CAPE CANAVERAL, Fla. — Spacewalking astronauts prepped the Hubble Space Telescope on Tuesday for its riskiest surgery yet: a power-unit replacement that has been likened to a heart transplant.
If the operation fails, the $2-billion-plus telescope could be crippled or rendered useless.
"Any major surgery entails a certain degree of risk," cautioned Hubble's project scientist Dave Leckrone.
Surgery was scheduled for this morning during the third spacewalk in as many days for shuttle Columbia's astronauts.
Assigned to the task: John Grunsfeld, an astrophysicist who has operated on Hubble before, and Richard Linnehan, a veterinarian who has cut into animals but not a 43-foot telescope.
NASA said it had little choice but to replace Hubble's original power control unit, a long, narrow box with 36 connectors jammed together.
The 12-year-old unit has a loose screw that is hampering its ability to circulate electricity through the telescope. The problem has occurred on and off for eight years.
If the power trouble worsened, astronomers would be able to use only one of Hubble's scientific instruments at a time. In the worst case, some of the telescope's batteries could overheat, rupture and wreck Hubble.
Before the repair work could begin, power to the telescope had to be turned off completely for the first time in orbit. NASA could not guarantee that all of Hubble's systems would come to life once the new power control unit was plugged in and the telescope turned back on.
Ground controllers will be racing against the clock; the systems cannot be without power too long, otherwise they could be damaged by the cold.
On Tuesday, spacewalkers James Newman and Michael Massimino loosened bolts on the doors leading to the power control unit and batteries. The men also installed Hubble's second new solar wing and replaced an unreliable steering mechanism.