The Mission Control Center in Korolyov, outside Moscow, believes that March 22 is the most likely day for bringing down and sinking the Mir space station.
The station's computer will send two control pulses, moving the station into an elliptical orbit with a perigee of 137 miles (220 kilometers) and an apogee of 102 miles (165 kilometers). The apogee will be over the sinking area in the Pacific Ocean. The first pulse will be generated March 21 at 7:32 p.m. EST (March 22 at 00:32 GMT; 3:32 a.m. Moscow time) and the second one, at 9:22 p.m. EST (March 22 at 02:22 GMT; 5:22 a.m. Moscow time) when the station is outside the Mission Control Center's range.
During the two subsequent orbits that will take up to 90 minutes, the center will determine the exact features of the resultant orbit and the timing of the final control signal to be sent from the center. They believe that a pulse lasting about 11 minutes will be sent between 12:28 and 12:48 a.m. EST (05:28 and 05:48 GMT; 8:28 a.m. and 8:48 a.m. Moscow time) March 22.
Fragments of the station that do not burn up in the atmosphere are expected to fall in the desired area of the Pacific Ocean at 1:21 a.m. EST (06:21 GMT; 9:21 a.m. Moscow time) on March 22.
The area where pieces of Mir will fall into the ocean has changed slightly because several deserted islands belonging to France are located in the area of the Pacific that had initially been selected, Mir flight director Vladimir Solovyov told a news conference at Mission Control on Wednesday.
Russian space officials also said Wednesday that the space station would not fly past Japan as initially expected before it plunges into the Pacific. A spokesman at the Russian aerospace control center said the change in the final flight path is the result of technical reasons and has nothing to do with fear in Japan that the falling Mir might strike Japanese territory
Initially, Mir's small maneuvering engines will be used to slow it down. In the final phase, the main engine of the Progress cargo ship that is docked with Mir, along with all the station's engines will be brought into play.
Solovyov said Mission Control has played out a large number of emergency scenarios and possible ways of dealing with them. For example, Mir's batteries could unexpectedly run down, shutting down the station's control systems. In that case Mission Control would switch to the backup system for controlling Mir's movements, and then switch to the computer on the Progress ship.
Solovyov said Mission Control specialists do not rule out malfunctions in the central onboard computer, which have happened previously. In that case, Mission Control would also have to use the computer on Progress to control the station's flight. He added that Mission Control has no doubts about the reliability of the control system on Progress, which is monitored round the clock. Solovyov said that many backup maneuvers for deorbiting Mir have been worked out in case something goes wrong.
The tourist planes and ships that plan to stay close to the area where fragments of Mir are expected to fall are not likely to see much, Solovyov told a news conference.
The Mission Control Center will not maintain contact with the planes and ships, Solovyov said. Once the final braking pulse signal is sent to Mir, the station's fall will be followed by Russian command and monitoring systems in Ulan-Ude, Ussuriysk and Petropavlovsk-Kamchatsky, he said.
The parts of Mir that have not burned up in the atmosphere will fall into an area of the Pacific where nobody resides and there is no shipping, Solovyov said.
Mir's altitude dropped 1.7 miles (2.7 kilometers) to 149.7 miles (240.9 kilometers) on Tuesday.
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