Cost and schedule risks in space projects can be minimized by applying technical concepts successfully flown previously to the subsequent missions. Examples from the development of three cold infrared instruments are discussed: ISOPHOT on ISO, PACS on HERSCHEL and MIRI on JWST. The progress achieved over two decades in the development of opto-mechanical elements like cold focal plane chopper and cold filter wheels will be demonstrated. While the instruments became larger and more complex, eventually the development consortia grew up to 20 institutes involved per instrument, requiring increasing resources for interface handling and coordination activities.

The payload of the Spitzer Space Telescope is the Cryogenic Telescope Assembly (CTA), a thermal and optical system that houses the science instruments and provides them a 1.2 K thermal sink. It also provides the 0.85-meter telescope, which is controlled between 5 K and 12 K to achieve the appropriate low photon background for the instruments while conserving helium. This cryogenic system supplies cooling through a combination of passive radiation and controlled vapor flow from a superfluid helium cryostat. Unlike previous cryogenic space infrared telescopes, the CTA allows the users to selectively cool Spitzer for particular science operations. Each science opportunity is both a benefit to the astronomical community and a cost to Spitzer's cryogen lifetime. CTA allows these benefits and costs to be weighed. Launched warm in August 2003 with 49 kg of helium, the CTA has been performing superbly with a current helium loss rate of only 9 kg per year after the initial cool-down period. Remaining helium is measured periodically so that mission lifetime can be accurately determined. Due in large part to the success of Spitzer, various aspects of the warm launch design have become the standard for future cryogenic space telescopes. This report describes the CTA and provides flight performance data for the cryogenic system.

EnMAP (Environmental Mapping and Analysis Program) is one of the selected proposals for the national German Space Program. The EnMap project includes the technological design of the Hyperspectral Spaceborne Instrument and the algorithms development of the classification. EnMap will be developed to meet the requirements of the observation and investigation of ecosystem parameters for forestry, soil/geological environments and coastal zones/inland waters. It provides high-quality calibrated data and data products to be used as inputs for improved modelling and understanding of biospheric/geospheric processes, high-spectral resolution observations of biophysical, biochemical, and geochemical variables. This contribution describes some technological and theoretical aspects of the technical solution of the Hyperspectral Pushbroom Sensor working in the VNIR and SWIR spectral range. The Hyperspectral Pushbroom Imaging Spectrometer requires at least two different 2−dimensional detector array types, with one dimension for the spatial and the second dimension for the image information. The VNIR quantum detector will be sensitive from 420 nm up to 1030 nm and the SWIR detector from 950 nm up to 2450 nm. The VNIR modelling shows the difficulties of the SNR of the blue channels. Some measures will be discussed to improve this situation. The discussion will be lead to the requirements of the CCD, focal plane and to the data acquisition scenarios. The SWIR stability modelling gives an overview of the requirements to the detector and of some problems of the detector related system design.

Measurements of spectrally resolved outgoing longwave radiation recorded in 1970, 1997 and 2003 are compared to determine the change in radiative forcing over that period. The changes are shown to be in agreements with that simulated by MODTRAN, a band model, using the known changes in atmospheric temperature and greenhouse gas concentrations when the effects of noise in the observed spectra are considered. The only region where the simulations are unable to reproduce the observations is in the _v4 band of methane around 1306cm^-1. The methane profiles used to simulate this region of the spectrum are shown to be in good agreement with all available data and the noise levels on the spectra are small. Therefore, it is proposed that the inability to model this region lies in the model formulation. Genln2, a line-by-line model, is shown to give very different results in this particular band to those obtained using MODTRAN. Sensitivity studies show that Genln2 is also not able to fully reproduce the spectrum observed. Errors in the spectroscopic parameters are shown to be smaller than the observed discrepancy and line mixing in methane is suggested as a possible cause of the discrepancy.

