Engineers work to stall Hubble's death

By Leonard David

Senior space writer

updated 4:10 p.m. ET Sept. 14, 2005

To keep the Hubble Space Telescope going, officials are changing how it operates and contemplating other actions for the aging observatory.

Engineers recently shut down one of the orbiting observatory’s three operational gyroscopes in an effort to preserve the operating life of the third gyro, thereby pushing Hubble’s science observations into mid-2008.

Other life-extension ideas are being studied — even downshifting Hubble onto one-gyro mode.

Scientists and engineers remain hopeful that the telescope will once again get a servicing makeover by astronauts. But such a shuttle mission depends on the health of that human spaceflight program. The shuttle is headed for retirement in 2010, with a vaguely defined Crew Exploration Vehicle to be its replacement. Meanwhile, it is not clear when the next flight will take place nor whether a trip to Hubble will be possible.

Keeping Hubble alive and scientifically valuable has become a race against the clock that involves aging hardware and dwindling battery life while solar activity that eats away at satellite’s orbit — and of course, budget considerations.

Shuttle stopover
Hubble packs six gyroscopes and four free-spinning steering devices called reaction wheels. This hardware is used to point the telescope for observations.

Late last month, Hubble Space Telescope engineers purposely shut down one of the three operational gyroscopes aboard the observatory. The system was originally designed to operate on three gyros, with another three in reserve.

The “two-gyro science mode” is expected to preserve the operating life of the third gyro and stretch out the telescope’s science observations halfway into 2008.

“The best idea for extending life beyond two gyros is to get up there with the shuttle and service it. And that’s what we’re working on,” said Preston Burch, program manager for the Hubble Space Telescope at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

While such a mission is not manifested for the shuttle program at the moment, Burch said his program is shooting for a Hubble servicing mission in December 2007. Preliminary discussions, he told SPACE.com, also point to shuttle Atlantis being tapped for that servicing stopover.

Science discovery factor
There are two new instruments ready and waiting to be plugged into Hubble:

• Wide Field Camera 3 that sees in both infrared and ultraviolet wavelengths and far more sensitive in the infrared than Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS).
• Cosmic Origins Spectrograph that is capable of studying the chemical composition of far-distant interstellar gas and replaces Corrective Optics Space Telescope Axial Replacement (COSTAR) hardware.

“What makes Hubble worthwhile,” Burch said, “is putting in new science instruments that have state-of-the-art detectors to really make the leaps forward ... what we call the ‘science discovery factor.’ Those are the things that are really going to make Hubble a useful and desirable space research vehicle beyond the 2008 time frame.”

A Hubble Servicing Mission 4 would have the visiting shuttle crew also boost Hubble into a higher orbit, replace a fine-guidance sensor, and place protective material on top of torn insulation.

Life-extension initiatives
Meanwhile, Hubble engineers have scoped out a non-shuttle priority list of things to do that can maintain the telescope’s well-being. There’s a list of roughly two dozen items that would be worth considering, Burch said. After the Columbia accident, he added, a Hubble life-extension initiatives program was put into force.

The two-gyro science mode was at the top of that list. New pointing algorithms had to be developed. Simulations were done on the ground to prove the idea workable. Then the concept was tested on Hubble itself.

“It worked far better than we had expected,” Burch said. Now, both government and industry teams are looking at the feasibility of a one-gyro science mode. “That could be very key in terms of keeping the science going if a shuttle [servicing] launch date drifts to the right a lot,” he added, say until late 2008 or perhaps early 2009.

Other life enhancing thoughts include tracking the number of cycles on Hubble transmitters and hours of operational use.

Endurance run
A key to Hubble’s endurance run are rechargeable nickel-hydrogen batteries, energized by the observatory’s solar panels. The telescope has its original batteries. They date back to 1990 and are deteriorating in power levels with age. When the batteries are no longer able to hold a charge, Hubble becomes inoperable.

Burch said that a Hubble battery test bed at NASA’s Marshall Space Flight Center in Huntsville, Alabama is helping to forecast battery lifetime. That test rig uses one of the Hubble flight-rated battery spares to assess power trends. Other Hubble-unique facilities try different charging and energy management schemes, he said.

“The projected life of Hubble batteries has been extended. We used to say we thought they were good until 2008-2009. Now we’re thinking 2010,” Burch said. “We think Hubble will remain serviceable until well into 2010…based on latest projections and test data we have.”

How productive Hubble will be at that time from a science perspective is a different matter.

“That’s driven principally by the gyros. And right now, we’re saying we think we’re good until the middle of 2008,” Burch said. “Hubble will still be worth servicing as long as the batteries hold out.”

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