HST Keyword Dictionary

Space Telescope Science Institute

3700 San Martin Drive

Baltimore, MD 21212

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Keyword Definitions for the

dated 14-APR-94

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ANGLESEP
angular separation of target from reference object 
Datatype: REAL*4              
Units:    ARCSEC
See PA_REF. This is the angular distance of the target from the reference object. (Not yet supported. Always zero.)

Source : SCS

ANNPARRA
annual parallactic shift for non-solar system target 
Datatype: REAL*4              
Units:    ARCSEC
The magnitude of the parallactic shift in the position of the non-solar system target at the time of observation. Always smaller than PARALLAX, and its magnitude of variation over the year depends on the ecliptic latitude of the target.

Source : SCS

APEROBJ
SI object aperture ID 
Datatype: CHARACTER*10        
Units:    NAME
Specifies the SI aperture and SI coordinate system to be used for the observation of the target. For a single aperture there may be multiple coordinate systems having different reference positions, orientations, or scaling.

Source : TRANS

APEROFFX
X comp of object offset in aperture 
Datatype: REAL*4              
Units:    ARCSEC
X component of the offset of the target from the center of the aperture. If coord_typ = SIAS, then units are pixels; if coord_typ = SICS, then units are arc-seconds.

Source : TRANS or SPSS

APEROFFY
Y comp of object offset in aperture 
Datatype: REAL*4              
Units:    ARCSEC
Y component of the offset of the target from the center of the aperture. If coord_typ = SIAS, then units are lines; if coord_typ = SICS, then units are arc-seconds.

Source : TRANS or SPSS

APERSKY
SI sky aperture ID 
Datatype: CHARACTER*10        
Units:    ARCSEC
Specifies the aperture and coordinate system of the instrument to be used for the sky background light observations in conjunction with the observation of the target.

Source : TRANS

APERTYPE
aperture type (SIAS, SICS) 
Datatype: CHARACTER*18        
Units:    NAME                
	SIAS = SI aperture system, a coordinate system based on the                    
		aperture or fov of the si;                                                    
	SICS = SI corrected system which in general differs from the                   
		sias by removal of distortions and scale changes. This                        
               is the default aperture coordinate type.

Source : TRANS or SPSS

DEC_MOON
declination of the Moon 
Datatype: REAL*8              
Units:    DEGREES
Geocentric J2000 coordinates. Epoch is at the predicted start of observation (PSTRTIME).

Source : SCS

DEC_REF
declination of reference object 
Datatype: REAL*8              
Units:    DEGREES
J2000.0 coordinates. Reference target is that used for target acquisition. (Not yet supported. Always same as DEC_TARG.)

Source : SCS

DEC_SUN
declination of the Sun 
Datatype: REAL*8              
Units:    DEGREES
Geocentric J2000 coordinates. Epoch is at the predicted start of observation (PSTRTIME).

Source : SCS

DEC_V1
declination of V1 axis of ST 
Datatype: REAL*8              
Units:    DEGREES
J2000.0 coordinates. The V1 axis is the optical axis of the Space Telescope, defined with respect to FGS2. The epoch of the position of the V1 axis is the predicted start of observation.

Source : SCS

DGESTAR
Dominant guide star ID concat. w/ FGS ID(F1,F2,F3) 
Datatype: Character*12        
Units:    NAME
The dominant GS controls the pointing. If blank, this observation was on gyro pointing control.

Source : GSSS

EPLONGPM
epoch of longitude of prime meridian 
Datatype: REAL*4              
Units:    SEC
For longitude of prime meridian of planetary target in seconds from 1980. (Not yet supported. Always zero.)

Source : NONE

EQRADTRG
equatorial radius of target 
Datatype: REAL*4              
Units:    KILOMETERS
Radius of planetary target at equator. (Not yet supported. Always zero.)

Source : NONE

FLATNTRG
flattening of target 
Datatype: REAL*4              
Units:    ratio
For planetary target, the difference between the equatorial and polar radius divided by the equatorial radius. (Not yet supported. Always zero.)

