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Can somebody knowledgeable speculate why they are not using RCS to try turning the probe? I am guessing RCS engines can be reignited and don't need a certain or

by Aspos 3y ago

Can somebody knowledgeable speculate why they are not using RCS to try turning the probe? I am guessing RCS engines can be reignited and don't need a certain orientation to work, right? Is Moon's gravity strong enough to cause damage to solar panels or antennas if probe tips?

numpad0 3y ago
IIUC, it has 12 strategically arranged RCS and 2(1 broken) main thrusters, ALL installed on a back facing mounting plate now pointing spaceward. I'm kind of suspecting there could have been cool factor involved in the decision leading to this design.
- Aspos 3y ago
  So, yeah, what prevents them from rolling the probe using RCS?
  - numpad0 3y ago
    The fact that it's all pointing up!
    - Aspos 3y ago
      But the roll thrusters are not pointing up, are they?
      - numpad0 3y ago
        So, a pair of thrusters tilted 45 degrees up and down like ailerons can be called roll thrusters, and anyone who says that in deadpan straight face as an actual spacecraft engineer is completely insane, right? 1: https://www.isas.jaxa.jp/home/slim/SLIM/assets/img/SLIM_exp.png https://www.isas.jaxa.jp/home/slim/SLIM/assets/img/SLIM_exp....
        Aspos 3y ago
        Was hoping a spacecraft engineer would explain why tilted thrusters can't create enough angular momentum to roll the probe in terms which a humble software engineer would understand.
        numpad0 3y ago
        :shrug: - they didn't elaborate on that. Probably just not worth it.
bell-cot 3y ago
IANARS (...not a rocket scientist), but the maximum thrust needed to rotate the lander, during decent (frictionless free-fall), would be rather low. Vs. the minimum thrust needed to turn it over, against lunar gravity would be far higher. And, after a hard landing, the RCS system may be damaged - so attempting to use it might result in a RUD event. Or the needed thrusters might be extremely close to the lunar surface (which could direct thruster exhaust and lunar soil back at the lander). Or the RCS might have been given a one-way ticket into a Safe Mode (to minimize potential issues) when the lander touched down. Or...

by Aspos 3y ago

numpad0 3y ago

IIUC, it has 12 strategically arranged RCS and 2(1 broken) main thrusters, ALL installed on a back facing mounting plate now pointing spaceward. I'm kind of suspecting there could have been cool factor involved in the decision leading to this design.

Aspos 3y ago
So, yeah, what prevents them from rolling the probe using RCS?
- numpad0 3y ago
  The fact that it's all pointing up!
  - Aspos 3y ago
    But the roll thrusters are not pointing up, are they?
    - numpad0 3y ago
      So, a pair of thrusters tilted 45 degrees up and down like ailerons can be called roll thrusters, and anyone who says that in deadpan straight face as an actual spacecraft engineer is completely insane, right? 1: https://www.isas.jaxa.jp/home/slim/SLIM/assets/img/SLIM_exp.png https://www.isas.jaxa.jp/home/slim/SLIM/assets/img/SLIM_exp....
      - Aspos 3y ago
        Was hoping a spacecraft engineer would explain why tilted thrusters can't create enough angular momentum to roll the probe in terms which a humble software engineer would understand.
        numpad0 3y ago
        :shrug: - they didn't elaborate on that. Probably just not worth it.

bell-cot 3y ago

IANARS (...not a rocket scientist), but the maximum thrust needed to rotate the lander, during decent (frictionless free-fall), would be rather low. Vs. the minimum thrust needed to turn it over, against lunar gravity would be far higher. And, after a hard landing, the RCS system may be damaged - so attempting to use it might result in a RUD event. Or the needed thrusters might be extremely close to the lunar surface (which could direct thruster exhaust and lunar soil back at the lander). Or the RCS might have been given a one-way ticket into a Safe Mode (to minimize potential issues) when the lander touched down. Or...