Sparrow, a low Size, Weight and Power (SWaP), high-end thermal imaging video core is presented, based on XBn- InAsSb Focal Plane Array (FPA) with 640×512 format and 10μm pitch, which is operated at 150K. The Sparrow video core offloads a range of functions from the host system, such as detector power supply, clocking and image processing, resulting in a very compact and low power module equipped with a miniature Split-Linear Stirling cooler. The Sparrow Module is optimized for a wide range of low SWaP applications, with a volume of 58×62×42 mm3, a weight of 300g, and typical power consumption of 5W at room temperature. It provides sub-frame video latency and supports a variety of output video formats and user-configurable advanced image processing algorithms.
Recent developments of small SWAP2 (Size, Weight, Power, and Price) cryocoolers designed for HOT IR electro-optical devices have already yielded a range of commercial products available from the leading companies in this area. To date, RICOR has contributed to this range the two cryocoolers – K580 rotary model, and K588 linear model. However, continuous demand of the market in further improvements did initiate further K588 model development, intended to meet even more challenging requirements of SWAP2 than its predecessors. The improvements implemented in this new development do involve the whole range of the SWAP2 parameters, still providing withstanding at challenging environmental conditions of shock, vibration and ambient temperature. This paper provides a report on the status of new K588 linear HOT cryocooler development, including specification, outline, prototype performance and pre-qualification test results under specified shock, vibration and ambient temperature. The current phase of the project resulted in meeting of the most specified parameters, while some of them still need further improvement at the next project phase.
The modern needs of the electro optical market for small low-power and light-weight IR systems are impelling development of High Operating Temperature (HOT) IR detectors, requiring development of dedicated cryocoolers. The development of cryocoolers focused on “SWAP-C” configuration means small size, low weight, low power consumption and attractive cost, in order to optimize IDDCA for modern compact thermal imagers. This paper will review the progress made with the new rotary K580 cryocooler for HOT detectors, update on qualification and life demonstration test results, present test results accumulated from production ramp-up and review the compliance with advanced HOT format arrays. The paper will also review planning for advanced Rotary version as further step of excellence with "SWAP-C" parameters.
The growing demand for EO applications that work around the clock 24hr/7days a week, such as in border surveillance systems, emphasizes the need for a highly reliable cryocooler having increased operational availability and optimized system's Integrated Logistic Support (ILS). In order to meet this need, RICOR developed linear and rotary cryocoolers which achieved successfully this goal. Cryocoolers MTTF was analyzed by theoretical reliability evaluation methods, demonstrated by normal and accelerated life tests at Cryocooler level and finally verified by field data analysis derived from Cryocoolers operating at system level. The following paper reviews theoretical reliability analysis methods together with analyzing reliability test results derived from standard and accelerated life demonstration tests performed at Ricor's advanced reliability laboratory. As a summary for the work process, reliability verification data will be presented as a feedback from fielded systems.
The modern needs of the electro-optical market for small low-power and light-weight IR systems are impelling research and development of High Operating Temperature (HOT) IR detectors, requiring development of dedicated “HOT” cryocoolers. The development of cryocoolers with emphasis on the “SWAP3” configuration means small size, low weight, improved performance, low power consumption and low price, in order to optimize IDDCA for future hand held thermal sights. This paper will present the development and the progress made with the new "HOT" cryocooler, including customer data after the evaluation process, performances achieved using a common cold finger, test results update on a large series of production coolers, life and qualification test update and acoustic noise reduction. All the above mentioned information relates to the FPA temperature range of 130 - 200K for various cryocooler models based on rotary and linear design concepts. The paper will also review the progress with the latest development activities implemented in the cryocoolers and the electronic control modules in order to improve reliability and minimize regulated power consumption.
