Marjorie P. Meinel

Late Twilight Glow of the Ash Stratum from the Eruption of Agung Volcano.

Observation of the height of the dust layer responsible for the onset of brilliant sunsets in the 30 � N zone since September 1963 gives evidence that the ash has diffused from the eruption of the volcano Agung on Bali. A height of 22 km is derived for the top of the primary stratum.

Physics looks at solar energy

The idea of using the sun as a source of energy has had a long history, but so far it has been a history of bright hope and dismal failure. In the middle 1950s newspaper headlines were full of glowing predictions of what solar energy could do for mankind; the first International Conference on Applied Solar Energy had been held, and solar energy seemed ready to take its place, along with peaceful uses of atomic energy and with interplanetary exploration, on Vannevar Bushs “endless frontier of science.” And now in the 1970s nuclear power reactors and spaceflight are realities, yet solar energy, as recently as a year ago, was dismissed by a National Academy of Science–National Research Council committee as of no importance in our future—despite the admitted “energy crisis” looming ahead. Whatever happened to the grand predictions? Our search into the history of solar energy started with this question, because we were curious to know if 1970 technology might yield a different result.

Stratospheric dust-aerosol event of november 1974.

A strong incursion of dust and aerosol at an altitude of 20 kilometers was noted over Baja California and southern Arizona in mid-November 1974, as indicated by bluish-ashen daylight skies and colorful twilight glows of the type usually associated with volcanic eruptions. Infrared satellite observations and reports from other sources eliminated a possible oceanic origin in the eastern Pacific. The stratum is probably from the extensive eruption of Volcan de Fuego in Gautemala in October 1974.

Large sparse-aperture space optical systems

The issue of how best to distribute a large optical collecting area is revisited, including the added integration time required for a scene imaged by sparse-aperture configurations to be processed to equal that of a filled aperture, and also its influence on system architecture. The optical performance of three sparse-aperture configurations arising from a 1998 study is presented as a function of field angle and optimization criteria. Optimization of these three specific configurations shows ray FWHM and residual rms values small enough to assure excellent diffraction-limited imagery. Practical issues concerning fabrication, assembly, testing, and on-orbit phasing are identified.

Optical Phased Array Configuration for an Extremely Large Telescope

Extremely large telescopes are currently under consideration by several groups in several countries. Extrapolation of current technology up to 30 m indicates a cost of over dollars 1 billion. Innovative concepts are being explored to find significant cost reductions. We explore the concept of an Optical Phased Array (OPA) telescope. Each element of the OPA is a separate Cassegrain telescope. Collimated beams from the array are sent via an associated set of delay lines to a central beam combiner. This array of small telescope elements offers the possibility of starting with a low-cost array of a few rings of elements, adding structure and additional Cass elements until the desired diameter telescope is attained. We address the salient features of such an extremely large telescope and cost elements relative to more conventional options.

Large membrane space optics: imagery and aberrations of diffractive and holographic achromatized optical elements of high diffraction order

The imagery and aberrations of a large space telescope using a 100-m-diam f/100 diffractive objective are evaluated. Excellent imagery can be obtained with flat membrane optical surfaces. Interactive effects of the spectral fan of a diffractive optical element with the free- flying system architecture are considered. The parametric relationships of achromatized diffractive optical elements (DOEs) and holographic optical elements (HOEs) are explored as a function of diffraction order, focal ratio, and wavelength. Practical aspects of a pair of crossed linear DOEs are discussed. Procedures to design achromatic DOE systems are detailed and typical results presented. A number of practical issues associated with making and using high-order transmissive and reflective DOEs and HOEs are identified.

Is it Time for a New Look at Solar Energy

The authors propose a solar power generating system which would produce 1,000 megawatts of electricity by the thermal conversion of sunshine to produce steam. They suggest the conversion can be done by the optical concentration of sunshine in ground collectors spread over desert regions. The collection of enough solar energy for a 1,000 megawatt generating system would require a solar power “farm” covering an area 3.8 kilometers on a side. Aden B. Meinel is director of the Optical Sciences Center, University of Arizona, his wife, Marjorie Pettit Meinel, has collaborated with him in this study.

Minimum-cost 4-m telescope developed at October 1979 Nanjing study of telescope design and construction

A lightweight 4-m telescope with a 6400-kg primary mirror of f/11.5 was developed during a two-week workshop at the Nanjing Astronomical Instruments Factory sponsored by the Purple Mountain Observatory, Academia Sinica, Nanjing, Peoples Republic of China. A central column supports the secondary mirror, thus eliminating all structures around the periphery of the primary mirror. The altazimuth mounting has the elevation axis behind the primary mirror and cell, requiring a counterweight. The Cassegrain focal position coincides with the elevation axis. A single secondary mirror and appropriate field correctors enable operations at the Harland Epps-Dan Schulte (HEDS), Cassegrain, Nasmyth, and coudé foci. Relay of the Cassegrain beam to the coudé is via an elliptical relay mirror. Cost scaling law considerations indicate that this 4-m design will have a cost comparable with that of a conventional 2.2-m telescope. A discussion of the double-tapered lightweight Cer-Vit-type mirror is included.

Trajectory of the Mt. St. Augustine 1976 Eruption Ash Cloud

The ash clouds from the 23 January 1976 eruption of Mt. St. Augustine in Alaska drifted over Arizona on 25 January at an altitude of 6 kilometers as deduced from air trajectories and the observation of an unusual cloud.

Comparison of lens and Fresnel null correctors

Fresnel null correctors are compared with classical Offner and Hindle null correctors for both optical performance and system sensitivities to errors of construction and placement in the test setup. Fresnel null correctors are closely related to circular diffractive null correctors, the main difference being that a Fresnel uses tilted grooves functioning like a blazed diffraction grating. The Fresnel has an advantage in that specific power terms can produce an aspheric wave front directly and not as the byproduct of bending lenses as in the traditional lens null correctors. The parametric relationships are summarized for a range of configurations of lens null correctors and for Fresnel null correctors. The sensitivities to construction and deployment errors are presented for each of these examples. The performance of two Fresnel correctors for an autocollimation test of a full three-mirror Cassegrain configuration is presented.