X ray pulsar can be used for spacecraft autonomous navigation.Pulsar clock can be used to stabilize onboard clock.Utilization in space of X ray pulsar clock is based on high precision determination of pulsar pulse Time of Arrival(TOA)at spacecraft.A method to obtain X ray pulsar pulse profile with individual photon arrival time records by onboard X ray detect system was discussed.In the case that an onboard clock is used as time reference for X ray pulsar timing recorded individual photon arrival time(space...