NASA taps SAN to store, back up data from Mars

FRAMINGHAM (01/30/2004) - The toughest thing about landing an unmanned probe on Mars is going from 12,000 mph to zero in six minutes, according to Prasun Desai, one of the NASA engineers who developed the descent and landing systems for the Spirit and Opportunity rovers.

"Things happen quickly," Desai said. Despite the abruptness of the landings, the computers aboard the two rovers sent plenty of data about the descents 80 million miles to Earth, where the information was transmitted to a storage-area network (SAN) set up at NASA's Langley Vehicle Analysis Branch in Hampton, Virginia.

Charles Davis, a systems administrator at Raytheon Corp. in Lexington, Massachusetts, was contracted by NASA to help develop the SAN, which stores and backs up data received at the space agency's Jet Propulsion Laboratory (JPL) in Pasadena, California.

Among the key information received by the Langley SAN was the flight trajectory data from Spirit's January 3 entry into the Martian atmosphere and its landing on the planet's surface. That data was especially valuable because Opportunity had to perform a similar entry and landing on the opposite side of Mars three weeks later.

Information from Spirit's descent was used by NASA engineers to adjust Opportunity's flight path, according to Davis. "We took the data they got and helped them make decisions around determining the landing sites," he said.

For primary storage, the Langley SAN includes two disk farms: an EMC Corp. Clariion array with 1.5TB capacity, and a Total Performance 9400 array made by Silicon Graphics Inc. that can store 4TB of data. Both arrays are configured for RAID 5, which overlaps read and write operations across all of their disk drives.

The storage network also includes a Fibre Channel switch from Brocade Communications Systems Inc. that supports up to 1Gbit/sec. throughput, Davis said. An eight-processor SGI Origin 2000 server is used to back up data to a Spectra Logic Corp. tape library that can accommodate 380 LTO-2 tapes, each with a capacity of 200GB.

Davis said BakBone Software Inc.'s NetVault product is used to manage the SAN. The software does incremental backups of the aircraft, trajectory and atmospheric data sent from the JPL on a daily basis, with full backups performed weekly.

The storage infrastructure is also fully redundant, Davis said. The SAN stores about 5TB of data each week, and information that gets corrupted during the tape backup process can be automatically recovered from the disk drives, he said.

Desai, who works at the JPL, helped build the parachute and airbag system to cushion the Spirit and Opportunity landings. With the landing stage of the Mars program completed, Desai now is working to convert and analyze the data sent back by the rovers.

The data, which traveled from Mars to Earth in 10 minutes at light speed, is being used to construct a telemetric model that characterizes how the probes slid through the Martian atmosphere.

Because of an atmospheric dust storm at the time of the Opportunity landing a week ago tomorrow, the probe was thrown to the outer limits of its landing zone, Desai said. He added that NASA engineers hope to use the data sent back from the craft about its descent to better prepare for future landings.

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