We present and compare experimental results in high contrast imaging representing the state of the art in coronagraph and starshade technology. These experiments have been undertaken with the goal of demonstrating the capability of detecting Earth-like planets around nearby Sun-like stars. The contrast of an Earth seen in reflected light around a Sun-like star would be about 1.2 × 10−10. Several of the current candidate technologies now yield raw contrasts of 1.0 × 10−9 or better, and so should enable the detection of Earths, assuming a gain in sensitivity in post-processing of a factor of 10. We present results of coronagraph and starshade experiments conducted at visible and infrared wavelengths. Cross-sections of dark fields are directly compared as a function of field angle and bandwidth. The strength and differences of the techniques are compared.
The Planetary Imaging Concept Testbed Using a Rocket Experiment (PICTURE 36.225 UG) was designed
to directly image the exozodiacal dust disk of ǫ Eridani (K2V, 3.22 pc) down to an inner radius of 1.5 AU.
PICTURE carried four key enabling technologies on board a NASA sounding rocket at 4:25 MDT on October
8th, 2011: a 0.5 m light-weight primary mirror (4.5 kg), a visible nulling coronagraph (VNC) (600-750 nm), a
32x32 element MEMS deformable mirror and a milliarcsecond-class fine pointing system.
Unfortunately, due to a telemetry failure, the PICTURE mission did not achieve scientific success. Nonetheless,
this flight validated the flight-worthiness of the lightweight primary and the VNC. The fine pointing system,
a key requirement for future planet-imaging missions, demonstrated 5.1 mas RMS in-flight pointing stability.
We describe the experiment, its subsystems and flight results. We outline the challenges we faced in developing
this complex payload and our technical approaches.
We report on progress at the Northrop Grumman Aerospace Systems (NGAS) starshade testbed. The starshade testbed is
a 42.8 meter vacuum chamber that replicates the Fresnel number of an equivalent full-scale starshade mission, namely
the flagship New Worlds Observer (NWO) configuration. This paper reports on recent upgrades to the testbed and
comparisons of previously published experimental results with computer simulations - which show encouraging
agreement to within a factor of 1.5. We also report on a new generation of sub-scale starshades that for the first time
allow us to exactly match the Fresnel number of a full-scale mission.
We present the results of the Astrophysics Strategic Mission Concept Study for the New Worlds Observer (NWO). We show that the
use of starshades is the most effective and affordable path to mapping and understanding our neighboring planetary systems, to opening
the search for life outside our solar system, while serving the needs of the greater astronomy community. A starshade-based mission
can be implemented immediately with a near term program of technology demonstration.
We report on progress at the Northrop Grumman Aerospace Systems (NGAS) starshade testbed. The starshade testbed
is a 42.8 m, vacuum chamber designed to replicate the Fresnel number of an equivalent full-scale starshade mission,
namely the flagship New Worlds Observer (NWO) configuration. Subscale starshades manufactured by the NGAS
foundry have shown 10-7 starlight suppression at an equivalent full-mission inner working angle of 85 milliarseconds. In
this paper, we present an overview of the experimental set up, scaling relationships to an equivalent full-scale mission,
and preliminary results from the testbed. We also discuss potential limitations of the current generation of starshades and
improvements for the future.
DAVINCI is a dilute aperture nulling coronagraph that has the potential of directly detecting an Earth in the habitable zone around ~100 nearby stars. The novel feature of this mission concept is to replace a filled aperture 5-6 meter telescope with 4 by 1.1 meter
telescopes in a phased array, dramatically reducing the cost by
potentially by a factor of 5-10.
We report progress on a nulling coronagraph intended for direct imaging of extrasolar planets. White light is suppressed
in an interferometer, and phase errors are measured by a second interferometer. A 1020-pixel MEMS deformable mirror
in the first interferometer adjusts the path length across the pupil. A feedback control system reduces deflections of the
deformable mirror to order of 1 nm rms.
Direct detection of exo-planets from the ground will become a reality with the advent of a new class of extreme-adaptive
optics instruments that will come on-line within the next few years. In particular, the Gemini Observatory will be
developing the Gemini Planet Imager (GPI) that will be used to make direct observations of young exo-planets. One
major technical challenge in reaching the requisite high contrast at small angles is the sensing and control of residual
wave front errors after the starlight suppression system. This paper will discuss the nature of this problem, and our
approach to the sensing and control task. We will describe a laboratory experiment whose purpose is to provide a means
of validating our sensing techniques and control algorithms. The experimental demonstration of sensing and control will
be described. Finally, we will comment on the applicability of this technique to other similar high-contrast instruments.
We describe the advantages of a nulling coronagraph instrument behind a single aperture space telescope for detection and spectroscopy of Earth-like extrasolar planets in visible light. Our concept synthesizes a nulling interferometer by shearing the telescope pupil into multiple beams. They are recombined with a pseudo-achromatic pi-phase shift in one arm to produce a deep null on-axis, attenuating the starlight, while simultaneously transmitting the off-axis planet light. Our nulling configuration includes methods to mitigate stellar leakage, such as spatial filtering by a coherent array of single mode fibers, balancing amplitude and phase with a segmented deformable mirror, and post-starlight suppression wavefront sensing and control. With diffraction limited telescope optics and similar quality components in the optical train (λ/20), suppression of the starlight to 10-10 is readily achievable. We describe key features of the architecture and analysis, present the status of key experiments to demonstrate wide bandwidth null depth, and present the status of component technology development.
The nulling coronagraph is one of 5 instrument concepts selected by NASA for study for potential use in the TPF-C
mission. This concept for extreme starlight suppression has two major components, a nulling interferometer to suppress
the starlight to ~10-10 per airy spot within 2 λ/D of the star, and a calibration interferometer to measure the residual
scattered starlight. The ability to work at 2 λ/D dramatically improves the science throughput of a space based
coronagraph like TPF-C. The calibration interferometer is an equally important part of the starlight suppression system.
It measures the measures the wavefront of the scattered starlight with very high SNR, to 0.05nm in less than 5 minutes
on a 5mag star. In addition, the post coronagraph wavefront sensor will be used to measure the residual scattered light
after the coronagraph and subtract it in post processing to 1~2x10-11 to enable detection of an Earthlike planet with a
SNR of 5~10.
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