Far infrared interferometers in space would enable extraordinary measurements of the early universe, the formation of galaxies, stars, and planets, and would have great discovery potential. Since half the luminosity of the universe and 98% of the photons released since the Big Bang are now observable at far IR wavelengths (40 - 500 micrometers ), and the Earth's atmosphere prevents sensitive observations from the ground, this is one of the last unexplored frontiers of space astronomy. We present the engineering and technology requirements that stem from a set of compelling scientific goals and discuss possible configurations for two proposed NASA missions, the Space Infrared Interferometric Telescope and the Submillimeter Probe of the Evolution of Cosmic Structure.

The ASTRO-F project is currently in its final stage of proto-model, which is constructed same as flight-model. Since instrument goals of the Far-Infrared Surveyor (FIS) are unprecedented achievement of high sensitivity and high spatial resolution in far-infrared wavelength, the proto- model stage is important to prove the performance as the flight instrument. We mainly present here the latest optical, thermal, and mechanical properties of the proto- model of the FIS.

The design overview and current development status of the Infrared Camera (IRC) onboard the Japanese infrared space mission, ASTRO-F (commonly called as the Infrared Imaging Surveyor, IRIS), are presented. The IRC is one of the focal plane instruments of ASTRO-F and will make imaging and low- resolution spectroscopy observations in the wide spectral range of the near- to mid-infrared of 2 - 26 micrometers . ASTRO-F will be brought into an IRAS-type sun-synchronous polar orbit. The IRC will be operated in the pointing mode, in which the telescope will be pointed at a fixed target position on the sky for about 10 minutes. The pointed observation may be scheduled up to three times per orbit. The IRC has three channels: NIR (2 - 5 micrometers ), MIR-S (5 - 12 micrometers ) and MIR-L (12 - 26 micrometers ). All of the three channels use refractive optics. Each channel has a field-of-view of 10' X 10' with nearly diffraction-limited spatial resolution. The NIR and MIR-S channels simultaneously observe the same field on the sky, while the MIR-L observes the sky about 20' away from the NIR/MIR-S position. State- of-the-art large format array detectors manufactured by Raytheon/IRCoE are employed for the IRC. The NIR channel uses a 512 X 412 InSb array, and 256 X 256 Si:As IBC arrays are used for the MIR channels. Fabrication of the proto-model has been completed and the preliminary performance test is under way.

Planck associated to FIRST is one of the ESA scientific missions belonging to the Horizon 2000 program. It will be launched by an Ariane 5 in 2007. Planck aims at obtaining very accurate images of the Cosmic Microwave Background fluctuations, thanks to a spaceborne telescope featuring a wide wavelength range and an excellent control of straylight and thermal variations.

FIRST, the `Far InfraRed and Submillimeter Telescope', is the fourth cornerstone mission in the European Space Agency science program. It will perform photometry and spectroscopy in the far infrared and submillimeter part of the spectrum, covering approximately the 60 - 670 micrometers range.

The FIRST/Planck ESA program combines two ESA missions of the HORIZON 2000 program, the cornerstone mission of the Far InfraRed and Submillimeter Telescope and the third medium sized mission, Planck. An overview is given in this paper of the current system design, the performance parameters and an outlook on the spacecraft development.

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.

Composite materials are an ideal choice for the FIRST Telescope, since they provide dimensional stability, excellent stiffness to weight ratios, near zero thermal expansion, and manufacturing flexibility. The most challenging aspect of producing an all-composite FIRST telescope, is the development of the lightweight primary mirror. The design of the primary mirror must satisfy requirements for surface accuracy to operating temperatures of 80 +/- K as well as stiffness and strength considerations during launch.

SPIRE, the Spectral and Photometric Imaging Receiver, will be a bolometer instrument for ESA's FIRST satellite. Its main scientific goals are deep extragalactic and galactic imaging surveys and spectroscopy of star-forming regions in own and nearby galaxies. The SPIRE detectors are feedhorn- coupled NTD spider-web bolometers. The instrument comprises a three-band imaging photometer covering the 250 - 500 micrometers range, and an imaging Fourier Transform Spectrometer (FTS) covering 200 - 670 micrometers . The photometer has a field of view of 4 X 8 arcminutes which is observed simultaneously at 250, 350 and 500 micrometers with dichroic beam dividers separating the three spectral bands. Its angular resolution is determined by the telescope diffraction limit, with FWHM beam widths of approximately 17, 24 and 35 arcseconds at 250, 350 and 500 micrometers , respectively. An internal beam steering mirror can be used for spatial modulation of the telescope beam, and observations can also be made by scanning the telescope without chopping, providing better sensitivity for source confusion-limited deep surveys. The FTS has a field of view of 2.6 arcminutes and an adjustable spectral resolution of 0.04 - 2 cm^-1 ((lambda) /(Delta) (lambda) equals 20 - 1000 at 250 micrometers ). It employs a dual-beam configuration with novel broad-band intensity beam dividers to provide high efficiency and separated output and input ports.

The SPIRE instrument for the FIRST mission will consist of a three band imaging submillimeter photometer and a two band imaging Fourier Transform Spectrometer (FTS) optimized for the 200 - 400 micrometers range, and with extended coverage out to 670 micrometers . The FTS will be used for follow-up spectroscopic studies of objects detected in photometric surveys by SPIRE and other facilities, and to perform medium resolving power (R approximately 500 at 250 micrometers ) imaging spectroscopy on galactic and nearby extra-galactic sources.

We report on aspects of the SPIRE design, with beam simulation examples from trade-off studies on Lyot-stop design, and end-to-end computations of instrument field-of- view response.

The Photoconductor Array Camera and Spectrometer is one of the three science instruments for ESA's Far Infra-Red and Submillimeter Telescope. It employs two 16 X 25 pixels Ge:Ga photoconductor arrays (stressed/unstressed) to perform imaging photometry and imaging line spectroscopy in the 60 - 210 micrometers wavelength band. In photometry mode, it will simultaneously image two bands, 60 - 90 or 90 - 130 micrometers and 130 - 210 micrometers , over fields of view of approximately 1' X 1.5' and approximately 2' X 3', respectively, with full beam sampling in each band. In spectroscopy mode, it will image a field of approximately 50' X 50', resolved into 5 X 5 pixels, with an instantaneous spectral coverage of approximately 1500 km/s and a spectral resolution of approximately 175 km/s. In both modes background-noise limited performance is expected, with sensitivities (5(sigma) in 1h) of 4 - 6 mJy or 2 - 8 X 10^-18 W/cm², respectively.

The Photoconductor Array Camera and Spectrometer (PACS) will be equipped with two sensor arrays consisting of 16 X 25 pixels each. Arranged in linear arrays of 16 detectors the sensitivity of the sensors is tuned to the wavelength ranges 60 micrometers to 130 micrometers and 130 micrometers to 210 micrometers , by applying different levels of stress to the Ge:Ga crystal utilizing a special leaf spring which is part of each of the 25 modules. The electronics of the sensors are mounted on the same module but thermally isolated from the sensor level which is at a lower temperature of about 2 K. The sensors are read out by a specially developed integrating and multiplexing cryogenic read-out electronics. With a fore optics made of light cones in front of the detector cavities a 100% filling factor is achieved and a high quantum efficiency close to 0.5 is expected. In order to achieve extremely good stress uniformity in all detectors and therefore equal cutoff wavelengths, a high degree of the quality of the Ge:Ga detectors and of the assembling components used for this dedicated stress mechanism is required. The first 6 engineering modules have been successfully manufactured and tested afterwards. The relative responsivity of a set of pixels has been determined and a good performance has been demonstrated for the sensors, which are very close to fulfilling the requirements for PACS aboard the infrared spectra telescope FIRST.

