Problems Mounting for Space Telescope : Astronomy: Hubble’s flawed mirror can’t be fixed for at least three years. Repair is also uncertain because a corrective lens must be built without direct examination of the instrument.
Officials with the space agency and the company that built the mirrors for the Hubble Space Telescope agreed Thursday that the fuzzy images produced by the $1.5 billion instrument resulted from a flawed mirror and there appears little chance of fixing it in much less than three years.
Even that is uncertain because scientists must build a “corrective lens” for a complex instrument that is 381 miles above the Earth and cannot be examined directly.
It all added up to a stunning setback for the National Aeronautics and Space Administration, which had counted on the telescope to help polish its image as a world leader in technological achievement. Instead, the agency has been left with a seriously crippled telescope, a troubled fleet of space shuttles, a sagging reputation and a bunch of disgruntled astronomers.
As they tried to put the best face on the situation, scientists insisted that the problems with the telescope--disclosed on Wednesday--amount to a setback that will delay, not deny, scientific results from the the most sophisticated and most expensive instrument ever put into orbit. But no one was denying that the development came as a profound surprise and a deep disappointment.
“All of us had things we worried about,” said James Westphal of Caltech, principal scientist on the telescope’s primary camera. “But this came out of left field.
Adding to the frustration was the fact that the problem stems from a fundamental manufacturing error, not a major design flaw.
“Damn it, this is a little technological problem,” Westphal said. “Somebody made a simple mistake and something got built wrong.”
What’s “wrong” is the heart of the system: The optics that must serve as a telephoto lens for the Hubble’s cameras and instruments.
“We are in agreement (with NASA) that there is a spherical aberration in the telescope system and that the most likely cause is one of the two mirrors,” said Thomas Arconti, spokesman for Hughes Danbury Optical Systems. The Connecticut firm was acquired by Hughes Aircraft Co. after the mirrors were completed.
At least two investigations into the problem have been launched, one by the manufacturer, and the other by NASA. Lew Allen, director of the Jet Propulsion Laboratory, will head NASA’s probe.
For the next three years, the mistake will deny the world the crisp photos that the Hubble was supposed to produce. The Hubble was designed to create the sharpest images of the most distant objects in the universe, opening vistas no one has seen before, but Westphal’s wide field camera will be out of service until astronauts replace it. Other instruments will also be affected, but the most serious loss will be the images that had been expected to revolutionize understanding of the universe.
The most troubling footnote to the affair is the fact that the flaw in the mirror should have been detected long before the telescope was launched last April, experts said.
“The discouraging thing is that this was inexcusable,” said one key astronomer who has been associated with the Hubble for many years.
“We had a very elaborate test program for these mirrors, and if this is a manufacturing defect it should have readily shown up” before the instrument was completed, he added.
Yet the flaw appears to be just that--a basic error in manufacturing.
The telescope uses two mirrors. A primary mirror, nearly 100 inches in diameter, captures the light from a celestial target and reflects it onto another mirror, called the secondary, which focuses the light on sensors that work with the Hubble’s five primary instruments.
What apparently is wrong, experts said, is that one of the mirrors is not curved quite the way it was supposed to be, and nobody knows which mirror is off. The curvature must match specifications perfectly in order to focus the light precisely enough to produce a sharp image.
Ironically, the mirrors are among the few items that were not designed to be replaced by visiting astronauts because such a chore is considered too difficult in space. There is virtually no chance that the telescope will be retrieved by a shuttle because it would likely be damaged, and certainly contaminated, during the shuttle’s descent through the atmosphere.
“That would put us out of service for several years,” said astronomer Stephen P. Maran of NASA’s Goddard Space Flight Center.
Westphal, like several others, insisted that the troubles with the Hubble are “a major setback, not a disaster. It can turn into a disaster, clearly, if somebody makes a decision to kill the whole program, and such a decision is not an impossible thing to imagine.”
Since the mirror cannot be corrected, the telescope’s camera must be replaced with a new one designed to compensate for the flaw in the mirror.
Westphal’s wide field camera--the Hubble’s primary eye on the sky that uses the telescope as a telephoto lens--was supplied by Caltech and the Jet Propulsion Laboratory. A replacement camera has been under construction for some time because scientists had expected to upgrade all of the instruments when the shuttle returns to the telescope in about three years for the first of several expected maintainance calls.
Kim Leschly, systems engineer at the Jet Propulsion Laboratory, said the replacement camera probably will not be completed until its scheduled launch in June of 1993.
“We’re already on an accelerated schedule for the June launch,” Leschly said. “It’s very difficult to accelerate it any further.”
Westphal said he thought about six months could be shaved off that.
The optics in the replacement camera will have to be fitted with a corrective lens that will focus the image much the same as corrective glasses are used to improve human vision.
But Leschly and his colleagues face a major engineering challenge because they cannot examine the telescope firsthand to determine the right prescription for the corrective lens. Instead, they will have to examine hundreds of images from the camera aboard the Hubble and try to determine the exact characteristics of the manufacturing flaw.
“But how do we make sure it will work when we put it on the telescope?” Leschly said. “The other piece is up there (in orbit, 381 miles above the Earth.) How do we make sure?”
The JPL team will create a computer model, based on what they think the mirror’s flaw is like, and then produce many images from the camera aboard the Hubble to see if the images match the model.
If everything checks out spacewalking astronauts will switch cameras. Then, and only then, will the JPL engineers know if they have done their homework right.
“It’s going to be a nervous time,” Leschly said.
Meanwhile, scientists expect to get some important data from the remaining instruments aboard the Hubble. But most experiments will be affected in some way by the problems with the telescope’s main optics.