The space agency was responding to a US news report that said NASA knew there was a problem with the Mars Polar Lander propulsion system prior to the December 3 landing attempt on Mars, but suppressed the information.

NASA said in a statement it "categorically denies this charge."

The lander and two mini-probes associated with NASA's Deep Space 2 program closed in on Mars in December, after an 11-month journey over 757 million kilometers (470 million miles).

However, contact with mission control was lost when the lander entered the Martian atmosphere, and it has never been heard from since.

NASA set up a commission to investigate the disappearance of the lander, and a report is to be published in the coming weeks.

According to media reports Wednesday, flaws in the MPL propulsion system were known to NASA engineers, who decided to take no action.

Stung by the allegations, NASA hit back with a lengthy press statement in which it said it had raised several issues relating to the MPL in a report, the Stephenson Phase 1 report, discussed at a press conference on November 10.

"The report made 11 different references to technical issues or concerns involving the propulsion system (of the MPL)," the statement said.

It said that the problems it had been accused of covering up were aired widely in public documents released on November 10 and available on NASA's Internet site.

"Based on this review, NASA knew about the concerns with the propulsion system, NASA took corrective action, and NASA hid nothing from the public. We made our concerns known in early November," NASA insisted.

The space agency, for whom the Mars Polar Lander disappearance was the latest in a series of setbacks, is examining theories about what may have happened to the craft, on a mission to explore for water under the surface of the planet.

Among theories under consideration is that the craft crashed into the planet after rockets which were supposed to slow its descent failed to fire.

NASA has been sharply criticized in recent months for a high failure rate in space exploration, technical problems in its space shuttle program, as well as delays and cost overruns in the International Space Station, a multi-national effort that has fallen behind schedule.

Among its most humiliating setbacks was the loss of the Mars Climate Orbiter last September, which was blamed on a mix-up over metric and imperial measures that cost the agency 125 million dollars.

NASA head Daniel Goldin defended the agency's record on Wednesday in testimony before a Congressional panel.

"Since 1992, NASA has launched 146 payloads valued at a total of 18 billion dollars," he told the Senate subcommittee on science, technology, and space.

"Of this number, 136 payloads were successful. Our total losses amounted to 10 payloads, measured at about half a billion dollars, or less than three percent."

He said 1999 was a bad year for NASA, but asserted that the agency's overall record was positive.

"NASA is resolved to make a great record even greater," he said.

FROM THE VAULT
NASA's Fear Of A "Non-Upright Touchdown"
Cameron Park - November 17, 1999 - In the weeks before last December's failed Mars south polar landing, SpaceDaily's Bruce Moomaw investigated the potential for a non-upright landing and found NASA had much to fear.