def ROStime_to_NTP64(ROStime):
    """ Convert rospy.Time object to a 64bit NTP timestamp

    @param ROStime: timestamp
    @type ROStime: rospy.Time
    @return: 64bit NTP representation of the input
    @rtype: int
    """
    NTPtime = ROStime.secs << 32
    # NTPtime |= nanoseconds * 2^31 / 1x10^9
    NTPtime |= int((ROStime.nsecs * 0x100000000) / 0x3b9aca00)
    return NTPtime