Two families of in-space propulsion
Chemical
- How: combust propellant, expand through a nozzle.
- Pros: high thrust (kN to MN), simple plumbing, short burn times.
- Cons: Isp capped near ~450 s by chemistry.
Electric
- How: accelerate ionised propellant (usually xenon or krypton) electromagnetically.
- Pros: Isp 1,500-9,000 s, great for high-Δv missions.
- Cons: thrust measured in mN, so burns last weeks to months.
When to pick what
- Launch: chemical (thrust dominates).
- LEO constellation station-keeping: electric (propellant mass dominates life).
- Geostationary orbit raising: electric increasingly common, trades launch mass for months of raising.
- Landers / re-entry: chemical.
- Deep space cruise: electric where feasible.