This paper describes a novel On-Board data compression concept of the FIRST/PACS mission of the European Space Agency. Using the lossy and lossless compression, the presented method offers a high compression rate with a minimal loss of potentially useful scientific data. It also provides higher signal to noise ratio than that for standard compression techniques. The various modules of the data compression concept are discussed in detail. We demonstrate the method on synthetic data.

In Bischof et al. (this conference) a novel on-board data reduction concept for FIRST/PACS is proposed, consisting of following modules: ramp fitting, integration, glitch detection and spatial/temporal redundancy reduction. In this paper we outline the experiments of the data reduction software on synthetic and astronomical data. These experiments demonstrate the feasibility of this novel approach. The evaluation of its core modules on observational data from ISO is presented. We mainly focus on the performances of the ramp fitting and the glitch detection modules.

The Heterodyne Instrument for FIRST is comprised of five SIS receiver channels covering 480 - 1250 GHz and two HEB receiver channels covering parts of 1410 - 1910 GHz and 2400 - 2700 GHz. Two local oscillator sub-bands derived from a common synthesizer will pump each receiver band. The synthesizer, control electronics and frequency distribution will be performed in the spacecraft service module. The service module will be connected in the local oscillator unit on the outside of the cryostat with a WR-28 waveguide for each of the 14 local oscillator sub-bands. the local oscillator unit will be passively cooled and thermally isolated from the cryostat wall. The module is comprised of seven units, one for each receiver band, containing two multiplier chains consisting of a k- to w-band multiplier, a MMIC power amplifier operating in one of five bands between 71 and 113 GHz, the high frequency multipliers, launching optics and electrical distribution. The entire assembly will be cooled to 120 K. The local oscillator system has the two field technical challenge of providing broad band frequency coverage at very high frequencies. This will be achieved through the use of high power GaAs MMIC amplifiers and planar diode multiplier technology in a passively cooled 120 Kelvin environment. The design criteria and the resulting overall system design will be presented along with a programmatic view of the development program and development progress.

The Heterodyne Instrument for the Far-Infrared and Sub- millimeter Telescope requires local oscillators well into the terahertz frequency range. The mechanism to realize the local oscillators will involve synthesizers, active multiplier chains (AMC's) with output frequencies from 71 - 112.5 GHz, power amplifiers to amplify the AMC signals, and chains of Schottky diode multipliers to achieve terahertz frequencies. We will present the latest state-of-the-art results on 70 - 115 GHz Monolithic Millimeter-wave Integrated Circuit power amplifier technology.

Several astrophysics and Earth observation space missions planned for the near future will require submillimeter-wave heterodyne radiometers for spectral line observations. One of these, the Far InfraRed and Submillimeter Telescope will perform high-sensitivity, high-resolution spectroscopy in the 400 to 2700 GHz range with a seven channel super- conducting heterodyne receiver complement. The local oscillators for all these channels will be constructed around state-of-the-art GaAs power amplifiers in the 71 to 115 GHz range, followed by planar Schottky diode multiplier chains. The Jet Propulsion Laboratory is responsible for developing the multiplier chains for the 1.2, 1.7, and 2.7 THz bands. This paper will focus on the designs and technologies being developed to enhance the current state- of-the-art, which is based on discrete planar or whisker contacted GaAs Schottky diode chips mounted in waveguide blocks. We are proposing a number of new planar integrated circuit and device topologies to implement multipliers at these high frequencies. Approaches include substrateless, framed and frameless GaAs membrane circuitry with single, and multiple planar integrated Schottky diodes. Circuits discussed include 200 and 400 GHz doublers, a 1.2 THz tripler and a 2.4 THz doubler. Progress to date, with the implications of this technology development for future Earth and space science instruments, is presented.

The Heterodyne Instrument for FIRST (HIFI) is a heterodyne receiver system which has an intermediate frequency (IF) amplifier that will likely exhibit 1/f-type gain fluctuations. Although the level of fluctuation is very small, wideband spectral observations require exceptional stability. A methodology for measuring 1/f fluctuations is described along with measurements of two amplifiers. Comparisons are made with previous 1/f measurements of HEMT amplifiers. The implications for HIFI are described.

We present a versatile digital autocorrelation spectrometer designed to suit the needs of HIFI, the sub-millimeter heterodyne instrument of the ESA's FIRST satellite. This spectrometer will offer a set of three observation modes with different `on-line resolution/total band-width' combinations (82 kHz/500 MHz, 163 kHz/1 GHz and 325 kHz/2 GHz). An original architecture based on mixed Gallium Arsenide and Silicon technologies, allowed us to realize a 1024 channel, low power consumption and high speed correlation module: 4 mW per channel at 550 MHz clock frequency. A prototype spectrometer has been developed. It includes a 2 X 250 MHz Image Rejection Mixer, a 500 MHz clock frequency analogue to digital converter, and two 1024 channel digital correlators. This model has been integrated and tested (in laboratory and on telescope). We expose these test results.

The wideband acousto-optical spectrometer (WBS) for HIFI- FIRST is comprised of two array-AOS with 4 times 1 GHz bands each. There are some advantages to this design, the most important one is that relative frequency and amplitude variations between the 4 bands are rather unlikely. This is demonstrated by laboratory tests, which verify also that fairly slow beam-switching at 0.5 Hz may be a sufficient chop speed for HIFI. The performance of array-AOS has also been demonstrated during measurements at ground-based observatories. WBS consists of three independent units, one IF-, one optics-, and one electronics-unit. Some of the details of the WBS design are described, and the present performance estimates are given.

An engineering model has been built for a space-borne 640- GHz SIS receiver. It is the key component of Superconducting Submillimeter-Wave Limb-Emission Sounder, which is to be operated aboard the Japanese Experiment Module of the International Space Station in 2005. The receiver includes two Superconductor-Insulator-Superconductor (SIS) mixers cooled at 4.5 K, as well as four High-Electron-Mobility- Transistor (HEMT) amplifiers, two of which cooled at 20 K and the other two at 100 K. These components are integrated in a compact cryostat with two-stage Stirling and Joule- Thomson refrigerators. The receiver components has been successfully cooled and the cryostat has survived random vibration tests. The 640-GHz SIS mixer, which uses a pair of Nb/AlOx/Nb junctions connected in parallel, is built so that a broad RF matching be achieved without mechanical tuners. It is followed by cooled low noise HEMT amplifiers with a noise temperature of less than 17 K. The total receiver noise temperature has been measured around 180 - 220 K over the bandwidth of 5.5 GHz.

Hybrid sensors performance critically depends on the performance of the analog read-out electronics. The analog design methodologies are very well known and documented provided the operating temperature stays above temperatures where freeze-out occurs. Even though the behavior of individual MOS transistors at low temperature, i.e. below 30 K, has been studied in detail, this has not yet led to design guidelines for the design of building blocks and or complete systems that will operate satisfactorily at these low temperatures. Here, we present some of these guidelines and their application to the design of a low power high gain amplifier.

A gallium arsenide photoconductive detector, which is sensitive in the far-infrared wavelength range from approximately 60 micrometers to 300 micrometers , offers the advantage of extending considerably the long wavelength cut-off of presently available photodetectors. FIRGA is an ESA sponsored GaAs detector development program which is approaching completion. The FIRGA study is intended to prepare the technology for large 2D GaAs detector arrays for far-infrared astronomy. The primary goal of the development is the preparation of a monolithic 32 element demonstrator array module with associated cryogenic read-out electronics. Continuous progress in material research has led to the production of pure and doped n-type GaAs layers using liquid phase epitaxy. We prepared sample detectors from those materials and investigated their electrical and infrared characteristics. Finally, a multi-layer structured detector device was manufactured. The 4 X 8 element array configuration is defined by sawing a split pattern into the layers with pixel size 1 mm X 1 mm. The device is back illuminated. The 32 pixels are connected to two cryogenic read-out electronics chips mounted close-by. Results of the initial detector performance tests are reported. We determined dark current, responsivity and response transients. Ongoing development activities will concentrate on material research, i.e. the production of n-GaAs layers of ultra-high purity and those with improved FIR characteristics using new centrifugal techniques for material growth.

