4 ms·

Was there no functioning laser or radar altimeter for the final descent phase?

by walrus01 2y ago

ceejayoz 2y ago
"However, the lander's altimeter had failed."
- 1970-01-01 2y ago
  Looking at this closely, it was working, however it was noisy. I speculate that they didn't correctly anticipate the moon dust problem. Laser rangefinders may not be a workable solution for future landings. So engineers at Intuitive Machines had checked, and re-checked, the laser-based altimeters on Athena. When the lander got down within about 30 km of the lunar surface, they tested the rangefinders again. Worryingly, there was some noise in the readings as the laser bounced off the Moon. However, the engineers had reason to believe that, maybe, the readings would improve as the spacecraft got nearer to the surface. https://arstechnica.com/space/2025/03/intuitive-machines-second-attempt-to-land-on-the-moon-also-went-sideways/ https://arstechnica.com/space/2025/03/intuitive-machines-sec... https://www.space.com/nasa-moon-landing-dust-concerns.html https://www.space.com/nasa-moon-landing-dust-concerns.html https://en.wikipedia.org/wiki/Lunar_horizon_glow https://en.wikipedia.org/wiki/Lunar_horizon_glow
  - ceejayoz 2y ago
    Noise at 30km altitude probably points more towards a sensor issue than dust.
    - Aspos 2y ago
      May it be that laser bounced off exhaust plume?
      - lightedman 2y ago
        I think it would be unlikely that a plume was caused from 30km away on something with no atmosphere.
      - echoangle 2y ago
        Unless their processing is very weird, that shouldn’t be the issue. You send a pulse and record the output of a detector to listen for the reflection. If the laser is reflected at the plume, you should get some pulses very quickly, but also faint and spread out in time, which you would be able to tune out. And the real response from the ground should be more narrow because it’s reflecting at a single distance. If very short range noise influences the signal when measuring 30km real distance, you’re doing something wrong.
      - inamberclad 2y ago
        Laser is angled outwards at approx 45 degrees, I think it's well away from the exhaust plume.
  - numpad0 2y ago
    LRFs and radars on the Moon has been fine for a long time, it can also be angled away from gravity axis and multiplied by sine theta if needed.

Was there no functioning laser or radar altimeter for the final descent phase?

ceejayoz 2y ago

"However, the lander's altimeter had failed."

1970-01-01 2y ago
Looking at this closely, it was working, however it was noisy. I speculate that they didn't correctly anticipate the moon dust problem. Laser rangefinders may not be a workable solution for future landings. So engineers at Intuitive Machines had checked, and re-checked, the laser-based altimeters on Athena. When the lander got down within about 30 km of the lunar surface, they tested the rangefinders again. Worryingly, there was some noise in the readings as the laser bounced off the Moon. However, the engineers had reason to believe that, maybe, the readings would improve as the spacecraft got nearer to the surface. https://arstechnica.com/space/2025/03/intuitive-machines-second-attempt-to-land-on-the-moon-also-went-sideways/ https://arstechnica.com/space/2025/03/intuitive-machines-sec... https://www.space.com/nasa-moon-landing-dust-concerns.html https://www.space.com/nasa-moon-landing-dust-concerns.html https://en.wikipedia.org/wiki/Lunar_horizon_glow https://en.wikipedia.org/wiki/Lunar_horizon_glow
- ceejayoz 2y ago
  Noise at 30km altitude probably points more towards a sensor issue than dust.
  - Aspos 2y ago
    May it be that laser bounced off exhaust plume?
    - lightedman 2y ago
      I think it would be unlikely that a plume was caused from 30km away on something with no atmosphere.
    - echoangle 2y ago
      Unless their processing is very weird, that shouldn’t be the issue. You send a pulse and record the output of a detector to listen for the reflection. If the laser is reflected at the plume, you should get some pulses very quickly, but also faint and spread out in time, which you would be able to tune out. And the real response from the ground should be more narrow because it’s reflecting at a single distance. If very short range noise influences the signal when measuring 30km real distance, you’re doing something wrong.
    - inamberclad 2y ago
      Laser is angled outwards at approx 45 degrees, I think it's well away from the exhaust plume.
- numpad0 2y ago
  LRFs and radars on the Moon has been fine for a long time, it can also be angled away from gravity axis and multiplied by sine theta if needed.