J. Clair Batty

SABER instrument design update

This paper describes the design of a 10-channel infrared (1.27 to 16.9 micrometers ) radiometer instrument known as SABER (sounding of the atmosphere using broadband emission radiometry) that will measure earth-limb emissions from the TIMED (thermosphere- ionosphere-mesosphere energetics and dynamics) satellite. The instrument telescope, designed to reject stray light from the earth and the atmosphere, is an on-axis Cassegrain design with a clam shell reimager and a one-axis scan mirror. The telescope is cooled below 210 K by a dedicated radiator. The focal plane assembly (consisting of a filter array, a detector array, a Lyot stop, and a window) is cooled to 75 K by a miniature cryogenic refrigerator. The conductive heat load on the refrigerator is minimized by a Kevlar support system that thermally isolates the focal plane assembly from the telescope. Kevlar is also used to thermally isolate the telescope from the spacecraft. Instrument responsivity drifts due to changes in telescope and focal plane temperatures as well as other causes are neutralized by an in-flight calibration system. The detector array consists of discrete HgCdTe, InSb, and InGaAs detectors. Two InGaAs detectors are a new long wavelength type, made by EG&G, that have a long wavelength cutoff of 2.33 micrometers at 77 K.

Optimum thickness of the nonconvective zone in salt gradient solar ponds

Abstract The nonconvective gradient zone of a salt gradient solar pond tends to more effectively transmit incident solar energy to the storage brine below as its thickness is reduced. However, that same gradient zone tends to more effectively reduce heat loss from the warm brines as its thickness is increased. Therefore, there exists an optimum gradient zone thickness for which the net rate of energy collected and retained is a maximum. This report describes a technique for using a numerical simulation model to determine the optimum thickness of the gradient zone in ponds; provided other basic design, operating and climatic factors are specified. Significant improvements in pond efficiency may be obtained if the thickness of the gradient zone is adjusted monthly, seasonally or even if maintained at the annual average optimum thickness as compared with operating the pond with other than an optimum gradient zone thickness.

Advanced solderless flexible thermal link

Flexible thermal links play an important role int he thermal management of cryogenically cooled components. The purpose of these links is to provide a means of transferring heat from a cooled component to a cooler reservoir with little increase in temperature. The standard soldered approach although effective proves to be time consuming and contributes to added thermal impedances which degrade the performance of the link. For system with little tolerance for temperature differences between cooled components and a cooling source this is undesirable. The authors of this paper have developed a technique by which thin metal foil or braided wire can be attached to metal end blocks without any solder using the swaging process. Swaging provides a fast, simple method for providing a low thermal impedance between the foils and blocks. This paper describes the characteristics of these thermal links in terms of length, mass, thermal resistance, flexibility, and survivability.

Sounding of the atmosphere using broadband emission radiometer (SABER): instrument overview

This paper provides an overview of the sounding of the atmosphere using broadband emission radiometer (SABER) instrument proposed by NASA Langley Research Center (LaRC) and the Space Dynamics Laboratory at Utah State University (SDL/USU). SABER is a 12-channel infrared radiometer designed to measure atmospheric emissions in the 1 to 17 micrometers spectral region. Radiometric, optical, thermal, and electronic aspects of the design are discussed.

A water requirement model for salt gradient solar ponds

A model for predicting the salt gradient solar pond (SGSP) area that could be maintained with a given water supply is presented together with several specific applications. For example, based on 30-year average water flows, the model predicts that 1.93 × 109 m2 (477,000 acres) of solar ponds, 1.02 × 109 m2 (253,000 acres) of evaporation ponds to recycle salt, and 0.51 × 109 m2 (125,000 acres) of freshwater storage reservoirs could be maintained at the Great Salt Lake of Utah. Water use requirements per unit of electrical energy from solar ponds are calculated as 600,000 m3/MW·yr. This is roughly 30 times the water evaporated per unit of electrical energy from coal-fired generating plants using wet cooling towers, but substantially less than water evaporation losses per unit of electrical energy produced from typical hydropower dams and reservoirs. It is concluded that water use requirements for solar ponds, although not necessarily prohibitive, are substantial; and in many locations may be the physical factor that limits solar pond development.