The Photoconductor Array Camera and Spectrometer (PACS) is one of the scientific core instruments on board of the ESA Horizon 2000 Cornerstone Mission FIRST: The PACS instrument can operate as a dual-band imaging photometer or as an integral-field spectrometer. The scientific instrument, designed for remote measurements of astronomical far- infrared emissions, incorporates several temperature levels between 1.7 and 15 K in order to keep the self-emission of the instrument at a low level.

The SPIRE instrument covers the 200 - 670 micron spectral range with a three-band, 4' X 8' diffraction limited field of view photometer, and a dual-band, 2.6' diameter field of view imaging FTS. Optimization of the photometer optics has been given a high priority in the instrument design, allowing an all-reflecting configuration with seven mirrors in one plane. The design corrects for the large tilt of the telescope focal plane due to the off-axis position of the SPIRE field of view, and provides two pupil images (where a beam steering mirror and a cold stop are located) and two field images (where a pick-off mirror for the spectrometer and the final image are located). A large back- focal length allows for dichroic band separators and beam folding mirrors. The spectrometer is a Mach-Zehnder-type, dual channel FTS providing two input and two output ports. The output ports are physically separated from the input ports, and the second input port is fed from a black-body source providing compensation of the telescope background, required to minimize the effect of jitter noise. Powered mirrors are used within the interferometer arms to minimize beam diameters and to leave maximum space for the scan mechanism. The complementary output ports are filtered by band-pass filters to provide the two spectral channels required.

The deployable optical telescope, the second project of the Air Force Research Laboratory's Integrated Ground Demonstration Laboratory, will demonstrate critical integration technologies associated with the next generation of beam expanders for space-based laser systems and large apertures for tactical surveillance systems. AFRL's development will be carried in cooperation with the contractor community and have direct ties to the future program offices that will utilize the DOT technologies. A flow down of total wavefront error acceptable for future operational systems has been used to derive DOT experiment requirements. The sub-scale DOT will demonstrate the initial deployment of a segmented primary and secondary tower in a 1-g laboratory environment.

The Air Force Research Lab is proposing a DoD partnership with NASA on NEXUS; a deployable optics flight demonstrator scheduled to launch in 2004. NEXUS is designed to demonstrate technologies for the Next Generation Space Telescope, primarily the deployment and wave front control of a 2.8 meter optical telescope in space.

Next generation optical space telescopes with apertures > 10 m for imaging, lidar, communications and directed energy focusing will be unable to use conventional technologies which are impractical or too costly. Our resolution is to construct a telescope from a lightweight, membrane primary, which is holographically corrected for surface distortions, in situ. In order to design a practical space telescope, a scheme by which temporal variations in the mirror surface, caused by thermal and gravitational stresses must be found. We present evidence that a primary static hologram combined with a secondary adaptive optics system may be the least expensive and simplest approach.

The aperture of monolithic space telescope primary mirrors placed on orbit is limited to payload faring diameters, the largest being about 4-meters. This requires a novel stowage approach for monoliths larger than 4-meters. Very large aperture telescopes, 50 to 100-meter diameters, planned for deployment in the next 10 to 20 years will also require very large mirror segments in an effort to manage the phasing of the entire surface. The larger the mirror panels the fewer that will be required for such apertures. If the mirrors can be made thin enough to be deformed into a cylinder or undeformed but closely nested, enough surface area can be placed on orbit to facilitate large aperture telescope mirrors. 8-meter monolithic mirrors can be rolled into a 2.5-meter diameter cylinder with the secondary support structure stowed in the cylinder to maximize the payload faring volume. Hyper-thin mirrors can be closely nested in order to maximize volume as well. Presented is a design and engineering model of a 0.9-meter diameter hyper-thin, ultra- lightweight spherical composite mirror and methods, which led to the fabrication of the mirror.

Future space telescopes rely on advances in technology to enable fabrication of primary mirrors with orders of magnitude more area, yet similar mass as current mirrors. This requires a shift of paradigm from the concept of the mirror as a rigid, stable unit, to the idea of the mirror as a system that uses active control to maintain the figure of a flexible surface. We discuss issues for this new class of optics and present status on a 2-m prototype mirror for NGST.

Large space based telescopes such as the Next Generation Space Telescope (NGST) have motivated the study of large deployable primary mirror concepts. This paper will explore the rationale used to develop the trade space between rigid body adjustment of segmented mirrors and full primary mirror active figure control. This discussion covers the relative merits of the two fundamental approaches with regard to complexity and system performance, including performance at cryogenic operating temperatures such as envisioned for NGST. Some of the areas covered will be mirror segment size as it relates to complexity of control, ability to address radius of curvature adjustment, impact of different mirror substrate materials choices, and other system implications such as launch loads. An area of trade considered is the amount of control achieved at the primary mirror compared to augmented control using a deformable mirror at a subsequent pupil plane.

This paper is intended to address accuracy issues associated with hygrothermal stability of ultra-lightweight composite mirror structures. Hygrothermal stability of a mirror is ultimately defined as its optical performance when subjected to temperature or moisture variations. Stability is dictated by a combination of material behavior and geometric configuration. Ideally, an isotropic material could be used that is lightweight, has high stiffness, and has no response to temperature or moisture variances. This type of material would therefore be independent of geometry. Quasi-isotropic laminated CFRP composite materials offer most of these characteristics, but are transversely isotropic with near zero hygrothermal response in the plane of the laminate and a relatively high response through the thickness. Typically, mirrors made from laminated material consist of a thin curved shell supported by an array of ribs. Interference problems arise at the rib/shell interface resulting in a `print-through' effect by the ribs. Also, adhesive used to bond the ribs to the shell pull the shell causing additional `print-through'. Additional sources of instabilities result from material variances, processing, and assembly. These multiple sources of instabilities superimpose onto each other resulting in the structures overall hygrothermal stability.

The mass of the primary mirror has dominated the mass of larger aperture (> 1 m class) telescopes. Spaceborne telescopes have much to gain from a significant reduction in areal density. Areal density is often limited by the stiffness to weight ratio of the primary mirror. Two key factors drive this criteria: telescope structural characteristics (launch and deployment) and fabrication requirements. A new class of hybrid composite mirrors has been designed, prototyped, and fabricated to demonstrate the advantage of the high stiffness to weight ratio of carbon fiber composite materials and the superior optical fabrication for low expansion glasses. This hybrid mirror utilizes a unique `set and forget' fabrication technique. A thin meniscus of glass is mounted to a stiff composite support structure using composite flexure rods. The meniscus is lightweighted using waterjet pocket milling and is conventionally polished to a precise radius of curvature. This meniscus is then supported on the flexures and actuated to a precise figure. The flexures are fixed and the actuators are removed. The substrate is then ion figured to achieve the final figure. The areal density of this mirror is 10 kg/m². Surface figure on a 0.25 m aperture prototype was demonstrated at better than (lambda) /4 (visible) prior to ion figuring. Two 0.6 m mirrors are under fabrication. The design of the mirror and results of the fabrication and testing will be discussed.

