As described by Cepollina, these crafts would have swappable parts and could potentially be fixed easily by space-walking astronauts.

It tumbled out of control then because of crew errors, and two space-walking astronauts had to go out and haul it in.

NASA reckoned the space station would need little maintenance by space-walking astronauts and budgeted for just 130 hours a year.

If the aperture door should jam, for example, space-walking astronauts could pry it open.

They also inspected the pressure suits the four space-walking astronauts are to wear when they go outside for the repairs.

The twin problems come amid debate over whether the planned $37 billion American space station, scheduled for launching in the late 1990's, can be readily repaired by space-walking astronauts.

Two space-walking astronauts hung the orbital equivalent of flypaper on the Russian space station Mir today to collect cosmic grit.

Astronomers said it would take two weeks just to verify the condition of the new camera, corrective optics and other equipment installed by the space-walking astronauts.

The space-walking astronauts in 1993 may have demonstrated that the Hubble could be refurbished with surprising efficiency, but space agency officials cautioned against taking anything for granted.

Corrective optics were installed last month by space-walking astronauts of the shuttle Endeavour.