Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Survey (ARRAKIHS) is an ESA science mission currently at pre-phase A stage. Selected as an F2 (fast, low-cost) class mission in November 2022, it is scheduled for adoption in 2027 and launch in 2031.
ARRAKIHS aims to perform observational tests of the Lambda Cold Dark Matter (ΛCDM) model, obtaining deep multi-band exposures of ultra-low surface brightness galaxies, and thus enabling detailed and systematic studies of extended galaxy haloes. The observations will allow to address a number of outstanding discrepancies between ΛCDM predictions and observations.
ARRAKIHS is designed as an experiment to quantify the mass and luminosity functions of satellite galaxies, satellite merger rates, and distribution of sub-haloes around Milky Way (MW)-type galaxies, and to detect and characterize the stellar streams around these galaxies that are predicted to be ubiquitous in ΛCDM scenarios. The mission has three main observational goals:
(i) to determine the abundance and locations of satellite galaxies, down to MV < -6 for a complete sample of MW-like galaxies beyond the Local Group;
(ii) to provide robust statistics of the numbers and shapes of wide and thin stellar streams;
(iii) to characterise the shape and extent of the ultra-faint intra-halo light.
In preparation for a call for industry proposals, a study was organized in ESA’s Concurrent Design Facility between February/March 2023 to address key open points relating to the spacecraft and overall mission design. I was assigned to support the study team as one of two Thermal experts.
As part of the study, I worked on the instrument thermal concept and sized the thermal control systems for the platform. The instrument is a set of two binocular optical telescopes, where one is a VIS imager and the other is a NIR imager. The NIR detectors require cooling to around 140 K, and for cost and complexity reasons it is required that this cooling is done completely passively. Since the spacecraft is in LEO, and the CONOPS includes a wide observational field of regard, we were faced with a significant challenge reaching 140 K within the size constraints due to environmental loads on the radiator (particularly Earth IR) and internal heat leaks.
A major conclusion of the study was that thermal would be a key design driver for the mission. For this reason, I was subsequently assigned to the ARRAKIHS Post-CDF Working Group, where I am conducting sensitivity analyses and more detailed thermal design studies in preparation for industry call for proposals in Summer 2023.
