At the July 1998 SPIE Conference, we reported about design and development as well as about fabrication, optical testing and integration of the grazing incidence ABRIXAS mirrors. In this paper we will describe the environmental and x-ray optical testing of the seven flight mirror modules and we will report about their achieved performance.

Segmented mirrors are one of the two approaches being investigated for both the Spectroscopy X-ray Telescope (SXT) and the Hard X-ray Telescope (HXT) on Constellation-X. Mirrors based on the grazing incidence foil optics pioneered by GSFC will meet the stringent Constellation-X SXT weight requirement, but the currently achieved resolution falls short of the 15 inch half-power diameter (HPD) required for Constellation-X. Significant contributions to the blur arise from the figure of individual reflectors and from inaccurate mounting. Only a small contribution to the HPD of the existing mirrors arises from the conical approximation. In this paper, we describe our program for improving the spatial resolution of segmented mirrors to meet the COnstellation-X requirement. Our effort incorporates accurately figured replication mandrels, mechanically more robust reflector substrates, high accuracy alignment, and ultimately a transition from conical to curved reflecting surfaces.

We have superpolished a diamond-turned aluminum mandrel to an axial roughness of 0.34 nm rms. The mandrel is made to the Astro-E secondary mirror design for the 81st shell. Precision metrology at 100 mm to submicron scales has established the power spectral density of the mandrel and ultralightweight gold coated replicated segments. Predicted image quality of a set of optimally aligned replicated segments of this and a matching primary is substantially improved as compared to the flight mirrors for Astro-E. This approach using metal mandrels, superpolishing, and replicated ultralightweight foil mirrors, may represent a cost-effective approach to meeting the 15 arcsec half-energy width and weight requirements for the Constellation-X mission. Descriptions of the polishing apparatus, the precision metrology instruments, and the surface data analysis are presented. The general methods describe dare applicable to precision optics for both normal incidence and grazing incidence optics.

The completed High Resolution Mirror Assembly (HRMA) of the Advanced X-ray Astrophysics Facility - Imaging (AXAF-I) was tested at the X-ray Calibration Facility (XRCF) at the NASA- Marshall Space Flight Center (MSFC) in 1997. The MSFC image model was developed during the development of AXAF-I. The MSFC model is a detailed ray-trace model of the as-built HRMA optics and the XRCF teste conditions. The image encircled-energy distributions from the model are found to general agree well with XRCF test data nd the preliminary Smithsonian Astrophysical Observatory (SAO) model. MSFC model effective-area result generally agree with those of the preliminary SAO model. Preliminary model effective-area results were reported by SAO to be approximately 5-13 percent above initial XRCF test results. The XRCF test conditions are removed from the MSFC ray-trace model to derive an on-orbit prediction of the HRMA image.

In the frame of the X-ray Multi Mirror Mission (XMM), the second European Space Agency (ESA) cornerstone project, in total five Flight Models of the Mirror Module have been built. The mirror Modules are the optical heart of the satellite. Each Mirror Module contains 58 x-ray optical quality MIrror Shells which have been produced and integrated by Media Lario. Each of these MIrror Modules has been tested in the Centre Spatial de Liege (CSL) FOCAL-X facility. The goal of these test was to measure the otpical performance of the Mirror Modules under simulated launch and in-orbit configurations, and to perform some calibration on the Mirror Modules. To achieve these goals, a full EUV collimated beam is used to assess the optical characteristic in a representative flight configuration. The x-ray performance is controlled by means of an x-ray pencil beam and an x-ray collimator. The pencil beam is used for the determination of the Mirror Shell position, wing scattering and x-ray reflectivity measurements, the later one for the effective area measurement over 1.5 to 8 keV energy range. This paper mainly deals with the latest results achieved on the Flight Model 4 Mirror Assembly and the fifth Flight Mirror Module. The first one is integrated on the spacecraft, the second has been built to serve as an additional spare flight MM of the highest quality and to further develop the mirror module production and measurement process. After the presentation of these test results, the lessons learned from the manufacturing and the testing of the mirrors will be presented.

XEUS: The X-ray Evolving Universe Spectroscopy mission represents a potential follow-on mission to the ESA XMM cornerstone currently nearing completion. XEUS represents the next logical step forward in x-ray astrophysics after the current set of mission have been launched and completed their operational lives. The development and ultimate success relies heavily on the capability of the International Space Station (ISS). In this paper we describe the key characteristics of the mission including the requirements placed specifically on the ISS and discuss the significant advances in high energy astrophysics expected from such an observatory.