NASA Langley Research Center (LaRC), in partnership with the Rensselaer Polytechnic Institute (RPI), developed photovoltaic infrared (IR) detectors suitable at two different wavelengths using Sb-based material systems. Using lattice-matched InGaAsSb grown on GaSb substrates, dual wavelength detectors operating at 1.7 and 2.5 micron wavelengths can be realized. P-N junction diodes are fabricated on both GaSb and InGaAsSb materials. The photodiode on GaSb detects wavelengths at 1.7 micron and the InGaAsSb detector detects wavelengths at 2.2 micron or longer depending on the composition. The films for these devices are grown by metal-organic vapor phase epitaxy (MOVPE). The cross section of the independently accessed back-to-back photodiode dual band detector consists of a p-type substrate on which n-on-p GaInAsSb junction is grown, followed by a p-on-n GaSb junction. There are three ohmic contacts in this structure, one to the p-GaSb top layer, one to the n-GaSb/n-GaInAsSb layer and one to the p-type GaSb substrate. The common terminal is the contact to the n-GaSb/n-GaInAsSb layer. The contact to the n-GaSb/p-GaInAsSb region of the photodiode in the dual band is electrically connected and is accessed at the edge of the photodiode. NASA LaRC acquired the fabricated dual band detector from RPI and characterized the detector at its Detector Characterization Laboratory. Characterization results, such as responsivity, noise, quantum efficiency, and detectivity will be presented.

This paper presents a description of the instruments on board the Metop series of satellites. Metop will be the first European operational meteorological satellite to operate in a polar heliosynchronous orbit. From a height of 835 km, Metop will provide a variety of geophysical data that will improve the weather and climate monitoring services in Europe.

The Orbiting Carbon Observatory, OCO, is a NASA Earth System Science Pathfinder (ESSP) mission to measure the distribution of total column carbon dioxide in the earth's atmosphere from an earth orbiting satellite. NASA Headquarters confirmed this mission on May 12, 2005. The California Institute of Technology's Jet Propulsion Laboratory is leading the mission. Hamilton Sundstrand is responsible for providing the OCO instrument. Orbital Sciences Corporation is supplying the spacecraft and the launch vehicle. The optical design of the OCO is now in the detail design phase and efforts are focused on the Critical Design Review (CDR) of the instrument to be held in the 4th quarter of this year. OCO will be launched in September of 2008. It will orbit at the head of what is known as the Afternoon Constellation or A-Train (OCO, EOS-Aqua, CloudSat, CALIPSO, PARASOL and EOS-Aura). From a near polar sun synchronous (~1:18 PM equator crossing) orbit, OCO will provide the first space-based measurements of carbon dioxide on a scale and with the accuracy and precision to quantify terrestrial sources and sinks of CO₂. The status of the OCO instrument optical design is presented in this paper. The optical bench assembly comprises three cooled grating spectrometers coupled to an all-reflective telescope/relay system. Dichroic beam splitters are used to separate the light from a common telescope into three spectral bands. The three bore-sighted spectrometers allow the total column CO₂ absorption path to be corrected for optical path and surface pressure uncertainties, aerosols, and water vapor. The design of the instrument is based on classic flight proven technologies.

A large format, area array, digital visible light camera was developed based on A/D conversion at each pixel. Production CMOS technology was used in the development of a monolithic front side illuminated photo diode pixel. Each pixel includes a one loop MOSAD, (Multiplexed Oversample A/D) converter, photo diode, and buffered output to support a very large array format operating at high frame rates. MOSAD is a modification of the delta sigma approach to A/D conversion. The 12 megapixel sensor consists of a 4,000X3,000 pixel array capable of up to 1,000 frames per second sample rate. To approximately fit a 35 millimeter optics format, a pixel size of 8.5 μm was selected. There are no operational amplifiers required at the pixel to perform the A/D function, thus allowing a high fill factor. With this pixel size, a 48% fill factor and 38% photo diode area was achieved. A single process run was completed yielding five 8 inch wafers each containing 27 camera die. The single poly, three metal AMIS 0.35 μm CMOS process was used in the fabrication process. Selected die were directly mounted on a specially designed carrier daughter board. Camera support electronics were designed and fabricated to allow sampling of the camera output using commercial standard Camera Link interfacing. Off the shelf 35 Millimeter optics was used to validate imaging capabilities of the sensor. Tests show that the first iteration sensor chip design works to the fundamental requirements and can image.

