Bernard Collaudin

Cryogenics in space: A review of the missions and of the technologies

Cryogenics has made a remarkable amount of progress over the last 15 years. The increased reliability and simplicity of operations of cryogenic equipment have allowed to install and to successfully operate them onboard spacecrafts. At the same time, the improved performance of cryogenic devices, such as sensors and cold electronics, has drastically enlarged their utilisation, creating new perspectives for space-based applications. In this paper we provide an up-to-date review of the non-military space missions making use of cryogenic instrumentation and a summary of the present and envisaged applications of cryogenic equipment in space. The impact of cryogenics on the spacecraft system design and the main technical solutions presently adopted are also discussed. Finally, this paper provides an outlook on near- and mid-term future activities involving cryogenics in space and on the related technology development, with particular emphasis on the work carried out by the European Space Agency.

Development of a superconducting tunnel junction camera for ground-based optical astronomy

The development of an optical camera based on superconducting tunnel junctions has now reached a stage where practical applications in optical or UV astronomy can be considered. A prototype cryogenic camera (named S-Cam) has been developed, based on a high quantum efficiency 6 X 6 detector array of tantalum Josephson junctions, and operating at a temperature of about 0.4 K. This paper describes the general characteristics of the camera, sensitive in the waveband from 350 to 700 nm and designed to be installed in 1998 at the Nasmyth focus of the William Herschel Telescope in La Palma, Spain. In addition to the performance of the overall system, the preliminary detector unit test results will also be presented. The present S-Cam system performance is discussed in view of future versions of the camera. Provided the field coverage of these cameras can be extended through the development of larger format detector arrays and adequate read-out electronics, they have the potential to provide a significant additional tool for optical and UV astronomy in the next century.

First astronomical results from S-Cam

Abstract S-Cam is a cryogenic camera for ground-based astronomy based on a 6×6 array of Superconducting Tunnel Junctions (STJs). The camera has been designed as a technology demonstrator, aiming to prove the potential of this new generation of single photon counting detectors at a ground-based telescope. In this article we provide an overview of the detector performance, a description of the S-Cam system and a summary of the test results. The first astronomical data obtained at the William Herschel Telescope (WHT) in La Palma (Canary Islands, Spain) are also described.

Design and performance of a portable 3He cryogenic system for ground based instrumentation

The availability of compact cryogenic refrigerators is of importance for the development of both ground and space-borne instrumentation based on cryogenic detectors. In this article we report on the design and performance of a complete ground based cryogenic system consisting of a 3He cryosorption refrigerator, and designed to cool a 6×6 element detector array of tantalum based superconducting tunnel junctions (STJs). The refrigerator provides an operating temperature of 330 mK, with a hold time in excess of 7 h. The system is designed to be portable, to provide a very stable focal plane, and to minimize the use of magnetic materials. Such a system has been used to host the focal plane assembly of S-Cam, the first optical camera for ground based astronomy utilizing an array of STJs, recently installed at the William Herschel Telescope, in La Palma.

FIRST/Planck mission cryogenic systems: current status

ESA is studying the possibility to merge two of the next scientific missions of its HORIZON 2000 Programme, the fourth cornerstone mission, the far IR and sub-millimeter telescope (FIRST) and the third medium-sized mission M3, Planck. FIRST is a multi-user observatory, which targets the IR and sub-millimeter part of the electromagnetic spectrum, in the wavelength range from 85 micrometers to 600 micrometers . The Planck mission is a survey mission dedicated to mapping the temperature anisotropies of the cosmic background radiation. The merger of the mission is presently being studied in view of the programmatic constraints on both missions, the fact that they use a similar orbit, the partial parallel development of both missions and the potential cost savings. The cryogenic system of FIRST is based on a Superfluid Helium Dewar at 1.65K with a design lifetime of more than 4.5 years. The very low temperature, required in the bolometer instrument will be obtained from a dedicated 3He-sorption cooler. The cryogenic system of Planck uses a sequence of passive radiator, H2 Joule-Thomson Sorption cooler, JT mechanical cooler, and dilution refrigerator.

FIRST payload module and accommodation of instruments

FIRST (Far Infrared and Sub-millimeter Telescope) is one of the satellites of the next ESA scientific mission. FIRST/Planck, which will be launched in 2007 to the 2nd Lagrangian libration point L2. It will be a multi-user observatory, watching the universe in the infrared and sub- millimeter wavelength range from 60 to 670 micrometers . The paper will describe the latest design status of the cryostat, and its interfaces to the instruments and the telescope.

Use of hafnium-based superconducting tunnel junctions as high-resolution spectrometers for x-ray astronomy

The next generation of superconducting tunnel junctions based on lower critical temperature superconductors such as hafnium are now under development. Such a material with a bandgap well below a meV has the potential to provide very high wavelength resolution at soft x-ray wavelengths. In this paper we report the first results on the characteristics of hafnium thin films deposited on r-plane sapphire. The physical properties of these films together with the electrical and superconducting characteristics are described. Currently the electrical conductivity of these films are limited by scattering from the films columnar grain structure. The superconducting transition temperature has been found to vary from approximately 137-200 mK, somewhat higher than that in the bulk, while the critical magnetic field applied in a direction parallel to the film is determined to be approximately 750 gauss far, larger than that observed in bulk hafnium.