To achieve the demanding aims of XEUS, which involve the detection of sources as faint as 10^-18 ergs cm^-2s^-1 a large x-ray mirror will need to be developed. This core scientific aim implies that the XEUS mirror needs to have an effective collection area at 1 keV of 30 m² coupled to a spatial resolution on-axis of between 2 and 5 arcsec, so as to avoid source confusion at these very faint flux levels. Finally a field of view of at least 5 arcmin must be covered so as to ensure that a significantly large population of high redshift x-ray sources can be observed in a single pointing over the energy band from 0.05-30 keV. Clearly the key characteristics of XEUS is the large x-ray mirror aperture coupled to the high spatial resolution. The XEUS mirror aperture of 10 m diameter is divided into annuli with each annulus subdivided into sectors. The basic mirror unit therefore consist of a set of heavily stacked thin mirror plates each retaining the correct geometry. This unit is known as a mirror petal and constitutes a complete free-standing calibrated part of the overall XEUS mirror.

The requirement set for the focal plane instruments on XEUS area addressed. The rationale for the selection of three focal plane instruments, a wide field imager with modest spectral resolution and tow narrow field imagers with high spectral resolution, is given. The principles and designs of all three instrument are shortly explained and their expected performances given. The cooling of the focal plane instruments, based on mechanical cryocoolers, is described as well.

ESA's future x-ray mission, the x-ray evolving ESA's future x-ray mission, the x-ray evolving universe spectroscopy mission (XEUS) is actually under study as a potential successor of the XMM satellite. Its collecting area for x- rays form 100 eV up to 20 eV will be about 200 times larger than compared to XMM. The angular resolution will be improved by a factor of five. The field of view will eventually be as large as 10 arcmin. Novel wide field images are needed to overcome the limitations by the state-of-the- art CCD type detectors, limited due to the high number of x- rays focused into the focal plane. To face the problem of high count rate and large formats with simultaneous good energy resolution and high quantum efficiency we have proposed two new focal plane x-ray detectors: (a) a back illuminated active pixel sensor and (b) a 200 readout channel back illuminated frame store pn-CCD. Both will be fabricated at the MPI semiconductor lab on 500 micrometers high resistivity silicon.

XEUS: The x-ray evolving universe spectroscopy mission aims to study the astrophysics of some of the most distant and hence youngest known discrete objects in the universe. In particular it specifically will measure the x-ray spectra of objects with a redshift z > 4 at flux levels below 10^-17 erg cm^-2s^-1. At these high redshifts line emission from helium-like iron and oxygen which may be observed in the x-ray spectrum will be shifted down into the soft x-ray band. This places requirements on the spectral resolution and efficiency of any instrument in the focal plane which is to measure the detailed spectra of these faint sources and through the detection of these lines determine the redshift, distance and age. A narrow field low temperature imaging spectrometer covering the energy range 0.05-3 keV is currently considered as a possible element of the suite of focal plane instruments. This instrument, with a field of view of 0.5 arc minutes, an imaging capability matched to the XEUS optics of approximately 2-5 inches, will need to achieve an energy resolution of below approximately 2 eV at 500 eV. Currently a close packed large format array of superconducting tunnel junctions is envisaged operation at a temperature of approximately 30-350 mK. Such an array will be cooled by a closed cycle system comprising a mechanical cooler with a base temperature of 2.5 K and either a low temperature ³He sorption pump providing the very low temperature stage and/or an Adiabatic Demagnetization Refrigeration. In this paper we describe the key requirements of the XEUS low energy imaging spectrometer, the performance based on prototype designs together with soft x-ray test results of prototype arrays.

A feasibility study of an imaging 32 by 32 pixel micro- calorimeter array, intended for the XEUS mission is presented. Three different concepts, theoretically leading to a detector that combines an energy resolution of 5 eV for 8 keV x-rays and a count rate of at least 100 counts/pixel, are presented and discussed. The starting point for this study is the current progress in the field of single pixel micro-calorimeters employing voltage biased transition edge sensors. The design concepts originate from different philosophies for the thermal design and geometrical lay-out and will use state of the art micro-machining and lithography. Moreover, both from an electrical and a cooling point of view SQUID read-out will be the challenge and grouping of pixels might be considered.

