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NASA NTRS2004

The EUSO Mission

The investigation of cosmic rays with energies in excess of 10(exp 20) eV holds the potential for discoveries in astrophysics, cosmology and/or fundamental physics. This has motivated the construction of very large ground-based experiments and has lead to the development of the first space mission to measure these cosmic rays, the Extreme Universe Space Observatory (EUSO). EUSO will use the Earth s atmosphere viewed from space as a detector of extreme energy cosmic rays (EECRs). EUSO s collecting power will exceed the present experiments by more than a factor of 10 and extend the cosmic ray spectrum beyond 10(exp 20) eV with high statistics.

Adams, James H., Jr.↗
NASA NTRS2004

The Millimeter-Wave Bolometric Interferometer

The Millimeter-wave Bolometric Interferometer (MBI) is a proposed ground-based instrument designed for a wide range of cosmological and astrophysical observations including studies of the polarization of the cosmic microwave background (CMB). MBI combines the advantages of two well-developed technologies - interferometers and bolometric detectors. Interferometers have many advantages over .filled-aperture telescopes and are particularly suitable for high resolution imaging. Cooled bolometers are the highest sensitivity detectors at millimeter and sub-millimeter wavelengths. The combination of these two technologies results in an instrument with both high sensitivity and high angular resolution.

Ali, S.↗
NASA NTRS1998

Method and apparatus for determining position using global positioning satellites

A global positioning satellite receiver having an antenna for receiving a L1 signal from a satellite. The L1 signal is processed by a preamplifier stage including a band pass filter and a low noise amplifier and output as a radio frequency (RF) signal. A mixer receives and de-spreads the RF signal in response to a pseudo-random noise code, i.e., Gold code, generated by an internal pseudo-random noise code generator. A microprocessor enters a code tracking loop, such that during the code tracking loop, it addresses the pseudo-random code generator to cause the pseudo-random code generator to sequentially output pseudo-random codes corresponding to satellite codes used to spread the L1 signal, until correlation occurs. When an output of the mixer is indicative of the occurrence of correlation between the RF signal and the generated pseudo-random codes, the microprocessor enters an operational state which slows the receiver code sequence to stay locked with the satellite code sequence. The output of the mixer is provided to a detector which, in turn, controls certain routines of the microprocessor. The microprocessor will output pseudo range information according to an interrupt routine in response detection of correlation. The pseudo range information is to be telemetered to a ground station which determines the position of the global positioning satellite receiver.

Ward, John↗
NASA NTRS2017

Calibrating the IXPE Observatory from Ground to Space

The Imaging X-ray Polarimetry Explorer (IXPE) will be the next SMEX mission launched by NASA in 2021 in collaboration with the Italian Space Agency (ASI). IXPE will perform groundbreaking measurements of imaging polarization in X-rays for a number of different classes of sources with three identical telescopes, finally (re)opening a window in the high energy Universe after more than 40 years since the first pioneering results. The unprecedented sensitivity of IXPE to polarization poses peculiar requirements on the payload calibration, e.g. the use of polarized and completely unpolarized radiation, both on ground and in orbit, and can not rely on a systematic comparison with results obtained by previous observatories. In this paper, we will present the IXPE calibration plan, describing both calibrations which will be performed on the detectors at INAF-IAPS in Rome (Italy) and the calibration on the mirror and detector assemblies which will be carried out at Marshall Space Flight Center in Huntsville, Alabama. On orbit calibrations, performed with calibrations sources mounted on a filter wheel and placed in front of each detector when necessary, will be presented as well.

X-ray astronomy Polarimetry Calibratio↗
NASA NTRS2021

Model-Independent Time-Delay Interferometry Based on Principal Component Analysis

With a laser interferometric gravitational-wave detector in separate free flying spacecraft, the only way to achieve detection is to mitigate the dominant noise arising from the frequency fluctuations of the lasers via postprocessing. The noise can be effectively filtered out on the ground through a specific technique called time-delay interferometry (TDI), which relies on the measurements of time-delays between spacecraft and careful modeling of how laser noise enters the interferometric data. Recently, this technique has been recast into a matrix-based formalism by several authors, offering a different perspective on TDI, particularly by relating it to principal component analysis (PCA). In this work, we demonstrate that we can cancel laser frequency noise by directly applying PCA to a set of shifted data samples, without any prior knowledge of the relationship between single-link measurements and noise, nor time-delays. We show that this fully data-driven algorithm achieves a gravitational-wave sensitivity similar to classic TDI.

