The Bradford Space Reaction Wheel Unit (RWU) W18E comprises of the Wheel Drive Electronics Box (WDE) and a Reaction Wheel Assembly (RWA). The RWA is made up of a rotating inertial mass that is powered by a brushless DC electric motor. The motor's power causes the wheel to accelerate, generating a counter torque that rotates the satellite body in the opposite direction. To enable control around the 3 axes, at least three sets of RWA are required per satellite, with an additional RWA typically included for redundancy.

Key features

  • Proven performance at low RPMs, with excellent micro-vibrationperformance, verified through lifetest and in-orbit heritage (used in SOHO,RadarSat, Seastar, Olympus, Integral, XMM, Rosetta, Aeolus, and BepiColombo)
  • Fixed torque rise time for precise and repeatable control overthe full speed/torque range
  • High torque level across the full speed range
  • Accurate wheel speed signal
  • Available in analogue or digital interface options

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Last updated: 2023-05-22

Reaction Wheel Unit W18E




momentum storage
22 N m s
maximum operational speed
4000 rpm
maximum gross torque
0.265 N m
static imbalance
0.5 g cm
dynamic imbalance
5.0 g cm^2
295 mm (RWA)
125 mm (RWA)
258 mm (2-channel WDE)
5.65 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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