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Special Semaphore Scheme for UHF Spacecraft CommunicationsA semaphore scheme has been devised to satisfy a requirement to enable ultrahigh- frequency (UHF) radio communication between a spacecraft descending from orbit to a landing on Mars and a spacecraft, in orbit about Mars, that relays communications between Earth and the lander spacecraft. There are also two subsidiary requirements: (1) to use UHF transceivers, built and qualified for operation aboard the spacecraft that operate with residual-carrier binary phase-shift-keying (BPSK) modulation at a selectable data rate of 8, 32, 128, or 256 kb/s; and (2) to enable low-rate signaling even when received signals become so weak as to prevent communication at the minimum BPSK rate of 8 kHz. The scheme involves exploitation of Manchester encoding, which is used in conjunction with residual-carrier modulation to aid the carrier-tracking loop. By choosing various sequences of 1s, 0s, or 1s alternating with 0s to be fed to the residual-carrier modulator, one would cause the modulator to generate sidebands at a fundamental frequency of 4 or 8 kHz and harmonics thereof. These sidebands would constitute the desired semaphores. In reception, the semaphores would be detected by a software demodulator.
Document ID
20110013622
Document Type
Other - NASA Tech Brief
Authors
Butman, Stanley
(California Inst. of Tech. Pasadena, CA, United States)
Satorius, Edgar
(California Inst. of Tech. Pasadena, CA, United States)
Ilott, Peter
(California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
August 25, 2013
Publication Date
December 1, 2006
Publication Information
Publication: NASA Tech Briefs, December 2006
Subject Category
Man/System Technology And Life Support
Report/Patent Number
NPO-42910
Distribution Limits
Public
Copyright
Public Use Permitted.
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