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Odysseus’ tip-over likely caused because it landed without good elevation data

It appears that the improvised switch to a NASA range finder instrument just before landing only partly worked during Odysseus’s landing attempt on the Moon, causing the spacecraft to hit the ground at too great a speed with too much laterial motion, resulting in the snapping of one leg and the lander tipping over.

Apparently, Odysseus could no longer process altitude data from the NASA instrument once it was within 15 kilometers of the surface. It had to rely on its optical cameras, a poor substitute.

By comparing imagery data frame by frame, the flight computer could determine how fast it was moving relative to the lunar surface. Knowing its initial velocity and altitude prior to initiating powered descent and using data from the inertial measurement unit (IMU) on board Odysseus, it could get a rough idea of altitude. But that only went so far. “So we’re coming down to our landing site with no altimeter,” Altemus said.

Unfortunately, as it neared the lunar surface, the lander believed it was about 100 meters higher relative to the Moon than it actually was. So instead of touching down with a vertical velocity of just 1 meter per second and no lateral movement, Odysseus was coming down three times faster and with a lateral speed of 2 meters per second.

Though the spacecraft landed upright, the high speed and sideways motion caused one leg to snap, and the spacecraft then fell over. In this sideways position Odysseus’ main solar panel could not get enough sunlight, forcing the mission to end prematurely.

A final press conference summing up the mission is scheduled for 2 pm (Eastern) today.

Was the mission a success? The failures and problems during touchdown illustrated engineering and management issues that must be addressed before the next flight. At the same time, the mission’s number one goal was to soft land on the Moon, and it did do so, even with those serious engineering problems.

More important, this flight’s first and foremost goal was an engineering test of that technology. In this sense that mission succeeded brilliantly, revealing those last technical issues.

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On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

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  • Skunk Bucket

    Okay, the NASA range finder instrument was nice, but what they really needed was Neil Armstrong at the controls, calmly and coolly guiding the craft to a soft landing.

  • J Fincannon

    Very odd. Its pretty flat there and the LRO digital elevation model should have got them there pretty well without an instrument. They could not store the data? They could not read their position and relate it to the model?

  • john hare

    It landed on a 12% slope. That is 50% steeper than a wheelchair ramp. Not flat.

  • Jeff Wright reports it broke a leg.

  • wayne

    I’m just an amateur, but this lander looks top-heavy, to me.
    Just sayin’….
    Do we know where the actual center-of-gravity is located?

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