A Coordinated Parallel Container designates a set of one or more parallel exposures (
<parallel-exp-list>) that will execute in parallel with a set of one or more primary exposures (
<primary-exp-list) in the same visit. The SI used in the first exposure defines the primary SI (and therefore defines the <primary-exp-list>). All other exposures that use the same SI will also be considered primary.
All exposures using a different SI will be considered parallel. Parallel exposures using the same SI will be executed in the order specified in the container. The first parallel exposure which uses a given instrument will be executed as early as possible, but not before the first primary exposure.
All exposures in <primary-exp-list> must have the same Instrument Configuration (Config) and the same Aperture or Field of View (Aperture). No exposure in <parallel-exp-list> may use the same SI as the primary exposures.
Coordinated parallels may specify fixed, generic, or solar system targets; the special target
ANY; or internal targets. However, the pointing of HST will be determined only by the primary exposures. Any pointing conditions to be applied on the primary+parallel combination must be specified on the
primary exposures via exposure-level special requirements, or on the visit as a whole via visit-level special requirements. All external exposures in a given <primary-exp-list> must have the same pointing. This generally means the same target, aperture, and POS TARG (see the discussion of optional parameters below).
If a parallel exposure specifies a fixed target, it should be a different target from the primary ones and should appear in the Target List. In this case, an
ORIENT special requirement is
required to ensure that the parallel target is in the aperture. It is the observer’s responsibility to verify that the specified orientation will place the parallel target in the aperture; STScI will not check the geometry. Contact your Program Coordinator if you need assistance.
If the parallel target is diffuse and the orientation does not matter, or if there is no parallel target as such and the intent is just to sample whatever the parallel aperture happens to fall on, you should select the
ANY target (which should not appear in your Target List).
The following exposure-level special requirements are disallowed for both primary exposures (any exposure in a <primary-exp-list>) and parallel exposures:
No parallel exposure may appear in the <exposure-list> of an RT ANALYSIS FOR Special Requirement, or be the <exposure> referenced by a
SAME POS AS special requirement.
The Number_Of_Iterations must be set to
1 for any COS exposure in a coordinated parallel container.
In Coordinated Parallel Containers, the SI used in the first exposure defines the “primary” SI.
If the exposures in the <parallel-exp-list> contain exposures that use different SIs, an attempt will be made to execute each set of exposures with the same SI in parallel with the other sets. All exposures within a given set must be contiguous in the container. Within a set, exposures will be executed in the order they appear.
Due to readout conflicts and limits on the number of SIs which may execute simultaneously, parallel exposures sometimes have to be delayed. If a parallel exposure conflicts with an exposure in its primary list, the parallel will be delayed. If two parallel exposures using different SIs conflict, the exposure which appears later in the container will be delayed.
Following a set of exposures in a Parallel Container, subsequent exposures not in the container will be delayed until after all the primary and parallel exposures have completed.
Within a set of coordinated-parallel exposures, the ground system will not break up sequences of exposures that are too long to fit in an orbit, as it does for non-coordinated-parallel exposures. Each group of exposures with the same SI
must be short enough to fit in one orbit. If it is necessary to take coordinated-parallel data over multiple orbits, a separate
Parallel Container – with a new set of exposures – should be specified for each orbit.
