Commercial-off-the-shelf event-based cameras for space surveillance applications.

Event-based cameras (EBCs) are of interest for potential application to space domain awareness (SDA). EBC attributes, including asynchronous response and low latency provide data reduction, break the trade-off between latency and power, and enable consideration of additional algorithms and processing architectures due to individual timestamps for each event. Potential data reduction by a factor of 10 or greater is particularly attractive for SDA from satellite platforms with constraints on system power, processing, and communication bandwidth. Here we report our initial evaluation of Prophesee third-generation commercial-off-the-shelf (COTS) EBCs, including development of, and comparison with, a limiting magnitude model. The analytic model is a function of sky background radiance; EBC parameters including contrast threshold, dark current, pixel pitch, and spectral quantum efficiency; and the optic aperture diameter and focal length. Using an 85 mm f/1.4 lens, the measured detection limits for the half-size video graphics array (HVGA) and video graphics array (VGA)-format EBCs are 6.9 and 9.8 visual magnitudes (mV), respectively, at a sky background level of about 20.3mV per square arcsecond. The empirical sensitivity limit for the VGA differs by 0.1mV from our analytic prediction of 9.7 (less than 10% difference in flux). The limiting magnitude model assumes slow motion of point objects across the EBC focal plane array. Additional experiments exploring temporal behavior show that no stars are detected while scanning across the night sky faster than 0.5 deg per second using the VGA-EBC mounted to a 200 mm f/2.0 lens. The limited sensitivity of the evaluated COTS EBCs prevents their use as a replacement for typical CCD/CMOS framing sensors, but EBCs show clear promise for small-aperture, large-field persistent SDA in terms of their efficient capture of temporal information.

Kepler planet-detection mission: introduction and first results.

The Kepler mission was designed to determine the frequency of Earth-sized planets in and near the habitable zone of Sun-like stars. The habitable zone is the region where planetary temperatures are suitable for water to exist on a planet's surface. During the first 6 weeks of observations, Kepler monitored 156,000 stars, and five new exoplanets with sizes between 0.37 and 1.6 Jupiter radii and orbital periods from 3.2 to 4.9 days were discovered. The density of the Neptune-sized Kepler-4b is similar to that of Neptune and GJ 436b, even though the irradiation level is 800,000 times higher. Kepler-7b is one of the lowest-density planets (approximately 0.17 gram per cubic centimeter) yet detected. Kepler-5b, -6b, and -8b confirm the existence of planets with densities lower than those predicted for gas giant planets.