The K527 linear cooler was developed in order to meet the requirements of reliability, cooling power needs and versatility for a wide range of applications such as hand held, 24/7 and MWS. During the recent years the cooler was incorporated in variety of systems. Some of these systems can be sensitive to vibrations which are induced from the cooler. In order to reduce those vibrations significantly, a Tuned Dynamic Absorber (TDA) was added to the cooler. Other systems, such as the MWS type, are not sensitive to vibrations, but require a robust cooler in order to meet the high demand for environmental vibration and temperature. Therefore various mounting interfaces are designed to meet system requirements. The latest K527 version was designed to be integrated with the K508 cold finger, in order to give it versatility to standard detectors that are already designed and available for the K508 cooler type. The reliability of the cooler is of a high priority. In order to meet the 30,000 working hours target, special design features were implemented. Eight K527 coolers have passed the 19,360 working hours without degradations, and are still running according to our expectations.
The world growth in research and development of High Operating Temperature (HOT) IR detectors impels the
development and optimization of suitable cryocoolers. The current developments at RICOR, which include three
different cryocooler models and two new controllers, are focused on the - oriented design process, meaning small
Size, low Weight, low Power consumption, improved performance and lower production cost, providing proper
cryocoolers for future hand held thermal imagers.
This paper shows the progress made during development of “HOT” cryocooler prototypes, engineering pre-production
series and qualified production series cryocoolers working at the FPA temperature range of 130 - 200K. The progress
with development of electronic control modules providing minimized regulated power consumption is also shown.
The progress in development of cryocoolers reliability is also reported in the paper.
KEYWORDS: Cryogenics, Space operations, Sensors, Aerospace engineering, Mars, Temperature metrology, Fermium, Frequency modulation, Climatology, Helium
Cryogenic refrigerators represent a significant enabling technology for Earth and Space science enterprises. Many of the space instruments require cryogenic refrigeration to enable the use of advanced detectors to explore a wide range of phenomena from space. RICOR refrigerators involved in various space missions are overviewed in this paper, starting in 1994 with “Clementine” Moon mission, till the latest ExoMars mission launched in 2016. RICOR tactical rotary refrigerators have been incorporated in many space instruments, after passing qualification, life time, thermal management testing and flight acceptance. The tactical to space customization framework includes an extensive characterization and qualification test program to validate reliability, the design of thermal interfacing with a detector, vibration export control, efficient heat dissipation in a vacuum environment, robustness, mounting design, compliance with outgassing requirements and strict performance screening. Current RICOR development is focused on dedicated ultra-long-life, highly reliable, space cryogenic refrigerator based on a Pulse Tube design
KEYWORDS: Cryocoolers, Reliability, Cryogenics, Sensors, Accelerated life testing, Systems modeling, Interfaces, 3D modeling, Chemical analysis, Algorithm development
Early rotary cryocoolers were designed for the lifetime of a few thousands operating hours. Ricor K506 model’s life
expectancy was only 5,000 hours, then the next generation K508 model was designed to achieve 10,000 operating hours
in basic conditions, while the modern K508N was designed for 20,000 operating hours.
Nowadays, the new challenges in the field of rotary cryocoolers require development of a new generation cooler that
could compete with the linear cryocooler reliability, achieving the lifetime goal of 30,000 operating hours, and even
more.
Such new advanced cryocooler can be used for upgrade existing systems, or to serve the new generation of high-temperature
detectors that are currently under development, enabling the cryocooler to work more efficiently in the field.
The improvement of the rotary cryocooler reliability is based on a deep analysis and understating of the root failure
causes, finding solutions to reduce bearings wear, using modern materials and lubricants. All of those were taken into
consideration during the development of the new generation rotary coolers.
As a part of reliability challenges, new digital controller was also developed, which allows new options, such as discrete
control of the operating frequency, and can extend the cooler operating hours due to new controlling technique. In
addition, the digital controller will be able to collect data during cryocooler operation, aiming end of life prediction.
The growth in world demand for infrared missile warning systems (MWS) has impelled the development of new technologies, in particular, special ruggedized cryogenic coolers. Since the cryocooler is a core component in ruggedized platforms, RICOR has met the challenge by developing new models able to withstand high ambient temperatures above 110°C, as well as harsh vibration levels, both derived from airborne fighter applications. One of the development efforts focused on a cryocooler regenerator and cold finger optimization, in order to achieve high cooling capacity at 95K FPA and the efficiency of about 5.3 % at 102 °C.
