NASA's Mars rover resumes work after computer glitch

CAPE CANAVERAL, Florida (Reuters) - NASA's Mars rover Curiosity resumed analysis of a sample of rock powder following a computer glitch that suspended operations for a week, scientists said on Monday.

Before the computer problem, results radioed back to Earth revealed that the rock, located near Curiosity's Gale Crater landing site, contains all the chemical ingredients necessary for microbial life, the over-arching goal of the planned two-year mission.

Scientists are eager for additional information about the rock sample, which was drilled out from what appears to be a slab of bedrock in an area known as Yellowknife Bay.

Curiosity automatically suspended its work on March 17 when it detected a problem with a computer data file. The glitch occurred as the rover was recovering from an earlier, unrelated computer problem.

The unplanned work hiatus ended over the weekend, NASA's deputy project manager Jim Erickson said.

"It's a slow recovery process, but we're back doing science," Erickson said.

Analysis of the rock powder will continue for about another week. Beginning April 4, radio communications between Earth and Mars will be blocked by the sun for a month, suspending most of the rover's science operations again.

When the planets re-align for communications after May 1, scientists plan to drill a second hole into the rock to verify the early results and look more closely for signs of organic carbon.

The $2.5 billion rover landed on Mars on August 6 to assess if the planet most like Earth has or ever had the chemical ingredients and environments for microbial life.

Scientists eventually plan to drive the rover to a 3-mile (5-km) high mound of what appears to be layered sediment rising from the floor of Gale Crater.

(Editing by Kevin Gray and Lisa Shumaker)

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Mars Rover Curiosity Resumes Science Work After Computer Glitch

NASA's Mars rover Curiosity has fully recovered from a glitch that knocked out its main computer system late last month, space agency officials say.  

The Curiosity rover has now resumed science work inside the Red Planet's huge Gale Crater. The car-size robot is monitoring Martian radiation and weather again, and it delivered more samples of powdered rock from a previous drilling operation to its onboard instruments on Saturday (March 23), rover team members said.

"We are back to full science operations," Curiosity deputy project manager Jim Erickson, of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., said in a statement Monday (March 25).

A complicated recovery

Curiosity had been operating pretty much flawlessly on the Red Planet until late February, when a memory glitch corrupted its main, or A-side, computer. Engineers swapped the rover over to its backup (B-side) computer, spurring Curiosity to go into a precautionary "safe mode" on Feb. 28. [Curiosity Rover's Latest Amazing Mars Photos]

As the team worked to fix the A-side, engineers also spent time checking out the B-side and configuring it for surface operations, as the A-side had been running Curiosity since a few weeks before the rover touched down on Mars the night of Aug. 5.

The rover's 10 science instruments can all be operated by either the A-side or the B-side computer, but other gear is not so flexible. For example, each of Curiosity's 12 engineering cameras is linked only to the main or the backup computer, researchers said.

"This was the first use of the B-side engineering cameras since April 2012, on the way to Mars," JPL's Justin Maki, team lead for these cameras, said in a statement. "Now we've used them on Mars for the first time, and they've all checked out OK."

Bringing the rover back up to speed has been delayed a few times by other events as well. In early March, engineers briefly put Curiosity on standby again to wait out a Mars-bound solar eruption. And on March 16, a separate software issue sent Curiosity into safe mode for a few days.

But all appears to be going well now. The B-side is running fine, NASA officials say, and the A-side is available as a backup if needed.

Communications blackout coming

Curiosity is getting back to work just in time for a lengthy communications blackout.

For much of next month, Mars will be almost directly behind the sun from Earth's perspective. Our star can disrupt interplanetary signals in this alignment, which occurs every 26 months and is known as a Mars solar conjunction.

Mission engineers don't want to take the chance of a corrupted command confusing the rover, so no directions will be sent to Curiosity from April 4 through May 1. Curiosity will continue to operate during this time, using a set of commands relayed in advance.

NASA's other Red Planet robots, such as the Opportunity rover and the Mars Reconnaissance Orbiter, will also be on their own for much of April.

