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Reaction Wheels

Overview

Bradford's Reaction Wheel Unit channel consists of one or more Reaction Wheel Assemblies and one Wheel Drive Electronics Box to control them. The wheel assembly contains a rotating inertial mass, driven by a brushless DC electric motor. When power is applied to the motor, the wheel accelerates, causing the satellite body to which the motor housing is attached to rotate in the opposite direction due to the induced counter torque.

This is used to provide highly accurate pointing and slewing capabilities to satellites. Typically, a minimum of three wheels are needed per satellite to allow rotational control around the 3 axes. One extra wheel is generally present for redundancy purposes.

Bradford offers a range of reaction wheels to the market, each specifically sized for a particular angular momentum control range. All wheels are based on the same proven design, maximizing the available heritage between them.

Datasheet

Selected
Key Advantages
  • High torque level over full speed range
  • Fixed torque rise time allowing precise and repeatable control over full speed/torque range
  • Analogue or digital interfaces available
  • Accurate wheel speed signal
  • Proven zero crossings and low RPM performance with excellent micro-vibration performance
  • Braking energy is dissipated internally - no energy is injected back into the S/C power bus
  • Ability to tune moment of inertia of the rotation mass to optimise the mass budget to your spacecraft
  • Extensive in-orbit heritage on SOHO, RadarSat, Seastar, Olympus, INTEGRAL, XMM, Rosetta, Aeolus and BepiColombo
General Specifications

The follow parameters apply to all Bradford reaction wheels:

ParameterSpecificationNotes
Maximum Operational Speed
4000 RPM
Pulses/Revolution
240
Typical Torque Loss
0.037 Nm
At maximum speed
Static/dynamic Imbalance
0.5 g.cm & 5.0 g.cm²
Torque rise/fall time
80 ms
Peak Power Consumption
168 W
At maximum torque and speed
Steady State Consumption
29 W
At maximum torque and speed
Quiescent Power Consumption
7.6 W
Drive Electronics Assembly Mass
4.67 kg
2-channel variant
Drive Electronics Assembly Size
258 × 181 × 143 mm
2-channel variant
Power Interface
28V or 50V
Data & Command Interface
MIL-STD-1553B or analogue
TM/TC frequency
< 10 Hz
Models Available
ParameterW18W18EW18ESW45W45E
Momentum Storage
18 Nms
22 Nms
25 Nms
40 Nms
45 Nms
Maximum Torque
0.265 Nm
0.265 Nm
0.265 Nm
0.248 Nm
0.248 Nm
Mass
5.20 kg
5.56 kg
6.02 kg
6.70 kg
7.45 kg
Wheel Dimensions
Ø 295 × 125 mm
Ø 295 × 125 mm
Ø 295 × 125 mm
Ø 365 × 125 mm
Ø 365 × 125 mm
Configurations

Wheel Drive Electronics

Electronic drive units are available for 1, 2, 4 or 5 wheel configurations, simplifying your integration and saving on repeated driver mass.

Moment Tuning

The wheels' moment of inertia of rotation mass can be tuned in order to minimise vibrations introduced to your spacecraft.

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