In order to withstand harsh environmental vibration and high ambient temperature range, the mechanical parts of the cryocoolers were designed and tested for a high structural safety factor along with weight minimization. The electronic design concept was based on encapsulated controllers, the PCB of which has been designed with internal heat sinking paths and special components able to withstand ambient temperatures of up to 125°C.
As a final stage of development, four cryocooler models (K544, K549, K527 and K508) were successfully qualified under harsh environmental conditions, both by RICOR and by system manufacturers. Also life demonstration tests were performed with these models. The cryocoolers were designed and tested successfully to meet requirements of military standards MIL- STD-704D, MIL-STD- 461E and MIL-STD-810F reflecting real mission profiles in harsh environment.
The world growth in research and development of High Operating Temperature (HOT) IR detectors impels development and optimization of suitable cryocoolers. The current developments at RICOR are focused on the SWAP-oriented design process, meaning small Size, low Weight and low Power consumption, providing proper cryocoolers for future hand held thermal imagers.
This paper shows the progress made during development of "HOT" cryocooler prototypes, and engineering preproduction series cryocoolers working at the FPA temperature range of 130 - 200K. Three different cryocooler models based on rotary & linear design concepts are presented below. The progress with development of electronic control modules providing minimized regulated power consumption is also shown.
In spite of a wide spreading the uncooled night vision technologies, the cooled systems are still known to be superior
in terms of working ranges, resolution and ability to recognize/track fast moving objects in dynamic infrared scenes.
Recent technological advances allowed development and fielding of high temperature infrared detectors working up
to 200K while showing performances typical for their 77K predecessors. The direct benefits of using such detectors are
the lowering of the optical, cooling and packaging constraints resulting in smaller and cost effective optics, electronics
and mechanical cryocooler.
The authors are formulating requirements and general vision of prospective ultra-compact, long life, lightweight,
power efficient, acoustically and dynamically quiet linear cryogenic cooler towards forthcoming infrared imagers.
In particular, the authors are revealing the outcomes of the feasibility study and discuss downscaling options.
The operation of the thermo-mechanical unit of a cryogenic cooler may originate a resonant excitation of the
spacecraft frame, optical bench or components of the optical train. This may result in degraded functionality of the
inherently vibration sensitive space-borne infrared imager directly associated with the cooler or neighboring
instrumentation typically requiring a quiet micro-g environment.
The best practice for controlling cooler induced vibration relies on the principle of active momentum cancellation.
In particular, the pressure wave generator typically contains two oppositely actuated piston compressors, while the single
piston expander is counterbalanced by an auxiliary active counter-balancer. Active vibration cancellation is supervised
by a dedicated DSP feed-forward controller, where the error signals are delivered by the vibration sensors
(accelerometers or load cells). This can result in oversized, overweight and overpriced cryogenic coolers with degraded
electromechanical performance and impaired reliability.
The authors are advocating a reliable, compact, cost and power saving approach capitalizing on the combined
application of a passive tuned dynamic absorber and a low frequency vibration isolator. This concept appears to be
especially suitable for low budget missions involving mini and micro satellites, where price, size, weight and power
consumption are of concern.
The authors reveal the results of theoretical study and experimentation on the attainable performance using a fullscale
technology demonstrator relying on a Ricor model K527 tactical split Stirling cryogenic cooler. The theoretical
predictions are in fair agreement with the experimental data. From experimentation, the residual vibration export is quite
suitable for demanding wide range of aerospace applications. The authors give practical recommendations on heatsinking
and further maximizing performance.
KEYWORDS: Cryogenics, Cryocoolers, Electronics, Space operations, Reliability, Digital signal processing, Sensors, Actuators, Aerospace engineering, Satellites
Cryogenic coolers are often used in modern spacecraft in conjunction with sensitive electronics and sensors of military,
commercial and scientific instrumentation. The typical space requirements are: power efficiency, low vibration export,
proven reliability, ability to survive launch vibration/shock and long-term exposure to space radiation.
A long-standing paradigm of exclusively using "space heritage" equipment has become the standard practice for
delivering high reliability components. Unfortunately, this conservative "space heritage" practice can result in using
outdated, oversized, overweight and overpriced cryogenic coolers and is becoming increasingly unacceptable for space
agencies now operating within tough monetary and time constraints.
