7.1 Introduction to Special Requirements:
Syntax and Rules

Special requirements provide flexibility in specifying the scheduling requirements of observations. Many Special Requirements, directly or indirectly, restrict the times when observations 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 program.

The Special Requirements are summarized in Table 7.1: Supported Formats for Visit Level Special Requirements and Table 7.2: Supported Formats for Exposure Level Special Requirements, and a detailed description of each requirement is provided in the following subsections.

Rules and Conventions

You should observe the following conventions and rules for Special Requirements:

• Items inside angular brackets (< >) in the Special Requirement descriptions are to be replaced with the relevant information. All indicated items must be provided, except for items inside square brackets ([ ]), which are optional.
• A <date> specification in a Special Requirement must either be a geocentric date expressed in Universal Time (UT) or a heliocentric Julian Date. A UT date must be entered in the form DD-MMM-YYYY:hh:mm:ss, where MMM represents the first three letters of the month name. Fractional seconds are not allowed and anything beyond the day specification is optional. For example, 14-DEC-2001:17:05:41 refers to 14 December 2001, geocentric UT 17H05M41S. Only the necessary precision need be employed (e.g., 14-DEC-2001 might be adequate). The SOGS day of the year format, YYY.ddd:hh:mm:ss (where ddd is the day of the year from 001 to 365), is also accepted.
  
  Julian Dates must be entered in the form JDnnnnnnn.nnn (e.g., JD2444123.4) and are legal only for the ZERO-PHASE special requirement. All Julian Dates will be interpreted as heliocentric.
• You should select the units of all <time> specifications from a list provided to you. The options are: days (D), orbits (ORBITS), hours (H), minutes (M), or seconds (S).
• A visit-level Special Requirement (Visit_Requirements) applies to ALL the exposures within that visit.
• An exposure-level Special Requirement (Special_Requirements) applies ONLY to that exposure and any other referenced exposures within the same visit.

Additional Rules and Conventions for the Text Proposal File

If you are editing the Text Proposal File to modify your program, please observe these additional syntax rules:

• You must use only the portions of the keywords that are shown in upper-case letters in Table 7.1 and Table 7.2 and in the discussion below. The portions in lower-case letters are included for clarity only. For example, SEQ must be entered rather than SEQUENTIAL.
• Exposures must be referred to by their exposure numbers. <exposure> must be replaced by the number of a single exposure. An <exposure-list> must be replaced by a single range of exposure numbers separated by a hyphen (e.g. SEQ 2-5 NON-INT). Commas are NOT allowed in exposure lists.
• Multiple Special Requirements must be separated by a semi-colon (;). Please note that separate lines are not sufficient to delimit items in a list. Do not use commas to separate Special Requirements items.

Table 7.2: Supported Formats for Exposure Level Special Requirements

FORMAT	EXAMPLE
Target Acquisition Requirements
INTeractive ACQuisition (obsolete)	No longer available; see text.
Target Position Requirements
POSition TARGet <X-value>,<Y-value>	POS TARG +6.3,-8.1
SAME POSition AS <exposure>	SAME POS AS 6
PATTERN <#> [<exposure-list>] (Replaced by Pattern Containers in the APT User Interface))	See 5.19 Exposure Containers: Exposure Groups, Coordinated Parallels and Patterns and Chapter 8: Pointings and Patterns PATTERN 5 1-4
Special Observation Requirements
PARallel <parallel-exp-list> WITH <primary-exp-list> (replaced by Coordinated Parallel Containers in the APT User Interface)	See 5.19 Exposure Containers: Exposure Groups, Coordinated Parallels and Patterns PAR 4-6 WITH 1-3
SAA CONTOUR <model number>: (supported only for WFPC2)	SAA CONTOUR 02
Special Communications Requirements
RT ANALYSIS	RT ANALYSIS
REQuires UPLINK	REQ UPLINK
REQuires EPHEMeris CORRection <id>	REQ EPHEM CORR OFF-13
Timing Requirements
EXPAND (pure parallel exposures only)	EXPAND
LOW-SKY	LOW-SKY
MAXimum DURation (time or %) <value> (supported only for pure parallel exposures)	MAX DUR 115%
MINimum DURation (time or %) <value> (supported only for pure parallel exposures)	MIN DUR 1800S
PHASE <number1> TO <number2>	PHASE 0.09 TO 0.11
SEQuence <exposure-list> NON-INTerruptible (replaced by Exposure Group Containers in the APT User Interface)	See 5.19 Exposure Containers: Exposure Groups, Coordinated Parallels and Patterns SEQ 2-5 NON-INT
SHADOW	SHADOW

1This special requirement is supported only for config=ACS/HRC, mode=ACCUM exposures that use one of the coronagraphic spot apertures (HRC-CORON1.8, HRC-CORON3.0, HRC-SUB1.8).