NASA knew Mars Polar Lander doomed

United Press International - March 21, 2000
By James Oberg, UPI Space Writer

HOUSTON, March 21 (UPI) -- The disappearance of NASA's Mars Polar Lander last December was no surprise to space officials, UPI has learned.

Prior to its arrival at Mars, a review board had already identified a fatal design flaw with the braking thrusters that doomed the mission, but NASA withheld this conclusion from the public.

The probe was lost while attempting to land near the martian south pole on December 3. Two small microprobes which had deployed separately also were never heard from again.

It was the second expensive setback for American interplanetary exploration in less than three months. On September 23, a companion probe had been destroyed when a navigation error sent it skimming too deeply into the atmosphere of Mars.

Following these failures, NASA commissioned several expert panels to review the accidents and recommend improvements in NASA procedures. A source close to the panel probing the second accident has told UPI that its conclusions are "devastating" to NASA's reputation. Unlike the previous accident, where management errors merely prevented the recognition of other human errors, in this case it was a management misjudgment which caused the fatal flaw in the first place.

"I'm as certain as I can be that the thing blew up," the source concluded. As explained privately to UPI, the Mars Polar Lander vehicle's braking thrusters had failed acceptance testing during its construction. But rather than begin an expensive and time-consuming redesign, an unnamed space official simply altered the conditions of the testing until the engine passed.

"That happened in middle management," the source told UPI. "It was done unilaterally with no approval up or down the chain of command."

The Mars Polar Lander employed a bank of rocket engines which use hydrazine fuel. The fuel is passed through metal grates which cause it to decompose violently, creating the thrust used by the engines. These metal grates are called "catalyst beds," or "cat beds." Their purpose is to initiate the explosive chemical reaction in the hydrazine.

"They tested the cat bed ignition process at a temperature much higher than it would be in flight," UPI's source said. This was done because when the cat beds were first tested at the low temperatures predicted after the long cruise from Earth to Mars, the ignition failed or was too unstable to be controlled.

So the test conditions were changed in order to certify the engine performance. But the conditions then no longer represented those most likely to occur on the real space flight.

Following the September loss of the first spacecraft due to management errors, NASA had initiated a crash review of the Mars Polar Lander to identify any similar oversights. According to UPI's source, the flaws in the cat bed testing were uncovered only a few days before the landing was to occur on December 3.

By then it was too late to do anything about it.

Garbled rumors of some temperature-related design flaw circulated in the days before the landing attempt. However, as in the September case when space officials possessed terrifying indications of imminent failure even before the arrival at Mars, NASA made no public disclosure of these expectations.

The Mars Polar Lander investigation team has also reportedly identified a second fatal design flaw that would have doomed the probe even if the engines had functioned properly.

The three landing legs of the probe contain small microswitches which are triggered when the legs touch the surface. This signal commands the engines to cease firing.

Post-accident tests have shown that when the legs are initially unfolded during the final descent, springs push them so hard that they "bounce" and trigger the microswitches by accident. As a result, the computer receives what it believes are indications of a successful touchdown, and it shuts off the engines.

Since this false signal actually occurs high in the air, the engine shutdown automatically leads to a free fall and destructive high-speed impact.

Ground testing prior to launch apparently never detected this because each of the tests was performed in isolation from other tests. One team verified that the legs unfolded properly. Another team verified that the microswitches functioned on landing.

No integrated end-to-end test was performed due to budget and time constraints. But UPI has been privately told that "this has been reproduceable on a regular basis" in post-flight tests. Perhaps by coincidence, in a safety memo to NASA employees distributed on March 20, NASA administrator Dan Goldin stressed "the importance of adequate testing." Reliability, he said, "requires well-thought-out verification and test activities."

Goldin explicitly described the adverse impact of "our difficulties with recent failures in late stages of development -- such as system integration and testing -- and during mission operations." The memo did not specifically attribute these problems to the Mars failures.

The Mars Polar Lander also deployed two small "penetrator" probes, both called Deep Space 2. They were designed to fall freely through the thin atmosphere, hit the ground at about 200 meters per second (400 miles per hour), and come to rest deep in the soil.

All attempts to pick up radio signals from these probes, relayed via another spacecraft already orbiting Mars, also failed. Reportedly, the review board believes that the probe radio equipment could not have survived the impact.

Alternately, the probes may simply have hit ground too rocky for survival. Engineers also suspected that their batteries, which had been charged before launch almost a year earlier and not checked since then, might not have retained sufficient power.

"Nobody in the know really expected either of the penetrators to work," UPI's primary source said. Dr. Carl Pilcher, head of NASA's planetary program, talked with space scientists at last week's Lunar and Planetary Science Conference in Houston. While expressing disappointment at the setbacks and skepticism of ambitious flight schedules -- "Our ambition exceeded our grasp," he told the scientists -- he would not discuss the results of the accident investigation.

The conclusions, he did admit, "make sober reading." The investigation was led by Tom Young, a former manager at NASA's Jet Propulsion Laboratory which runs most of NASA's deep space probes. "Goldin recently told his managers that the Young report will be the Rogers Commission of space science," Andrew Lawler wrote in the March 10 issue of Science magazine, "referring to the devastating critique delivered by a panel that examined the 1986 Challenger disaster."

And in a March 9 internal memo from JPL director Ed Stone, which UPI has obtained, space workers are warned that "the days ahead may at times be difficult."

According to Lori Garver, NASA's associate administrator for plans, the report on NSA's failures will be reviewed internally and then will be sent to the White House before being released to the public.

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