NASA's $2.5 billion Mars Science Laboratory rover is in good shape and on target for a nail-biting seven-minute plunge to a bull's-eye landing on the red planet in early August, thanks to upgraded software and post-launch improvements that will enable the craft to make a more precise descent to the floor of Gale Crater, mission managers said Monday.
While engineers are continuing to troubleshoot a contamination issue with Teflon seals inside a high-tech rock drill on the rover's robot arm, the project scientist said he is confident workarounds will be in place by the time the nuclear-powered rover is lowered to the surface by its rocket-propelled "sky crane" descent stage.
"We are gaining a greater understanding of that contamination issue," John Grotzinger told reporters in a teleconference. "The testing so far continues to give us reasonable confidence we'll be able to meet all the mission success criteria for the use of the drill."
Launched November 26, 2011, the Mars Science Laboratory "Curiosity" rover is the most sophisticated robotic lander ever built, equipped with six electrically-driven wheels, a robot arm, multiple cameras and a suite of state-of-the-art instruments. The goal of the costly mission, expected to last at least two Earth years, is to explore Gale Crater's intriguing sedimentary formations to help scientists understand whether Mars ever had, or still has, the raw materials and an environment hospitable to life.
Because of the enormous distance between Earth and Mars on landing day -- about 154 million miles -- confirmation of touchdown is expected no earlier than 14 minutes after the fact, around 1:31 a.m. ET (GMT-4) on August 6.
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During the long cruise to Mars, engineers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., have been testing and upgrading the craft's complex entry, descent, and landing software as well as the computer programs that will take over once the spacecraft is safely on the surface.
Engineers originally predicted Curiosity would set down in a landing ellipse, or zone of uncertainty, measuring 12 by 16 miles. Thanks to post-launch improvements and analysis, the ellipse now is expected to be in the range of 4 by 12 miles and positioned closer to the central peak of Gale Crater where most of Curiosity's high-priority science targets are located.
Given the distance between Earth and Mars at the time of the rover's arrival, the entry, descent and landing will be carried out autonomously by the craft's main computer. To give engineers insight into the descent, the orbits of three NASA science satellites already circling Mars are being tweaked to make sure they are passing within sight of the rover on landing day to relay telemetry back to Earth.
Curiosity is the size of a small car and weighs nearly 2,000 pounds. It is too big to use an airbag landing system like those employed for the Mars Pathfinder and the Spirit and Opportunity rovers. Instead, engineers came up with the novel sky crane design, lowering the rover directly to the surface attached to a cable unreeled from a rocket-powered descent stage.
"We start the entire process of landing at about 13,200 miles an hour relative to the planet, 78 miles above the surface," said Dave Lavery, the Mars Science Laboratory program executive at NASA Headquarters. "Hopefully, if all goes well, about seven minutes later we'll be down on the surface with a relative velocity of zero, safely resting on six wheels."
But he cautioned that nothing is guaranteed and that Mars missions have a mixed-bag history of dramatic successes and devastating failures.
"We've done everything we can to ensure the greatest probability of success," he said. "The reality is, this is a very risky business. Historically, only about 40 percent of the missions to Mars have been successful for any of a number of various different reasons...There is never a guarantee of success. We've done everything prudently possible to ensure that our probability of success is as high as possible, but it's never a guarantee."
The only technical issue of any significance has been the Teflon contamination problem in the drill, which was discovered shortly before launch. The drill in question is mounted in a turret on the end of Curiosity's robot arm. It is designed to operate in rotary or percussive mode, moving rock fragments through the drill's interior and on to an instrument designed to look for signs of carbon compounds.
Testing shows internal Teflon seals can degrade during normal operation, allowing small amounts of Teflon to mix in with the sample material. A detailed analysis indicates the problem will not prevent the drill from being used but it's not yet clear what effect the expected contamination might have on the analysis of soil samples.
NASA spent about $2 million in Mars Science Laboratory program reserve funds to build test equipment and simulators to characterize the problem and develop workarounds. Engineers are now running tests to determine "when this might begin to happen on Mars, how many rocks we'd need to drill, how hard the rocks need to be, what kind of mode of drilling are we in, is it percussion mode or is it rotary only mode?" Grotzinger said.
"So there's a very extensive matrix of potential ways in which we would drill, weighed against the very broad matrix of the types of rocks we might drill," he said. "So basically now, ever since launch, we have been in the back room working away, plowing through this matrix. We don't have enough information yet to really know how serious the problem is. But right now, the thought is...that it's not a serious problem because we see so many potential ways to work around this."