XEUS Research Articles

300 mK and 50 mK cooling systems for long-life space applications

The X-ray Evolving Universe Spectroscopy mission is a candidate for the ESA Cosmic Vision 2015–2025 plan, with two possible instruments at 300 mK and 50 mK. Astrium, under ESA contract, has worked with MSSL, RAL, and CEA-SBT, to propose a suitable payload accommodation scheme meeting ESA’s requirements. Exhaustive trade-offs were performed, according to a described methodology, leading to two designs incorporating closed-cycle active coolers maximizing well proven heritage concepts. These concepts are described, and although they have been prepared for XEUS, there are other future mission concepts which could also benefit from 50 mK cooling with a lifetime greater than 10 years.

Potential cooling chains for the NFI instruments of XEUS

The X-ray observatory (XRO), also known as XEUS (X-ray evolving-universe spectroscopy), is one of the potential future missions identified in the framework of the European Space Agency Cosmic Vision Programme. The core instruments have been selected and include at least one Narrow Field Imager working either in the 300 mK range (NFI-1) or in the 50 mK range (NFI-2). In this article, we describe potential cooling chains compatible with the requirements of these instruments as presently defined. We also give elements on alternative solutions.

Fundamental spatial resolution of an x-ray pore optic

We investigate the fundamental spatial resolution of an x-ray pore optic as a function of the pore dimensions, the photon energy, and the focal length. We achieve this by calculating the shape of the focal spot, using diffraction integrals such that the half-energy width is determined. Quantitative results are presented for the X-Ray Evolving Universe Spectroscopy (XEUS) telescope, showing that a resolution of better than 2 arc sec half-energy width is possible by use of an optic with pore sizes of approximately 0.5 mm.

The effect of the prompt particle environment at L2 on optical CCDs for astronomy and astrophysics

The increasing number of probes carrying large focal planes consisting of many charge-coupled devices (CCDs), planned to be sent to the L2 Lagrangian point, 1.5 million kilometres from Earth in the next 15 years, implies that a detailed study of the effects of the prompt particle environment at L2 on CCDs is required. The focus of this study will be on CCDs for optical astronomy, astrometry and photometric applications. This study will be of particular interest to GAIA the European Space Agency's (ESA) cornerstone optical astronomy mission to further explore and map sections of our galaxy in greater detail. The results will also have implications for future X-ray astronomy missions like the X-ray Evolving Universe Spectroscopy Mission (XEUS). Both the above missions will require large area focal planes incorporating many CCD detectors. The sources of the instrument background are both solar and galactic and if a probe is launched around the peak in the next solar cycle (2010), the possible false detection rate or the amount of data that could be lost during a mission must be determined. This paper presents measured data for a spacecraft in a geostationary orbit, specifically Geosynchronous Operational Environmental Satellites (GOES) data, and makes predictions of the flux and energy of the particle environment at L2. The solar and galactic cosmic ray background was determined by using the Cosmic Ray Effects on Micro-Electronics or CREME96 code. A comparison was then made between the GOES data and the output from the CREME96 code in order to make predictions about the L2 environment.

Space science applications of cryogenic detectors

The improved performance of cryogenic detectors has drastically enhanced their utilization range, allowing a number of space-based applications, with particular emphasis on astronomical observations. In this paper we provide an overview of the main applications of cryogenic detectors onboard spacecraft, together with a description of the key technologies and detection techniques used or being considered for space science missions. A summary of the cryogenic instrumentation technologies is also presented. Possible instruments for future astrophysics space missions are also discussed, using X-ray Evolving Universe Spectroscopy mission, presently proposed by ESA as a post XMM-Newton project as a reference.

Studying the evolution of the hot universe with the X-ray evolving universe spectroscopy mission – XEUS

Europe is one of the major partners building the International Space Station (ISS) and European industry, together with ESA, is responsible for many station components including the Columbus Orbital Facility, the Automated Transport Vehicle, two connecting modules and the European Robotic Arm. Together with this impressive list of contributions there is a strong desire within the ESA Member States to benefit from this investment by utilizing the unique capabilities of the ISS to perform world-class science. XEUS is one of the astronomical applications being studied by ESA to utilize the capabilities of the ISS. XEUS will be a long-term X-ray observatory with an initial mirror area of 6 m 2 at 1 keV that will be expanded to 30 m 2 following a visit to the ISS. The 1 keV spatial resolution is expected to be 2–5″ half-energy-width. XEUS will consist of separate detector and mirror spacecraft (MSC) aligned by active control to provide a focal length of 50 m. A new detector spacecraft, complete with the next generation of instruments, will also be added after visiting the ISS. The limiting 0.1–2.5 keV sensitivity will then be 4 × 10 −18 erg cm −2 s −1, around 200 times better than XMM-Newton, allowing XEUS to study the properties of the hot baryons and dark matter at high redshift.