The recent trend in developing mini and micro satellites for relatively inexpensive missions has prompted attempts to
adapt leading-edge tactical cryogenic coolers for suitability in the space environment. The primary emphasis has been
on reducing cost, weight and size. The authors are disclosing theoretical and practical aspects of a collaborative effort to
develop a space qualified cryogenic refrigerator system based on the tactical cooler model Ricor K527 and the Iris
Technology radiation hardened Low Cost Cryocooler Electronics (LCCE). The K27/LCCE solution is ideal for
applications where cost, size, weight, power consumption, vibration export, reliability and time to spacecraft integration
are of concern.
Wide use of so called "dry-cooling" technology, eventually replacing the LN2 cooling approach in high-resolution
instrumentation, such as Scanning Electronic Microscopes, Helium Ion Microscopes, Superconductive Quantum
Interference Devices, etc., motivates further quieting of appropriate cryogenic refrigerators.
Linear Stirling cryogenic refrigerators are known to be a major source of harmful vibration export compromising the
overall performance of vibration-sensitive equipment. The dual-piston approach to a design of a linear compressor yields
inherently low vibration export and, therefore, is widely accepted across the industry. However, the residual vibration
disturbance originated even from the technological tolerances, natural wear and contamination cannot be completely
eliminated. Moreover, a vibration disturbance produced by a pneumatically driven cold head is much more powerful as
compared to this of a compressor.
The authors successfully redesigned the existing Ricor model K535 Stirling cryogenic refrigerator for use in vibration-sensitive
electronic microscopy, where the image resolution is specified in angstroms.
The objective was achieved by passive mechanical counterbalancing of the expander portion of the refrigerator, in a
combination with an active two-axis control of residual vibrations, relying on National Instruments CompactRIO
hardware, incorporating a real-time processor and reconfigurable FPGA for reliable stand-alone embedded application,
developed using LabVIEW graphical programming tools.
The attainable performance of the Ultra-Low Vibration linear Stirling cryogenic refrigerator RICOR model K535-ULV
was evaluated through the full-scale experimentation.
Novel tactics employed in carrying out military and antiterrorist operations call for the development of a new generation
of warfare, among which sophisticated portable infrared (IR) imagers for surveillance, reconnaissance, targeting and
navigation play an important role. The superior performance of such imagers relies on novel optronic technologies and
maintaining the infrared focal plane arrays at cryogenic temperatures using closed cycle refrigerators.
Traditionally, rotary driven Stirling cryogenic engines are used for this purpose. As compared to their military off-theshelf
linear rivals, they are lighter, more compact and normally consume less electrical power.
Latest technological advances in industrial development of high-temperature (100K) infrared detectors initialized R&D
activity towards developing microminiature cryogenic coolers, both of rotary and linear types. On this occasion, split
linearly driven cryogenic coolers appear to be more suitable for the above applications. Their known advantages include
flexibility in the system design, inherently longer life time, low vibration export and superior aural stealth. Moreover,
recent progress in designing highly efficient "moving magnet" resonant linear drives and driving electronics enable
further essential reduction of the cooler size, weight and power consumption.
The authors report on the development and project status of a novel Ricor model K527 microminiature split Stirling
linear cryogenic cooler designed especially for the portable infrared imagers.
KEYWORDS: Cryogenics, Sensors, Head, Scanning electron microscopy, Finite element methods, Thermodynamics, Imaging systems, Fluctuations and noise, Vibration isolation, Electron microscopes
As is known, a cold finger of a pulse tube cryogenic refrigerator does not contain moving mechanical components and,
therefore, is traditionally thought of as producing low vibration and having extended lifespan. Because of these
outstanding features, such cryogenic engines are especially attractive for use in a variety of vibration-sensitive
instrumentation, such as infra-red imagers, scanning electron microscopes (SEM), superconductive quantum interference
devices (SQUID), etc. However, even relatively low-level vibration produced by a cold tip of a pulse tube, resulting
from oscillation of a gas pressure along with a vibration transmitted from a compressor through a metallic gas transfer
tube, may sometimes appear to be excessive for the above vibration-sensitive applications.