Curiosity is the centerpiece of NASA's $2.5 billion Mars Science Laboratory mission, which seeks to determine if the Red Planet could ever have hosted microbial life.

The rover has already accomplished its main goal. Earlier this month, Curiosity scientists announced that Mars was indeed habitable billions of years ago, basing their conclusion on the rover's analysis of rock samples it drilled from deep within a Red Planet outcrop.

The powdered rock samples Curiosity recently delivered to its instruments are additional specimens collected from that initial drilling operation. The rover won't drill another rock until after the Mars solar conjunction, team members have said.

Follow Mike Wall on Twitter @michaeldwall. Follow us @Spacedotcom, Facebook or Google+. Originally published on SPACE.com.

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Quasars Still Mystify Scientists 50 Years After Discovery

Half a century after first getting a bead on quasars, astronomers still lack a basic understanding of how the most luminous objects in the universe work, a prominent researcher says. 

Scientists first measured the distance to a quasar — an incredibly bright galactic core powered by a supermassive black hole — 50 years ago this Saturday (March 16), finding that it lay billions of light-years away.

The discovery was a seminal one in astronomy, opening the distant, ancient universe to observation and study. But in the decades since, researchers have shed little light on the powerful engine that drives quasars, says astrophysicist Robert Antonucci of the University of California, Santa Barbara.

"We have found thousands of quasars in the past 50 years, but we still don't have good physical models for how they radiate their prodigious energy," Antonucci writes in the current issue of the journal Nature, which was published online today (March 13). "Without predictive the­ories, we have nothing. Our best hope for understanding quasars is that extraterrestrials might drop in and explain them to us." [Most Powerful Quasar Discovered (Video)]

The brightest objects in the universe

Quasars radiate energy broadly across the electromagnetic spectrum, but they take their name from their radio emissions. Astronomers dubbed them"quasi-stellar radio sources" because the signals appeared to be coming from one place, like a star. The shortened version of the moniker, "quasar," stuck.

Many quasars blast out twin jets of particles that travel at nearly the speed of light, which in turn create enormous, radio-emitting "lobes" near the quasars, Antonucci writes.

Scientists think quasars and other types of active galactic nuclei mark a particular stage in the lifetime of galaxies, one at which their central black holes, which can be more massive than 10 billion suns, are gobbling up lots of gas, dust and other matter.

"This trait was more com­mon in the past, so there are fewer quasars today," Antonucci writes. "Now starved of fuel, black holes linger in galaxies, including our Milky Way."

Questions remain

Astronomers have been documenting ever-more distant quasars, pushing back closer and closer to the Big Bang that created our universe 13.7 billion years ago. But a fundamental understanding of quasars remains elusive, Antonucci says.

"The theory of radio sources has not changed significantly in the past 30 years," he writes. "Basic questions remain: do the jets and lobes comprise electrons and protons or electron-positron pairs? Do the protons carry a lot of energy, as cosmic rays do? Is the energy divided evenly between electric and magnetic fields? Without answers to these [questions], we can set only lower limits on how much energy the jets and lobes hold."

It doesn't help that astrophysicists continue to investigate quasars using models developed for much smaller black holes, Antonuccci says.

"These models simply don't match the observations without lots of special pleading," he writes. "The properties of small accretion disks that are inferred to exist around stel­lar-mass black holes cannot be scaled up to explain the spectra of much more luminous quasars."

But a better understanding of quasars is achievable, Antonucci adds, urging his colleagues to work on developing advanced computational models of black-hole systems. And more sensitive X-ray telescopes could make a difference, too.

"The important thing is that the X-rays come from so extremely close to the black hole, much closer than the optical light," Antonucci told SPACE.com via email. "So it offers a hope of giving us a picture of the 'central engine' of the black hole, where the gravitational potential energy is actually produced. That's where the money is."

Antonucci voiced optimism that astronomers will unlock quasars' key mysteries, though he's not sure about the timeline.

"Eventually, I suppose we'll get it, although I may be in heaven by then, or else in the other place!" he told SPACE.com.

