XMM-Newton Data Files Handbook

4.1.11.1 Spacecraft Time Correlation File

The Spacecraft Time Correlation file (*SC*TCS.FIT) contains the On-Board Data Handler (OBDH) time and the corresponding UTC. The epoch for UTC time reference is: 1958, January 1. More details about the definition of the time packets is given by [12] and [13]. One file is created for each observation and for each slew period. Each file consists of a single binary table whose columns are listed in Table 25.

The UTC is calculated as follows:

$${\rm UTC} = {\rm CORRPARA} \times {\rm OBT} + {\rm CORRPARB}$$ (1)

The UTC is expressed in units of 100 nanoseconds from the epoch 1858-11-17T00:00:00.000 (base date of the U.S. Naval Observatory's ephemerides). The number is then split in its day, ms, and $\mu$s units, as indicated in Table 25.

Alongside the Spacecraft Time Correlation file, a Spacecraft Reconstructed Time Correlation file (*SC*TCX.FIT) is available as well and has been used by the SAS since version v6.0 (March 2004). The Reconstructed Time Correlation data is Time Correlation Data corrected for known anomalies in the correction of Earth Reception Time (ERT) for signal propagation delay and corrected for symmetric discontinuities in Corrected ERT introduced by differences in Ground Station Clocks. The binary table columns are given in Table 25. The first 12 columns are the same as in the *SC*TCS.FIT file, and six additional columns are present. Details of the orbit files are provided in [11].

Table 25: Spacecraft Time Correlation file (*SC*TCS.FIT) binary table columns. The Reconstructed Time Correlation file (*SC*TCX.FIT) has the same columns plus those in the bottom part.

Name	Type$^a$	Units	Description
FRAME	1J	COUNTER
OBTCOARS	1J	SECOND	Coarse COBT
OBTFINE	1J		Fine COBT
UTCDAY	1I		UTC day corresponding to COBT
UTCMILLI	1J		UTC ms of day corresponding to COBT
UTCMICRO	1I		UTC $\mu$s of day corresponding to COBT
CORRPARA	A39		Slope of least squares fit
CORRPARB	A39		Abscissa of least square fit
UTCFLAG	1I		UTC quality flag
ERTIME	27A		Corrected Earth received time
GSID	5A		Ground station identifier
ERTIMERAW	27A		RAW Earth received time
Additional columns only in reconstructed file
UTCREAL	D		UTC
OBTREAL	D		COBT
PASS	I		Pass Number
GS	I		Ground Station Identifier
PREDUTC	D
RESIDUAL	D

$^a$See Sect. 9 for convention