Two of Hubble's six stabilizing gyroscopes have failed outright since the most recent servicing mission, and a third is no longer usable because of erratic behavior.
The failures apparently are not caused by how long the devices have been spinning. They are caused by the age of the machines.
Two of the three remaining operational gyros are original equipment, launched with Hubble in 1990.
The telescope requires three gyroscopes for science operations, and another failure would knock the space observatory out of action until a shuttle crew could be launched for repairs.
"Hubble is a priceless, irreplaceable resource, and it's got a finite life. So every month lost is a month lost forever to science," chief project scientist David Leckrone told CBS News.
Although NASA already had planned a repair flight (the third of its kind) for June 2000, Hubble project managers want a flight sooner.
They want to split the flight into two missions. The first would take place around Oct. 14, and the second, in early 2001.
The managers say six new gyroscopes would be installed during the first repair flight, in addition to other new hardware. A new computer might also be installed, although that issue is still under discussion.
The flight, aboard the shuttle Discovery, would last eight days and include at least three spacewalks.
During the second mission, the Hubble would get a new camera, new solar arrays, and new cooling systems.
The Hubble is not in any danger of being permanently sidelined, according to Bill Readdy, a veteran shuttle commander who manages the shuttle program at NASA headquarters.
Readdy says the issue is when the fourth gyroscope might fail and how long Hubble might be out of action before repairs could be made.
"It's a question of losing science," Readdy said. "There isn't any reason to suspect [additional gyros] might fail tomorrow or six months from now. But the probability is that, by summer of 2000, one or more of the gyros would have failed. That's what's driving us."
Standing in the way of an October Hubble repair launch is the Russian launch of the service module, a key space station component, scheduled for around Sept. 20.
If that takes place, a shuttle logistics and supply mission would need to be launched shortly thereafter.
Also complicating the picture is the possible launch of the station's first permanent crew in the fall of 1999.
Despite the wrangling about when the repair flight would happen, the Hubble team stands ready to go.
Four spacewalkers, Steven Smith, Michael Foale, Claude Nicollier, and John Grunsfeld, have been training for months.
A commander, pilot, and robot-arm operator, howevr, would need to be named immediately to support an October flight.