The Infrared Multi-Object Spectrometer (IRMOS) is a principle investigator class instrument for the Kitt Peak National Observatory 4 and 2.1 m telescopes. IRMOS is a near-IR (0.8 - 2.5 μm) spectrometer with low- to mid-resolving power (R = 300 - 3000). IRMOS produces simultaneous spectra of ~100 objects in its 2.8 - 2.0 arc-min field of view (4 m telescope) using a commercial Micro Electro-Mechanical Systems (MEMS) micro-mirror array (MMA) from Texas Instruments. The IRMOS optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the MMA field stop, and the spectrograph images the MMA onto the detector. We describe ambient breadboard subsystem alignment and imaging performance of each stage independently, and ambient imaging performance of the fully assembled instrument. Interferometric measurements of subsystem wavefront error serve as a qualitative alignment guide, and are accomplished using a commercial, modified Twyman-Green laser unequal path interferometer. Image testing provides verification of the optomechanical alignment method and a measurement of near-angle scattered light due to mirror small-scale surface error. Image testing is performed at multiple field points. A mercury-argon pencil lamp provides a spectral line at 546.1 nm, a blackbody source provides a line at 1550 nm, and a CCD camera and IR camera are used as detectors. We use commercial optical modeling software to predict the point-spread function and its effect on instrument slit transmission and resolution. Our breadboard and instrument level test results validate this prediction. We conclude with an instrument performance prediction for cryogenic operation and first light in late 2003.

We present the Fabry-Perot designed for FIBRE and its evolution for its use in the SAFIRE imaging spectrometer for the SOFIA airborne telescope. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer for the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by SQUID multiplexers. During the first light of FIBRE in June 2001, we measured a spectral resolution of about 1200. The Fabry-Perot concept has its heritage in the ISO/LWS instrument, scaled and adapted to the submillimeter range. The semi-reflecting optics consist of a metallic meshe deposited on a lens and a wedged plate made of monocrystalline quartz. We use three voice coil actuators in the Fabry-Perot design to achieve a displacement of 600 microns of the moving plate. The use of NbTi superconducting wire for the coils allows operation at 1.5 K without any Joule dissipation. Capacitive sensors in line with each actuator and their AC readout provide three independant position measurements. These measurements are fed into a triple PID amplifier controlling the actuators. Because of the high level of vibrations present on an airborne instrument platform, it it necessary to reject the vibrations in the Fabry-Perot up to the resonance frequencies. We propose an original method to obtain a frequency response of the PID system up to 60 Hz. The updated Fabry-Perot will be used for the next FIBRE run in autumn 2003, aiming to detect the Doppler-broadened line emission from external galaxies.

We present the results of an on-going test program designed to empirically determine the effects of different stress relief procedures for aluminum mirrors. Earlier test results identified a preferred heat treatment for flat and spherical mirrors diamond turned from blanks cut out of Al 6061-T651 plate stock. Further tests were performed on mirrors from forged stock to measure the effect of this variable on cryogenic performance. The mirrors are tested for figure error and radius of curvature at room temperature and at 80 K for at least three thermal cycles. We correlate the results of our optical testing with heat treatment and metallographic data.

We describe the population, optomechanical alignment, and alignment verification of near-infrared gratings on the grating wheel mechanism (GWM) for the Infrared Multi-Object Spectrometer (IRMOS). IRMOS is a cryogenic (80 K), principle investigator-class instrument for the 2.1 m and Mayall 3.8 m telescopes at Kitt Peak National Observatory, and a MEMS spectrometer concept demonstrator for the James Webb Space Telescope. The GWM consists of 13 planar diffraction gratings and one flat imaging mirror (58x57 mm), each mounted at a unique compound angle on a 32 cm diameter gear. The mechanism is predominantly made of Al 6061. The grating substrates are stress relieved for enhanced cryogenic performance. The optical surfaces are replicated from off-the-shelf masters. The imaging mirror is diamond turned. The GWM spans a projected diameter of ~48 cm when assembled, utilizes several flexure designs to accommodate potential thermal gradients, and is controlled using custom software with an off-the-shelf controller. Under ambient conditions, each grating is aligned in six degrees of freedom relative to a coordinate system that is referenced to an optical alignment cube mounted at the center of the gear. The local tip/tilt (R_x/R_y) orientation of a given grating is measured using the zero-order return from an autocollimating theodolite. The other degrees of freedom are measured using a two-axis cathetometer and rotary table. Each grating's mount includes a one-piece shim located between the optic and the gear. The shim is machined to fine align each grating. We verify ambient alignment by comparing grating diffractive properties to model predictions.

