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Engineering Data Processing System

Jitter File Format Definition

Revision of Obslog File Format

 


 

Introduction

1

 

This document defines the current format of the jitter file products of the Engineering Data Processing System (EDPS). These products are similar to the Observation Logs (Obslogs) produced by the Observation Monitoring System (OMS) that no longer exists. The OMS was replaced because it was too costly to maintain and it was hosted on a platform that is no longer supported at the ST ScI. The EDPS is a less ambitious system that does not attempt to monitor instrument problems. The EDPS jitter files are limited to the engineering data that describes the performance of the Pointing Control System (PCS) including the Fine Guidance Sensors that are used to control the vehicle pointing. The jitter files report on PCS engineering data during the duration of the observation. The old name for these jitter files, observation logs (Obslogs), is now inappropriate, because of the absence of instrument monitoring. However the FITS header and extension formats of the jitter files are not radically different from the original Obslogs. FITS-based tools that access only the PCS related data should be able to handle both the old Obslogs and the new jitter files. The jitter files retain the same file naming conventions as the old obslogs.

 

One way to distinguish the new jitter files from the old obslogs files is to check the existence of the OPUS_VER keyword (system version id) that replaced the OMS_VER keyword. The EDPS software is part of the larger OPUS system that also supports the Science Data Processing System (SDPS) and the On-the-Fly Reprocessing (OTFR) system. Most of the format changes involve deletions of keywords. Six keywords have been added. There are some improvements in the new files. The accuracy of HST orbit-related statistics has been improved by ignoring the values in the telemetry that must be interpolated. Instead, an orbit model is used to recalculate the orbit position and velocity at the exact time needed. The new jitter files have been generated since mid-February, 2003, but there is no specific date since the OMS ran in parallel with EDPS for about a week.

 

The Data Systems Branch maintains a Web tool that allows access to detailed information on the most recent header formats and keyword definitions. The information is accessed by instrument mnemonic, which for jitter files is JIT. This Web page can be accessed from the HST Keyword Dictionary entry found on the DSB home page.


 

 

Comparison

2

 

 

The old format is well documented by the Observatory Support Web page maintained by the Telescopes Branch of the Instrument Division at http://www.stsci.edu/instruments/observatory/. This document is supplemental to the Observation Log (jitter file) Documentation.

Changes in image file

There are six new keywords for the jitter image file that has the file extension .jif or .jwf. Keywords that are in the primary header are assigned the extension (Ext) value 0. Keywords in other extensions have the extension value >0 since there can be more than one extension for associated products.

 

Keyword

Ext

Comment

ASN_PTYP

0

Association Product Type

GSD_FGS

0

1, 2 or 3: FGS ID of dominant FGS

GSR_FGS

0

1,2 or 3: FGS ID of subdominant (roll) FGS

GS_PRIM

0

DOMINANT or ROLL: GS that was acquired first

OPUS_VER

0

Build version: replaces OMS_VER

WCSAXES

>0

2: Number of axes for WCS parameters

 

There are 43 OMS Obslog keywords that were dropped for the new jitter image file.

 

Keyword

Ext

Comment

OMS_VER

0

Replaced by OPUS_VER. OMS is gone.

