NASA is going ahead with a plan to restart the flow of science data from the Hubble Space Telescope by routing around circuitry that failed a little more than two weeks ago, officials said Tuesday.
The unprecedented switchover is due to begin early Wednesday, and if all goes well, the telescope should be beaming imagery back down to Earth by Friday, said Art Whipple, manager of the Hubble Space Telescope Systems Management Office at NASA's Goddard Space Flight Center.
Last month's glitch forced the postponement of the shuttle Atlantis' servicing mission to the world's best-known space observatory. That mission had been due for launch on Tuesday, but it's now been put off until next February at the earliest. Whipple said the plan for that orbital service call was "still being hashed out."
The operation planned for this week will be done entirely by remote control, from Hubble's operations center on the Goddard campus in Maryland. Controllers will switch Hubble's command and data handling system from the channel it was using, known as Side A, to a backup channel called Side B.
Whipple said NASA's experts were confident that Side A was the source of the glitch that cut off the flow of science data. "As far as we can tell, nothing else was affected," he told journalists during a teleconference Tuesday.
Over the past couple of weeks, teams at Goddard have been testing a spare data-handling unit and checking diagnostics from the telescope to make sure the plan for the switchover was solid. The electronic components on Side B have never been used before during Hubble's 18 years of operation, and it's not certain that they will work this time.
"It is a complicated procedure, and it's one that we have not done end to end before," Whipple said. But he said experts determined that even under the worst-case scenario — for example, if there were a hidden flaw in the Side B electronics — the telescope would not be left in worse shape than it is now.
In order to do the switchover, controllers at Goddard will have to put the telescope into safe mode, issue commands to reroute circuitry through Side B rather than Side A, then return the telescope to its operating condition.
"This is something that is a little out of the norm of what you would do around the house, but it's probably not unlike what an IT professional might do with an office network," Whipple said.
"The difference is, on the ground, you tend to power things on and off and reconfigure by pushing buttons and swapping cables," he said. "Since we can't do that, of course, with something in space, there are ... switches that do the functional equivalent of swapping cables, and remotely commanded relays that allow us to send a command and power something on or off."
In all, 40 to 50 people will be involved in the operation. "People will be working 24/7 for the total time here," said Jon Morse, director of the Astrophysics Division in NASA Headquarters' Science Mission Directorate.
The most critical time in the switchover will last from about 8:30 to 11 a.m. ET Wednesday, Whipple said. If the recovery is successful, the first data should be received from one science instrument late Thursday, with full operation restored on Friday, he said.
The very first image is due to show an internal lamp that is part of the apparatus for Hubble's Advanced Camera for Surveys, which is currently inoperative due to an earlier glitch.
"Nothing could be aesthetically less pleasing," Whipple said, "but it will be a great relief to everyone when we see that flat field illuminated by that internal lamp."
Hubble's managers expect that the first science instrument to be revived would be the Wide Field and Planetary Camera 2, which has produced some of the telescope's most famous images in the visible-light spectrum. Another imaging device, the Near Infrared Camera and Multi-Object Spectrometer, could come back into service later.
The big upgrade for the telescope, involving the installation of two new instruments and the hoped-for repair of two others, will have to wait until Atlantis gets off the ground. NASA would also send up the spare command and data-handling unit for installation as a replacement part, assuming that the unit passes its ground testing. The telescope would continue to use Side B on the replacement unit, Whipple said.
He said experts may not know exactly why Side A on the current unit suddenly went bad until the apparatus is brought back down to Earth for analysis. But he wouldn't rule out a diagnosis that the normal wear and tear experienced during 18 years of use led to the breakdown.
"Unfortunately, nothing lasts forever," he said.