GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

Figure 13-32. Measurement axes of the payload magnetometers.Power and data signals are routed between the ECU and payload magnetometers through a 15-pin connector onthe side of each unit. The measurement coils for the magnetometers are mounted on the side plate containingthe power/data connector as shown in Figure 13-33.Figure 13-33. Mounting locations of the payload magnetometers.The orientation of these coils determines the measurement axes of the magnetometer. For magnetometers 1 and2, this plate is mounted on the left side of the unit as seen from the front end (the end opposite of the end thatcontains the mounting structure). Thus, these magnetometers are said to be “left-handed”. For magnetometers3 and 4, this plate is mounted on the right side of the unit, and thus these magnetometers are said to be “righthanded”.Data is sampled by each magnetometer unit every five seconds and transmitted down to Earth in counts (eachvolt corresponds to 3276.7 counts). The GP-B science team then performs several processing functions on thisdata. First, the data is converted from counts to volts. Next, crosstalk in the data, the interference that eachmeasurement coil receives from the other coils, is eliminated through multiplication with a matrix of groundmeasurements. Finally, the measurements are converted from the magnetometer frame to the spacecraft framethrough multiplication with direction cosine matrices.Gravity Probe B — Post Flight Analysis • Final Report March 2007 377