Richard Lyon/NASA Goddard Space Flight Center
The direct detection and spectroscopic characterization of exoplanets in our local neighborhood requires starlight to be suppressed relative to the planet at small angular separations. The only known internal coronagraph capable of achieving high contrast imaging with either filled, segmented and sparse/dilute aperture telescopes systems is a visible nulling coronagraph (VNC). Herein we propose to leverage our past and ongoing work, coupled with the lessons learned on the Vacuum Nuller Testbed (VNT), to complete the development of a compact achromatic visible nulling coronagraph engineering test unit (ETU) and utilize this ETU to advance the VNC technology from its current NASA technology readiness level (TRL) of 4 to TRL-5. The VNT currently achieves a contrast of > 108 at an inner working angle of 2 λ/D through the use of a hex-packed MEMS based DM and adaptive wavefront and amplitude control using both interferometer outputs. The VNC approach has a net advantage in terms of wavefront and amplitude control in that for a given target star the control bandwidth is independent of the state of the errors of the telescope plus instrument. This is due to the VNC being an interferometer, but such that the sum of the interferometric output photon counts is constant for a given source, and the outputs have a coherent amplitude and wavefront relationship between them which allows for robust yet simple sensing and control at high bandwidth (15 Hz or higher). This has the net effect of relaxing the stability tolerances on the optical telescope to manageable levels as compared to approaches with increasingly longer integrations that levy excessive stability requirements on the large optical telescope element (OTE).
We propose to complete the development of an engineering test unit known as compact achromatic visible nulling coronagraph and to environmentally test this unit to achieve a NASA technology readiness level of 5.
Strategic Astrophysics Technology