Operational Constraints
This page provides information about Roman Coronagraph Instrument operational constraints. The information is based these two papers: "Real-time commanding and data processing for high-order wavefront sensing and control on the Roman Coronagraph" (Greenbaum et al. 2025) and “Flight mask designs of the Roman Space Telescope coronagraph instrument” (Riggs et al. 2021).
Operational Constraints of the Roman Coronagraph Instrument
The Coronagraph Instrument on the Roman Space Telescope is a technology demonstration with approximately six months of total observing time during the five-year mission. It is not used for survey operations and cannot observe during telescope slews or thermal settling periods. Operations are restricted by the South Atlantic Anomaly, Sun-angle constraints, spacecraft roll limitations, and the requirement for fine pointing mode.
The Coronagraph Instrument requires a thermally stable telescope environment for several hours before observations to maintain contrast and support the LOWFS/C system. Internal and external calibrations are frequent and interleaved with science operations. Limited visibility windows due to orbital geometry may necessitate repeated observations of the same target.
Observation sequences are long and include target acquisition, configuration, wavefront correction, and integration. Individual sequences may span more than a day. Coronagraph performance is sensitive to thermal variation and jitter, and interruptions may invalidate an observation. These constraints reduce scheduling flexibility and limit the number of unique targets that can be observed.
Figure 1: The figure above shows an example of a typical tech demo observation scenario for the coronagraph, including the initial HOWFSC data collection and end HOWFSC touch-up. Note that only a few iterations are shown of the HOWFSC data collection in this figure. The figure shows the typical reference star-target star + roll dither pattern for the coronagraph instrument.
Target and Reference Star Guidelines
The target brightness limit for optimal LOWFSC control is V<=5.
The Coronagraph instrument will observe a reference star, in order to guide the wavefront sensor and to enable Reference Differential Imaging (RDI) in Post-Processing. There are guidelines on the reference star:
- V<3
- Stellar diameter <2 mas
- Single Star
The ground portion of GITL is allocated 30 minutes (each iteration) to downlink the data and upload commands.