The Special Requirements and their parameters are described below. 

Fiducial Point Override

(added using the Pass Plan form)

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. 

FIDUCIAL POINT OVERRIDE = Aperture Name

This requirement takes only one parameter (a selected 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 for Apertures for a list of available apertures.

Settle Mode Exit Override

(added using the Pass Plan form)

SETTLE MODE EXIT OVERRIDE = COARSE FINE

When  SETTLE MODE EXIT OVERRIDE is set to COARSE , there will be no Fine Guidance System (FGS) guiding for the Visits resulting from that Observation.

Non Interruptible Passes

(added using the Survey Plan form)

This requirement specifies that each Pass in a survey step must execute without interruption by other science programs. Interruptions by any required calibrations, momentum unloads, or station keeping maneuvers are permitted. If a Pass is repeated, each Pass must not be interrupted, but interruptions are allowed between repeated passes. This special requirement has no parameters.

  NON INTERRUPTIBLE PASSES is not available for Survey Steps that include a Region Target.

V3 PA Range

(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.

V3 PA RANGE is specified by MIN-ANGLE   and MAX-ANGLE values.

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 V3 PA RANGE crosses zero, the MIN-ANGLE value would be greater than the MAX-ANGLE value. For example: V3 PA RANGE = 350 TO 10 degrees specifies a 20 degree range across zero. MIN-ANGLE should be less than MAX-ANGLE otherwise.

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

Multiple V3 PA RANGE requirements may be applied to the same survey plan step to allow multiple acceptable angle ranges. For example:

V3 PA RANGE = MIN-ANGLE 1 TO MAX-ANGLE 1

V3 PA RANGE = MIN-ANGLE 2 TO MAX-ANGLE 2

V3 PA RANGE = MIN-ANGLE 3 TO MAX-ANGLE 3

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

Background Limited

(added using the Survey Plan form)

BACKGROUND LIMITED does not take any additional values.

This requirement specifies that the visits of a survey plan step to which the requirement is applied are background-limited and should be scheduled such that the total background is not more than 50% larger than the minimum background at the given location. I.e., the background at the time of the observations will be less than or equal to 1.5 times the lowest background level at any time of the year for which the specific target is observable. This ensures that in the background-limited signal-to-noise-ratio (SNR) regime the SNR will be not lower than 75% of the best SNR attainable at the specified location.

Note that SNR ~ $//<![CDATA[ \begin{array}{l}1/\sqrt{background}\end{array} //]]>$ in such regime, so a 50% increase in background corresponds to a 25% decrease in SNR. 

Between

(added using the Survey Plan form)

This requirement specifies that all visits of a survey plan step must start (but not necessarily end) between START-DATE and END-DATE   For example,  BETWEEN 14-SEP-2027 AND 21-SEP-2027 indicates that all visits of the survey plan step must be started after 14 September 2027 and before 21 September 2027.

Valid date formats are listed in the Table of Date formats. A date chooser is available in APT.

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

On Hold

(added using the Survey Plan form)

ON HOLD   COMMENT

This requirement specifies that the visits of a survey plan step should not be executed without further guidance from the observer (such as with a Target of Opportunity).  Enter a comment describing the reason for the hold.

Target of Opportunity

(added using the Survey Plan form)

This requirement indicates that the visits of a survey plan step will be executed as a Target of Opportunity. See Target of Opportunity in Fixed Targets.

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