The Infrared Multi-Object Spectrograph (IRMOS) is a facility instrument for the Kitt Peak National Observatory Mayall Telescope (3.8 meter). IRMOS is a low- to mid-resolving power (R = λ/Δλ = 300-3800), near-IR (0.8-2.5 µm) spectrograph that produces simultaneous spectra of ~100 objects in its 2.8 × 2.0 arcmin field of view using a real-time programmable, multi-aperture field stop. The instrument operating temperature is ~80 K to allow for IR detector operation and for improved K-band performance. The optical bench and mirrors are machined from aluminum 6061-T651, allowing easier ambient temperature optical alignment. IRMOS utilizes four powered mirrors, three flat mirrors, two rotary mechanisms, one linear mechanism, a commercial MEMS multi-mirror array device and a large format, HgCdTe detector. The final design of the instrument and all of its components evolved through several iterations and a series of requirement/feasibility trades. During the design process, we found the heritage of past instruments with similar operating conditions to be invaluable in understanding our challenge, maximizing performance, and minimizing cost. The decision-making process of our design, as well as some of the major technical achievements, are described from a systems point of view in order to provide a list of "lessons learned" for future cryogenic instrument design and construction.

Xinetics is working with NASA to develop a cryogenic deformable mirror (DM) specific to the needs of future Origins Program missions such as TPF and JWST. Of utmost importance was the development of an electroceramic material that exhibited electrostrictive properties at cryogenic temperatures. In this paper, the actuator developmental tests and subsequent cryogenic deformable mirror design and cryogenic testing performance of the 349-channel discrete actuator deformable mirror demonstrator are discussed. The cofired actuator stroke response was nearly constant from 35 to 65 K such that at 150V the actuator free-stroke was ~3 microns. The 349-ch cryogenic DM was designed and built with as few parts and materials as possible to minimize the CTE mismatch. The polished mirror was cycled twice from 300 to 35 K. The rms surface figure was monitored using a Zygo interferometer on cooling and consistent data was measured during both temperature cycles. The figure changed from 0.5 waves (P-V) at 300 K to 5 waves at 35 K and returned to 0.6 waves at 300K. The actuators were powered and the influence functions were measured between 35 and 65 K. Even though it is not a functional DM at 35 K, it is a substantial step forward in the development of a cryogenic deformable mirror technology.

To provide cryocooling across a gimbaled joint still remains a difficult challenge for spacecraft engineers. Gimbaled cryogenic infrared payloads have very difficult-to-meet requirements for 2-axis motion and low torque. Thus the difficulty of making a cryogenic thermal connection across a gimbaled joint cannot be overstated. Because of the cryogenic nature of the connection, thermal joint flexibility, durability, reliability, material compatibility, differential expansion/contraction, and parasitic heat loss, are all complex technical concerns. Thus two primary issues of the proposed across-gimbal passive cryocooling system - management of heat parasitics and flexible/durable thermal connection between heat sources (infrared sensors/detectors) and heat sinks (cryocooler coldfingers) - are the main focus of the current development effort. A cryogenic Advanced Loop Heat Pipe proof-of-concept test loop that was developed in Phase I demonstrated a heat transport capability of 50W-m (20W over a distance of 2.5m) in 3/32"O.D. stainless steel lines. But more importantly, the test loop started up and operated reliably even in a 300K environment. In the follow-on Phase II, the research focus shifted to the development and demonstration of a low-torque durable flexure mechanism for a 2-axis gimbal.

