The space shuttle Discovery was successfully launched this morning taking a new crew to the International Space Station. As the new space station is being readied for occupancy, the old space station, Mir, has finished its tour of duty and will soon be brought back to Earth. The Russian Mir space station has been a work horse for the better part of 15 years. Like many of the spacecraft made by the former Soviet Union, Mir is an example of the tortoise approach to going somewhere. This is not meant to be disrespectful. Just like the great weight-lifter Vasily Alexeyev, who broke dozens of his own lifting records in the 1970s by increasing the weight by a kilogram nearly every time he entered a competition, the former Soviet space program was designed to plod along using a methodical approach. No tremendous strides are made, and the technological learning curve is at times fairly steep. Nevertheless, in the end, things get done. At times Mir has behaved like a leaky old clunker that just keeps working. It starts nearly time you turn the key, but it only runs on 7 cylinders instead of 8, and smoke belches out of the exhaust every time you accelerate. The US approach has been more akin to taking that brand new sports car for a spin. It has all of the latest gadgets, and has a high eye catching quotient, but it seems to be spend a lot of time in the shop. Still, ingenuity, a "can do spirit" and our government's willingness to fund a variety of projects has produced some amazing results in a lot of different areas over the years.

Through the 1980s, and until the break up of the Soviet Union in 1991, the Soviet program's annual launch rate was 5 times that of the US rate. To launch their payloads into orbit, the Soviets used reliable big boosters, and unlike the US rockets that use solid propellants, their rockets relied on relatively "low tech" liquid fuel. However, the Russians have seemed to show more consistency and persistence in working toward their space goals than their US counterparts. For example, in the late 1970s, the US took advantage of their technology and "know how" to move toward using reusable rockets and launch vehicles (space shuttles), but the Soviets continued to pursue a manned-presence in space by launching and occupying space stations, first Salyut and then Mir.

Salyut and Mir have now logged about 27 years of space travel. In the 1980s, their space budget was approximately equivalent to ours, but their effort was nearly double ours in terms how much of their gross national product was devoted to space issues. The Russians were deeply committed to space until the "break up," but now they don't have the funding to maintain Mir or even adequately pay their cosmonauts.

Mir weights 130 tons and it can fly manned or unmanned, depending upon the mission objectives. Designed for but 3 years of service, the former jewel crown of the Russian space program, has lasted 5 times this long and broken about every record for space endurance. It was occupied for the last time in June of 2000. Mir is being brought back to Earth for several reasons. It has been obviously deteriorating for a number of years, and foreign investors who bought it last year in an attempt to keep it going a bit longer haven't been able to meet their financial commitments. Additionally, Russia seems to want to direct its energy to the International Space Station currently being assembled. So, Mir is being brought down now in a more or less controlled fall, in a remote area of the globe, rather than and waiting too long and take the chance that it might crash in an area where lots of people live. In preparation for its final fling, its orbit has been programmed to decay at a rate of about 1 km per day, and it's projected to crash to Earth sometime between March 13 and 20. The exact date will be known more clearly as the orbit continues to decay.

Mir will be the biggest thing ever dropped from orbit. Though most of it will burn up upon re-entry into our atmosphere, because of it's so massive, there's a good chance that part of it may reach the surface Although all of the Mir return landings take place on the steppes of Kazakhstan, near the Aral Sea, it's simply too risky to bring down a bus-sized hunk of metal over land. Even in desolate areas like Siberia, the outback of Australia, or the Sahara Desert, there are isolated villages and settlements that could be just unlucky enough to take a direct hit. Perhaps as much as 50 tons could survive the fall through our atmosphere and reach the surface at speeds sufficient to pulverize 6 feet of reinforced concrete. For the few people who see Mir re-enter, the pyrotechnics will likely be pretty spectacular.

A real concern with bringing down something as big as Mir is that it needs to be brought down at a sufficiently steep angle so that it won't "skip" off of the atmosphere. A lot of atmospheric energy is required to slow it down and make it more easy to manage. If it does "skip," the re-entry will no longer be controlled, and where and when it comes down is a lot more problematic. When the Gamma Ray Observatory (GRO) was brought down last spring, the debris field was several thousand kilometers in length. Mir is bigger than GRO, and its debris can be expected to scatter over a larger area. It could come down over a populated region. With GRO, it was calculated that if it fell out of control during the re-entry process, the chances that it could injure or kill someone was 1 in 1000!

Antarctica might be a good place to try to bring it down, except that its orbit doesn't bring it close enough to either pole to make a re-entry over Antarctica or the Arctic Ocean practical. The most reasonable location for re-entry then is the sea. However, the western, central and south Pacific can be ruled out since there are too many inhabited islands. Because Mir will be moving approximately 12,000 miles per hour, there's a rather large geographic window where it could renter through our atmosphere. The US Space Command has provided the Russian space agency with a 30 minute window as to how much Mir can be expected to deviate from it's targeted re-entry point. This means that the confidence level is such that it could come down somewhere within 6,000 miles of the hoped-for target point. This distance basically rules out the north Atlantic, south Atlantic, and Indian Ocean. So there's really not much left except for the stretch of sea between 45 and 60 degrees south latitude that lies above Antarctica and below South America, Africa and Australia. The target point is approximately 1,850 miles east of New Zealand's southernmost tip. With only a handful of islands occupying Mir's soon to be watery grave, the odds that anyone will be crushed by wayward pieces of metal, if in fact it goes down where planned, are extremely small. Although, a few fish may be in for a big surprise.

For more about this see the October 1986 issue of National Geographic Magazine and the Science Question for March 30, 2000.