Quentin Baghi↗
NASA NTRS1999

The Geoscience Laser Altimeter System (GLAS) for the ICESAT Mission

Accurate measurements of surface heights and atmospheric backscatter have been demonstrated with the SLA, MOLA and LITE space lidar. Recent MOLA measurements of the Mars surface have 40 cm resolution and have reduced the global uncertainty in Mars topography from a few km to approx. 10 m. GLAS is a next generation lidar being developed as part of NASA's Icesat Mission for Earth orbit . The GLAS design combines a 10 cm precision surface lidar with a sensitive dual wavelength cloud and aerosol lidar. GLAS will precisely measure the heights of the Earth's polar ice sheets, determine the height profiles of the Earth's land topography, and profile the vertical backscatter of clouds and aerosols on a global scale. GLAS will fly on a small dedicated spacecraft in a polar orbit at 598 km altitude with an inclination of 94 degrees. GLAS is scheduled to launch in summer 2001 and to operate continuously for a minimum of 3 years with a goal of 5 years. The primary mission for GLAS is to measure the seasonal and annual changes in the heights of the Greenland and Antarctic ice sheets. GLAS will measure the vertical distance to the ice sheet from orbit with 1064 nm pulses from a Nd:Yag laser at 40 Hz. Each 5 nsec wide laser pulse is used for a single range measurement. When over land GLAS will profile the heights of the topography and vegetation. The GLAS receiver uses a I m diameter telescope and a Si APD detector. The detector signal is sampled by an all digital receiver which records each surface echo waveform with I nsec resolution and a stored echo record lengths of either 200, 400, or 600 samples. Analysis of the echo waveforms within the instrument permits discrimination between cloud and surface echoes. Ground based echo analysis permits precise ranging, determining the roughness or slopes of the surface as well as the vertical distributions of vegetation illuminated by the laser, Errors in knowledge of the laser beam pointing angle can bias height measurements of sloped surfaces. For surfaces with 2 deg. slopes, knowledge of pointing angle of the beam centroid to about 8 urad is required to achieve 10 cm height accuracy. GLAS uses a stellar reference system (SRS) to determine the pointing angle of each laser firing relative to inertial space. The SRS uses a high precision star camera oriented toward local zenith whose measurements are combined with a gyroscope to determine the inertial orientation of the SRS optical bench. The far field pattern of each laser pulse is measured with a laser reference system (LRS). Optically measuring each laser far field pattern relative to the star camera and gyroscope permits the angular offsets of each laser pulse to be determined. GLAS will also determine the vertical distributions of clouds and aerosols by measuring atmospheric backscatter profiles at both 1064 and 532 nm. The 1064 nm measurements use an analog detector and profile the height and vertical structure of thicker clouds. Measurements at 532 nm use new highly sensitive photon counting detectors, and measure the height distributions of very thin clouds and aerosol layers. With averaging these can be used to determine the height of the planetary boundary layer. The instrument design and expected performance will be discussed.

Abshire, James B.↗
NASA NTRS1986

Diffraction-limited 10 microns imaging with 3 meter telescopes

An IR imaging system that achieves diffraction-limited spatial resolution (about 0.8 arcsec) at 10 microns on 3-meter ground-based telescopes. The system uses a linear array of sensitive HgCdTe photodiodes, scanned in the direction perpendicular to the array axis, to form two-dimensional images. Scans are completed rapidly enough to freeze atmospheric fluctuations. Individual detectors are small compared to the diameter of the Airy disk, and images are oversampled heavily in the scan direction. This method has a number of advantages for studying small fields with very high spatial resolution, and has been applied successfully to the problem of directly imaging faint circumstellar dust shells.

