Radiometry for Nighttime Sub-Cloud Imaging of Venus' Surface in the Near-InfraRed Spectrum

Does radiometry (e.g., signal-to-noise ratio) limit the performance of near-IR subcloud imaging of our sister planet's surface at night? It does not. We compute subcloud radiometry using above-cloud observations, an assumed ground temperature, sub-cloud absorption and emission modeling, and Rayleigh scattering simulations. We thus confirm both archival and recent studies that deployment of a modest subcloud camera does enable high-resolution surface imaging.Comment: 14 pages, 8 figure

An IR Search for Extinguished Supernovae in Starburst Galaxies

IR and Radio band observations of heavily extinguished regions in starburst galaxies suggest a very high SN rate associated with such regions. Optically measured supernova (SN) rates may therefore underestimate the total SN rate by factors of up to 10, due to the high extinction to SNe in starburst regions. The IR/radio SN rates come from a variety of indirect means, however, which suffer from model dependence and other problems. We describe a direct measurement of the SN rate from a regular patrol of starburst galaxies done with K' band imaging to minimize the effects of extinction. A collection of K' measurements of core-collapse SNe near maximum light is presented. Results of a preliminary SN search using the MIRC camera at the Wyoming IR Observatory (WIRO), and an improved search using the ORCA optics are described. A monthly patrol of starburst galaxies within 25 Mpc should yield 1.6 - 9.6 SNe/year. Our MIRC search with low-resolution (2.2" pixels) failed to find extinguished SNe, limiting the SN rate outside the nucleus (at > 15" radius) to less than 3.8 Supernova Rate Units (SRU or SNe/century/10^10 L(solar); 90% confidence). The MIRC camera had insufficient resolution to search nuclear starburst regions, where SN activity is concentrated, explaining why we found no heavily obscured SNe. We conclude that high-resolution, small field SN searches in starburst nuclei are more productive than low resolution, large-field searches, even for our large galaxies. With our ORCA high-resolution optics, we could limit the total SN rate to < 1.3 SRU at 90% confidence in 3 years of observations, lower than the most pessimistic estimate.Comment: AJ Submitted 1998 Dec. 13. View figures and download all as one file at http://panisse.lbl.gov/public/bruce/irs

Determining the Shape, Size, and Sources of the Zodiacal Dust Cloud using Polarized Ultraviolet Scattered Sunlight

The solar system's Zodiacal Cloud is visible to the unaided eye, yet the origin of its constituent dust particles is not well understood, with a wide range of proposed divisions between sources in the asteroid belt and Jupiter Family comets. The amount of dust contributed by Oort Cloud comets is uncertain. Knowledge of the Zodiacal Cloud's structure and origins would help with NASA's aim of characterizing potentially Earth-like planets around nearby stars, since the exo-Earths must be studied against the light scattered from extrasolar analogs of our cloud. As the only example where the parent bodies can be tracked, our own cloud is critical for learning how planetary system architecture governs the interplanetary dust's distribution. Our cloud has been relatively little-studied in the near-ultraviolet, a wavelength range that is important for identifying potentially-habitable planets since it contains the broad Hartley absorption band of ozone. We show through radiative transfer modeling that our cloud's shape and size at near-UV wavelengths can be measured from Earth orbit by mapping the zodiacal light's flux and linear polarization across the sky. We quantify how well the cloud's geometric and optical properties can be retrieved from a set of simulated disk observations, using a Markov chain Monte Carlo analysis. The results demonstrate that observations with sufficient precision, covering a set of fields distributed along the ecliptic and up to the poles, can be used to determine the division between asteroidal, Jupiter Family, and Oort Cloud dust components, primarily via their differing orbital inclination distributions. We find that the observations must be repeated over a time span of several months in order to disentangle the zodiacal light from the Galactic background using the Milky Way's rotation across the sky.Comment: submitted to PAS

