Thursday, February 4, 1999 Published at 06:07 GMT
Turning night into day
By BBC News Online Science Editor Dr David Whitehouse
You could see a new star in the sky on Thursday night, if you live in Europe or North America and if you are lucky.
Although it has been done before, Thursday's mission, Znamya 2.5, will be the world's first controlled space mirror.
Under ideal conditions it could be the brightest star in the sky for a few seconds.
Two cities in North America will be illuminated by Znamya 2.5 during the 24-hour experiment, as well as some in Europe.
The reflected light from Znamya 2 was only visible as a flash of light as it sped over the Earth.
Russian space officials have been receiving complaints from astronomers and environmentalists that Znamya will pollute the night sky with unwanted light.
Such concerns are premature given the brief nature of Thursday's mission. But if Russian scientists can get the money, they hope to follow Znamya 2.5 with a much larger reflector.
On Thursday morning, at about 1000 GMT the Progress will undock from the Mir space station. It will then perform several manoeuvres and fly to about 100 metres from Mir.
The craft will then be commanded to spin and the reflector, 25 m across, will be unfurled by centrifugal force. During the next several orbits, the reflector will illuminate the night side of Earth.
The cosmonauts will control the direction of the light beam every 90 minutes or so when Mir is at its most northerly point above the Earth.
The spot of light on the Earth's surface will be about six kilometres in size. However from any one point it should be visible for only a minute at most. It would be as bright as a very bright star.
The cosmonauts will observe the spot of light on the Earth and try to keep it fixed on the same spot. It will be a difficult task.
After 12 hours the reflector will be jettisoned and it and the Progress craft will burn up in the Earth's atmosphere.
The first time this was tried was in 1993 during the Znamya 2 experiment. This 20-metre diameter, thin, reflective film was unfurled from another Progress craft.
The reflected spot of light, about five kilometres in diameter, travelled at a speed of 8 km/hour from France through Switzerland, Germany, Poland and disappeared in early sunlight in Belorussia. Many people reported seeing a flash of light.
In the past Russian scientists had great plans to illuminate the Siberian cities with light from space. This they believed would be cheaper than using conventional power given the remoteness of their location.
Calculations suggest that a constellation of large light reflectors could provide lighting to several large cities, especially in the polar regions.
However environmentalists have said that the ecological balance could be altered. But the vast sums of money required to build such a fleet of large space reflectors is far beyond the abilities of Russia's ailing space effort.
It now seems unlikely that the space mirror experiment will be more than just an experiment.
One further Znamya experiment is planned. It will involve a larger reflecting surface, about 70 metres. It may fly in 2001, if funding is secured
The light beam will pass over Karaganda in Kazahkstan at about 1812 local time; Saratov, Russia at about 1745 local time; over Poltava, Ukraine at about 1920 local time and over Liege and Frankfurt in Western Europe at about 1855 local time.
In the UK, only people in southern England will have a chance of seeing Znamya. They should look south 1730 and 1750 GMT.
It will pass over Winnipeg in Canada at 1754 local time and over Devil's Lake, North Dakota in the USA at 1932 local time.