After traveling roughly 95 percent of its 300 million mile journey since launching last August, NASA's Mars Reconnaissance Orbiter is preparing for the riskiest phase of its mission on March 10 - insertion into the red planet's orbit.

NASA has only a 65 percent success rate with Mars Orbit Insertion (MOI), according to the agency. "Now we're starting to enter into the realm where we've lost two spacecraft in the last 15 years," said Orbiter Project Manager Jim Graf, referring to the 1999 Mars Climate Orbiter and the 1993 Mars Observer.

As the spacecraft nears the planet, ground controllers expect a signal shortly after 4:24 p.m. Eastern time on March 10, indicating that the engine burn intended to slow the spacecraft and put it into orbit has started. The burn will end during a "suspenseful" 30 minutes when the orbiter will be behind Mars and out of radio contact, according to NASA.

If all goes well during MOI, the spacecraft will be in a highly elliptical 35-hour orbit. Over the next seven months, it will carefully dip into the planet's atmosphere hundreds of times to slow itself down and lower its orbit into a nearly circular two-hour loop suitable for science observations.

Following aerobraking, the spacecraft will spend two years studying the planet's surface. With its six instruments, the Lockheed Martin-built orbiter is expected to return more data than all previous Mars missions combined, according to NASA.

MRO carries a telescopic camera that will reveal rocks and layers as small as the width of an office desk, according to NASA, as well as another camera that will expand the present area of high-resolution surface coverage tenfold. A third camera will provide global maps of martian weather.

MRO's other three instruments are: a spectrometer for identifying small patches of water-related minerals; a ground-penetrating radar supplied by the Italian Space Agency that will look for subsurface layers of rock, ice or possibly water; and a radiometer to monitor atmospheric dust, water vapor and temperature.

After the science phase the spacecraft will act primarily as a telecommunications relay for other missions - a responsibility made more critical by last year's cancellation of the Mars Telecom Orbiter (DAILY, July 22, 2005). It will relay communications for the Phoenix lander, due to arrive in 2008, and the Mars Science Laboratory rover, which arrives in 2010. At that point NASA may consider using leftover fuel on MRO to raise its orbit to an altitude more conducive to communications relay.