A Progress M1 spacecraft. Photo: NASA

After a three-day chase, an unmanned cargo ship successfully reached space station Mir today, becoming most likely the last arrival from Earth to the outpost.

The Progress M1-5 spacecraft, carrying propellant for Mir deorbiting, docked to the station's Kvant-1 module at 0534 GMT (12:34 a.m. EST).

Counting the Progress M1-5, total 110 spacecraft were launched toward Mir during its 15-year history, including the additional modules, manned Soyuz transport ships and U.S. space shuttles. Many Soyuz and Progress ships conducted multiple dockings with the station. Today's docking was the 121st linkup.

Unless a major malfunction onboard Mir disrupts the station's controlled deorbiting, no other launches toward the outpost are scheduled to take place before the station reenters the atmosphere and burns up in March.

Still, one more crew prepares to fly to Mir to assist with the deorbiting operations if necessary. The Soyuz TM spacecraft for the possible emergency mission to Mir reportedly could be ready for launch as soon as February 10, in case today's docking failed. However, a successful arrival of the Progress M1-5 to the station makes the manned mission to Mir less likely.

Space station Mir. Photo: NASA

Another possible scenario, which might still require the crew onboard Mir would be the failure of the station's flight control system. The cosmonauts could replace failed elements onboard the station, or manually control all but last firing of the braking engines.

RKK Energia representatives said that under no circumstances would the crew remain onboard Mir during its last reentry maneuver, even though such situation is technically possible.

According to plan, the Progress M1-5 will use its own engines to gradually lower Mir's orbit and then perform final braking maneuver to knock Mir out of its orbit. The station will then plunge into the atmosphere and its flaming debris falling into the Pacific Ocean.

Depending on the condition of the upper atmosphere, the station might reenter sometime between the beginning and middle of March. The regular peak of solar activity, which takes place approximately every 11 years, causes wild fluctuations in the density of the atmosphere. The phenomena makes it more difficult to predict atmospheric drag, which causes low-orbit spacecraft, including Mir, to gradually spiral down toward denser atmosphere and ultimately reenter.