Engineering topics

Waluschka, Eugene

Publications and source records attributed to Waluschka, Eugene.

At least 37 records · Page 2

NASA NTRS2004

MODIS Solar Calibration Simulation Assisted Refinement

A detailed optical radiometric model has been created of the MODIS instruments solar calibration process. This model takes into account the orientation and distance of the spacecraft with respect to the sun, the correlated motions of the scan mirror and the sun, all of the optical elements, the detector locations on the visible and near IR focal planes, the solar diffuser and the attenuation screen with all of its hundreds of pinholes. An efficient computational scheme, takes into account all of these factors and has produced results which reproduce the observed time dependent intensity variations on the two focal planes with considerable fidelity. This agreement between predictions and observations, has given insight to the causes of some small time dependent variations and how to incorporate them into the overall calibration scheme. The radiometric model is described and modeled and actual measurements are presented and compared.

Waluschka, Eugene↗

NASA NTRS2004

Polarization Modeling of the MODIS Instrument

Sunlight reflected from the earth is, to a certain extent, polarized. Radiometers, such as the MODIS instrument on board the TERRA and AQUA spacecraft, are to a certain extent polarizers. Accurate radiometric measurements must take into account both the polarization state of the scene and the polarization sensitivity of the measuring instrument. The measured polarization characteristics of the MODIS instruments are contained in various radiometric models. Continued use of these radiometric math models, over a number of years, have shown where these models can be improved. The current MODIS polarization modeling effort is discussed in the context and limitations of past modeling efforts.

Waluschka, Eugene↗

NASA NTRS2004

Polarization Ray Trace Model of the MODIS Instrument

Sunlight reflected from the earth is, to a certain extent, polarized. Radiometers, such as the MODIS instrument on board the TERRA and AQUA spacecraft, are to a certain extent polarizers. Accurate radiometric measurements must take into account both the polarization state of the scene and the polarization sensitivity of the measuring instrument. The measured polarization characteristics of the MODIS instruments are contained in various radiometric models. Continued use of these radiometric math models, over a number of years, have shown where these models can be improved. Currently a MODIS polarization ray trace model has been created which models the thin film structure on the optical elements. This approach is described and modeled and measured instrument polarization sensitivity results presented.

Waluschka, Eugene↗

NASA NTRS2003

Tilt-Sensitivity Analysis for Space Telescopes

A report discusses a computational-simulation study of phase-front propagation in the Laser Interferometer Space Antenna (LISA), in which space telescopes would transmit and receive metrological laser beams along 5-Gm interferometer arms. The main objective of the study was to determine the sensitivity of the average phase of a beam with respect to fluctuations in pointing of the beam. The simulations account for the effects of obscurations by a secondary mirror and its supporting struts in a telescope, and for the effects of optical imperfections (especially tilt) of a telescope. A significant innovation introduced in this study is a methodology, applicable to space telescopes in general, for predicting the effects of optical imperfections. This methodology involves a Monte Carlo simulation in which one generates many random wavefront distortions and studies their effects through computational simulations of propagation. Then one performs a statistical analysis of the results of the simulations and computes the functional relations among such important design parameters as the sizes of distortions and the mean value and the variance of the loss of performance. These functional relations provide information regarding position and orientation tolerances relevant to design and operation.

Papalexandris, Miltiadis↗

NASA NTRS2003

LISA Optics Model: Early Results

The Laser Interferometer Space Antenna (LISA) optics model is used to generate a synthetic data stream in the absence of gravitational waves. The simulation has the spacecraft in moving in their respective Keplerian orbits. The pointing of the spacecraft and station keeping about the proof masses is accomplished using a control scheme, which minimizes the disturbance on the proof masses in the sensitive direction. The resulting data stream gives an indication of the magnitude of instrumental noise due to pointing jitter and motions of the spacecraft with respect to the proof masses. Computational details are presented and the results discussed.

Waluschka, Eugene↗

NASA NTRS2003

LISA Optics Model: Computational Steps

The Laser Interferometer Space Antenna (LISA) optics model is used to propagate a laser beam inside and between widely, five million kilometers, separated spacecraft moving in orbits about the sun. Numerical beam propagation models have been around for a long time. However, because of the somewhat extreme requirements on the model, namely very large distances while still requiring sub-picometer accuracies, a detailed exposition of the computational steps is necessary to ensure that the results are understood.

