ESA Science & Technology - Publication Archive

The X-ray telescope forms the core of the high energy astrophysics observatory XEUS, currently under study at ESA as a well positioned candidate for its Cosmic Visions 1525 Science Programme, which is presently under formulation. The science requirements of XEUS are particularly demanding, combining a large effective area (10m2 at 1 keV), moderate angular resolution (5 requirement, with a goal of 2), and a low mass for the optics system. The preferred operational orbit for XEUS is a halo orbit around the Lagrangian Point 2 (L2). Background and costing considerations led to the requirement of a single focal plane location, which in combination with the required broad energy response function, in turn requires a focal length of 50m. The mission design is based on formation flying, with the Mirror Spacecraft (MSC) flying inertially, and the Detector Spacecraft (DSC) actively following the focal point. The ambitious XEUS telescope relies on the novel X-ray technology currently under development in Europe. The X-ray optics technology development activities and status as well as the telescope design in general are addressed.

Future missions that may be deployed in the European Space Agencys Cosmic Visions 2025 scientific programme may include high energy astrophysics observatories that require focusing optics with unprecedented collection area. We describe scientific drivers for such missions, and discuss various implementations of optics designs that could satisfy the requirements. Options for lightweight reflectors and a possible implementation scenario are described and trade-offs for various coatings are presented.

The next generation astronomical X-ray telescopes (e.g. XEUS) require extremely large collecting area (10 m²) in combination with good angular resolution (5 arcsec). The existing technologies such as polished glass, nickel electroforming and foil optics would lead to excessively heavy and expensive optics, and/or are not able to produce the required large area or resolution. We have developed an entirely novel technology for producing X-ray optics which results in very light, stiff and modular optics which can be assembled into almost arbitrarily large apertures, and which are perfectly suited for XEUS. The technology makes use of commercially available silicon wafers from the semiconductor industry. The latest generation silicon wafers have a surface roughness that is sufficiently low for X-ray reflection, are planparallel to better than a micrometer, have almost perfect mechanical properties and are considerably cheaper than other high-quality optical materials. The wafers are bent into an accurate cone and assembled to form a light and stiff pore structure with pores of the order of a millimeter. The resulting modules form a small segment of a Wolter-I optic, and are easily assembled into an optic with large collecting area. We present the production principle of these silicon pore optics, the facilities that have been set up to produce these modules and experimental results showing the excellent performance of the first modules that have been produced. With further improvement we expect to be able to match the XEUS requirements for imaging resolution and mass.

Producing the next generation of X-ray optics, both for large astrophysics missions and smaller missions such as planetary exploration, requires much lower mass and therefore much thinner mirrors. The use of pore structures allows very thin mirrors in a stiff structure. Over the last few years we have been developing ultra-low mass pore optics based on microchannel plate technology in glass, resulting in square, open-core glass fibres in a concentric geometry. The surface roughness inside the pores can be as low as 0.5 nm due to the extreme stretching of the surface during production. We show how improvements in the production process have led to an improved quality of the fibers and the quality of stacking the fibers in the required geometry. To achieve a higher imaging quality as required for XEUS we have developed in parallel a novel pore optics technology based on silicon wafers. The production process of silicon wafers is extremely optimised by the semiconductor industry, leading to optical qualities that are sufficient for high-resolution X-ray focussing. We have developed the technology to stack these wafers into accurate X-ray optics, set up automated assembly facilities for the production of these stacks and present very promising X-ray test results of 5.3 arcsec HEW from single reflection off such a stack, showing the great potential of this technology for XEUS and other high-resolution low mass X-ray optics.

With Photonis and cosine Research BV, ESA has been developing and testing micro pore optics for X-ray imaging. Applications of the technology are foreseen to reduce mass and volume in, for example, a planetary X-ray imager, X-ray timing observatory or high-energy astrophysics. Photonis, a world leader in the design and development of micro pore optics, have developed a technique for manufacturing square channel pores formed from extruded glass fibres. Single square fibres, formed with soluble glass cores, are stacked into a former and redrawn to form multifibres of the required dimension. Radial sectors of an optic are then cut from a block formed by stacking multifibres and fusing them to form a monolithic glass structure. Sectors can be sliced, polished, etched and slumped to form the segment of an optic with specific radius. Two of these sectors will be mounted to form, for example, a Wolter I optic configuration. To improve reflectivity of the channel surfaces coating techniques have also been considered. The results of X-ray tests performed by ESA and cosine Research, using the BESSY-II synchrotron facility four-crystal monochromator beamline of the Physikalisch-Technische Bundesanstalt (PTB), on multi-fibres, sectors and slumped sectors will be discussed in this paper. Test measurements determine the X-ray transmission and focussing characteristics as they relate to the overall transmission, X-ray reflectivity of the channel walls, radial alignment of the fibres, slumping radius and fibre position in a fused block. The multifibres and sectors have also been inspected under microscope and SEM to inspect the channel walls and determine the improvements made in fibre stacking.

