Washington

Cook: targeting margin was thought to be adequate. Credit: AP

The US space agency NASA declared its Mars Climate Orbiter a total loss last week, after a targeting error apparently caused it to burn up in the Martian atmosphere just as it was about to enter orbit.

Project managers at the agency's Jet Propulsion Laboratory in Pasadena, California, were stunned on 23 September to learn that the $125 million spacecraft, which they had predicted only a day before would skim the planet at a safe altitude of 140 km, had come only 60 km from the surface — close enough for atmospheric friction to destroy it.

The loss of a second Mars spacecraft in four attempts during the 1990s has been a distressing surprise to scientists and engineers who have come to expect pinpoint targeting of planetary spacecraft.

Investigators are likely to examine a discrepancy between two types of tracking information — one based on Doppler shifting of radio signals from the craft, the other on range data — that emerged several days before the orbiter was lost.

According to project manager Richard Cook, the discrepancy was not large, nor was it unprecedented in planetary missions. But it did prompt a discussion among project engineers, some of whom argued that the spacecraft should perform another ‘trajectory correction manoeuvre’ just before reaching Mars. Project managers decided against the manoeuvre, believing that the potential targeting error was within safe limits, says Cook.

The orbiter was to have spent two years studying the Martian climate, making daily weather observations similar to those returned by satellites around the Earth, says Daniel McCleese, principal investigator for one of the orbiter's two scientific instruments.

The mission would also have investigated the exchange of water between the Martian atmosphere and the surface. NASA has no plans to fly a replacement climatology mission, says McCleese, but atmospheric sensors could be included on future Mars orbiters.

Carl Pilcher, who heads NASA's planetary exploration programme, plays down the loss. He says the climate orbiter's role in supporting another Mars mission — a lander due to touch down in December — can be filled by other means, and that some failures had to be expected when the agency was launching so many spacecraft.

But the news comes when NASA space scientists are demoralized by cuts to their budget proposed by the US Congress. The Senate last week voted for a spending bill that would trim NASA's science budget request by $184 million next year.

This is better than the $265 million cut recommended by the House of Representatives, but NASA says it would still result in significant losses.

Rather than cancelling missions, the agency would opt to delay programmes such as the Discovery planetary series and the MIDEX astronomy explorers. NASA estimates that some 500 research grants — a third of each year's total for academic scientists — would be in jeopardy, and the agency's advanced technology programme would be gutted.

That, in turn, would slow the development of several spacecraft missions integral to the Origins programme to investigate phenomena ranging from galactic evolution to the nature of life in the Universe.