Space

June 14, 2012

Mars Rover Curiosity set to land Aug. 5

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by Raphael Jaffe
Staff Writer

This image shows changes in the target landing area for Curiosity, the rover of NASA’s Mars Science Laboratory project. The larger ellipse was the target area prior to early June 2012, when the project revised it to the smaller ellipse centered nearer to the foot of Mount Sharp, inside Gale Crater. This oblique view of Mount Sharp is derived from a combination of elevation and imaging data from three Mars orbiters. The view is looking toward the southeast.

There’s both good news and not-so-good news about the mission of the rover Curiosity, now speeding to its Aug. 5 contact date within the Gail crater, near the Mars equator.

The good news is that the probable landing area will be smaller than first calculated. The other news is that the rotary drill may introduce Teflon contamination of the samples.

The mission progress report is that there are no problems. There were the planned course corrections on Jan. 21 and March 5. The backup computer was used March 5, but the operation has been switched back. There will be another course correction June 26. One of the science instruments, the radiation detector has been operating as planned during transit. It recorded valuable data during the recent large solar flare.

The Mars Science Laboratory, or MSL or Curiosity, is about the size of an SUV and weighs 1,982 pounds. Its science payload is 165 pounds.

This artist’s concept depicts the rover Curiosity of NASA’s Mars Science Laboratory using its Chemistry and Camera (ChemCam) instrument to investigate the composition of a rock surface. ChemCam fires invisible laser pulses at a target (simulated here with a red line) and views the resulting spark with a telescope and spectrometers to identify chemical elements.

MSL’s size and weight meant that a new method of landing a vehicle on a remote heavenly body had to be found. The system used carries Curiosity inside the Entry Descent Landing system. At 78 miles above Mars, it is descending at 13,200 mph. Atmospheric friction slows the system and then a parachute deploys at 7 miles above the surface when the descent velocity is 900 mph. Landing radars start measuring height above the surface. The back shell is then separated at about 1 mile and 190 mph. What remains on the course to the surface is Curiosity, attached to the Sky Crane. It takes a powered descent to bring itself to 66 feet above the surface, at 1.7 mph. At that condition, Curiosity is lowered on cables. Upon ground contact, the cables are severed, and the Sky Crane flies away.

At a June 11 briefing, JPL project manager Pete Theisinger said that all the steps in the entry sequence have been analyzed and tested completely. He said that the sequence makes it practical to do a guided entry to the landing point.

The landing target ellipse had been approximately 12 miles wide and 16 miles long. Continuing analysis of the new landing system’s capabilities has allowed mission planners to shrink the area to approximately 4 miles wide and 12 miles long, assuming winds and other atmospheric conditions are as predicted. With the smaller ellipse, Curiosity will be able to touch down closer but at a safe distance from steep slopes at the edge of Mount Sharp. That will mean a shorter travel distance to the Mount Sharp features that attract the science team.

“We’re trimming the distance we’ll have to drive after landing by almost half,” said Theisinger. “That could get us to the mountain months earlier.”

This artist’s concept shows the sky crane maneuver during the descent of NASA’s Curiosity rover to the Martian surface. The sky crane is capable of delivering the large rover to a precise location on the surface.

Since the spacecraft was launched in November 2011, engineers have continued testing and improving its landing software. Mars Science Laboratory will use an upgraded version of flight software installed on its computers during the past two weeks. Additional upgrades for Mars surface operations will be sent to the rover about a week after landing.

The science payload includes 10instruments: Alpha Particle X-ray Spectrometer, Chemistry and Camera, Chemistry and Mineralogy, Dynamic Albedo of Neutrons, Mars Descent Imager, Mars Hand Lens Imager, Mast Camera, Radiation Assessment Detector, Rover Environmental Monitoring Station, and Sample Analysis at Mars.

A rotary percussive drill is used to prepare rock samples for analysis. This is a first for Mars investigations. A sample processing tool on the robotic arm puts the powdered rock or soil through a sieve designed to remove any particles larger than 0.006 inch (150 microns) before delivering the material into the Chemistry and Mineralogy or Sample Analysis at Mars instrument inlet funnels.

Experiments at JPL indicate that Teflon from the drill could mix with the powdered samples. Testing with copies of the drill will continue at JPL.

“The material from the drill could complicate, but will not prevent analysis of carbon content in rocks by one of the rover’s 10 instruments. There are workarounds,” said John Grotzinger, the mission’s project scientist at the California Institute of Technology in Pasadena. “Organic carbon compounds in an environment are one prerequisite for life. We know meteorites deliver non-biological organic carbon to Mars, but not whether it persists near the surface. We will be checking for that and for other chemical and mineral clues about habitability.”

“We have been preparing for years for a successful landing by Curiosity, and all signs are good,” said Dave Lavery, Mars Science Laboratory program executive at NASA. “However, landing on Mars always carries risks, so success is not guaranteed. Once on the ground we’ll proceed carefully. We have plenty of time since Curiosity is not as life-limited as the approximate 90-day missions like NASA’s Mars Exploration Rovers and the Phoenix lander.”




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