Bloemhof, E. E.↗
NASA NTRS1993

A motion detection system for AXAF X-ray ground testing

The concept, implementation, and performance of the motion detection system (MDS) designed as a diagnostic for X-ray ground testing for AXAF are described. The purpose of the MDS is to measure the magnitude of a relative rigid body motion among the AXAF test optic, the X-ray source, and X-ray focal plane detector. The MDS consists of a point source, lens, centroid detector, transimpedance amplifier, and computer system. Measurement of the centroid position of the image of the optical point source provides a direct measure of the motions of the X-ray optical system. The outputs from the detector and filter/amplifier are digitized and processed using the calibration with a 50 Hz bandwidth to give the centroid's location on the detector. Resolution of 0.008 arcsec has been achieved by this system. Data illustrating the performance of the motion detection system are also presented.

Arenberg, Jonathan W.↗
NASA NTRS2004

Theoretical Studies of Gamma-Ray Bursts with Swift

Graduate student L.J. Gou , P. Meszaros, T. Abel and B. Zhang investigated the detectability of long GRB afterglows from very high redshifts, where bright reverse shock emission last longer in the observer frame, and its importance for detection and analysis purposes relative to the forward shock increases. They consider two different models for the GRB environment, based on current ideas about the redshift dependence of gas properties in galaxies and primordial star formation. They calculate the observed flux as a function of the redshift and observer time for typical GRB afterglows, taking into account intergalactic photoionization and Lyman-alpha absorption opacity as well as extinction by the Milky Way Galaxy. The fluxes in the X-ray and near IR bands are compared with the sensitivity of different detectors such as Chandra, Swift and JWST. They find that Chandra and Swift can potentially detect GRBs out to very high redshifts z above 13 and 30, respectively. In the K and M bands, the JWST and ground-based telescopes are potentially able to detect GRBs even one day after the trigger out to z approximately 16 and 33, if present. While the X-ray band is insensitive to the external density and to reverse shocks, the near IR bands provides a sensitive tool for diagnosing both the environment and the reverse shock components.

Meszaros, Peter↗
NASA NTRS2022

Spatial Characterization of PACE OCI ETU Using Time-Delay Mode

The OCI (Ocean Color Instrument) is the main sensor on the upcoming PACE (Plankton Aerosol Cloud ocean Ecosystem) mission. OCI has two hyperspectral CCD sensors covering 340nm to 885nm and 9 SWIR (Short Wave IR) bands from 940nm to 2260nm. SWIR bands have nominal 1km ground pixel size and CCD bands have native 1/8 km ground pixel size in diagnostic mode that will be aggregated into 1km pixels to improve SNR and meet the data rate constraints. OCI has a rotating telescope that is synchronized to the readout of the CCD and SWIR detectors. Full pre-launch system level testing for the OCI ETU (Engineering Test Unit) was completed in June 2021.With time-delayed scan mode, a sub-pixel level time-delay step is applied to the detector readout. This sub-pixel level time-delay step causes a sub-pixel level shift in the start of the data collection. After collecting time-delay step scans with different step sizes, a scan profile with sub-pixel resolution can be constructed. 1/8 and 1/4 of CCD pixel resolutions were achieved using this mode. In this paper, the OCI time-delayed scan mode will be described as well as how it was used to calculate OCI’s high spatial resolution PSF (Point Spread Function), IFOV (instantaneous Field of View), MTF (Modulation Transfer Function), and BBR (Band to Band Registration).