Follow Mike Wall @michaeldwall. Follow us @Spacedotcom, Facebook or Google+. Originally published on SPACE.com.

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Space trio lands in Kazakhstan after bad weather delay

ALMATY (Reuters) - A Russian Soyuz capsule made a "bull's eye" landing in the steppes of Kazakhstan on Saturday, delivering a Russian-American trio from the International Space Station, a day after its originally scheduled touchdown was delayed by foul weather.

NASA's Kevin Ford and Russian cosmonauts Oleg Novitskiy and Evgeny Tarelkin, who had manned the $100 billion orbital outpost since October as Expedition 34, landed in cloudy weather at 7:06 a.m. Moscow time (0306 GMT) northeast of the town of Arkalyk.

They had spent 144 days aboard the multinational ISS on their space journey of almost 61 million miles (98 million km).

"The landing was energetic and exciting," Russian TV showed Novitskiy as saying.

NASA television said the deorbit burn and other events during the descent had gone flawlessly. It said the capsule had landed upright, almost hitting its bull's eye target in thick fog.

"Oleg Novitskiy reported to search and recovery teams that the crew is feeling good," NASA television said. "Everything seems to be in order."

Due to hampered visibility, it took a few minutes before helicopters with Russian search and recovery teams could locate the Soyuz capsule after its landing.

The first images shown by Russia's Vesti-24 television featured rescue workers standing in a snow-covered steppe opening the hatch of the capsule.

The three smiling astronauts were seated on semi-reclined chairs and covered with blue thermal blankets. They were then carried to a nearby inflatable medical tent.

On Friday, fog and freezing rain at the landing site in Kazakhstan prevented helicopters from setting up for the crew's return to Earth.

In preparation for their departure, Canadian astronaut Chris Hadfield took the helm of the space station on Wednesday, becoming the first Canadian to take command of the outpost.

It is only the second time in the 12-year history of the station, a project of 15 nations that has been permanently staffed since November 2000, that command has been turned over to someone who is not American or Russian.

Hadfield will be part of a three-man skeleton crew until NASA astronaut Chris Cassidy and cosmonauts Pavel Vinogradov and Alexander Misurkin arrive later this month.

(Reporting by Dmitry Solovyov; Editing by Lisa Shumaker)

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After victory lap, Endeavor rolls to retirement

LOS ANGELES (AP) — Space shuttle Endeavour rocketed beyond Earth orbit 25 times. Its 26th mission: A 12-mile commute through the streets of Los Angeles to its new retirement home in a museum.

With Endeavour permanently on the ground after a majestic aerial spin Friday around California, crews over the weekend will begin unbolting the shuttle from the 747 jumbo jet and putting it on a special flatbed trailer, a process that will take a few weeks.

The road trip in early October to the California Science Center has been billed as a parade, but some residents along the route have objected to the cutting down of some 400 trees to make room for the five-story-high shuttle with a 78-foot wingspan.

A crowd recently packed a public meeting where concerns were raised about the loss of shade and greenery in their neighborhoods. Museum officials have pledged to replant at least double the number of lost trees.

But Friday brought nothing but good feelings as the shuttle became California's biggest star, the people its paparazzi.

From the state Capitol to the Golden Gate Bridge to the Hollywood sign, massive crowds of spectators pointed their cellphones and cameras skyward as the shuttle, riding piggyback atop a 747 jumbo jet, buzzed past.

Peggy Burke was among the hordes of camera-toting tourists who jammed the waterfront along the San Francisco Bay, reflecting on the end of an era.

"It's just a shame that the program has to end, but I'm so glad they came to the Bay area especially over the Golden Gate Bridge," she said. "Onward to Mars."

At the Hollywood & Highland Center, a shopping complex with a view of the Hollywood sign, revelers yelled and screamed.

"It was like being in Times Square for the millennium," said Blue Fier, a college photography professor. "This is right up there. It was pretty cool."

Known as the baby shuttle, Endeavour replaced Challenger, which exploded during liftoff in 1986. Endeavour rolled off the assembly line in the Mojave Desert in 1991 and a year later, rocketed to space. It left Earth 25 times, logging 123 million miles.

