How NASA tests an against-all-odds Mars rover landing
The space agency has dubbed Curiosity's imminent landing "seven minutes of terror." And that's even after months of excruciating, exacting preparation.
It's not every day that you land a spacecraft on Mars, even if you're NASA. And in the case of the Curiosity rover, hurtling toward a Mars landing as Sunday night turns into Monday morning, the space agency is tempting fate with a novel approach that involves a big parachute, a specially designed winch, and some very high hopes.
The rover's descent through the Martian atmosphere, which NASA has dubbed the "Seven Minutes of Terror," will be an edge-of-your-seat experience, despite the space agency's excruciating preparations.
Consider, for instance, just one key element that couldn't be precisely replicated here in Earth's gravity -- the tug that Curiosity will feel from the red planet's own gravitational field.
To learn more about how NASA's Jet Propulsion Laboratory got ready for the big moment, CNET spoke with Tim Nichols, vice president of aerospace and defense global marketing at Siemens, about the design and testing of Curiosity, the heart and soul and muscle of the $2.5 billion Mars Science Laboratory mission. NASA used Siemens PLM Software to account for the thousands of data points -- in over half a million lines of code -- to recreate the out-of-this-world conditions needed to test the final minutes of Curiosity's journey to Mars.
"The digital models that they [NASA engineers] created with our software become the backbone of the repeated simulations," Nichols said. "They constantly refine it. It is important to mitigating risk and mission success."
Curiosity is the most scientifically powerful robotic spacecraft ever built to explore the surface of another planet. It is the size of a small car and weighs 1,982 pounds. It is equipped with 17 cameras, a 7-foot-long robot arm, and a suite of 10 state-of-the-art scientific sensors and experiments weighing 125 pounds.
In the design and testing of the rover, engineers did not want to have to constantly build costly prototypes, so much of the work was done with tailored computer models -- from the design to assembly to extreme scenario simulations. Siemens' NX software, which consisted of CAD, CAE, and CAM applications, was used for all of the modeling. Specific code was created to model extreme temperatures that imitated the conditions on Mars with its thin and carbon dioxide-rich atmosphere, extremely cold surface, and intense radiation.
"They fed all of this into computers to stack up worst-case conditions," Nichols said. "The most complex part of the mission is the final 20 minutes from the point at which the rover enters the atmosphere of Mars, because it starts to heat up."
Once a prototype was built, engineers at the Jet Propulsion Laboratory began a whole new litany of testing and then retesting -- putting the rover into a vacuum chamber and again simulating the hazards it would have to endure. Curiosity was subjected to a "shake table," which violently shook it to see if it could withstand the vibrations it would experience in its journey. And again it had to survive hot and cold temperatures. Finally, its enormous parachute was successfully tested in NASA's 80-by-120-foot wind tunnel, as was its drop capabilities with a simulated sky crane landing in the laboratory.
The rover was launched last November, beginning its voyage to Mars. NASA engineers have set up a complex sequence of procedures that must be followed in order to avoid disaster when Curiosity makes its final descent onto the planet. First, they will deploy a parachute to slow its blazing descent. Then cutting off the chute, they'll fire up rockets to slow the vertical velocity even more, and lastly they will lower the rover on a tether into the Gale Crater. The main purpose of the complex system: avoid a grievous bounce or crash, or even a modest dust cloud, that would render the rover inoperable or less than fully functional.
"The project early on engaged in an awful lot of reviews--internal, external, headquarters reviews--to really establish the design of the sky crane was solid," MSL Project Manager Pete Theisinger told CNET in 2010. "And the support equipment that's been required for it, the radar, the valves for the throttle-able engines, all the things that are required to support EDL, their performance has been as good or better than expected."
The rover is slowed from more than 13,000 miles per hour down to a much, much gentler 2 mph, and it's this intense slowdown that causes the vehicle to increase in temperatures as high as 1,447 degrees Celsius. Curiosity also had to be able to endure the deep chill of deep space, which is about 2 degrees Kelvin, or just above absolute zero, on its journey to Mars. Researchers used hundreds of temperature sensors to test the vehicle's capabilities to withstand these extremes down to 1/100 of 1 degree. It was through repeated simulations that engineers better understood space's hostile environment and eventually were able to build the carbon, titanium, and aluminum rover.
Once Curiosity safely reaches the surface of Mars at about 1:17 a.m. ET on Monday (10:17 p.m. PT on Sunday), it will be on a two-year, 12-mile mission, taking samples from the planet and sending data back to Earth. In studying these samples, scientists may be able to confirm if there was ever water, or life, on Mars. "It's a one-way journey" for Curiosity itself, Nichols notes. Like the smaller rovers that have gone before it, when its job is done, Curiosity will remain as a relic on the red planet.
If the mission is successful, Curiosity will likely have made giant leaps in humankind's quest to learn more about the solar system we call home, and will likely set the stage for further missions -- including, perhaps, a manned flight -- to Mars. "It was a huge challenge going in and they have engineered the system to the highest level," Nichols said. "Now the proof will be on Sunday night."