Requirements for cryocooling of large-area heat sources begin to appear in studies of future space missions. Examples are the cooling of (i) the entire structure/mirror of large Far Infrared space telescopes to 4-40K and (ii) cryogenic thermal bus to maintain High Temperature Superconductor electronics to below 75K. The cryocooling system must provide robust/reliable operation and not cause significant vibration to the optical components. But perhaps the most challenging aspect of the system design is the removal of waste heat over a very large area. A cryogenic Loop Heat Pipe (C-LHP)/ cryocooler cooling system was developed with the ultimate goal of meeting the aforementioned requirements. In the proposed cooling concept, the C-LHP collected waste heat from a large-area heat source and then transported it to the cryocooler coldfinger for rejection. A proof-of-concept C-LHP test loop was constructed and performance tested in a vacuum chamber to demonstrate the feasibility of the proposed C-LHP to distribute the cryocooler cooling power over a large area. The test loop was designed to operate with any cryogenic working fluid such as Oxygen/Nitrogen (60-120K), Neon (28-40K), Hydrogen (18-30K), and Helium (2.5-4.5K). Preliminary test results indicated that the test loop had a cooling capacity of 4.2W in the 30-40K temperature range with Neon as the working fluid.

Next generation space infrared sensing instruments and spacecraft will require drastic improvements in cryocooling technology in terms of performance and ease of integration. Projected requirements for cryogenic thermal control systems are: high duty cycle heat loads, low parasitic heat penalty, long transport distances, highly flexible transport lines, and lower cooling temperatures. In the current state of cryocooling transport technology, cryogenic Loop Heat Pipes (CLHPs) are at the forefront of intensive research and development. CLHPs are capable of dispersing heat quickly from an IR heat source and transporting it to remotely located cryocoolers via small and flexible transport lines. Circulation of working fluid in a CLHP is accomplished entirely by capillary action developed in fine pore wicks of the system capillary pumps. Thus they contain no mechanical moving parts to wear out or to introduce unwanted vibrations to the spacecraft. A recently developed CLHP using Hydrogen as the working fluid performed extremely well in the temperature range of 20-30K under the most severe operating conditions. However, it was not optimized for spacecraft applications due to cost and schedule constraints of the initial research phase. Design optimization of the Hydrogen Advanced Loop Heat Pipe is the main objective of the follow-on research. Chief among the system improvements is the weight and volume reduction of the loop components.

Today, remote sensing is one of the fastest growing technologies around. It is a multibillion-dollar industry and remote thematic images are routinely used in an increasing number of fields. The solution of many important practical problems depends on a large-scale usage of the measurement systems and underlying physical principles. These problems include monitoring of the natural resources based on the analysis of the gravity anomalies, studying of global geodynamic processes and evolution of the Earth gravity field, analysis of movement of the Earth poles, etc. In spite of the existence of the considerable achievements in the area of gravity measurements, some important aspects of the problem have not been solved yet due to the absence of appropriate sensitive elements (SE) and sensors with the relevant parameters. The author of the report has proposed a functional structure of the cryogenic-optical sensor based on magnetic bearing phenomenon. A functional structure of the sensitive element consists of a controlled magnetic suspension, a high-precision optical system for registration of levitating body mechanical coordinates, and a signal processing toolbox. This toolbox contents the adaptive compensator, digital filters, inverse mathematical models of the SE, the Kalman filter, the control system, the dynamical analysis system, the mathematical modeling system, the simulation system, the information statistical system, the wavelet analysis system, a neural network, and data base. Mathematical models of the signal and noise are conventionally based on the principles of nonlinear electro-mechanics. Such models explains most basic features of the superconducting sensitive element. We will also discuss a new theoretical framework for adaptive estimation of gravitation perturbations and compare program models to conventional robust estimation models.

There currently exists a great void in high quality, cryogenic, infrared (IR) refractive index data, even for the most common IR optical materials. Meanwhile, as the designs of many future refractive IR optical systems and instruments will rely critically on very accurate knowledge of the indices of refraction of their constituent optical components at design operating temperatures, there has been increasing demand for such data within the IR community. We present our progress to date in the design and construction of a Cryogenic, High-Accuracy Refraction Measuring System (CHARMS), which will measure absolute indices of refraction accurate to better than ±1 x 10^-5. We will operate at wavelengths from 0.105 μm in the far ultraviolet to 20 μm in the mid-IR for sample temperatures ranging from near absolute zero to somewhat above room temperature. Technical challenges, accomplishments, and component developments necessary for successful implementation of the refractometer are discussed. We also present component level accuracy measurements and initial ambient index of refraction measurements for fused silica.

