The Raytheon Cryocooler Product Line tested the Low Temperature Stirling / Pulse Tube Hybrid 2-Stage (LTRSP2) cryocooler for an airborne application during 2012. Several tests were carried out to verify the ability of the machine to operate in an airborne environment. The vacuum level and heat rejection surface temperatures were varied to determine the performance over the excursions. Vibration testing was performed to prove that the LT-RSP2 cryocooler can operate on an airborne platform. This paper will present the results of the airborne characterization testing.

Significant progress has been made on the Raytheon Dual-Use Cooler (DUC) which is a low cost space cryocooler for long life, cost sensitive missions. The DUC has been integrated and tested with an advanced regenerator intended to be a direct replacement for stainless steel screens and has shown significant thermodynamic performance improvements. This paper will compare the performance of two different regenerators and explain the benefits of the advanced regenerator.

Infrared sensors face a multitude of cryocooler integration challenges such as exported disturbance, efficiency, scalability, maturity, and cost. As a result, cryocooler selection has become application dependent, oftentimes requiring extensive trade studies to determine the most suitable architecture. To optimally meet the needs of next generation passive infrared (IR) sensors, the Compact Inline Raytheon Single Stage Pulse Tube (CI-RP1) and Compact Inline Raytheon Hybrid Stirling/Pulse Tube 2-Stage (CI-RSP2) cryocoolers are being developed to satisfy this suite of requirements. This lightweight, compact, efficient, low vibration cryocooler combines proven 1-stage and 2-stage cold-head architectures with an inventive set of warm-end mechanisms into a single mechanical module, allowing the moving mechanisms for the compressor and the Stirling displacer to be consolidated onto a common axis and in a common working volume. The CI cryocooler is a significant departure from the current Stirling cryocoolers in which the compressor mechanisms are remote from the Stirling displacer mechanism. Placing all of the mechanisms in a single volume and on a single axis provides benefits in terms of package size (30% reduction), mass (30% reduction), thermodynamic efficiency (<20% improvement) and exported vibration performance (≤25 mN peak in all three orthogonal axes at frequencies from 1 to 500 Hz). The main benefit of axial symmetry is that proven balancing techniques and hardware can be utilized to null all motion along the common axis. Low vibration translates to better sensor performance resulting in simpler, more direct mechanical mounting configurations, eliminating the need for convoluted, expensive, massive, long lead damping hardware.

Fifteen years ago, CEA started the development of cryogenic rotating actuators for the astrophysical infrared camera (VISIR) that is set on the Very Large Telescope (VLT). At the time of the VISIR first light in 2004, 10 cryogenic rotating actuators, also known as “CryoMechanisms” (CM), were present in the instrument. Today VISIR is still operating and the CM that are actuated several times a day, have no reported failure up to now. In continuation of the VISIR project, CEA undertook space qualification tests with the aim of making the CM compatible with space missions. Relying on this background, a smaller model of the mechanism has been built and tested at cryogenic temperatures. Today, the cryomechanisms are selected for the ESA/EUCLID [1] space mission. The qualification program will run throughout 2014. This paper first describes the VISIR’s baseline specification, the CM design and its operation principle. Then, the upgrades for the space constrains are shown and the qualification plan with respect to vibrations, thermal cycling and life testing campaigns is given. Some results of the tests carried out on a qualification model are addressed. At end, the design improvements for the EUCLID project are presented and a summary of the CM capabilities is highlighted.

The JWST Optical Telescope Element Simulator (OSIM) is a configurable, cryogenic, optical stimulus for high fidelity ground characterization and calibration of JWST’s flight instruments. OSIM and its associated Beam Image Analyzer (BIA) contain several ultra-precise, cryogenic mechanisms that enable OSIM to project point sources into the instruments according to the same optical prescription as the flight telescope will image stars – correct in focal surface position and chief ray angle. OSIM’s and BIA’s fifteen axes of mechanisms navigate according to redundant, cryogenic, absolute, optical encoders – 32 in all operating at or below 100 K. OSIM’s encoder subsystem, the engineering challenges met in its development, and the encoders’ sub-micron and sub-arcsecond performance are discussed.

