The Russian space station Mir reached the first leg of its final descent Wednesday morning, having orbited slowly down to the critical altitude designated as the point of no return.
The aging station will become the largest manmade shooting star ever when it falls to its fiery doom on Friday. Russian mission control plans to use a cargo ship full of fuel to guide the 15-year-old Mir down. By firing its thrusters in 20 minute bursts three times over the course of six hours, the ship should angle Mir towards a watery grave in the South Pacific, between New Zealand and Chile.
Mir began its concluding journey when it reached the altitude of 220 kilometers (136 miles) above Earth early Wednesday morning, the height at which Russian mission control began delicate maneuvers to stabilize Mir for a controlled descent. Russian officials plan to fire the ship's engines beginning about 7:30 p.m. EST on Thursday for a final reentry time of 1 a.m. EST on Friday. However, Russia has pushed back Mir's death date for several weeks now, and atmospheric conditions make the exact reentry time uncertain.
Most of the 137-ton station will burn up during reentry, but about 20 to 30 tons of debris fragments are expected to rain down in a swath 6,000 kilometers (3,700 miles) long and 200 kilometers (125 miles) wide, leaving in their wake bright meteor-like streaks and smoke trails.
"It should look like a tremendous fireworks display," said Jordan deBree, spokesperson for the Mir Reentry Observation Expedition. "The racing lines of fire across the sky may also be accompanied by giant explosions, when the station's superheated fuel tanks and pressurized modules blow up due to the enormous heat."
Some 50 paying members of the expedition will watch Mir's descent from Fiji. "The island is some 200 miles away from any possible impact area," deBree said.
Russia has assured Japan, Australia and New Zealand that Mir's controlled reentry will bring debris far away from any populated areas. Still, Russia has taken out a $200 million in insurance just in case, because Mir's irregular shape makes it hard to predict how the station's parts will fall.
The aging orbiter was intended to operate for only five years when it was launched in 1986. When the Soviet Union collapsed in 1991, however, the Russians extended Mir's lifetime rather than building another station. Last year, Russia decided to scrap Mir, because its maintenance costs became too expensive for the unstable Russian economy.
Mir is the largest and longest-lasting space station built so far. During its life, cosmonauts and astronauts used the station to observe distant galaxies and study the effects of weightlessness on biology, physics and chemistry. Despite its proven successes, Mir also had its share of problems, ranging from computer failures and power glitches to jammed airlocks and fungal contamination. An unmanned cargo ship even crashed into a science module in 1997, causing a momentary loss of air pressure and damaging a solar panel.
While popular U.S. entertainment has lampooned Mir's many mishaps, the U.S. Skylab space station was similarly plagued with problems. Roughly a minute after Skylab was launched in 1973, its meteoroid shield deployed early and tore off, leading to the further loss of a solar array and resulting in continuous power deficiencies.
Skylab fell to Earth a year or two earlier than expected in 1979 due to unanticipated sunspot activity that greatly increased atmospheric drag on the station. In its uncontrolled descent, the U.S. station broke up over sparsely populated areas in western Australia. If Mir were allowed to naturally plummet down in a similarly uncontrolled manner, its fiery trail of debris could cover a stretch from Wyoming to Louisiana.