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Wednesday, 24 October, 2001, 11:31 GMT 12:31 UK
Mars spacecraft success
Graphic BBC
By BBC News Online science editor Dr David Whitehouse

A spacecraft has successfully entered orbit around Mars, to the jubilation of scientists and the relief of the American space agency Nasa.

The last time Nasa tried to put a probe into orbit around the Red Planet it was a dismal failure, but researchers are saying that the success, and promise, of Mars Odyssey will make up for past losses.

How sweet it is

Dan Goldin, Nasa
There were hugs and cheers in the mission control room at the Jet Propulsion Laboratory (JPL) in Pasadena, California, when the craft signalled that it had reached orbit.

Nasa administrator Dan Goldin said: "How sweet it is. Putting the Odyssey spacecraft into orbit about Mars is an achievement that every American ought to take pride in. We can win after we've been knocked down a few times."

After hours of waiting, the final events at Mars happened quickly. At just before 0230 GMT, the onboard rocket motor on Mars Odyssey fired for 20 minutes, slowing the spacecraft so that it could be captured by the planet's gravity.

We are on orbit around Mars. We are pretty excited

Scott Henderson, Mission control
But the wait for confirmation that Mars Odyssey was in orbit was a nail-biting one.

Shortly after the burn started, the spacecraft passed behind Mars and out of contact. It was an anxious 10 minutes before the giant radio telescopes of Nasa's Deep Space Network once more picked up the probe's signal.

Mission controllers then hurriedly analysed the signal to determine if Mars Odyssey had made it into the desired orbit around the Red Planet. It had.

"We are in orbit around Mars. We are pretty excited," said one of JPL's mission managers, Scott Henderson.

Nail-biting time

Superficially, the odds were not on Mars Odyssey's side. Fewer than one-third of the 30 missions launched towards the planet since 1960 have succeeded.

This is the first time a probe has approached Mars since the back-to-back losses of the Mars Climate Orbiter and the Mars Polar Lander in 1999.

The Mars Climate Orbiter burnt up when entering the planet's orbit - a mix-up of English and metric units used in calculating its trajectory sent the spacecraft too close to Mars.

If that was not bad enough, barely three months later, Mars Polar Lander plummeted to the surface of the planet, probably because a software fault silenced its engines prematurely.

But project members said Mars Odyssey was among the most scrutinised missions ever launched by Nasa and they were more confident that this time orbital entry would go well.

Science goals

Over the next few weeks scientists will gradually adjust the spacecraft's orbit until it reaches an optimal position to begin its mineralogical survey of Mars and its search for water.

The plan calls for Mars Odyssey to initially orbit Mars once every 20 or so hours. That period will be reduced as it brushes the atmosphere of Mars for a section of each orbit. The atmospheric drag will be used to further slow it and bring it closer to Mars in a fuel-saving process called aerobraking.

Graphic BBC
Marie: The instrument will assess the radiation environment
Limited mapping operations should begin within days. But the aerobraking will last until late January, at which point Odyssey will whip around Mars once every two hours about 400 km (250 miles) above the planet's surface. It will then begin its mapping in earnest.

When Mars Odyssey turns its three scientific instruments towards the planet, it will join another Nasa satellite, the Global Surveyor, which is already at work.

Global Surveyor has mapped Mars since 1997, taking more than 78,000 images of the planet.

Among them are high-resolution pictures that suggest water may have coursed across the surface of Mars in the recent geological past, raising the tantalising possibility that the planet harbours life.

The BBC's Fergus Walsh at McLaren Composites
"Relief was soon replaced by celebrations"
See also:

27 Jun 01 | Sci/Tech
Martian water hunt leads to poles
23 Jun 00 | Sci/Tech
Water may flow on Mars
23 Jun 00 | Sci/Tech
What now for Mars?
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