In less than a month, NASA expects to make a life-or-death decision regarding the Compton Gamma Ray Observatory (CGRO). The crucial meeting that will decide the fate of one of NASAs major science spacecraft is currently scheduled for February 16.
One of the observatory's three gyroscopes malfunctioned on December 6, and the failure of the second unit would leave the 16-ton spacecraft uncontrollable.
The only real hope CGRO scientists have in salvaging the observatorys mission is an alternative flight control scenario currently being evaluated at Goddard Space Flight Center, the NASA facility in Greenbelt Maryland that controls the CGRO.
"(Saving the observatory) is a technical issue, not financial."
By February 16, Goddard scientists will have to present NASA management with two options: One plan is to de-orbit the lab with a controlled reentry into the Pacific Ocean, just southeast of Hawaii, before a second gyro failure occurs. The second offers an alternative that maintains control of the spacecraft in orbit even if the second of its three gyroscopes is no longer online.
Two scenarios
The plan to de-orbit the lab will require multiple firings of the spacecrafts engines to eventually lower its 311-mile (500-kilometer) orbit for a controlled reentry on March 14.
The alternative flight control scenario, if approved by Dr. Edward Weiler, NASA's associate administrator for space science, would use the observatory's on-board sun sensors, magnitometers and reaction wheels in conjunction with the remaining gyroscope in an effort to keep the craft in space.
Speaking at the meeting of the American Astronomical Society recently, Dr. Weiler expressed hope that the CGRO could be spared. However, according to Goddard scientists and NASA headquarters officials it won't be easy convincing NASA to continue with the mission.
Preston Burch, deputy program manager for Goddard's space science operations, said during the December 17 meeting on the observatory's fate that the general mood was not optimistic.
Although there have been no signs that a second gyroscope is failing, and given the fact that these devices have proven to be reliable in the past, NASA still does not want to take any chances if a second failure does occur. With the control system disabled, NASA would have no way to predict where the CGRO's fiery debris would fall.
An uncontrolled reentry would be a matter of concern for the space agency. As big as a large pickup truck, CGRO is built around a titanium structure. The gamma ray detectors on board weigh a total of 6 tons, this includes shield covers made of lead that are used to screen scattered radiation. According to estimates, fiery debris from the CGRO would rain over the area hundreds of miles long.
"Goddard will have to make it pretty certain to us that the alternative flight control plan would work," said Alan Bunner, science program director for structure and evaluation of the universe at NASA headquarters.
Goddard experts said that it will take some time to develop the algorithms and write the new software to augment the observatory's failing gyros with alternative devices. According to different estimates it could take anywhere from less than six months to just over a year to implement new methods of control.
To make matters worse, Goddard will need additional funding and possibly have to hire more programmers to do the job. Bunner said that if Goddard comes up with a plausible plan to control the CGRO, funding would not be a problem.
"This is a technical issue, not financial," Bunner said.
At present, the possibility of retrieving the observatory with the space shuttle has all been but ruled out by NASA due to high risk and the cost of such operation. Only three people are currently evaluating this option at Goddard, Burch said.
advertisement
