6.4 Implementation Only Special Requirements

HST has special requirements that are used to specify scheduling constraints that are used by the Program Coordinators, and this article contains the descriptions of those requirements.

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Format definitions

Boldface type indicates the name of an APT parameter or a value for a parameter.

(red star) Black text indicates an important note.

Magenta text indicates available but unsupported parameters (requires prior approval from STScI).

Red text indicates restricted parameters (for STScI use only).

Brown text indicates text file parameters.

Items in brackets - <value> - are required values.

Items in square brackets - [<value>] - are optional.

Introduction

Most general special requirements directly or indirectly restrict the times when observations (and/or their component visits) can be scheduled. These should be used to provide the schedulers at STScI with enough constraints to ensure that the observations are properly scheduled. Special requirements should not be used unless necessary to accomplish the scientific objectives of the proposal.

Visit Special Requirements

VISIBILITY INTERVAL <time>

This Special Requirement will override the visibility interval normally computed for the visit. No pads will be added, nor will any adjustment be performed based on the target declination. This should not be used in conjunction with the CVZ or SCHEDulability <percentage> Special Requirements.

This Special Requirement may also have the value CORON.

Exposure Special Requirements

MAXimum DURation (time or %) <value>

Allows the Program Coordinator to set limits on the expansion of primary exposures to take advantage of unused orbital visibility. The TRANS tunable constant (enable--adjust t) must be set in a proposal override file to activate MAX DUR. If <time> is specified, the exposure will not be lengthened beyond <time>.If <percentage> is specified, the exposure will not be lengthened beyond <percentage> of the specified exposure time. If <time or percentage> is omitted, the exposure will not be lengthened at all.

MINimum DURation (time or %) <value>

Allows the Program Coordinator to limit shortening of exposures to allow them to fit in a orbital visibility period. The TRANS tunable constant (enable--adjust t) must be set in a proposal override file to activate MIN DUR. If <time> is specified, the exposure may be shortened until its duration is <time>, but not further. If  <percentage> is used, the exposure will be shortened until its duration is decreased to, at most, <percentage> of the specified exposure time.If <time or percentage> is omitted, the exposure will not be shortened at all.

EXPAND (pure parallel exposures only)

Allows the proposer to choose which exposures within an orbit will be expanded to take advantage of unused time at the end of the orbit (note that the exposures will be expanded to fill the orbit unless the MAXimum DURation (time or %) value Special Requirement is also listed). This special requirement can only be used in pure parallel observations; it has no effect on primary exposures. If there is no EXPAND within the orbit, the last exposure in the orbit will be considered for expansion (up to an additional 20%) first, followed by the previous one and the one before that, etc. Exposures containing the EXPAND requirement are considered first for expansion. 

NEW OBSET [FULL ACQ]

NEW ALIGNMENT

These Special Requirements will override the normal decision of whether an exposure will be merged into the same alignment or OBSET as the previous. Using it will force the exposure to start a new OBSET or alignment regardless of the existence or the criticality of any merging rules to the contrary (but error checking will be performed).

In addition, it is possible to force a full guide star acquisition at the beginning of an obset, even if TRANS would not insert one there. The syntax for this capability is NEW OBSET FULL ACQ.

SAME OBSET <exposure-list>

(red star) This has been replaced in the APT GUI with the use of Exposure Groups. See Exposure Containers: Exposure Sequences, Coordinated Parallels and Patterns.

This Special Requirement will override the normal decision of whether the exposures in the same list will be merged into the same OBSET. Using it will force the exposures in <exposure-list> to be included in the same OBSET regardless of the existence or the criticality of any breaking rules to the contrary (but error checking will be performed).

Note that this differs from the SAME GUIDE STARS Special Requirement, which does not necessarily place any requirements on how exposures are to be arranged into obsets.

SAME ALIGNMENT <exposure-list> 

(red star) This has been replaced in the APT GUI with the use of Exposure Groups. See Exposure Containers: Exposure Sequences, Coordinated Parallels and Patterns.

