Cassini's main engine and engine cover during spacecraft assembly.


The main engine was used for spacecraft velocity and trajectory correction changes. To be on the safe side, there were two identical main engines: One was in use and the other was a backup. There were also 16 monopropellant hydrazine thrusters of which eight were prime and eight were backups. The thrusters were used for attitude control and also for small velocity-change maneuvers.

At a Glance

Two completely isolated systems:

  • Monopropellant System - Hydrazine (N2H4)
    • 16 Redundant ~1 Newton thrusters, 4 per “cluster”
    • Used for attitude control and small (< 0.3 m/s) trajectory control maneuvers
  • Bipropellant system- Nitrogen Tetroxide (NTO)/Monomethylhydrazine (MMH)
    • Main (445 Newton) engine for propulsive maneuvers – Burns can be blow-down or pressurized (with Helium)
    • Engines are protected from micrometeoroid particles by articulating cover
    • Redundant main engine (never used in flight)