Landing Looms for Mars Probe

 
By Robert Lee Hotz

PASADENA, Calif.—The biggest and best-equipped robotic rover ever launched to another planet is hurtling toward a rendezvous with Mars, in a $2.5 billion mission that tests the engineering limits of interplanetary exploration and takes the search for alien life to a new level.
 
If all goes well, the National Aeronautics and Space Administration's Mars Science Laboratory mission expects to land a one-ton mobile rover, called Curiosity, on the Red Planet in early August to begin a two-year exploration of the Gale Crater near the Martian equator. There, under pink skies and blue clouds, the six-wheeled robot will sniff, scan and, for the first time, drill for geochemical signs that Mars once was habitable.
 
As the space agency contends with cost overruns, shrinking government funding and competing ambitions—from next-generation telescopes to the next stage of human spaceflight—the nuclear-powered Curiosity, itself $1 billion over budget, may be the last U.S. landing on the Red Planet for the foreseeable future, several independent space experts said.

Already, NASA has withdrawn from a joint venture to Mars with the European Space Agency, which plans to launch missions for several probes, including a lander, in 2016 and in 2018. After NASA pulled out, the European agency in March turned to Russia for help building and launching the spacecraft.
 
"There is really no clear path forward for U.S. Mars exploration after this [Curiosity] landing," said Scott Pace, director of the Space Policy Institute at George Washington University.
 
While NASA planners rejigger the agency's Mars exploration program, Mission-operations engineers at the Jet Propulsion Laboratory in Pasadena, Calif., last week ordered the final course correction for the Curiosity spacecraft, nudging it onto the last and most perilous leg of its nine-month, 352-million-mile voyage. which culminates with a landing attempt.
 
.Bristling with sensors, antennas, a laser and a robotic arm, the Curiosity robot, about the size of a small SUV, is twice the length and four times the weight of any of the three prior rovers that explored Mars.
 
It is much too heavy to land inside the airbags that successfully cushioned the previous Spirit and Opportunity landings. Intead, the Curiosity depends on an elaborate four-part landing system that so far has worked only in computer simulations. Moreover, mission controllers on Earth will have no contact with the craft once it begins its seven-minute, automated descent—and no way to control it—until it has safely landed.
 
"It's a big bet, with a risky landing method and no back-up," said space analyst Howard McCurdy at American University.
 
If events go as planned, the Curiosity spacecraft late on Aug. 5 will plunge into the thin Martian atmosphere at 13,200 miles per hour and quickly brake by swooping back and forth in aerodynamic S-curves, much like the Space Shuttle. It would be the first time a Mars-bound craft uses the braking maneuver.
 
Once the craft has slowed to 1,000 miles per hour, its computer is programmed to trigger an electronic ripcord and deploy the largest supersonic parachute ever made. The nylon parachute—70 feet in diameter—will slow the craft to just under the speed of sound. When it reached about a mile or so above the surface, the chute will be jettisoned and a cluster of eight landing rockets would fire.
 
In the final landing phase, the spacecraft will hover on its jets about 65 feet above the surface and unreel the rover on three Kevlar cables in what NASA engineers call a "sky crane," lowering it to the ground at less than two miles per hour.
 
"You probably would not damage your bumper if you hit a car at this speed," said landing-system engineer Devin Kipp at the Jet Propulsion Laboratory, who helped design the parachute.
 
NASA engineers, though, are haunted by past failures. Since efforts to explore Mars began in 1960, the U.S., Russia, Japan and Europe have launched 40 missions to Mars. More than half crashed, misfired, malfunctioned or disappeared. The most recent Russian probe, which was launched to the Mars moon Phobos last November, never made it out of Earth orbit. Only NASA has ever successfully landed a rover on the planet.
 
If all goes well, the Curiosity spacecraft will film the last two or three miles of its descent in high-definition video at five frames a second, recording for the first time an actual landing on another planet. It may take months, however, for the full HD video footage to be relayed to Earth."We will get a perspective that no one has seen before, of a spacecraft doing its final descent onto the Mars surface," said deputy project scientist Ashwin Vasavada.
 
As a mobile laboratory, Curiosity will focus first on Gale Crater's 14,700-foot-high central peak. Dubbed Mount Sharp, it appears to be an unusual layer-cake of clay and other sedimentary deposits that may be relics of ancient water flows and organic chemistry.
 
Curiosity's robot arm will drill into the Martian rocks and feed the powdered samples into its onboard chemistry laboratory.
 
"It will be the first time we are drilling into another planet," said Dr. Vasavada. "By climbing this mountain and sampling these layers, we can piece together the history and determine whether any of these periods represent a habitable environment."
 
NASA managers, however, are worried small amounts of Teflon from the drill bit may contaminate the soil and rock samples. "We want to be sure that what we are testing is Mars, and not Earth contaminants," said MSL mission operations manager Michael Watkins.