Posted on 08/15/2003 6:36:49 AM PDT by bedolido
The Hubble Space Telescope, astronomy's vaunted time machine, was granted a conditional reprieve yesterday when an expert panel recommended that NASA consider sending a crew of astronauts at the end of the decade to extend its career, rather than dropping it out of orbit, as has been planned.
But the committee said its recommendation should be carried out only if the science to be performed in those additional years was able to beat competing proposals for new NASA science projects.
For the last 13 years, floating above the Earth's murky atmosphere, the telescope has beamed down crisp images of galaxies still forming at the dawn of cosmic time, peering into the hearts of galaxies and quasars in search of black holes, and investigating the mysterious "dark energy" that seems to be wrenching the cosmos apart.
"By any standards the H.S.T. has been a spectacular success — one of the most remarkable facilities in the entire history of science," said the committee, whose chairman is Dr. John Bahcall of the Institute for Advanced Study in Princeton, in a report posted yesterday on the Web site of the National Aeronautics and Space Administration.
The committee members and other astronomers pointed out, however, that since the breakup of the Columbia shuttle, the telescope's future has been threatened because it is hostage to the ability of a space shuttle to pay periodic visits for maintenance and to replace old instruments with new ones.
Those repair missions would take the shuttle too far from the orbit of the International Space Station in case of trouble. As a result, the space agency should be prepared for a range of possibilities, the report said, from no more shuttle missions to two.
More is likely to be heard on that score in a couple weeks when the report of the Columbia Accident Investigation Board is released. But ultimately, Dr. Bahcall said, Congress, the White House and the NASA administrator will decide whether the shuttle may visit the telescope.
Dr. Anne Kinney, who is in charge of astronomy and physics in the space agency's office of space science, said that the Bahcall committee's report was "a good report."
"It reminds us that we need to be flexible," Dr. Kinney said. But she added that there was no budget for the extra mission and no precedent for the kind of competition that Dr. Bahcall and his colleagues had proposed.
"It's going to be a challenge," she said.
Astronomers were generally pleased with the report. Dr. Wendy Freedman, director of the Carnegie Observatories in Pasadena, Calif., called it "balanced and thoughtful."
Dr. George Rieke, an infrared astronomer at the University of Arizona, said the idea of a competition was "a sensible way to deal with limited resources."
Dr. Steven V. W. Beckwith, director of the Space Telescope Science Institute, praised the report, saying, "I couldn't be happier."
He added:"Everyone here is tremendously grateful to NASA for its support of the Hubble. We're delighted to have the chance to compete to continue this extraordinary story."
The story of the $1 billion Hubble, launched in 1990, is one of the great comeback stories in modern science. It was designed to take advantage of an orbital vantage point above the Earth's atmosphere, which smears images and blocks some wavelengths of light from reaching ground-based telescopes.
Once it was in orbit, however, astronomers were devastated to discover that the telescope had a flawed mirror.
The flaw was corrected in 1993 by sky-walking astronauts who, in effect, fitted the telescope's instruments with corrective lenses, enabling Hubble to attain the glory for which it was designed.
NASA has long planned to end Hubble's spectacular run and bring it down to make way in the budget for the James Webb Space Telescope, now scheduled to be launched in 2011. But some astronomers have urged that Hubble's life be extended, arguing that the telescope has grown even more productive in its years in orbit, and that the Webb could be delayed.
Moreover, the Webb is being designed for the infrared wavelengths that very distant galaxies would be emitting as they sped away in the expanding universe, not the visible wavelengths that Hubble sees so exquisitely.
The panel that NASA asked to review the issue also includes Dr. Barry Barish of the California Institute of Technology, Dr. Jacqueline Hewitt of the Massachusetts Institute of Technology, Dr. Christopher McKee and Dr. Charles Townes, both of the University of California, and Dr. Martin Rees of Cambridge University in England.
One of the main elements in their thinking, Dr. Bahcall said, was the realization that NASA might have to mount a mission to the telescope anyway at the end of the decade to attach a rocket to bring it out of orbit safely. The telescope is too big to be left to tumble out of orbit by itself.