The X-ray Evolving Universe Spectroscopy (XEUS) mission is under study by ESA and JAXA in preparation for inclusion in the ESA long term Science Programme (the Cosmic Vision 2015-2025 long-term plan). With very demanding science requirements, missions such as XEUS can only be implemented for acceptable costs, if new technologies and concepts are applied. The identification of the key technologies to be developed is one of the drivers for the early mission design studies, and in the case of XEUS this has led to the development of a novel approach to building X-ray optics for ambitious future high-energy astrophysics missions. XEUS is based on a single focal plane formation flying configuration, building on a novel lightweight X-ray mirror technology. With a 50 m focal length and an effective area of 10 m2 at 1 keV this observatory is optimized for studies of the evolution of the X-ray universe at moderate to high redshifts. This paper describes the current status of the XEUS mission design, the accommodation of the large optics, the corresponding deployment sequence and the associated drivers, in particular regarding the thermal design of the system. The main results were obtained in two Concurrent Design Facility (CDF) studies and other internal activities at ESTEC.

The X-ray telescope forms the core of the high energy astrophysics observatory XEUS, currently under study at ESA as a well positioned candidate for its Cosmic Visions 1525 Science Programme, which is presently under formulation. The science requirements of XEUS are particularly demanding, combining a large effective area (10m2 at 1 keV), moderate angular resolution (5" requirement, with a goal of 2"), and a low mass for the optics system. The preferred operational orbit for XEUS is a halo orbit around the Lagrangian Point 2 (L2). Background and costing considerations led to the requirement of a single focal plane location, which in combination with the required broad energy response function, in turn requires a focal length of 50m. The mission design is based on formation flying, with the Mirror Spacecraft (MSC) flying inertially, and the Detector Spacecraft (DSC) actively following the focal point. The ambitious XEUS telescope relies on the novel X-ray technology currently under development in Europe. The X-ray optics technology development activities and status as well as the telescope design in general are addressed.

The Xeus mission is designed to explore the X-ray emission from objects in the Universe at high redshifts, and the success of the mission depends critically on the deployment of a 10 square metre class telescope system in a suitable orbit for science observations. The minimisation of the telescope mass and volume becomes of critical importance for such a large facility. We describe developments of novel light weight optics that enable a reduction in mass per unit area of more than an order of magnitude, compared with traditional replication optics technology. With such a large collection area, image confusion limits become a scientific driver as well, demanding arcsecond class resolution. We describe measurements that demonstrate the improvement in resolution that gives very high confidence that these requirements can be met. Some implementation details of the mission are briefly mentioned.

If sensitive enough, future missions for nuclear astrophysics will be a great help in the understanding of supernovae explosions. In comparison to coded-mask instruments, both crystal diffraction lenses and grazing angle mirrors offer a possibility to construct a more sensitive instrument to detect gamma-ray lines in supernovae. We report on possible implementations of grazing angle mirrors and simulations carried out to determine the performance. In this study we differentiate between single and multilayer mirrors. Moreover we discuss the possibilities of double reflection implementations.

We study the gas mass fraction, f(gas), behavior in the XMM-Newton Omega project. The typical f(gas) shape of high redshift galaxy clusters follows the global shape inferred at low redshift quite well. This result is consistent with the gravitational instability picture leading to self similar structures for both the dark and baryonic matter. However, the mean f(gas) in distant clusters shows some differences to local ones, indicating a departure from strict scaling. This result is consistent with the observed evolution in the luminosity-temperature relation. We quantitatively investigate this departure from scaling laws. Within the local sample we used, a moderate but clear variation of the amplitude of the gas mass fraction with temperature is found, a trend that weakens in the outer regions. These variations do not explain departure from scaling laws of our distant clusters. An important implication of our results is that the gas fraction evolution, a test of the cosmological parameters, can lead to biased values when applied at radii smaller than the virial radius. From our XMM clusters, the apparent gas fraction at the virial radius is consistent with a non-evolving universal value in a high matter density model and not with a concordance.

