However, astronomers believe it will still be able to make its astronomical observations.

An engine firing over the weekend raised the high point of the Chandra X-ray Observatory's orbit to 148,300 km (86,433 miles) or about one-third of the way to the moon.

Engine problems

Programme manager Fred Wojtalik said one of two engines used to boost the telescope performed slightly below expectations. As a result, a backup pair of engines will be used to raise the low end of Chandra's orbit on Wednesday and again on Saturday.

The observatory will spend the next five years looking for black holes and studying stars, galaxies and quasars.

The Mir cosmonauts last space walk ended early

The Mir space station is also having difficulties. Mir's main computer shut down last Friday but officials said on Monday that there was no problem and it would be switched back on Wednesday.

"The computer shut-down cut off the power supply to some parts of the craft, something the cosmonauts would have had to do themselves for maintenance work," said a duty officer at Mission Control outside Moscow. "So, they just jumped at the opportunity."

The crew had planned to start installing some new electronic equipment on Monday. But the operation was able to start two days earlier because the computer glitch had already disconnected the electricity supply.

The station is currently being kept on track by the alignment system of the cargo craft, which is docked to Mir.

The three-man crew aboard Mir is due to return to earth this month, leaving the station unmanned. Russia has said a crew may return to Mir if it finds more funds for the programme. However, Deputy Prime Minister Ilya Klebanov said last month that Mir had fulfilled its goals and should be abandoned gracefully.