Source : NONE

LONGPMER
longitude of prime meridian 
Datatype: REAL*4              
Units:    DEGREES
Prime meridian of planetary target. (Not yet supported. Always zero.)

Source : NONE

MTFLAG
moving target flag; T if it is a moving target 
Datatype: CHARACTER*01        
Units:
Set to T (for true) if moving target is being tracked, otherwise blank.

Source : SCS

NPDECTRG
north pole declination of target 
Datatype: REAL*4              
Units:    DEGREES
Direction of north pole of planetary target. Used with NPRATRG. (Not yet supported. Always zero.)

Source : NONE

NPRATRG
north pole right ascension of target 
Datatype: REAL*4              
Units:    DEGREES
Direction of north pole of planetary target. Used with NPDECTRG. (Not yet supported. Always zero.)

Source : NONE

PAR_CORR
parallax correction used 
Datatype: CHARACTER*01        
Units:    T/F
Indicates that HST-orbit parallax is applied for solar system targets. Not meaningful for fixed targets where Earth-orbit parallax is always applied when PARALLAX is supplied in proposal.

Source : TRANS or SPSS

PA_APER
position ang of aperture used with target 
Datatype: REAL*4              
Units:    DEGREES
This value is computed before the observation, rather than spacecraft measured. This is the angle from North, towards East, of the +Y axis of the Science Instrument Corrected System (SICS) coordinates for the aperture designated by APEROBJ. The direction of North is taken at the target even when he target is not centered in the FOV. For FOC, the zoomed FOV have the SICS Y axis aligned with the direction of increasing pixel. In the group data, the Y axis (for the CD matrix and ORIENTAT) is always the direction of increasing line. For these zoomed FOC apertures, that can be identified as those with a Z in the fourth caharcter in APEROBJ, the value of PA_APER will be 90 degrees larger than the ORIENTAT value in the group data. For FOS, in the right-handed XY coordinate system of the detector, this is the angle one rotates the image clockwize in order for North to coincide with +Y. The FOS APEROBJ values that end in "BAR" have a PA_APER value 90 degrees larger than ORIENTAT.

Source : SCS

PA_REF
position ang of target from ref. object 
Datatype: REAL*4              
Units:    DEGREES
See ANGLESEP. Reference target is used for target acquisition. (Not yet supported. Always zero.)

Source : SCS

PA_V3
position angle of v3 axis of st 
Datatype: REAL*4              
Units:    DEGREES
This is the angle from North, towards East, of the V3-axis of the vehicle coordinate system. The direction of North is taken at the V1 axis. Position angles measured from North at different right ascensions, such as at the target position for PA_APER or the aperture reference position for ORIENTAT, will include a small correction for the difference in the direction of North.

Source : SCS

POSTNSTX
position of Space Telescope X axis 
Datatype: REAL*8              
Units:    KILOMETERS
X-axis coordinate of the Space Telescope position in orbit at the predicted start time of observation. The coordinates are in the geocentric J2000.0 inertial coordinate system. This is a right-handed coordinate system centered in the Earth, with the X axis pointing towards the vernal equinox for the year 2000, the Z-axis pointing towards the north celestial pole for the year 2000, and the Y axis orthogonal to both.

Source : SCS

POSTNSTY
position of Space Telescope Y axis 
Datatype: REAL*8              
Units:    KILOMETERS
Y-axis coordinate of the Space Telescope position in orbit at the predicted start time of observation. The coordinates are in the geocentric J2000.0 inertial coordinate system. This is a right-handed coordinate system centered in the Earth, with the X axis pointing towards the vernal equinox for the year 2000, the Z-axis pointing towards the north celestial pole for the year 2000, and the Y axis orthogonal to both.

Source : SCS

POSTNSTZ
position of Space Telescope z axis 
Datatype: REAL*8              
Units:    KILOMETERS
Z-axis coordinate of the Space Telescope position in orbit at the predicted start time of observation. The coordinates are in the geocentric J2000.0 inertial coordinate system. This is a right-handed coordinate system centered in the Earth, with the X axis pointing towards the vernal equinox for the year 2000, the Z-axis pointing towards the north celestial pole for the year 2000, and the Y axis orthogonal to both.

