Jeffrey Olson

Very high capacity aerospace cryocooler

Long-term cryogenic propellant storage requires mechanical cryocoolers to maintainzero or very low cryogen boil-off rates. Very large cryogen tanks such as those proposedfor orbital fuel depots may require cryocoolers with very high cooling capacity. In-situresource generation and storage of oxygen and methane on Mars also requires highcapacity cryocoolers, and low mass is extremely desirable for planetary missions becauseof the cost associated with landing mass on the surface of another planet. LockheedMartins Advanced Technology Center has developed a high capacity low mass aerospacecryocooler with very high power density. This 7 kg pulse tube cryocooler can provide20 W of cooling at 70 K while rejecting heat at 300 K. This large cooling capability couldalso be used to cool large optical structures or other devices with high heat loads. Testingof the cooler with a secondary heat exchanger attached to the pulse tube was alsoconducted, and results are discussed.

Lockheed Martin microcryocoolers

Lockheed Martin’s Advanced Technology Center, part of Lockheed Martin Space Systems Company, has developed a series of long life microcryocoolers for avionics and space sensor applications. We report the development and testing of three varieties of single-stage, compact, coaxial, pulse tube microcryocoolers. These coolers support emerging large, high operating temperature (100-150K) infrared focal plane array sensors with nominal cooling loads of 200-2000 mW, and all share long life technology attributes used in space cryocoolers, which typically provide 10 years of continuous operation on orbit without degradation. These three models of microcryocooler are the 345 gram Micro1-1, designed to provide 1 W cooling at 150 K, the 450 gram Micro1-2, designed to provide 2 W cooling at 105 K, and the 320 gram Micro1-3, designed to provide 300 mW cooling at 125 K while providing the capability to cool the IR focal plane to 125 K in less than 3 minutes. The Micro1-3 was also designed with a highly compact package that reduced the coldhead length to 55 mm, a length reduction of more than a factor of two compared with the other coldheads. This paper also describes recent design studies of 2-stage microcryocoolers capable of providing cooling at 25-100K. LMSSC is an industry leader in multiple-stage coolers, having successfully built and tested eight 2-stage coolers (typically cooling to 35-55K), and four coolers with 3 or 4 stages (for cooling to 4-10K). The 2-stage microcryocooler offers a very low mass and compact package capable of cooling HgCdTe focal planes, while providing simultaneous optics cooling at a higher temperature.

Optimization of display viewing distance for human observers in the noise-limited case

In the pursuit of fully-automated display optimization, the US Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate (NVESD) is evaluating a variety of approaches, including the effects of viewing distance and magnification on target acquisition performance. Two such approaches are the Targeting Task Performance (TTP) metric, which NVESD has developed to model target acquisition performance in a wide range of conditions, and a newer Detectivity metric, based on matched-filter analysis by the observer. While NVESD has previously evaluated the TTP metric for predicting the peak-performance viewing distance as a function of blur, no such study has been done for noise-limited conditions. In this paper, the authors present a study of human task performance for images with noise versus viewing distance using both metrics. Experimental results are compared to predictions using the Night Vision Integrated Performance Model (NV-IPM). The potential impact of the results on the development of automated display optimization are discussed, as well as assumptions that must be made about the targets being displayed.

Fast cool-down coaxial pulse tube microcooler

We report the development and initial testing of the Lockheed Martin first-article, single-stage, compact, coaxial, Fast Cooldown Pulse Tube Microcryocooler (FC-PTM). The new cryocooler supports cooling requirements for emerging large, high operating temperature (105-150K) infrared focal plane array sensors with nominal cooling loads of ~300 mW @105K @293K ambient. This is a sequel development that builds on our inline and coaxial pulse tube microcryocoolers reported at CEC 20137, ICC188,9, and CEC201510. The new FC-PTM and the prior units all share our long life space technology attributes, which typically have 10 year life requirements1. The new prototype microcryocooler builds on the previous development by incorporating cold head design improvements in two key areas: 1) reduced cool-down time and 2) novel repackaging that greatly reduces envelope. The new coldhead and Dewar were significantly redesigned from the earlier versions in order to achieve a cooldown time of 2-3 minutes-- a projected requirement for tactical applications. A design approach was devised to reduce the cold head length from 115mm to 55mm, while at the same time reducing cooldown time. We present new FC-PTM performance test measurements with comparisons to our previous pulse-tube microcryocooler measurements and design predictions. The FC-PTM exhibits attractive small size, volume, weight, power and cost (SWaP-C) features with sufficient cooling capacity over required ambient conditions that apply to an increasing variety of space and tactical applications.

Display MTF measurements based on scanning and imaging technologies and its importance in the application space

Measuring the Modulation Transfer Function (MTF) of a display monitor is necessary for many applications such as: modeling end-to-end systems, conducting perception experiments, and performing targeting tasks in real-word scenarios. The MTF of a display defines the resolution properties and quantifies how well the spatial frequencies are displayed on a monitor. Many researchers have developed methods to measure display MTFs using either scanning or imaging devices. In this paper, we first present methods to measure display MTFs using two separate technologies and then discuss the impact of a display MTF on a system’s performance. The two measurement technologies were scanning with a photometer and imaging with a CMOS based camera. To estimate a true display MTF, measurements made with the photometer were backed out for the scanning optics aperture. The developed methods were applied to measure MTFs of the two types of monitors, Cathode Ray Tube (CRT) and Liquid Crystal Display (LCD). The accuracy of the measured MTFs was validated by comparing MTFs measured with the two systems. The methods presented here are simple and can be easily implemented employing either a Prichard photometer or an imaging device. In addition, the impact of a display MTF on the end-to-end performance of a system was modeled using NV-IPM.