PACE↗
NASA NTRS2000

The Geoscience Laser Altimeter System (GLAS) for the ICESAT Mission

The Laser In space Technology Experiment, Shuttle Laser Altimeter and the Mars Observer Laser Altimeter have demonstrated accurate measurements of atmospheric backscatter and Surface heights from space. The recent MOLA measurements of the Mars surface have 40 cm vertical resolution and have reduced the global uncertainty in Mars topography from a few km to about 5 m. The Geoscience Laser Altimeter System (GLAS) is a next generation lidar for Earth orbit being developed as part of NASA's Icesat Mission. The GLAS design combines a 10 cm precision surface lidar with a sensitive dual wavelength cloud and aerosol lidar. GLAS will precisely measure the heights of the Earth's polar ice sheets, establish a grid of accurate height profiles of the Earth's land topography, and profile the vertical backscatter of clouds and aerosols on a global scale. GLAS is being developed to fly on a small dedicated spacecraft in a polar orbit with a 590 630 km altitude at inclination of 94 degrees. GLAS is scheduled to launch in the summer 2001 and to operate continuously for a minimum of 3 years with a goal of 5 years. The primary mission for GLAS is to measure the seasonal and annual changes in the heights of the Greenland and Antarctic ice sheets. GLAS will continuously measure the vertical distance from orbit to the Earth's surface with 1064 nm pulses from a ND:YAG laser at a 40 Hz rate. Each 5 nsec wide laser pulse is used to produce a single range measurement, and the laser spots have 66 m diameter and about 170 m center-center spacings. When over land GLAS will profile the heights of the topography and vegetation. The GLAS receiver uses a 1 m diameter telescope and a Si APD detector. The detector signal is sampled by an all digital receiver which records each surface echo waveform with I nsec resolution and a stored echo record lengths of either 200, 400, or 600 samples. Analysis of the echo waveforms within the instrument permits discrimination between cloud and surface echoes. Ground based echo analysis permits precise ranging, determining the roughness or slopes of the surface as well as the vertical distributions of vegetation illuminated by the laser. Accurate knowledge of the laser beam's pointing angle is needed to prevent height biases when over sloped surfaces. For surfaces with 2 deg. slopes, knowledge of pointing angle of the beam's centroid to about 8 urad is needed to achieve 10 cm height accuracy. GLAS uses a stellar reference system (SRS) to determine the pointing angle of each laser firing relative to inertial space. The SRS uses a high precision star camera oriented toward local zenith and a gyroscope to determine the inertial orientation of the SRS optical bench. The far field pattern of each laser is measured pulse relative to the star camera with a laser reference system (LRS). Optically measuring each laser far field pattern relative to the orientation of the star camera and gyroscope permits the precise pointing angle of each laser pulse to be determined. GLAS will also determine the vertical distributions of clouds and aerosols by measuring the vertical profile of laser energy backscattered by the atmosphere at both 1064 and 532 nm. The 1064 nm measurements use the Si APD detector and profile the height and vertical structure of thicker clouds. The measurements at 532 nm use new highly sensitive photon counting, detectors, and measure the height distributions of very thin Clouds and aerosol layers. With averaging these can be used to determine the height of the planetary boundary layer. The instrument design and expected performance will be discussed.

Abshire, James B.↗
NASA NTRS2004

WaFIRS, a Waveguide Far-IR Spectrometer: Enabling Space-Borne Spectroscopy of High-z Galaxies in the Far-IR and Submm

The discovery of galaxies beyond z approximately equal to 1 which emit the bulk of their luminosity at long wavelengths has demonstrated the need for high sensitivity, broadband spectroscopy in the far-IR/submm/mm bands. Because many of these sources are not detectable in the optical, long wavelength spectroscopy is key to measuring their redshifts and ISM conditions. The continuum source list will increase in the next decade with new ground-based instruments (SCUBA2, Bolocam, MAMBO) and the surveys of HSO and SIRTF. Yet the planned spectroscopic capabilities lag behind, primarily due to the difficulty in scaling existing IR spectrograph designs to longer wavelengths. To overcome these limitations, we are developing WaFIRS, a novel concept for long-wavelength spectroscopy which utilizes a parallel-plate waveguide and a curved diffraction grating. WaFIRS provides the large (approximately 60%) instantaneous bandwidth and high throughput of a conventional grating system, but offers a dramatic reduction in volume and mass. WaFIRS requires no space overheads for extra optical elements beyond the diffraction grating itself, and is two-dimensional because the propagation is confined between two parallel plates. Thus several modules could be stacked to multiplex either spatially or in different frequency bands. The size and mass savings provide opportunities for spectroscopy from space-borne observatories which would be impractical with conventional spectrographs. With background-limited detectors and a cooled 3.5 telescope, the line sensitivity would be better than that of ALMA, with instantaneous broad-band coverage. We have built and tested a WaFIRS prototype for 1-1.6 mm, and are currently constructing Z-Spec, a 100 mK model to be used as a ground-based lambda/DELTAlambda approximately equal to 350 submillimeter galaxy redshift machine.