The Atmospheric Chemistry Experiment (ACE) is the mission on-board Canadian Space Agency's science satellite, SCISAT-1. ACE consists of a suite of instruments in which the primary element is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible (525 nm) and near infrared imager (1020 nm). A secondary instrument, MAESTRO, provides spectrographic data from the near ultra-violet to the near infrared, including the visible spectral range. In combination, the instrument payload covers the spectral range from 0.25 to 13.3 micron. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature are being made by solar occultation from this satellite in low earth orbit. The ACE mission measures and analyses the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A high inclination (74⁰), low earth orbit (650 km) allows coverage of tropical, mid-latitude and polar regions. The ACE/SciSat-1 spacecraft was launched by NASA on August 12^th, 2003. This paper presents the status of the ACE-FTS instrument after two years on-orbit. On-orbit performances are also covered. The health and safety status of the instrument payload is discussed. Optimization of on-orbit performance is presented as well as operational aspects.

The High Resolution Dynamics Limb Sounder (HIRDLS) instrument was launched on NASA's Aura spacecraft on 15 July 2004. When activation was completed 25 days later, it was discovered that the measured radiances were very different from those that were expected. After a long series of analyses and diagnostic tests, the cause was confirmed to be a blockage that covers much of the front aperture, preventing even one completely clear view of the atmosphere. In this paper the steps required to correct the radiances for the effects of the blockage are noted. These are calibrating the radiances, removing the effects of the blockage oscillating, and the radiance coming from the blockage, correcting for the effects of the partial aperture, and filtering the noise. The paper describes the algorithms needed, and presents the results of their application. The success of the procedures will be demonstrated by the quality of the resulting radiances and retrieved profiles of temperature and trace species. The difficulties that have been eliminated, and that still remain are noted, along with plans for further improvement. Finally, the scientific implications are briefly discussed.

The High Resolution Dynamics Limb Sounder (HIRDLS) instrument was launched on the NASA Aura satellite in July 2004. HIRDLS is a joint project between the UK and USA, and is a mid-infrared limb emission sounder designed to measure the concentrations of trace species and aerosol, and temperature and pressure variations in the Earth's atmosphere between about 8 and 100 km. The instrument is performing correctly except for a problem with radiometric views out from the main aperture. A series of tests has led to the conclusion that optical beam is obstructed between the scan mirror and the aperture by what is believed to be a piece of Kapton film that became detached during the ascent to orbit. The paper describes measurements aimed at mapping the geometric and radiometric properties of the obstruction using different positions of the aperture door, including in some cases where the sun was made to illuminate the aperture. The aim of the work is to facilitate atmospheric observations through a small part of the aperture which remains clear.

The functional performance of the NASA Aura HIRDLS instrument since launch on the 15^th July 2004 is presented and discussed. The HIRDLS (High Resolution Infra-red Limb Sounder) is a 21-channel infra-red radiometer, using actively cooled MCT detectors on a common focal plane. It has many features that provide considerable flexibility of the commanding, control and the format and content of the telemetry. HIRDLS also features a precision 2-axis scan mirror and gyroscopes that are attached to the optical bench and together they provide additional data on the line of sight on small time scales. The stability of the temperature control of the focal plane and critical optical components is also presented and discussed. To-date the instrument has performed functionally without fault and in many aspects well within specifications. The only problem (and a serious one) so far encountered has been the optical blockage of the main aperture, which is discussed in other papers. Some aspects of the instrument that have been utilised to help characterise the blockage are outlined.

A pre-launch calibration of the High Resolution Dynamics Limb Sounder (HIRDLS) flight instrument was performed at Oxford University in Fall 2002. The in-band spectral characterization was performed was performed as part of this exercise. Spectral response data for all 21 channels were obtained for three different experimental conditions (nominal and two off-nominal operating conditions). Results from these data sets will be presented, as well as the analysis procedures used, along with a discussion on error analysis.

