KEYWORDS: Interferometry, Interferometers, Space operations, Transmitters, Space telescopes, Control systems, Optical correlators, Signal detection, Receivers, Satellites
Interferometry in space has marked advantages: long integration times and observation in spectral bands where the
atmosphere is opaque. When installed on separate spacecraft, it also has extended and flexible baselines for better
filling of the uv plane. Intensity interferometry has an additional advantage, being insensitive to telescope and path
errors, but is unfortunately much less light-sensitive. In planning towards such a mission, we are experimenting with
some fundamental research issues. Towards this end, we constructed a system of three vehicles floating on an air table
in formation flight, with an autonomous orbit control. Each such device holds its own light collector, detector, and
transmitter, to broadcast its intensity signal towards a central receiving station. At this station we implement parallel
radio receivers, analogue to digital converters, and a digital three-way correlator.
Current technology limits us to ~1GHz transmission frequency, which corresponds to a comfortable 0.3m accuracy in
light-bucket shape and in its relative position. Naïve calculations place our limiting magnitude at ~7 in the blue and
ultraviolet, where amplitude interferometers are limited. The correlation signal rides on top of this huge signal with its
own Poisson noise, requiring a very large dynamic range, which needs to be transmitted in full. We are looking at
open questions such as deployable optical collectors and radio antennae of similar size of a few meters, and how they
might influence our data transmission and thus set our flux limit.
The Princeton University Terrestrial Planet Finder (TPF) has been working on a novel method for direct imaging of extra solar planets using a shaped-pupil coronagraph. The entrance pupil of the coronagraph is optimized to have a point spread function (PSF) that provides the suppression level needed at the angular separation
required for detection of extra solar planets. When integration time is to be minimized, the photon count at the planet location in the image plane is a Poisson distributed random process. The ultimate limitation of these high-dynamic-range imaging systems comes from scattering due to imperfections in the optical surfaces of the collecting system. The first step in correcting the wavefront errors is the estimation of the phase aberrations. The phase aberration caused by these imperfections is assumed to be a sum of two-dimensional sinusoidal functions. Its parameters are estimated using a global search with a genetic algorithm and a local optimization with the BFGS quasi-Newton method with a mixed quadratic and cubic line search procedure.
The Princeton University Terrestrial Planet Finder (TPF) group has been working on a novel method for direct imaging of extra solar planets using a shaped-pupil coronagraph. The entrance pupil of the coronagraph is optimized to have a point spread function (PSF) that provides the suppression level needed at the angular separation required for detection of extra solar planets. When integration time is to be minimized, the photon count at the planet location in the image plane is a Poisson distributed random process. The ultimate limitation of these high-dynamic-range imaging systems comes from scattering due to imperfections in the optical surfaces of the collecting system. The first step in correcting the wavefront errors is the estimation of the phase aberrations. The phase aberration caused by these imperfections is assumed to be a sum of two-dimensional sinusoidal functions. Assuming one uses a deformable mirror to correct these aberrations, we propose an algorithm that
optimally decreases the scattering level in specified localized areas in the image plane independent of the choice of influence function of the deformable mirror.
This paper presents new families of geocentric orbits in the Sun-Earth spatial elliptic three-body problem (ER3BP) useful for deep space science missions such as planet finding and characterization. The main driver for this study is the need to find practical geocentric orbits that remain within a bounded distance from Earth, thus allowing high data-rate communication while ensuring safe operational environment far from thermal perturbations and visual occultations as well as Earth's magnetic and radiation fields, yet free of the stability and stationkeeping concerns associated with libration point missions or Halo orbits. The orbit characterization procedure is performed using a novel approach. Optimal initial conditions are found using niching genetic algorithms, which render global optimization while permitting several optimal or sub-optimal solutions to co-exist. This approach yields diverse families of orbits, both planar and three-dimensional, including out-of-ecliptic orbits that greatly reduce the impact of the local zodiacal cloud. Stability of the orbits is determined using the notion of practical stability. The effect of solar radiation pressure and the Moon's gravitational perturbation are simulated, showing that the orbits are not significantly affected. This feature implies that no station-keeping is required. Optimal direct transfer trajectories from Low Earth orbit are briefly presented, showing that insertion into the characterized orbits may be performed using modest energetic requirements.
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