Fast cooldown coaxial pulse tube microcooler

We report the development and initial testing of the Lockheed Martin first-article, single-stage, compact, coaxial, Fast Cooldown Pulse Tube Microcryocooler (FC-PTM). The new cryocooler supports cooling requirements for emerging large, high operating temperature (105-150K) infrared focal plane array sensors with nominal cooling loads of ~300 mW @105K @293K ambient. This is a sequel development that builds on our inline and coaxial pulse tube microcryocoolers reported at CEC 20137, ICC188,9, and CEC201510. The new FC-PTM and the prior units all share our long life space technology attributes, which typically have 10 year life requirements1. The new prototype microcryocooler builds on the previous development by incorporating cold head design improvements in two key areas: 1) reduced cool-down time and 2) novel repackaging that greatly reduces envelope. The new coldhead and Dewar were significantly redesigned from the earlier versions in order to achieve a cooldown time of 2-3 minutes-- a projected requirement for tactical applications. A design approach was devised to reduce the cold head length from 115mm to 55mm, while at the same time reducing cooldown time. We present new FC-PTM performance test measurements with comparisons to our previous pulse-tube microcryocooler measurements and design predictions. The FC-PTM exhibits attractive small size, volume, weight, power and cost (SWaP-C) features with sufficient cooling capacity over required ambient conditions that apply to an increasing variety of space and tactical applications.

Spatial frequency dependence of target signature for infrared performance modeling

The standard model used to describe the performance of infrared imagers is the U.S. Army imaging system target acquisition model, based on the targeting task performance metric. The model is characterized by the resolution and sensitivity of the sensor as well as the contrast and task difficulty of the target set. The contrast of the target is defined as a spatial average contrast. The model treats the contrast of the target set as spatially white, or constant, over the bandlimit of the sensor. Previous experiments have shown that this assumption is valid under normal conditions and typical target sets. However, outside of these conditions, the treatment of target signature can become the limiting factor affecting model performance accuracy. This paper examines target signature more carefully. The spatial frequency dependence of the standard U.S. Army RDECOM CERDEC Night Vision 12 and 8 tracked vehicle target sets is described. The results of human perception experiments are modeled and evaluated using both frequency dependent and independent target signature definitions. Finally the function of task difficulty and its relationship to a target set is discussed.

Multiple-Stage Pulse Tube Cryocoolers for Very Low Temperature Cooling

Recent advances in multiple-stage pulse tube cryocoolers provide the capability to cool scientific instruments and detectors to temperatures previously achievable only with liquid helium or solid hydrogen stored cryogens. Whereas stored cryogen systems are very heavy, with mission lifetimes of at most a few years, pulse tube coolers are simple, lightweight, power efficient, and offer mission lifetimes in excess of 10 years. This paper describes the capabilities and limitations of multiple-stage pulse tube coolers, and presents a simple formula useful for systems engineers who want to estimate the electrical power required by the cryocooler.

Test Results of an Engineering Model 2‐stage Pulse Tube Cryocooler for Cooling at 75 K and 130 K

Under contract with the Space Dynamics Laboratory, Lockheed Martin’s Advanced Technology Center (LM‐ATC) has built and tested the two‐stage Engineering Model of a space flight pulse tube cryocooler, which provides simultaneous cooling at 75 K and 130 K. The cryocooler is robust and simple, consisting of a two‐stage coldhead with no moving parts, driven by a linear flexure‐bearing compressor and powered by a high‐efficiency electronic controller that includes ripple suppression and vibration cancellation. A distance of up to one meter separates the coldhead and compressor.The cryocooler was designed to simultaneously provide 0.75 W of cooling at 75 K and 6 W cooling at 130 K while conductively rejecting heat at 313 K. Total system power is 125 W. Performance data is presented, showing excellent cryocooler performance.

Test for mechanical-cooler-induced noise in a low-noise infrared 2D detector array: spaceborne application for sensing wave structure in thermal CO2 emission

For IR detectors that require cooling to temperatures lower than viable by passive radiative cooling, the mechanical refrigerator is an attractive alternative to expendable cryogen. It provides dramatic reduction in mass, and increased lifetime. For very low noise detectors, there may be some concern that mechanical cooler operation could provide an additional significant detector noise source. Here at LMAATC we have developed a mini-cooler for space borne application, a Stirling compressor driving a pulsetube, and have conducted test to determine if it would induce significant additional noise no cooling a low noise Mie HgCdTe 2D detector array with 3800 nm cutoff. We set up to cool the detector with our mini-cooler, and measure the noise with the cooler running, and with it turned off. We found that cooler operation increased noise barely perceptibly over the cooler off case. We will present implications for our planned space borne instrument, the Source Wave and Propagation Imager. It is an imaging spectrometer that will obtain measurements just below the limb in the 4180 to 4250 nm region of the CO2 band. Tropospheric production of atmospheric internal gravity waves, and their subsequent propagation through stratospheric will be retrieved from these data.