Time Synchronization and Distribution Mechanisms for Space Networks
- Tuesday, 29 November 2011
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 timeclient.
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 time-stamping
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
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.