How does Soyuz detect the ground to fire its retro rocket at the end stage?
Is there any paper/reference describing the full entry descent and guidance algorithm and sensor suite used in Soyuz?
If Soyuz uses the sonar principle (just guessing), then one can't use Soyuz to land on the Moon.
If Soyuz uses a laser altimeter, then at such low altitude the time to return will be too small. I wonder if a laser altimeter can detect such resolution. Even if it does one will be pushing the sensor to its limits. Not a good idea.
If Soyuz uses a stereo camera, then one can't land on night.
The Luna and Surveyor series used a single extended ground contact sensor for engine cutoff. Soyuz does not definitely have it.
So what is used in Soyuz? Is there any sensor which will be better than what Soyuz uses?