Dawn Spacecraft Reaction Wheel

The Dawn spacecraft was propelled by three xenon ion thrusters derived from NSTAR technology used by the Deep Space 1 spacecraft, using one at a time. They have a specific impulse of 3,100 s and produce a thrust of 90 mN. The whole spacecraft, including the ion propulsion thrusters, was powered by a 10 kW (at 1 AU) triple-junction gallium arsenide photovoltaic solar array manufactured by Dutch Space. Dawn was allocated 247 kg (545 lb) of xenon for its Vesta approach, and carried another 112 kg (247 lb) to reach Ceres, out of a total capacity of 425 kg (937 lb) of on-board propellant. With the propellant it carried, Dawn was able to perform a velocity change of approximately 11 km/s over the course of its mission, far more than any previous spacecraft achieved with onboard propellant after separation from its launch rocket. However, the thrust was very gentle; it took four days at full throttle to accelerate Dawn from zero to 60 mph (96 km/h). Dawn is NASA’s first purely exploratory mission to use ion propulsion engines. The spacecraft also has twelve 0. 9 N hydrazine thrusters for attitude control (orientation), which were also used to assist in orbital insertion.