Bradford, C. M.↗
NASA NTRS1985

Suggestions for improving the efficiency of ground-based neutron monitors for detecting solar neutrons

On the occasion of the June 3, 1982 intense gamma-ray solar flare a significant increase in counting rate due to solar neutrons was observed by the neutron monitors of Junsfraujoch and Lomnicky Stit located at middle latitudes and high altitudes. In spite of a larger detector employed and of the smaller solar zenith angle, the amplitude of the same event observed at Rome was much smaller and the statistical fluctuations of the salactic cosmic ray background higher than the ones registered at the two mountain stations, because of the greater atmospheric depth at which the Rome monitor is located. The effeciency for detecting a solar neutron event by a NM-64 monitor as a function of the Sun zenith angle, atmospheric depth and threshold rigidity of the station was studied.

Iucci, N.↗
NASA NTRS1990

Helicopter Airborne Laser Positioning System (HALPS)

The theory of operation, configuration, laboratory, and ground test results obtained with an HALPS developed by Princeton University is presented. The HALPS measures the relative position between two aircraft in three dimensions using two orthogonal fan-shaped laser beams sweeping across an array of four detectors. Specifically, the HALPS calculates the relative range, elevation, and azimuth between an observation aircraft and a test helicopter with a high degree of accuracy. The detector array provides a wide field of view in the presence of solar interference due to compound parabolic concentrators and spectral filtering of the detector pulses. The detected pulses and their associated time delays are processed by the electronics and are sent as position errors to the helicopter pilot who repositions the aircraft as part of the closed loop system. Accuracies obtained in the laboratory at a range of 80 ft in the absence of sunlight were + or - 1 deg in elevation; +0.5 to -1.5 deg in azimuth; +0.5 to -1.0 ft in range; while elevation varied from 0 to +28 deg and the azimuth varied from 0 to + or - 45 deg. Accuracies in sunlight were approximately 40 deg (+ or - 20 deg) in direct sunlight.

Eppel, Joseph C.↗
NASA NTRS1999

Near-Infrared Hyperspectral Image Cubes of Mars during the 1999 Opposition

We used the Goddard Space Flight Center, Acousto-Optic Tunable Filter (AOTF) Camera to obtain near-IR spectral image sets of Mars over the 1.6-3.6 micron region during the April 1999 opposition. A complete image set consists of 280 images with a spectral full-width-half maximum of 10 wavenumbers (fixed in frequency), 90 images in H-band (1.55-1.80 micron), 115 images in K-band (1.95-2.50 micron) and 75 images in L-band (2.90-3.70 micron). The short-wavelength limit is set by transmission of AOTF cell and long-wavelength limit is imposed by sensitivity of PICNIC, 256x256, HgCdTe array detector. We will discuss the new array performance and provide preliminary interpretations of some of these results. These measurements were part of a 4-observatory coordinated effort whose overall objective was to assemble a photometrically calibrated, spectrally complete ground-based image cube over the visible and near-IR spectral region. To accomplish this, four observing teams conducted the investigations with instruments spanning 0.4 to 5.0 micron. The instruments and observing facilities were (a) AOTF camera at Apache Point Observatory, 3.5m, f/10, Nasymth focus (this abstract). Primary science targets included the 3 micron water-of hydration feature and CO2, H2O ice (polar regions and clouds); (b) Visible/NIR interference-filter (24 filters) camera at Lowell Observatory, 72" telescope. 430-1050 nm. Science targets were Fe(2+), Fe(3+) mineralogy and coarse grain hematite search; (c) NMSU Tortugas Mountain Observatory, 60 cm telescope, CCD photometry with same filter set as Lowell; (d) KPNO cryogenic grating/slit spectrometer (CRSP/SALLY) at KPNO 2.1 m, f/15 Cassegrain focus (see abstract by D. Glenar, et. al., this meeting). Selected wavelengths in 3-5 micron region (L, M band). Science targets included water-of-hydration feature (3-4 micron long wave extension) and sulfate mineralogy. Observers participating in this campaign included Dave Glenar, John Hillman, Gordon Bjoraker and Fred Espenak from GSFC, Nancy Chanover, Jim Murphy and A. S. MurTell from NMSU, Leslie Young from BU, Diana Blaney from JPL and Dick Joyce from KPNO.