Planck is the third Medium-Sized Mission (M3) of ESA Horizon 2000 Scientific Programme. It is designed to image the anisotropies of the Cosmic Background Radiation Field over the whole sky, with unprecedented sensitivity and angular resolution. Planck carries two main experiments named HFI (High Frequency Instrument) and LFI (Low Frequency Instrument). The first is based on bolometers, the latter is an array of tuned radio receivers, based on High Electron Mobility Transistors (HEMTs) amplifier technology, and covering the frequency range from 30 to 70 GHz. The Front-End Electronics Modules (FEM’s) are cooled at 20K by a H₂ sorption cooler. The high frequency signals (up to 70 GHz) are amplified, phase lagged and transported by means of waveguides to the warm back-end electronics at temperatures of the order of 300K. The 20 K cooling is achieved exploiting a two-stage cooling concept. The satellite is passively cooled to temperatures of the order of 60K using special designed radiators called V-grooves. An H₂ sorption cooler constitutes the second active cooling stage, which allows focal plane temperatures of 20K, i.e. compatible with the tight noise requirements of the Low Noise Amplifiers (LNA’s). Each FEM needs 22 bias lines characterised by a high immunity to external noise and disturbances. The power required for each FEM ranges from 16 to 34mW, depending on the radiometer frequency. Due to the limited cooling power of the sorption cooler (about 2W), the heat transport through the harness and therefore the parasitics on the focal plane, shall be minimised. A total of 290 wires have to be routed from the warm electronics (300K) to the cold focal plane (20K), along a path of about 2200mm, transporting currents ranging from a few uA up to 240mA. The present paper analyses the thermal and electrical problems connected with the design of a suitable cryo-harness for the bias of the radiometers cryogenic front-end modules of LFI. Two possible approaches are proposed, and a solution presented.

The instrumentation for VLT/VLTI 1 facility of the European Southern Observatory at Paranal (Chile)includes the infrared beam-combiner called AMBER, that covers the near infrared bands up to 2.5 μm. The cold spectrograph we describe is the AMBER subsystem responsible of wavelength analysis and several other functions, all of them performed by means of optics, analyzers, and mechanisms working at the temperature of liquid nitrogen boiling at atmospheric pressure. The cryo-mechanical design of the spectrograph we describe here used extensively the methods of finite element analysis and the laboratory tests validated this approach. The final optical quality we measured in the laboratory before shipping the instrument to Grenoble or integration (December 2002),is well inside the specification the AMBER staff assigned to the spectrograph. Simulations show that its total contribution to visibility loss of AMBER is less than 2%.

The Gravity Probe B Relativity Mission uses a fused-quartz optical star tracking telescope as the sensor for the control system which points the spacecraft towards its guide star. The telescope is cooled to <5 K while the readout which uses photodiodes and JFET preamps operates at 72 K. It is mounted on the front end of the telescope with a thermal standoff. Analysis indicates that the telescope is capable of providing sub-milli-arc- second (marcs)pointing stability information with an angular pointing noise of (formula available in paper) for the guide star IM Pegasi. We describe the design of the telescope and test results under nominal operating conditions. Analysis of the expected performance of the telescope in flight, based on the test results, is also presented.

Accurate, high precision, refractive index data for infrared (IR) optical materials at cryogenic temperatures is scarce. CHARMS has been designed to take advantage of the conceptually simplest and most accurate method for determining the real part of refractive index, namely minimum deviation prism refractometry, in order to populate the world’s database of optical constants for IR materials with accurate index values, measured over the full range of practical operating temperatures. Chief among the challenges in obtaining high accuracy index measurements - to levels of 2 to 3 parts in the fifth decimal place of index - at the lowest cryogenic temperatures are satisfactory cooling of the sample and accurate measurement and maintenance of its temperature. We discuss the thermal design aspects of our refractometer system which enable cooling of prismatic samples to temperatures near that of liquid helium (LHe) in a vessel which provides a windowless optical path for the highest accuracy refractometry.