A signaling-and-detection scheme has been proposed for use in conjunction with the remote-monitoring concept described in "Beacon Monitoring Would Reduce Interactions With Remote Systems" (NPO-19706), NASA Tech Briefs, Vol. 21, No. 5 (May 1997), page 54. To recapitulate: A remote system (a spacecraft in the original intended application) would contain a semiautonomous computer-based monitoring subsystem that would analyze data acquired by onboard instrumentation and would produce a summary assessment of the status of the system. The summary assessment would be represented by one of four messages. To minimize the demand on communication resources and thereby minimize the cost of operation, the subsystem would ordinarily not transmit full telemetric data to a control station (a ground station in the original application). Instead, the subsystem would transmit one of the four messages as a radio beacon signal. Operators on the ground could decide, partly on the basis of the received beacon message, whether and when full telemetric data were needed. Full telemetric data would be transmitted from the remote system to the control station only on command by operators on the ground.
In the proposed scheme, each of the four beacon messages would be represented by a pair of subcarrier tones with unique frequency spacing. These tones would be phase-modulated onto a carrier signal with a modulation angle of 90°. The tones would be detected noncoherently at the control station. At the low data rate inherent in the four beacon messages, this scheme offers adequate performance at a signal level 10 dB below that needed for a bit-based, binary-phase-shift-keying (BPSK) scheme that is used to transmit full telemetric data. This 10-dB performance advantage could be exploited by reducing the transmitted power at the remote station and/or using a smaller antenna to receive the signal at the control station. The larger antenna needed to receive full telemetry could thus be allocated to other tasks until there was a need to receive full telemetric data from the remote system.
The proposed scheme, and two alternative weak-signal-detection techniques that could be used in the scheme, have been tested in a laboratory, but have not yet been tested in an operational system. In both detection techniques, decision statistics are derived from incoherent sums of power spectra and compared with thresholds. In one technique, the frequency drift of the signal is modeled after evaluation of the power spectra; in the second technique, the frequency model is applied before computation of the power spectra.
This work was done by Miles K. Sue, Robert Kahn, Gabor Lanyi, Victor Vilnrotter, Marvin Simon, Ted Peng, John Caraway, and Bruce Crow of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Electronic Systems category, or circle no. 121on the TSP Order card in this issue to receive a copy by mail ($5 charge).
NPO-20187
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Signaling-and-detection scheme for beacon monitoring
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Overview
The document discusses a novel approach to spacecraft health monitoring aimed at improving efficiency in the use of the Deep Space Network (DSN). Traditional methods require spacecraft to routinely transmit extensive engineering data to large ground antennas, which are becoming increasingly burdened due to the rising number of low-cost missions. This situation not only strains the existing infrastructure but also incurs higher operational costs.
To address these challenges, the proposed solution involves a semiautonomous onboard monitoring subsystem that assesses the spacecraft's health and transmits one of four simplified messages instead of full telemetry data. This system is designed to operate with minimal communication demands, allowing for a significant reduction in the frequency and volume of data sent to ground stations. The spacecraft will send these messages once per day, with the ground station monitoring the signals for up to half an hour.
The document outlines the technical aspects of the new signaling and detection scheme, which utilizes a tone-based signaling method with a non-coherent detection approach. This method offers a 10 dB performance advantage over traditional bit-based BPSK signaling, particularly in low-data-rate scenarios where signals may be affected by phase noise. The use of this tone-based system enables the possibility of employing smaller antennas for monitoring, thereby alleviating the load on larger DSN antennas and reducing operational costs.
The monitoring messages are determined by onboard software based on the spacecraft's health status. Each message is relayed to the onboard executive, which commands the telecommunications subsystem to transmit the appropriate monitoring signal. The ground monitoring station is fully automated, processing received signals through downconversion, digitization, and decoding before disseminating the information to mission operations teams.
Overall, this innovative approach not only enhances the efficiency of spacecraft monitoring but also allows for more flexible and cost-effective operations in deep space missions. By leveraging onboard intelligence and streamlined communication protocols, the new system represents a significant advancement in the management of spacecraft health and operational readiness.
