Solar viewing interferometer prototype

Abstract

The Earth Atmospheric Solar-Occultation Imager (EASI) is a proposed interferometer with 5 telescopes on an 8-meter boom in a 1D Fizeau configuration. Placed at the Earth-Sun L2 Lagrange point, EASI would perform absorption spectroscopy of the Earth's atmosphere occulting the Sun. Fizeau interferometers give spatial resolution comparable to a filled aperture but lower collecting area. Even with the small collecting area the high solar flux requires most of the energy to be reflected back to space. EASI will require closed loop control of the optics to compensate for spacecraft and instrument motions, thermal and structural transients and pointing jitter.The Solar Viewing Interferometry Prototype (SVIP) is a prototype ground instrument to study the needed wavefront control methods. SVIP consists of three 10 cm aperture telescopes, in a linear configuration, on a 1.2-meter boom that will estimate atmospheric abundances of O 2 , H 2 O, CO 2 , and CH 4 versus altitude and azimuth in the 1.25 -1.73 micron band. SVIP measures the Greenhouse Gas absorption while looking at the sun, and uses solar granulation to deduce piston, tip and tilt misalignments from atmospheric turbulence and the instrument structure. Tip/tilt sensors determine relative/absolute telescope pointing and operate from 0.43 -0.48 microns to maximize contrast. Two piston sensors, using a robust variation of dispersed fringes, determine piston shifts between the baselines and operate from 0.5 -0.73 microns. All sensors are sampled at 800 Hz and processed with a DSP computer and fed back at 200 Hz (3 dB) to the active optics. A 4 Hz error signal is also fed back to the tracking platform. Optical performance will be maintained to better than λ/8 rms in closed-loop.

Balloon exoplanet nulling interferometer (BENI)

“…This approach has the advantage that a balloon at 30 -37 km altitude is above most of the turbulent atmosphere thereby mitigating the very difficult adaptive optical (AO) control systems required by the ground based exoplanet imagers, and, can be performed for a fraction of the cost of the space flight mission. BENI would use an existing instrument, previously known as the Solar Viewing Interferometry Prototype (SVIP) (Lyon et al, 2004), retrofitted for a balloon mission with the addition of a nulling interferometer and payload fine pointing and tracking system. It would be capable of directly detecting the confirmed Jovian planet in Eri, directly imaging its dust disk and potentially looking for gaps that are indicative of terrestrial planets.…”