[HN Gopher] Ispace Announces Results of the "Hakuto-R" Mission 1...
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       Ispace Announces Results of the "Hakuto-R" Mission 1 Lunar Landing
        
       Author : spazz
       Score  : 21 points
       Date   : 2023-05-26 18:17 UTC (4 hours ago)
        
 (HTM) web link (ispace-inc.com)
 (TXT) w3m dump (ispace-inc.com)
        
       | guardiangod wrote:
       | >The analysis reveals that the lander fully completed the entire
       | planned deceleration process, slowing to the target speed of less
       | than 1 m/s in a vertical position at an altitude of approximately
       | 5 kms above the lunar surface.
       | 
       | Ouch.
       | 
       | What seemed to happened was
       | 
       | 1. The probe descended normally.
       | 
       | 2. Glided horizontally over a 3km deep cliff of a crater
       | 
       | 3. Sensor suddenly gives large altitude change
       | 
       | 4. Onboard computer sees the sensor value change is larger than
       | expected, deduced the sensor is mis-reading, and filtered the
       | (correct) value.
       | 
       | >as the lander was navigating to the planned landing site, the
       | altitude measured by the onboard sensors rose sharply when it
       | passed over a large cliff approximately 3 kms in elevation on the
       | lunar surface, which was determined to be the rim of a crater.
       | According to the analysis of the flight data, a larger-than-
       | expected discrepancy occurred between the measured altitude value
       | and the estimated altitude value set in advance. The onboard
       | software determined in error that the cause of this discrepancy
       | was an abnormal value reported by the sensor, and thereafter the
       | altitude data measured by the sensor was intercepted. This filter
       | function, designed to reject an altitude measurement having a
       | large gap from the lander's estimation, was included as a robust
       | measure to maintain stable operation of the lander in the event
       | of a hardware issue including an incorrect altitude measurement
       | by the sensor.
        
         | Dalewyn wrote:
         | It's also explained further down in the article why the
         | software was programmed the way it was:
         | 
         | >One major contributing factor to this design issue was a
         | decision to modify the landing site after critical design
         | review completed in February 2021. This modification influenced
         | the verification and validation plan despite numerous landing
         | simulations carried out before the landing. ispace as the
         | mission operator maintained overall program management
         | responsibility and took into account the modifications in its
         | overall analysis related to completing a successful mission. It
         | was determined that prior simulations of the landing sequence
         | did not adequately incorporate the lunar environment on the
         | navigation route resulting in the software misjudging the
         | lander's altitude on final approach.
         | 
         | TL;DR: Plans were modified after the software was programmed,
         | software was not sufficiently reprogrammed due to overreliance
         | on old, pre-modification simulation data.
         | 
         | As human errors go this looks egregious. One hopes their
         | subsequent missions don't run afoul of the same screw ups.
        
           | krisoft wrote:
           | > overreliance on old, pre-modification simulation data
           | 
           | It somewhat reminds me of the Genesis sample-return mission's
           | landing failure.
           | 
           | There the parachutes failed to open. The parachutes failed to
           | open because the accelerometer intended to trigger them did
           | not trigger. And it did not trigger because it wqs installed
           | according to the plans, but the plans had them upside down.
           | And they didn't catch the issue because the submodule in
           | question has already flown, and thus was deemed not necessary
           | to review it in details. But what changed from the previously
           | succesfully flown configuration that they turned the
           | submodule around. So they introduced a change without
           | realising that this change invalidated some of their previous
           | tests/analysis.
           | 
           | Obviously the technical root cause is very different here
           | (software vs hardware; landing site change vs submodule
           | orientation change), but the organisational root cause is
           | similar. A change invalidates assumptions in previously
           | performed tests/analysis/review, and nobody spots this thus
           | the test/analysis/review is not performed again and a problem
           | sneaks in.
        
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       (page generated 2023-05-26 23:01 UTC)