Friday's high-flying tour was a homecoming of sorts.

After a nearly five-hour loop that took Endeavour over some of the state's most treasured landmarks, it turned for its final approach, coasting down the runway on the south side of the Los Angeles International Airport, where elected officials and VIPs gathered for an arrival ceremony.

As the jumbo jet taxied to the hangar, an American flag popped out of the jet's hatch. Endeavour will stay at the airport for several weeks as crew prepare it for its 12-mile trek through city streets to the California Science Center, its new permanent home, where it will go on display Oct. 30.

NASA retired the shuttle fleet last year to focus on destinations beyond low-Earth orbit. Before Endeavour was grounded for good, Californians were treated to an aerial farewell.

Endeavour took off from Edwards Air Force Base in the Mojave desert Friday after an emotional cross-country ferry flight that made a special flyover of Tucson, Ariz., to honor its last commander, Mark Kelly, and his wife, former Arizona Rep. Gabrielle Giffords.

It circled the high desert that gave birth to the shuttle fleet before veering to Northern California. After looping twice around the state Capitol, it swung over to the San Francisco Bay area and Silicon Valley and then headed down the coast, entering the Los Angeles air space over the Santa Monica Pier. En route to LAX, it passed over a slew of tourist sites including Dodger Stadium, Disneyland and the Queen Mary.

The cost for shipping and handling Endeavour was estimated at $28 million, to be paid for by the science center. NASA officials have said there was no extra charge to fly over Tucson because it was on the way.

Endeavor's carefully choreographed victory lap was by far the most elaborate of the surviving shuttle fleet. Discovery is home at the Smithsonian Institution's hangar in Virginia after flying over the White House and National Mall. Atlantis will remain in Florida, where it will be towed a short distance to the Kennedy Space Center's visitor center in the fall.

Derek Reynolds, a patent attorney from a Sacramento suburb who saw the last shuttle launch last year, felt the flyover in Sacramento was a rare opportunity to share a firsthand experience of the space program with his 5-year-old son, Jack, who he pulled out of kindergarten for the day.

"I want him to experience it and give him the memory since it's the last one," Reynolds said.

As Endeavour approached LAX, other airplanes were forced to circle and wait. Passengers on an American Airlines flight from Miami snapped pictures and shot video out their windows as the shuttle arrived.

"This was a once-in-a-lifetime event," said pilot Doug Causey, who has been flying for 29 years. "That was a real treat to see something like that."

___

Contributing to this report were Associated Press staff members Tom Verdin and Juliet Williams in Sacramento; Terry Chea and Marcio Sanchez in San Francisco; John Antczak in Pasadena; Jae Hong in Santa Monica; and Greg Risling, Martha Mendoza, Raquel Maria Dillon, Richard Vogel and Chris Carlson in Los Angeles.

___

Alicia Chang can be followed at http://twitter.com/SciWriAlicia

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Chinese astronauts parachute land after mission

BEIJING (AP) — China's first female astronaut and two other crew members emerged smiling from a capsule that returned safely to Earth on Friday from a 13-day mission to an orbiting module that is a prototype for a future space station.

The Shenzhou 9 parachuted to a landing on the grasslands of the country's sprawling Inner Mongolia region at about 10 a.m. (0200 GMT). China declared the first manned mission to the Tiangong 1 module — the space program's longest and most challenging yet — a major stride ahead for the country's ambitious space program.

About an hour later, mission commander and veteran astronaut Jing Haipeng, 45, emerged from the capsule, followed by crew mates Liu Wang, 43, and 33-year-old Liu Yang, China's first female astronaut.

The three, all experienced air force pilots, were lifted on to folding chairs and appeared in good health. They smiled, waved, chatted and saluted as state television ran live footage from the landing site.

"Tiangong 1, our home in space, was comfortable and pleasant. We're very proud of our nation," Liu Yang told national broadcaster CCTV.

Space program commander, Gen. Chang Wanchuan, declared the astronauts in good health and declared the mission "completely successful."

He was followed by Premier Wen Jiabao, who said the mission marked "absolutely important progress" for the space program.