The space agency had originally hoped to grab it with the shuttle, bring it back to Earth and put it in the Smithsonian Air and Space Museum, but the Columbia disaster scuttled that option.
NASA is looking into developing a robotic spacecraft that could attach itself to the telescope, but many astronomers argued that the job could be done more reliably by astronauts. And if the astronauts are there anyway, they said, the telescope could be spiffed up for another few years of science.
Another element was the inspirational qualities that Hubble has both for astronomers and for the public, Dr. Bahcall said.
Why not use the ion engines for station keeping and re-boosting the current orbit? If you put it in geo synch, you can no longer service it, until such time as we build something that can take the servicemen that high.
By 2010 the shuttle will have been in service for 20 yrs and it was originally designed for 15. Its doubtful you could even get to 25; what with some of the 70's technology on-board systems and outer shell/ honeycomb panel structure, batteries, etc that cant be swapped out during repair missions, etc. If we let the last couple years be out of the way of Earth's effects; ie not forced to cycle the Earth every 90 minutes with all the resultant thermal jitter,lost science, etc.. the science retrieval would be great! At least that would be the plan.
Not a possible option. The control laws and torque rods for momentum control would not work at Geo.
From Balrog666: Exactly! Why should it join Sky Lab?
I agree to an extent. It depends on the tradeoffs as the equipment degrades on orbit.
From RonF: Being in geosynchronous orbit doesn't make it magcially stable. Geosynchronous orbits degrade, too
Except they degrade as you call it along the geo orbit path due to a non-spherical Earth. There are two "gravity wells" geo birds fall into. When a geo bird is at end of life, we usually (if able) boost them to what is known as a super-synch orbit.
during a station-keeping manuever, someone made a mistake and put the sattelite into a spin that prevented it's command antenna from maintaining an Earth fix, so it couldn't receive the command to stop
It did not have a low gain omni??? WOW!
From Nonstatist: There another servicing mission next year, all ready to go. Theyre just waiting on shuttle use ok. If the next gyro goes, no more science until the shuttle gets there, and that could be moved up, providing this report goes through and theres no flack from the politicos..
Its feasable to boost HST with its own power source (attached somehow); Im just not sure about whether it gets funded.
Cannot be done.
From RonF: I don't know if the ion engines have sufficient specific impulse for station keeping for Hubble.
Why do it? Redesign of the flight code? Gyros and torque rods work great.
I agree, I have done studies on ion propulsion. However, the Hubble cannot work at Geo.
What the heck are reaction wheels I hear you cry! Remember ol Newton? For every action there is an equal and opposite reaction. We spin a mass (reaction wheel) and the spacecraft/satellite spins in the opposite direction. We use the torque rods to unload the excess momentum buildup on the reaction wheels. To do all of this requires only electricity. Solar arrays do quite nicely.
The rub is, that at geosync, the Earth's magnetic field is not strong enough for torque rods to work. The geo birds I have dealt with used a monoprop Hydrazine jet to unload momentum or maneuver.
Possible. However, it does not help the Hubble and there is a real fear of optics/sensor contamination from the jets. For looking at the Universe, low Earth works quite well.
I would love to see a radio telescope array on the far side of the moon though. :-)
I would have to go back and look. I think you would let the momentum build during the shot, then unload as you swung the telescope.
The control laws on the Hubble are incredible.
Hmmm..I'm not as think, as drunk I am...that kind??? :/
This is only true if you are broadcasting something like digital TV back to earth. There is plenty of physical room in geosynchronous orbit. The spacing is to assure that a receiving antenna can be pointed at the correct satelite. A "silent" satelite can be parked there with no problem.
The stability issue is a reasonable objection. Actuallyt any high orbit will be maintained for significantly longer than a low one. If we can predict 10,000 years until orbital decay brings it back to earth we can presume that either:
1. Mankind will be better able to deal with the problem then, or
2. Civilization will have sunk to a point where the crash won't be meaningful.
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