Solar System Special Requirements (e.g. ANGULAR RATE, SOLAR PHASE) are used to restrict the scheduling of JWST observations by moving target constraints. The Astronomer’s Proposal Tool (APT) is used to enter the requirements into the proposal.

Introduction

Solar System special requirements are provided to allow the proposer to define geometric and timing constraints (observing windows) for solar system targets. The proposer should specify any constraints necessary to achieve the scientific objectives of the proposal. However, care should be taken in specifying constraints, since they can render the observations difficult or impossible to schedule.

In general, observing windows which define when the target is visible to JWST need not be explicitly identified, since these windows will be calculated by STScI. Observing windows in this category include:

• Times when the target is within the JWST Field of Regard.
• If the target is a planetary satellite, the times when it is not occulted by any other object in the planetary system.
• If the target is a surface feature on a body, the times when the feature is within the field of view of the JWST (i.e. the feature is on that part of the body “facing” JWST).

If you require other specific conditions to be satisfied (e.g. to observe when a satellite is near elongation, to observe when the central meridian longitude lies in a particular range, etc.), then these conditions must be specified using the special requirements below. However, the proposer must recognize that proposer-supplied requirements might not overlap with the “visibility” windows defined above (calculated by STScI), in which case the observation cannot be scheduled.

For most observations the exact definition of when a visit starts is not important. But for a very tight Solar System Target observing window it could be important.  

The window constrains when the beginning of the first science activity in the observation should begin.The start of the science activities in a visit is after the end of the slew and guide star acquisition activities. If the visit has a target acquisition then the start time is after the end of the target acquisition, and any slew to the first science pointing. Otherwise, the start time is the start of the science observation activity, which includes any mechanism and science instrument configuration.

Rules and Conventions 

You should observe the following conventions and rules for special requirements:

• A <date> specification in a Special Requirement must be a geocentric date expressed in Universal Time (UT). There are several formats for specifying a UT date, and these are described in General Rules for Specifying Dates/Times (future link). For example, 2011-DEC-14:17:05:41 refers to 14 December 2011, geocentric UT 17H05M41S. Only the necessary precision need be employed (e.g., 2011-DEC-14 might be adequate), but four-digit years are mandatory.

• An observation-level special requirement applies to ALL the visits within that observation.

 

 Table 1. Supported Formats for Solar System Special Requirements

Solar System Requirements Operators 

The following operators are available for Solar System special requirements:

• LESS THAN
• GREATER THAN
• LOCAL MAXIMUM (i.e. inflection point) with non-zero tolerance
• LOCAL MINIMUM (i.e. inflection point) with non-zero tolerance
• NOT (logical complement; may be used to specify when a condition does not exist. Invoked by selecting Not Within.)

The operator NOT, if present, should precede the special requirement as in these examples:

NOT TRANSIT OF IO ACROSS JUPITER FROM EARTH

NOT ECLIPSE UMBRAL OF JUPITER BY GANYMEDE

NOT OCCULTATION OF EUROPA BY JUPITER FROM EARTH

Individual Solar System Requirements

 SEPARATION OF <object1> <object2> FROM <observer> <condition> <angle>

This requirement is used to find the times when the apparent separation between two objects, as observed from a third object, satisfies certain conditions. The separation between two bodies is defined as the angle between the closest points on the observed limbs of the spheres representing the objects as viewed from the observer (the radius of the sphere is equal to the largest radius of the tri-axial ellipsoid representation of the object). <object1>, <object2>, and <observer> must either be standard bodies, or objects that have been previously defined in the target position fields. Degrees, arc-minutes, or arc-seconds are selectable as units of <angle>. The interpretation of the SEPARATION keyword is that when the <condition> is either LESS THAN or GREATER THAN, times are found when the separation of <object1> and <object2>, as viewed from <observer>, is LESS THAN <angle> or greater than <angle>. When the <condition> is LOCAL MAXIMUM (MINIMUM), then times are found when <object1> and <object2> are at maximum elongation (minimum separation), as viewed from <observer>.

 DISTANCE <object1> <object2> <condition> <distance>

This requirement is used to select windows based on the separation of objects in terms of distance (AU).

 ANGULAR RATE <object1> [RELATIVE <object2>] FROM <observer> <condition> <rate>

This requirement is used to select windows based on the angular rate of objects in terms of arcsec/sec. When <condition> is GREATER THAN or LESS THAN, then <rate> is interpreted as the apparent angular rate of <object1> as observed from <observer> - unless <object2> is also specified. If <object2> is specified, then <rate> is interpreted as the apparent angular rate of <object1> relative to <object2> as observed from <observer>. When <condition> is LOCAL MINIMUM or LOCAL MAXIMUM, then <rate> is interpreted as a tolerance relative to local minimum or maximum inflection points rather than as a absolute angular rate.