EARTHMOD

0

No stray light modeling in EDPS

GALACTIC

0

Never implemented in OMS

MOONMOD

0

No stray light modeling in EDPS

ZODMOD

0

No stray light modeling in EDPS

OPERATE

0

No SI data in EDPS

PRODNAMn

0

n=(0..9): unneeded

T_ACQ2FL

0

Related keyword ACQ2FAIL is gone

ACQ2FAIL

>0

No SI specific data in EDPS

T_CLMPER

0

Related keyword CLAMPERR is gone

CALMPERR

>0

No SI specific data in EDPS

T_DCFUNC

0

Related keyword DCFUNCHG is gone

DCFUNCHG

>0

No SI specific data in EDPS

T_FGSFAL

0

Related keyword FGS_FAIL is gone

FGS_FAIL

>0

Astrometry specific value not supported

T_FOSOPN

0

Related keyword FOS_OPEN is gone

FOS_OPEN

>0

SI not supported

T_FW_ERR

0

Related keyword FW_ERROR is gone

FW_ERROR

>0

No SI specific data in EDPS

T_HVTOFF

0

Related keyword HVOLTOFF is gone

HVOLTOFF

>0

No SI specific data in EDPS

T_NO_EPH

0

Related keyword NO_EPHEM is gone

NO_EPHEM

>0

EDPS now gets ephemeris from database

T_NO_SAM

0

Related keyword NO_SAM is gone

NO_SAM

>0

EDPS does not monitor slews

T_NOSLEW

0

Related keyword NO_SLEW is gone

NO_SLEW

>0

EDPS does not monitor slews

T_SISAFE

0

Related keyword SI_SAFED is gone

SI_SAFED

>0

No SI specific data in EDPS

T_SISPND

0

Related keyword SISUSPND is gone

SISUSPND

>0

No SI specific data in EDPS

T_TAPDRP

0

Related keyword TAPEDROP is gone

TAPEDROP

>0

No tape recorders in HST now


 

Changes in table file

The jitter table file that has the file extension .jit or .jwt has very few changes. There are still 28 columns of data in the table. Two of the columns have been replaced. Column 23 has changed from EarhMag, that was an estimate of stray light from the Earth based on a model that is no longer support by EDPS, to BrightLimb, which is a short integer value, where 1 indicated that the limb position closest to the target is bright, and 0 indicates it is dark. Column 24 has changed from SI_Specific, that is not supported by EDPS, to FGS_flags, that provides status data for all three FGS. In addition the comment for the DayNight flag has been corrected. The day value is 1 and the night value is 0. These changes affected the values of the keywords: TTYPE23, TUNIT23, TFORM23, TUNIT24, TTYPE24, and TUNIT24. The value of keyword NAXIS1 changed from 116 to 114 because the size of column 23 change from a four-byte floating value to a two-byte short integer value. The keyword ASN_PTYP was added to the association keywords. It has the same value as that keyword in the image file header.

Changes in association file structure

 

In the old obslogs, the jitter files for associated exposures were always collected into files with the same filename extension, .jit, .jwt, .jif, or .jwf, as the member exposures. The file name has the association rootname that is found in keyword ASN_ID. Each member exposure provides a FITS extension for a table or image, having the keyword ASN_MTYPE that describes the type of member. The primary header of the association image file has the following keywords updated to reflect statistics for the set of FITS extensions: TSTRTIME, TENDTIME, MGSSPRMS, TNLOSSES, TLOCKLOS, TNREENT, TRECENTR, TV2_RMS, MV2_P2P, TV3_RMS, MV3_P2P, TRA_AVG, TROLLAVG, T_GDACT, T_ACTGSP, T_GSFAIL, T_SGSTAR, T_TLMPRB, T_NOTLM, T_NTMGAP, T_GSGAP, T_SLEWING, and T_TFDDWN. For STIS associations, the wavecal members are separated from the science members by different file extensions: .jwt and .jwf. The structure for STIS associations has not changed. But for NICMOS and ACS, the file rootnames now match the rootnames of the association products. Only the members that are used to generate the association product are collected into FITS extension for that product. The old obslogs used only the association rootname. The new jitter-file associations may have multiple rootnames, ending in 0, 1, 2, etc. The statistical keywords in the primary header listed above are calculated for the subset of members collected for the specific association product. The ACS associations reserve the rootname of the ASN_ID for dithered data combined from multiple positions. At each position, there is an association product having the last character of its rootname being a sequence starting from 1. If there is no dithered product for ACS, the associated exposures at the single position have a product with a rootname ending in 1.

 


 

 

Header Samples

3

 

Jitter Image File Headers

Here is a sample of a primary header of a jitter image file.

 

SIMPLE = T / data conform to FITS standard

BITPIX = 32 / bits per data value

NAXIS = 0 / number of data axes

EXTEND = T / File may contain standard extensions

NEXTEND = 1 / Number of standard extensions

GROUPS = F / image is in group format

DATE = '2003-05-20' / date this file was written (yyyy-mm-dd)

FILENAME= 'f63b0104j_jif.fits ' / name of file

FILETYPE= 'JIM ' / type of data found in data file

TELESCOP= 'HST' / telescope used to acquire data

INSTRUME= 'FGS ' / identifier for instrument used to acquire data

EQUINOX = 2000.0 / equinox of celestial coord. system

OPUS_VER= 'OPUS 14.0 ' / OPUS software system version number

PDB_VER = 'CCS ' / Project Database version in use

ROOTNAME= 'f63b0104j ' / rootname of the observation set

TARGNAME= 'ADS14859-3-REF ' / proposer's target name

PROC_TYP= 'NORMAL ' / type of pipeline processing

CONFIG = 'FGS ' / proposed instrument configuration

PROPOSID= 8772 / PEP proposal identifier

PROGRMID= '63B' / program id (base 36)

