Solar System Targets Position Level 1
The Solar System Targets form is used to specify moving targets in some JWST observations. This article provides a description of the Level 1 specifications needed for the Astronomer’s Proposal Tool (APT).
Purple text indicates the parameter is Limited Access.
Boldface italics type indicates the name of an APT parameter or a value for a parameter.
Red text indicates restrictions on a parameter.
Black text indicates an important note.
Brown text indicates notes for the developers.
Green text indicates the name of the parameter used by Commanding.
Items in brackets - <value> - are required values.
Items in square brackets - [<value>] - are optional.
For the Level 1 position, specify your target in one of the following ways:
- STD = <object name>, where the name must be from the list of Solar System Standard Targets, or
- TYPE = <name>.
The TYPE = <name> target description allows the specification of non-standard targets in a variety of formats and must be the first entry in the field if it is used.
- If COMET is chosen, then a set of 2-body heliocentric orbital elements in the IAU Circular format must be supplied for the target.
Table 1. Positional Parameters for TYPE = COMET
| Parameter | Definition |
|---|---|
| Orbital Elements | |
Q = <value> | Perihelion distance, in AU |
E= <value> | Eccentricity |
I =<value> | Inclination, in degrees |
O= <value> | Longitude of ascending node, in degrees |
W = <value> | Argument of perihelion, in degrees |
T = <value> | Time of perihelion passage, in TDB, TDT, or UTC |
EQUINOX = <value> | either B1950, or J2000 |
EPOCH = <value> | Osculation date, in TDB, TDT, or UTC |
| Non-gravitational Model Parameters | |
[A1 = <value>] | Radial component of non-gravitational acceleration (AU/day2) |
[A2 = <value>] | Component of non-gravitational acceleration lying in the orbital plane and parallel to the instantaneous velocity vector (AU/day2) |
[A3 = <value>] | Component of non-gravitational acceleration directed perpendicular to the plane defined by A1 and A2 (AU/day2) |
| [R0 = <value>] | Sublimation radius as normalizing radius (AU) |
| [ALN = <value>] | Normalizing factor |
| [NM = <value>] | Primary radial scaling law exponent |
| [NN = <value>] | N distance exponent |
| [NK = <value>] | K distance exponent |
| [DT = <value>] | Delay parameter (days) |
| [AMRAT = <value>] | Solar radiation pressure term (m2/kg) |
| SOURCE = <value> | A comment describing the source of the orbital elements. |
- If ASTEROID is chosen, then a set of 2-body heliocentric orbital elements in the Minor Planet Circular format must be supplied.
Table 2. Positional Parameters for TYPE = ASTEROID
| Parameter | Definition |
|---|---|
| Orbital Elements | |
A = <value> | Semi-major axis, in AU |
E = <value> | Eccentricity |
I = <value> | Inclination, in degrees |
O = <value> | Longitude of ascending node, in degrees |
W = <value> | Argument of perihelion, in degrees |
M = <value> | Mean anomaly at EPOCH, in degrees |
EQUINOX = <value> | J2000 |
EPOCH = <value> | Osculation date, in TDB, TDT, or UTC |
| Non-gravitational Model Parameters | |
[A1 = <value>] | Radial component of non-gravitational acceleration (AU/day2) |
[A2 = <value>] | Component of non-gravitational acceleration lying in the orbital plane and parallel to the instantaneous velocity vector (AU/day2) |
[A3 = <value>] | Component of non-gravitational acceleration directed perpendicular to the plane defined by A1 and A2 (AU/day2) |
| [R0 = <value>] | Scaling radius as normalizing radius (AU) |
| [ALN = <value>] | Normalizing factor |
| [NM = <value>] | Primary radial scaling law exponent |
| [NN = <value>] | N distance exponent |
| [NK = <value>] | K distance exponent |
| [AMRAT = <value>] | Solar radiation pressure term (m2/kg) |
| SOURCE = <value> | A comment describing the source of the orbital elements. |
For all cases, the required input data are described below. If the data are valid only over a specific period of time, then specify this time interval using the Solar System special requirements .
| It is the responsibility of the observer to supply accurate orbital elements to STScI when specifying TYPE=COMET or TYPE=ASTEROID. Note that the requirement on how fast JWST can track a moving target is 30 milliarcsec/second. |
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