Aden B. 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.

Aperture synthesis using independent telescopes.

Study of a design for a large infrared telescope, consisting of six independent optical systems shows that it is possible to control the optical path differences and phases such that aperture synthesis can be achieved. A thin compensating prism in each optical path can compensate simultaneously the path errors for all objects in the field of view of the telescope. Design parameters for a 5.6-m system are given.

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.

Collisional excitation of atomic spectra in accelerated beams of light elements.

The light emitted by high-speed particles produced by a Van de Graaff accelerator and excited by passage through a thin foil of carbon has been studied in the wavelength range 2700–6600 A. Lines from deuterium, helium, nitrogen, and oxygen are presented including some that have not previously been reported. Qualitative observations are presented on the mean lives of the excited states and on the dependence of spectral line intensity upon particle energy.

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.

Cost-Scaling Laws Applicable To Very Large Optical Telescopes

Cost and weight data for optical and radio telescopes are analyzed to derive scaling laws appropriate to the design and costing of very large telescopes of the future. A scaling law exponent close to the 2.0 power of aperture diameter is found for telescopes of comparable sophistication ranging from a 0.4 m to 5.0 m aperture, in contrast to the often cited 2.7 exponent. Predicted characteristics for a 25-meter aperture steerable dish Next Generation Telescope (NGT) are 5 x 10 6 kg, 20

Cost relationships for nonconventional telescope structural configurations

/kg and a total cost of 1.3 x 10 8

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

.