Jeff Raab

High Performance Flight Cryocooler Compressor

In this paper we report on the development of a next generation flexure bearing compressor which features high efficiency, high capacity per unit mass, enhanced producibility and ease of integration into payloads. The compressor was developed for the 95K High Efficiency Cryocooler programme.

High efficiency cryocooler

The High Efficiency Cryocooler (HEC) is a highly reliable, >10 year life, space cryocooler. Design goals included very high capacity with low mass. The HEC achieved its 10 W at 95 K load while rejecting to 300 K with considerable margin and a flight configured mass of 4 Kg. This flight cooler design is being fabricated for a number of payloads. This paper describes the cooler, its measured performance, and its flight qualification.

Optical Design of the EPIC-IM Crossed Dragone Telescope

The Experimental Probe of Inflationary Cosmology - Intermediate Mission (EPIC-IM) is a concept for the NASA Einstein Inflation Probe satellite. EPIC-IM is designed to characterize the polarization properties of the Cosmic Microwave Background to search for the B-mode polarization signal characteristic of gravitational waves generated during the epoch of Inflation in the early universe. EPIC-IM employs a large focal plane with 11,000 detectors operating in 9 wavelength bands to provide 30 times higher sensitivity than the currently operating Planck satellite. The optical design is based on a wide-field 1.4 m crossed-Dragone telescope, an aperture that allows not only comprehensive measurements of Inflationary B-mode polarization, but also measurements of the E-mode and lensing polarization signals to cosmological limits, as well as all-sky maps of Galactic polarization with unmatched sensitivity and angular resolution. The optics are critical to measuring these extremely faint polarization signals, and any design must meet demanding requirements on systematic error control. We describe the EPIC-IM crossed Dragone optical design, its polarization properties, and far-sidelobe response.

Scaling of Cryocooler Compressors

The successful HEC cryocooler compressor has been used as the basis for two very similar compressors, one smaller and one larger than the original. The new compressors were designed largely by a direct scaling of the original.

Producibility of Cryocooler Compressors

This paper describes the high yield rate, the quality process, and the high performance uniformity among the 12 space qualified HEC (High Efficiency Cryocooler) compressors that have been fully assembled and tested over a period of 15 months. The number of compressors produced allows initial SPC (Statistical Process Control) results of process capabilities to be assessed. 100% yield in final assembly as well as in sub-assembly processes and tests have been achieved. Acceptance tests include compression tests and high temperature friction tests to assure frictionless non-wearing operation of the compressors over their wide operating temperature range. A summary of the manufacturing experience of producing small clearance frictionless compressors is presented. The paper also recommends process enhancements and new testing methods and equipment for future manufacturing.

Small Space Cryocoolers

Mechanical long life cryocoolers are an enabling technology used to cool a wide variety of detectors in space applications. These coolers provide cooling over a range of temperatures from 2K to 200K, cooling powers from tens of mW to tens of watts. Typical applications are missile warning, Earth and climate sciences, astronomy and cryogenic propellant management. Northrop Grumman Aerospace Systems (NGAS) has delivered most of the US flight cryocooler systems and has 16 long life pulse tube coolers on orbit with a cumulative 100 years of continuous orbital operation with no degradation. This paper will describe these cooler capabilities and the performance of the 800 gram microcooler.

Thermal control design of the lightning mapper sensor narrowband spectral filter

The performance of the Lightning Mapper Sensor is dependent on the temperature shifts of its narrowband spectral filter. To perform over a 10 degree FOV with an 0.8 nm bandwidth, the filter must be 15 cm in diameter and mounted externally to the telescope optics. The filter thermal control required a filter design optimized for minimum bandpass shift with temperature, a thermal analysis of substrate materials for maximum temperature uniformity, and a thermal radiation analysis to determine the parameter sensitivity of the radiation shield for the filter, the filter thermal recovery time after occultation, and heater power to maintain filter performance in the earth-staring geosynchronous environment.