Challenges in high-resolution space telescopes have led to the desire to create large primary mirror apertures. One such telescope is the Next Generation Space Telescope (NGST, 8-m primary). In order to accommodate launch vehicles, the optical systems using these large apertures are being designed to accommodate extremely lightweight, deployable, segmented primary mirrors. The requirements for these segments include: meter-class diameter, areal densities of the order of 15 kg/m², aspheric surface figure, near infrared and visible spectrum operation, diffraction limited surface figure, high stiffness, tight radius of curvature matching, and excellent thermal stability. Operating temperatures for various systems include ambient as well as cryogenic ranges. A unique ceramic, carbon fiber reinforced silicon carbide, developed by the Industrieanlagen- Betriebsgesellschaft mbH, has shown potential for use as a mirror substrate. This paper presents the deign and predicted performance of this mirror system in various applications. Also included are issues related to the fabrication of the Advanced Mirror System Demonstrator.

Large space optics technologies are developed for government support civilian and defense applications. Within a funding constrained environment, partnerships among members of the large space optics community serve to accelerate the pace of technology development and insertion of technology products into space operations. Although missions and operating requirements are quite different for the partners, NASA and DOD have teamed to address areas of common concern. One particularly successful partnership activity is aimed at significantly reducing areal density, cost and fabrication time for large optics. Other opportunities are being explored among the government partners.

Lightweight, deployable space optics has been identified as a key technology for future cost-effective, space-based systems. The United States Department of Defense has partnered with the National Aeronautical Space Administration to implement a space mirror technology development activity known as the Advanced Mirror System Demonstrator (AMSD). The AMSD objectives are to advance technology in the production of low-mass primary mirror systems, reduce mirror system cost and shorten mirror- manufacturing time. The AMSD program will offer substantial weight, cost and production rate improvements over Hubble Space Telescope mirror technology. A brief history of optical component development and a review of optical component state-of-the-art technology will be given, and the AMSD program will be reviewed.

This paper presents experimental results relating to the Air Force Research Laboratory Precision Deployable Optics System (PDOS) ground demonstration. The PDOS experiment represents a sub-scale experimental test-bed for the demonstration of science and technology related to a large-aperture deployable space-based telescope systems. A description of the experimental test-bed is included. A description of microdynamic phenomena, referred to as `events' or `microlurches', observed during the test phase of the ground demonstration is presented. The performance of a three input, three output, high bandwidth structural controller operating in the presence of these events is presented and compared to the performance of the uncontrolled system.

In this communication, we propose a novel method for estimating the aberrations of a space telescope from phase diversity data. The images recorded by such a telescope can be degraded by optical aberrations due to design, fabrication or misalignments. Phase diversity is a technique that allows the estimation of aberrations. The only estimator found in the relevant literature is based on a joint estimation of the aberrated phase and the observed object. By means of simulations, we study the behavior of this estimator. We propose a novel marginal estimator of the sole phase by Maximum Likelihood. It is obtained by integrating the observed object out of the problem; indeed, this object is a nuisance parameter in our problem. This reduces drastically the number of unknown and provides better asymptotic properties. This estimator is implemented and its properties are validated by simulation. Its performance is equal or even better than that of the joint estimator for the same computing cost.

We present a novel and fast method for utilizing wavefront information in closed-loop phase-diverse image data. We form a 2D object-independent error function using the images at different focus positions together with OTFs of the diffraction limited system. Each coefficient in an expansion of the wavefront is estimated quickly and independently by calculating the inner produce of a corresponding predictor function and the error function. This operation is easy to parallelize. The main computational burden is in pre- processing, when the predictors are formed. This makes this method fast and therefore attractive for closed loop operation. Calculating the predictors involves error function derivatives with respect to the wavefront parameters, statistics of the parameters, noise levels and other known characteristics of the optical system. The predictors are optimized so that the RMS error in the wavefront parameters is minimized rather than consistency between estimated quantities with image data. We present simulation results that are relevant to the phasing of segmented mirrors in a space telescope, such as the NGST.

We have developed a focus-diverse phase retrieval algorithm to measure and correct wavefront errors in segmented telescopes, such as the Next Generation Space Telescope. These algorithms incorporate new phase unwrapping techniques imbedded in the phase retrieval algorithms to measure aberrations larger than one wave. Through control of a deformable mirror and other actuators, these aberrations are successfully removed from the system to make the system diffraction limited. Results exceed requirements for the Wavefront Control Testbed. An overview of these techniques and performance results on the Wavefront Control Testbed are presented.

Control algorithms developed for coarse phasing the segmented mirrors of the Next Generation Space Telescope (NGST) are being tested in realistic modeling and on the NGST wavefront control testbed, also known as DCATT. A dispersed fringe sensor (DFS) is used to detect piston errors between mirror segments during the initial coarse phasing. Both experiments and modeling have shown that the DFS provides an accurate measurement of piston errors over a range from just under a millimeter to well under a micron.

To eliminate the mounting stress of three flat reflective mirrors in Balloon-borne Solar Telescope, these optics were attached to their mounts with a thin adhesive layer. This method will also be used in Space Solar Telescope. The primary mirror will be attached to its mount with a thin adhesive layer after first procedure of polishing, then polished to its ultimate demand. In this paper, the theory of adhesive layer analysis is given, and FE model of mirror and its mount is established to analyze the behavior of adhesive layer and the mirror stress. Some experiments are taken to measure Young's modulus of adhesive layer. The possibility of this method in ground-based telescope is also analyzed.

Wavefront sensing in monochromatic light is insensitive to segment piston errors that are a whole number of waves. If the wavefront sensing is performed in several wavelengths, this ambiguity can be resolved. We give an algorithm for finding the correct phase, given multiple measurements in different wavelengths. Using this algorithm, the capture range of a wavefront sensor can be extended from on the order of +/- (lambda) /2 in piston to several waves. This relaxes the demands on an initial, coarse alignment method. The extended capture range depends on the selection of wavelengths available for phase measurements and the expected accuracy of the wavefront sensing method used.

A telescope simulator was built as part of the Nexus wavefront control testbed, an NGST technology experiment at NASA's Goddard Space Flight Center. This testbed was designed to demonstrate complete control of a segmented telescope, from initial capture of light, through coarse alignment and phasing, to fine phasing and wavefront control. The existing telescope simulator allows testing of the fine phasing and wavefront control steps. A small deformable mirror in the simulator allows generation of an unobscured aberrated wavefront, for use in exploring the range of measurement and correction using the testbed's image-based wavefront sensor and larger deformable mirror. An alternate path under development for the simulator will create a segmented wavefront using three spherical mirrors; three-degree-of-freedom mounts under each mirror enable alignment and phasing experiments that will cover most of the operation sequence. Details of the hardware design and performance will be presented.

The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched into orbit on June 24, 1999. FUSE is now making high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 angstroms). Its high effective area, low background, and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. In this paper, we describe the on- orbit performance of the FUSE satellite during its first nine months of operation, including measurements of sensitivity and resolution.

The Advanced Camera for Surveys (ACS) is a third generation instrument for the Hubble Space Telescope (HST). It is currently planned for installation in HST during the fourth servicing mission in Summer 2001. The ACS will have three cameras.

The Cosmic Origins Spacecraft (COS) is a new instrument for the Hubble Space Telescope that will be installed during servicing mission 4, currently scheduled for July 2003. The primary science objectives of the mission are the study of the origins of large scale structure in the universe, the formation, and evolution of galaxies, the origin of stellar and planetary systems and the cold interstellar medium. As such, COS has been designed for the highest possible sensitivity on point sources, while maintaining moderate ((lambda) /(Delta) (lambda) equals 20,000) spectral resolution. in this paper, the instrument design and predicted performance is summarized, as well as summary of the instrument flight and prototype component performance to date.

The Cosmic Origins Spacecraft (COS) will be the most sensitive UV spectrograph to be flown aboard the Hubble Space Telescope. The COS FUV and NUV channels will provide high sensitivity at resolution greater than 20000 over wavelengths ranging from 115 nm to 320 nm. We present a brief review of the instrument design and grating test plan as well optical test results for the first FUV grating delivered.

