A Space Environment Monitor (SEM) subsystem architecture has been developed and demonstrated that can benefit future spacecraft by providing (1) real-time knowledge of the spacecraft state in terms of exposure to the environment; (2) critical, instantaneous information for anomaly resolution; and (3) invaluable environmental data for designing future missions. The SEM architecture consists of a network of plug-and-play (PnP) Sensor Interface Units (SIUs), each servicing one or more environmental sensors. The SEM architecture is influenced by the IEEE Smart Transducer Interface Bus standard (IEEE Std 1451) for its PnP functionality. A network of PnP Spacecraft SIUs is enabling technology for gathering continuous real-time information critical to validating spacecraft health in harsh space environments.
The demonstrated system that provided a proof-of-concept of the SEM architecture consisted of three SIUs for measurement of total ionizing dose (TID) and single event upset (SEU) radiation effects, electromagnetic interference (EMI), and deep dielectric charging through use of a prototype Internal Electro-Static Discharge Monitor (IESDM). Each SIU consists of two stacked 2×2 in. (≈5×5 cm) circuit boards: a Bus Interface Unit (BIU) board that provides data conversion, processing and connection to the SEM power-and-data bus, and a Sensor Interface Electronics (SIE) board that provides sensor interface needs and data path connection to the BIU. The figure illustrates the demonstration system components and connectivity where SIU #1 functions as a radiation monitor, servicing a RADiation Field Effect Transistor (RADFET) TID sensor and a RADiation MONitor (RADMON) SEU sensor, SIU #2 monitors EMI through use of two RF antenna, and SIU #3 monitors spacecraft charging conditions by interfacing to an IESDM sensor. The heart of the BIU is a Silicon Laboratories C8051F060, a mixed-signal in-circuit-programmable (ISP) flash micro controller unit (MCU) with controller-area network (CAN) bus interface.
At the time of this reporting, follow-on work is needed to develop designs that use space-qualified parts, in developing a standard fault-tolerant spacecraft interface, which would spawn a multidrop backbone SIU bus (i.e. CAN), and in developing the PnP software that leverages off IEEE Std 1451.
This work was done by Jagdish Patel, David E. Brinza, Tuan A. Tran, and Brent R. Blaes of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47340