Source : SCS

PSTPTIME
predicted observation stop time 
Datatype: CHARACTER*          
Units:    DATE
Actually, this is the start time for the next non-parallel observation on the SMS. The format is (yyyy.ddd:hh:mm:ss) where 
		yyyy is year,                                                                 
		ddd is day of year,                                                           
		hh is hour,                                                                   
		mm is minutes,                                                                
		ss is seconds.

Source : SCS

PSTRTIME
predicted observation start time 
Datatype: CHARACTER*          
Units:    DATE
This prediction can be in error by a few minutes, since it is determined in orbit relative time before the actual flight HST orbit model is generated. The format is (yyyy.ddd:hh:mm:ss) where 
		yyyy is year,                                                                 
		ddd is day of year,                                                           
		hh is hour,                                                                   
		mm is minutes,                                                                
		ss is seconds.

Source : SCS

RA_MOON
right ascension of the Moon 
Datatype: REAL*8              
Units:    DEGREES
Geocentric J2000 coordinates. Epoch is at the predicted start of observation (PSTRTIME).

Source : SCS

RA_REF
right ascension of reference object 
Datatype: REAL*8              
Units:    DEGREES
J2000.0 coordinates. Reference target is that used for target acquisition. (Not yet supported. Always same as RA_TARG.)

Source : SCS

RA_SUN
right ascension of the Sun 
Datatype: REAL*8              
Units:    DEGREES
Geocentric J2000 coordinates. Epoch is at the predicted start of observation (PSTRTIME).

Source : SCS

RA_V1
right ascension of v1 axis of st 
Datatype: REAL*8              
Units:    DEGREES
J2000.0 coordinates. The V1 axis is the optical axis of the Space Telescope. The epoch of the position of the V1 axis is the predicted start of observation.

Source : SCS

ROTRTTRG
rotation rate of target 
Datatype: REAL*4              
Units:    DEGREES/DAY
For planetary targets. (Not yet supported. Always zero.)

Source : NONE

S0INVMAG
S0 inverse magnitude 
Datatype: REAL*8              
Units:    1/KM
The S0 is the initial position vector of the moving target in GCI coordinates. This keyword is the inverse distance.

Source : SCS

S0XDIR
S0 X direction 
Datatype: REAL*8              
Units:    NONE
The X component of the unit vector for the direction of the initial position (S0) of the moving target in GCI system.

Source : SCS

S0YDIR
S0 Y direction 
Datatype: REAL*8              
Units:    NONE
The Y component of the unit vector for the direction of the initial position (S0) of the moving target in GCI system.

Source : SCS

S0ZDIR
S0 Z direction 
Datatype: REAL*8              
Units:    NONE
The z-component of the unit vector for the direction of the initial position (S0) of the moving target in GCI system.

Source : SCS

SAAAVOID
SAA model for SAA Avoidance (range 02-99) 
Datatype: CHARACTER*02        
Units:    MODEL_NUM
South Atlantic Anomaly (SAA) avoidance. An integer value with range of 02-99. The SAA/RFI region is modelled by a convex polygon, the arcs between whose vertices lie along great circles. The vertices are ordered such that the interior of the SAA/RFI region remains to the left as the boundary of the polygon is traced.

Source : TRANS

SGESTAR
Subdominant guide star ID concat. w/ FGS ID(F1,F2,F3) 
Datatype: CHARACTER*12        
Units:    NAME
The subdominant GS controls the roll. If blank, this observation was on gyro roll control.

Source : GSSS

SURFALTD
surface feature altitude 
Datatype: REAL*4              
Units:    KILOMETERS
Planetary surface feature. (Not yet supported. Always zero.)

Source : NONE

SURFLATD
surface feature latitude 
Datatype: REAL*4              
Units:    DEGREES
Planetary surface feature. (Not yet supported. Always zero.)

Source : NONE

SURFLONG
surface feature longitude 
Datatype: REAL*4              
Units:    DEGREES
Planetary surface feature. (Not yet supported. Always zero.)

