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NASA knew Mars Polar Lander doomed
United Press International - March 21, 2000 15:01
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.
Copyright 2000 by United Press International.
All rights reserved.
----------------
"I have it on excellent authority that JPL wants no major discoveries on
Mars because they oppose manned landings. They want to keep it an
academic exercise," Brandenburg charges. "Mars needs to be turned over
to Johnson Space Center in Houston."
-- plasma physicist John Brandenburg
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