Authored by:
Stephen J. Mraz
stephen.mraz@penton.com

Resources
NASA, tiny.cc/hlgie

Engineers at NASA are preparing Curiosity, the next Martian rover, for its flight to the Red Planet late next year. It should land on Mars in mid-2012. Unlike past rovers — Sojourner, Spirit, and Opportunity — this one will do more than just observe and send data back to Earth. It will carry an entire lab and do some serious analytical work as it spends 23 months looking for evidence of past or present microbial life, or at least signs the planet once could have supported it.

New landing technique
NASA plans on a soft landing for Curiosity because it is too heavy to land cushioned by air bags like previous rovers. (For comparison, Curiosity will weigh 1,984 lb on Earth, while Spirit and Opportunity weighed about 375 lb.) Instead, a spacecraft carrying Curiosity will descend through the planet’s atmosphere. As it approaches its designated landing area, it will steer itself through a series of long hypersonic S-curves similar to those astronauts use when landing the Space Shuttle. It steers using thrusters and spring-ejected weights to control the spacecraft’s lift.

Three minutes before touchdown, the craft slows its descent using a parachute, releases its heat shield and back shell, then fires four retro rockets to slow its fall to about 1.7 mph. When the craft is about 65 ft from the ground, gravity-driven cables unwind as Curiosity detaches from its belly and is lowered to the ground. The cables are then cut, the unneeded spacecraft flies off a distance and crashes, and Curiosity lands on its wheels ready to explore.

This landing method should let the rover touch down within 12 miles of its target, a fivefold improvement over the accuracy of previous Marian landings.

NASA is currently studying possible landing sites, having narrowed the field from 30 down to four based on images from the Mars Reconnaissance Orbiter. NASA wants a site with exposed geologic features and minerals that formed under wet conditions, an assumed precondition for life.

The rover
Curiosity measures 10-ft long and carries 10 times more equipment than any previous rover. That’s because it will be tasked with gathering and processing rock and soil samples, then distributing them to various analytical instruments onboard. However, there are some similarities to previous rovers. For example, it will have a hub motor on each of its six wheels, use a rocker-bogie suspension, and carry a mast-mounted camera that gives the mission’s team on Earth a better vantage point from which to select targets and pinpoint obstacles.

While each of Curiosity’s six wheels has a motor, the front and rear wheels also have steering motors. They let the rover make 360° in-place turns. The wheels are 20 in. in diameter — twice as tall as those on previous rovers — and are covered in cleats for a better grip in soft sand and for rolling over 29-in.-tall rocks. The suspension and a relatively low center of gravity let the rover tilt 45° in any direction without overturning. But the vehicle’s hazard avoidance programming should keep it from tilting any more than 30°. Curiosity’s top speed is about 300 ft/hr, but the Martian terrain and caution on the part of NASA will likely limit that to 100 ft/hr.

The rover gets electricity, about 110 W at launch, from a radioisotopic generator that uses heat from the radioactive decay of plutonium-238. Excess heat from the generator will warm fluids plumbed throughout the rover to keep sensitive electronics and other devices at acceptable operating temperatures. The generator will let the rover operate for a Martian year (687 Earth days) without NASA worrying about dust clouding solar cells or time of day, both issues for earlier rovers, which all relied on solar panels. The thermoelectric generator also lets NASA choose a landing site farther north or south than previous missions because the rover doesn’t depend on sunlight, which becomes less intense with distance from the Martian equator.

Roving eyes and an arm
Curiosity will carry cameras for navigation, obstacle avoidance, and scientific investigations. For example, four Hazcams (hazard-avoidance cameras), two on the front and two on the rear, use visible light to capture 3D images which should help keep the rover from getting lost or crashing into obstacles. Onboard software will use the images to determine the safest path to designated targets. The cameras have a 120° field-of-view to compensate for being rigidly mounted to the rover. They will map out a pie-shaped slice of the terrain that centers on the rover and measures 10-ft long and 13-ft wide.

A pair of black-and-white navigation cameras mounted atop the rover’s mast will provide stereoscopic images over a 45° field of view. Sitting atop the mast — about 6 ft off the ground — they will give scientists on Earth a good view of the vehicle’s surroundings and help them plan travel routes.

The mast also carries MastCam, which will get high-quality color pictures, along with HD video (10 fps). It uses two mast-mounted cameras to create stereoscopic images, and one of the cameras has a zoom lens. MastCam can store thousands of images or several hours of HD video before transmitting them to Earth at up to 32,000 bps.

The rover’s Hand Lens Imager gives Earthbound scientists close-up views of Martian rocks. The self-focusing, 1.5-in.-wide color camera can record features as small as 12.5 microns. It will also have UV and white-light lamps, for taking pictures day or night. And the UV lamp will induce fluorescence, helpful in detecting carbonate and evaporite minerals, both indicators of water’s presence. The Imager will help geologists understand the history of the landing site and let them select samples for further investigation.

The Hand Lens mounts on the end of the rover’s robotic arm. The arm carries the Imager and four other tools in a rotating turret: an X‑ray spectrograph for examining samples and sites, and three tools for taking and preparing samples. Thus, the turret will be able to grind or drill away layers of soil, examine rocks beneath the surface, and take microscopic images and samples. The arm has three joints, analogous to a shoulder, elbow, and wrist, and can extend 7.5 ft. The arm’s agility lets it both pick up samples and deliver them to Curiosity’s onboard lab through a port.

A laser sensor is another tool that will aid in picking samples that should be investigated more closely. It will vaporize rocks and soils up to 30 ft away, letting an onboard spectrograph determine the site’s minerals and microstructures. If these two parameters indicate the site might yield important data, samples can be taken and analyzed.

A lab’s worth of equipment
The rover will carry a suite of instruments to analyze samples taken from the surface. These include a gas chromatograph, mass spectrometer, and a tunable laser spectrometer that can identify a wide range of organic compounds and determine the ratio of key elements’ isotopes.

The Radiation Assessment Detector will examine radiation on the surface of Mars, critical for planning any human exploration of the planet. A mini-weather station developed jointly by Spanish and Finnish engineers will record atmospheric pressure, temperature, humidity, winds, and UV levels. And a Russian-built device will look for hydrogen buried up to 3 ft below the surface. It could indicate the presence of water.

And finally, a robotic nose will “sniff” the air using vents that open to the atmosphere. It’s another way of helping the team decide where to take samples. For example, if it detects methane in the area, that could signal there are microbes in the soil nearby or liquid water reacting with rocks under the surface. The robotic nose will also sniff gases released after processing rock and soil samples in Curiosity’s onboard oven.

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