Note that this differs from the SEQ NON-INT Special Requirement, which is purely a timing requirement (it requires exposures not to be separated by earth occultation), and does not necessarily place any requirements on how exposures are to be arranged into alignments. This Special Requirement will override the normal decision of whether the exposures in the same list will be merged into the same alignment. Using it will force the exposures in <exposure-list> to be included in the same alignment regardless of the existence or criticality of any breaking rules to the contrary (but error checking will be performed). The exception is that the alignment may be split if it exceeds the time constraints of the orbital visibility period.

SAME GUIDE STARS <exposure-list> 

(red star) This has been replaced in the APT GUI with the use of Exposure Groups. See Exposure Containers: Exposure Sequences, Coordinated Parallels and Patterns.

This Special Requirement will override the normal decision of whether two obsets must share the same set of guide stars. If two members of <exposure-list> are placed in different obsets, those two obsets will be forced to share the same guide stars regardless of the existence or criticality of any rules which would otherwise assign them separate guide star sets.

GSPAIR <pair-id->

This Special Requirement will tell NGSS to use the specific guide star pair indicated. For pairs, <pair-id> is the 24-character NGSS guide star pair id and is of the form nnnnnnnnnnFdmmmmmmmmmmFe, where nnnnnnnnnn and mmmmmmmmmm are the 10-character guide star ids of the two stars. The Fs are required; d and e are the FGS numbers that the stars are to appear in (that is, 1, 2, or 3). Note that the ordering of the stars is as NGSS will construct the pair.

For singles, <pair-id> is as above except mmmmmmmmmm = ‘0000000000’ and e = ‘0.’

OBSET ID <id>

This allows a non-default OBSET id to be chosen. <id> must be a two-character alphanumeric string and may be specified only once per obset.

EXP PCS MODE [FINE | GYRO] (counterclockwise arrows button EXP PCS MODE=GYRO is not possible under Reduced Gyro Mode)

These Special Requirements allow the PCS requirements for a particular exposure to be overridden. The PCS mode for an OBSET is still computed based on the most restrictive PCS mode in that OBSET. Therefore, in order to override the PCS mode for an entire OBSET with a less restrictive value, it is necessary to place this Special requirement on every exposure within the OBSET, or it should be used at the Visit level.

It is possible for an alignment to be executed on GYRO in an OBSET that uses FGS guiding. If EXP PCS MODE GYRO is included on every exposure within an alignment, it will be executed using gyro guiding, even if it is included in an OBSET which uses FGS guiding.

These may also be entered as EXP PCS MODE F and EXP PCS MODE G.

GS ACQ SCENARIO [PAIR | SINGLE | GYRO | <scenario>] (counterclockwise arrows button Many Scenarios are not possible under Reduced Gyro Mode)

This Special Requirement allows the guide star acquisition scenario for an obset to be overridden. This may be specified only once per obset.

(red star) The uncertainty associated with single guide star acquisition poses a danger to the ACS/SBC, STIS/MAMA and COS detectors. Use of any single guide star acquisition scenario requires approval after an appropriate additional bright object check.

Tables 1 and 2 summarize the legal values for <scenario>.

Table 1: FGS Guiding Scenarios

Scenario NameGyro ModeFGS Guiding ModeSAA Free Orbits OnlyUse FGS 3Comments

One Gyro Scenarios

BASE1O

1G

Pair

No

No

Default for "PAIR" Scenario

BASE1O3

1G

Pair

No

Yes

 

BASE1ONS

1G

Pair

Yes

No

 

BASE1ON3

1G

Pair

Yes

Yes

 

ONEB1O

1G

Single

No

No

Default for "SINGLE" Scenario

ONEB1O3

1G

Single

No

Yes

 

ONEB1ONS

1G

Single

Yes

No

 

ONEB1ON3

1G

Single

Yes

Yes

 

BASE1OR

1G

Pair

No

Yes

counterclockwise arrows button Default Scenario for MT and Spatial Scan Obsets (to turn off FGS2)

BASE1ONR

1G

Pair

Yes

Yes

counterclockwise arrows button available to turn off FGS2 for MT and Spatial Scan Obsets

ONEB1OR

1G

Single

No

Yes

counterclockwise arrows button available to turn off FGS2 for MT and Spatial Scan Obsets