Development of arrays of transition edge sensors for application in X-ray astronomy

The development of an array of voltage biased superconducting transition edge microcalorimeters is described. This work is directed to an application in future X-ray Astronomy missions, such as Constellation-X (USA) and the X-ray Evolving Universe Spectroscopy Mission (XEUS, Europe). After several years of very successful development of single pixel microcalorimeters (SRON showed a record energy resolution Δ E FWHM=3.9 eV for 5.9 keV photons, combined with an effective time constant of 150 μs and high X-ray absorption efficiency (94%)) work towards an array of 32×32 pixels has started. Aiming at a prototype of 5×5 pixels, several options for fabrication, using micromachining techniques are under study, both experimentally and theoretically. Measurement of thermal transport in detector support structures at sub-Kelvin temperatures indicates ballistic phonon transport. The detector development is accompanied by finite element modeling.

A New Method to Map Flares in Quasars

Recently, Chartas et al. detected a rapid X-ray flare in the gravitationally lensed, multiple-image quasar RX J0911.4+0551. Dramatic events, such as rapid X-ray flares, are useful for providing high-precision measurements of the time delays between multiple images. In this paper we argue that there is a new possibility for measuring time delays between multiple images of gravitationally lensed quasars and constraining the locations of putative flares that give rise to the intrinsic rapid variabilities of quasars. The realization of these goals, however, cannot be achieved at present because of the limited accuracy of the current measurements. We predict that timing flares with accuracies of the order of a few seconds will be needed to probe the location of the flares. The method that we are proposing will work with better instruments in near future, such as the X-Ray Evolving Universe Spectroscopy Mission.

Robotics in the service of astronomy

Robotics is an engineering discipline that has much to offer astronomy. Although its application to planetary science is broadly appreciated, its potential for astronomy is not so widely known, We present a brief outline of some of the benefits of using robots in space-based astronomy. We hope to engage the astronomy community in demonstrating the capabilities of robotics and how this type of technology can be deployed to maximize the scientific return from space-based astronomy missions. We consider in particular the role of the European Robotic Arm (ERA) mounted on the International Space Station (ISS) in the proposed XEUS (X-ray Evolving Universe Spectroscopy) mission. We also consider other potential areas in which robotics can enhance astronomical technology. We submit that robotics will become increasingly important for astronomy as an observational discipline for future generations of astronomy platforms in space.

Superconducting tunnel junctions as photon- counting imaging spectrometers from the optical to the x-ray band

Superconducting tunnel junctions (STJs) have been exten- sively investigated as photon detectors. They combine intrinsic energy resolution with good detection efficiency and high responsivity, thus pro- viding energy-resolved photon-counting performance in a wide energy range, from the near IR (NIR) to the x rays. On this basis, STJs offer advantages with respect to alternative photon detection systems, such as an intrinsic energy resolution, higher speed, and when compared to wavelength dispersive systems, increased detection efficiency. We over- view the STJ development in the Astrophysics Division of the European Space Agency (ESA), including STJ fabrication and operation, spectro- scopic performance of single STJs, small arrays, and STJ-absorber structures in the UV-NIR and x-ray bands. As a first application we de- scribe S-Cam, a cryogenic camera for ground-based optical astronomy exploiting a 636 array of Ta STJs. This camera has undergone four campaigns at the 4.2-m William Herschel Telescope at La Palma (Spain), and future generations of the camera are under active develop- ment. For the soft x-ray band (50 to 3000 eV) a STJ-based instrument with an active area of 73 7m m 2 is proposed as part of the payload of the X-ray Evolving Universe Spectroscopy (XEUS) mission, which is cur- rently under study at ESA. Future developments include devices based on lower Tc superconductors for improved energy resolution as well as larger format detector arrays combined with alternative readout schemes. © 2002 Society of Photo-Optical Instrumentation Engineers.

