93 Antenna Reflectors 

The two Antenna Reflectors are designed from aluminium. The required rms value is 5 µm minimum. This  value was exceeded by spli tting the manufacturing process into seve ral individual sub tasks at different  specialized suppliers. The coordination of the related ta sks was followed and closely supported in order to  minimize the technical and subsequent programmatic risks. The major working steps were:  • Coarse manufacturing of the Reflectors (at leaving additional material on the Reflector surface for  later fine turning)  • Heat treatment of the pre-shaped Reflectors  • Intermediate fine surface manufacturing  • Inspection of Quality including surface accuracy measurement  • Cleaning process  • Final surface shaping with diamond tool  • Inspection of quality including surface accuracy measurement  • Cleaning process  • Pre- and post surface treatment by applying gold coating 

Motor Control Electronics   The Motor Control Electronics (MCDE) is designed as  a completely cold redundant unit, each part acting  to the main respectively redundant motor stat or and receiving feedback from the redundant high  resolution encoders. The controller is implemented into the FPGA.  

The MCDE is a two-channel, 3-phase, brushless DC motor controller, which has been especially adapted  to MWHS. It has linear power stages for extremely accurate, wide-bandwidth and high precision tracking control. It incorporates redundancy both in the power stage and the encoder input. It employs extensive use of FPGA logic, which have been adapted to support serial interface protocol s, sequencing, digital  velocity and position control, profile generation, redundancy management etc.   The power stages are linear (non-switching) and are designed to operate at 27V and at a peak current of  up to 2A. These power stages possess two current sensors in the output phases to support full sine-wave commutation, which ensures optimum torque and velocity control characteristics. The use of linear power control and precise control of the operational current guarantees an exce llent performance at low drift,  high bandwidth and high linearity.  Control of the MCDE is by means of a serial bus inte rface, which also feeds status information back to the  host. In addition there are two enable and status si gnals for each of the redundant power stages and  encoder feedback channels.   Specific Development and Test Issues 

Mass and Inertia Minimization of Welded Baffle 

In order to achieve the required scan performance (minimum time between the operational points which  are earth scan, cold and hot calibration), the system had to be designed for maximum acceleration capability. Since the available torque is limited by the available motor powe r, the moment of inertia of the  rotating part of the mechanism had to be minimized.   This was achieved firstly by designing light weight Re flectors. However, for thermal reasons a cylindrical  thermal baffle (“barrel”) surrounding the Reflectors wa s needed in order to keep the Reflector temperature  as stable as possible. The thermal baffles (two of them) provide significant co ntribution to the overall  moment of inertia and its mass and radius had ther efore to be minimized. Consequently the baffle was  designed as a very thin walled structural cylinder (1-mm wall thickness) manufactured out of a bent  aluminium plate and stiffened up by means of a radial ring at its one end (close to the Front Ends). The  NASA/CP-2010-216272