March 10, 2006

NASA spacecraft makes risky final approach to Mars

By Dan Whitcomb

PASADENA, California -- A $450 million NASA orbiter designed to circle Mars for two years, searching for signs of life and scouting possible landing spots for future astronauts, neared its dangerous first rendezvous with the red planet on Friday.

The unmanned Mars Reconnaissance Orbiter is designed to send back 10 times the data of all previous probes put together, but only if it can successfully slip into orbit around the planet -- a feat that has proven notoriously difficult.

"After a six-month cruise and 300 million mile (480 million km) journey we're finally there," said Doug McCuistion, director of NASA's Mars Exploration Program. "But the first thing we have to do is get into orbit. It's not an easy task."

The tricky part is getting the robot spacecraft -- which is as tall as two-story building and will be cruising at about 11,000 miles per hour as it nears Mars -- to slow down enough to be captured by the planet's gravity.

The orbiter will do that by spinning around to face its main thrusters forward and firing them for about 27 minutes. Some 21 minutes into that burn, flight engineers will lose contact with the orbiter while it passes behind Mars.

If the spacecraft is not grabbed by Mars, it will shoot past the planet and off into space -- a fate that befell a 1998 Japanese mission. Japanese scientists managed to gain control of the Nozomi orbiter and send it back to Mars, but the craft was damaged by solar flares and ultimately lost.

"Mars is just for some reason harder to get a mission to than other places in the solar system," said NASA lead mission planner Rob Lock. "I might even use the word 'unluckier' because there's nothing intrinsically more difficult than other planets."

If the Mars Reconnaissance Orbiter "threads the needle," as scientists say, and goes into an elliptical orbit, it must still spend the next six months using the drag of the planet's atmosphere to reel itself in from an elongated 35-hour loop to a nearly circular two-hour orbit.

The orbiter, the most advanced spacecraft ever sent to another planet, is expected to spend two years circling Mars and could help NASA determine where to land rovers and even scout out sites for a human landing site on Mars.

"What we're really looking for is that sweet spot where we can go down with other instruments and look for evidence of life," said project scientist Rich Zurek.