Cleartran® ZnS is a water clear form of CVD ZnS and a popular material for infrared optical designs. In order to enable the highest quality lens designs with this material at cryogenic temperatures, we have measured the absolute refractive indices of two prisms as a function of both wavelength and temperature using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA’s Goddard Space Flight Center (GSFC). While conventional CVD ZnS has received considerable study at cryogenic temperatures, to our knowledge, cryogenic indices of Cleartran have not been measured by other investigators. For our measurements of Cleartran, we report absolute refractive index, spectral dispersion (dn/dλ), and spectral thermo-optic coefficient (dn/dT) at temperatures ranging from 20 to 300 K at wavelengths from 0.50 to 5.6 μm. We provide temperature-dependent Sellmeier coefficients based on our data to allow accurate computation of index at any applicable wavelength and temperature. We compare our measured indices with those of the material’s manufacturer, Rohm & Haas, at room temperature where we find good agreement to within our measurement uncertainty, and we compare our refractive indices and their aforementioned derivatives to cryogenic temperatures with those for conventional ZnS from the literature

Using NASA Goddard Space Flight Center’s Cryogenic High Accuracy Refraction Measuring System (CHARMS), we measured absolute refractive indices for three infrared glasses from Ohara for lens designs for instruments at two of the world’s largest, ground-based, astronomical observatories – the present W.M. Keck Observatory and the future Giant Magellan Telescope (GMT). MOSFIRE (Keck), a near-infrared multi-object spectrograph and wide-field camera, has demonstrated diffraction limited performance at 120 K in part owing to our absolute refractive index measurements of Ohara S-FPL51 and S-FTM16 covering wavelengths and temperatures from 0.5 to 2.6 μm and 30 to 300 K, respectively. Measured index uncertainties range from 0.7–3.5E-5 and 0.7–2.9E-5 for S-FPL51 and S-FTM16, respectively, depending on wavelength and temperature, and for the latter on which test prism. NIRMOS (GMT), a near infrared multiple object imager/spectrograph, uses S-TIM28 in its imaging lens design. We measured S-TIM28’s indices for wavelengths and temperatures from 0.40 to 2.8 μm and 25 to 300 K, respectively with uncertainties ranging from 1.6– 3.0E-5. Absolute indices and their wavelength and temperature derivatives for these infrared glasses are reported along with coefficients for temperature-dependent Sellmeier fits of the measured index data to enable accurate computation of index to other wavelengths and temperatures. We compare our measurements to those in the literature.

The S-TIH1 glass from Ohara Inc. is a type of material that exhibits a high room-temperature refractive index as well as a wide variation in dispersion as a function of wavelength. Because of these properties, this material could be a suitable candidate for use in a refractive system based on a prism design. In order to broaden its applicable uses, this paper reports on the results from a temperature-dependent refractive index measurement program performed on this type of glass to enable a high-fidelity refractive system design that would operate at cryogenic temperatures. These measurements were performed using the Cryogenic High Accuracy Refraction Measuring System (CHARMS) facility at the Goddard Space Flight Center (GSFC). We report on the absolute refractive index and thermo-optic coefficient (dn/dT ) at temperatures ranging from 100 to 300 K and at wavelengths from 0.455 to 2.536 μm. We compare our index of refraction measurements to the material manufacturer’s data at room temperature. We also provide temperature-dependent Sellmeier coefficients based on our measured data to allow accurate interpolation of index as a function of wavelength and temperature. These studies are also complemented with measurements of the coefficient of thermal expansion (CTE) to further validate the use of this type of glass in a cryogenic optical systems.

Disordered thin film SiO₂/SiO_x coatings undergoing electron-beam bombardment exhibit cathodoluminescence, which can produce deleterious stray background light in cryogenic space-based astronomical observatories exposed to high energy electron fluxes from space plasmas. As future observatory missions push the envelope into more extreme environments and more complex and sensitive detection, a fundamental understanding of the dependencies of this cathodoluminescence becomes critical to meet performance objectives of these advanced space-based observatories. Measurements of absolute radiance and emission spectra as functions of incident electron energy, flux, and power typical of space environments are presented for thin (~60-200 nm) SiO₂/SiO_x optical coatings on reflective metal substrates over a range of sample temperatures (~40-400 K) and emission wavelengths (~260-5000 nm). Luminescent intensity and peak wavelengths of four distinct bands were observed in UV/VIS/NIR emission spectra, ranging from 300 nm to 1000 nm. A simple model is proposed that describes the dependence of cathodoluminescence on irradiation time, incident flux and energy, sample thickness, and temperature.