The High Resolution Dynamics Limb Sounder (HIRDLS) flight instrument, which is currently in orbit on the NASA Aura Satellite, went through a pre-launch calibration at Oxford University during Autumn 2002. One of the calibration exercises was to characterize the radiometric signals of the HIRDLS proto-flight model (PFM). It was discovered during the data-analysis phase, that the radiometric data required special treatment. Because of the stringent radiometric requirements imposed on HIRDLS, these additional analyses were necessary. This manuscript will detail these specific analysis techniques that were used on the data and present results based on a full analysis of the data, including a complete accounting of the statistical error analysis.

Germanium detectors are extensively used in astronomical instruments for far infrared observations. To meet the science objectives of future space projects, large-format far IR detectors are needed. As a first step toward this goal, we have fabricated a 2x16 Ge:Sb array with the 1x32, SB-190 CTIA cryogenic readout. The detector design as well as the preliminary results of our parametric tests are presented here. The array exhibits very good noise performance with an NEP as low as 4.0E-18 W/√Hz, and confirms the viability of the design for large format arrays.

The far-infrared detectors on the Multiband Imaging Photometer for Spitzer (MIPS) represent a significant advancement in both format and sensitivity. We describe some of the operational experience since launch in August 2003. MIPS has three infrared detector arrays, a 128x128 format Si:As impurity band conduction detector operating at 24 μm, a 32x32 format Ge:Ga array operating at 70 μm and a 2x20 format stressed Ge:Ga array operating at 160 μm. Since both germanium detectors utilize conventional bulk photoconductors, they are subject to a number of non-ideal behaviors that are inherent in these types of devices when operated in ultra-low backgrounds. The principal problems are nonlinear time response, changing responsivity in a radiation environment, and flux non-linearities. We describe observing strategies that are used on MIPS to minimize the impact of these effects.

We are developing a GaAs photoconductive detector for far-infrared (FIR) astronomy. A detector based on GaAs in the blocked impurity band (BIB) con.guration is expected to extend the long wavelegth limit of currently available stressed Ge:Ga photoconductors up to about 330 microns. Without the need of uniaxial stress applied to the crystal, this would furthermore allow the fabrication of single chip arrays with a large number of pixels. We are reporting results of the characterization of preliminary GaAs BIB test structures. The experimental work is supported by numerical modeling that includes all contact and space charge effects.

Numerical modeling of Blocked Impurity Band (BIB) detectors is performed using a four-region finite difference approach to study the role of blocking layer thickness and minority doping concentration in alternate bias operation and the role of space charge in C-V (capacitance-voltage) profiling of minority carrier doping. Compensation in the blocking layer is found to play a critical role in determining the net voltage drop in this part of the device under alternate polarity bias. The effect of space charge at the blocking layer/active layer interface on the measured low temperature C-V distribution is modeled as a function of the doping interface between the two layers. The magnitude of the space charge can cause large deviations in the measurement of minority doping concentration from the idealized case which assumes a space-charge free blocking layer and interface.

We report the development of novel porous silicon IR filters. The key component of the filter technology is a porous silicon multilayer obtained by the electrochemical etching of single-crystal silicon wafers. The unique property of such a material is the extremely wide transparency range. It will be shown that the transparency range of porous silicon extends from the visible to the far IR region (up to 100μm and above). Good control over the porosity obtained with the electrochemical fabrication method permits the fabrication of the narrow band-pass, band-pass, long wave pass or band-blocking types of filters with pass bands centered anywhere within the transparency range of the material. Such filters have a number of important advantages over multilayer interference filters. Since the filters are made from a single material (rather than through the deposition of multilayers of dissimilar materials), these filters do not exhibit delamination problems and are well suited for operation at cryogenic temperatures. Further, several hundreds of micrometer thick multilayers can be obtained on 4- or 6-inch diameter wafers in a single process run with high lateral uniformity of the transmission spectrum. Methods of enhancement of the environmental and mechanical stability of these filters have been developed as well. The results of experimental testing of such filters are presented.