For every observation of a solar system target, the following default ANGULAR RATE requirement is added: ANGULAR RATE <object1> FROM JWST LESS THAN <rate>. This requirement may not be removed by the user. The user is allowed to edit the <rate>, but rates ≥ 1.0 (max_moving_target_velocity) are not allowed. (PRD values referenced in this section are converted to units of arcseconds/second).

For all observations (except observations in SURVEY proposals):

• <rate> initially defaults to .075 (spacecraft_parameters.max_moving_target_science_velocity).
• <rate> greater than .075 is allowed but with a warning.  

For observations in SURVEY proposals:

• <rate> initially defaults to .01 (spacecraft_parameters.max_moving_target_survey_velocity).
• <rate> greater than .01  is allowed but with a warning.

 RADIAL VELOCITY <object1> <object2> <condition> <velocity>

This requirement is used to select windows based on the change in distance between two objects (i.e. the Radial Velocity) in km/sec. Positive values of <velocity> mean that the objects are moving away from each other while negative values mean that the objects are moving closer to each other.

 APPARENT DIAMETER <object> <condition> <angle>

This requirement is used to select windows based on the apparent angular diameter of an object in arc-seconds.

 SOLAR PHASE OF <object> FROM <observer> BETWEEN <min-angle> <max-angle>

This requirement is used for solar phase angle, and is used to find times when the angular phase of one body as seen from another is within a specified range. <angle> is the observer-object-sun angle, in degrees.

 OCCULATATION OF <occulted object> BY <occulting object> FROM <observer>

This requirement is used to find times when one body appears to pass behind another body as viewed from a third body. The <occulted object>, <occulting object>, and <observer> must be standard bodies from Solar System Standard Targets. An occultation is defined to begin when the limb of the sphere representing the <occulted object> first touches the limb of the sphere representing the <occulting object>, as seen from the vantage point of the <observer>.

 TRANSIT OF <transiting object> ACROSS <transited object> FROM <observer>

This requirement is used to find times when one body appears to pass across the disk of another body as viewed from a third body. The <transiting object>, <transited object>, and <observer> must be standard bodies from Solar System Standard Targets. A transit is defined to begin when the disk representing the <transiting object> is entirely in front of the disk representing the <transited object>, as seen from the vantage point of the <observer>. The transit ends when the limbs of the two disks come into contact again. Thus at any time in the transit the <transiting object> is entirely surrounded by the <transited object>.

 ECLIPSE <shadow type> <completeness> OF <eclipsed object> BY <eclipsing object> FROM <observer>

This requirement is used to find times when one body is in the shadow (cast in sunlight) of another body. The <eclipsed object>, <eclipsing object>, and <observer> must be standard targets from Solar System Standard Targets. <shadow type> must be specified as either PENUMBRAL or UMBRAL. <completeness> must be specified as either FULL or PARTIAL. <observer> defaults to JWST.

A partial eclipse is defined to begin when the observer would see the limb of the eclipsed sphere enter the umbra or penumbra of the eclipsing sphere. The partial eclipse ends when the last part of the limb of the eclipsed body would be observed to leave the umbra or penumbra of the eclipsing sphere.  A full eclipse is defined to begin when the observer would see the entire eclipsed sphere enter the umbra or penumbra of the eclipsing sphere. The full eclipse ends when the entire eclipsed body would be observed to leave the umbra or penumbra of the eclipsing sphere.

Note for developers: the options for completeness are new, so they must be given a reactive check. Also note that observer should default to JWST.

 CENTRAL MERIDIAN LONGITUDE OF <object> FROM <observer> BETWEEN <min-angle> <max-angle>

This requirement is used to find times when the sub-observer meridian of an object lies within a particular range. For planets and their satellites, planetographic coordinates are used. For dwarf planets, a right-handed coordinate system is used. The <object> and <observer> must be standard bodies from Solar System Standard Targets. The requirement specifies those times when the central meridian longitude lies between <min-angle> and <max-angle> (both in degrees) as seen by the <observer>. <observer> defaults to JWST.

By definition, east is the direction to one's right hand side if you were on the body and facing north. For the Sun, the planets, and their satellites, the north pole is defined as parallel to the rotation axis and pointing to the north side of the plane whose normal vector is the angular momentum vector of the solar system (i.e. the north side of the ecliptic plane). For those dwarf planets and their satellites that have been visited by spacecraft (currently Ceres, Pluto, and Charon), north is defined as the spin axis around which they rotate in the right hand sense.

Planetographic longitude only equals planetocentric longitude (e.g. as produced by JPL Horizons) if the target body's rotation is retrograde.

ORBITAL LONGITUDE OF <object1> [FROM <observer>] BETWEEN <min-angle> <max-angle>

This requirement is used to select observation times based on a geocentric view (usually) of the object. ORBITAL LONGITUDE can be used on either a Level 1 or a Level 2 object. <min-angle> and <max-angle> are in degrees. ORBITAL LONGITUDE specifies those times when the orbital longitude lies between <min-angle> and <max-angle>. The default for <observer> is the Earth. If <object1> refers to a Level 2 body, usually a satellite, the orbital longitude is defined as follows (see Figure 1. Orbital Longitude for Satellites):

1. Construct a vector from <object 2> (Earth) to the Level 1 parent (planet) of the <object 1> (satellite).
2. Extend the vector “behind” the planet and project it onto the orbital plane of the satellite. This is the reference axis.
3. The orbital longitude is the angle from the reference axis to the position of the satellite measured in the direction of motion of the satellite. Valid values for the orbital longitude lie in the range 0–360 degrees.

