Advanced Technologies Demonstrated by the Miniature Integrated Camera and Spectrometer (MICAS) Aboard Deep Space 1

MICAS is an integrated multi-channel instrument that includes an ultraviolet imaging spectrometer (80–185 nm), two high-resolution visible imagers (10–20 μrad/pixel, 400–900 nm), and a short-wavelength infrared imaging spectrometer (1250–2600 nm). The wavelength ranges were chosen to maximize the science data that could be collected using existing semiconductor technologies and avoiding the need for multi-octave spectrometers. It was flown on DS1 to validate technologies derived from the development of PICS (Planetary Imaging Camera Spectrometer). These technologies provided a novel systems approach enabling the miniaturization and integration of four instruments into one entity, spanning a wavelength range from the UV to IR, and from ambient to cryogenic temperatures with optical performance at a fraction of a wavelength. The specific technologies incorporated were: a built-in fly-by sequence; lightweight and ultra-stable, monolithic silicon-carbide construction, which enabled room-temperature alignment for cryogenic (85–140 K) performance, and provided superb optical performance and immunity to thermal distortion; diffraction-limited, shared optics operating from 80 to 2600 nm; advanced detector technologies for the UV, visible and short-wavelength IR; high-performance thermal radiators coupled directly to the short-wave infrared (SWIR) detector optical bench, providing an instrument with a mass less than 10 kg, instrument power less than 10 W, and total instrument cost of less than ten million dollars. The design allows the wavelength range to be extended by at least an octave at the short wavelength end and to ∼50 microns at the long wavelength end. Testing of the completed instrument demonstrated excellent optical performance down to 77 K, which would enable a greatly reduced background for longer wavelength detectors. During the Deep Space 1 Mission, MICAS successfully collected images and spectra for asteroid 9969 Braille, Mars, and comet 19/P Borrelly. The Borrelly encounter was a scientific hallmark providing the first clear, high resolution images and excellent, short-wavelength infrared spectra of the surface of an active comet’s nucleus.     

Mass Profiles of Galaxy Clusters from X-ray Analysis

We review the methods adopted to reconstruct the mass profiles in X-ray luminous galaxy clusters. We discuss the limitations and the biases affecting these measurements and how these mass profiles can be used as cosmological proxies.     

Linear stability of ring systems around oblate central masses

In this paper, we consider the stability of a ring of bodies of equal mass uniformly distributed around a large oblate central mass. The purpose of this and previous papers is to shed light on the stability of Saturn’s rings. Previous papers have been limited by the assumptions that (1) all ring bodies are at the same distance from the central body, (2) the central body acts like a point mass (i.e., is a perfect sphere), and (3) the ring bodies all have the same mass and are evenly spaced around the ring. The third limitation is probably the least important; as long as there are a large number of masses and the mass distribution is approximately uniform then the system should behave as a system of equally-spaced, equal-mass bodies. The first main purpose of this paper is to remove the second limitation. But, the paper also aims to address limitation (1). Recent computer simulations of single-ring systems have shown that the threshold for stability, as determined by a linear stability analysis, matches precisely the stability threshold predicted by simulation. In other words, a linear stability analysis while presumably just a mathematical abstraction actually tells us something quite real. Furthermore, simulations of multi-ring systems suggest that instability comes from azimuthal perturbations; small azimuthal changes are more destabilizing that small radial perturbations. Hence, in this paper, we also consider the situation where the central body consists not just of an oblate central mass but also incorporates a flat ring representing in aggregate all ring bodies at radii other than the one under consideration. The central oblate body together with a flat ring is modeled simply by introducing two oblateness terms to the gravitational potential associated with the central mass. The subsequent analysis is almost identical to the case of a single oblateness term. For Saturn, the oblateness of the central mass is six orders of magnitude more significant than the rings at other radii as a destabilizing influence.     

OLTARIS: On-line tool for the assessment of radiation in space

OLTARIS (On-Line Tool for the Assessment of Radiation In Space) is a space radiation analysis tool available on the World Wide Web. It can be used to study the effects of space radiation for various spacecraft and mission scenarios involving humans and electronics. The transport is based on the HZETRN transport code and the input nuclear physics model is NUCFRG. This paper describes the tools behind the web interface and the types of inputs required to obtain results. Typical inputs are mission parameters and slab definitions or vehicle thickness distributions. Radiation environments can be chosen by the user. This paper describes these inputs as well as the output response functions including dose, dose equivalent, whole body effective dose equivalent, LET spectra and detector response models.     

Gemini Orbital Tracking

One purpose of the GEMINI program is to study the problem of and establish techniques associated with acquisition, tracking, and photography of terrestrial objects from the orbiting spacecraft. This paper describes a ground-based simulation which was performed to obtain a realistic understanding of this problem and to provide the astronauts with preflight experience. The results presented evaluate the test subjects' performance in terms of tracking-rate errors, position errors, and fuel consumption for various orbital altitudes and target offsets.     

O5+ in High Speed Solar Wind Streams: SWICS/Ulysses Results

Recent observations with UVCS on SOHO of high outflow velocities of O⁵⁺ at low coronal heights have spurred much discussion about the dynamics of solar wind acceleration. On the other hand, O⁶⁺ is the most abundant oxygen charge state in the solar wind, but is not observed by UVCS or by SUMER because this helium-like ion has no emission lines falling in the wave lengths observable by these instruments. Therefore, there is considerable interest in observing O⁵⁺ in situ in order to understand the relative importance of O⁵⁺ with respect to the much more abundant O⁶⁺. High speed streams are the prime candidates for the search for O⁵⁺ because all elements exhibit lower freezing-in temperatures in high speed streams than in the slow solar wind. The Ulysses spacecraft was exposed to long time periods of high speed streams during its passage over the polar regions of the Sun. The Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is capable of resolving this rare oxygen charge state. We present the first measurement of O⁵⁺ in the solar wind and compare these data with those of the more abundant oxygen species O⁶⁺ and O⁷⁺. We find that our observations of the oxygen charge states can be fitted with a single coronal electron temperature in the range of 1.0 to 1.2 MK assuming collisional ionization/recombination equilibrium with an ambient Maxwellian electron gas. This revised version was published online in June 2006 with corrections to the Cover Date.     

A molecular probe of dark energy

Many theoretical models of dark energy invoke rolling scaler fields which in turn predict time varying values of the fundamental constants. Establishing the value of the fundamental constants at various times in the universe can probe and test the various dark energy theories. One of the constants that is predicted to vary is the ratio of the electron to proton mass μ. It was established early on that molecular spectra are sensitive to the value of μ and can be used as probes of that value. This article describes the use of the spectrum of molecular hydrogen in high redshift Damped Lyman Alpha systems (DLAs) as a sensitive probe of the time evolution of μ.