For staring, wide-field applications, such as a solar x-ray imager, the severe off-axis aberrations of the classical Wolter Type-I grazing incidence x-ray telescope design drastically limits the 'resolution'. Since surface scattering effects from residual optical fabrication errors are always substantial at these very short wavelengths, the field-weighted-average half-power radius is a far more appropriate measure of aerial resolution. If an ideal mosaic detector array is being used in the focal plane, the finite pixel size provides a practical limit to this system performance. Thus, the total number of aerial resolution elements enclosed by the operational field-of-view, expressed as a percentage of the number of ideal detector pixels, is a further improved image quality criterion. In this paper we describe the development of an image quality criterion for wide-field applications of grazing incidence x-ray telescopes which leads to a new class of grazing incidence designs described in a following companion paper.

The off-axis aberrations of the classical Wolter Type 1 X- ray telescope consisting of a confocal paraboloid and hyperboloid severely limit the useful angular field that can be imaged onto a flat detector. A family of alternative designs based on two hyperboloids has been developed that improves the wide-field imaging performance by aberration balancing. A particular member of this family, designated as H-T number 17, has been selected for use in the SXI instrument. The development of the SXI optical prescription and its defining parameters are first presented, then detailed otpical performance predictions are compared to those of the SXI baseline design.

We have performed x-ray specular reflectivity and scattering measurements of thermally slumped glass substrates on x-ray diffractometers utilizing a rotating anode x-ray source at the Danish Space Research Institute (DSRI) and synchrotron radiation at the European Synchrotron Radiation Facility (ESRF) optics Bending Magnet beamline. In addition, we tested depth graded W/Si multilayer-coated slumped glass using x-ray specular reflectivity measurements at 8.048 keV and 28 keV and energy-dispersive measurements in the 20-50 keV rang at a double-axis diffractometer at the Orsted Laboratory, University of Copenhagen. The thermally slumped glass substrates will be used to fabricate the hard x-ray grazing incidence optics for the High-Energy Focusing Telescope. We compared the measurements to the SODART- mirrors from the SRG telescope mission program. The surface scatter measurement of the thermally slumped glass substrates yields Half Power Diameters (HPD's) of single- bounce mirrors of full-illuminated lengths of approximately 40 arcseconds for typical substrates and as low as approximately 10 arcseconds for the best substrates, whereas the SODART mirrors yields HPD's of approximately 80 arcseconds with very little variation. Both free-standing glass substrates and prototype mounted and multilayer-coated optics were tested. The result demonstrate that the surface scatter contribution, plus any contribution from the mounting procedure, to the Half Power Diameter from a telescope using the slumped glass optics will be in the subarcminute range.In addition we measured low surface microroughness, yielding high reflectivity, from the glass substrates, as well as from the depth graded W/Si multilayer-coated glass.

Wide field x-ray telescope (WFXT) is the core instrument of the Wide Angle X-ray Survey (WAXS) mission, which is aimed at conducting a high angular resolution, high sensitivity x- ray survey over a large solid angle of the sky. The project has been developed as a feasibility study in the frame of the Agenzia Spaziale Italiana (ASI) program for small-medium satellite mission. WFXT uses grazing incidence optics based on a new design where the Wolter I profile is substituted by a five term polynomial profile. The coefficients of the polynomium are optimized to obtain high spatial resolution over a field of view of about 1 degree. The WFXT optics consist of 25 nested shells. In order to have both a large effective area at low energies and a meaningful area at higher energies, a design consisting of 9 large mirror shells and 16 smaller shells, contributing mainly at higher energies, has been developed. The outermost and innermost mirror shells have a diameter of 600 and 226 mm, respectively. The total length of the mirror shells is 120 + 120 mm, while the focal length of the optical system is 3000 mm. For the WFXT optics, in addition to the well proved manufacturing process by nickel electroforming, we considered a novel replication technique for the manufacture of the mirrors which make use of ceramic material like Silicon Carbide in order to meet the stringent requirements of high spatial resolution and low weight. In this paper we give the details of the optical design and report the rest of the x-ray measurements of the prototypes of the outermost mirror shell manufactured with nickel and SiC.

