Everyone’s talking about the $2.5 billion Curiosity rover‘s “terrifying” Hollywood-blockbuster-worthy landing: seven knuckle-in-teeth minutes in early August during which its aeroshell-armored bulk will plummet through Mars’ thin atmosphere at incredible speeds, snap apart to shed its back-shell, then fire rockets to slow its descent. It’ll be like Iron Man pulling out of a planetary dive, finally hovering dozens of feet above the designated Martian landing site — Gale Crater, near an 18,000-foot tall mound of debris — to gently lower the Mini-Cooper-sized rover itself from a nylon tether.
That’s the story you’ll see grabbing eyeballs as we roll toward touchdown on August 6, 2012 — and with good reason, given the landing’s almost mad-sounding chain of must-occur-exactly-so events.
But what happens once the rover’s safely on the ground and NASA’s popping champagne corks? Assuming Curiosity — aka the Mars Science Laboratory, or MSL — survives the journey, what about the technology it’s hauled for over eight months through 354 million miles of vacuum at close to 48,000 miles per hour, and that it’ll deploy during its nearly two-year exploratory mission?
To understand the tech, you have to first understand Curiosity’s purpose.
“If you had to reduce the MSL’s scientific mission to one word, it would be habitability,” says MSL deputy project scientist Dr. Ashwin Vasavada. “For better than a decade, we’ve been doing what we call ‘following the water.’”
Water is one of the common factors for all known life on Earth, and therefore at the crux of any investigative journey to understand whether Mars could have contained — or ever harbored — life itself.
“So now we’re asking the next question, which is not just water, but what about the other ingredients that life would require,” says Vasavada, noting that Curiosity has a much broader mission than prior rovers: looking for life sources like carbon, water, sunlight and chemical energy, as well as hazards to life in the form of radiation.
“We do this broad survey of the environmental conditions at our landing site to see if we can call anything we find a habitable environment,” he says.
Radiation Assessment Detector (RAD)
Speaking of radiation, Curiosity’s RAD — the first of 10 instruments turned on — was designed to analyze radiation from the Martian surface, but also in the confines of the spacecraft carrying the rover to Mars during its eight month journey, to help assess the impact of radiation on astronauts who might someday participate in a manned mission to the Red Planet.
“The RAD instrument is unique in that we’re carrying it on behalf of the Human Exploration & Operations branch of NASA,” says Vasavada. “We have nine scientific instruments that come from the scientific community with the goal of addressing human habitability on Mars, and then we have this one instrument, RAD, trying to understand what astronauts would have to deal with on the surface. It also plays well into our habitability investigation, because it measures the same radiation that would harm humans or any other microbial life. So it has a dual purpose.”
But the key point, says Vasavada, is that with RAD, we’ll be able to acquire data we’ve never had before: radiation levels on the journey from Earth to Mars, and at the surface of the planet itself.
Radioisotope Thermoelectric Generator (RTG)
Like the Apollo spacecraft and deep space vessels deployed to Jupiter and Saturn, Curiosity will sip power during its two-year mission from electricity produced by the heat from 32 marble-sized pellets containing plutonium-238 dioxide (think “nuclear battery”). That adds up to about 10 pounds, which is pretty substantial, whether you’re a consumer laptop or a multibillions interplanetary mobile science lab.
“We’re a big rover, and because of the science we’re doing, we have to carry these big laboratories and a huge arm to take samples,” says Vasavada. “Once you have a big enough rover, you can afford to carry around this RTG. If you mounted this on smaller rovers, like Spirit or Opportunity, they’d keel over. We have a big spacecraft that needs to last a long time, and so we could afford to attach this power source that we’ve used on many missions before to a rover for the first time.”
How much power are we talking? “Only 100 watts, so about like a light bulb,” says Vasavada, noting that that’s still better than the power generated by solar panels averaged over the entire day.
“We generate 100 watts, 24-and-a-half hours a day, and we store that in a big battery,” he says. “And when we actually run the rover, we do so for five or six hours during the daytime on Mars. We run off the stored energy, so it’s sort of like charging a cellphone.”
Heat Rejection System (HRS)
Curiosity will have to withstand temperatures that can range from a balmy 86 F to nearly -200 F. By comparison, the lowest recorded non-laboratory surface temperature on Earth to date was about -130 F (in Antarctica, no surprise). To maintain a more stable temperature range, Curiosity employs a thermal regulation system not unlike the liquid-based ones sometimes found at the core of over-clocked do-it-yourself computers.
“We use a fluid loop system inside the rover to transfer heat in both directions,” says Vasavada. “The problem is that we have to endure these huge temperature changes. Mars is basically like a desert in having ground that changes temperature drastically between day and night. So we use the fluid loop system to pump heat from the RTG into the electronics at night, when it’s cold. And then in the daytime when it’s hot, especially with all the electronics running, it’ll draw heat from them and radiate it out into the Mars environment.”
And everything has to be designed perfectly, too, including the packaging, say the way one piece of material is glued to another — material which Vasavada says can expand and contract at different rates. Get this wrong, and pieces could eventually peel apart or break.
Rover Compute Element (RCE)
Curiosity employs two computers, one for daily operation and one for backup, each packing a 200 MHz IBM RAD750 (based on IBM’s late 1990s 32-bit PowerPC processors), 256 MB of RAM, 2GB of flash storage and running a multitasking operating system called VxWorks (used in multiple other spacecraft, including both Spirit and Opportunity rovers).
“All of our electronics have to be built in a way that allows them to withstand the environmental conditions,” says Vasavada. “So in addition to the temperature, there’s the extremely dry Martian air, where we have to address concerns about electrical arcing, for instance.”
But the biggest thing separating computing equipment designed for use on Mars from its consumer-grade counterparts on Earth is its resistance to radiation.
“Within Earth’s atmosphere we’re protected from a lot of cosmic rays and solar particles that would cause problems with electronics,” says Vasavada. “But on Mars, as well as on the way to Mars, you’re constantly bombarded by cosmic rays.”
The problem, especially with modern computing equipment, is that a single cosmic ray can flip the bit of a particular circuit, explains Vasavada. That can introduce software errors, causing things to fault or execute incorrectly.
“All of Curiosity’s electronics are built with fault protection, so they’re always double- or even triple-checking themselves, sending multiple signals and ensuring they match,” he says. “And the computing equipment itself is commercial grade, but in a special radiation-hardened configuration.”
(MORE: A Cosmic SUV Blasts Off for Mars)