I hit another Wikipedia tunnel of information, starting with the first link and progressing to the last:
- Why do two Starships dock in such a manner their heat shields face opposite sides?
- Crooke's Radiometer
- Thermal Transpiration
- Knudsen Pump
- Thesis on the Scalability of Knudsen Pumps from Louisville.edu
- Thesis on Possibility of using a Knudsen Pump for Attitude Control
So, after reading everything (until hitting my knowledge limit when starting the papers)...
The Knudsen pump also referred to as "thermal transpiration pump" or "Knudsen compressor" is a gas pump that utilizes no moving parts. Instead it uses thermal transpiration, the phenomenon that gas molecules drift from the cold end to the hot end of a narrow channel.
Wikipedia has a link to a paper about using this to control attitude, but has this ever been used?
The paper seems to conclude it's possible at a 150km high orbit, but not beyond 200km. So has this been done? Any more information (in more laymans terms) on how this attitude control system would work? That paper was admittedly dense for my brain.
My overall impression is that this is a relatively cheap non-mechanical method for transferring liquids/gasses, using a low flow rate and temperature gradients. If you end up scaling it by making an array of them, higher and higher throughput an be achieved alongside other benefits (and, of course, complications).
My main question is:
- Has this principle of a non-mechanical pump been used in space exploration?
- If it has not:
- Why not?
- What may be applications of this in terms of space exploration.
- If it has:
- What was the application (this does not have to be related to the papers)?
- Has the attitude application been seriously considered beyond theoretical?