The Bradford Space Reaction Wheel Unit (RWU) W45E is a system that consists of a Wheel Drive Electronics Box (WDE) and a Reaction Wheel Assembly (RWA). The RWA is driven by a brushless DC electric motor and consists of a rotating inertial mass. When power is applied to the motor, the RWA accelerates and generates a counter torque that rotates the satellite body in the opposite direction. This enables precise control around the three axes. To ensure redundancy, an additional RWA is typically included in each satellite, requiring at least three sets of RWA for full control around the three axes.

Key features

  • Proven performance at low RPMs with excellent micro-vibration performance, verified through lifetest and in-orbit heritage. Used in SOHO, RadarSat, Seastar, Olympus, Integral, XMM, Rosetta, Aeolus, and BepiColombo.
  • Fixed torque rise time enabling precise and repeatable control over the full speed/torque range.
  • High torque level available across the full speed range.
  • Provides an accurate wheel speed signal.
  • Available with both analogue and digital interface options.

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Last updated: 2023-05-22

Reaction Wheel Unit W45E




momentum storage
45 N m s
maximum operational speed
4000 rpm
maximum gross torque
0.248 N m
static imbalance
0.5 g cm
dynamic imbalance
5.0 g cm^2
365 mm (RWA)
125 mm (RWA)
258 mm (2-channel WDE)
7.45 kg (RWA)
4.67 kg (2-channel WDE)
181 mm (2-channel WDE)
143 mm (2-channel WDE)
peak power consumption at max. torque and speed
168 W
steady state consumption at max. constant speed
29 W
quiescent power consumption
7.6 W
power bus interface
data interface
qualification operational temperature
-15°C to +60°C (RWA)
-30°C to +60°C (WDE)


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