In June 1997, NASA made the decision to extend the end of the Hubble Space Telescope (HST) mission from 2005 until 2010. As a result, the age of the instruments on board the HST became a consideration. After careful study, NASA decided to ensure the imaging capabilities of the HST by replacing the Wide Field Planetary Camera 2 with a low-cost facility instrument, the Wide Field Camera 3. This paper provides an overview of the scientific goals and capabilities of the instrument.

The Space Sciences of Astronomy, Astro-Physics, and Astro- Biology could be advanced by ten years, perhaps more, if a faster, cheaper, better way than an entirely new spacecraft could be found to implement an 8-meter class observatory in space. Why 8 meters? Recent science results such as the Hubble Deep Field and other observations from the very large ground-based observatories suggest that to achieve the two prominent Space-Science goals of establishing the era of initial galaxy formation, and imaging and spectroscopy of Earth-like planets requires at least two magnitudes deeper imaging and a factor of six better resolution than anything now in existence or planned for UV/Optical wavelengths. The UVOWG Final Report lists agonizing details of critical science objectives toward these goals, agonizing because we cannot achieve them from the ground even with the four 8- meter mirrors of the VLTI. An 8-meter class space telescope will provide about 2.5 magnitudes deeper imaging and a factor of 6.5 better spatial resolution than the best we have now, HST. This paper describes a feasibility study for augmenting HST with 8-meter class optics. The results are very interesting, and surprising.

We will describe the development of the design and processing of the near ultraviolet (NUV, 1800 - 3000 angstroms) and far ultraviolet (FUV, 1350 - 1800 angstroms) sealed tube microchannel plate cross delay line detectors for the NASA Galaxy Evolution Explorer Satellite. Specifications for the two detector systems for GALEX define a large 65 mm diameter circular format, with high spatial resolution (< 30 micrometers FWHM, approximately 2200 X 2200 resolution elements) and good image linearity (+/- 50 micrometers ), low diffuse background rates of < 1 event cm^-1 sec^-1, and event processing rates of > 2 X 10⁵ events sec^-1. We have implemented a detector design using a microchannel plate Z stack to amplify the signals detected by the photocathodes, and a cross delay line anode to provide the photon event position encoding. These detectors were produced using a new sealed tube production facility installed at the Space Sciences Laboratory, University of California, Berkeley.

We have studied the UV sensitivity degradation of CsI and KBr thin films under UV illumination and the stability of their visible light rejection for CsI and KBr opaque photocathodes evaporated on microchannel plates. For both materials the greatest degradation of the relative quantum detection efficiency was observed near the photocathode sensitivity cut off, while there was almost no change in their EUV response. The aging of the photocathodes is likely to be independent of the angle of radiation incidence. Of the two materials the CsI films appeared to be more solar blind and less subject to visible sensitivity activation by UV exposure.

A sounding rocket observation of G191-B2B, a hot white dwarf star, was made on 27 September 1999 over a wavelength range of 220 - 340 angstroms with the Extreme ultraviolet Opacity Rocket (EOR), an EUV spectrograph. EOR acquired over 200 seconds of data above 200 km. Two broadband multilayer- coated diffraction gratings in Wadsworth mounts provide EOR with a peak effective area of 2.5 cm² near 280 angstroms and spectral resolution of (lambda) /(Delta) (lambda) equals 2500 - 3000. Preliminary examination of the flight spectrum suggests the presence of absorption features which are not apparent in lower resolution spectra.

We report on the status of a novel imaging spectrometer design based on aberration-corrected holographic gratings. The goal of the work is to develop optical designs with high spatial resolution and high sensitivity over a narrow wavelength bandpass, thus effectively creating a narrow-band imaging capability. Ideally the narrow-band capability can be used to observe astrophysical phenomena at key diagnostic lines short-ward the short-wavelength transmission cut-off of lithium fluoride (1050 angstroms) while simultaneously controlling the intense geocoronal Lyman alpha emission at 1216 angstroms. For example OVI 1032, 1038 angstroms emission from a fast shock can be observed with arc-second resolution over a 5 arc-minute field of view.

We investigate a broad system design for a space-based observatory operating at mid-infrared and visible wavelengths to perform physical characterization and discovery of near-Earth objects (NEOs) in the inner solar system. Our goals require measurements that are much more efficiently done from space. The mission objectives are to obtain accurate diameters, albedos and multiband reflectance properties for the known NEOs, and to conduct a search for objects spending most or all their orbital period inside Earth's orbit. The purpose is to observe a large fraction of the existing population during a mission operational lifetime of two years. A rather modest sized telescope (70 cm primary mirror and Ritchey-Chretien optical configuration) is found to be adequate to meet the objectives.

When the first exciting results of helioseismology were published little more than 20 years ago, the idea established soon to also apply this new tool to stars. Due to the extremely low photometric signal expected for solar type pulsation it was obvious to take advantage of the very low photometric noise level and inherent stability of space experiments, as well as of the possibility to obtain very long uninterrupted homogeneus data sets in space. Compared to what can reasonably be obtained from ground an improvement of the photometric accuracy of about two orders of magnitude is expected for such a space experiment, which, over all, will be obtained simultaneously for a relatively large number of stars. Despite these clearly identified advantages, it took some time for this new science field to be established in space programmes, as is illustrated by the history of COROT. The basic scientific concept dates back to 1981 when EVRIS (Etude de la Variabilité, de la Rotation et des Interieurs Stellaires) was proposed to CNES. The following year a similar experiment (PSIVA) was presented to ESA as a free-flyer mission, but complemented by instrumentation devoted to study stellar activities, and again in 1985 with European CoInvestigators as project PRISMA. The photometric section of PRISMA was proposed in 1987 as an experiment on the SOHO service module, but unfortunately, budget cuts and cost overruns caused a cancellation of all scientific experiments scheduled for this module. In parallel, implementations on EURECA-B were studied and as a small payload attached to the Space Station. At about the same time, EVRIS was proposed to the Sovjet Space Agency, IKI, as a photometric experiment on VESTA, a mission to asteroids, and (1986 to 1988) as a cruise-time experiment for MARS 92 and for MARS 94. Finally, end of 1988, EVRJS was accepted by IKI for MARS 94 and in 1990 by the main funding agency, CNES. While the EVRIS experiment was developed and optimized for the Mars mission, a study for a larger and more powerful follow-up mission started and lead to a concept called COROT (Convection, Rotation and Planetary Transits). The failure of the last stage of the MARS 96 launcher caused a total loss of all on board experiments, and hence also of EVRIS, but already few weeks later, CNES approved a study for COROT which was welcome with much relieve by the hitherto unlucky science team. For completeness, we have to mention that meanwhile two ESA calls for proposals of medium size missions were answered with participation of EVRIS science team members: 1989 to the M2-call with project PRISMA, a space experiment focussed on asteroseismology and stellar activities, and in 1993 to the M3-call with project STARS, specialized on asteroseismology and the detection of extrasolar planets. After fierce competition both projects were selected for full ESA Phase A studies, but lost the final selection for an ESA medium size mission. Only recently it has been realized that the same technique optimized for asteroseismology can also be efficiently used to search for extrasolar planets by observing the faible stellar luminosity decrease during the transit of a planet in front of the parent star. The requirements for such an ultra-high photometric precision put severe constraints on the instrument design, in particular on the stability, the elimination and/or control of a large variety of perturbations. COROT is the first project aiming simultaneously on asteroseismology and the detection of extrasolar planets. It has now fmished phase B and launch is planned for 2004. In the following we present a bibliography which should allow the interested reader to find a detailed description of most of the technical and scientific aspects of COROT, as well as some historical notes

GAIA is the astrophysics candidate for the ESA Cornerstone 5 mission, which is to be selected in September 2000. The GAIA mission will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our Galaxy and throughout the Local Group. This amounts to about 1 per cent of the Galactic stellar population. Combined with astrophysical information for each star, provided by on-board multi-color photometry, these data will have the precision necessary to quantify the early formation, and subsequent dynamical, chemical and star formation evolution of the Milky Way Galaxy. Additional scientific products include detection and orbital classification of tens of thousands of extra-solar planetary systems, a comprehensive survey of objects ranging from huge numbers of minor bodies in our Solar System, through galaxies in the nearby Universe, to some 500 000 distant quasars. It will also provide a number of stringent new tests of general relativity and cosmology. A complete satellite design has been developed, including the proposed payload, corresponding accuracy assessments, and results from a prototype data reduction development. GAIA can be launched in 2009, within the specific budget for the next generation ESA Cornerstone missions.

