> We also know that the previous OTV-4 mission involved the test of Aerojet Rocketdyne's XR-5A Hall-effect thruster, a type of electric propulsion system that offers greater efficiency for satellites and spacecraft maneuvering in orbit. This was officially in support of the Advanced Extremely High Frequency (AEHF) satellite program, but the technology could be valuable for other space-based systems, as you can read about more here. In August 2018, during OTV-5, the X-37B modified its orbit using an unspecified onboard propulsion system.
If I had to guess, they're experimenting with novel, relatively untested ion and hall effect type thruster systems that have very low thrust in newtons or kilonewtons, but very high specific impulse. Before putting things like that on billion dollar geostationary military communications satellites (or LEO/MEO radar imaging satellites, or billion dollar NRO satellites), they'd want to qualify them in space.
Maybe the spaceplane design that can return a used thruster was a happy coincidence between two different programs, allowing them to do a destructive teardown on a thruster that's been used for two years, to better determine its possible failure modes.
Things in the same general category as this, but with new and radical designs.
Extremely high specific impulse thrusters can result in satellites with much longer operating lives, for the same weight (in kilograms) of pressurized fuel tank storage, and same volume. Either from LEO things that can accelerate themselves periodically to maintain orbit, counteracting the effects of drag, or for geostationary satellites, keeping position longer than a nominal 12-15 year life span.
> A propulsion system with a higher specific impulse uses the mass of the propellant more efficiently. In the case of a rocket or other vehicle governed by the Tsiolkovsky rocket equation, less propellant needed for a given delta-v.[1][3] In rockets, this means the vehicle the engine is attached to can more efficiently gain altitude and velocity. This effectiveness is less important in jet aircraft that are lifted by aerodynamic forces, use outside air for combustion, and carry payloads that are much heavier than the propellant.
If I had to guess, they're experimenting with novel, relatively untested ion and hall effect type thruster systems that have very low thrust in newtons or kilonewtons, but very high specific impulse. Before putting things like that on billion dollar geostationary military communications satellites (or LEO/MEO radar imaging satellites, or billion dollar NRO satellites), they'd want to qualify them in space.
Maybe the spaceplane design that can return a used thruster was a happy coincidence between two different programs, allowing them to do a destructive teardown on a thruster that's been used for two years, to better determine its possible failure modes.
Things in the same general category as this, but with new and radical designs.
https://en.wikipedia.org/wiki/Ion_thruster
Extremely high specific impulse thrusters can result in satellites with much longer operating lives, for the same weight (in kilograms) of pressurized fuel tank storage, and same volume. Either from LEO things that can accelerate themselves periodically to maintain orbit, counteracting the effects of drag, or for geostationary satellites, keeping position longer than a nominal 12-15 year life span.