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 Table7.1: Supported Formats for Visit Level Special Requirements and Table7.2: Supported Formats for Exposure Level Special Requirements, and a detailed description of each requirement is provided in the following subsections.
The following conventions and rules should be observed when reading the descriptions of the Special Requirements and when entering them.
- It is permissible to 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 could be entered rather than SEQUENTIAL.
- 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. For example, the general specification SEQuential <visit-list> [WITHIN <time>] means that SEQ 5Ð7 WITHIN 10D and SEQ 5Ð7 are acceptable, but SEQ WITHIN 10D is not.
- Exposures must be referred to by their exposure numbers. <exposure> must be replaced by the number of a single exposure. <exposure-list> must be replaced by one of the following: A single exposure number; several exposure numbers separated by commas or spaces; or a range of exposure numbers separated by a hyphen. The following are all valid examples for SEQuence <exposure-list> NON-INTerruptible:
SEQ 2-5 NON-INT, SEQ 4, 5, 11 NON-INT, SEQ 6-7 14-15 NON-INT. Hyphens may be used in exposure lists to indicate a range (e.g., SEQ 15Ð17 NON-INT).
- 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.s, where MMM represents the first three letters of the month name. For example, 14-DEC-2001:17:05:41.1 refers to 14 December 2001, geocentric UT 17H05M41.1S. Only the necessary precision need be employed (e.g., 14-DEC-2001 might be adequate), but four-digit years are now mandatory. Julian Dates must be entered in the form JDnnnnnnn.nnn (e.g., JD2444123.4). Only the required precision need be provided. All Julian Dates will be interpreted as heliocentric.
- All <time> specifications must be expressed in one of the following: days (D), orbits (ORBITS), hours (H), minutes (M), or seconds (S). All other time units (such as weeks, months or years), as well as combined time units (such as 14D 15H), are not permitted.
- Multiple Special Requirements entered on the same line may be separated by a semi-colon (;) for the sake of readability, but this is now optional. Multiple Special Requirements separated by different lines need no further delimiting. Under no circumstances should a comma be used to separate Special Requirements.
- 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. For example, SEQ 4Ð6 NON-INT on exposure 1 means that exposures 4-6 MUST be in the same visit as the exposure 1.
Table 7.1: Supported Formats for Visit Level Special Requirements
Table 7.2: Supported Formats for Exposure Level Special Requirements
