The official said the Progress cargo ship's computer will be used as a backup if Mir's own main computer fails when MCC begins the 15-year-old station's series of deorbiting burns, set for the early hours of March 22.

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Mir's primary digital computer was activated on March 12 and MCC specialists successfully completed testing it one day later. The station's guidance control system was also turned on March 15. It was tested and turned off on March 16, the official said.

The control system will be fully activated for the deorbiting of the aged scientific outpost only when the station reaches the critical mark of 137 miles (220 kilometers), he said.

The Progress cargo ship's guidance system will be turned on and used only in case any part of the Mir control system malfunctions -- for instance, if the electrical power supply plummets or if the station's main computer breaks down.

The complex has, meanwhile, continued its descent. Mir's altitude decreased 1.6 miles (2.5 kilometers) from March 15 to March 16, dropping to 146 miles (235 kilometers), the official said.

Both Kiryushkin and deputy flight control chief at Korolyov, Viktor Blagov, insisted that they do not expect Mir's main computer to fail, even though the station will be flying on its final day at an altitude ranging from 110 to 124 miles (180 to 200 kilometers) where it "can start scraping against" the denser layers of the atmosphere, according to one official at the Russian Aviation and Space Agency.