The mission had included both remote control and piloted dockings with the module and extensive medical monitoring of the astronauts as part of preparations for manning a permanent space station.

China's next goals include another manned mission to the module originally scheduled for later this year but which may be delayed depending on an evaluation of the Shenzhou 9 mission and the condition of the Tiangong 1. China has been extremely cautious and methodical in its manned missions, with more than three years passing since the previous one, and all four have been relatively problem-free.

Chen Shanguang, director for the Chinese Astronaut Research and Training Center, told a news conference that preparations and selection of astronauts were already under way for the Shenzhou 10 mission.

Tiangong 1 is due to be retired in a few years and replaced with a permanent space station around 2020 that will weigh about 60 tons, slightly smaller than NASA's Skylab of the 1970s and about one-sixth the size of the 16-nation International Space Station that China was barred from participating in, largely on objections from the United States. Possible future missions could include sending a rover to the moon, possibly followed by a manned lunar mission. Launched June 16 from the Jiuquan center on the edge of the Gobi desert in northern China, Shenzhou 9 is the latest success for China's manned space program that launched its first astronaut, Yang Liwei, into space in 2003, making China just the third nation after Russia and the U.S. to achieve that feat. China would also be the third country after the United States and Russia to send independently maintained space stations into orbit.

Earlier in the week, a spokeswoman said China spent 20 billion yuan ($3.1 billion) on its space program between 1992 and 2005 — a rare admission for a program with close links to the secretive military. By the time the next Shenzhou mission is completed, Beijing will have spent an additional 19 billion yuan ($3 billion), the spokeswoman said.

Wang Zhaoyao, director of China's manned space program office, said the program mirrors the rising global status of China.

"For any country, for any people, a space program is indispensable," Wang said.

___

Associated Press writer Didi Tang contributed to this report.

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NASA Sets Sights on Mars After Unmanned Moon Shot (SPACE.com)

NASA successfully launched a set of twin spacecraft into orbit today (Sept. 10) to study the moon's gravity, but the new mission isn't the first — or the last — robotic planetary expedition for the space agency year.

The two Grail spacecraft launched toward the moon from Florida's Cape Canaveral Air Force Station to begin a 3 1/2-month trip to lunar orbit. The liftoff came just one month after another NASA observatory launched toward Jupiter to study the gas giant's composition and atmosphere. That flight, the Juno mission to Jupiter, is also expected to beam back the best photos yet of the solar system's largest planet.

"Today we had the second of NASA's planetary science launches in what we've been calling the 'Year of the Solar System,'" Jim Adams, deputy director of the planetary science division at NASA Headquarters in Washington, D.C., told reporters in a post-launch news briefing. "Just over a month ago, Juno was thrust on its way off to Jupiter, and today we sent a set of twin spacecraft off to the moon." [Photos: NASA Launches Grail Probes to the  Moon]

The $1.1 billion Juno mission is expected to arrive at the giant planet in July 2016.

And NASA's not done yet.

Mars is next

In late November, NASA will launch the sophisticated Mars Science Laboratory (MSL) mission toward the Red Planet. The centerpiece of the ambitious MSL mission is a Mini Cooper-size rover named Curiosity, which will roam the surface of the planet searching for clues of its wet past and potential habitability.

The $2.5 billion Curiosity rover will land in Gale Crater, a 96-mile (154-kilometer) wide scar in the Martian surface that has a central peak which rises higher than Mount Rainer near Seattle. The states of Rhode Island and Connecticut could fit inside it.

The Mars Science Laboratory is expected to land on Mars in August 2012. Once on the surface, Curiosity will explore Gale Crater in hopes of determining if the region could have once supported some form of primitive life on Mars. [Photos: Last Look at Mars Rover Curiosity Before Launch]

But Curiosity needs to launch into space first before even contemplating its Mars mission. So for today, all NASA eyes were on Grail moon probes.

Inside the moon

NASA's new mission to the moon continues in the footsteps of previous robotic and manned lunar expeditions, but the Grail probes are expected to greatly expand our knowledge of Earth's natural satellite.

