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.