NASA rover being readied for risky Red Planet landing

PASADENA, Calif. -- After a journey of seven months and 303 million miles, a six-wheeled NASA rover will speed like a bullet tonight toward the surface of Mars and, if all goes as planned, stop with a bounce.

The plunge through the Martian atmosphere at 12,300 mph will mark the start of the riskiest portion of the voyage thus far.

As the unmanned spacecraft Spirit plummets to the rocky surface 80 miles below, it will rely on the precisely choreographed use of heatshields, parachutes and rockets to slow its descent. Just eight seconds before hitting the ground, the golf cart-size Spirit should inflate a set of airbags to cushion its impact.

The entire harrowing trip down should take just six minutes. A gust of wind or a single sharp boulder could doom the entire enterprise.

"It's going to be six minutes from hell. It's going to be high anxiety," Ed Weiler, NASA's associate administrator for space science, said Friday at NASA's Jet Propulsion Laboratory.

Early Friday, Spirit was 231,000 miles from Mars, or about the distance separating the Earth and its moon.

The $820 million project also includes a twin rover, Opportunity, which is set to arrive on Mars on Jan. 24.

The camera- and instrument-laden rovers are designed to spend 90 days analyzing Martian rocks and soil for clues that could reveal whether the Red Planet was ever a warmer, wetter place capable of sustaining life.

'Death planet'

If successful, the 384-pound Spirit and its twin would become the fourth and fifth U.S. spacecraft to survive landing on Mars. If neither survives, they will join the wretched ranks of some 20 other spacecraft from various nations that failed to successfully reach the planet.

"Some, including myself, call it the 'death planet,'" Weiler said.

The latest to fail, apparently, were Japan's Nozomi satellite and Britain's Beagle 2 lander. Nozomi was unable to enter Mars orbit last month; Beagle 2 has been silent since it was to have landed on Christmas Day.

NASA hopes to learn whether Spirit has landed safely within 10 minutes of its expected 10:35 p.m. arrival. If scientists have not heard from Spirit within 22 hours of landing, the likelihood that it survived is low, project manager Pete Theisinger said.

In 1999, NASA's last attempt at landing on Mars failed when a software glitch sent the Polar Lander crashing to the ground. Its descent took place in a communications blackout, and the lack of data later stymied the investigation into the failure.

Spirit, in contrast, is designed to transmit a series of tones to Earth throughout its descent to signal engineers each time onboard computers order a critical action, such as the deployment of the parachute. Even if Spirit crashes, engineers on Earth should be able to reconstruct its last minutes.

"Entering into Mars is always very tricky, as everyone knows, and we can fail. But we want to learn from those failures, so next time -- of course, we have another rover coming three weeks later, so we do have our own next time -- we can learn from the experience so we can correct any problems," said Polly Estabrook, who is in charge of telecommunications for the landing.

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