Structural analysis of a cryogen-free refrigerator for space

Future X-ray observatories in space, such as European Space Agency's (ESA) X-ray evolving universe spectroscopy (XEUS) mission, will require cooling to the region 10–100 mK to enable the utilisation of advanced cryogenic photon detectors in cryogenic spectrometer instruments. Such missions are envisaged to be completely cryogen-free, replacing the traditional superfluid liquid helium cryostat with a space worthy mechanically cooled system. As part of the Mullard Space Science Laboratory's (MSSL) adiabatic demagnetisation refrigerator (ADR) development programme, we have investigated the construction of a flight cryostat containing a 10 mK ADR (the MSSL double ADR (dADR)) that can be cooled by a single Astrium (formally Matra Marconi Space (MMS)) 4 K mechanical cooler. A proto-type dADR has been constructed and will be flight proven as part of a sounding rocket payload, where the dADR system will be used to cool an array of superconducting tunnel junction (STJ) detectors at the focus of an X-ray telescope.

Active pixel matrix for X-ray satellite missions

Presents an active pixel matrix for high rate, spectroscopic and imaging X-ray detection. It is foreseen as a wide field imager on the XEUS (X-ray Evolving Universe Spectroscopy) satellite. A 1024/spl times/1024 pixel device with pixel sizes of 50-75 /spl mu/m shall cover an area of 76 mm/spl times/76 mm. A single pixel consists of a p-channel DEPFET (DEPleted Field Effect Transistor). It is realized on high-Ohmic detector grade silicon allowing the bulk to be fully depleted to achieve high quantum efficiency. In a matrix arrangement pixels are interconnected in such a way that single rows can be randomly accessed and read-out. Various read-out modes can be realized making this detector an ideal instrument for the high dynamics in the photon flux on XEUS. A 64/spl times/64 pixel matrix prototype has been produced at the Max-Planck-Institut fu/spl uml/r Physik Halbleiterlabor (HLL). The authors describe the test system setup, and present measurements, which characterize the expected performance for a focal plane instrument.

Wide field imaging spectrometer for ESA's future X-ray mission: XEUS

An active pixel sensor (APS) based on the DEpleted P-channel junction Field Effect Transistor (DEPFET) concept will be described as a potential wide field imager for ESA's high resolution, high throughput mission: `X-ray Evolving Universe Spectroscopy’ (XEUS). It comprises a parallel multichannel readout, low noise at high speed readout, backside illumination and a fill factor of 100% over the whole field of view. The depleted thickness will be 500 microns. These design parameters match the scientific requirements of the mission. The fabrication techniques of the DEPFET arrays are related to the high resistivity process of the X-ray pn-CCDs. Potential extensions of the already realized DEPFET structures are a non-destructive repetitive readout of the signal charges. This concept will be presented. As an alternative solution, frame store pn-CCDs are considered having the same format and pixel sizes as the proposed DEPFET arrays. Their development is a low risk, straightforward continuation of the XMM devices. Potential extensions of the already realized DEPFET structures are a non-destructive repetitive readout of the signal charges. This concept will be presented.

High-Energy Astronomy From The International Space Station

The European Space Agency, ESA, is currently studying 3 high-energy astronomy missions that use the International Space Station (ISS). These are Lobster-ISS, an all-sky imaging X-ray monitor, the Extreme Universe Space Observatory (EUSO) which will study the highest energy cosmic rays by using the Earth's atmosphere as a giant detector and XEUS — the X-ray Evolving Universe Spectroscopy Mission, a potential successor to ESA's XMM-Newton X-ray observatory. These first 2 missions will he attached to the external platforms on the Columbus module, while XEUS will visit the ISS to attach additional X-ray mirrors to enlarge the original 4.5 m diameter mirrors to the 10 m diameter required to observed redshifted iron lines from massive black holes in the early Universe.

Thermal conductivity of several fibre-reinforced composites between 2 K and 300 K

Future X-ray observatories in space, such as European Space Agency's (ESA) X-ray evolving universe spectroscopy (XEUS) mission, will require cooling to the region 10–100 mK to enable the utilisation of advanced cryogenic photon detectors in cryogenic spectrometer instruments. Such missions are envisaged to be completely cryogen-free, replacing the traditional superfluid liquid helium cryostat with a space worthy mechanically cooled system. As part of the Mullard Space Science Laboratory's (MSSL) adiabatic demagnetisation refrigerator (ADR) development programme, we have investigated the construction of a flight cryostat containing a 10 mK ADR (the MSSL double ADR (dADR)) that can be cooled by a single Astrium (formally Matra Marconi Space (MMS)) 4 K mechanical cooler. A proto-type dADR has been constructed and will be flight proven as part of a sounding rocket payload, where the dADR system will be used to cool an array of superconducting tunnel junction (STJ) detectors at the focus of an X-ray telescope.