Description
Objective: The objective of this activity is to improve reaction wheel torque stability and repeatability via the application of aninternal wheel speed control loop, and to demonstrate the feasibility and effectiveness by test at Breadboard level. A secondary objective is to assess the possibility of achieving a cost reduction for the electronics via the wholesale migration towards adigitalwheel drive electronics.
Targeted Improvements:
- Improved pointing performances, lower mass and lower overall cost solution at spacecraft level.
- The reaction wheel electronics cost, mass and volume is targetted to be reduced by 25%.
- A reaction wheel digital signalinterface is expected to further reduce costs at system level.
Description: All conventional reaction wheels have to face bearing lubrication related phenomena that result in torque instabilities. These, together with any variation/deviation in the reaction torquerealisation profile, have an impact on S/C pointing performance. Currently, all reaction wheels for GEO telecom applications arebased on heritage designs relying on analogue discrete wheel drive electronics. These are bulky and costly to assemble and test. Further, they impact significantly the system AIT process and are not readily interchangeable with similar wheelsfrom other manufacturers creating potential supply chain issues. The choice of analogue interfaces is driven by current equipment availability and potential re-use.
Digital motor controllers and embedded motor speed control are used extensively in other applications and have also been demonstrated on some small wheels. Such approaches have the potential to react quickly to (erratic) changes in the friction torqueby rapid local detection of wheel speed changes while simultaneously allowing the integration of several functions in asingle component and shrinking the overall electronics. Such an implementation naturally leads itself also to digital interfaces, which open the way for more exchangeability between units.Other approaches also exist (e.g. external to the reaction wheel equipment), but theseare likely to lead to higher cost and mass than current products and so are not considered here. The increasing demand for high pointing stability, for e.g. multi-spot missions and optical inter-satellite links, shows a clear need for improving the reaction wheeltorque stability. And the digital speed control embedded in the wheel is the most promising way to improve torque stability withoutlarge scale bearing technology changes, and potentially leads to important system budget savings at satellite attitude control level.
The proposed work logic is the following:ï
- Define gather requirements (including interface, commanding, mass, cost and performance requirements) - in close collaboration with primes operators covering 20 to 100Nmswheels.
- Propose and study wheel speed control loop algorithms, for the full wheel speed range, enabling the improvement of the performances (in particular torque stability and torquerealisation repeatability) as well as the required wheel speed measurement techniques needed to ensure sufficient accuracy over the full wheel speed range. This study shall considerboth compatibility with existing Reaction Wheel Assembly (RWA) designs and theirwheel speed measurement hardware as well as produce proposals for improved wheel speedmeasurement solutions. It is expected that different techniques are required for different wheel speed ranges in order to ensure the maximum performance. The algorithms shall alsoensure that they are designed such as to not have any adverse reactions with AOCS measurement and control loops (e.g. shall be sufficiently high bandwidth as to fall well outside ofthe AOCS measurement and control domain).
- Propose a new electrical design embedding not only the wheel speed loop, but also as many of the required wheel drive electronic functions (motor controller,external interface,housekeeping etc.) in a single component (i.e. FPGAA or ASIC) with the goal of reaching a new WDE design with reduced footprint, assembly/test effort and cost.
- Design, build test this solution at breadboard level and demonstrate the performances achievable with an existing RWA hardware and from there extrapolate what could beachieved with updated RWA hardware and also to determine how much degradation bearing/lubrication or other (e.g. cogging torque) induced torque instabilities could be potentiallyremovedby such methods.
- Propose a roadmap (with associated cost) to reach a recurring fully qualified product based on the concepts demonstrated.
Tender Specifics