Source : NONE

T51_ANGL
position angle of motion of aperture 
Datatype: REAL*4              
Units:    DEGREES
This parameter is determined only for moving targets. The position angle in degrees from North towards East of the slew that tracks the target.

Source : SCS

T51_RATE
rate of motion commanded 
Datatype: REAL*4              
Units:    ARCSECS/SEC
This parameter is determined only for moving targets. The magnitude of the angular velocity of the slew that tracks the target.

Source : SCS

TARAQMOD
target acquisition mode (values 00, 01, 02, 03) 
Datatype: CHARACTER*02        
Units:    N/A                 
		00 = null, no external target                                                 
		01 = ground assisted,                                                         
		02 = onboard computer assisted,                                               
		03 = fixed simple pointing.

Source : TRANS

TARGDIST
distance to target from Earth's center 
Datatype: REAL*8              
Units:    KM
This parameter is determined only for moving targets. This is calculated using the time of the observation and the Chebychev Interpolating Polynomial coefficients for the position vector of the target. The target distance is the norm of this position vector.

Source : SCS

TARG_ID
SPSS target ID from proposal+target no. 
Datatype: CHARACTER*15        
Units:    N/A
This target ID is unique within SPSS. It can be used to collect observations within one proposal having the same target. This name was generated by TRANS. See TARGNAME for the name found in the proposal.

Source : TRANS

TRK_TYPE
track 48 or track 51 commanding used (T48, T51, NO) 
Datatype: CHARACTER*03        
Units:    N/A
Specifies the ST pointing mode. If the pointing mode is track48 or track 51, the target must be a moving target. Track 51 mode is a single uninterruptable profiled slew command which tracks along a great circle. Track 48 is the secondary motion command which can follow more complicated motions using fourth degree polynomials. (T48 is not yet supported.)

Source : TRANS

V2APERCE
V2 offset of target from aper. center 
Datatype: REAL*4              
Units:    ARCSEC
The X component of the aperture offset position in the ST coordinate system. The V2 offset of the target from the aperture center.

Source : PEP and TRANS

VELABBRA
aberration in position of the target 
Datatype: REAL*4              
Units:    ARCSEC
Magnitude of aberration due to ST and Earth velocities. This is the absolute angular correction that must be applied to the apparent position of the target as seen from the ST to compensate for the velocity of the ST and the Earth. This is the value calculated at SMS generation rather than the value applied by flight software.

Source : SCS

VELOCSTX
velocity of Space Telescope along X axis 
Datatype: REAL*8              
Units:    KM/SEC
X component of the velocity of Space Telescope in geocentric J2000,0 inertial coordinates. This is a orthogonal right handed coordinate system centered in the Earth, with the X axis pointing towards the vernal equinox for the year 2000, the Z axis pointing towards the north celestial pole for the year 2000, and the Y axis orthogonal to both.

Source : SCS

VELOCSTY
velocity of Space Telescope along Y axis 
Datatype: REAL*8              
Units:    KM/SEC
Y component of the velocity of Space Telescope in geocentric J2000,0 inertial coordinates. This is a orthogonal right handed coordinate system centered in the Earth, with the X axis pointing towards the vernal equinox for the year 2000, the Z axis pointing towards the north celestial pole for the year 2000, and the Y axis orthogonal to both.

Source : SCS

VELOCSTZ
velocity of Space Telescope along z axis 
Datatype: REAL*8              
Units:    KM/SEC
Z component of the velocity of Space Telescope in geocentric J2000,0 inertial coordinates. This is a orthogonal right handed coordinate system centered in the Earth, with the X axis pointing towards the vernal equinox for the year 2000, the Z axis pointing towards the north celestial pole for the year 2000, and the Y axis orthogonal to both.

Source : SCS

WRD11_14
word 11/14 (0-255) 
Datatype: INTEGER*2           
Units:    COUNT
The science telemetry word 11/14 is a count which is kept for each instrument an updated for each observation using the instrument. The count rolls over every 255.

Source : SCS

HST Keyword Dictionary: 14-APR-94: (rose@stsci.edu)