The Full-sky Astrometric Mapping Explorer (FAME) is a MIDEX class Explorer mission designed to perform an all-sky, astrometric survey with unprecedented accuracy, determining the positions, parallaxes, proper motions, and photometry of 40 million stars. It will create a rigid, astrometric catalog of stars from an input catalog with 5 < m_v < 15. For bright stars, 5 < m_v < 9, FAME's goal is to determine positions and parallaxes accurate to < 50 (mu) as, with proper motion errors < 50 (mu) as/year. For fainter stars, 9 < m_v < 15, FAME's goal is to determine positions and parallaxes accurate to < 500 (mu) as, with proper motion errors < 500 (mu) as/year. It will also collect photometric data on these 40 million stars in four Sloan DSS colors.

FAME is a MIDEX astrometry mission designed to map the position of 40,000,000 stars to an accuracy of 50 micro-arc seconds. Optimized between mission requirements, size, weight, and cost, the FAME instrument consists of a 0.6 X 0.5 m² aperture whose point spread function central peak is linearly sampled by two pixels. To achieve its astrometric mapping mission requirements, this instrument must achieve a single look centroiding accuracy on a visual magnitude 9.0 (or brighter) star of < 0.003 pixels while operating the focal plane in a time domain integration, TDI, mode. As this performance requirement represents a significant improvement over the current state of the art of 0.02 to 0.01 pixel resolution, a risk reduction experiment was conducted to determine our centroiding ability using a flight traceable CCD operated in TDI mode.

Very large space telescopes with primary mirrors made of flat segments have been recently proposed. The segments would be extremely lightweight, made like pellicles from stretched, reflective membranes. Here we consider the use of such membrane primary mirrors in which slight concave curvature is induced by electrostatic force, by application of a potential difference between the membrane and a control electrode behind. In this way segmented spherical or paraboloidal primaries of long focal length can be made directly, eliminating the correction optics needed when flat segments are used. The electric potential would be spatially and temporally controlled to obtain uniform curvature despite non-uniformity in membrane tension, to create slight asphericity if needed and to provide active damping of vibrations. We report the operation of a small prototype telescope with a SEMC primary.

As a cornerstone in NASA's Origins program, the primary goal of the Terrestrial Planet Finder (TPF) mission is to directly detect the existence of Earth-like planets around nearby stars. This paper presents a process and a software tool, based on a quantitative systems engineering methodology, to conduct architectural trade studies during the TPF mission conceptual design phase.

The thirty or so extrasolar planets that have been discovered to date are all about as large as Jupiter or larger. Finding Earth-size planets is a substantially more difficult task. We propose the use of spacebased differential photometry to detect the periodic changes in brightness of several hours duration caused by planets transiting their parent stars. The change in brightness for a Sun-Earth analog transit is 8 X 10^-5. We describe the instrument and mission concepts that will monitor 100,000 main-sequence stars and detect on the order of 500 Earth-size planets, if terrestrial planets are common in the extended solar neighborhood.

We have performed end-to-end laboratory and numerical simulations to demonstrate the capability of differential photometry under realistic operating conditions to detect transits of Earth-sized planets orbiting solar-like stars. Data acquisition and processing were conducted using the same methods planned for the proposed Kepler Mission. These included performing aperture photometry on large-format CCD images of an artificial star fields obtained without a shutter at a readout rate of 1 megapixel/sec, detecting and removing cosmic rays from individual exposures and making the necessary corrections for nonlinearity and shutterless operation in the absence of darks. We will discuss the image processing tasks performed `on-board' the simulated spacecraft, which yielded raw photometry and ancillary data used to monitor and correct for systematic effects, and the data processing and analysis tasks conducted to obtain lightcurves from the raw data and characterize the detectability of transits. The laboratory results are discussed along with the results of a numerical simulation carried out in parallel with the laboratory simulation. These two simulations demonstrate that a system-level differential photometric precision of 10^-5 on five- hour intervals can be achieved under realistic conditions.

On the basis of the measured NICMOS performance in HST-Cycle 7 and Cycle 7N programs, we analyze the behavior of the HST optical assembly at IR wavelengths. An accurate analysis of the telescope thermal status allows us to estimate the background flux observed by NICMOS, and compare it with the flux actually measured in different filters. The very close match between expected and measured fluxes confirms the validity of our model. A good understanding of the HST emissivity, which turns out to be lower than previous estimates, allows to predict with higher accuracy the performance of the future IR instruments on HST like NICMOS+cooling system and to specify critical design parameters for WFC3. Also, issues related to the long term stability of the system can be addressed more properly, providing useful quantitative insight on future missions such as the Next Generation Space Telescope.

In the XX Century in Astrometric observations of the Sun participated more than 14 observatories. It were obtained about 31000 astrometric positions of the Sun, some observatories were very active (U.S. Naval Observatory--7490 observations, Pulkovo Observatory--5495 observations, Nikolaev--3948 observations etc.).

The Space Astronomy Laboratory has built and flown a very- low-cost (approximately 50K) star tracker and digital imaging system with embedded compression. The star tracker is suitable for all rocket and spacecraft applications, and provides pitch, yaw, and roll updates at rates up to 10 Hz. The digital imaging subsystem uses a novel NASA-funded scheme of `progressive image transmission' in which the image is sent out over a very-low-bandwidth channel, such as a telemetry downlink, in such a way that it can be reconstructed `on the fly' and updated as more data arrive. Large (768 X 474) useful images can be obtained over a 4- kbit/s downlink in as little as 10 seconds. This device can act as an aspect camera, a deployment monitor, or a science imager in situations where low bandwidth is desired or high bandwidth is not available.

A one-meter Space Solar Telescope (SST) is being developed in Beijing Astronomical Observatory. This paper introduces its polarimeter that can get a polarimetric accuracy of 10^-4. By the optical design of this polarimeter we succeed in reducing the crosstalk between incident circular and linear polarization light when the polarimeter is installed in front of a birefringent filter. In this article, we select Mueller Matrix to describe the polarization characteristics of optical elements, and compare three kinds of design of polarimeter. From the error analysis we determine the orientation and retardation tolerance of the optical elements in order to control the instrumental polarization less than 10^-4. As a result of this analysis, we demonstrate the polarimeter that utilizes a rotatable polarizer and a half waveplate, which has a rotary angle of half quantity of polarizer's, is the best design for minimizing the circular crosstalk and thus is the choice for the SST Polarimeter.

