M. Linder

Vibration-free 5 K sorption cooler for ESA's Darwin mission

ESAs Darwin mission is an Infrared Space Interferometer that will search for terrestrial planets in orbit around other stars. It uses six free-flying telescopes that are stabilized with respect to each other to less than 10 nm by utilizing micro-Newton ion thrusters. As a consequence, hardly any vibration of the optical system with integrated cryocoolers can be tolerated. A sorption cooler is a favorite cooler option because it has no moving parts and it is, therefore, essentially vibration-free. An efficient two-stage helium/hydrogen sorption cooler is proposed with a cooling power of 10 mW at 5 K. It needs only 3 W of input power and applies two passive radiators at 50 and 70 K. Application of such low-temperature radiators is made possible by Darwins far-away orbit L2 where earth-radiation is limited. In this paper, first Darwins cooler requirements are discussed and different cryocooler options are compared. Next, sorption cooler operation is explained, after which six different sorption cooler configurations are described and compared.

Status of the ESA L1 mission candidate ATHENA

ATHENA (Advanced Telescope for High Energy Astrophysics) was an L class mission candidate within the science programme Cosmic Vision 2015-2025 of the European Space Agency, with a planned launch by 2022. ATHENA was conceived as an ESA-led project, open to the possibility of focused contributions from JAXA and NASA. By allowing astrophysical observations between 100 eV and 10 keV, it would represent the new generation X-ray observatory, following the XMM-Newton, Astro-H and Chandra heritage. The main scientific objectives of ATHENA include the study of large scale structures, the evolution of black holes, strong gravity effects, neutron star structure as well as investigations into dark matter. The ATHENA mission concept would be based on focal length of 12m achieved via a rigid metering tube and a twoaperture, x-ray telescope. Two identical x-ray mirrors would illuminate fixed focal plane instruments: a cryogenic imaging spectrometer (XMS) and a wide field imager (WFI). The S/C is designed to be fully compatible with Ariane 5 ECA. The observatory would operate at SE-L2, with a nominal lifetime of 5 yr. This paper provides a summary of the reformulation activities, completed in December 2011. An overview of the spacecraft design and of the payload is provided, including both telescope and instruments. Following the ESA Science Programme Committee decision on the L1 mission in May 2012, ATHENA was not selected to enter Definition Phase.

HERITAGE OVERVIEW: 20 YEARS OF COMMERCIAL PRODUCTION OF CRYOCOOLERS FOR SPACE

The paper presents an overview of the results of industrialization of the ISAMS Stirling cooler technology, achieved through cooperation with the Rutherford Appleton Laboratory. Seven batches of coolers have been produced and delivered to international customers for various space applications. A summary of in-orbit flight heritage is presented showing flight telemetry data for detector and mounting interface temperatures, vibration and other drive parameters. Thirteen of the 50–80K cooler models have been launched, with many of the coolers having already exceeded their required lifetimes. Highlights of cooler commissioning and performance in orbit are presented, with discussion of lessons learned, focusing on the last three production batches of the 50–80K Stirling cooler.

ATHENA: system studies and optics accommodation

ATHENA is currently in Phase A, with a view to adoption upon a successful Mission Adoption Review in 2019/2020. After a brief presentation of the reference spacecraft (SC) design, this paper will focus on the functional and environmental requirements, the thermo-mechanical design and the Assembly, Integration, Verification & Test (AIVT) considerations related to housing the Silicon Pore Optics (SPO) Mirror Modules (MM) in the very large Mirror Assembly Module (MAM). Initially functional requirements on the MM accommodation are presented, with the Effective Area and Half Energy Width (HEW) requirements leading to a MAM comprising (depending on final mirror size selected) between ~700-1000 MMs, co-aligned with exquisite accuracy to provide a common focus. A preliminary HEW budget allocated across the main error-contributors is presented, and this is then used as a reference to derive subsequent requirements and engineering considerations, including: The procedures and technologies for MM-integration into the Mirror Structure (MS) to achieve the required alignment accuracies in a timely manner; stiffness requirements and handling scheme required to constrain deformation under gravity during x-ray testing; temperature control to constrain thermo-elastic deformation during flight; and the role of the Instrument Switching Mechanism (ISM) in constraining HEW and Effective Area errors. Next, we present the key environmental requirements of the MMs, and the need to minimise shock-loading of the MMs is stressed. Methods to achieve this Ø are presented, including: Selection of a large clamp-band launch vehicle interface (LV I/F); lengthening of the shock-path from the LV I/F to the MAM I/F; modal-tuning of the MAM to act as a low-pass filter during launch shock events; use of low-shock HDRMs for the MAM; and the possibility to deploy a passive vibration solution at the LV I/F to reduce loads.

