Chapter 4: Solar System Targets

4.1 Target Number [Target_Number]

4.2 Target Name [Target_Name]

4.3 Target Description [Description]

4.4 Target Position

4.5 Ephemeris Center [Ephem_Center]

4.6 Ephemeris Uncertainty [Ephem_Uncert]

4.7 Acquisition Uncertainty [Acq_Uncert]

4.8 Observing Windows [Windows]

4.9 Flux Data [Flux and Other_Fluxes]

4.10 Comments [Comments]

4.11 Illustrations of Orbital Longitude

4.12 Examples of Target List Blocks

Tables and Figures

Table 4.1: Solar System Standard Targets

Table 4.2: Target Description Keywords

Table 4.3: Positional Parameters for TYPE = COMET

Table 4.4: Positional Parameters for TYPE = ASTEROID

Table 4.5: Parameters for TYPE = PGRAPHIC

Table 4.6: Parameters for TYPE = POS_ANGLE

Table 4.7: Parameters for TYPE = MAGNETO

Table 4.8: Parameters for TYPE = TORUS

Table 4.9: Parameters for TYPE = SAT

Table 4.10: Parameters for TYPE = PCENTRIC

Table 4.11: Keywords for Observing Windows

Table 4.12: Operators for Observing Windows

Table 4.13: Formats for Specification of Target Flux Data

Figure 4.1: Orbital Longitude for Satellites / 85

Figure 4.2: Orbital Longitude for Planets / 86

 

HST is able to point at and track solar system targets with sub-arcsecond accuracy. In order for target acquisition and tracking to succeed, planetary observers must specify positions for their targets in a precise and unambiguous manner. Therefore, it is imperative that the Solar System Target List (SSTL) be carefully and correctly completed. This section explains how to fill out the SSTL for any solar system target.

Ephemerides are generated using fundamental ephemeris information from NASA’s Jet Propulsion Laboratory (JPL). Ephemerides can be generated for all known types of solar system targets, including planets, satellites, comets, asteroids, surface features on planets and satellites, and offset positions with respect to the centers of all the above bodies. The following instructions demonstrate how to define solar system targets in a way that allows accurate ephemeris generation.

The body-axes definitions, body dimensions, directions of rotation poles, rotation rates, and the definitions of cartographic coordinates used by STScI are normally identical to the values adopted in the report of the “IAU Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites: 1982” (Davies, M.E., et al., Celestial Mechanics, 29, 309-321, 1983). In a few instances, the latter data have been updated due to new results obtained from the flyby spacecraft. Also, some new bodies have been added which were unknown at the time of the IAU report. For Jupiter and Saturn, the lambda(III) coordinate system is assumed, but lambda(I) or lambda(II) can be used. For Uranus and Neptune, coordinates follow the “Report of the IAU/IAG/COSPAR Working Group on Cartographic Coordinates and Rotation Rates of the Planets and Satellites” (Celestial Mechanics and Dynamic Astronomy, 46, 197, 1989). If you need further information on these, please contact your Program Coordinator.

One exception exists to the requirements outlined above. Observers for solar system Targets of Opportunity (e.g. a “new” comet or asteroid, a solar-wind disturbance reaching the Jovian magnetosphere, etc.), should complete the Generic Target List (See “Generic Targets List [Generic_Targets]” in Chapter 3.) and the Visit and Exposure Specifications (to the extent possible) in time for the Phase II deadline. If and when a suitable target appears, the proposer must complete the Solar System Target List and update the Visit and Exposure Specifications. No target can be observed until the complete Phase II information is provided.

In this chapter, each heading has a description followed by a keyword in square brackets (e.g., [Target_Number]). Elsewhere, items in boldface (e.g., RA) show words or phrases that are used as APT Phase II items or properties. Items in <> brackets (e.g., <value>) show values you provide. Items listed in square brackets (e.g., [A1 : <value>]) are optional, whereas those not in square brackets are required. As you enter information in the APT interface. You will be told (via a tooltips message) if an item is required, and its format.