AIRBUS DS’ HCA: HIGH CAPACITY ACTUATOR FOR SMALL SATELLITE MISSIONS
Authors:   Airbus Defence & Space, Toulouse, France, Segon Fabien , Dupuis Aurélien 
Published: January 2024

The result of several years of design and development, the HCA reaction wheel provides the satellite with an unmatched effective torque/consumption ratio. Geared towards the small satellite market (200-500 kg), it brings high speed manoeuvres and enhanced pointing control to this segment by combining ease of use and cost efficiency.
CUTTING-EDGE EQUIPMENT
HCA reaction wheels are unique actuators on the market. They are the result of more than 15 years of development closely aligned with the needs of high resolution Earth observation missions. They feature several technological breakthroughs:
•Recovery of mechanical energy: Through a Bank Of SuperCapacitors (BOSC), the equipment can recover the mechanical energy from the rotor during the braking phases and reinject it during the acceleration phases. Only internal losses must be compensated by the energy taken from the satellite bus. This makes it possible to achieve unrivalled torque capability without affecting the power budget of the system.
•Angular measurement: the equipment is instrumented with an angular measurement for precise speed estimation over the entire operational range. The local speed loop efficiently rejects internal disruptions of the equipment (oil drops, zero crossing) significantly improving the performance, while simplifying the AOCS. The equipment also provides an angular increment measurement which, by hybridisation with other platform sensors, can provide information on the satellite’s attitude.
MATURITY
From the initial concept studies in 2006 until now, many milestones have been achieved to reach an FM maturity level:
•The mechanism has been qualified since 2018, the lifespan has been demonstrated on 6 ball bearing units as well as on the qualification mechanism.
•The BOSC has been qualified since 2021 with ESA support
•The electronics have also been qualified in 2022.
•12 FM are currently in manufacturing and test phases, 4 FM are already delivered to satellite client
FUNCTIONAL PERFORMANCE
The equipment was designed and tested on the basis of the following requirements:
•Maximum reaction torque of 0,98 Nm (1,20 Nm is expected as result of margin reduction test campaign – in progress)
•Maximum angular momentum of 4 Nms in normal mode, 6 Nms with a reduced torque range.
•Precision of angular momentum realization better than 1 mNms in imaging conditions.
A VERSATILE FUNCTIONAL ARCHITECTURE
The result of a comprehensive reflection at the satellite system level, HCA wheels offer several operating and control modes to adapt to the needs of the different phases of the missions.
There are two modes used to manage the trade-offs between performance, consumption and lifespan. Manoeuvre mode (MAN) is the nominal operating mode enabling high torque capabilities. The quasistatic mode (QS) is used outside of the mission phases. In this mode, the torque range is reduced in order to limit losses and optimise the lifespan.
The equipment also offers three speed or torque control modes:
•Speed mode: a coherent torque/speed pair is sent by the AOCS. The equipment uses the torque in open loop and in speed setpoint interpolation.
•Closed loop torque mode: in this mode, only torque command is required. The speed loop is activated in order to reject the internal perturbations and ensure that the requested reaction torque is produced.
•Open loop torque mode: in this mode, only torque command is required. The speed loop is deactivated, and the controlled torque corresponds to the motor torque without compensation of the perturbations. This corresponds to the conventional wheel control mode and is compatible with an angular measurement malfunction.
All of these operating and control modes make it possible to adapt to the AOCS requirements in the best way possible, while respecting the constraints associated with the equipment.
POSITION IN THE REACTION WHEEL MARKET
Due to its unique operating principle, HCA stands out from the competition with an excellent maximum torque to consumption ratio. This characteristic makes integration on small platforms possible and paves the way for wheel hyper-agility.
PRODUCT DATASHEET
Maximum output torque : 0,98 Nm (1,20 Nm expected after margin reduction campaign)
Maximum angular momentum : 4,0Nms (6,0 Nms with reduced output torque)
Mass : Mechanism : 6,20kg, Electronics : 5,56 kg (for two channels in the same box driving one mechanism each), BOSC : 1,25kg
Volume : Mechanisme : Ø240 mm, H 106 mm, Electronics : L 219 mm, l 186 mm, H 146 mm (two channels), BOSC : L 190 mm, l 128 mm, H 58 mm
Consumption at null torque : 10 W @ 0,5Nms; 21 W @ 4Nms
Consumption at maximum torque : 34 W @ 0,5Nms; 45 W @ 4Nms
Stiffness : > 140 Hz
Life duration in flight : 10 years
Communication interface : RSR422/485 or SoCAN
Maturity : Qualified