A Concept for a Transparent Data Acquisition and Distribution System for Spaceflight Applications

Abstract

The emergence of "smart" sensors onboard space missions is forcing a reexamination of the procedures by which NASA acquires, multiplexes, transmits, annotates, and distributes sensor data to the user community. Increasingly we find that "smart" sensors are being planned for future space missions which will search for specific unusual phenomena and, when present, record these phenomena in great detail. This gives rise to the need for a widely varying bandwidth requirement from each instrument in response to the occurrence of phenomena that cannot be anticipated in advance. An asynchronously multiplexed packet telemetry concept is described which, within broad limits, permits instruments to acquire and transmit information at the rate appropriate for the experimental phenomena being observed. Data from a single instrument, along with the necessary ancillary data (typically time, position, and attitude), will be assembled into self-contained packets and will be subsequently transmitted over various communications links (i.e., space telemetry channel, ground communications circuits, etc.) to the experimenter's facility in near real time. Reliable error control coding will be included in each link transmission to protect the integrity of the data packets. A major objective is to make the entire data acquisition and distribution process completely transparent to the experimenter in the sense that the output terminal of the distribution system will be physically, logically, and electrically identical to that of the experiment output channel. To provide greater inter-mission portability of instruments and to reduce the instrument interfacing costs, the emerging national and international telecommunications standards (ADCCP/HDLC/SDLC, X.25, etc.) will be utilized as the instrument interface standards wherever practical. Except for the time delay imposed by propagation and nominal queueing considerations, the experimenters will observe an interface identical to that which would occur if the instrument were physically located at their facilities.