"Mir swansong": review of space station history

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The run-up to the de-orbiting of Mir was full of worry and speculation; now we can breathe a sigh of relief. (Perhaps this will be GICC's final Mir posting on Mir?) But, read the last sentence of this interesting essay--just wait for the International Space Station!


Headline: The re-entry of Mir: swansong and swandive for man's first great outpost in space

Source: Phil Clark, Jane’s Weekly, 23 March 2001

URL: http://www.janes.com/aerospace/civil/news/misc/mir010322_n_1.shtml

An April of anniversaries

The final descent of the Mir complex from its orbit to a watery grave in the South Pacific marked not just the end for the world's first long-term outpost in space but also the end of the Soviet/Russian independent manned space programme. This comes as Russia prepares to mark the 40th anniversary of Yuri Gagarin becoming the first man in space on 12 April.

April 2001 is also the 30th anniversary of the launch of the world's first space station: the Soviet Salyut. The Soyuz 11 cosmonauts spent three weeks on board the station, completing a successful residency. Sadly, a pressure leak during the return to Earth killed the crew.

April is also the anniversary of another remarkable achievement that will gain little publicity. On 22 April it will be a full 30 years since the Russians had to take a crew off a spacecraft (Soyuz 10) because of a last-minute launch delay. Compare that with the regular astronaut treks to and from US space shuttles before a launch finally takes place!

Living in space: the Soviet way

After losing the Moon 'race' the Soviets concentrated on a space station programme. Salyut was flown in two versions: the 'military' Almaz stations (Salyuts 2, 3 and 5) and the 'civil' DOS stations (Salyuts 4, 6 and 7, plus a 1972 launch failure and a 1973 in-orbit failure).

While the USA had the first fully successful visit of a crew to a space station in 1973, Skylab was simply a one-off station. The Soviets looked upon Salyut as a step-by-step programme to expand their experience of working in orbit. The final visit to Skylab had lasted for 84 days. In 1975 the Soviets flew missions of 30 and 63 days to Salyut 4.

The launch of Salyut 6 in September 1977, timed almost to mark the 20th anniversary of the first Sputnik launch, started a series of duration records which the Americans still dream of surpassing. The first Salyut 6 residency lasted for 96 days -- the longest manned flight to that date -- and subsequent residencies extended the record to 139 days, 175 days and then 185 days.

Salyut 7, launched on the 11th anniversary of the first Salyut, extended the duration record to 211 days and then 238 days. As the Salyut 7 mission was drawing to a close, the Soviets were ready to begin the assembly of a much larger station, originally called Salyut 8, which could be occupied on a permanent basis.

The first launch in the programme, the now-renamed Mir core module, came on 19 February (GMT) 1986; the station was so heavy that a lot of experiments had to be omitted with the promise that they would be sent into orbit aboard future cargo freighters.

The first crew to visit Mir completed a unique experiment: they flew their Soyuz-T ferry from Mir to the ageing Salyut 7, completed experiments on the older station and then brought equipment from Salyut back to Mir on their return trip. No other crew has had the opportunity to transfer between orbital stations.

The assembly of the Mir complex was thus much slower than originally planned because of budget restrictions. The small (around 11 tonnes) Kvant module was launched to dock at the back of Mir in 1987, and the launch of the large c20-tonne modules (roughly the same size as Mir's core) did not start until 1989 when Kvant 2 was launched. This was followed by Kristall (1990), Spektr (1995) and Priroda (1996). The first long visit to Mir in 1987 saw one cosmonaut spend 326 days in orbit, and during December 1987-December 1988 two cosmonauts spent 366 days in orbit.

The permanent occupation of Mir began on 7 September 1989 and continued until 27 August 1999; the station had been occupied without a break for 3,640 days, 22 hours and 52 minutes. The duration record was extended to 438 days, and while NASA tried to extrapolate from Skylab data the optimum space station stay for astronauts -- from a psychological and medical view -- by the late-1980s the Soviets knew from actual experience that the optimum mission duration was around six months.

