The Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) observatory launched on 12 January 2003, and
was the first and only successful GSFC UNEX (NASA Goddard Spaceflight Center University Explorer
class) mission. The UNEX program was conceived by the National Aeronautics and Space Administration
(NASA) as a new class of Explorer mission charged with demonstrating that significant science and/or
technology experiments can be performed by small satellites with constrained budgets and a limited schedule.
The purpose of the observatory was to examine details of the local bubble thermal pressure, spatial
distribution and ionization history. The observatory was also used to observe solar spectra, both scattered
from the Lunar surface and via a fortuitous 2nd order scattering path. CHIPS confirmed that spectral features
within the 90-260Å band were much dimmer than was predicted by contemporary theories, and operated four
years beyond its design lifetime. The observatory was placed in an extended safe-hold mode in April of 2008
for budgetary purposes. The spectrometer consisted of six spectrograph channels which delivered >λ/100
resolution spectra to a single detector. Cost constraints of UNEX led to a design based on a traditional
aluminum structure, and an instrument with a large field of view (5° x 26°). All optical and optomechanical
systems on the spectrometer performed flawlessly on orbit. We discuss the challenges, difficulties and
lessons learned during the design, fabrication and execution stages of the mission.
A solar ultraviolet detector prototype for the GOES spacecraft has been calibrated using the X24C beamline at the Brookhaven NSLS. Similar in design to the 3-channel SOHO CELIAS SEM, the GOES EUV uses a combination of transmission gratings and silicon photodiodes with thin-film metal overcoats to provide the required bandpasses. Four of the channels position the photodiodes at the first to fourth orders of 2500 and 5000 L/mm transmission gratings to provide spectral information over four wavelength bands from approximately 5-80 nm. The fifth channel positions the photodiode at first order of a 1667 L/mm transmission grating in combination with a bandpass filter centered at approximately 120 nm to provide coverage in the Lyman alpha region of teh solar spectrum. The GOES EUV will provid continuous monitoring of solar EUV in bandpasses that are known to have a large variability in the amount of energy deposition in the earth's ionosphere over a solar cycle. Prototype detector design and calibration procedure are discussed. Absolute responses of the design model and synchrotron beamline properties relevant to calibration are presented.
The CHIPS observatory was launched on 12 January 2003, and is the first UNEX (NASA Goddard Spaceflight Center University Explorer class) mission. It is currently on-orbit and performing diffuse spectroscopy in the 90-260Å wavelength band. The instrument is integrated with a custom 3-axis stabilized mini-satellite, designed for roughly one year of operation. The purpose of the observatory is examination of details of the local bubble thermal pressure, spatial distribution and ionization history. The spectrometer consists of six spectrograph channels which deliver >lambda/100 resolution spectra to a single detector. Cost constraints of UNEX led to a design based on a traditional aluminum structure, and an instrument with a large field of view (5° x 26°) for the dual purpose of increasing sensitivity in the photon-starved 90-260Å band, and to reduce requirements on spacecraft pointing. All optomechanical systems on the spectrometer, including coalignment, thermal, front cover and vacuum door release are performing well on orbit. We discuss design, test and operational performance of these systems, as well as launch loads and thermal system considerations.
We describe the design and development of the CHIPS microchannel plate detector. The Cosmic Hot Interstellar Plasma Spectrometer will study the diffuse radiation of the interstellar medium in the extreme ultraviolet band pass of 90Å to 260Å. Astronomical fluxes are expected to be low, so high efficiency in the band pass, good out-of-band rejection, low intrinsic background, and minimal image non-linearities are crucial detector properties. The detector utilizes three 75mm diameter microchannel plates (MCPs) in an abutted Z stack configuration. A NaBr photocathode material deposited on the MCP top surface enhances the quantum detection efficiency. The charge pulses from the MCPs are centroided in two dimensions by a crossed-delayline (XDL) anode. A four panel thin-film filter array is affixed above the MCPs to reduce sensitivity to airglow and scattered radiation, composed of aluminum, polyimide/boron, and zirconium filter panes. The detector is housed in a flight vacuum chamber to preserve the hygroscopic photocathode, the pressure sensitive thin-film filters, and to permit application of high voltage during ground test.
The Cosmic Hot interstellar Plasma Spectrometer (CHIPS), successfully launched on 2003 January 12, provides astronomers with an observatory dedicated to observation of the hot interstellar medium in the extreme ultraviolet. We describe here the otpical and photometric performance of the spectrograph based on calibrations of the individual components, end-to-end vacuum tests, and in-orbit observations of the Moon.
We present a status report on CHIPS, the Cosmic Hot Interstellar Plasma Spectrometer. CHIPS is the first NASA University-Class Explorer (UNEX) project. CHIPS was selected in 1998 and is now scheduled for launch in December of 2002. The grazing incidence CHIPS spectrograph will survey the sky and record spectra of diffuse emission in the comparatively unexplored wavelength band between 90 and 260 Å. These data will provide important new constraints on the temperature, ionization state, and emission measure of hot plasma in the "local bubble" of the interstellar medium.
