Goddard Engineering and Technology Directorate

Supporting the Key Instrument of the Roman Space Telescope

The Roman WFI detector focal plane consists of 18 H4RG-10 detectors in a 6 x 3 array that combined provide an 0.281 deg2 active FOV. This image shows the focal plane Engineering Test Unit with non-flight candidate detectors.
The Roman WFI detector focal plane consists of 18 H4RG-10 detectors in a 6 x 3 array that combined provide an 0.281 deg2 active FOV. This image shows the focal plane Engineering Test Unit with non-flight candidate detectors.

The Wide-Field Instrument (WFI) is the primary instrument of the Roman Space Telescope

On the Roman Space Telescope (RST), the Widefield Instrument (WFI) is the primary instrument (for science imaging) and acts as a kind of ultra-precise star tracker. The WFI Instrument Command and Data Handling (ICDH) Flight Software (FSW) is the mechanism which controls the Fine Guidance System (FGS), which allows the observatory to make incredibly precise pointing and attitude adjustments.

The Software Engineering Division played a vital role in the RST project by developing and implementing the Instrument Command and Data Handling (ICDH) Flight Software (FSW) for the WFI. This software serves as the backbone for controlling the FGS, enabling the observatory to achieve unparalleled precision in pointing and altitude adjustments. Through meticulous design, testing, and optimization, the division ensured that the WFI FSW operates flawlessly, facilitating the RST’s mission to capture high-resolution scientific imagery and track celestial objects with unprecedented accuracy.

The WFI ICDH FSW Fine Guidance System processes “guide windows” (small pictures of star pointing of the observatory) from the detectors and compares them to data sets of where the observatory should be pointed for the given observation. The FGS software computes an attitude correction estimate of the difference and sends that data to the spacecraft’s attitude control system (ACS), which can make the precise adjustments to the observatory’s pointing. The FGS-to-ACS loop continues until the attitude error is within limits. Because of RST’s sensitive detectors and mission parameters to look far back in time, precise pointing and maintaining attitude is extremely important. The WFI FSW enables this precision.

Roman Space Telescope (RST), the Widefield Instrument (WFI)
Roman Space Telescope (RST), the Widefield Instrument (WFI)

A key component of WFI is its chain of image detector hardware called the Focal Plane System (FPS). The FPS consists of 18 4k H4RG detectors, providing a combined image resolution of over 300 Mpixels. The flight software is responsible for the configuration of these detectors, along with the setup of the filter wheels and shutter. Each astronomical imaging requires a unique configuration of the telescope and setup of the detectors. Once imaging is complete, the WFI ICDH packages the images to be transmitted to the ground station.

From providing accurate pointing data to managing the imaging detectors, the WFI ICDH FSW has an essential role in the success of the WFI instrument as well as the success of the mission.