NASA's Lunar Prospector spacecraft, to be launched in October, has been given a "real" mission, thanks to the military. The plan for the Prospector to be used to map the chemical composition of the Moon has been made all the more tantalising by the apparent discovery of an "ice lake" on Earth's nearest neighbour by the Ballistic Missile Defense Organization (BMDO) and the US Navy's $75 million Clementine I.

The US Department of Defense says that the discovery "-has enormous implications for a permanent human return to the Moon".

It is ironic that, after NASA sent Moon scouts and ten men to the lunar surface as part of the Pioneer, Ranger, Surveyor and Apollo programmes in 1960-72, it should be a military craft which has been the vehicle for one of the most surprising discoveries, opening up the possibility that lunar water could lead to the construction of self-sustaining manned Moon bases. All the data gathered from the Apollo missions indicated that the Moon is dry.


Lake of ice

During a Pentagon briefing on 3 December, Dr Paul Spudis of the Lunar and Planetary Institute said that the Clementine had found what appears to be a "dirty lake of ice". He adds: "We think we have found ice. We are not positive-it's not an ice rink-it's basically ice mixed into the dirt" - much like the Earth's tundra.

It is believed that, if there is water it would have come from comets (which are about 90% water), which hit the deep, dark and extremely cold region of the Moon around the South Pole. The region where the "ice" has been found is near what is called the South Pole-Aitken Basin ,in a crater about 12km deep.

When the first images were released in 1994, the BMDO speculated that the area might hold water (Flight International, 13-19 July, 1994). The crater has a central peak high enough to receive sunlight 85% of the time, raising the possibility that it could be the site of a solar power station for a base at the crater itself.

Comets have been hitting the Moon for over 4 billion years, say scientists, but that most of the water evaporates in the high daytime temperatures. Any vapour which has dropped into the polar basin would have been trapped and frozen at near-absolute zero temperatures in the Solar System's deepest-known crater. The ice-dirt lake is estimated to be about 360m long and up to 10m deep. The ice was detected by the Clementine's radar, which displayed the electronic-signature characteristics of water ice.

This quantity of ice would be sufficient to support a manned space colony. It could be refined into liquid oxygen and hydrogen for rocket fuel, as well as providing water and oxygen for the colony for 50 years.

"This hydrogen and oxygen is a prime rocket fuel, giving the space programme an ability to re-fuel rockets at a lunar 'filling station' and making transport to and from the Moon more economical," says the US Department of Defense.

Other scientists are sceptical about the find and the usefulness of the ice. Processing it on the Moon would also require technologies not yet demonstrated.

Many people are passionate about a Moon colony, says John Wood, a scientist at the Harvard-Smithsonian Centre for Astrophysics, Maryland. "Personally, I've always been sceptical of that whole proposition. I think it is a lot of wishful thinking".

He could be right in the context of today's fiscal environment and NASA's new-found Mars ambitions. Life on Mars seems a lot more attractive than a dirty lake on the Moon. The late scientist and author Arthur Clarke said before his death in December that the finding is "extremely important and quite plausible", but he cautioned that confirmation is necessary.

The Clementine was developed and flown to demonstrate new lightweight systems and their radiation tolerances in a programme to build low-cost spacecraft. This complements NASA's "faster, smaller, better, cheaper" approach, illustrated by the Mars Global Surveyor and Pathfinder spacecraft now en route to the Red Planet. The Clementine was originally built to support "Star Wars" research, but was sent on a another mission - with NASA's help - when that project effectively folded.


First US lunar mission since 1972

It was launched by a Titan 2G booster from Vandenberg AFB, California, on 23 January, 1994, and became the first US lunar mission since 1972 when it entered orbit on 22 February. The craft returned over 1.8 million images of the Moon and, on 4 May, the first of a series of manoeuvres was conducted, which sent it en route for the asteroid Geographos.

The success story came to end, however, when a computer fault exhausted its hydrazine propellant and the spacecraft ended up lost forever in a solar orbit (Flight International, 11-17 March, 1994).

Source: Flight International