"Six miles from where we launched this morning was the pad where Apollo 11 launched," said Maria Zuber, Grail principal investigator at MIT. "Grail now continues the story of exploring the moon." [Related: 20 Most Marvelous Moon Missions]

The $496 million Grail mission will precisely and accurately map the moon's gravitational field. The probes will also peer inside the moon and examine its composition, from crust to core, and attempt to piece together its evolutionary history.

Observations from the Grail spacecraft will also help researchers understand how other large, rocky planets in the inner solar system formed and evolved.

The probes, called Grail-A and Grail-B, are embarking on a circuitous and energy efficient path to the moon. The spacecraft are expected to arrive at their lunar destination by New Year's Day.

The three-month science mission will begin in early March, when Grail-A and Grail-B begin collecting data.

In the meantime, students of all ages across the U.S. are invited to enter a contest for more creative names for the lunar probes. NASA will announce additional details about the naming contest soon, but Zuber explained that students will be invited to submit essays explaining their choice of names. The contest will run from Oct. 14 to Nov. 11, and the winning names will be announced before the Grail spacecraft reach lunar orbit.

Today's launch came after windy weather and a technical glitch postponed Grail's liftoff by two days. Even this morning's success was not without its share of suspense. The probes blasted off at 9:08 a.m. EDT (1308 GMT) from Florida's Cape Canaveral Air Force Station, but high-altitude winds forced the agency to stand down during an initial attempt earlier this morning.

"That was the most drama, I think, of the entire day," Zuber said. "It was such a relief once we got the 'go' to launch … that I was extremely calm during the launch."

You can follow SPACE.com staff writer Denise Chow on Twitter @denisechow. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

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What happens to those 3-D glasses after 'Avatar'?

Laid end-to-end, the 3-D glasses worn by avid Avatar-goers since the blockbuster movie opened 46 days ago would reach from Los Angeles to Angmagssalik, Greenland — about 3,987 miles.That's a whole lot of plastic. With about 75% of people who see Avatar seeing it in 3-D, it works out to about 42.1 million pairs of glasses worn, or 935,834 a day.

Four companies provide 3-D systems for showing the wildly popular sci-fi epic in the USA: Dolby Laboratories, IMAX, Real-D and XpanD.

Each has a recycling program in place, for hygiene and to keep what would otherwise be a mountain of plastic out of landfill.

IMAX, which has about 2% of the 3-D screens showing Avatar, says its glasses can be washed up to 500 times. "When we put them through our glasses-cleaning machine, they come out as clean and sterile as they come out of a dishwasher in a restaurant," says Brian Bonnick, the Canadian company's vice president of technology.

Dolby and XpanD are the next-largest in terms of screens, though exact numbers are hard to come by. Dolby's glasses are also reusable. Each gives theater owners instructions on how to clean its reusable specs.

"We have glasses that have been used and washed thousands of times without degradation," says director of marketing Page Huan. "There's no need to throw them away. They're very environmentally friendly." She says Dolby suggests exhibitors simply buy a commercial dishwasher and clean them with soap and high heat.

XpanD's glasses also are built tough to be washed, though the company's Michael Williams suggests keeping the dishwater temperature "under 120 degrees or you might have a little glob of plastic" come out at the end of the wash cycle.

The glasses, which require batteries and cost about $50 each, have built-in security strips, Williams says. Theater owners can get rollable security barriers that beep if patrons forget to return them.

Real-D has the lion's share of 3-D projection systems in the USA, accounting for at least 700,000 3-D glasses used a day. It distributes cardboard containers so movie-goers can recycle their glasses. According to Real-D's Rick Heineman, the glasses are shipped to a cleaning facility near Los Angeles, where they're sanitized, checked for defects, repackaged and shipped out.

Moore Theaters in Otsego, Mich., has done away with recycling altogether. It sells a plastic reusable bucket for popcorn that patrons fill themselves and charges $3 for 3-D glasses patrons keep, says owner Carol Moore. "By this weekend, we had 22% coming back with glasses. Most of the time that means they're returning to see the movie or they're giving them to friends."

