 It will take six months for the MRO to attain its final orbit |
The US space agency's latest mission to Mars reaches the Red Planet on Friday. The Mars Reconnaissance Orbiter (MRO) has travelled about 500 million km over seven months to reach its target.
The MRO's first major task will be to execute the critical engine burn needed to slow it down and place it safely in an orbit around the planet.
If all goes to plan, by November 2006, the craft will begin to study Mars' atmosphere, surface features and underground geological structure.
The probe's arrival brings the number of satellites at the Red Planet to four.
Nasa already has Mars Global Surveyor and Mars Odyssey in orbit; and the European Space Agency is represented by Mars Express.
On the surface, the two American robotic rovers - Spirit and Opportunity - continue to return data long after some thought they might have broken down.
'Dangerous phase'
If this current fleet of space technology makes it sound as though going to the Red Planet is easy - it is not.
Since 1960, 21 of the 35 missions to Mars have failed.
"We are very excited about the arrival of the MRO at Mars... but my heart rate is going up for different reasons," said Fuk Li, programme manager of the MRO mission.
"The mission is entering into a very dangerous phase."
At 2124 GMT (1324 PST), as the US space agency craft closes in on Mars, its thrusters will fire to slow its approach and allow the probe to be captured into an ellipse around the planet.
About 21 minutes into the burn, as MRO reaches some 400km (250 miles) above the Martian surface, the craft will pass behind the planet, and enter into a tense 30 minutes of radio silence.
 |  We have a tremendous amount of anxiety and concern at this particular point in time  |
Engineers and scientists managing the mission at Nasa's Jet Propulsion Laboratory in Pasadena, California, will have no information on how the burn is progressing.
Only when the orbiter emerges at 2216 GMT (1416 PST), and radio contact is re-established, will the mission team discover if the orbit insertion has been successful.
"We have a tremendous amount of anxiety and concern at this particular point in time," said Jim Graf, MRO project manager.
"At the same time, we feel confident; we have a very good spacecraft and an excellent, well-trained team."
If the burn proceeds as planned, the spacecraft will begin a 35-hour elliptical orbit of Mars. At its furthest point, it will swing out as far as 44,000km (27,000 miles) from the surface of the Red Planet.
Corrected orbit
Once equipment on board has been tested, the MRO will begin the slow process of gradually shrinking its orbit around Mars, until, in October 2006, it has reached a final tight, near-circular trajectory around the planet.
This six-month process involves a manoeuvre known as aerobraking.
| MARS RECONNAISSANCE ORBITER 1) 3m high-gain antenna 2) High-resolution Imaging Science Experiment 3) Electra UHF comms relay 4) Mars Climate Sounder 5) Compact Reconnaissance Imaging Spectrometer for Mars 6) Orbit insertion thrusters 7) Shallow subsurface radar 8) Thrusters 9) Optical Navigation camera 10) Low-gain antennas |
This technique sees the craft brush against Mars' atmosphere on every close pass, using the friction from "air" molecules to slow the probe down and reduce the size and shape of its flight path. The MRO will have to do this over 500 times to get into the optimal position to study the planet.
The final orbit will last only two hours, and will bring the craft much closer to Mars than the other operational Mars orbiters.
The two-year science phase of the mission will begin in November 2006, and the mission team says it will be able to collect 10-times more data than all past Mars missions put together.
Richard Zaruk, MRO project scientist, said the mission would be "following the water" to learn about Mars' climate, geological history and the planet's ability to harbour life.
The spacecraft carries six observation and analysis instruments. On board are cameras able to take incredibly clear pictures of the planet, a spectrometer to identify water-related minerals, a radiometer to monitor the atmosphere, and a radar to probe the Martian surface for ice.
"With this capable pay-load, we're all looking forward to [later in the year] when we can start operating it," said Zaruk.
"But first there is this little matter of turning the spacecraft from a cruiser to Mars into a true orbiter around Mars."