PARALLEL= 'NO ' / indicates if observation taken in parallel

PRIMESI = 'FGS1 ' / instrument designated as prime

TSTRTIME= '2000.215:14:19:34 ' / Predicted Association Window Start Time

TENDTIME= '2000.215:14:20:57 ' / Predicted Association Window End Time

/ POINTING CONTROL DATA

GUIDECMD= 'FINE LOCK ' / Commanded Guiding mode

GSD_ID = '0316902757' / Dominant Guide Star ID

GSD_RA = 319.411350 / Dominant Guide Star RA (deg)

GSD_DEC = 38.379890 / Dominant Guide Star DEC (deg)

GSD_MAG = 10.743000 / Dominant Guide Star Magnitude

GSD_FGS = '3' / Dominant GS Fine Guidance Sensor Number

GSR_ID = '0316901292' / Roll Guide Star ID

GSR_RA = 319.470520 / Roll Guide Star RA (deg)

GSR_DEC = 38.096450 / Roll Guide Star DEC (deg)

GSR_MAG = 11.746000 / Roll Guide Star Magnitude

GSR_FGS = '2' / Roll GS Fine Guidance Sensor Number

GS_PRIM = 'ROLL ' / Guide star that is primary (dominant or roll)

PREDGSEP= 1034.010 / Predicted Guide Star Separation (arcsec)

MGSSPRMS= 0.1 / maximum Guide Star Separation RMS in assoc.

TNLOSSES= 0 / Number of loss of lock events

TLOCKLOS= 0.000000 / Total loss of lock time

TNRECENT= 0 / Number of recentering events

TRECENTR= 0.000000 / Total recentering time

/ LINE OF SIGHT JITTER SUMMARY

TV2_RMS = 2.5 / total association V2 Axis RMS

MV2_P2P = 18.0 / maximum association V2 Axis peak to peak

TV3_RMS = 2.1 / total association V3 Axis RMS

MV3_P2P = 13.2 / maximum total association V3 Axis peak to peak

TRA_AVG = 319.8427236 / total association Average RA

TDEC_AVG= 38.2369780 / total association Average DEC

TROLLAVG= 7.7885872 / total association Average Roll

T_GDACT = T / Actual guiding mode same for all exposures

T_ACTGSP= T / Actual Guide Star Separation same in all exps.

 

/ PROBLEM FLAGS and WARNINGS

 

T_GSFAIL= F / Guide star acquisition failure in any exposure

T_SGSTAR= F / Failed to single star fine lock

T_TLMPRB= F / problem with the engineering telemetry in any e

T_NOTLM = F / no engineering telemetry available in all exps.

T_NTMGAP= 0 / total number of telemetry gaps in association

T_TMGAP = 0.000000 / total duration of missing telemetry in asn. (s)

T_GSGAP = F / missing telemetry during GS acq. in any exp.

T_SLEWNG= F / Slewing occurred during observations

T_TDFDWN= F / Take Data Flag NOT on throughout observations

/ ASSOCIATION KEYWORDS

ASN_ID = 'NONE ' / unique identifier assigned to association

ASN_TAB = 'NONE ' / name of the association table

ASN_MTYP= ' ' / Role of the Member in the Association

ASN_STAT= 'N/A ' / status of association (COMPLETE/INCOMPLETE)

ASN_PROD= F / product created (T/F)

END

 

Here is the sample image extension for the jitter image file.

