Special Requirements are used to modify elements of an observation specification or other scheduling element. A Special Requirement may modify the overall timing or pointing for that element (and all lower-level elements it is composed of), or may provide specific settings to be applied to the component exposures (e.g., the APT Value Field LAMP STATE under APT Parameter Field CALIBRATION ). There are two types of Special Requirements: General and Restricted.

General Special Requirements

The General Special Requirements and their parameters are described below.

FIDUCIAL POINT OVERRIDE

This requirement specifies an aperture for pointing (instead of the default aperture) for all exposure pointings in the Observation.

The target is placed at the fiducial point of the override aperture, but data are collected in all apertures regardless of this pointing change. Default apertures and pointing apertures are listed in the APT pointings report.

APT Parameter Field FIDUCIAL POINT OVERRIDE = APT Value Field APERTURE NAME

This requirement takes only one parameter (APERTURE NAME), which is required. Users may select any aperture defined in the Science Instrument Aperture File (SIAF). The SIAF defines apertures and their fiducial points. See Table 1 for a list of available apertures.

Table 1. Apertures for APT Parameter Field FIDUCIAL POINT OVERRIDE

APT Value Field APERTURE NAME (from SIAF)	Description
WFI_01_FULL through WFI_18_FULL	Detectors 1 through 18 on the WFI detector array may be selected individually
BORESIGHT	Telescope boresight
WFI_CEN	Default for WFI instrument
CGI_CEN	Default for CGI instrument

SETTLE MODE EXIT OVERRIDE

APT Parameter Field SETTLE MODE EXIT OVERRIDE = APT Value Field COARSE APT Value Field FINE

Upon exit from Settle Mode (after guide star acquisition), by default the attitude offset is set to zero. The APT Parameter Field SETTLE MODE EXIT OVERRIDE special requirement is used to set attitude offset to either COARSE or FINE instead upon Settle Mode exit.

NON INTERRUPTIBLE PASSES

(added using the Survey Plan form)

This requirement specifies that each Pass in a survey plan step must execute without interruption. If a Pass is repeated, each Pass must not be interrupted, but interruptions are allowed between repeated passes. This special requirement has no parameters.

ORIENT RANGE <min-angle> TO <max-angle>

(added using the Survey Plan form)

This requirement limits the spacecraft orientation to the specified range of angles for each observation in a survey plan step.

APT Parameter Field ORIENT RANGE is specified by APT Value Field MIN-ANGLE and APT Value Field MAX-ANGLE values.

Both APT Value Field MIN-ANGLE and APT Value Field MAX-ANGLE must each be between 0 and 360 degrees.

Each angle indicates a rotation of the spacecraft V3 axis on the sky measured in a counterclockwise direction (North through East) around the target. Note that if the APT Parameter Field ORIENT RANGE crosses zero, the APT Value Field MIN-ANGLE value would be greater than the APT Value Field MAX-ANGLE value. For example: APT Parameter Field ORIENT RANGE = 350 TO 10 degrees specifies a 20 degree range across zero. APT Value Field MIN-ANGLE should be less than APT Value Field MAX-ANGLE otherwise.

In general, a larger range increases opportunities for scheduling. If necessary, it is possible for APT Value Field MIN-ANGLE and APT Value Field MAX-ANGLE to be equal, thus restricting scheduling to a narrow time window when observations at that orient are possible.

Multiple APT Parameter Field ORIENT RANGE requirements may be applied to the same survey plan step to allow multiple acceptable angle ranges. For example:

APT Parameter Field ORIENT RANGE = APT Value Field MIN-ANGLE 1 TO APT Value Field MAX-ANGLE 1

APT Parameter Field ORIENT RANGE = APT Value Field MIN-ANGLE 2 TO APT Value Field MAX-ANGLE 2

APT Parameter Field ORIENT RANGE = APT Value Field MIN-ANGLE 3 TO APT Value Field MAX-ANGLE 3

Multiple Orient Ranges on the same survey plan step may not overlap.

Note for many observations, two angle ranges can have a 180 degree offset and still be schedulable. If this is possible (for greater scheduling flexibility), please specify the additional possible angles. It is also possible for the position angle region to be larger than 180 degrees

If a visit uses multiple targets, the direction of North from the first target will be used to interpret position angle range special requirements. The spacecraft will not roll between targets within a visit, so the position angle range at the subsequent targets may be slightly different from that of the first target.

BETWEEN <START-DATE> AND <END-DATE>

(added using the Survey Plan form)

This requirement specifies that all visits of a survey plan step must start (but not necessarily end) between APT Value Field START-DATE and APT Value Field END-DATE For example, APT Parameter Field BETWEEN 14-SEP-2025 AND 21-SEP-2025 indicates that all visits of the survey plan step must be started after 14 September 2025 and before 21 September 2025.

Valid date formats are listed in Table 1. A date chooser is available in APT.

Multiple APT Parameter Field BETWEEN Special Requirements may be specified on a survey plan step.

Table 1. Date formats for APT Parameter Field BETWEEN Special Requirement

Date formats	Example	Comment
DD-MMM-YYYY:hh:mm:ss	19-APR-2025:00:00:00	MMM is the first three characters of the name of the month in English
YYYY.DDD:hh:mm:ss	2025.109:00:00:00	DDD is the number of the day in the year (1-365, or 1-366 in leap years)

Multiple APT Parameter Field BETWEEN intervals on the same survey plan step may not overlap: all the other intervals must either end earlier than APT Value Field START-DATE or start later than APT Value Field END-DATE

Linking Requirements

These requirements link two or more Survey Steps and specify constraints that apply to the the linked steps.