We use XMM-Newton blank-sky and closed-cover background data to explore the background subtraction methods for large extended sources filling the EPIC field of view, such as nearby galaxy clusters, for which local background estimation is difficult. We find that to keep the 0.8-7.0 keV band background modeling uncertainty tolerable, one has to use a much more restrictive filter than that commonly applied. In particular, because flares have highly variable spectra, not all of them are identified by filtering the E>10 keV light curve. We tried using the outer part of the EPIC FOV for monitoring the background in a softer band (1-5 keV). We find that one needs to discard the time periods when either the hard-band or the soft-band rate exceeds the nominal value by more than 20% in order to limit the 90% CL background uncertainty to between 5% at E=4-7 keV and 20% at E=0.8-1 keV, for both MOS and PN. This compares to a 10-30% respective PN uncertainty when only the hard-band light curve is used for filtering, and to a 15-45% PN uncertainty when applying the commonly used 2-3 sigma filtering method. We illustrate our method on a nearby cluster A1795. The above background uncertainties convert into the systematic temperature uncertainties between 1% at r=3-4 arcmin and 20--25% (~1 keV for A1795) at r=10-15 arcmin. For comparison, the commonly applied 2-3 sigma clipping of the hard-band light curve misses a significant amount of flares, rendering the temperatures beyond r=10 arcmin unconstrained. Thus, the background uncertainties do not prohibit the EPIC temperature profile analysis of low-brightness regions, like outer regions of galaxy clusters, provided a conservative flare filtering such as the double filtering method with 20% limits is used.

The improved performance of cryogenic detectors has drastically enhanced their utilisation 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. Specific emphasis is given to space based astronomy in the soft X-ray regime, where superconducting tunnel junctions and cryogenic calorimeters offer well identified advantages. Possible instruments for future astrophysics space missions are also discussed, using XEUS (X-ray Evolving Universe Spectroscopy mission, presently proposed by ESA as a post XMM-Newton project) as a reference.

We report the results of a series of synchrotron characterizations of two epitaxial GaAs detectors of active areas 2.22 mm² and thicknesses 40 and 400 microns. In spite of an order of magnitude difference in depletion depths, the detectors were found to have comparable performances at ~ -40 °C, with energy resolutions of ~1 keV fwhm at 7 keV rising to ~2 keV fwhm at 200 keV and noise floors in the range 1-1.5 keV. At the lower energies, the energy resolution was dominated by leakage current and electromagnetic pick-up. At the highest energies, however, the measured resolutions appear to approach the expected Fano limit; e.g., ~950 eV at 200 keV. Both detectors were remarkably linear, with average rms non-linearities of 0.2% over the energy range 10-60 keV. By raster scanning the active areas with 20 x 20 micron² monoenergetic photon beams, it was found that the non-uniformity in the spatial response of both detectors was less than 1% and independent of energy. The material used to fabricate the detector is extremely pure. For example, low temperature photoluminescence measurements indicate that the density of the As anti-site defect (EL2) is of the order of 10¹² cm^-3, which is ~ 2-3 orders of magnitude lower than that generally reported. This indirect measurement of material purity is confirmed by Monte-Carlo simulations of the detector X-ray response, which show that in order to reproduce the observed energy-loss spectra, electron and hole trapping cross-section/density products must be <<1 cm^-1.

Future planetary missions will require advanced, smart, low resource payloads and satellites to enable the exploration of our solar system in a more frequent, timely and multi-mission manner. A viable route towards low resource science instrumentation is the concept of Highly Integrated Payload Suites (HIPS), which was introduced during the reassessment of the payload of the BepiColombo (BC) Mercury Planetary Orbiter (MPO). Considerable mass and power savings were demonstrated throughout the instrumentation by improved definition of the instrument design, a higher level of integration, and identification of resource drivers.

The higher integration and associated synergy effects permitted optimisation of the payload performance at minimum investment while still meeting the demanding science requirements. For the specific example of the BepiColombo MPO, the mass reduction by designing the instruments towards a Highly Integrated Payload Suite was found to be about 60%. This has endorsed the acceptance of a number of additional instruments as core payload of the BC MPO thereby enhancing the scientific return.

This promising strategic approach and concept is now applied to a set of planetary mission studies for future exploration of the solar system. Innovative technologies, miniaturised electronics and advanced remote sensing technologies are the baseline for a generic approach to payload integration, which is here investigated also in the context of largely differing mission requirements. A review of the approach and the implications to the generic concept as found from the applications to the mission studies are presented.

