The propulsion subsystem features sets of small thrusters and a main engine. The thrusters are needed to perform Odyssey's attitude control and trajectory correction maneuvers, while the main engine is used to place the spacecraft in orbit around Mars.

The main engine, which uses hydrazine propellant with nitrogen tetroxide as an oxidizer, produces a minimum thrust of 65.3 kilograms of force (144 pounds of force). Each of the four thrusters used for attitude control produce a thrust of 0.1 kilogram of force (0.2 pound of force). Four 2.3-kilogram-force (5.0-pound-force) thrusters are used for turning the spacecraft.

In addition to miscellaneous tubing, pyro valves and filters, the propulsion subsystem also includes a single gaseous helium tank used to pressurize the fuel and oxidizer tanks.

The propulsion subsystem weighs 49.7 kilograms (109.6 pounds).