Orbital Longitude of 0 degrees corresponds to superior conjunction, Orbital Longitude of 180 degrees corresponds to inferior conjunction, and 90 degrees and 270 degrees correspond to greatest eastern and western elongation, respectively.

If <object1> refers to a Level 1 body, e.g. a planet, asteroid, or comet, the orbital longitude is defined to be the angle between the Sun-Earth vector and the Sun-Planet vector, projected onto the planet’s orbital plane, increasing in the direction of the planet’s orbital motion (see Figure 2. Orbital Longitude for Planets).

Orbital Longitude of 0 degrees corresponds to opposition, Orbital Longitude of 180 degrees corresponds to conjunction with the Sun. However, Orbital Longitude of 90 degrees or 270 degrees does not correspond with quadrature. Orbital Longitude is not synonymous with “elongation” or “separation” from the sun.

GALACTIC LATITUDE OF <object> FROM <observer> <condition> <min-angle> <max-angle>

This requirement is used to find times when the Galactic latitude of one object (as seen from a selected observer) is within a specified range. The <observer> defaults to JWST. <min-angle> and <max-angle> are the Galactic latitude in degrees. <max-angle> is only available when <condition> is BETWEEN.

Moving Target Implementation Flags 

These flags should only be set by a Program Coordinator. By default, the Start and End dates are not specified and Show Windows is unchecked.

MOSS Planning Start <date> - Overrides the start date for MOSS processing of Solar System Target Windows

MOSS Planning End <date> - Overrides the end date for MOSS processing of Solar System Target Windows

MOSS Show Windows - Indicates whether MOSS files should include SHOW WINDOW commands

Default Target Windows 

Please note that the following defaults apply for solar system targets.

 All observations:

ANGULAR RATE <target> FROM JWST LESS THAN <rate> 

(for more details see the section on ANGULAR RATE)

All targets in the Martian system except Mars:

NOT OCCULTATION OF <target> BY MARS FROM JWST

SEPARATION OF <target> MARS FROM JWST GREATER THAN 10"

 

All targets in the Jovian system except Jupiter:

NOT OCCULTATION OF <target> BY JUPITER FROM JWST

 

Observations of Jupiter, Jupiter surface features, and offsets from Jupiter:

NOT ECLIPSE PENUMBRAL PARTIAL OF <target> BY IO FROM JWST

NOT ECLIPSE PENUMBRAL PARTIAL OF <target> BY EUROPA FROM JWST

NOT ECLIPSE PENUMBRAL PARTIAL OF <target> BY GANYMEDE FROM JWST

NOT ECLIPSE PENUMBRAL PARTIAL OF <target> BY CALLISTO FROM JWST

 

All targets in the Jovian system except Io:

SEPARATION OF  <target> IO FROM JWST GREATER THAN 10"

 

All targets in the Jovian system except Europa:

SEPARATION OF  <target> EUROPA FROM JWST GREATER THAN 10"

 

All targets in the Jovian system except Ganymede:

SEPARATION OF  <target> GANYMEDE FROM JWST GREATER THAN 10"

 

All targets in the Jovian system except Callisto:

SEPARATION OF  <target> CALLISTO FROM JWST GREATER THAN 10"

 

All targets in the Saturnian system except Saturn:

NOT OCCULTATION OF <target> BY SATURN FROM JWST

Observations of Saturn, Saturn surface features, and offsets from Saturn:

NOT ECLIPSE PENUMBRAL PARTIAL OF <target> BY TITAN FROM JWST

All targets in the Saturnian system except Rhea:

SEPARATION OF <target> RHEA FROM JWST GREATER THAN 10"

All targets in the Saturnian system except Titan:

SEPARATION OF <target> TITAN FROM JWST GREATER THAN 10"

All targets in the Uranian system except Uranus:

NOT OCCULATION OF <target> BY URANUS FROM JWST

All targets in the Neptunian system except Neptune:

NOT OCCULTATION OF <target> BY NEPTUNE FROM JWST

 

Observations of Neptune, Neptune surface features, and offsets from Neptune:

NOT ECLIPSE PENUMBRAL PARTIAL OF <target> BY TRITON FROM JWST

All PLANETOGRAPHIC, PLANETOCENTRIC, and MAGNETO targets:

NOT OCCULTATION OF <target> BY <parent body> FROM JWST

These default windows will be superseded by any similar windows specified via the special requirements above. For example, if the target is Io and an Io-Callisto separation window is specified by the observer, then the observer’s Io-Callisto separation window will apply and the default will not.

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