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Mars Probe Poised For 'Hair-Raising' Orbit Entry
Date: Tuesday, February 28, 2006 @ 03:43:51 EST

NASANASA's Mars Reconnaissance Orbiter is preparing for a "hair-raising" entry into orbit around the Red Planet on 10 March, mission managers say. If successful, the spacecraft will spend seven months spiralling towards the planet until it skims just 300 kilometres from its surface – where it will study the planet's geology and climate in unprecedented detail.

The Mars Reconnaissance Orbiter must fire its thrusters for 27 minutes to enter orbit around Mars (Illustration: NASA/JPL-Caltech)The spacecraft has travelled 459 million kilometres (285 million miles) – 95% of the way to Mars – since its launch from Florida's Kennedy Space Center, US, in August 2005. It has already fired its thrusters twice to correct its course towards Mars. Those firings were so successful that mission managers cancelled two further trajectory tweaks that had been scheduled.

"We're right on the money now, heading towards our encounter at Mars on the 10th," James Graf, the mission's project manager at NASA's Jet Propulsion Laboratory in Pasadena, California, US, said at a press briefing on Friday.

But that encounter is very risky, he said: "We're starting to enter into the realm where we've lost two spacecraft in 15 years." NASA's Mars Observer spacecraft fell silent in 1993 when it approached the planet – probably because of a leak caused when its propulsion system was pressurised.

And the Mars Climate Orbiter is thought to have broken up in the planet's atmosphere in 1999 due to the accidental use of both metric and Imperial units by collaborating teams, which scuppered a critical manoeuvre.

Nervous half hour

For MRO's orbit insertion at 2124 GMT, it will aim its main thrusters forward and fire them for 27 minutes to slow down by 18%. "If we don't succeed in firing the thrusters, it will be a flyby spacecraft," Graf said.

But mission controllers will not know immediately whether the manoeuvre worked, since the spacecraft will travel behind the planet as seen from Earth for about 30 minutes before the end of the thruster firing and will therefore be out of radio contact.

If the "hair-raising" orbital insertion is successful, the spacecraft will then begin a seven-month "aerobraking" phase, said Michael Meyer, the lead scientist for NASA's Mars programme in Washington DC, US.

During this phase, it will dip into the Red Planet's atmosphere hundreds of times, using the friction of atmospheric drag to move from a 35-hour orbit that extends 35,000 miles (56,000 kilometres) above the planet to a two-hour orbit that skims just 190 miles (300 kilometres) above its surface. At that point, it will begin to collect "more data than all of the previous missions combined," Meyer said.

Landing sites

The spacecraft will use a suite of six instruments - including the most powerful camera ever sent to another planet, which will image objects as small as 1-metre wide and should be able to snap pictures of the Spirit and Opportunity rovers – now on opposite sides of the planet. The instruments will track the planet's weather, geology and mineralogy, and even probe about a kilometre beneath its surface to hunt for water.

The mission will collect 34 trillion bytes of data from Mars. "That's about as much as in a video store," said Meyer. "It will revolutionise our understanding of the planet." He adds that it will also help determine where future missions – including the Phoenix lander due to launch in 2007, the Mars Science Laboratory (MSL) rover set to launch in 2009, and eventually a human mission – should land.

The spacecraft will focus on science for two years after aerobraking manoeuvres are completed. After this pure science phase, it will begin its "relay" phase. During this time it will continue to take science data but will give priority to relaying data from other Mars missions, such as Phoenix and MSL, to Earth. The spacecraft carries an antenna that will be able to transmit 10 times as much data per minute as any previous spacecraft. The probe's expected operational lifespan is 10 years.

Source: New Scientist

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