The Implementation of the Ariel FGS Application Software

The Ariel space telescope in the ESA Cosmic Vision program aims to uncover the chemical composition of ex-oplanetary atmospheres. Ariel achieves this by using multi-wavelength spectroscopy and photometry with high photometric precision across a planet’s orbit. During these observations, the telescope requires stable pointing to reduce the photometric noise caused by spacecraft jitter. This task is covered by a dedicated instrument: the Fine Guidance Sensor (FGS). The FGS is a science instrument providing photometry and spectroscopy in the visual and near-infrared. While the gathering of science data is a key aspect of the FGS, the images are also used for the guiding of the telescope. Both tasks are carried out by the Instrument Application Software (IASW) which is implemented on the instrument’s data processing unit. The key scientific tasks of the IASW involve up the ramp sampling, data reduction and compression. Additionally, the IASW also handles more general tasks such as the instrument health, housekeeping management, commanding of the detectors, the handling of telecommands and telemetry, as well as fault detection, isolation and recovery. The software development is facilitated with a suite of tools and utilities that were created over the course of previous projects. These allow us to cut down the needed workload. This paper explores the design to code workflow and our test-driven development approach while also covering the peculiarities and challenges of the Ariel FGS IASW implementation.