Washington - NASA's newest spacecraft at Mars has completed the challenging six-month task of shaping its orbit to the nearly circular, low-altitude pattern from which it will scrutinize the planet.

The bus-sized Mars Reconnaissance Orbiter (MRO) fired its six intermediate-size thrusters for 12.5 minutes on September 11, shifting the low point of its orbit to stay near the Martian south pole and the high point to stay near the north pole.

The orbit’s altitude ranges from 250 kilometers to 316 kilometers above the surface, according to a September 12 NASA press release.

"This maneuver puts us into our science orbit," said Dan Johnston, deputy mission manager at NASA's Jet Propulsion Laboratory in California. "Getting to this point is a great achievement." (See related story.)

Challenging activities remain ahead this month, such as deploying an antenna 10 meters long and removing a lens cap from a crucial instrument.

The main science investigations will begin in November. During its two-year science phase, the mission will return more data about Mars than all previous Mars missions combined.

The MRO flight team sent the spacecraft through the upper fringe of Mars' atmosphere 426 times between early April and August 30.

This "aerobraking" technique used friction with the Martian atmosphere to decrease gradually the highest-altitude point of the elliptical orbit from 45,000 kilometers to 486 kilometers.

One key remaining preparation for the mission's science payload is deployment of the antenna for the Shallow Subsurface Radar, an instrument provided by the Italian Space Agency. The antenna remained safely stowed during aerobraking.

Later in September, it will be released to unfold itself and extend 5 meters on either side of the spacecraft.

After this ground-penetrating radar has been checked and calibrated, it "has the potential to detect buried channels, buried craters and ice layers," said Roberto Seu of the University of Rome La Sapienza, leader of the instrument's science team.

"Our most important goal is to find where past environments on Mars were wet long enough to leave a mineral signature on the surface," said Scott Murchie of Johns Hopkins University Applied Physics Laboratory in Maryland, principal investigator for the mineral-mapping Compact Reconnaissance Imaging Spectrometer.

A series of trial observations by all the instruments will complete the spacecraft checkouts at the end of the month, including tests of all observing modes.

In addition to data gathered by the radar and spectrometer, images will be taken by the high resolution imaging science experiment and the context imager. The Mars color imager and Mars climate sounder also will begin monitoring Mars' atmosphere.

During the next four years, the MRO instruments will examine Mars to learn about processes that have affected it and to inspect potential landing sites for future missions. The spacecraft also will serve as a communications relay for Mars surface missions.

Additional information about the orbiter is available on the NASA Web site.

The full text of the press release is available on the Jet Propulsion Laboratory Web site.