Unlike prior designs, the MARA design provides for correlated double sampling, which offers the advantage of subtraction of correlated noise between reset samples and data samples, thereby reducing spurious offsets and the effects of low-frequency noise.
The event-detection circuits of prior instruments do not employ hysteresis and, as a result, spurious trigger signals are generated during the rising and falling edges of pulses being detected. The use of hysteresis in the MARA design ensures that only one pulse is produced for each rising edge and for each radiation event.
Prior designs do not employ distributed processing: Instead, they rely on central computers or processors to poll, sample, and store data from multiple boards in the instruments. In contrast, the present architecture provides for distributed processing with local memory, enabling each board to independently sample events and store data pertaining to them. This architecture facilitates prompt reading of time-critical data signals in a consistent operation. Distributed processing with local memory also allows identification of coincident detections by multiple radiation- detection boards through comparison of time stamps attached to data collected by individual boards.
Prior designs employ custom bus interfaces rather than industry-standard ones. Adherence to the PC/104 bus-interface standard in the present architecture (1) makes the architecture more amenable to diverse applications, (2) facilitates customization and reconfiguration of a suite of radiation detectors through stacking of multiple circuit boards, (3) enables incorporation of other interface hardware that also adhere to the PC/104 standard (this saves costs, time and risk), and (4) enables inclusion or exclusion of various communication interfaces through addition or removal of circuit cards of different types.
Prior designs do not provide for in-system reprogrammability of radiationdetection firmware. The MARA design enables remote loading of modifications of firmware and/or replacement of corrupted firmware files with firmware files of known integrity.
Prior designs used a text-based user interface for command and control. MARA employs an easy-to-use graphical user interface, with point-and-click functionality. The control console application also provides several real-time displays, when in the ground mode. Data received from MARA is displayed as detector pulse height spectrum graph, coincident data x–y scatter plot, and historical event count tracking. These displays enable rapid system configuration and calibration.
This work was done by Paul Delaune, Kathryn Turner, and S. Douglas Holland of Johnson Space Center; William R. Carson of Muniz Engineering; and Fadi Riman of Lockheed Martin.
Inquiries concerning rights for the commercial use of this invention should be addressed to the Technology Transfer Office, Johnson Space Center, (281) 483-3089. Refer to MSC- 24042/38/41/228.