Design of the ULTRASAT UV camera

TL;DR

This paper presents the preliminary design of the ULTRASAT UV camera, a key component of a space telescope for ultraviolet transient astronomy, highlighting its innovative optical and thermal design features.

Contribution

It introduces the novel design of the ULTRASAT UV camera, including sensor arrangement, thermal management, and integration within the telescope's optical system.

Findings

Design of the CMOS sensor array with 22.4 MP per sensor

Thermal control system enabling cooling to 200K and heating to 343K

Compact Schmidt optical design with integrated detector placement

Abstract

The Ultraviolet Transient Astronomical Satellite (ULTRASAT) is a scientific UV space telescope that will operate in geostationary orbit. The mission, targeted to launch in 2024, is led by the Weizmann Institute of Science (WIS) in Israel and the Israel Space Agency (ISA). Deutsches Elektronen Synchrotron (DESY) in Germany is tasked with the development of the UV-sensitive camera at the heart of the telescope. The camera's total sensitive area of ~90mm x 90mm is built up by four back-side illuminated CMOS sensors, which image a field of view of ~200 deg2. Each sensor has 22.4 megapixels. The Schmidt design of the telescope locates the detector inside the optical path, limiting the overall size of the assembly. As a result, the readout electronics is located in a remote unit outside the telescope. The short focal length of the telescope requires an accurate positioning of the sensors within +-50 mu along the optical axis, with a flatness of +-10 mu. While the telescope will be at around 295K during operations, the sensors are required to be cooled to 200K for dark current reduction. At the same time, the ability to heat the sensors to 343K is required for decontamination. In this paper, we present the preliminary design of the UV sensitive ULTRASAT camera.