Physics / mechanism
In-space propulsion covers any system that moves a spacecraft once it has left the launch vehicle — orbit raising, station-keeping, lunar/interplanetary transfer, and deorbit. Orbital transfer vehicles (OTVs) are reusable or expendable upper stages that execute high-delta-v maneuvers between orbits. Key parameter is specific impulse (Isp): chemical bipropellants (MMH/NTO, LOX/LH2) deliver Isp ~300–460 s; electric propulsion (Hall-effect, gridded ion) reaches 1,500–10,000 s but at low thrust, suiting slow spirals. Cold/warm gas and green monopropellants (AF-M315E, LMP-103S) sit below 250 s Isp, used for fine attitude control. Emerging options — nuclear thermal (Isp ~900 s), solar thermal, and rotating detonation engines — are at TRL 3–5.
Competitive landscape
| Approach | Isp (s) | Thrust class | Maturity |
|---|---|---|---|
| Chemical biprop | 300–460 | High (N–kN) | Flight-proven |
| Hall / gridded ion | 1,500–10,000 | Low (mN–N) | Flight-proven (SmallSat scale) |
| Nuclear thermal | ~900 | Medium | TRL 3–4, regulatory risk |
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.