Course of Mars Lander corrected for December landing

Before its launch, the Mars Polar Lander is lowered toward a spin table for testing

October 30, 1999
Web posted at: 5:00 p.m. EDT (2100 GMT)

In this story: Sister ship was Climate Orbiter Craft can analyze chemical composition of soil RELATED STORIES, SITES

PASADENA, California (CNN) -- NASA engineers say they successfully performed a critical course correction Saturday that should send the Mars Polar Lander spacecraft to a desired landing zone near the planet's south pole in December.

A 12-second thruster burst successfully shifted the course of the 1,200-pound Lander during the 1:28 p.m. EDT maneuver.

"Preliminary indications are it went well," said Mary Beth Murrill, spokesperson for the Jet Propulsion Laboratory in Pasadena, California.

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"The spacecraft performed as it was supposed to." Engineers will watch navigational data over the next few hours to confirm their initial conclusion, she said.

Saturday's trajectory correction maneuver was the fourth since the Lander blasted off on January 3 from Cape Canaveral, Florida. Another such maneuver is scheduled for November 30, days before a planned December 3 landing.

The lander's sister ship, the $125-million Mars Climate Orbiter, was lost as it entered the orbit of Mars in September. Mission managers say the cause of the mishap was confusion over the type of units used to measure the strength of thruster firings.

While JPL engineers assumed they were using metric measurements (Newtons), engineers at Lockheed Martin Astronautics in Denver, the prime contractor for the mission, were feeding them data in English units (pounds).

The problem has been corrected for the Mars Polar Lander, space engineers said.

The lander's projected landing site is located near the northern edge of the south pole's layered terrain.

Mission scientists and engineers opted on Tuesday not to redirect the craft to a backup landing site, which had been considered after high-resolution images showed the primary site was rougher than originally anticipated.

"At the scale of the lander, even something like a table could represent an obstacle," said Richard Zurek, project manager for the Mars Polar Lander.

"Something that is a meter up here and down here can give you problems when you are landing on three legs."

While the polar lander has a radar altimeter and rocket thrusters to guide and slow the craft before landing, they can't guide it away from potential hazards.

Landing on a steep slope could be catastrophic. It could leave the orbiter intact but listing, placing it in a bad position for six solar panels to capture the sun's energy and convert it into power.

Yet the same features that pose the greatest landing hazards have also enticed scientists. Alternating light and dark bands beneath the surface of the south pole appear to be deposits of ice and dust. Scientists think the layers could offer clues about the climate history of Mars, like growth rings on a tree.

Should the craft land near a steep hill or cliff, it could document some exposed layering. Equipped with a shovel and small furnace, the lander will dig into the Martian surface and heat the soil to analyze the chemical composition.

The lander is also equipped with three cameras. One will capture its descent to the surface. Another will offer stereoscopic panoramas. The third, located on the wrist of the shovel arm, will show scientists close-ups of Martian soil.

The lander is scheduled to conduct a 60-day mission, but it could transmit data for up to 90 days if the conditions are right.