Another Opportunity for Mars landing

As the Mars Exploration Rover named Opportunity glides toward its expected landing on the red planet this weekend, it will draw on earthbound simulations of landing sites and procedures.

Engineers at NASA Langley Research Center in Hampton, Va., adapted a flight-mechanics application, originally developed for planning space shuttle missions in the 1970s, to model the complex interactions of the Spirit and Opportunity rovers' hardware and software.

The engineers conducted multibody simulations of the parachute, rover capsule and back shell behavior during entry into the thin Martian atmosphere, said Eric Queen, a Langley research engineer.

Using a 128-processor SGI supercomputer at the Jet Propulsion Laboratory, the Langley team studied thousands of possible landing scenarios via a mathematical technique called Monte Carlo simulation. Each of the thousands of simulated trajectories differed by some random amount, 'because we don't know what the weather's going to be,' Queen said.

The supercomputer crunched through the simulations in a few hours, instead of taking two weeks as it did in the days of the 1997 Mars Pathfinder program, Queen said.

The simulations took into account the rovers' onboard software for controlling parachute deployment, heat shield removal and other maneuvers. Although the Spirit and Opportunity computers have less processing power than modern PCs, they have 'a lot more intelligence onboard than any previous Mars mission,' Queen said.

Last August, while Spirit and Opportunity were flying toward the red planet, Queen's group did additional landing simulations of potential sites. Planetary scientists were interested in Gusev Crater and a plain called Meridiani Planum, but they wanted some assurance that the sites would not be overly hazardous. Queen said his group predicted a better than 90 percent probability of success.

They are using the same code to reconstruct Spirit's entry trajectory from spacecraft data and compare it against the preflight predictions. Similar reconstructions will follow the Opportunity landing.

Earlier this week, the Mars rover team at JPL scrambled to solve the first major problem of the Spirit mission. Spirit, which landed Jan. 3, had ceased communicating this Wednesday, although JPL scientists received two sessions of limited data early this morning.

Opportunity is scheduled to land on Mars early Sunday morning Eastern time. JPL, in Pasadena, Calif., manages both rover missions for NASA. Scientists there are using sophisticated graphics technology to reconstruct the Martian surface in three dimensions to guide the Earth-based driver of the rover.

JPL has two eight-processor SGI Onyx 300 computers, each with a dual-pipeline SGI InfiniteReality 4 graphics subsystem, said Bob Peach, president of Rand Federal LLC of Phoenix. Rand Federal was the integrator under a six-year contract with SGI and JPL.

The Onyx systems convert the rover's high-resolution photos into 3-D images, which the rover driver sees through stereo goggles while sending motion commands to the rover on the Martian surface, Peach said.

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