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Shuttle Endeavour lands after its final flight

Astronauts of STS-134 pose for a group photograph shortly after landing onboard the space shuttle Endeavour at the Shuttle Landing Facility (SLF) at Kennedy Space Center in Cape Canaveral, Florida, June 1, 2011. From left: Flight engineer Roberto Vittori with the Italian Space Agency, pilot Greg Johnson, commander Mark Kelly and spacewalkers Mike Fincke, Greg Chamitoff, and Andrew Feustel.

Credit: Reuters/NASA/Bill Ingalls/Handout

By Irene Klotz

CAPE CANAVERAL, Florida | Wed Jun 1, 2011 2:54pm EDT

CAPE CANAVERAL, Florida (Reuters) - The space shuttle Endeavour touched down at its Florida home base early on Wednesday, capping a 16-day mission to deliver a premier science experiment to the International Space Station on NASA's next-to-last shuttle flight.

Sailing through night skies, the shuttle and its six-man crew glided toward the Kennedy Space Center, circling high overhead to burn off speed and setting off a pair of sonic booms, heralding the ship's homecoming.

Commander Scott Kelly, a four-time shuttle veteran, gently eased the 100-tonne spaceship onto the runway, touching down at 2:35 a.m. EDT to complete Endeavour's 25th and final flight.

"Your landing ends a vibrant legacy for this amazing vehicle that will long be remembered. Welcome home, Endeavour," astronaut Barry Wilmore radioed to Kelly from NASA's Mission Control in Houston.

"It really is an incredible ship," Kelly replied. "It's sad to see her land for the last time but she really has a great legacy."

Endeavour racked up 123 million miles (198 million kms) in 25 spaceflights. It will now be prepared to be put on display at the California Science Center in Los Angeles.

NASA's attention shifts to sister ship Atlantis, which was rolled out to the shuttle's seaside launch pad as Endeavour headed back to Earth.

Atlantis is slated to launch on July 8 on NASA's final planned shuttle mission, a supply run to the space station.

'AS BEAUTIFUL AS THAT'

"It's going to be a long time until you see a vehicle roll out to the pad that looks as beautiful as that," said Atlantis astronaut Rex Walheim, who was at the Kennedy Space Center along with his three crew mates to watch NASA's final shuttle roll-out.

"An airplane on the side of a rocket. It's absolutely stunning," he said.

The United States is retiring its three-ship fleet due to high operating costs and to free up funds to develop new spacecraft that can travel beyond the space station's 220-mile-high (346-km-high) orbit.

The space shuttle Discovery returned from its final voyage in March.

The primary goal of Endeavour's flight, the 134th in shuttle program history, was to deliver the $2 billion Alpha Magnetic Spectrometer particle detector and a pallet of spare parts to the station.

The crew also made four spacewalks to complete assembly of the U.S. side of the $100 billion outpost, a project of 16 nations that has been under construction since 1998. The last piece to be installed was the shuttle's 50-foot-long inspection boom, which will now be used to extend the reach of the station's robotic crane.

Kelly and his crew mates -- pilot Greg Johnson, flight engineer Roberto Vittori with the Italian Space Agency, and spacewalkers Drew Feustel, Mike Fincke and Greg Chamitoff -- also tested a new automated rendezvous system that NASA plans to use on its next spaceship and on a new robotic science mission to an asteroid.

It will be at least four years before NASA astronauts can fly out of the United States again. Until new ships are ready, Russia will transport crews to the station at a cost of more than $50 million per person.

Kelly and his crew are scheduled to return to Houston on Thursday.

Before leaving orbit, he said he was looking forward to seeing his wife, U.S. Representative Gabrielle Giffords, an Arizona Democrat. The congresswoman is recovering from a January 8 assassination attempt.

Kelly initially took himself off the mission to care for his wife, but rejoined his crew after she was transferred to a Houston hospital for rehabilitation.

Giffords, who traveled to Florida to see the Endeavour launch, was not at the space center for the landing.

(Editing by Kevin Gray and Will Dunham)

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