ONEB1ONR

1G

Single

Yes

Yes

counterclockwise arrows button available to turn off FGS2 for MT and Spatial Scan Obsets

Two Gyro Scenarios

BASE1T

2G

Pair

No

No

Default for "PAIR" Scenario

BASE1T3

2G

Pair

No

Yes

 

BASE1TNS

2G

Pair

Yes

No

 

BASE1TN3

2G

Pair

Yes

Yes

 

ONEB1T

2G

Single

No

No

Default for "SINGLE" Scenario

ONEB1T3

2G

Single

No

Yes

 

ONEB1TNS

2G

Single

Yes

No

 

ONEB1TN3

2G

Single

Yes

Yes

 

Three Gyro Scenarios (3GFHST)

BASE1

3GFHST

Pair

No

No

Default for "PAIR" Scenario

BASE13

3GFHST

Pair

No

Yes

 

BASE1NDS

3GFHST

Pair

Yes

No

 

BASE1N3

3GFHST

Pair

Yes

Yes

 

ONEB1

3GFHST

Single

No

No

Default for "SINGLE" Scenario

ONEB13

3GFHST

Single

No

Yes

 

ONEB1NDS

3GFHST

Single

Yes

No

 

ONEB1N3

3GFHST

Single

Yes

Yes

 

COURS1

3GFHST

Pair

 

 

Requires Special Permission

ONEC1

3GFHST

Single

 

 

Requires Special Permission

Three Gyro Scenarios (3GOBAD)

BASE1B

3GOBAD

Pair

No

No

Default for "PAIR" Scenario

BASE1B3

3GOBAD

Pair

No

Yes

 

BASE1BE3GOBADPairNoYes


60s extended time compared to BASE1B3, default "PAIR" Scenario for MT and Spatial Scan Visits

BASE1BR3GOBADPairNoYes

Default Scenario for MT and Spatial Scan Obsets (to turn off FGS2)

BASE1BNE3GOBADPairYesYes

60s extended time compared to BASE1BN3, recommended for use with MT and Spatial Scan Visits

BASE1BNR3GOBADPairYesYes

available to turn off FGS2 for MT and Spatial Scan Obsets

BASE1BNS

3GOBAD

Pair

Yes

No

 

BASE1BN3

3GOBAD

Pair

Yes

Yes

 

ONEB1B

3GOBAD

Single

No

No

Default for "SINGLE" Scenario

ONEB1B3

3GOBAD

Single

No

Yes

 

ONEB1BE3GOBADSingleNoYes


60s extended time compared to ONEB1B3, default "SINGLE" Scenario for MT and Spatial Scan Visits

ONEB1BR3GOBADSingleNoYes

available to turn off FGS2 for MT and Spatial Scan Obsets

ONEB1BNE3GOBADSingleYesYes

60s extended time compared to ONEB1BN3, recommended for use with MT and Spatial Scan Visits

ONEB1BNR

3GOBAD

Single

Yes

Yes

available to turn off FGS2 for MT and Spatial Scan Obsets

ONEB1BNS

3GOBAD

Single

Yes

No

 

ONEB1BN3

3GOBAD

Single

Yes

Yes

 

Mode Independent Scenarios

PAIR

 

Pair

No

No

Use Default Pair Scenario

SINGLE

 

Single

No

No

Use Default Single Scenario

 

Table 2: Gyro Guiding Scenarios

Name (Cannot be set in APT)Gyro Mode

GYROO

1G

GYROT

2G

GYRO

3GFHST

GYROB

3GOBAD



Table of Contents


Change Log

Version Cycle 32 June 2024

  1. PROPINST-91418  - Document new GSACQ scenarios for RGM
  2. PROPINST-91419  - Document changes in availability of features due to change to RGM

Version Cycle 31 June - Aug 2023

  1. PROPINST-91397  - New Guide Star Acquisition Scenarios added to Table 1
  2. Removed old PR link from Change Log.

Version Cycle 26 October 2018

  1. PR.91178 New 3GOBAD guiding scenarios

Initial Conversion HST Cycle 25 Phase II Proposal Instructions (Engineering) Version Cycle 25 (June 2018)