Mir in decline

When NASA astronauts started to visit Mir in the mid-1990s as part of the Shuttle-Mir programme, they found a 10-year-old space station that was showing its age. Originally designed to operate for five to six years, the Russians knew that after Mir there was no funding for a replacement station.

The nadir in Mir's story came in 1997 when there was a fire on board, and later in the year a Progress-M cargo freighter collided with it, de-pressurising the Priroda module.

With their experience of real-time trouble-shooting the Russians were able to gradually bring Mir back to almost full operations, but from that point on the Western media portrayed Mir as an orbiting scrap-heap. The Russian Government stopped funding visits to Mir after the crew returned in August 1999.

Falling to Earth

In 2000 it was hoped that commercial funding could extend Mir's operational life, with MirCorp being established. The company funded a single visit to the station, but the expected funds were not forthcoming, and with the Russians unable to afford both Mir and the new International Space Station (ISS), coupled with pressure from NASA, it was decided to abandon Mir and bring it out of orbit.

The original Salyut space stations had been designed so their propulsion systems would be fired a final time to bring them out of orbit, over the Pacific Ocean, away from inhabited areas and shipping lanes. Salyuts 1, 3, 4, 5 and 6 were disposed of this way; Salyut 2 and Cosmos 557 -- two failed Salyuts -- re-entered naturally without any debris being found; and Salyut 7 came down under partial control, although fragments were found in South America.

NASA had not designed its much larger (around 75 tonnes) Skylab space station for a fully controlled de-orbit. First, the roughly 35-tonne second stage of Skylab's launch vehicle re-entered on 11 January 1975 under no control but away from civilisation. When Skylab itself came down on 11 July 1979 NASA had a little control for targeting the re-entry, although debris was scattered across part of Australia.

In 2000 it was decided to bring NASA's 13.7-tonne Compton Gamma Ray Observatory, launched in April 1991, out of orbit as its gyros were failing and there were worries about how long its control could be maintained. Starting on 31 May, a series of orbit-reducing burns began, with the de-orbit coming on 4 June with around 6 tonnes of debris thought to have impacted in the Pacific Ocean.

Mir's last moments

The final de-orbiting procedure for Mir ultimately went off without a hitch. The Russians had originally planned to bring Mir down as a single object, using three to five Progress-M1 cargo freighters to lower the station's orbit. In the end it was decided that a single freighter docked at the rear of the first Kvant would be used. A series of three manoeuvres using both Mir's attitude control thrusters and also the main Progress-M1 propulsion system took place early on the morning (GMT) of 23 March (about a week before the predicted uncontrolled decay of Mir from orbit) to initially lower the orbit and finally bring Mir out of orbit. The last burn, the command for which was sent by the Russian controllers at 0507 GMT, lasted slightly longer than planned, allowing the size of the final impact zone to be narrowed.

Mir's fragile solar panels, exterior crane and science platforms would have been torn off by aerodynamic forces fairly early during atmospheric entry and burned up. Eyewitnesses watching the re-entry from Fiji saw up to a dozen principal pieces of debris dashing across the sky. The remaining shower of debris - estimated at up to 25 tonnes-worth - finally hit the ocean surface at about 0600 GMT. The point of impact, as calculated by Australian officials and confirmed by the Russians, was 160° West, 40° South, placing it 5800km off Australia's eastern coast.

And so, with its fiery demise, the world's first long-term outpost in space has been destroyed. Despite the bad publicity, the 15-year flight of Mir can only be counted as a major success. In a further 15 years will the ISS have shown itself to be as successful and a worthy successor? Looking further into the future, when it is time for the ISS to be retired, NASA's current plan is to de-orbit it as a single object. We will then be watching a 400-tonne space object returning from space, making Mir look decidedly small.

-- Andre Weltman (aweltman@state.pa.us), March 23, 2001

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