On Thursday astronauts on the orbiting Mir space station will unravel a mirror made of plastic coated in aluminium. Once deployed, it will be 25 metres across, with a fan-like structure, and able to shine light down to the Earth's surface. The experiment will run for 18 hours, during which time Mir will circumnavigate the Earth 12 times.
The Space Regatta Consortium, a group of companies led by Energia of Moscow, has been trying to bring the project to fruition for six years.
The Russians say there would be potential benefits, including illuminating the scenes of natural disasters during hours of darkness - such as areas of Colombia recently hit by an earthquake.
If this test works, they say they could send a further 200 mirrors into orbit to light up parts of Siberia which are normally shrouded in near- darkness for months on end.
Western scientists think the scheme is self-aggrandising and likely to make tracking stellar events more difficult, by adding to the man- made "light pollution" that already interferes with work by astronomers. Environmental campaigners worry that nocturnal and hibernating animals will be affected by the lack of darkness.
"It will not exactly flood our bedrooms with a blinding light, but it could be up to 10 times brighter than a full moon," said Colin Pillinger, professor of astronomy at the Open University. "It ought to have a global health warning slapped on it."
The sun will actually appear to observers on Earth as a spot of light about half the size of the moon, but flashing rather than shining steadily.
Prof Pillinger's is concerned because the mirror is the product of a Russian project which does not need international approval, yet could have widespread effects. Some uses for reflecting systems could be entirely beneficial. By keeping the mirror's reflection focused on a particular point on Earth, solar energy systems could keep working through the darkness. That would overcome their most fundamental drawback. Using a parabolic design could also allow the beam of reflected light to be made more intense, potentially raising the power generated by a given area of solar panels.
The negative side effects keep surfacing. "It may herald a future in which night is banished," said Prof Pillinger. "Living things would be thrown into chaos: think of nocturnal animals which evolved over millions of years to take advantage of the cover of night to hunt for food.
"And what would happen to seeds that require darkness to germinate?"
Astronomers are upset because ground-based telescopes increasingly have to be located in remote areas where the effects of terrestrial "light pollution" from streetlights and other artificial sources are minimised.
A bright, rapidly-moving source of light would create havoc for those searching for dim stars or incredibly brief astronomical events. Prof Pillinger believes that an international treaty is required to prevent individual countries or companies from abusing their ability to put objects into space.
The latest project is an extension of an earlier test in 1993, when a 20-metre mirror was deployed from the back of a supply rocket as it left the Mir space station. In the minutes before dawn it lit parts of Europe in a thin, weak, shaft of sunlight travelling from France across to Gomel in Belorussia.
That attempt was judged a failure, which stalled funding for five years.
The Russian company funding the latest attempt had intended to send up a separate satellite last November, but was delayed due to lack of funds. Then the Russian Space Agency cut back on the number of Progress supply ships it sent up to Mir, making it impossible to deliver the mirror.
Now the midnight sun is set to shine in space again.