Electron irradiation experiments have investigated the diverse electron-induced optical and electrical signatures observed in ground-based tests of various space observatory materials at low temperature. Three types of light emission were observed: (i); long-duration cathodoluminescence which persisted as long as the electron beam was on (ii) short-duration (<1 s) arcing, resulting from electrostatic discharge; and (iii) intermediate-duration (~100 s) glow—termed “flares”. We discuss how the electron currents and arcing—as well as light emission absolute intensity and frequency—depend on electron beam energy, power, and flux and the temperature and thickness of different bulk (polyimides, epoxy resins, and silica glasses) and composite dielectric materials (disordered _SiO2 thin films, carbon- and fiberglass-epoxy composites, and macroscopically-conductive carbon-loaded polyimides). We conclude that electron-induced optical emissions resulting from interactions between observatory materials and the space environment electron flux can, in specific circumstances, make significant contributions to the stray light background that could possibly adversely affect the performance of space-based observatories.

The Observational Cosmology Laboratory at NASA’s Goddard Space Flight Center (GSFC), in collaboration with the University of Maryland, is building the Rapid Infrared Imager/Spectrometer (RIMAS) for the new 4.3 meter Discovery Channel Telescope (DCT). The instrument is designed to observe gamma-ray burst (GRB) afterglows following their initial detection by the Swift satellite. RIMAS will operate in the near infrared (0.9 – 2.4 microns) with all of its optics cooled to ~60 K. The primary optical design includes a collimator lens assembly, a dichroic dividing the wavelength coverage into the “YJ band” and “HK band” optical arms, and camera lens assemblies for each arm. Additionally, filters and dispersive elements are attached to wheels positioned prior to each arm’s camera, allowing the instrument to quickly change from its imaging modes to spectroscopic modes. Optics have also been designed to image the sky surrounding spectroscopic slits to help observers pass light from target sources through these slits. Because the optical systems are entirely cryogenic, it was necessary to account for changing refractive indices and model the effects of thermal contraction. One result of this work is a lens mount design that keeps lenses centered on the optical axis as the system is cooled. Efforts to design, tolerance and assemble these cryogenic optical systems are presented.

The filter wheel assembly (FWA) is an integral and important sub-system of the Near Infrared Camera (NIRCam) instrument on the James Webb Space Telescope (JWST). The optic elements in each of the four FWA mechanisms on NIRCam are used to conduct science operations as well as calibration of the NIRCam instrument and the JWST observatory. The FWA mechanism can position one of 12 different filters in the optical path of the camera and position one of 12 different pupil optics in the same path. The filters and pupil optics are mounted in two separate wheel assemblies in the FWA that can be positioned independently to provide the desired optical configuration for imaging. Along with the rest of the instrument, the FWA operates at cryogenic temperatures and is used for both short and long wavelength imaging. This paper reviews significant elements of the FWA mechanism design.

The optics train of the Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) includes a pick-off mirror (POM) mounted in the focus and alignment mechanism (FAM). Over the course of the mission, the POM will have a narrow view of the L2 space environment. Charged particles will impinge and collect on the mirror surface increasing the possibility of arcing to the adjacent baffle. A technique to ground the POM and remove accumulated charge has been qualified and implemented on the flight instrument. This paper will provide an overview of the qualification process including cryogenic resistance measurements, vibration testing and optical surface error measurements. To measure the efficiency of this grounding technique, a POM engineering model was exposed to representative mission electron fluence and results with the POM grounded and ungrounded will be presented.

The Gaia mission¹ will create an extraordinarily precise three-dimensional map of more than one billion stars in our Galaxy. The Gaia spacecraft², built by EADS Astrium, is part of ESA's Cosmic Vision programme and scheduled for launch in 2013. Gaia measures the position, distance and motion of stars with an accuracy of 24 micro-arcsec using two telescopes at a fixed mutual angle of 106.5°, named the ‘Basic Angle’, at an operational temperature of 100 K. This accuracy requires ultra-high stability at cryogenic conditions, which can only be achieved by using Silicon Carbide for both the optical bench and the telescopes. TNO has developed, built and space qualified the Silicon carbide Basic Angle Monitoring (BAM) on-board metrology system³ for this mission, measuring the relative motion of Gaia’s telescopes with accuracies in the range of 0.5 micro-arcsec. This is achieved by a system of two laser interferometers able to detect Optical Path Differences (OPD) as small as 1.5 picometer rms. Following a general introduction on Gaia and the use of Silicon Carbide as base material this paper addresses the specific challenges towards the cryogenic application of the Gaia BAM including design, integration and verification/qualification by testing.