The time assignment system of ASTRO-H

ASTRO-H is an X-ray astronomy satellite to be launched in 2014. The data acquisition system of this mission is realized with a standard network protocol, SpaceWire. Although the protocol itself is well designed, a new concept to grantee the quality of service will be installed to the ASTRO-H data acquisition system. Therefore, the verification of the design of the concept is essential in the initial phase of the development. The time assignment function is one of the important issues for the SpaceWire development. The accuracy of the absolute time of about 30 μs is required from science goals. The key point of the time assignment with SpaceWire network in the ASTRO-H system is how accurately sharing the time information. In this paper, our design of the time distribution and assignment system for ASTRO-H is shown. The results of our measurements of timing accuracy are also presented to show that the design will fulfill the goal of absolute timing accuracy.