Waluschka, Eugene↗

NASA NTRS2003

LISA Optics and Orbital Motions

The Laser Interferometer Space Antenna (LISA) telescopes must be able to send to and receive light from the other two distant spacecraft. The angle between the distant spacecraft will vary by about one degree in the course of a year. In addition the send and receive directions, for any one telescope, will also vary because of changes in distance, relative velocities of the spacecraft and the flight time of the light. All of these (angular) motions place requirements on the telescope pointing mechanism and the compensating proof mass motions. In this paper we will present the magnitudes of these angular motions, within the context of Keplerian orbits, and the resulting image motions on the detectors.

Waluschka, Eugene↗

NASA NTRS2002

LISA Optics Model

The LISA experiment has six telescopes, in three spacecraft, in orbit about the sun. There is a continuous laser link between all of the spacecraft. Because of the large, 5 million kilometer distances, between the spacecraft and the need to perform picometer level interferometry and the fact that the optical system is dynamic precludes the use of standard optical codes in the design and analysis of this optical system. A detailed description of the approach used to model all of the optics, in the spacecraft in orbit, is presented and the ability of this model to analyze requirements is discussed. A dynamic computer simulation will be shown to illustrate the laser link and the effects of this dynamic environment on the interferometry.

Waluschka, Eugene↗

NASA NTRS2002

LISA Telescope Sensitivity Analysis

The Laser Interferometer Space Antenna (LISA) for the detection of Gravitational Waves is a very long baseline interferometer which will measure the changes in the distance of a five million kilometer arm to picometer accuracies. As with any optical system, even one with such very large separations between the transmitting and receiving, telescopes, a sensitivity analysis should be performed to see how, in this case, the far field phase varies when the telescope parameters change as a result of small temperature changes.

Waluschka, Eugene↗

NASA NTRS2002

LISA Optics Model

The Laser Interferometer Space Antenna (LISA) experiment has six telescopes, in three spacecraft, in orbit about the sun. There is a continuous two-way laser link between all of the spacecraft. The ability to make sub picometer level performance predictions about the interferometry for such a large optical system which has major subassemblies separated by 5 million kilometer distances which are constantly moving with respect to each other requires a slight extension of existing optical analysis techniques. To see this a description of the approach used to model all of the optics, in the spacecraft in orbit, is presented and the ability of this model to analyze requirements is discussed.

Waluschka, Eugene↗

NASA NTRS2001

MODIS Solar Diffuser: Modelled and Actual Performance

The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument's solar diffuser is used in its radiometric calibration for the reflective solar bands (VIS, NTR, and SWIR) ranging from 0.41 to 2.1 micron. The sun illuminates the solar diffuser either directly or through a attenuation screen. The attenuation screen consists of a regular array of pin holes. The attenuated illumination pattern on the solar diffuser is not uniform, but consists of a multitude of pin-hole images of the sun. This non-uniform illumination produces small, but noticeable radiometric effects. A description of the computer model used to simulate the effects of the attenuation screen is given and the predictions of the model are compared with actual, on-orbit, calibration measurements.

Waluschka, Eugene↗

NASA NTRS2001

Constellation-X Cylinder Figuring and Polishing Studies

In support of Goddard's Constellation-X mandrel manufacturing effort a series of fabrication experiments are being performed to determine a best approach. Currently, polishing immediately after diamond turning, produces a RMS surface roughness of 0.31 nm, on a nickel plated aluminum mandrel. Studies currently under way will incorporate an abrasive figuring step followed by a polishing operation. The current diamond turning, figuring and polishing procedures will be described and the results presented.

Waluschka, Eugene↗

NASA NTRS2001

LISA Telescope Sensitivity Analysis

The results of a LISA telescope sensitivity analysis will be presented, The emphasis will be on the outgoing beam of the Dall-Kirkham' telescope and its far field phase patterns. The computed sensitivity analysis will include motions of the secondary with respect to the primary, changes in shape of the primary and secondary, effect of aberrations of the input laser beam and the effect the telescope thin film coatings on polarization. An end-to-end optical model will also be discussed.