The OAB design for the Wide-Field X-ray Telescope (WFXT) employs 5-term-polynomial modifications to the Wolter-I prescription, to optimize the angular resolution over a wide field. The goal is to achieve a half-power diameter, including manufacturing errors, better than 15 arcseconds over a 1-degree field of view. The WFXT optical system will provide an effective area of 360 cm2 at 1.5 keV and 85 cm2 at 4.5 keV. It comprises 25 nested shells, with diameters from 226 mm to 600 mm and total length of 240. Here we describe the x-ray measurements made at the NASA Marshall Space Flight Center x-ray Calibration Facility of the performance of a prototype 600-mm-diameter shell. The tested shell, replicated onto a Silicon Carbide carrier to satisfy WFXT's stringent angular-resolution and weight requirements, exhibits a half-power diameter of about 10 arcseconds at 0.1 keV.

The FAR_XITE is a proposed Balloon Payload that consists of 10 nested mirror modules. The mirrors are coated with multilayers that allow FAR_XITE to reach 100 keV with better than 1 arcminute angular resolution. We describe the science objectives, optical design and specifications, and present out recent result of advances in X-ray mirror fabrication techniques.

We describe a new payload, the Chromospheric/Coronal Spectroheliograph (CCS), that is optimized for the study of the chromospheric/coronal interface and the search for the sources of energy that sustain the quiescent solar atmosphere. We will utilize the existing optical bench, electronics, and some imaging system from the inventory of multilayer telescopes built up in our previous successful rocket flights of the Multi-Spectral Telescope Array. We will develop several new optical systems to explore more fully the thermal structure of the transition region and introduce a multilayer grating spectroheliograph to permit a more precise determination of the temperature of the structures that control the flow of energy between the chromosphere and the corona.

We demonstrate a water-window condenser arrangement for transmission x-ray microscopy based on table-top sources. A spherical normal-incidence multilayer mirror is used to focus and monochromatize water-window x-ray emission from a high-brightness droplet-target laser-plasma source. The condenser arrangement is compact, has high collection efficiency, and is easy to align. The maximum normal- incidence reflectivity at the desired wavelength, (lambda) equals 3.37 nm, was determined to be up to 3 percent. The potential for compact water-window transmission x-ray microscopy using the condenser arrangement is discussed.

The new calibration x-ray/extreme UV facility for plasma diagnostics and bio-medical x-ray microscopy includes a compact solid state high-repetition laser and a universal, computer controlled target vacuum chamber with calibrated x- ray spectrometers, fast x-ray diodes and time-gated pin-hole cameras. Experimental results are presented.

A mathematical model has been developed for the calculation of the film thickness distribution on flat, spinning, and curved substrates deposited by the magnetron sputtering technique. With the use of the model it is possible to design shield or mask shapes to intercept material between source and substrate to achieve a particular gradient in film thickness. Such considerations have significant relevance in the deposition of multi-layer thin films for x- ray and neutron optics in which the allowable deviation in the measured thickness gradient from the desired is a few tenths of a percent. Examples of the procedure used to obtain uniform coatings on flat and curved substrates has been given. Further, the consequences of target wear on the film thickness distribution has been considered. Finally, the consequence of spinning the substrate through the deposition region to improve uniformity has also been considered. Good agreement between initial experimental result sand the theoretical calculations has been shown.

In this paper we will report on an activity undertaken with the aim of setting up a method for the realization of hard x-ray multilayer mirror astronomical optics based on a replication process. Our approach foresees the direct deposition of the multilayer stack on to the mandrel by ion-beam sputtering followed by the deposition of the Nickel by means of an electrolytic bath. The Nickel gives the mechanical strength to the mirrors. All deposited materials are later on separated from the mandrel by cooling it. This is a natural extension of the method already successfully used for the production of the soft x-ray optics with Au monolayer coating for the SAX, JET-X and XMM telescopes. This method is particularly convenient because permits not only of keeping the mirror supports very thin but also of achieving good imaging performances. Here we will present the main features of this method and the x-ray reflectivity and topographic results obtained from a first prototype flat sample we produced following this way.

The shape of the angular and spectral reflection curves of depth-graded x-ray multilayer mirrors may be controlled by the proper variation of the layer thicknesses. The determination of the thickness distribution of the layers that gives the best possible approximation to the desired reflection curve profile is a complicated mathematical problem. The present work reports on the application of the needle variations method to the design of graded x-ray multilayer mirrors in both angular and spectral domain.

