Red Planet rendezvous

NASA's latest craft is scheduled to begin orbiting Mars today, provided it beats the odds and succeeds where so many others have failed


Scientists and engineers are prepared to defy the grim odds against Mars missions and slip one more NASA spacecraft into orbit around the Red Planet today.

The $720 million Mars Reconnaissance Orbiter was racing toward its afternoon rendezvous point, where a blast from its six main engines was scheduled to nudge the spacecraft into orbit over the Martian poles.

Controllers should know by 5:16 p.m. whether it worked. If it did, MRO will join a squadron of three smaller spacecraft sending data from Mars orbit - along with two spunky landers that are still exploring after two years on the Martian surface.

If it fails, MRO will join a long list of doomed missions. In fact, 22 of mankind's 34 attempts to reach Mars have crashed, vanished, broken, missed the planet or otherwise flopped en route. At least half of those failures occurred during final approach.

"Those are very sobering numbers," said Fuk Li, the Mars program manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The mission is entering into a very dangerous phase."

But MRO project manager Jim Graf said he feels confident as well as anxious. "We have a very good spacecraft," he said, and "an excellent, well-trained team that's ready to go forward."

The latest Mars orbiter blasted off from the Cape Canaveral Air Force Station in Florida on Aug. 12, riding atop a two-stage Atlas V rocket.

Its assignment includes two years of advanced geological and climate studies, followed by an extended period as a communications link for future missions.

Since liftoff, the 4,800-pound spacecraft has flown nearly 310 million miles and tests show it's in good working order as it approaches the planet's southern hemisphere.

Today the flight engineers will try to thread MRO through an orbital needle's eye some 249 miles above the planet's surface, then slow it down by 2,200 mph - just enough for Martian gravity to pull the craft into a safe orbit.

It's a harrowing time for controllers. They are 134 million miles from their spacecraft and, even at the speed of light, it would take 24 minutes for news of trouble and their corrective commands to make the round trip.

"There is no time for the team to react," Graf said. So MRO has all its instructions on board - it will be on its own during today's critical maneuvers.

Worse, the spacecraft will disappear behind Mars and be out of radio contact for 29 minutes. For that perceived eternity, Graf said, "We are in white-knuckle time." The engineers will learn the spacecraft's fate at 5:16 p.m. when MRO is due to re-emerge from behind the planet.

So far, the mission has gone well. The craft's trajectory was so accurate that controllers in Pasadena skipped two of four planned mid-course corrections - saving 55 pounds of precious fuel for future use in Mars' orbit.

Navigators got help this week from a novel experiment using Mars' two moons, Phobos and Deimos, as landmarks. With the spacecraft's Optical Navigation Camera, controllers double-checked MRO's position by comparing the moons' actual positions relative to background stars with predictions. "With that, we can find our place relative to Mars down to about a kilometer, which is pretty astounding," Graf said.

NASA hopes the technique will steer future spacecraft to more precise landings on Mars, and guide rockets returning samples from the Martian surface back to the orbiting craft that will deliver them to scientists on Earth.

Entering Martian orbit today will be just the beginning for MRO's handlers. If all goes as planned, the maneuver will place the spacecraft in a 35-hour orbit that ranges from 249 miles above the planet at one end to 27,340 miles at the other.

Over six months, controllers will use a technique called "aerobraking" to dip the craft into the upper atmosphere more than 500 times, gradually slowing it into a nearly circular, two-hour orbit 150 to 200 miles above the surface.

It's tricky work from so far away, but it saves money. Doing the job with rocket engines would have doubled MRO's fuel requirements and increased the mission's weight and launch budget. Aerobraking will also yield data on Mars' upper atmosphere, which is important to future missions using the same technique.

In November, after MRO's orbit is closer to the surface than the three current orbiters, its primary scientific work will begin. The spacecraft carries the most powerful telescopic camera ever hauled to another planet. It will snap color photos of surface features as small as living room furniture, in swaths 3.7 miles wide.

Each photo will contain 28 gigabits of information, "more data than both [Mars] rovers returned to Earth in the first 90 days of operations," Graf said.

The instruments will study landforms and reveal the ancient geological processes that formed the planet's surface, as well as the impact of climate and weather.

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