Suppression of wind-induced hydrodynamics in ponds

Abstract Significant economies of scale are an incentive for the design of large salt gradient solar ponds; however, wind induced mixing is more difficult to suppress on larger ponds because of the greater distance (or fetch) between dikes. Quantitative data are needed on the hydrodynamic effects of wind action on ponds protected with wave suppression systems. Experiments conducted at the Utah Water Research Laboratory measured wave height, wave length, and depth of disturbance of water in a test flume exposed to various air flows and wave suppression devices. Water depth was 30 cm in the 12.2-m-long test flume having a cross section 61 cm square. Air velocities ranged from 4.50 to 11.8 m/s. Experiments also were conducted with a sharply stratified system consisting of 15 cm of fresh water floating on 15 cm of salt brine in which the air velocities were observed at the point where gravity return currents and wave motion occur at the density interface. Results indicate that circulation currents may persist even if waves are effectively suppressed.

SABER thermal management update

This paper addresses the current thermal management techniques of the Sounding of the Atmosphere using broadband emission radiometry (SABER) instrument. The SABER instrument is being developed jointly by NASA Langley and the Space Dynamics Laboratory at Utah State University. This instrument will fly on the Thermosphere-Ionosphere- Mesosphere Energetics and Dynamics spacecraft being built at the Applied Physics Laboratory at John Hopkins University. The infrared sensors on SABER must be cooled to 75 K for a 2 year period and at a 100 percent duty cycle. Because of SABERs stringent mass, size, and power constraints, the TRW miniature pulse tube refrigerator has been baselined to cool the focal plane assembly. A passive radiator will maintain the telescope at an average temperature near 230 K. Heat from the cryo-cooler and electronics will be dissipated by a separate radiator maintained at approximately 273 K. Approaches and advances in thermal management technology currently employed on the SABER instrument to ensure that heat loads and temperature ranges are met are also discussed.

SABER on Orbit Performance Evaluation and Lessons Learned

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, launched into orbit December 7, 2001, utilized a miniature pulse‐tube cryocooler to maintain the SABER focal plane assembly (FPA) at 75 K. The limited cooling capacity of the cryocooler necessitated the development of a new never before flown Fiber Support Technology (FiST) for supporting and thermally isolating the FPA. A very precise predictive thermal modeling effort to ensure successful operation was also needed due to the very small capacity margin of the cryocooler. A high performance thermal link that minimized the temperature difference between the FPA and the cryocooler cold block and also the mechanical dynamic loading on the fragile pulse tube was developed and space qualified. This paper presents a comparison of the thermal modeling predictions with on orbit measurements, and discusses the lessons learned concerning long term performance issues of thermal isolation systems which utilize cryocoolers for cooling focal plane assemblies (FPA’s). The effect of ice deposition on the thermal blankets and other FPA cooled structures, as well as the lessons learned in dealing with this ice deposition, will also be presented.

Status and design concepts for the hydrogen on-orbit storage and supply experiment

This paper studies concepts for the Hydrogen On-Orbit Storage And Supply Experiment (HOSS). HOSS is a space flight experiment whose objectives are: Show stable gas supply for storage and direct gain solar-thermal thruster designs; and evaluate and compare low-g performance of active and passive pressure control via a thermodynamic vent system (TVS) suitable for solar-thermal upper stages. This paper shows that the necessary experimental equipment for HOSS can be accommodated in a small hydrogen dewar of 36 to 80 liter. Thermal designs for these dewars which meet the on-orbit storage requirements can be achieved. Furthermore ground hold insulation and shielding concepts are achieved which enable storing initially subcooled liquid hydrogen in these small dewars without venting in excess of 144 hours.

Optical stability testing of the fiber support technology (FiST) focal plane assembly of the SABER instrument

The focal plane assembly of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument is supported using Fiber Support Technology (FiST) which utilizes high performance fibers in tension to mechanically support and thermally isolate a cooled component from a warm environment. Details of this approach were presented in detail at SPIE meeting in Denver in 1996. The SABER team deemed it necessary to perform optical stability testing on this never-before-flown technology for supporting focal plane assemblies to determine if precise positioning could be maintained through vibration and thermal cycling. After subjecting the support system to vibration and thermal cycling, the angular orientation between the warm outer support structure and the inner cold block was measured. Since the outer support structure serves as the reference location for positioning the focal plane assembly and the cold block is where the detectors reside, it was possible to determine if FiST meets the optical stability requirements for the SABER instrument. The results from this testing are presented, discussed, and compared to the optical requirements of the SABER instrument. A brief summary of current thermal and mechanical enhancements to the system will also be discussed.