The Hubble Space Telescope is arguably one of the most important and successful scientific endeavors undertaken in the twentieth century. Hubble, a modest-sized 2.4-m telescope, outperforms much larger terrestrial telescopes because it is diffraction limited, and because the sky seen from orbit is darker than the terrestrial night sky. If we increase the diameter of Hubble to 8.4-m, a diameter comparable to Keck and the VLT, the increase in capability will be comparable to that which was first achieved by Hubble's launch and subsequent repair. HST10X will allow a fast track solution of outstanding problems in astronomy. Perhaps foremost among these is the detection of earth-like planets orbiting nearby stars. HST10X can detect earth-like planets around stars at distances up to 10 parsecs. Furthermore, HST10X will enable spectroscopic examination of earth-like planets to search for atmospheric oxygen, a certain sign of life.

The Next Generation Space Telescope, planned for launch in 2009, will be an 8-m class radiatively cooled infrared telescope at the Lagrange point L2. It will cover the wavelength range from 0.6 to 28 micrometers with cameras and spectrometers, to observe the first luminous objects after the Big Bang, and the formation, growth, clustering, and evolution of galaxies, stars, and protoplanetary clouds, leading to better understanding of our own Origins. It will seek evidence of the cosmic dark matter through its gravitational effects. With an aperture three times greater than the Hubble Space Telescope, it will provide extraordinary advances in capabilities and enable the discovery of many new phenomena. It is a joint project of the NASA, ESA, and CSA, and scientific operations will be provided by the Space Telescope Science Institute.

An overview of the Lockheed Martin Team's NGST Reference Architecture is discussed. Our f/1 NGST concept includes a lightweight 8-meter primary mirror consisting of eight deployed petals. Alignment and figure control employs wavefront-sensing techniques. Infrared observations are enabled by using a tennis court size multi-layer deployed sunshield permitting the primary mirror to be passively cooled to < 40 K. Candidate Science Instruments cover the spectral range from 0.6 microns to greater than 20 microns. The Integrated Science Instrument Module (ISIM) is passively cooled to approximately 30 K. The Observatory is launched on an AtlasV-531M in 2008 and operates at the L2 LaGrange Point. Science Planning and Mission Operations are the responsibility of the Space Telescope Science Institute in Baltimore Maryland. The ISIM is the responsibility of Goddard Space Flight Center (GSFC). The Lockheed Martin Team, including Raytheon, Honeywell, and Jackson and Tull, is an NGST Phase 1 Prime Contractor. The GSFC manages the NGST Project in Greenbelt Maryland.

The Next Generation Space Telescope will be the premier instrument for astrophysical research a decade from now. This paper describes the reference concept for the observatory being studied by a prime contractor team led by TRW and Ball Aerospace. We give an overview of the space segment of the mission, and the rationale for its heliocentric orbit at the Sun-Earth L2 Lagrangian point. At the time of this meeting many details of the engineering design are still open for trade studies. We highlight a few whose resolution will have implications for the scientific performance of the observatory, and for which preferences and recommendations from the scientific community are welcomed.

The Next Generation Space Telescope (NGST) is a major element of NASA's Origins Program. It is planned to be a deployable infrared telescope with an 8 m diameter aperture and a sensitivity approximately equals 1000 times greater than any currently existing infrared telescope. The scientific goals of NGST include imaging and spectroscopic characterization of the earliest galaxies and proto-galaxies, which formed following the `big bang'. Several years ago, NASA embarked on an aggressive technology development effort covering a number of technical areas including optics, detectors, deployable structures, wavefront control, passive cooling, operations, etc. This paper presents an overview of the status of the program NASA is pursuing to provide the necessary technologies, which will enable an exciting, affordable NGST mission.

A brief overview of the Next Generation Space Telescope science instrument module is given, development plans for engineering design, enabling technologies, and science instruments are discussed. Up-coming schedule milestones of community interest are also presented.

This paper summarizes the findings of the Next Generation Space Telescope (NGST) Detector Requirements Review Panel. This panel was comprised of NGST Integrated Science Instrument Module study representatives, detector specialists, and members of the NGST project science team. It has produced a report that recommends detector performance levels, and has provided rationale for deriving these levels from basic, anticipated NGST science goals and programs. Key parameters such as detector array format, quantum efficiency, and noise are discussed and prioritized.

Advanced space telescopes which will eventually replace the Hubble Space Telescope will have 8 - 20 m diameter apertures. Primary mirrors of these dimensions will fold to fit into the space launcher. By necessity, these mirrors will be extremely lightweight and flexible. The historical approaches to mirror designs, where the mirror is made as rigid as possible to maintain figure and to serve as the anchor for the entire telescope, can no longer be applied. New design concepts and verification will depend entirely on analytical methods to predict optical performance. Integrated modeling of the structural, thermal, and optical performance of such mirrors is becoming the tool for advanced space mirror designs. This paper discusses some of the tasks and study results which are currently the basis for the design and integrated modeling studies of the Next Generation Space Telescope.

An Integrated Product Team was formed to develop a detailed concept for optical test methodology for testing of the NGST individual primary, secondary and tertiary mirrors and the full telescope system on the ground. The large, lightweight, deployable primary mirror, and the cryogenic operating environment make optical testing of NGST OTA (Optical Testing Assembly) extremely challenging. A telescope of the complexity of NGST has never been built and tested on the ground in 1-g environment. A brief summary of the preliminary metrology test plan at the mirror component and telescope system level is presented.

A near and a mid infrared imaging camera for the NGST are presented, which were studied under ESA contract. Imaging in the 1 to 5 microns domain, possibly extended to 0.6 microns is a strong requirement for the core programs identified for NGST. Our compact near-IR camera design emphasizes simplicity with a single optical train covering a field 6 X 3 arcmin² with a fixed spatial sampling of 0.03 arcsec/pixel on a 12 k X 6 k detector array. Three filter wheels allow for broad band and narrow band imaging. A mid- IR camera on NGST will be capable of carrying out aspects of many programs in the DRM. In addition to mid-IR is relatively unexplored at the spatial resolution and sensitivity NGST will be capable of, and so there is great potential for serendipitous science. A compact mid-IR camera design is presented covering a field 2.5 X 2.5 arcmin² in the spectral range from 5 - 28 micrometers with two optical channels and a critical spatial sampling of 0.075 arcsec at 5 micrometers and 0.15 arcsec at 10 micrometers wavelengths.

An Integral Field and Multiobject Spectrograph (IFMOS) for NGST has been studied for the European Space Agency by a European consortium. This paper describes the design of the integral field unit (IFU), the optical system which divides up the 2D field and reformats in into one or more slits. The IFU uses the Advanced Image Slicer concept, which has many advantages over other designs of IFU and is particularly well suited to space applications.

We discuss work in progress on a near-infrared tunable bandpass filter for the Goddard baseline wide field camera concept of the Next Generation Space Telescope Integrated Science Instrument Module. This filter, the Demonstration Unit for Low Order Cryogenic Etalon (DULCE), is designed to demonstrate a high efficiency scanning Fabry-Perot etalon operating in interference orders 1 - 4 at 30 K with a high stability DSP based servo control system. DULCE is currently the only available tunable filter for lower order cryogenic operation in the near infrared. In this application, scanning etalons will illuminate the focal plane arrays with a single order of interference to enable wide field lower resolution hyperspectral imaging over a wide range of redshifts. We discuss why tunable filters are an important instrument component in future space-based observatories.

We present the design of a mid-IR (5 - 28 micrometers ) integral field spectrometer for NGST. Details of the opto-mechanical design are given with particular attention being paid to those aspects influenced by the cryogenic, low background space environment in which the instrument needs to work. The instrument consists of three subsections: fore-optics and image slicing integral field units (IFU's), a 5 - 10 micrometers spectrograph and 10 - 28 micrometers spectrograph. Two co-aligned fields of view are separated into two wavelength channels (5 - 10 and 10 - 28 micrometers ) by a dichroic mirror in the fore- optics which also re-image the telescope focal plane onto the slicing mirrors of two IFU's.

