NASA Future In-Space Operations: SmallSat Thrusters
NASA FISO Presentation: The Film Evaporation MEMS Tunable Water Microthruster Array
“Miniaturization of satellite systems provides potential for reduced launch and operations costs
– Small sats i.e. micro, pico, nanosats are emerging technologies.
– Cubesats (4 inches cube) are low cost alternative for some applications.
Propulsion systems resist miniaturization
– Viscous losses at small scale
– Low mass fraction due to power processing mass
– Excessive power demands for small sat applications”
Note: The audio file and presentation are available online and to download.
The use of surface tension to confine the propellant fluid is clever but these thrusters are for attitude control only. Don’t most cubesats use gravity gradient and magnetic torquing for this?
If it has a magnetometer, torque rods aren’t an option. For non-LEO missions, gravity gradient stabilization doesn’t work. So this is mostly about expanding CubeSat capabilities beyond their current applications. The technology in question might also be viable for orbital maintenance or correction, as well as attitude control. Not major maneuvers, but small trajectory changes.
I wonder if the optimal size for a lunar or planetary probe, even a minimal cost mission, isn’t a bit larger than a cubesat? It’s going to cost something significant to put it on a planetary trajectory regardless of size.
I have serious doubts about a stand-alone planetary CubeSat (or, more properly, nanosatellite.) I know they are trying to fly one, MarCO, with the InSight mission. But things like the operational costs of planetary navigation are basically independent of mass. Communications is a fairly inflexible function of antenna size and transmitted power. So I see some real limits for a stand-alone nanosat.
On the other hand, I can see quite a few applications for nanosat subspacecraft. This is something people have been talking about. There is a recent NRC study on doing science with CubeSats which mentions it. The idea involves a larger spacecraft, which carries the nanosats to the target and which provides some services such as telecommunications. The idea could range from a small number of nanosats supplementing the mission’s main science goals, to a main spacecraft which was simply a support vehicle for a large number of nanosats. The advantages include multi-point measurements and measurements from trajectories too risky for the main spacecraft.