APT Program Elements
An APT Observing Program consists of a number of distinct Program Elements that can be classified into Planning Elements (user inputs into to APT) and Survey Activities (APT processes the input into activities for the Roman telescope and the Wide Field Instrument).
Introduction
Survey Specifications are used to define the proposed sequence of events that will execute on the Roman observatory to perform the desired Survey. The figure below addresses the relationship between what the user inputs into APT and how APT processes that input.
Figure Connecting User Input to the Activity Hierarchy
Visual representation of the relationships between the APT Planning Elements (left) and the Survey Activities (right).
APT Program Elements
The APT Planning Elements are the inputs provided by the user. Each of these are described below.
Program
An approved specification for a science, calibration, or engineering investigation to be pursued using Roman Space Telescope mission resources.
Fixed Target
A set of celestial coordinates for use as the base pointing of an Observation. (Used when a Region Target is not selected.)
Region Target
A specification of a region on the sky requiring a set of pointings (RA, Dec) at a given attitude of a mosaic pattern to achieve full sky coverage.
Mosaic Pattern
A specification in APT of a sequence of offsets for mosaicking a Roman Observation. Offsets are defined in a reference frame relative to telescope-centric spherical coordinates. A mosaic pattern may be instantiated at different pointings and orients within a program.
Tile
The region covered by the detector array at one step of a mosaic pattern traversal. The location is determined by the base pointing and orient for the Observation, combined with the offset of the corresponding mosaic pattern step.
Survey Plan
A specification in APT of the Pass Plans comprising a Program.
Survey Step
A specification in APT of a Pass Plan to execute together with how many times to repeat that Pass Plan and any associated scheduling special requirements.
Pass Plan
A specification in APT of how to execute a Pass. The Pass Plan consists of a Segment Plan, along with options that may be selected to repeat the sequence of observations (generating multiple Segments within a Pass), either spatially via a Region Target, or in time via a Repeat.
Segment Plan
A specification in APT of an ordered sequence of Observations for a Pass Plan. (Typically scheduled without interruption, but not guaranteed.)
Observation Specification
A specification in APT of the instrument configuration, Dither Pattern, and mosaic pattern for a single Observation.
Survey Activities
Survey activities are organized hierarchically: Survey → Execution Plan → Pass → Segment → Observation → Visit → Exposure. Each level is described.
Survey
The complete set of activities for a Roman Space Telescope Program.
Execution Plan
A version of a complete set of activities for a Survey in APT. A Survey may include portions of multiple Execution Plans: A new Execution Plan is required whenever there is a change in the Program.
Pass
The collection of activities generated from each iteration of a Pass Plan. Multiple Passes may be generated from the same Pass Plan to allow repetition or execute at different orientations (via special requirements).
Segment
The sequence of activities produced by each iteration of the a Segment Plan (Observation Sequence) in a Pass. A Segment may include multiple traversals of Mosaic Pattern(s), with filter wheel moves occurring between Observations. The Segment will be the unit of planning, while short term scheduling will be done at the Visit level.
Observation
A single traversal of a Mosaic Pattern, using a single, constant instrument configuration (i.e., with no filter wheel moves).
Visit
The smallest scheduling unit for Roman: A sequence of exposures executed without interruption, including Dither Patterns. A visit corresponds to one Tile of the selected mosaic pattern. (May include multiple guide star acquisitions.)
Dither Pattern
A predefined sequence of small offsets from the initial pointing of a Visit, such as for gap-filling slews.
Exposure
A single multi-accum sequence of the detector array at a single dither point in the dither pattern.