Waluschka, Eugene↗

NASA NTRS2000

Cylindrical Optic Polishing Dwell Time Optimization

The Constellation-X x-ray telescope consists of replicated grazing incidence optics. The polishing of the "master' mandrel is accomplished by moving a polishing tool along a helical path on the surface of this almost cylindrical surface. The measurement of the surface is, however, performed along "axial" scan lines which intercept this helical path. This approach to polishing and measuring permits a relatively simple scheme to be implemented for the determination of the optimal dwell times of the polishing tool. These optimal dwell times are determined by a deconvolution which approaches the problem as a linear programming problem and uses the simplex method. This approach maximizes the amount of material removed at any point subject to inequality constraints. The effects of using these "optimum" dwell times is to significantly improve the "tools" effectiveness at removing the higher spatial frequencies while staying (strictly) within the bounds and constraints imposed by the hardware. In addition the "ringing" at the edges of the optic, frequently present in deconvolution problems, is completely eliminated.

Waluschka, Eugene↗

NASA NTRS2000

Laser Interferometer Space Antenna (LISA) Far Field Phase Patterns

The Laser Interferometer Space Antenna (LISA) consists of three spacecraft in orbit about the sun. The orbits are chosen such that the three spacecraft are always at (roughly) the vertices of a equilateral triangle with 5 million kilometer leg lengths. Even though the distances between the three spacecraft are 5 million kilometers, the expected phase shifts between any two beams, due to a gravitational wave, only correspond to a distance change of about 10 pico meters, which is about 10(exp -5) waves for a laser wavelength of 1064 nm. To obtain the best signal-to-noise ratio, noise sources such as changes in the apparent distances due to pointing jitter must be controlled carefully. This is the main reason for determining the far-field phase patterns of a LISA type telescope. Because of torque on the LISA spacecraft and other disturbances, continuous adjustments to the pointing of the telescopes are required. These pointing adjustments will be a "jitter" source. If the transmitted wave is perfectly spherical then rotations (Jitter) about its geometric center will not produce any effect at the receiving spacecraft. However, if the outgoing wave is not perfectly spherical, then pointing jitter will produce a phase variation at the receiving spacecraft. The following sections describe the "brute force" computational approach used to determine the scalar wave front as a function of exit pupil (Zernike) aberrations and to show the results (mostly graphically) of the computations. This approach is straightforward and produces believable phase variations to sub-pico meter accuracy over distances on the order of 5 million kilometers. As such this analyzes the far field phase sensitivity to exit pupil aberrations.

Waluschka, Eugene↗

NASA NTRS2000

Cylindrical Optic Figuring and Dwell Time Optimization

Grazing incidence x-ray telescopes consist of surfaces which are nearly cylindrical in shape. The abrasive figuring of these surfaces is accomplished by moving a grinding tool along a helical path on this almost cylindrical surface. The measurement of the surface is, however, performed along "axial" scan lines which intercept this helical path. This approach to figuring and measuring permits a relatively simple scheme to be implemented for the determination of the optimal dwell times of the figuring tool. These optimal dwell times are determined by a deconvolution which approaches the problem in a linear programming context and uses the Simplex Method. The approach maximizes the amount of material removed at any point subject to inequality constraints. The effect of using these ''optimum" dwell times is to significantly improve the tools effectiveness at removing the higher spatial frequencies while staying (strictly) within the bounds and constraints imposed by the hardware. In addition, the ringing at the edges of the optic, frequently present in deconvolution problems, is completely eliminated.

Waluschka, Eugene↗

NASA NTRS1999

Laser Interferometer Space Antenna (LISA) Far Field Phase Pattern

The Laser Interferometry Space Antenna (LISA) for the detection of Gravitational Waves is a very long baseline interferometer that will measure the changes in the distance of a five million kilometer arm to pico meter accuracies. Knowledge of the phase deviations from a spherical wave and what causes these deviations are needed considerations in (as a minimum) the design of the telescope and in determining pointing requirements. Here we present the far field phase deviations from a spherical wave for given Zernike aberrations and obscurations of the exit pupil.

Waluschka, Eugene↗

NASA NTRS1999

Laser Interferometer Space Antenna (LISA) Far Field Phase Patterns

The Laser Interferometer Space Antenna (LISA) for the detection of Gravitational Waves is a very long baseline interferometer, which will measure the changes in the distance of a five million kilometer arm to picometer accuracies. Knowledge of the phase deviations from a spherical wave and what causes these deviations are needed considerations in (as a minimum) the design of the telescope and in determining pointing requirements. Here we will present the far field phase deviations from a spherical wave for given Zernike aberrations of the exit pupil and discuss how these results affect the choice of a telescope design.

Waluschka, Eugene↗