It is important to enhance the reflectivity of multilayer supermirrors in 10-100 keV region used for hard x-ray optical systems. For this purpose design methods of multilayer supermirrors have been investigated at the grazing angle of 0.3 degrees by means of the x-ray etalon or phase matching configuration. It means that the 1st and higher order Bragg reflections emanated from different periodic lengths cooperatively enhance the reflectivity at energy bands concerned. The x-ray etalons method is useful for multi-band mirror with the band width of 5 keV or so, but becomes a bit difficult to make the energy band wider connecting gaps between isolated bands. Because heavy oscillation of reflectivity curve occurs due to adjacent destructive and constructive interference. The phase matching method is useful to get smooth reflectivity in the broad energy band and is possible to enhance the 2nd order Bragg reflection in higher energy region. We present the design of hard x-ray telescope sensitive in 25-40 keV region by means of multi-block supermirrors of Pt/C multilayers. The effective area was obtained to be more than 100 cm².

CVD SILICON CARBIDE shells have been fabricated by a scalable chemical vapor deposition vapor deposition process to demonstrate the feasibility of producing thin, lightweight optics for x-ray applications. These shells were produced by depositing SiC on shaped graphite mandrels in a CVD chamber, removing the graphite mandrels from SiC deposit followed with controlled machining to produce the required double cone surface. the size of these shells is as follows: diameter equals 250-600 mm, length equals 240-400 mm and thickness equals 1.5-2.7 mm. The roundness of the inside surface of these shells was the inside surfaces of a few shells by the epoxy replication process. Testing of two SiC shells for x-ray applications yielded a half energy width of < 15 arcsecs over a wide field of view. Important issues involved in near-net-shaping and machining of these shells are discussed.

New design concepts and materials can be used to produce very lightweight, thin foil approximations, to Wolter I and other x-ray optics. Structures are designed around a central hub and spacers that connect one spoked wheels. Figure defining, thin pins span the distance between the wheels. Thin, metal coated or multilayered, plastic foils can be formed into cones, cylinders or spirals for x-ray telescopes or lenses. Imaging and spectroscopic data obtained with x- ray lenses are presented and they indicate that a 60 cm diameter, 4.65 m focal length x-ray telescope can have a half power diameter of < 2 arcmin.

The normal incidence efficiencies of a 2400 groove/mm master grating and a replica gratin were measured using synchrotron radiation in the extreme UV region. As a result of the replication process, the replica grating had an aluminum surface with an oxide layer. An additional thin SiO₂ coating was applied to the oxidized aluminum surface for the purpose of reducing the microroughness. The efficiency of the replica grating as a function of wavelength had an oscillatory behavior that resulted from a thin-film interference effect associated with the SiO₂ coating. The measured efficiencies were compared to the efficiencies calculated by a computer program that is based on the modified integral approach. The calculation accounts for the groove profile as determined from atomic force microscopy, the optical properties of the grating surface and the three layers, and the polarization of the incident radiation. The measured and calculated efficiencies are in good overall agreement.

The multilayer coated grating for high energy x-ray spectroscopy above 6 keV was developed. We study the grating optics for high energy region using multilayer. We coated the laminar type grating, groove density/mm and depth of groove is 40 nm, with Pt/C multilayer, number of layer pairs is 10 and periodic length is 4.8 nm. We measured this gratings using the x-ray beam-line Nagoya University with the x-ray CCD system. The efficiency at the first order of grating was about 30 percent at the energy of Cu-K(alpha) with energy resolution of 128.

With holographic-ion beam etching technique, a number of self-supporting transmission gratings have been fabricated for inertial confinement fusion diagnosis. In addition to the general process, a practical method for monitoring the evolution of the grating structures exposed in photoresist during development of the resist. The real-time monitor technique developed here is relatively simple in comparison with a He-Ne laser and detector, which needs delicate control.

New generation x-ray instruments for spacecraft such as ASTRO-E and CONSTELLATION-X have very specialized requirements, notably operation at cryogenic temperatures. Luxel Corporation, under a NASA Phase I SBIR contract, undertook the demonstration of feasibility of producing polyimide films suitable for use as x-ray filter substrates specifically optimized for cryogenic applications. 5000 angstrom thick polyimide films were processed using different cure cycles, and burst pressure analyses were performed at 293, 77, and 4 Kelvin. Test data showed that polyimide films are inherently stronger at cryogenic temperatures than at room temperature. Through cure modification, film strength was increased an additional 9 percent at 4K over that of the standard cure clearly showing the feasibility of film optimization.

