Every rocket obeys the Tsiolkovsky rocket equation, trading exhaust velocity for burn duration:
Δv = Isp · g0 · ln(m0 / m1)
F = ṁ · ve = ṁ · (Isp · g0)
Chemical engines have huge thrust but low Isp (~300-450s) so they burn propellant fast. Ion drives have tiny thrust but Isp above 3000s, so they burn for months to reach the same Δv. Nuclear thermal (NTP) heats propellant directly for ~900s Isp at moderate thrust. Solar sails have no propellant at all — thrust comes from reflected photon momentum and decays with distance from the sun.
- Engine type — swaps thrust, Isp and exhaust plume color/speed to match the real technology.
- Throttle — scales thrust and mass flow rate together.
- Dry + payload mass — the mass left after all propellant burns; sets final acceleration.
- Propellant load — total burnable mass; more propellant means longer burn and higher Δv.
- Time scale — speeds up slow burns (ion/sail) so their trajectory is visible in real time.
Real spacecraft mix these: chemical stages for launch and quick burns, ion engines for efficient deep-space cruise (e.g. Dawn, Psyche), NTP proposed for crewed Mars transit, and solar sails for propellant-free missions like LightSail 2.