 

XTENSION= 'IMAGE ' / extension type

BITPIX = 32 / bits per data value

NAXIS = 2 / number of data axes

NAXIS1 = 64 / length of first data axis

NAXIS2 = 64 / length of second data axis

PCOUNT = 0 / number of group parameters

GCOUNT = 1 / number of groups

INHERIT = T / inherit the primary header

EXTNAME = 'jit ' / extension name

EXTVER = 1 / extension version number

ROOTNAME= 'f63b0104j ' / rootname of the observation set

EXPNAME = 'f63b0104j ' / exposure identifier

DATAMIN = 0.0 / the minimum value of the data

DATAMAX = 138.0 / the maximum value of the data

ASN_MTYP= ' ' / Role of the Member in the Association

/ World Coordinate System and Related Parameters

WCSAXES = 2 / number of World Coordinate System axes

CRPIX1 = 32.0 / x-coordinate of reference pixel

CRPIX2 = 32.0 / y-coordinate of reference pixel

CRVAL1 = 319.8423281 / first axis value at reference pixel

CRVAL2 = 38.2369176 / second axis value at reference pixel

CTYPE1 = 'RA---TAN' / the coordinate type for the first axis

CTYPE2 = 'DEC--TAN' / the coordinate type for the second axis

CD1_1 = 7.5303224E-08 / partial of first axis coordinate w.r.t. x

CD1_2 = 5.5042838E-07 / partial of first axis coordinate w.r.t. y

CD2_1 = 5.5042838E-07 / partial of second axis coordinate w.r.t. x

CD2_2 = -7.5303224E-08 / partial of second axis coordinate w.r.t. y

/ IMAGE PARAMETERS

COORDSYS= 'FGS1 ' / Image coordinate system

XPIXINC = 2.0 / Plate scale along X in mas per pixel

YPIXINC = 2.0 / Plate scale along Y in mas per pixel

BETA_1 = 0.00 / Angle from +V3 to image +x(toward +V2)

BETA_2 = 90.00 / Angle from +V3 to image +y(toward +V2)

/ OBSERVATION DATA

OBSET_ID= '01' / observation set id

OBSERVTN= '04 ' / observation number (base 36)

PROCTIME= '2003.140:18:36:52 ' / Date-Time When Observation Processed

/ Date-Time Format is YYYY.DDD:HH:MM:SS

STARTIME= '2000.215:14:19:34 ' / Predicted Observation Window Start Time

ENDTIME = '2000.215:14:20:57 ' / Predicted Observation Window End Time

/ SCIENTIFIC INSTRUMENT DATA

TLMFORM = 'FN ' / Telemetry Format

APERTURE= 'FGS1 ' / Aperture

APER_V2 = 720.740 / V2 Aperture position in Vehicle frame (arcsec)

APER_V3 = -7.350 / V3 Aperture position in Vehicle frame (arcsec)

/ SPACECRAFT DATA

ALTITUDE= 585.83 / Average altitude during observation (km)

LOS_SUN = 123.81 / Minimum Line Of Sight to Sun (deg)

LOS_MOON= 125.32 / Minimum Line Of Sight to Moon (deg)

SHADOENT= '2000.215:13:49:29 ' / Earth shadow last entry (predicted)

SHADOEXT= '2000.215:12:46:58 ' / Earth shadow last exit (predicted)

LOS_SCV = 63.94 / Minimum line of sight to S/C veloc. (deg)

LOS_LIMB= 80.5 / Average line of sight to Earth limb (deg)

 

/ POINTING CONTROL DATA

GUIDEACT= 'FINE LOCK ' / Actual Guiding mode at end of GS acquisition

GSACQ = '2000.215:13:49:49 ' / Actual time of GS Acquisition Completion

ACTGSSEP= 1034.431 / Actual Guide Star Separation (arcsec)

GSSEPRMS= 0.1 / RMS of Guide Star Separation (milli-arcsec)

NLOSSES = 0 / Number of loss of lock events

LOCKLOSS= 0.000000 / Total loss of lock time (sec)

NRECENT = 0 / Number of recentering events (sec)

RECENTR = 0.000000 / Total recentering time

/ LINE OF SIGHT JITTER SUMMARY

V2_RMS = 2.5 / dominant guide star V2 axis RMS (mas)

V2_P2P = 18.0 / dominant guide star V2 axis peak to peak (mas)

V3_RMS = 2.1 / dominant guide star V3 axis RMS (mas)

V3_P2P = 13.2 / dominant guide star V3 axis peak to peak (mas)

RA_AVG = 319.8427236 / Average RA (deg)

DEC_AVG = 38.2369780 / Average DEC (deg)

ROLL_AVG= 7.7885872 / Average Roll (deg)

/ PROBLEM FLAGS and WARNINGS (present only if problem exists)

END

 

Here is the list of optional keywords.

The first two keywords below occur in the primary header of the jitter image file for STIS target acquisition exposures. The optional keywords in the image extension are used for problem flags. These keywords were not present in the sample headers.

