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Time Synchronization and Distribution Mechanisms for Space Networks
NTRS Full-Text: Click to View  [PDF Size: 77 KB]
External Online Source: http://www.techbriefs.com/component/content/article/12246
Author and Affiliation:
Woo, Simon S.(California Inst. of Tech., Pasadena, CA, United States)
Gao, Jay L.(California Inst. of Tech., Pasadena, CA, United States)
Clare, Loren P.(California Inst. of Tech., Pasadena, CA, United States)
Mills, David L.(Delaware Univ., DE, United States)
Abstract: This work discusses research on the problems of synchronizing and distributing time information between spacecraft based on the Network Time Protocol (NTP), where NTP is a standard time synchronization protocol widely used in the terrestrial network. The Proximity-1 Space Link Interleaved Time Synchronization (PITS) Protocol was designed and developed for synchronizing spacecraft that are in proximity where proximity is less than 100,000 km distant. A particular application is synchronization between a Mars orbiter and rover. Lunar scenarios as well as outer-planet deep space mother-ship-probe missions may also apply. Spacecraft with more accurate time information functions as a time-server, and the other spacecraft functions as a time-client. PITS can be easily integrated and adaptable to the CCSDS Proximity-1 Space Link Protocol with minor modifications. In particular, PITS can take advantage of the timestamping strategy that underlying link layer functionality provides for accurate time offset calculation. The PITS algorithm achieves time synchronization with eight consecutive space network time packet exchanges between two spacecraft. PITS can detect and avoid possible errors from receiving duplicate and out-of-order packets by comparing with the current state variables and timestamps. Further, PITS is able to detect error events and autonomously recover from unexpected events that can possibly occur during the time synchronization and distribution process. This capability achieves an additional level of protocol protection on top of CRC or Error Correction Codes. PITS is a lightweight and efficient protocol, eliminating the needs for explicit frame sequence number and long buffer storage. The PITS protocol is capable of providing time synchronization and distribution services for a more general domain where multiple entities need to achieve time synchronization using a single point-to-point link.
Publication Date: Dec 01, 2011
Document ID:
20120001245
(Acquired Jan 25, 2012)
Subject Category: MAN/SYSTEM TECHNOLOGY AND LIFE SUPPORT
Report/Patent Number: NPO-47403
Document Type: NASA Tech Brief
Publication Information: NASA Tech Briefs, December 2011; 26; (SEE 20120001209)
Financial Sponsor: Jet Propulsion Lab., California Inst. of Tech.; Pasadena, CA, United States
Organization Source: California Inst. of Tech.; Pasadena, CA, United States
Description: 1p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Distribution as joint owner in the copyright
NASA Terms: TIME SYNCHRONIZATION; ERROR CORRECTING CODES; BUFFER STORAGE; TIME FUNCTIONS; PROTOCOL (COMPUTERS); SPACE PROBES; MARS SURFACE; DEEP SPACE; PROTECTION; PROXIMITY; ROVING VEHICLES
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