QPOE event times are typically expressed in units of an on-board spacecraft clock. Because of clock drifts and resets, the relationship between spacecraft time and UTC may be non-linear, and may even vary with time. For Einstein and ROSAT, the relationship is expressed in terms of interpolating polynomials determined through in-flight calibration. The conversion is automatically performed as part of the timing corrections in 8.7.2. The stand-alone task scc_to_utc allows conversion of an arbitrary spacecraft time to UTC.
input files: xtimingdata$scc_to_utc.tab
ti> scc_to_utc tbl_fname = xtimingdata$scc_to_utc.tab # ROSAT
# conversion table
input spacecraft clock time (1606720.): 1606720.0
SCC->UTC conversion table is calibrated to SCC 110883482.0000
SCC time = 1606720.00000000
UTC time (integer part) 2448062 (real part) 0.97604379056608
ti>