Double injection into extrinsic semiconductor infrared detectors can lead, in some cases, to considerable increase of their current responsivity without essential change of detectivity. These detectors are called extrinsic double-injection photodiodes. They are especially effective under low background conditions. The BLIP-detection responsivity of studied Ge:Hg double injection photodiodes has reached about 2000 A/W at a wavelength of 10 micrometers under a background of 6 x 10¹¹cm^-2s^-1. This is more than 100 times the responsivity of the same material and same size photoconductive detector used under the same conditions. Under periodically pulsing bias, when a sufficiently high steady-state voltage is applied to such a diode on which relatively short voltage pulses of rectangular shape are imposed, the realization of charge accumulation in the detector bulk proves to be possible for the period of voltage variation and readout with amplification during the voltage pulse. A model of this effect was developed. It was shown, in particular, that the pulse readout current of the diode under some conditions was equal to its steady-state current multiplied by the ratio of the integration time to the readout time, i.e., great amplification takes place during the readout: the reading-out charge equals the charge generated in diode bulk for the pulse voltage variation period multiplied by the steady-state photocurrent gain of the diode. The pulse responsivity for Ge:Hg diodes has reached about 10⁵ A/W. It was determined as the ratio of the pulse readout current to the power of steady-state incident radiation flux. This operation mode is especially convenient for detector arrays.

We described a new method to determine tissue density using a modified interferometric scattering experiment.¹ The most critical aspect of the tissue characterization problem is calibration of experimental measurements. During the calibration step, the absorption and scattering indices βa and βsc are determined as a function of concentration, for each material or tissue of interest, using a set of containers to vary travel distance D. It is assumed that linear scattering coefficient, ksc (absorption coefficient, αa), is proportional to number of scattering particles per unit volume, or particle concentration, c, in [ml/l]. Attenuation is proportional to concentration of scattering/absorption centers and sample length. The calibration method relates the fringe irradiance (power modulation in one interferometer arm) with the sample concentration under controlled conditions.

We previously developed theory¹ on new method for early detection of tissue anomaly with modified interferometric scattering experiment. The method is based on the ability of photons, passing through sample without scattering or absorption, to preserve their coherence (polarization and phase). These photons produce interference pattern. We describe experimental setup and initial results that predict feasibility of new method. The amplitude of the fringe pattern contains the information about the sample transmission characteristics. The zero phase for each pixel contains the phase information due to travel inside the tissue.

We developed a new method of determining tissue density and anomaly using modified interferometric scattering experiment.^1-3 The amplitude of the interferometric pattern formed by the unscattered pass-through beam and the reference beam contains information about the integrated sample density coordinate. In this paper, we introduce a new concept, complex material coherence function. It contains information about material's capacity to decrease degree of coherence of coherent beam that passes through it. This concept significantly simplifies expressions related to matter - beam interactions, described elsewhere.

We describe a new method of determining path-integrated tissue density using a modified interferometric scattering experiment. The method is based on the ability of the photons, passing through the sample without scattering (or absorption) to preserve their coherence (polarization and phase). We present the theory that predicts the feasibility of this method. The highest value of fringe incidance contains the information about the sample transmission.

Accurate simultaneous retrievals of temperature and pressure are key to retrieving high quality mixing ratio profiles from occultation sensors. Equally important is accurate determination of the vertical separation between measurement points. Traditionally, these tasks are complicated by platform motion and CO₂ model errors. We present a new approach that is independent of platform motion and CO₂ concentration, using inexpensive modern 2D focal-plane arrays and an innovative refraction-angle measurement. This provides both accurate temperature retrievals and precise vertical separation of measurement samples, greatly improving the quality of mixing ratio retrievals. We show recent studies demonstrating the expected performance of the SOFIE instrument (Solar Occultation For Ice Experiment) to be launched as part of the AIM (Aeronomy of Ice Mission) in September 2006. This system will have the ability to retrieve accurate temperature, through mild particulate contamination (such as volcanic aerosol and cirrus) from cloud-top to stratopause, independent of mixing ratio knowledge. Additional CO₂ absorption channels will provide retrieved temperature and CO₂ mixing ratios through the mesosphere and into the lower thermosphere.