This continues and extends the description of a Fourier synthesis hard x-ray polycapillary telescope which appeared in Volume 2803 of these Proceedings (1996). Topics include i) the use of a fiber optic gyroscope to stabilize fringe phase and obtain subarcminute resolution; ii) implementation of dual imaging and high-sensitivity concentrator modes; iii) differential telescope rotating to eliminate imaging systematics; iv) telescope scaling to orbital platforms with weight constraints.

The capillary focusing system has been installed into the entrance arm of the station for time-resolved studying otpical luminescence of solid state materials under soft x- ray excitation. A sensitivity of the installation as well as a spectral resolution of the analyzing monochromator can be strongly enlarged by means of the lens giving a small spot of radiation on the sample with considerably higher photon flux compared with a direct synchrotron radiation beam.

The results of the study and application of the prototype of the novel imaging spectrometer with a glass-capillary multiplexer of a 2D x-ray image of Z-pinch plasma are presented. Output channels are used to obtain an array of time-resolved spectra, which covers the full plasma evolution. A spatial resolution of the spectrometer is about 100-250 micrometers for plasma size up to 5 by 20 mm. A spectral resolution is 700-1000. A time-gated resolution is 1-2 ns.

Propagation of the x-rays generated by a small incoherent source through the capillary, is studied using the Fresnel- Kirchhoff diffraction theory. The influence of the diffraction on the propagation is demonstrated. The diffraction is manifested by the appearance of the diffraction fringes in both the guide channel and the far- field zone of the capillary output. The experimental data which confirms such a behavior of the x-rays is also presented. The result give a confirmation for the interference effects recently observed in capillary optics.

Innovative x-ray grazing incidence micromirrors have been studied theoretically and experimentally. Micromirrors are of conical, ellipsoidal or paraboloidal shape with superior surface quality. Reflecting surfaces are nickel or gold coated. These mirrors with only one reflection find most of their applications in the laboratory either as collimating or focusing elements. Calculated micromirror parameters, experimental beam profiles and input/output spectra are presented. The intensity at the mirror focus is comparable with intensities obtained with conventional arrangements with x-ray tubes dissipating more than 100 times the power of the microfocus tube. Current and potential areas of applications are discussed.

The imaging x-ray telescopes in current use mostly have limited field of view. The alternative x-ray optics geometries achieving very large fields of view have been theoretically suggested in the 70's but have been not constructed and used so far. We review the design and basic properties of the wide-field x-ray optical system based on one- and two-dimensional lobster-eye geometry and suggest technologies for their development and construction. First results of the development of replicated x-ray reflecting cells for use in 2D x-ray optics of Angel lobster eye type are presented and discussed.

The development of x-ray optics with focus on replicated grazing incidence mirrors has a long tradition in the Czech Republic. The design of the first x-ray imaging lenses stated in late 60's and the first mirrors have been available since 1970. They were flown on 8 space probes and/or experiments so far. Recently, we participate in the design and development of innovative x-ray optics for future space missions, especially for those with very large field of view. These lenses are believed to allow the first deep monitoring of the sky sphere in x-rays. There are also numerous ground-based laboratory applications.

The Multi-Spectral Solar Telescope Array (MSSTA) is a sounding rocket-borne observatory composed of a set of normal-incidence multilayer-coated telescopes that obtained selected bandpass spectroheliograms of the Solar atmosphere. These spectroheliograms were recorded on specially fabricated XUV and FUV 70mm Kodak film. Rocket launches of this instrument payload took place in 1991 and 1994 at the White Sands Missile Test Range in New Mexico, sponsored by the NASA sounding rocket experiment program. Immediately prior to the 1994 launch, visible light focusing test of each telescope were performed in-situ using a 1951 Standard Air Force High Resolution Test-target, to measure optical resolution performance. We determined that the MSSTA II telescopes performed at diffraction-limited resolutions down to 0.70 arc-second at visible wavelengths. Based on these measurements, we calculated an upper-bound to the focusing errors that incorporate the sum of all uncorrelated system resolution errors that affect resolution performance. Coupling these upper-bound estimates with the in-band diffraction limits, surface scattering errors and payload pointing jitter, we demonstrate that eleven of nineteen MSSTA II telescopes - having negligible figures of focus errors in comparison to the corresponding visible diffraction limits - performed at sub arc-second resolution at their operation FUV/EUV/XUV wavelengths during flight. We estimate the in-band performance down to 0.14 +/- 0.08 second of arc.