to assume the lead role in astronomy that it is expected to hold for at least the next decade.

It will take a lot more fine-tuning for the craft to perform properly.

“When you are born you learn how to crawl, and then you learn how to walk, and then how to run,” said the University of Colorado’s Brandt. “And if you’re good, they send you off to the Olympics. The Hubble Space Telescope is the Olympics.”