This paper will discuss sunshield requirements, technology development, component and system level testing, development of analytical modeling tools, and the Inflatable Sunshield in Space flight experiment.

In the frame of an ESA program, as a potential contribute to NASA-ESA NGST project, this study focuses on the On Board Data Management System, starting from the requirements defined by a European Science Team. The expected amount of data collected in a single day of observation will be about 1600 GBytes, while the downlink capacity is at present in the range of 5 to 40 GBytes/day. Given these figures, on- board data reduction will be mandatory. It should include detector and signal conditioning, non-linearity correction, cosmic rays detection and rejection, source intensity (photon flux) estimation and data compression. The paper emphasizes different data reduction algorithms and compares their performances with respect to cosmic ray detection efficiency and source intensity estimation error.

This paper describes the engineering-level phenomenology code (LRAD) environment models for the deep magnetotail (X_GSE < -100 Re) and solar wind, and presents predictions of the charged particle environment for NGST.

NGST represents a challenging problem from the point of view of maintaining a milli-arcsecond level pointing accuracy and diffraction limited wavefront performance in the presence of dynamic onboard disturbances during science observations in a cryogenic environment. A Dynamics-Optics-Controls- Structures framework is being developed in support of the NGST dynamics and controls modeling program.

This paper presents a status of the development of the 1.6 meter hybrid mirror demonstrator for the Next Generation Space Telescope (NGST) Program. The COI design approach for the NGST program combines the optical performance of glass, with the high specific stiffness capabilities of composite materials.

A test program has been implemented to evaluate candidate thin film materials for the sun-facing layer of the Next Generation Space Telescope (NGST) sunshield. Various polymers are being tested to determine if any can survive the radiation environment of the proposed NGST orbit (the second Sun-Earth lagrangian point or L2). This testing will characterize the mechanical and thermal properties before and after exposure to a simulated NGST sunshield environment. In addition, because the sunshield will be folded and stowed before launch, the candidate materials will be folded, stowed and unfolded (deployed) to determine if they can survive this type of handling and storage. Based on the results of this testing, candidates will be down selected for further development and testing. Future development will include the addition of optical coatings, rip-stop for tear resistance, and seaming techniques.

An imaging FTS would be capable of carrying out many of the programs in the DRM, namely all those which require imaging and/or low spectral resolution wide field/multi-object spectroscopy. We review the DRM science areas, describing the relevance of an imaging FTS. Required instrumental capabilities are then derived from the science goals. Our compact camera and imaging FTS instrument design emphasizes simplicity with a single optical train covering a field 6 X 3 arcmin², with a fixed spatial sampling of 0.03 arcsec/pixel on a 12 k X 6 k detector array.

The plasma environment encountered by the Next Generation Space Telescope satellite in a halo orbit about L2 can include the Earth's magnetotail and magnetosheath in addition to the solar wind depending on the orbital radius chosen for the mission. Analysis of plasma environment impacts on the satellite requires knowledge of the average and extreme plasma characteristics to assess the magnitude of spacecraft charging and materials degradation expected for the mission lifetime. This report describes the analysis of plasma data from instruments onboard the IMP 8 and Geotail spacecraft used to produce the plasma database for the LRAD engineering-level phenomenology code developed to provide the NGST L2 environment definition.

The Space Infrared Telescope Facility (SIRTF) is in the middle of the development phase and on track for a December, 2001 launch. This exciting mission takes advantage of innovative engineering choices to make groundbreaking science available in a cost-effective way. SIRTF, the fourth of NASA's Great Observations, takes advantage of tremendous advances in infrared sensor technology as well as a high level of observatory efficiency in order to promise a rich scientific legacy. The presentation provides an overview of the SIRTF Project and describes the Cryogenic Telescope, Science Instruments, and Spacecraft. In addition, investigation opportunities for the scientific community are described. A detailed report on the current status and future plans is also provided.

By segmenting and folding the primary mirror, quite large telescopes can be packed into the nose cone of a rocket. Deployed after launch, initial optical performance can be quite poor, due to deployment errors, thermal deformation, fabrication errors and other causes. We describe an automatic control system for capturing, aligning, phasing, and deforming the optics of such a telescope, going from initial cm-level wavefront errors to diffraction-limited observatory operations. This system was developed for the Next Generation Space Telescope and is being tested on the NGST Wavefront Control Testbed.

This paper describes the results of a few of the initial series of tests being conducted with the first configuration of the Next Generation Space Telescope Wavefront sensing and Control Testbed (WCT1). WCT1 is a 1:1, f/16.6 re-imaging system, incorporating two deformable mirrors located at pupil conjugate positions with 6 actuators/diameter (SM/DM) and 20 actuators/diameter (AO/DM). A CCD on a precision stage is used for obtaining defocused images providing phase diversity for wavefront determination using phase retrieval. In a typical experiment, wavefront error is injected into the optical path with the SM/DM and then corrected using the more densely actuated AO/DM. Wavefront analysis is provided via a phase retrieval algorithm, and control software is used to reshape the AO/DM and correct the wavefront. A summary of the results of some initial tests are presented.

We report here on the calibration tests developed to measure the charge transfer efficiency performance in flight, on the results of those tests, on the monitoring of the CCD dark current, and on potential amelioration strategies for minimizing the scientific impact of the decline in STIS CCD performance.

In this paper we describe a potential new Explorer-class space mission, the AstroBiology Explorer (ABE), consisting of a relatively modest dedicated space observatory having a 50 cm aperture primary mirror which is passively cooled to T < 65 K, resides in a low-background orbit (heliocenter orbit at 1 AU, Earth drift-away), and is equipped with a suite of three moderate resolution spectrographs equipped with first-order cross-dispersers and large format (1024 X 1024 pixel) near- and mid-IR detector arrays cooled by a modest amount of cryogen.

A Multi-Object Spectrograph (MOS) based on micro-opto- electro-mechanical systems is one of the three core instruments selected for the NGST. Our group is involved in the preliminary studies on a promising solution for this instrument using a Micro-Mirror Array (MMA). We have focused our work towards three main topics: surface characterization of the micro-mirrors, MMA optical modeling, and optical design for the MOS. An accurate surface characterization method, based upon Foucault's knife-edge test has been developed, for measuring sub-nanometer deformations. Using the non-sequential ray tracing ability of our ray-tracing program, we have simulated a block of nine micro-mirrors with individual tilt angles, for properly designing an MMA- MOS. Finally, two different concepts for the MOS have been studied: a spectrograph with focal reduction, and a unit- magnification spectrograph preceded by a focal adaptator. The unit-magnification all-reflecting spectrograph is very promising, with a compact design, a perfectly plane image surface, and geometrical spots smaller than the detector pixels.

Specular and diffuse reflectance (BRDF) of black absorbing coatings, meant to be used for the HIFI instrument aboard the FIRST satellite, has been studied in the sub-millimeter region (0.1 < (lambda) < 0.9 mm). These coatings have to meet space qualification requirements and must be usable for at least the overall wavelength band (0.1 - 0.6 mm) covered by the HIFI spectrometer. Existing materials, coatings obtained from other research groups and home made samples have been studied. Optical characterization of these coatings has been performed at wavelengths of 96.5 micrometers , 118.8 micrometers , 184.3 micrometers , 496 micrometers and 889 micrometers , for a large range of directions of incident and reflected light and for different polarization directions. A limited number of reflectance measurements at cryogenic temperatures have been carried out too. A simple experimental set up to study the effect of double scattering has been constructed to investigate the accuracy of numerical simulations based on experimental BRDF values. Data show that the best samples (home made) have BRDF values below about 2.10^-2 Sr^-1 throughout the wavelength range of interest, quite independent of directions of incidence, reflection and polarization. The Total Hemispherical Reflection of such a coating will then be 0.06.