 

TACXSLEW= / total target acquisition x-slew in SIAS pixels 
TACYSLEW= / total target acquisition y-slew in SIAS pixels 
 
 / PROBLEM FLAGS and WARNINGS (present only if problem exists)
 
GSFAIL = / Guide star acquisition failure 
SGSTAR = / Scheduled use of guide star 
TLM_PROB= F / problem with the engineering telemetry 
NO_TLM = F / no engineering telemetry available for obs. 
N_TM_GAP= 0 / number of telemetry gaps during observation 
TM_GAP = 0.0 / total duration of missing telemetry (sec.)
GS_GAP = 0.0 / duration of missing tlm. during GS acquisition 
SLEWING = F / Slewing occurred during this observation 
TDF-DOWN= F / take-data-flag not up during entire exposure 

 


 

Jitter Table File Headers

Here is a sample of a primary header of a jitter table file.

 

SIMPLE = T / data conform to FITS standard

BITPIX = 32 / bits per data value

NAXIS = 0 / number of data axes

EXTEND = T / File may contain standard extensions

NEXTEND = 1 / Number of standard extensions

GROUPS = F / image is in group format

DATE = '2003-05-20' / date this file was written (yyyy-mm-dd)

FILENAME= 'f63b0104j_jit.fits ' / name of file

FILETYPE= 'JTB ' / type of data found in data file

TELESCOP= 'HST' / telescope used to acquire data

INSTRUME= 'FGS ' / identifier for instrument used to acquire data

EQUINOX = 2000.0 / equinox of celestial coord. system

OPUS_VER= 'OPUS 14.0 ' / OPUS software system version number

PDB_VER = 'CCS ' / Project Database version in use

ROOTNAME= 'f63b0104j ' / rootname of the observation set

TARGNAME= 'ADS14859-3-REF ' / proposer's target name

PROC_TYP= 'NORMAL ' / type of pipeline processing

CONFIG = 'FGS ' / proposed instrument configuration

PROPOSID= 8772 / PEP proposal identifier

PROGRMID= '63B' / program id (base 36)

/ ASSOCIATION KEYWORDS

ASN_ID = 'NONE ' / unique identifier assigned to association

ASN_TAB = 'NONE ' / name of the association table

ASN_MTYP= ' ' / Role of the Member in the Association

END

 

Here is the sample bintable extension for the jitter table file.

 

XTENSION= 'BINTABLE' / extension type

BITPIX = 8 / bits per data value

NAXIS = 2 / number of data axes

NAXIS1 = 114 / length of first data axis

NAXIS2 = 28 / length of second data axis

PCOUNT = 0 / number of group parameters

GCOUNT = 1 / number of groups

TFIELDS = 28 / number of fields in each table row

INHERIT = T / inherit the primary header

EXTNAME = 'jit ' / extension name

EXTVER = 1 / extension version number

ROOTNAME= 'f63b0104j ' / rootname of the observation set

EXPNAME = 'f63b0104j ' / exposure identifier

OBSET_ID= '01' / observation set id

PROCTIME= '2003.140:18:36:52 ' / Date-Time When Observation Processed

/ JITTER TABLE COLUMNS

TTYPE1 = 'Seconds ' / three second intervals from start

TUNIT1 = 'seconds ' / units of field 1

TFORM1 = 'E ' / format in which field 1 is coded

TTYPE2 = 'V2_dom ' / dominant FGS V2 coordinate

TUNIT2 = 'arcsec ' / units of field 2

TFORM2 = 'E ' / format in which field 2 is coded

TTYPE3 = 'V3_dom ' / dominant FGS V3 coordinate

TUNIT3 = 'arcsec ' / units of field 3

TFORM3 = 'E ' / format in which field 3 is coded

TTYPE4 = 'V2_roll ' / roll FGS V2 coordinate

TUNIT4 = 'arcsec ' / units of field 4

TFORM4 = 'E ' / format in which field 4 is coded

TTYPE5 = 'V3_roll ' / roll FGS V3 coordinate

TUNIT5 = 'arcsec ' / units of field 5

TFORM5 = 'E ' / format in which field 5 is coded

 

