The IBEX-Lo sensor covers the low-energy heliospheric neutral atom spectrum from 0.01 to 2 keV. It shares significant energy overlap and an overall design philosophy with the IBEX-Hi sensor. Both sensors are large geometric factor, single pixel cameras that maximize the relatively weak heliospheric neutral signal while effectively eliminating ion, electron, and UV background sources. The IBEX-Lo sensor is divided into four major subsystems. The entrance subsystem includes an annular collimator that collimates neutrals to approximately 7°× 7°in three 90°sectors and approximately 3.5°× 3.5°in the fourth 90°sector (called the high angular resolution sector). A fraction of the interstellar neutrals and heliospheric neutrals that pass through the collimator are converted to negative ions in the ENA to ion conversion subsystem. The neutrals are converted on a high yield, inert, diamond-like carbon conversion surface. Negative ions from the conversion surface are accelerated into an electrostatic analyzer (ESA), which sets the energy passband for the sensor. Finally, negative ions exit the ESA, are post-accelerated to 16 kV, and then are analyzed in a time-of-flight (TOF) mass spectrometer. This triple-coincidence, TOF subsystem effectively rejects random background while maintaining high detection efficiency for negative ions. Mass analysis distinguishes heliospheric hydrogen from interstellar helium and oxygen. In normal sensor operations, eight energy steps are sampled on a 2-spin per energyThe IBEX-Lo Sensor 119 step cadence so that the full energy range is covered in 16 spacecraft spins. Each year in the spring and fall, the sensor is operated in a special interstellar oxygen and helium mode during part of the spacecraft spin. In the spring, this mode includes electrostatic shutoff of the low resolution (7°× 7°) quadrants of the collimator so that the interstellar neutrals are detected with 3.5°× 3.5°angular resolution. These high angular resolution data are combined with star positions determined from a dedicated star sensor to measure the relative flow difference between filtered and unfiltered interstellar oxygen. At the end of 6 months of operation, full sky maps of heliospheric neutral hydrogen from 0.01 to 2 keV in 8 energy steps are accumulated. These data, similar sky maps from IBEX-Hi, and the first observations of interstellar neutral oxygen will answer the four key science questions of the IBEX mission.

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The WINKLER spectrometer is a matrix of nine highpurity n-type germanium detectors developed for astrophysical observations and terrestrial radiation monitoring. The spectrometer has been fitted with a set of modulation collimator grids designed for imaging hard X-ray and gamma-ray sources by the Mertz, Nakano, and Kilner method. This technique employs a pair of gridded collimators in front of each detector with the number of grid bars varying from one to N, where N is the number of detectors. When the collimator pairs are rotated through a full 360-degree angular range, the detector signals provide the information for a two-dimensional band-limited Fourier reconstruction of orderN. Tests of the spectrometer with single and multiple point sources as well as continuous source distributions are reported. The spectrometer field-of-view is 20 degrees, and the observed FWHM of the point spread function is 1.6 degrees, in good agreement with simulation results. Images have been obtained for gamma-ray energies from 60 keV to 1.3 MeV, although transmission through the grids reduces contrast at the higher energies. Potential capabilities of the spectrometer for locating the position of single point sources or resolving structure in closely spaced source distributions are discussed, as well as proposed upgrades to improve angular resolution.

The concept of temperature control of an electronic component using a single Loop Heat Pipe (LHP) is well established for Aerospace applications. Using two LHPs is often desirable for redundancy/reliability reasons or for increasing the overall heat source-sink thermal conductance. This effort elaborates on temperature controlling operation of a thermal system that includes two small ammonia LHPs thermally coupled together at the evaporator end as well as at the condenser end and operating "in parallel". A transient model of the LHP system was developed on the Thermal Desktop TM platform to understand some fundamental details of such parallel operation of the two LHPs. Extensive thermal-vacuum testing was conducted with two thermally coupled LHPs operating simultaneously as well as with only one LHP operating at a time. This paper outlines the temperature control procedures for two LHPs operating simultaneously with widely varying sink temperatures. The test data obtained during the thermal-vacuum testing, with both LHPs running simultaneously in comparison with only one LHP operating at a time, are presented with detailed explanations.

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The WINKLER spectrometer is a matrix of nine high -purity, n -type germanium detectors developed for astrophysical observations and terrestrial radiation monitoring.The spectrometer has been fitted with a set of modulation collimator grids designed for imaging hard x -ray and gamma -ray sources by the method of Mertz, Nakano, and Kilner. This technique employs a pair of gridded collimators in front of each detector with the number of grid bars varying from one to N, where N is the number of detectors. When the collimator pairs are rotated through a full 360 degree angular range, the detector signals provide the information for a two -dimensional bandlimited Fourier reconstruction of order N.Tests of the spectrometer with single and multiple point sources as well as continuous source distributions are reported. The spectrometer field -ofview is 20 deg, and the observed FWHM of the point spread function is 1.6 deg, in good agreement with simulation results.Images have been obtained for gamma -ray energies from 60 keV to 1.3 MeV, although transmission through the grids reduces contrast at the higher energies. Potential capabilities of the spectrometer for locating the position of single point sources or resolving structure in closely-spaced source distributions are discussed, as well as proposed upgrades to improve angular resolution.