The flight microchannel plate detectors to be used in the Cosmic Origins Spectrograph, a fourth generation instrument for the Hubble Space Telescope, have been calibrated in the laboratory before being integrated into the spectrograph. This paper presents the results of these calibrations that include measurements of the detector quantum efficiency, spatial resolution, spatial linearity, flat field, electronic livetime and the local count rate limit.
The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched into orbit on June 24, 1999. FUSE is designed to make high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 Angstrom). Its high effective area, low background and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. The FUSE instrument includes two large format microchannel plate detectors. Each detector system consists of two microchannel plate segments in a Z-stack configuration with double delay line anodes and associated electronics. High detector spatial resolution was required in order to obtain scientific data with high spectral resolving power, and low detector background was necessary in order to observe faint objects. We describe the performance of the FUSE detectors during their first year on orbit, including the mechanical and thermal stability, throughput, background, and flat field of the detector system. We will also discuss the regular single event upsets of the detector electronics, and the strategy adopted in order to minimize their impact on mission efficiency.
The Far Ultraviolet (FUV) detector for the Cosmic Origins Spectrograph (COS), scheduled to be installed in the Hubble Space Telescope in June 2003, is currently being built by the Experimental Astrophysics Group at The University of California, Berkeley. The COS FUV detector system is based on the detectors flown on the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite with changes to take advantage of technological improvements since the development of those detectors. The COS FUV detector is a dual segmented, cylindrical input face, MCP detector with cross delay line (XDL) readouts. Each segment is a Z-stack of MCPs with an active area 85 mm by 10 mm. The segments are abutted end to end to form a total active area approximately 180 mm by 10 mm (with a gap in the middle). Detector spatial resolution in the long (spectral) dimension is better than 25 microns and in the short dimension (cross-dispersion) is better than 50 microns. The MCPs are coated with a CsI photocathode to achieve the optimal quantum detection efficiency (QDE) in the 1150 - 1750 angstrom bandpass. Improvements in the understanding of the processing required to produce higher QDE MCPs has lead to significant improvements in the FUV QDE relative to previous missions. This paper presents the basic design parameters and performance characteristics of the COS FUV detector.
The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched into orbit on June 24, 1999. FUSE is now making high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 angstroms). Its high effective area, low background, and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. In this paper, we describe the on- orbit performance of the FUSE satellite during its first nine months of operation, including measurements of sensitivity and resolution.
The microchannel plate, delay line, detectors developed for the far ultraviolet spectroscopic explorer mission to be launched in 1998 are described. The two FUSE detectors have a large format (approximately equals 184 mm by 10 mm split into two 88.5 by 10 mm segments), with high spatial resolution (less than 20 micrometers by 50 micrometers FWHM, greater than 9000 by 200 resolution elements) and good linearity (plus or minus 25 micrometers), high image stability, and counting rates in excess of 4 by 104 events sec-1. KBr opaque photocathodes have been employed to provide quantum detection efficiencies of 30 - 40% in the 900 - 1200 angstrom range. Microchannel plates with 10 micrometer pores and an 80:1 pore length to diameter ratio, with a 95 mm by 20 mm format have been used in a Z stack configuration to provide the photon amplification (gain approximately equals 2 by 107). These show narrow pulse height distributions (less than 35% FWHM) even with uniform flood illumination, and good background levels (less than 0.3 event cm-2sec-1). Flat field images are demanded by the microchannel plate multifiber boundary fixed pattern noise and are stable.
The microchannel plates for the detectors in the SUMER and UVCS instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in late 1995 are described. A low resistance Z stack of microchannel plates (MCPs) is employed in a detector format of 27 mm multiplied by 10 mm using a multilayer cross delay line anode (XDL) with 1024 by 360 digitized pixels. The MCP stacks provide gains of greater than 2 multiplied by 107 with good pulse height distributions (as low as 25% FWHM) under uniform flood illumination. Background rates of approximately equals 0.6 event cm-2 sec-1 are obtained for this configuration. Local counting rates up to approximately equals 800 events/pixel/sec have been achieved with little drop of the MCP gain. MCP preconditioning results are discussed, showing that some MCP stacks fail to have gain decreases when subjected to a high flux UV scrub. Also, although the bare MCP quantum efficiencies are close to those expected (approximately equals 10%), we found that the long wavelength response of KBr photocathodes could be substantially enhanced by the MCP scrubbing process. Flat field images are characterized by a low level of MCP fixed pattern noise and are stable. Preliminary calibration results for the instruments are shown.
