Lawrence A. Wade

Continuous and Periodic Sorption Cryocoolers for 10 K and Below

This paper presents the current status of both continuous and periodic operation sorption cryocooler development for astrophysics missions requiring refrigeration to 10 K and below. These coolers are uniquely suited for cooling detectors in planned astrophysics missions such as the Exploration of Neighboring Planetary Systems, the Next Generation Space Telescope, and Darwin. The cooler requirements imposed by these missions include ten year life and the ability to scale designs to provide only a few milliwatts of refrigeration while consuming only a few watts of input power. In addition, the ExNPS and Darwin missions add stringent requirements for zero-vibration and zero EMI/EMC operation.

Texture-specific elemental analysis of rocks and soils with PIXL: The Planetary Instrument for X-ray Lithochemistry on Mars 2020

PIXL (Planetary Instrument for X-ray Lithochemistry) is a micro-focus X-ray fluorescence instrument for examining fine scale chemical variations in rocks and soils on planetary surfaces. Selected for flight on the science payload for the proposed Mars 2020 rover, PIXL can measure elemental chemistry of tiny features observed in rocks, such as individual sand grains, veinlets, cements, concretions and crystals, using a 100 μm-diameter, high-flux X-ray beam that can be scanned across target surfaces.

Performance Test Results for a 25 K Sorption Cryocooler Designed for the UCSB Long Duration Balloon Cosmic Microwave Background Radiation Experiment

A continuous operation, vibration-free, long-life 25 K sorption cryocooler has been built and is now in final integration and performance testing. This cooler will be flown on the University of California at Santa Barbara Long Duration Balloon Cosmic Microwave Background Radiation experiment in Antarctica in December 1997. The cooler will refrigerate a focal plane composed of eight microwave feed horns, two working at 30 GHz and six at 42 GHz, with InP High Electron Mobility Transistor amplifiers. This will be the first hydride sorption cooler used to support an astrophysics experiment. As such, it is an important milestone in the development of vibration-free coolers for astrophysics applications.

Exo-zodiacal disk mapper: a space interferometer to detect and map zodiacal disks around nearby stars

We propose a concept for a space mission designed to make a survey of potential zodiacal dust disks around nearby stars in the mid-IR. We show that a 10-meter baseline nulling interferometer with two 0.6-meter apertures located in a 1 X 1 AU heliocentric orbit would allow for the survey of about 400 stars in the solar neighborhood and permit a first order determination of the disk inclination and of the dust density and temperature radius dependence. The high dynamic range of the instrument may also be used to study an additional astrophysical phenomena. Beyond its own scientific merit, such a mission would also serve as a technological precursor to a larger interferometer of the type being considered for the detection of earth-like planets.

Midinfrared optimized resolution spacecraft

A concept study was performed in 1994 to develop a mission design for a telescope to achieve the highest possible spatial resolution in the 10 - 30 micron range within a

THE EXO-ZODIACAL DISK MAPPER: A SPACE INTERFEROMETER TO DETECT AND MAP ZODIACAL DUST DISKS AROUND NEARBY STARS

DOL200 million mission cost cap. The selected approach for the resulting Mid-InfraRed Optimized Resolution Spacecraft (MIRORS) concept design utilizes a partially filled five meter aperture. A simple deployment scheme permits this spacecraft to be fit within the volume envelope and mass capabilities of a Med-Lite launch vehicle. Low bandwidth cryogenic actuators, which dissipate no heat once set, will align the optics after on-orbit thermal stability is achieved. Image stabilization, fine point and stray-light control are achieved through use of a novel actuated Offner relay. Image reconstruction techniques developed for IRAS will be used to deconvolve nearly diffraction-limited images at 10 microns (FWHM approximately 0.5 arcsec). A Lissajous orbit about the L2 sun-earth libration point (sun-earth- L2 on a straight line) is adopted because its extremely stable thermal environment results in correspondingly high telescope mechanical stability and optical performance. This orbit, combined with a spacecraft configuration which incorporates an inflatable sunshield and a deployable four- stage v-groove thermal shield, enables the optics to radiatively cool <25 K. The large format focal plane will be actively cooled to <8 K by a vibration-free, long-life sorption refrigerator.