ESA GNC Conference Papers Repository

In 2006 Bradford Engineering acquired the Reaction Wheels technology from Airbus Defence and Space (Mechanism Product Group, Stevenage). These Reaction Wheels have a long heritage with several missions as, among others, SOHO, XMM, INTEGRAL and Rosetta. After modernizing the design, several processes were revalidated and qualification was reached in 2010. After this initial activity, there was the need to focus on reaction Wheel industrialization, supply chain consolidation and design upgrades, which was concluded in 2015 with successful delta-qualification. These Reaction Wheels are currently integrated into the Mercury Planetary Orbiter (MPO) of BepiColombo waiting for launch. In the course of ESA spacecraft projects (BepiColombo) and in-orbit observations (Rosetta and XMM), there was the need to further consolidate and develop the existing design and technical solutions in order to demonstrate adequate robustness and further confidence. Under ESA GSTP (General Support Technology Program), Bradford Engineering is currently performing a technology consolidation of the Reaction Wheels, regarding micro-vibration and re-lubrication system. For the micro-vibration of the Reaction Wheels, the study involves several tests, including vibration, thermal environment and long-term operation, with the objective to further understand the induced micro-disturbances of the main engine orders and their potential evolution. Three fully flight representative Reaction Wheel Assemblies (RWA) are assembled and consequently tested. One RWA is subjected to qualification levels and the other two are exposed to acceptance levels. The impact of on-ground S/C tests and launch vibrations are also included. Micro-vibration tests at elevated temperatures and in vacuum are performed. The first test aims to evaluate the impact of thermal expansions of different components within the RWA and the change in lubrication regime. The second test aims to assess the effects of deformation of the housing and absence of air damping. The unit to unit variability is additionally assessed taking into account other RWA from previous programmes. In the second part of this study, the re-lubrication system of the Reaction Wheels is evaluated. Initially, a flight representative Bearing Housing Assembly (BHA) is assembled and tested at different levels of oil with torque characterization performed at different speeds levels, from 1 RPM, to high speed up to 4000RPM. Additionally, stiction effects under different levels of oil and lubrication regime such as EHD lubrication are evaluated. From here, four BHA are assembled and the re-lubrication system is performed via high temperature environment and several heater activations. The torque levels obtained are correlated with the initial test and the oil ejected by the reservoir is estimated. With this campaign, the re-lubrication procedure for in-orbit use will be validated and possibly preventive measures can be made to avert performance degradation due to oil starvation. An additional section will address the status of the lifetime test of the Reaction Wheel assembled and tested by Bradford Engineering. Initiated in 2012, this RWA already reached more than 4 billion revolutions and more than 30.000 zero crossings. In this paper the preliminary results are presented as well as the preliminary conclusions and findings obtained until now. Recommendations will be made for future studies.