The on-line engineering analysis of the Hubble upgrade makes compelling reading.

"The space sciences of astronomy, astro-physics, and astro-biology could be advanced by ten years, perhaps more, if a faster, cheaper, better way than an entirely new spacecraft could be found to implement an 8-meter class observatory in space," the study panel wrote in its executive summary.

EVA Day 1 Remove Old Light-Shield section and install IESS. EVA Day 2 Install New Light-Shield using RMS Arm and deploy radially. EVA Day 3 Install New Mirror Assembly. EVA Day 3 The New Light-Shield is deployed axially completing the installation.

The analysis was led by Jim Crocker of Johns Hopkins University and included participants from the University of Arizona; the University of Colorado; NASA's Jet Propulsion Laboratory; Lockheed Martin; Swales Aerospace; Raytheon Optics Systems; Ball Aerospace; and Orbital Sciences Corp.

The key to the project is a folding, lightweight circular mirror made, perhaps, from an existing Very Large Telescope blank. All but about 2 millimeters of glass would be ground away and 5,000 actuators would be used to control the mirror's shape once unfolded and in place.

"The 5,000 actuators add complexity but have a nice advantage of providing the capability to control wavefront and, in the case of the secondary mirror, control line of sight," the team concluded.

To install the new mirror, spacewalking shuttle astronauts first would remove Hubble's current lightshield, that is, the forward section of the observatory's telescope tube just above the spacecraft's two solar arrays.

A new light shield would be installed, followed by the new mirror assembly and upgraded science instruments. At least four spacewalks would be required, but the work is no more challenging than tasks already planned for space station assembly.

But the additional mass - about 3,500 pounds - would affect the performance of Hubble's guidance and attitude control system and its star trackers would have a restricted field of view because of blockage from the new mirror.

The telescope would not be able to slew to new targets as quickly as it can now and the increased cross section would increase the effects of atmospheric friction, or drag. That, in turn, likely would require the attachment of an ion propulsion system to keep the spacecraft above 300 nautical miles.

But the study team concluded the obstacles are surmountable and that the project is feasible. The team believes:

Increased atmospheric drag would necessitate periodic shuttle reboosts or the addition of a small propulsion package.

"The design, development and construction could be done in a five- to eight-year time frame, perhaps less depending on funding," the study team wrote. "The cost will be of order less than half that of an entirely new spacecraft and observatory."

<Outlandish plan to upgrade Hubble