Phoenix spacecraft successfully lands on Mars

NASA's Phoenix spacecraft successfully touched down on the surface of Mars Sunday night, the first time in 32 years that the space agency has landed a probe on the Red Planet using retrorockets.

Jubilant officials at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., burst into cheers when Phoenix's radio signal came in as scheduled at 7:53 p.m. ET, indicating that the $457 million lander is in position near Mar's northern polar cap.

About two hours later, the mission controllers got word that the craft's solar arrays had successfully deployed. The twin 6-foot circular disks are the power source. If they hadn't deployed, Phoenix would only have had about three hours of battery power.

And immediately after that, images began to arrive — the scientists' best-case scenario. "What we're looking at is a surface of Mars that we've never seen before," said Dan McCleese, JPL's chief scientist. The "crystal clear" images showed a flat surface with very few rocks.

"This was just perfect. It didn't seem real," said Peter Smith, the planetary sciences professor at the University of Arizona who proposed and helped develop the mission. "I'm on Cloud 9."

Robert Shotwell, the mission's project systems engineer, described the landing as "almost exactly perfect — flat and aligned where we wanted it to be."

He said the parachute deployed seven seconds later than anticipated, which had a "slight" effect on the landing site. Otherwise, he said, "Everything looked as good as could possibly be expected. Everyone is thrilled."

"As icing on the cake, we've found that the lander is tilted only one quarter of a degree, which means we've landed nearly perfectly level," blogged Brent Shockley on NASA's Phoenix website (www.nasa.gov/mission_pages/phoenix).

"Engineers in Mission Control are saying that our actual landing went far smoother than any simulation or test that was ever done," said Shockley, the mission's configuration and information management Engineer.

It takes 15 minutes for Phoenix's radio signal to reach Earth, which meant a long, suspenseful wait in the home stretch for members of the mission staff assembled in the JPL's mission control room.

As the mission team awaited word of the craft's fate, the early stages of its entry into the Martian atmosphere appeared to go well. As the news arrived that each challenge had been met — that the cruise-stage hardware had been jettisoned and the craft had pivoted to turn its heat shield towards the planet's surface; that the parachute had deployed and the radar had been activated — the control room filled with applause.

This happy ending to Phoenix's 423-million-mile, nine-month journey was far from a safe bet. Of the 11 missions that have tried to land probes on Mars since 1971 — by the United States, Russia and Great Britain — only five have succeeded.

Adding to the risk of failure is the fact that every successful Mars landing since 1976 has involved huge air bags that let the craft bounce to a soft landing. But the air bags don't allow for precise landings and NASA scientists want to hit the targeted landing site.

So Phoenix was equipped with retrograde rockets, set to fire less than a minute before touchdown to decelerate the craft. The last mission to land this way was the Viking 2 lander, on Sept. 3, 1976. A later mission, the Mars Polar Lander, was using retro rockets when it crashed in 1999.

And there was another danger: rocks.

Phoenix has three legs. If one of them had come down on a large rock, the craft could have been knocked over or become unstable, ending the mission. NASA surveyed the 60-by-12-mile landing area by satellite, looking for spots with as few rocks as possible.

There were six "trajectory correction maneuvers" (carefully calculated rocket blasts) planned for Phoenix but not all proved necessary. A May 17 maneuver, when the craft was 6 million miles from Mars, was just a nudge, moving the landing point 11 miles to a slightly better location.

Early Sunday, mission controllers decided there was no need to use their last chance to tweak the flight path, leaving them with nothing to do but wait for Phoenix to carry out the landing on its own.

The lander is beaming back images of a Martian landscape never before seen by humans— one near the north polar cap, where scientists believe there is abundant water, if frozen and buried.

Finding evidence of water has long been the goal of NASA's Mars program. Water is essential to all known life. The Mars missions are aimed at giving scientists more information about where, when and in what form water existed there.

The Phoenix lander is designed to collect and examine ice and rock samples for evidence of microscopic life. NASA scientists hope that if a rudimentary form of life existed there millions of years ago, traces of it might remain.

There's a reason this Mars mission is named Phoenix, after the mythical bird that rises from the ashes of its own funeral pyre. The spacecraft originally was scheduled to launch in 2001 as the Mars Surveyor, but it was grounded because of the Mars Polar Lander crash.

Phoenix's equipment includes a robotic arm that will dig up soil samples and a portable laboratory that will test the soil. The Martian soil is expected to be a frozen matrix of rocks, gravel, sand and ice as hard as concrete.

The samples will be viewed by an onboard microscope, and high-resolution images will be beamed to scientists on Earth.

Phoenix also is a weather station with a mast that will rise 4 feet, allowing scientists to calculate the extent of water vapor and cloud cover.

Phoenix isn't alone on Mars. NASA has had the golf cart-sized rovers, mobile geology labs called Spirit and Opportunity, on the surface since January 2004. Overhead are the Mars Odyssey, which began its orbit on Oct. 24, 2001, and the Mars Reconnaissance Orbiter, which reached Mars in March 2006. The European Space Agency's Mars Express orbiter also has been circling the planet since 2003.

The mission is being led by scientists at the University of Arizona. When NASA put out a call in 2002 for Mars mission proposals, the one chosen came from Smith, who proposed using the mothballed Surveyor.

Smith's team designed the science experiments and worked with JPL and Lockheed-Martin to recondition the spacecraft, which launched on Aug. 4, 2007 from Cape Canaveral in Florida.

About two days after the landing, the mission's center of operations is scheduled to shift to the University of Arizona's Science Operations Center in Tucson.

The mission is expected to last 90 days. In three months, winter will come to the Martian north pole and the sun won't rise again for 100 days. The solar-powered craft is not expected to survive the frigid temperature.

http://www.usatoday.com/tech/science...s-lander_N.htm