Hillman, John J.↗
NASA NTRS2003

Energy Scales in X-Ray Microcalorimeters

Microcalorimeter pulse shape characteristics, such as pulse height, decay time and rise time, are dependent on the detector temperature and bias as well as the photon energy and flux. We examine the nature of the temperature dependency by illuminating the ASTRO-E2 X-ray Spectrometer (XRS) microcalorimeter array with X-rays generated by electron impact on a range of foil targets. The resulting pulses are collected for a range of detector temperatures. We observe and model the temperature dependence of the pulse shape characteristics by fitting the data with non-linear pulse models. Our aim is to determine a robust method for correcting the energy scale obtained in ground calibration for slight differences in the operating conditions while in orbit.

Tillotson, W. A.↗
NASA NTRS2008

Ultra-Stable Beacon Source for Laboratory Testing of Optical Tracking

The ultra-stable beacon source (USBS) provides a laser-beam output with a very low angular jitter and can be used as an absolute angular reference to simulate a beacon in the laboratory. The laser is mounted on the top of a very short (approximately equal to 1 m) inverted pendulum (IP) with its optical axis parallel to the carbon fiber pendulum leg. The 85-cm, carbon fiber rods making up the leg are very lightweight and rigid, and are supported by a flex-joint at the bottom (see figure). The gimbal-mounted laser is a weight-adjustable load of about 1.5 kg with its center of rotation co-located with the center of percussion of the inverted pendulum. This reduces the coupling of transverse motion at the base of the pendulum to angular motion of the laser at the top. The inverted pendulum is mounted on a gimbal with its center of rotation coinciding with the pivot position of the inverted pendulum flexure joint. This reduces coupling of ground tilt at the inverted pendulum base to motion of the laser mounted at the top. The mass of the top gimbal is adjusted to give the pendulum a very low resonant frequency (approximately equal to 10 mHz) that filters transverse seismic disturbances from the ground where the base is attached. The motion of the IP is monitored by an optical-lever sensor. The laser light is reflected by the mirror on the IP, and then is detected by a quadrant photo-detector (QPD). The position of the beam spot on the QPD corresponds to the tilt of the IP. Damping of this motion is provided by two coil and magnet pairs. The bottom gimbal mount consists of two plates. The IP is mounted on the second plate. The first plate is supported by two posts through needles and can be rotated about the axis connecting the tips of the needles. The second plate hangs from the first plate and can be rotated about the axis perpendicular to the first plate. As a result, the second plate acts as a two-axis rotation stage. Its center of rotation is located at the effective bending point of the flex-joint. The second plate is pressed against two screw actuators by the weight of the IP. The screw actuators are orthogonal to each other and are used to adjust the inclination of the second plate. The actuators are driven by stepper motors. The whole IP system is housed in a box made of Lexan plastic plates to provide isolation from air currents and temperature variations. The signals from the sensors are processed and recorded with a PC using the xPC Target realtime environment of Math- Works. The control algorithms are written using the Simulink package from The MathWorks.

Aso, Yoichi↗
NASA NTRS2010

Progress in Measurement of Carbon Dioxide Using a Broadband LIDAR

Innovative active system using advanced source technology development will enable precise daytime or nighttime measurements of column CO2. Directly responds to NRC DS ASCENDS mission. Number of lasers is reduced compared to competing technologies which reduces the complexity of sensor and thus the cost and risk of failure. Knowledge gained from previously developed passive sensor decreases the risk and cost of the present lidar system development. The instrument can play a significant role as an intercomparison instrument for OCO (Orbiting Carbon Observatory) if it is rebuilt and launched as well as other laser based instruments under development for participation in ASCENDS. It can play a role as an airborne instrument in its own right in addressing the problems of scale arising from differences between point observations by the existing ground based CO2 network and wider area measurements obtained by satellites. Developed 2.0 micron broadband system as well and will compare performance of both systems to choose optimal approach for ASCENDS. Have begun development of approach that uses array detectors instead of APD. This approach will have lower noise than APD and may simplify design of the detector optical train.

Heaps, William S.↗