Engineering topics

Levy, Eugene H.

Publications and source records attributed to Levy, Eugene H..

10 records

NASA NTRS1994

The Astrometric Imaging Telescope: Detection of planetary systems with imaging and astrometry

The Astrometric Imaging Telescope (AIT) is a proposed spaceborne observatory whose primary goal is the detecton and study of extra-solar planetary systems. It contains two instruments that use complementary techniques to address the goal. The first instrument, the Coronagraphic Imager, takes direct images of nearby stars and Jupiter-size planets. It uses a telescope with scattering-compensated optics and a high-efficiency coronagraph to separate reflected planet light from the central star light. Planet detections take hours; confirmations occur in months. With a program duration of about 2 years, about 50 stars are observed. The second instrument, the Astrometric Photometer, shares the same telescope and focal plane. It uses a Ronchi ruling that is translated across the focal plane to simultaneously measure the positions of each target star and about 25 reference stars with sufficient accuracy to detect Uranus-mass planets around hundreds of stars. Enough stars of several spectral types are observed to obtain a statistically significant measurement of the prevalence of planetary systems. This observing program takes about 10 years to complete. The combination of both instruments in a single telescope system results from a number of innovative solutions that are described in this paper.

Pravdo, Steven H.↗

NASA NTRS1991

Generation and behavior of solar system magnetic fields

A range of problems aimed primarily at elucidating the character and consequences of magnetic-field generation in the solar system and at testing ideas against known properties of natural magnetic fields are covered. Among the specific subjects currently under investigation are the magnetohydrodynamic (MHD) character of the protosolar nebula, including the generation and behavior of magnetic fields, the electrical conductivity of dusty nebular gas, transient magnetodynamic and electrodynamic nebular phenomena, and the generation and dynamical behavior of planetary magnetic fields. During the past year, the focus of this research was on disk magnetic field generation and transient MHD heating events possibly associated with the protoplanetary nebula.

Levy, Eugene H.↗

NASA NTRS1991

High accuracy image centroiding with a moving Ronchi ruling

A moving Ronchi ruling at the focal plane of a telescope has been employed to measure the relative motions of stars with great accuracy. The method has long-term stability and exceptional linearity over a relatively large field-of-view. This measurement technique may prove useful in other applications where such capabilities are required. This paper employs Fourier optics to describe the operation of the device, explore performance at very long and very short periods, and consider ruling profiles and other means of optimizing performance.

Lawrence, George N.↗

NASA NTRS1991

Steady state toroidal magnetic field at earth's core-mantle boundary

Measurements of the dc electrical potential near the top of earth's mantle have been extrapolated into the deep mantle in order to estimate the strength of the toroidal magnetic field component at the core-mantle interface. Recent measurements have been interpreted as indicating that at the core-mantle interface, the magnetic toroidal and poloidal field components are approximately equal in magnitude. A motivation for such measurements is to obtain an estimate of the strength of the toroidal magnetic field in the core, a quantity important to our understanding of the geomagnetic field's dynamo generation. Through the use of several simple and idealized calculation, this paper discusses the theoretical relationship between the amplitude of the toroidal magnetic field at the core-mantle boundary and the actual amplitude within the core. Even with a very low inferred value of the toroidal field amplitude at the core-mantle boundary, (a few gauss), the toroidal field amplitude within the core could be consistent with a magnetohydrodynamic dynamo dominated by nonuniform rotation and having a strong toroidal magnetic field.

Levy, Eugene H.↗

NASA NTRS1991

Conceptual design considerations for the Astrometric Telescope Facility

The system of an astrometric telescope on the Space Station and its support by the Station are described and its feasibility demonstrated. The conceptual design shows that such a facility provides a basis for the study of design alternatives and a point of departure for a detailed design. Basic requirements for this preliminary design are outlined.

Dyer, John W.↗

NASA NTRS1991

Magnetohydrodynamic puzzles in the protoplanetary nebula

The following subject areas are covered: (1) magnetization of meteorites; (2) the possible origin of a nebular magnetic field; (3) the possibility of magnetic flares; (4) external manifestations; (5) dynamical effects of the magnetic fields; and (6) the problem of ionization.

Levy, Eugene H.↗

NASA NTRS1990

International cooperation for Mars exploration and sample return

The National Research Council's Space Studies Board has previously recommended that the next major phase of Mars exploration for the United States involve detailed in situ investigations of the surface of Mars and the return to earth for laboratory analysis of selected Martian surface samples. More recently, the European space science community has expressed general interest in the concept of cooperative Mars exploration and sample return. The USSR has now announced plans for a program of Mars exploration incorporating international cooperation. If the opportunity becomes available to participate in Mars exploration, interest is likely to emerge on the part of a number of other countries, such as Japan and Canada. The Space Studies Board's Committee on Cooperative Mars Exploration and Sample Return was asked by the National Aeronautics and Space Administration (NASA) to examine and report on the question of how Mars sample return missions might best be structured for effective implementation by NASA along with international partners. The committee examined alternatives ranging from scientific missions in which the United States would take a substantial lead, with international participation playing only an ancillary role, to missions in which international cooperation would be a basic part of the approach, with the international partners taking on comparably large mission responsibilities. On the basis of scientific strategies developed earlier by the Space Studies Board, the committee considered the scientific and technical basis of such collaboration and the most mutually beneficial arrangements for constructing successful cooperative missions, particularly with the USSR.

Levy, Eugene H.↗

NASA NTRS1989

United States and Western Europe cooperation in planetary exploration

A framework was sought for U.S.-European cooperation in planetary exploration. Specific issues addressed include: types and levels of possible cooperative activities in the planetary sciences; specific or general scientific areas that seem most promising as the main focus of cooperative efforts; potential mission candidates for cooperative ventures; identification of special issues or problems for resolution by negotiation between the agencies, and possible suggestions for their resolutions; and identification of coordinated technological and instrumental developments for planetary missions.

Levy, Eugene H.↗

NASA NTRS1989

Space Station utilization for the Astrometric Telescope Facility

It is shown how it is possible for the Astrometric Telescope Facility (ATF) to utilize the Space Station Freedom as an attached payload by complying with changes in the Station concept and schedule. The ability of the station to accommodate ATF's firm requirements is also addressed. The main factors that led the ATF to utilize the Space Station Freedom are the Station's relative orbital stability and longevity, the availability of maintenance and repair services, and the provision of utilities.

Nishioka, Kenji↗

NASA NTRS1987

Performance analysis of the multichannel astrometric photometer

It has been proposed that extrasolar planetary systems may be observed if perturbations in star position due to the orbit of Jupiter-type planets could be detected. To see this motion, high accuracy measurements of 0.01 milliarcsecond are required over a relatively large field of view. Techniques using a moving Ronchi grating have been proposed for this application and have been successful in ground-based lower resolution tests. The method may have application to other precision angular measurement problems. This paper explores the theoretical description of the method, considers certain of the error sources, and presents a preliminary calculation of the performance which may be achieved.

Huang, Chunsheng↗