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The BBC's Lindsay Marnoch
"There have been anxious faces at NASA mission control"
 real 28k

Richard Cook, MPL Roject Manager
"It's not unexpected"
 real 28k

The entry procedure
Nasa simulation of MPL's landing
 real 28k

Probing the surface
Two probes should have penetrated the Martian surface
 real 28k

Saturday, 4 December, 1999, 02:06 GMT
Nervous wait for Nasa scientists
A parachute should have slowed the entry

By BBC News Online Science Editor Dr David Whitehouse

Nasa engineers are facing an anxious wait after the Mars Polar Lander spacecraft missed a second chance to signal its safe arrival on the Red Planet.

The next few hours will be fraught ones for NASA scientists, but mission controllers say there are a lot more opportunities for the probe to get in touch and that it is a game of "waiting and hoping."

Despite this many privately realise that the longer that MPL stays silent the less are the chances that it will ever be heard of again.

The spacecraft was supposed to have touched down on the surface of the Red Planet at 2015GMT Friday. Signals from it were detected up to ten minutes before landing. But since then, nothing.

There was no signal from the MPL at 2039GMT, the first opportunity it had to contact mission controllers at the Jet Propulsion Laboratory in California, US.

Since then it has been a long and anxious wait for scientists who have spent years working on the $165m probe.

Nasa stressed the lack of a call did not mean the spacecraft was lost.

"This is not entirely unexpected," said Richard Cook, MPL's Project Manger. "Obviously we're a little disappointed not to see a signal (right away). But we were prepared for this, and we're going to go ahead and execute our plan as we described it."

Richard Cook Richard Cook: Still waiting
One possibility was that the lander's computer slipped into protective safe mode immediately after landing, in which case it would delay sending its first signal.

Another scenario was that the probe did not correctly predict where to point its antenna. As it descended through the atmosphere, the lander had to keep track of every twist and turn to keep its bearing.

During the communication windows with the lander the large radio telescopes that for NASA's Deep Space Tracking Network are listening out for the probe. MPL's antenna may be going through a pre-programmed search pattern hoping to point towards Earth.

The worst possibility is that the lander touched down on a severe southward facing slope and cannot point its antenna back at Earth. It may have even fallen into a pit.

The first data sent to Earth was supposed to include information about MPL's health and a black and white image of the landing site.

Scientists sent MPL to Mars to learn about the planet's climate by studying layers of dust and possibly ice during the 90-day mission. It incorporated Instruments that would measure vapour in the atmosphere and a claw that could collect samples to be cooked and analysed for water.

It even had a microphone on board to record the first sounds from another world.

Loss of the lander would be a devastating blow to Nasa. Only 10 weeks ago, the lander's sibling spacecraft, the $125m Mars Climate Orbiter, burned up in the planet's atmosphere because of an embarrassing mix-up over English units (pounds, feet and inches) and metric units.
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See also:
02 Dec 99 |  Sci/Tech
Mars Polar Lander on track
30 Nov 99 |  Sci/Tech
Polar lander ready for Mars
30 Nov 99 |  Sci/Tech
Martian mysteries under microscope
11 Nov 99 |  Sci/Tech
Orbiter loss blamed on 'silly mistakes'

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