The Venus Entry Probe is one of ESA's Technology Reference Studies (TRS). The purpose of the Technology Reference Studies is to provide a focus for the development of strategically important technologies that are of likely relevance for future scientific missions. The aim of the Venus Entry Probe TRS is to study approaches for low cost in-situ exploration of Venus and other planetary bodies with a significant atmosphere. In this paper, the mission objectives and an outline of the mission concept of the Venus Entry Probe TRS are presented.

A conventional Mercury sample return mission requires significant launch mass, due to the large delta-v required for the outbound and return trips, and the large mass of a planetary lander and ascent vehicle. Solar sailing can be used to reduce lander mass allocation by delivering the lander to a low, thermally safe orbit close to the terminator. In addition, the ascending node of the solar sail parking orbit plane can be artificially forced to avoid out-of-plane manoeuvres during ascent from the planetary surface. Propellant mass is not an issue for solar sails so a sample can be returned relatively easily, without resorting to lengthy, multiple gravity assists. A 275 m solar sail with an assembly loading of 5.9 g m^-2 is used to deliver a lander, cruise stage and science payload to a forced Sun-synchronous orbit at Mercury in 2.85 years. The lander acquires samples, and conducts limited surface exploration. An ascent vehicle delivers a small cold gas rendezvous vehicle containing the samples for transfer to the solar sail. The solar sail then spirals back to Earth in 1 year. The total mission launch mass is 2353 kg, on an H2A202-4S class launch vehicle (C₃=0), with a ROM mission cost of 850 Million Euro. Nominal launch is in April 2014 with sample return to Earth 4.4 years later. Solar sailing reduces launch mass by 60% and trip time by 40%, relative to conventional mission concepts.

The Interstellar Heliopause Probe (IHP) is one of four Technology Reference Studies (TRS) introduced by the Planetary Exploration Studies Section of the Science Payload & Advanced Concepts Office (SCI-A) at ESA. The overall purpose of the TRSs is to focus the development of strategically important technologies of likely relevance to future science missions. This is accomplished through the study of several technologically demanding and scientifically interesting missions, which are currently not part of the ESA science programme. The TRS baseline uses small satellites (~ 200kg), with highly miniaturized and highly integrated payload suites. By using multiple low resource spacecraft in a phased approach, the risk and cost, compared to a single, high resource mission can be reduced.

Equipped with a Highly Integrated Payload Suite the IHP will answer scientific questions concerning the nature of the interstellar medium, how the interstellar medium affects our solar system and how the solar system impacts the interstellar medium.

This paper will present an update to the results of the studies being performed on this mission. The current mission baseline and alternative propulsion systems will be described and the spacecraft design and other enabling technologies will be discussed.

The European Space Agency is currently studying the Jovian Minisat Explorer (JME), as part of its Technology Reference Studies (TRS). TRS are model science-driven studies contributing in the ESA strategic development plan of technologies that will enable future scientific missions.

The JME focuses on the exploration of the Jovian system and particularly the exploration of its moon Europa. The Jupiter Minisat Orbiter (JMO) study, which is the subject of the present paper, concerns the first mission phase of JME that counts up to three missions spaced in time by 6 years using pairs of minisats. The scientific objectives are the investigation of Europa's global topography, the composition of its (sub)surface and the demonstration of existence of a subsurface ocean below Europa's icy crust.

The present paper describes the candidate JMO system concept, based on a Europa Orbiter (JEO) supported by a communications relay satellite (JRS), and its associated technology development plan. It summarizes an analysis performed in 2004 jointly by ESA and the EADS-Astrium Company in the frame of an industrial technical assistance to ESA.

It addresses the interplanetary transfer, the hostile radiation environment, the power generation issue, the communication system, as well as the need for high autonomy on-board.

ESA's Science Payload and Advanced Concepts Office (SCI-A) has recently introduced the Technology Reference Studies (TRS) as a technology development tool to provide a focus for the development of strategically important technologies that are of likely relevance for future scientific missions. This is accomplished through the study of several technologically demanding and scientifically interesting missions, which are not part of the ESA science programme.

The goal of the Deimos Sample Return (DSR) TRS is to study the means of collecting a scientifically significant sample from Deimos' surface and returning it to Earth. The DSR mission profile consists of a small spacecraft, launched on a Soyuz-Fregat 2B. After transferring to the Martian system, the spacecraft will enter into a co-orbit with Deimos where it will perform remote sensing observations and ultimately perform a series of sampling maneuvers. Upon completion of sampling the spacecraft will return to Earth, where the sample canister will perform a direct Earth entry.

This paper will outline the preliminary mission architecture of the DSR TRS, as well as the critical technology drivers. This will include an outline of sampling tools and methods appropriate for a small, low gravity body, as well as planetary protection and re-entry technologies.