By making an extensive use of the finite element analysis supported by the full-scale experimentation, the authors are
attempting to identify the sources of vibration occurring in a cold tip of a pulse tube.
Numerous military thermal imagers operating under hostile environmental conditions rely on tactical rotary split Stirling cryocoolers, the pneumatically driven expanders of which are known to be the source of considerable vibration export. The cold tip temperature in such a cooler is typically stabilized by controlling the driving frequency in accordance with thermal loading and ambient temperature, leading to a frequency-swept harmonic vibration export into the optomechanical structure of the thermal imager. The active vibration cancellation systems are basically capable of suppressing such vibration, but are still quite bulky, complicated and expensive.
In this paper, the authors report on the recent efforts towards developing a low cost vibration counterbalancer for a pneumatically driven expander in a rotary cryogenic cooler. In this approach, the flexurally suspended auxiliary mass - counterbalancer - is arranged to oscillate coaxially with the expander’s displacer and is driven pneumatically by the pulses of the working fluid produced by the compressor. Based on the results of analytical modeling and Sage optimization, the counterbalancer was designed and manufactured as an integral part of such an expander. The full-scale experimentation has shown essential cancellation of vibration export within the working frequency range from 30 to 60Hz without noticeable effect on cryocooler performance.
Low vibration Stirling cryocoolers, which find use in numerous vibration sensitive electronic and electro-optic applications, typically comprise a dual-piston linear compressor and a pneumatically driven expander. While such compressors have inherently low level of vibration export, the unbalanced motion of the displacer-regenerator of the traditional expander inevitably leads to an essential vibration export into the supporting structure to which the cryogenic cooler is normally rigidly attached. The authors report on the novel approach to a passive cancellation of vibration export from a pneumatically driven displacer of a split Stirling cryogenic cooler. This patent pending technique relies on the principle of dynamic counterbalancing, where an auxiliary movable mass is flexibly attached to a hot part of the movable displacer-regenerator assembly and to the stationary expander casing using two auxiliary mechanical low-damped springs. A theoretical analysis yields the simple condition of canceling the fundamental component of vibration export at the same power consumption and cooling performance. The authors successfully attempted to redesign the existing expander of the Stirling Ricor model K535 cryocooler, where the vibration export at the driving frequency was reduced 150-fold under typical thermal loading at the same power consumption.
Modern electro-optic applications often contain a cryogenically cooled IR imager placed upon a stabilized platform which is connected to an outer housing by low-friction gimbals. Since the active system of gumball stabilization is dedicated primarily to maintaining the steady line-of-sight control by eliminating the relatively slow effects of yaw, pitch or roll, it may have insufficient resources to suppress an excessive high-frequency vibration exported from the internal active components such as the linear compressor of a cryogenic cooler. To reduce the above vibration export, the authores use an optimally stiffened and damped all-metal vibration isolator is combination with a tuned dynamic absorber. For effective heat sinking, a commercially available metallic plain bearing allowing the compressor to slide freely inside the above plain bearing, which is further thermally connected to the appropriate 'cold wall' of the device. The vibration protective and thermally conductive interface developed allows the use of a split Stirling cryocooler, relying on a highly efficient, cheap and durable linear single-piston compressor within the IR imager mounted upon the gimbaled stabilized platform.
In 1986, the first model K506A micro IDCA (integral dewar cooler assembly) was introduced as a pioneer in the market of the infrared thermal imaging community. Since then, more than 2000 K506 coolers have been sold by Ricor and fielded in a variety of electro-optical instruments. A vast majority of these microcoolers have been integrated with Cincinnati Electronics detector/dewar assemblies. During the last year, two additional models of this family were introduced, model K508A -- having 500 mW at 80 K cooling power, and model K543 -- having 1000 mW at 80 K cooling power. These two models are in final qualification programs and are in a preliminary fielding process. A general view of these models is presented. As part of the qualification program, a life demonstration test is carried out under the supervision of EL-OP LTD. The mean time to first failure as based on the June 12, 1995 status of these ongoing tests is: MTTF > 3000 hours for the model K508A and MTTF > 3800 hours for model K543. Testing is continuing until all units have failed, as the coolers continue to run, the MTTF values will increase proportionately.
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