Microchannel plate based detectors with cross delay line image readout have been rapidly implemented for the SUMER and UVCS instruments aboard the Solar Orbiting Heliospheric Observatory (SOHO) mission to be launched in July 1995. In October 1993 a fast track program to build and characterize detectors and detector control electronics was initiated. We present the detector system design for the SOHO UVCS and SUMER detector programs, and results from the detector test program. Two deliverable detectors have been built at this point, a demonstration model for UVCS, and the flight Ly (alpha) detector for UVCS, both of which are to be delivered in the next few weeks. Test results have also been obtained with one other demonstration detector system. The detector format is 26mm x 9mm, with 1024 x 360 digitized pixels,using a low resistance Z stack of microchannel plates (MCP's) and a multilayer cross delay line anode (XDL). This configuration provides gains of approximately equals 2 X 107 with good pulse height distributions (<50% FWHM) under uniform flood illumination, and background levels typical for this configuration (approximately equals 0.6 event cm-2 sec-1). Local counting rates up to approximately equals 400 event/pixel/sec have been achieved with no degradation of the MCP gain. The detector and event encoding electronics achieves approximately equals 25 micrometers FWHM with good linearity (+/- approximately equals 1 pixel) and is stable to high global counting rates (>4 X 105 events sec-1). Flat field images are dominated by MCP fixed pattern noise and are stable, but the MCP multifiber modulation usually expected is uncharacteristically absent. The detector and electronics have also successfully passed both thermal vacuum and vibration tests.
We have evaluated several square pore microchannel plates (MCP's) (25 mm MCP's with 85 micrometers diameter pores, 50:1 channel length to diameter (L/D) ratio, and 46 mm MCP's with 25 micrometers pores, 80:1 L/D ratio) from Philips. Measurements of the grain and pulse height distribution (PHD) vs voltage, PHD vs angle, background rate, flat field, quantum detection efficiency (QDE) vs angle, wavelength retarding field were made on these MCP's. The gain levels reach 2 - 3 X 107, with PHD's of < 55%, and background rates of < 0.5 events cm-2 sec-1. Flat field measurements show the 25 micrometers square pore MCP's to have periodic modulation, but the 85 micrometers square pore MCP's to have no measurable modulation. The difference is thought to be due to the MCP stacking configurations. The QDE as a function of wavelength for the square pore MCP's is not markedly different from that of normal uncoated round pore MCP's. The only significant difference is that the QDE variation with angle is much more rapid for the 25 micrometers square pore MCP's. Microscope examination reveals that the pore alignment is quite good for the imaging quality square pore MCP's. Low radioactivity MCP's from Galileo with an 80:1 L/D ratio, 10 micrometers pores, and a 32 mm active area were also tested as a stacked back-back pair. Background events were uniformly distributed over the field of view with an average rate of 0.063 events cm-2 sec-1. Surrounding the detector chamber by lead shield blocks reduced the background rate to only 0.028 events cm-2 sec-1 which is only a factor of 2 to 3 higher than the expected cosmic ray rate.
Measurements of the EUV quantum detection efficiency (QDE) of opaque RbBr, CsBr, and KBr photocathodes are described and investigations of their photoemission characteristics over the 44-1560 A wavelength range are reported. The results show that high QDEs can be obtained in the EUV. Narrow QDE peaks at soft X-ray wavelengths occur at slightly different wavelengths for each of the materials studied. The long-wavelength thresholds vary according to the material band gap. Data on the photoemission from the photocathode layer on the microchannel plate interchannel web area are used to determine the number and energy distribution of the emitted photoelelectrons as a function of wavelength.
Several spherically curved microchannel plate (MCP) stack configurations were studied as part of an ongoing astrophysical detector development program, and as part of the development of the ALEXIS satellite payload. MCP pairs with surface radii of curvature as small as 7 cm, and diameters up to 46 mm have been evaluated. The experiments show that the gain (greater than 1.5 x 10 exp 7) and background characteristics (about 0.5 events/sq cm per sec) of highly curved MCP stacks are in general equivalent to the performance achieved with flat MCP stacks of similar configuration. However, gain variations across the curved MCP's due to variations in the channel length to diameter ratio are observed. The overall pulse height distribution of a highly curved surface MCP stack (greater than 50 percent FWHM) is thus broader than its flat counterpart (less than 30 percent). Preconditioning of curved MCP stacks gives comparable results to flat MCP stacks, but it also decreases the overall gain variations. Flat fields of curved MCP stacks have the same general characteristics as flat MCP stacks.
The Array of Low Energy X-ray Imaging Sensors (ALEXIS) experiment consists of six wide angle EUV/ultrasoft Xray
telescopes utilizing normal incidence multilayer mirrors, flown on a miniature satellite to map out the sky in three narrow
bandpasses around 66, 7 1, and 95eV.The 66 and 7 1 eV bandpasses are centered on intense Fe emission lines which are
characteristic of million degree plasmas such as the one thought to produce the soft X-ray background. The 95eVbandpass
has a higher throughput and is more sensitive to continuum sources. The mission will be launched into orbit on the Pegasus
Air Launched Vehicle in mid-1991.
We will present the details of the ALEXIS telescope optical design, initial characterizations of the first flight mirrors
and detectors, and the current schemes for characterizing and calibrating the completed telescope assemblies. We will also
discuss the details of a novel "wavetrap" feature incorporated into the multilayer mirror structure to greatly reduce the mirror's
reflectivity at 304A, a major background contamination flux of He II emission from the geocorona.