Hello, and welcome to This Week In Engineering, brought to you by engineering.com. Today, weÆre taking a special, in-depth look at NASAÆs Mars Science Laboratory.
Martian Mission History
The first probes on Martian surface were actually Soviet -- Mars 2 and Mars 3, in 1971. They didnÆt last long -- Mars 2 failed during descent, and Mars 3 just 20 seconds after landing. In 1974, the twins Viking 1 and 2 operated for years, broadcasting the first decent pictures from the surface. After that, we had some orbiters, but no landings until 1997, when NASAÆs Mars Pathfinder, with the rover Sojourner, landed in Ares Vallis and gave us awesome 3D images.
Since then, weÆve had Spirit, the six-Earth-year robot that was only supposed to last 3 months; its twin Opportunity, which is still operating; and the Phoenix lander in 2008, which confirmed water ice in the north polar region. All-in-all, Mars has a bad reputation -- including orbiters, about two-thirds of all Martian missions have failed, including Mars Climate Orbiter due to a missed metric conversion, and RussiaÆs 2011 Phobos-Grunt. Makes you wonder, is there a rover brave enough to dare go up against those odds?
That brings us to the Mars Science Laboratory, equipped with the Curiosity rover. All the NASA rovers have six wheels and look fairly similar. HereÆs a picture showing an engineer with a 2-foot Sojourner clone. But look behind them, and thereÆs a Spirit and Opportunity clone, at 5.2 feet. Much bigger. But wait, thereÆs the Curiosity rover Truck-a-saurus, ten feet long, weighing one ton on Earth. Makes you wanna climb aboard and do some real six-wheel-drive Martian dune surfing! Well, buckle-up, because sheÆs powered by plutonium in a radioisotope thermoelectric generator, redlining at -- can you believe it -- three hundred feet per hour. Well, she was built for reliability, not thrill-seeking. Still, I figured plutonium could get you to at least 88 miles per hour.
Flightpath and Control
The MSL launched on November 26, 2011, and is due to land at around 1:30 am Eastern on August 6th, 2012 -- about an eight-month flight that will take it over three hundred fifty-two million miles. That presents a challenge on arrival, because the landing process takes only seven minutes, at a time when Mars is fourteen light-minutes away from Earth. That means the landing has to be completely automated -- in fact, by the time we finally get the signal that deceleration has begun, over on Mars, the landing process is already over. Is that a tough control problem? I guess itÆs like flying one of those remote controlled helicopters, only when you hit the power, you have to wait 28 minutes to see how high it is, or rather was, fourteen minutes ago.
Preparing for Entry
Once the cruise stage -- the part of the spacecraft that fires rockets for course corrections during the flight -- has separated, the rest of the craft has to stop spinning and orient itself so the heat shield points toward the oncoming atmosphere. In order to do that, it has to eject some ballast, roughly equivalent to the mass of the MER rovers, Spirit and Opportunity. I imagine Opportunity will see Curiosity passing overhead, yelling, ôHey, Opportunity! Know what your mass is worth these days?ö (hocks and spits.) ôHahaha!ö
The landing process will take the spacecraft from twelve thousand miles per hour to a standstill, all in about seven minutes. The first Martian rover, Sojourner, was considerably lighter than Curiosity, and landed by bouncing inside a giant airbag. But the Mars Science Laboratory is a lot heavier, with a more complicated landing procedure. After using the heat shield to slow down in the Martian atmosphere, it deploys a parachute, and jettisons the heat shield. Then the