Design and Characterization of a Miniature Pulse Tube Cooler

The design of an advanced Miniature Pulse Tube Cooler (MPTC) for long-life space applications is presented. The cooler system incorporates a balanced compressor, with an in-line pulse tube configuration, yet retains the flexibility of a transfer line. The ‘split’ configuration provides obvious advantages for instrument design, while maintaining economical options for drive electronics and maximising potential for vibration isolation between compressor and detector. It also potentially allows the pulse tube end to be separately placed within a pre-cooled enclosure at temperatures beyond the range of operation for typical compressor mechanisms.

Completion of the EChO phase 0/A study

EChO is an M-class mission candidate within the science program Cosmic Vision 2015-2025 of the European Space Agency. It aims at characterising the atmosphere of known transiting exoplanets, potentially from giant Hot Jupiters down to Super-Earths orbiting in the habitable zone of M-dwarf stars. It was selected in February 2011 to enter an assessment phase (phase 0/A). Following the completion of the Concurrent Design Facility study conducted by ESA in June/July 2011, two parallel industrial studies were carried out throughout 2012, and were then extended till August 2013. Similarly, two parallel instrument studies were conducted till mid-2012, following which an Announcement of Opportunity was released and concluded in February 2013 by the selection of a single instrument consortium. This paper describes the status of EChO upon completion of the system level and instrument studies. It includes a discussion on the evolution of the science and mission requirements, the description of the final preliminary design and performance parameters, as well as programmatic estimates in terms of technology readiness and schedule. The next step for EChO will consist of passing the Preliminary Requirements Review, planned by the end of 2013, followed by the down-selection of a single M3 mission.

Interfacing issues in microcooling of optical detectors in space applications

Miniature Joule-Thomson coolers were developed at the University of Twente and are able to cool to 100 K with a typical cooling power of 10 to 20 mW. These coolers have a high potential for space applications in cooling small optical detectors for future earth observation and science missions. Under contract of the European Space Agency, we investigate on-chip detector cooling for the temperature range 70 K-250 K. To identify the detectors that can be cooled by a JT microcooler, a literature survey was performed. Following this survey, we selected a micro digital CMOS image sensor. A conceptual design of this cooler-sensor system is made. Among various techniques, indium soldering and silver paint are chosen for the bonding of the silicon sensor to the glass microcooler. Electrical connections from the sensor to the outside will be realized by structuring them in a thin layer of gold that is sputtered on the outside of the cooler to minimize the radiative heat load. For the electrical connections between the sensor and the structured leads, aluminum or gold bond wires will be used

15 K liquid hydrogen thermal Energy Storage Unit for future ESA science missions

A thermal Energy Storage Unit (ESU) using liquid hydrogen has been developed as a solution for absorbing the heat peaks released by the recycling phase of a 300 mK cooler that is a part of the cryogenic chain of one of ESAs new satellites for science missions. This device is capable of storing 400 J of thermal energy between 15 and 16 K by taking advantage of the liquid-to-vapor latent heat of hydrogen in a closed system. This paper describes some results obtained with the development model of the ESU under different configurations and using two types of hydrogen storage: a large expansion volume for ground testing and a much more compact unit, suitable for space applications and that can comply with ESAs mass budget.

Design and performance of the Exo-planet Characterisation Observatory (EChO) integrated payload

The Exoplanet Characterisation Observatory (EChO) mission was one of the proposed candidates for the European Space Agency’s third medium mission within the Cosmic Vision Framework. EChO was designed to observe the spectra from transiting exoplanets in the 0.55-11 micron band with a goal of covering from 0.4 to 16 microns. The mission and its associated scientific instrument has now undergone a rigorous technical evaluation phase and we report here on the outcome of that study phase, update the design status and review the expected performance of the integrated payload and satellite.

Assessment study of the SPICA telescope assembly

The paper provides a summary of the results of the assessment study conducted on the SPICA Telescope Assembly (STA). SPICA (SPace Infrared telescope for Cosmology and Astrophysics) was selected for study as a mission of opportunity within the science programme Cosmic Vision 2015-2025 of the European Space Agency, with a planned launch in 2017. Observing in the 5 - 210 micron waveband, one of its major goals is the discovery of the origins of planets and galaxies. ESAs main contribution is the provision of the SPICA Telescope Assembly (STA) featuring a 3.5 m primary mirror cooled to < 6K. A nationally funded European FIR instrument (SAFARI) would also be part of SPICAs payload. Following an internal ESA study carried out in Q1 and Q2 2008, a parallel competitive industrial study (phase A level) has been performed. The main results achieved during this study are summarised.