Engineering topics

Shaklan, Stuart B.

Publications and source records attributed to Shaklan, Stuart B..

42 records · Page 3

NASA NTRS2003

Optimizing coronagraph designs to minimize their contrast sensitivity to low-order optical aberrations

The presence of optical aberrations in the entrance pupil of a coronagraph causes the stellar light to scatter about the occulting spot, reducing the effective contrast achievable. Even if these aberrations are sufficiently corrected with a deformable mirror to enable planet detection, small drifts in the optical alignment of the telescope introduce additional low-order aberrations.

Shaklan, Stuart B.↗

NASA NTRS1999

A Multichannel Averaging Phasemeter for Picometer Precision Laser Metrology

The Micro-Arcsecond Metrology (MAM) team at the Jet Propulsion Laboratory has developed a precision phasemeter for the Space Interferometry Mission (SIM). The current version of the phasemeter is well-suited for picometer accuracy distance measurements and tracks at speeds up to 50 cm/sec, when coupled to SIM's 1.3 micron wavelength heterodyne laser metrology gauges. Since the phasemeter is implemented with industry standard FPGA chips, other accuracy/speed trade-off points can be programmed for applications such as metrology for earth-based long-baseline astronomical interferometry (planet finding), and industrial applications such as translation stage and machine tool positioning. The phasemeter is a standard VME module, supports 6 metrology gauges, a 128 MHz clock, has programmable hardware averaging, and a maximum range of 232 cycles (2000 meters at 1.3 microns).

Halverson, Peter G.↗

NASA NTRS1996

Astrometric Detection of Extrasolar Planets: Results of a Feasibility Study with the Palomar 5 Meter Telescope

The detection of extrasolar planets around stars like the Sun remains an important goal of astronomy. We present results from Palomar 5 m observations of the open cluster NGC 2420 in which we measure some of the sources of noise that will be present in an astrometric search for extrasolar planets. This is the first time that such a large aperture has been used for high-precision astrometry. We find that the atmospheric noise is 150 micro-arcsec hr(exp 1/2) across a 90 sec field of view and that differential chromatic refraction (DCR) can be calibrated to 128 micro-arcsec for observations within 1 hr of the meridian and 45 deg of zenith. These results confirm that a model for astrometric measurements can be extrapolated to large apertures. We demonstrate, based upon these results, that a large telescope achieves the sensitivity required to perform a statistically significant search for extra solar planets. We describe an astrometric technique to detect planets, the astrometric signals expected, the role of reference stars, and the sources of measurement noise: photometric noise, atmospheric motion between stars, sky background, instrumental noise, and DCR. For the latter, we discuss a method to reduce the noise further to 66 micro-arcsecond for observations within 1 hr of the meridian and 45 deg of zenith. We discuss optimal lists of target stars taken from the latest Gliese & Jahreiss catalog of nearby stars with the largest potential astrometric signals, declination limits for both telescope accessibility and reduced DCR, and galactic latitude limits for a sufficiant number of reference stars. Two samples are described from which one can perform statistically significant searches for gas giant planets around nearby stars. One sample contains 100 "solar class" stars with an average stellar mass of 0.82 solar mass; the other maximizes the number of stars, 574, by searching mainly low-mass M stars. We perform Monte Carlo simulations of the statistical significance of the expected results by using measured and estimated noise quantities. We show the semimajor axis parameter spaces that are searched for each star and how an increase in the length of the observing program expands these spaces. The search over semimajor axis parameter space relates to the theory of gas giant planet formation.

Pravdo, Steven H.↗

NASA NTRS1996

Three Weak-Lined T Tauri Stars in Orion

We have identified three new weak lined T Tauri stars in Orion using the Double Spectrograph and 5-m telescope at Palomar Observatory. One of these is a candidate for the X-ray source RX0535-0633. H(alpha) and H(beta) line emisison are detected and equivalent widths measured in all three stars, and in V942 Ori. We also searched without success for H(alpha) line variability in V942 Ari.

stars emission line be stars flare stars V942 Ori ↗

NASA NTRS1995

Measuring Pixel-Position Errors On CCD Imagers

Deviations of positions of pixels on charge-coupled-device (CCD) image detector from nominal rectangular grid pattern measured by method in which coherent-light interference fringes used as reference pattern. Conceived for use in determining pixel-position errors in astrometric cameras flown aboard spacecraft. Also applied to determination of similar errors in (and calibration of) terrestrial CCD cameras used as position sensors; for example, position-measuring cameras that are parts of robotic systems.

Shaklan, Stuart B.↗

NASA NTRS1992

Phasing of a space based segmented submillimeter wavelength telescope using focal plane measurements

As part of a technology development program for realizing a space based submillimeter telescope, two different approaches to the absolute phasing of a segmented primary mirror using focal plane measurements have been implemented for feasibility. The method of optimization by simulated annealing evaluates the image quality of a point spread function after all the telescope segments have been randomly moved. It accepts each iteration which improves the image quality, as well as a random number of iterations which do not, thus keeping the Strehl in the initialization procedure from falling into local maxima. Methods for determining the annealing schedule, and the step size for random segment movements are presented and discussed. Using phase diversity and a model for the telescope imaging system, a nonlinear least squares algorithm has also been implemented which parameterizes each of the segment actuator movements. Using multiple out of focus images, the segment actuator positions are estimated using an iterative procedure. Nonlinear least squares, although computationally intensive, offers a large savings in the actuator movements over simulated annealing and pairwise phasing methods for large numbers of segments. These algorithms have been integrated into a general simulation program which models the behavior of the telescope under anticipated space conditions.

Levine, B. M.↗