TTYPE6 = 'SI_V2_AVG ' / mean jitter in V2 over 3 seconds

TUNIT6 = 'arcsec ' / units of field 6

TFORM6 = 'E ' / format in which field 6 is coded

TTYPE7 = 'SI_V2_RMS ' / rms jitter in V2 over 3 seconds

TUNIT7 = 'arcsec ' / units of field 7

TFORM7 = 'E ' / format in which field 7 is coded

TTYPE8 = 'SI_V2_P2P ' / peak jitter in V2 over 3 seconds

TUNIT8 = 'arcsec ' / units of field 8

TFORM8 = 'E ' / format in which field 8 is coded

TTYPE9 = 'SI_V3_AVG ' / mean jitter in V3 over 3 seconds

TUNIT9 = 'arcsec ' / units of field 9

TFORM9 = 'E ' / format in which field 9 is coded

TTYPE10 = 'SI_V3_RMS ' / rms jitter in V3 over 3 seconds

TUNIT10 = 'arcsec ' / units of field 10

TFORM10 = 'E ' / format in which field 10 is coded

TTYPE11 = 'SI_V3_P2P ' / peak jitter in V3 over 3 seconds

TUNIT11 = 'arcsec ' / units of field 11

TFORM11 = 'E ' / format in which field 11 is coded

TTYPE12 = 'RA ' / Right Ascension of aperture reference

TUNIT12 = 'degrees ' / units of field 12

TFORM12 = 'D ' / format in which field 12 is coded

TTYPE13 = 'DEC ' / declination of aperture reference

TUNIT13 = 'degrees ' / units of field 13

TFORM13 = 'D ' / format in which field 13 is coded

TTYPE14 = 'Roll ' / position angle between north and +V3

TUNIT14 = 'degrees ' / units of field 14

TFORM14 = 'D ' / format in which field 14 is coded

TTYPE15 = 'LimbAng ' / angle between V1 axis and Earth limb

TUNIT15 = 'degrees ' / units of field 15

TFORM15 = 'E ' / format in which field 15 is coded

TTYPE16 = 'TermAng ' / angle between V1 axis and terminator

TUNIT16 = 'degrees ' / units of field 16

TFORM16 = 'E ' / format in which field 16 is coded

TTYPE17 = 'LOS_Zenith' / angle between HST zenith and target

TUNIT17 = 'degrees ' / units of field 17

TFORM17 = 'E ' / format in which field 17 is coded

TTYPE18 = 'Latitude ' / HST subpoint latitude

TUNIT18 = 'degrees ' / units of field 18

TFORM18 = 'E ' / format in which field 18 is coded

TTYPE19 = 'Longitude ' / HST subpoint longitude

TUNIT19 = 'degrees ' / units of field 19

TFORM19 = 'E ' / format in which field 19 is coded

TTYPE20 = 'Mag_V1 ' / magnetic field along V1

TUNIT20 = 'Gauss ' / units of field 20

TFORM20 = 'E ' / format in which field 20 is coded

TTYPE21 = 'Mag_V2 ' / magnetic field along V2

TUNIT21 = 'Gauss ' / units of field 21

TFORM21 = 'E ' / format in which field 21 is coded

TTYPE22 = 'Mag_V3 ' / magnetic field along V3

TUNIT22 = 'Gauss ' / units of field 22

TFORM22 = 'E ' / format in which field 22 is coded

TTYPE23 = 'BrightLimb' / Earth limb of LimbAng is bright (1 or 0)

TUNIT23 = ' ' / units of field 23

TFORM23 = 'I ' / format in which field 23 is coded

TTYPE24 = 'FGS_flags ' / FGS status flags

TUNIT24 = ' ' / units of field 24

TFORM24 = 'E ' / format in which field 24 is coded

TTYPE25 = 'DayNight ' / observation taken during day (1) or night (0)

TUNIT25 = ' ' / units of field 25

TFORM25 = 'I ' / format in which field 25 is coded

TTYPE26 = 'Recenter ' / recentering status flag, event in progress = 1

TUNIT26 = ' ' / units of field 26

TFORM26 = 'I ' / format in which field 26 is coded

TTYPE27 = 'TakeData ' / vehicle guiding status, nominal GS tracking = 1

TUNIT27 = ' ' / units of field 27

TFORM27 = 'I ' / format in which field 27 is coded

TTYPE28 = 'SlewFlag ' / vehicle slewing status, slewing = 1

TUNIT28 = ' ' / units of field 28

TFORM28 = 'I ' / format in which field 28 is coded

END