Engineers recently shut down one of the Hubble Space Telescope’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.
Scientists and engineers remain hopeful that the telescope will once again get a servicing makeover by astronauts, but 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 eats away at the satellite’s orbit — and of course, budget considerations.
Hubble packs six gyroscopes and four free-spinning steering devices called reaction wheels, which are used to point the telescope for observations.
In late August , Hubble engineers purposely shut down one of the three operational gyroscopes to preserve its operating life and stretch out the telescope’s science observations halfway into 2008 . The system was originally designed to operate on three gyros, with another three in reserve.
“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, M d.
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 said , also point to shuttle Atlantis being tapped for that servicing .
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 is far more sensitive in the infrared than Hubble’s Near Infrared Camera and Multi-Object Spectrometer .
- Cosmic Origins Spectrograph, which is capable of studying the chemical composition of far-distant interstellar gas and replaces the Corrective Optics Space Telescope Axial Replacement hardware.
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.
Meanwhile, Hubble engineers have compiled a non-shuttle priority list of ways to maintain the telescope’s well-being — roughly two-dozen items that would be worth considering, Burch said. After the Feb. 1, 2003 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 ideas for prolonging Hubble’s life include tracking the number of cycles on Hubble’s transmitters and the hours of operational use.
In addition, key to Hubble’s endurance are rechargeable nickel-hydrogen batteries, energized by the observatory’s solar panels. The telescope has its original batteries, which date back to 1990 and are deteriorating . Once they 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, Ala., is helping to forecast battery lifetime.
“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.
“They are not degrading as fast as we had feared,” said James Crocker, vice president of civil space programs atCompany near Denver, Colo . Past experience with batteries in space suggest that they tend to degrade gracefully, he said, perhaps allowing use of select Hubble instruments at some point.
Crocker said that NASA chief Michael Griffin has the Hubble team marching toward a shuttle servicing mission, given a couple of good shuttle flights.
Given Hubble’s batteries and the gyro fixes, “I think we’ve got a nice window” for shuttle servicing, Crocker added, probably no sooner than December 2007 — with a goal of perhaps pulling it in a few months earlier if necessary.
Meanwhile, Lockheed Martin was advised to stop work on the deorbit module, in a letter dated Sept. 2, Burch said. However, that communique also called for “partial termination” of some related work by the company.
The contract was not totally cancel ed, and Lockheed Martin expertise is being requested for both sensor technology ideas and an attachment fixture to be outfitted to Hubble, which could be secured to the telescope by either astronauts or by a robotic mission, he said.
The company has been informed that all propulsion hardware for the deorbit module that is 75 percent complete or greater should be wrapped up and turned over to the Lunar Reconnaissance Orbiter (LRO) project.
“Scrapping hardware that is three-quarters complete is, I think, sinful,” Burch said. So the plan is to use deorbit module-related valves, thrusters and other items for the Goddard Space Flight Center-managed LRO project, he said, with the LRO office reimbursing the Hubble project for that hardware.