To add a linking requirement, click Linking Requirements on the Survey Plan form, click Add, then select a link.

After

schedule APT Value Field SURVEY STEP after APT Value Field SURVEY STEP by APT Value Field MIN INTERVAL to APT Value Field MAX INTERVAL

This requirement links two Survey Steps and specifies that observation of one step must start within a specified time interval after the start of the other step.

Survey Step

The step to be observed first. Select a step from the list of all Survey Steps in the program.

After Survey Step

The step to be observed after the first. Select a step from the list of Survey Steps in the program.

Min Interval/Max Interval

Minimum/Maximum interval between steps.

Enter a minimum and a maximum interval. Range is APT Range Field 0 seconds to 10000 days .
Select units. Options are Days, Hours, Minutes, or Seconds.

Same V3 PA

same V3 PA APT Value Field SURVEY STEP ... APT Value Field SURVEY STEP

This requirement links two or more Survey Steps and specifies that all linked steps must be observed at the same orient (V3 position angle).

V3 PA Offset

V3 PA offset APT Value Field SURVEY STEP from APT Value Field SURVEY STEP by APT Value Field MAX PA OFFSET to APT Value Field MIN PA OFFSET degrees

This requirement links two Survey Steps and specifies that one step must be observed at a V3 Position Angle offset from V3 Position Angle of the other step by a specified range (in degrees).

Orient Survey Step

The step that is to be observed at an offset. Select a step from the list of all Survey Steps in the program.

Offset From

The step to offset from. Select a step from the list of all Survey Steps in the program.

Min/Max PA Offset

Enter the minimum and maximum offset in degrees. Range is APT Range Field -180 to 180 degrees .

If necessary, it is possible for APT Value Field MIN PA OFFSET and APT Value Field MAX PA OFFSET to be equal, which greatly restricts the time the observation can be scheduled. For this reason, the difference between the two limits should be as large as possible to make scheduling easier.

Both angles are measured in a counterclockwise direction:

If the position angle region crosses a point 180 degrees from the first APT Value Field SURVEY STEP , APT Value Field MIN PA OFFSET should be positive and APT Value Field MAX PA OFFSET negative.
Otherwise, APT Value Field MIN PA OFFSET should be less than APT Value Field MAX PA OFFSET . It is possible for the position angle region to be larger than 180 degrees.

Restricted Special Requirements

Restricted Special Requirements are only available if the APT Parameter Field ALLOW RESTRICTED checkbox is selected in Program Information. Restricted Special Requirements are described below.

CALIBRATION

APT Restricted Field CALIBRATION

This special requirement specifies the type of calibration and lamp usage for a calibration observation (see Calibration).

ENGINEERING

APT Restricted Field ENGINEERING = APT Value Field ENGINEERING MODE APT Value Field VISIT DURATION

This special requirement specifies the type of engineering observation and duration.

Options for APT Value Field ENGINEERING MODE are APT Value Field MOMENTUM UNLOAD . APT Value Field STATION KEEPING , and APT Value Field GENERAL ENGINEERING . Only one option is allowed.
APT Value Field VISIT DURATION is the duration of the visit in seconds. The range is APT Range Field 1 TO 172800 seconds.

When APT Restricted Field ENGINEERING is used:

The APT Parameter Field PASS TARGET may be any Fixed Target in the program or NONE, but may not be APT Value Field MULTIPLE FIXED TARGETS or a APT Value Field REGION TARGET .

APT Parameter Field MOSAIC , APT Parameter Field DITHER , and APT Parameter Field SUBPIXEL DITHER are set to NONE and are not editable.
APT Parameter Field OPTICAL ELEMENT , APT Parameter Field EXPOSURES/DITHER , APT Parameter Field MA TABLE , APT Parameter Field RESULTANT , and APT Parameter Field OBSERVATION REPEAT are not editable and any values are removed.
All observations in the segment plan must include APT Restricted Field ENGINEERING .
APT Restricted Field CALIBRATION and APT Restricted Field ENGINEERING special requirements are not allowed on the same observation.

FOCUS TYPE OVERRIDE

This special requirement specifies an override of the Focus Type for all exposure pointings in the observation.

APT Restricted Field FOCUS TYPE OVERRIDE = APT Value Field SMALL APT Value Field MODERATE APT Value Field LARGE

REAL TIME

This requirement specifies that the current (engineering) observation should have real time access (i.e. be executed during a contact) to Roman. The APT Restricted Field REAL TIME special requirement has no parameters. When present, a flag is set indicating APT Restricted Field REAL TIME will be used for the observation.

WAVEFRONT CONTROL FILE

This requirement provides the filename of a Wavefront Control File for the selected observation. The wavefront control file name may contain no more than 31 characters and may contain only ASCII letters, numbers, underscore (_), dash (-), and period (.)

For additional questions not answered in this article, please contact the Roman Help Desk at STScI.

Latest Update	29 Mar 2024	Added section on Linking Requirements.
Publication	15 Dec 2022	Initial publication of the article.