A NASA spacecraft bound for Mars is nearing the end of its seven-month journey but still faces a white-knuckle arrival at a planet known for swallowing scientific probes, mission managers said Friday.

The Mars Reconnaissance Orbiter, or MRO, is on course to enter orbit around the Red Planet on March 10. If successful, it will spend the next two years photographing the surface and scouting for future landing sites.

The spacecraft is performing so well that engineers have canceled two final maneuvers to adjust its course in the last leg of the trip, said James Graf, project manager from NASA's Jet Propulsion Laboratory in Pasadena.

"We're right on the money right now, heading toward our encounter with Mars," Graf told a news conference at NASA headquarters in Washington.

Despite the optimism, the greatest challenge of the $720 million mission is yet to come. Within the last 15 years, NASA has lost two spacecraft during the tricky orbit-insertion phase around Mars.

In 1993, scientists lost contact with the Mars Observer just before it was to enter orbit. The space agency was dealt another blow six years later when the Mars Climate Orbiter failed on arrival.

Engineers hope the two-ton Reconnaissance Orbiter, which has journeyed nearly 300 million miles, will not suffer the same fate.

During the March 10 rendezvous, the spacecraft will fire its thrusters to slow down so that it can be caught by Mars' gravity. At one point during the maneuver, the orbiter will fly behind Mars, temporarily cutting off radio contact with ground controllers.

After it begins circling the planet, the spacecraft will for the next seven months adjust its orbit by dipping down into Mars' upper atmosphere, using friction to slow its speed and lower its altitude.

Launched from Cape Canaveral, Fla., last August, the Reconnaissance Orbiter is loaded with cameras, antenna and radar. It is expected to collect more data on the Red Planet than all previous Martian missions combined.