Visit Special Requirements summary

HST has special requirements that are used to specify scheduling constraints at the visit level, 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.

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.

Summary Table of Visit-Level Special Requirements

Use the table below to go directly to information for a particular visit-level special requirement.

The following Special Requirements are applicable at the visit level, and they will affect all the exposures within that particular visit. (Visit level Special requirements that are no longer possible under Reduced Gyro Mode are noted.)

Supported Formats for Visit-level Special Requirements

FORMAT	EXAMPLE
Special Observation Requirements
CVZ	CVZ	*Must be indicated in Phase 1 proposal*
SCHEDulability <percentage>	SCHED 100%	Default has changed to 70% due to Reduced Gyro Mode
NOTRACK	NOTRACK
TARGET OF OPPORTUNITY MINIMUM RESPONSE TIME <time> MAXIMUM RESPONSE TIME <time>	TOO MIN RESPONSE TIME 15.0D MAX RESPONSE TIME 18.0D	*Must be indicated in Phase 1 proposal*
TARGET OF OPPORTUNITY FLEX DAY (FLEXIBLE THURSDAY)	TARGET OF OPPORTUNITY FLEX DAY (FLEXIBLE THURSDAY)	*Must be indicated in Phase 1 proposal*
Conditional Requirements
ON HOLD FOR [<visit>]	ON HOLD FOR 15	*Must be indicated in Phase 1 proposal*
Target Orientation Requirements
ORIENTation <angle1> TO <angle2>	ORIENT 18° TO 22°	*Must be indicated in Phase 1 proposal*
ORIENTation <angle1> TO <angle2> FROM <visit>	ORIENT 18° TO 22° FROM 5	*Must be indicated in Phase 1 proposal*
SAME ORIENTation AS <visit>	SAME ORIENT AS 5	*Must be indicated in Phase 1 proposal*
Timing Requirements
AFTER <date>	AFTER 12-JUL-2001:12:06	*Must be indicated in Phase 1 proposal*
AFTER <visit> [BY <time1> TO <time2>]	AFTER 6 BY 7D TO 9D	*Must be indicated in Phase 1 proposal*
BEFORE <date>	BEFORE 14-SEP-1999	*Must be indicated in Phase 1 proposal*
BETWEEN <date1> AND <date2>	BETWEEN 21-DEC-1999 AND 31-DEC-1999	*Must be indicated in Phase 1 proposal*
GROUP <visits> WITHIN <time>	GROUP 5-10 WITHIN 60D	*Must be indicated in Phase 1 proposal*
PERIOD <time> ZERO-PHASE (HJD) <date>	PERIOD 1.23H AND ZERO-PHASE (HJD) 2444000	*Must be indicated in Phase 1 proposal*
SEQuence <visits-checked> WITHIN <time>	SEQ Visits 5-7 WITHIN 24H	*Must be indicated in Phase 1 proposal*
VISIBILITY INTERVAL CORON	VISIBILITY INTERVAL CORON	Not possible under Reduced Gyro Mode
GYRO BIAS UPDATE	GYRO BIAS UPDATE
Guiding Requirements
PCS MODE Fine	PCS MODE Fine
PCS MODE Gyro	PCS MODE Gyro	Not possible under Reduced Gyro Mode
GUIDing TOLernace <angle> (arcsec)	GUID TOL 0.020"	Not possible under Reduced Gyro Mode
DROP TO GYRO [NO REACQuisition]	DROP TO GYRO	Not possible under Reduced Gyro Mode
NO SINGLE STAR GUIDING	NO SINGLE STAR GUIDING
Limited-Access Requirements
BRIGHT EARTH AVOIDance <angle in degrees>	BRIGHT EARTH AVOID 25
PARallel	PAR
GYRO MODE <value>	GYRO MODE 2G	Default and currently only possible value is 1G due to Reduced Gyro Mode

Change Log

Version Cycle 34 June 2026

Moved the Guiding Requirements down on the page since most are no longer relevant.

Version Cycle 34 April 2026

PROPINST-91440 Correct the documentation of the BEA (removed detailed footnote)
PROPINST-91421 Removed NO GYRO BIAS UPDATE ON MOVING TARGET and added GYRO BIAS UPDATE
PROPINST-91442 TARGET OF OPPORTUNITY RESPONSE TIME Should Specify Min and Max
PROPINST-91452 New Special Requirement to opt out of new single-star guiding defaults

Version Cycle 32 June 2024

PROPINST-91419 Document changes in availability of features due to change to RGM

Version Cycle 31 June-July 2023

PROPINST-91390 Add "Flexible Thursday" Target of Opportunity

Version Cycle 30 April 2022

PROPINST-91383 Emphasize which special requirements should have been preapproved in Phase I (Added to table)

Version Cycle 29 April 2021

PROPINST-91379 - VISIBILITY INTERVAL MOVING TARGET

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6.2 Visit-level Special Requirements