In-Situ Focusing Inside a Thermal Vacuum Chamber

Traditionally, infrared (IR) space instruments have been focused by iterating with a number of different thickness shim rings in a thermal vacuum chamber until the focus meets requirements. This has required a number of thermal cycles that are very expensive as they tie up many integration and test (I&T)/ environmental technicians/engi neers work ing three shifts for weeks. Rather than creating a test shim for each iteration, this innovation replaces the test shim and can focus the instrument while in the thermal vacuum chamber. The focus tool consists of three small, piezo-actuated motors that drive two sets of mechanical interface flanges between the instrument optics and the focal- plane assembly, and three optical-displacement metrology sensors that can be read from outside the thermal vacuum chamber. The motors are used to drive the focal planes to different focal distances and acquire images, from which it is possible to determine the best focus. At the best focus position, the three optical displacement metrology sensors are used to determine the shim thickness needed. After the instrument leaves the thermal vacuum chamber, the focus tool is replaced with the precision-ground shim ring. The focus tool consists of two sets of collars, one that mounts to the backside of the interface flange of the instrument optics, and one that mounts to the backside of the interface flange of the focal plane modules. The collars on the instrument optics side have the three small piezo-actuated motors and the three optical displacement metrology systems. Before the instrument is focused, there is no shim ring in place and, therefore, no fasteners holding the focal plane modules to the cameras. Two focus tooling collars are held together by three strong springs. The Orbiting Carbon Observatory (OCO) mission spectrometer was focused this way (see figure). The motor described here had to be moved five times to reach an acceptable focus, all during the same thermal cycle, which was verified using pupil slicing techniques. A focus accuracy of .20.100 microns was achieved

Smoke Detection for the Orion Crew Exploration Vehicle

The Orion Crew Exploration Vehicle (CEV) requires a smoke detector for the detection of particulate smoke products as part of the Fire Detection and Suppression (FDS) system. The smoke detector described in this paper is an adaptation of a mature commercial aircraft design for manned spaceflight. Changes made to the original design include upgrading the materials and electronic to space-qualified parts, and modifying the mechanical design to withstand launch and landing loads. The results of laboratory characterization of the response of the new design to test particles are presented

Generalized shot noise model for time-reversal in multiple-scattering media allowing for arbitrary inputs and windowing

A theoretical shot noise model to describe the output of a time-reversal experiment in a multiple-scattering medium is developed. This (non-wave equation based) model describes the following process. An arbitrary waveform is transmitted through a high-order multiple-scattering environment and recorded. The recorded signal is arbitrarily windowed and then time-reversed. The processed signal is retransmitted into the environment and the resulting signal recorded. The temporal and spatial signal and noise of this process is predicted statistically. It is found that the time when the noise is largest depends on the arbitrary windowing and this noise peak can occur at times outside the main lobe. To determine further trends, a common set of parameters is applied to the general result. It is seen that as the duration of the input function increases, the signal-to-noise ratio (SNR) decreases (independent of signal bandwidth). It is also seen that longer persisting impulse responses result in increased main lobe amplitudes and SNR. Assumptions underpinning the generalized shot noise model are compared to an experimental realization of a multiple-scattering medium (a time-reversal chaotic cavity). Results from the model are compared to random number numerical simulation

VAMOS: a SmallSat mission concept for remote sensing of Venusian seismic activity from orbit

International audienceThe apparent youthfulness of Venus' surface features, given a lack of plate tectonics, is very intriguing; however, longduration seismic observations are essentially impossible given the inhospitable surface of Venus. The Venus Airglow Measurements and Orbiter for Seismicity (VAMOS) mission concept uses the fact that the dense Venusian atmosphere conducts seismic vibrations from the surface to the airglow layer of the ionosphere, as observed on Earth. Similarly, atmospheric gravity waves have been observed by the European Venus Express's Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument. Such observations would enable VAMOS to determine the crustal structure and ionospheric variability of Venus without approaching the surface or atmosphere. Equipped with an instrument of modest size and mass, the baseline VAMOS spacecraft is designed to fit within an ESPA Grande form factor and travel to Venus predominantly under its own power. Trade studies have been conducted to determine mission architecture robustness to launch and rideshare opportunities. The VAMOS mission concept was studied at JPL as part of the NASA Planetary Science Deep Space SmallSat Studies (PSDS3) program, which has not only produced a viable and exciting mission concept for a Venus SmallSat, but has also examined many issues facing the development of SmallSats for planetary exploration, such as SmallSat solar electric propulsion, autonomy, telecommunications, and resource management that can be applied to various inner solar system mission architectures