>Tony,
I don't think it was actually EMC. The report I saw on CNN said the legs
opened with a "jolt", fooling the sensors which were supposed to cut the
retro rockets when they detected the shock of landing.
Scott Lacey<
It looks like Scott Lacey is right, thank you! I made the assumption that
"spurious signal" was electrically generated. It appears it was
mechanically or magnetically generated! Is a Hall effect sensor
"microphonic"?
Well, I guess another lesson for me not to jump to conclusions before all
the data is available!
Tony
Colorado
Below is an excerpt from the complete NASA report.
<<Premature shutdown of descent engines.
PLAUSIBLE. A magnetic sensor is provided in each of the three landing legs
to sense touchdown when the lander contacts the surface, initiating the
shutdown of the descent engines. Data from MPL engineering development unit
deployment tests, MPL flight unit deployment tests, and Mars 2001
deployment tests showed that a spurious touchdown indication occurs in the
Hall Effect touchdown sensor during landing leg deployment (while the
lander is connected to the parachute). The software logic accepts this
transient signal as a valid touchdown event if it persists for two
consecutive readings of the sensor. The tests showed that most of the
transient signals at leg deployment are indeed long enough to be accepted
as valid events, therefore, it is almost a certainty that at least one of
the three would have generated a spurious touchdown indication that the
software accepted as valid. The software - intended to ignore touchdown
indications prior to the enabling of the touchdown sensing logic - was not
properly implemented, and the spurious touchdown indication was retained.
The touchdown sensing logic is enabled at 40 meters altitude, and the
software would have issued a descent engine thrust termination at this time
in response to a (spurious) touchdown indication.
MOST PROBABLE CAUSE OF LOSS OF MISSION>>
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