Qian Gong

Conceptual design of the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) for the Subaru telescope

Recent developments in high-contrast imaging techniques now make possible both imaging and spectroscopy of planets around nearby stars. We present the conceptual design of the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS), a lenslet-based, cryogenic integral field spectrograph (IFS) for imaging exo-planets on the Subaru telescope. The IFS will provide spectral information for 140x140 spatial elements over a 1.75 arcsecs x 1.75 arcsecs field of view (FOV). CHARIS will operate in the near infrared (λ = 0.9-2.5μm) and provide a spectral resolution of R = 14, 33, and 65 in three separate observing modes. Taking advantage of the adaptive optics systems and advanced coronagraphs (AO188 and SCExAO) on the Subaru telescope, CHARIS will provide sufficient contrast to obtain spectra of young self-luminous Jupiter-mass exoplanets. CHARIS is in the early design phases and is projected to have first light by the end of 2015. We report here on the current conceptual design of CHARIS and the design challenges.

Technology development towards WFIRST-AFTA coronagraph

NASA’s WFIRST-AFTA mission concept includes the first high-contrast stellar coronagraph in space. This coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. In this paper we present the plan for maturing coronagraph technology to TRL5 in 2014-2016, and the results achieved in the first 6 months of the technology development work. The specific areas that are discussed include coronagraph testbed demonstrations in static and simulated dynamic environment, design and fabrication of occulting masks and apodizers used for starlight suppression, low-order wavefront sensing and control subsystem, deformable mirrors, ultra-low-noise spectrograph detector, and data post-processing.

ATLAST-9.2m: a large-aperture deployable space telescope

We present results of a study of a deployable version of the Advanced Technology Large-Aperture Space Telescope (ATLAST), designed to operate in a Sun-Earth L2 orbit. The primary mirror of the segmented 9.2-meter aperture has 36 hexagonal 1.315 m (flat-to-flat) glass mirrors. The architecture and folding of the telescope is similar to JWST, allowing it to fit into the 6.5 m fairing of a modest upgrade to the Delta-IV Heavy version of the Evolved Expendable Launch Vehicle (EELV). We discuss the overall observatory design, optical design, instruments, stray light, wavefront sensing and control, pointing and thermal control, and in-space servicing options.

Manufacturing and Integration Status of the JWST OSIM Optical Simulator

OSIM is a full field, cryogenic, optical simulator of the James Webb Space Telescope (JWST) Optical Telescope Element (OTE). It provides simulated point source/star images for optical performance testing of the JWST Integrated Science Instrument Module (ISIM). OSIM is currently being assembled at the Goddard Space Flight Center (GSFC). In this paper, we describe the capabilities, design, manufacturing and integration status, and uses of the OSIM during the optical test program of ISIM and the Science Instruments. Where applicable, the ISIM tests are also described.

Optical Design of WFIRST-AFTA Wide-Field Instrument

The WFIRST-AFTA Wide-Field Infrared Survey Telescope TMA optical design provides 0.28-sq°FOV Wide Field Channel at 0.11” pixel scale, operating at wavelengths between 0.76-2.0μm, including a spectrograph mode (1.35-1.95μm.) An Integral Field Channel provides a discrete 3”x3.15” field at 0.15” sampling.

The Large UV/Optical/Infrared Surveyor (LUVOIR): Decadal Mission Concept Design Update

In preparation for the 2020 Astrophysics Decadal Survey, NASA has commissioned the study of four large mission concepts, including the Large Ultraviolet / Optical / Infrared (LUVOIR) Surveyor. The LUVOIR Science and Technology Definition Team (STDT) has identified a broad range of science objectives including the direct imaging and spectral characterization of habitable exoplanets around sun-like stars, the study of galaxy formation and evolution, the epoch of reionization, star and planet formation, and the remote sensing of Solar System bodies. NASA’s Goddard Space Flight Center (GSFC) is providing the design and engineering support to develop executable and feasible mission concepts that are capable of the identified science objectives. We present an update on the first of two architectures being studied: a 15- meter-diameter segmented-aperture telescope with a suite of serviceable instruments operating over a range of wavelengths between 100 nm to 2.5 μm. Four instruments are being developed for this architecture: an optical / near-infrared coronagraph capable of 10-10 contrast at inner working angles as small as 2 λ/D; the LUVOIR UV Multi-object Spectrograph (LUMOS), which will provide low- and medium-resolution UV (100 – 400 nm) multi-object imaging spectroscopy in addition to far-UV imaging; the High Definition Imager (HDI), a high-resolution wide-field-of-view NUV-Optical-IR imager; and a UV spectro-polarimeter being contributed by Centre National d’Etudes Spatiales (CNES). A fifth instrument, a multi-resolution optical-NIR spectrograph, is planned as part of a second architecture to be studied in late 2017.

A comprehensive radial velocity error budget for next generation Doppler spectrometers

We describe a detailed radial velocity error budget for the NASA-NSF Extreme Precision Doppler Spectrometer instrument concept NEID (NN-explore Exoplanet Investigations with Doppler spectroscopy). Such an instrument performance budget is a necessity for both identifying the variety of noise sources currently limiting Doppler measurements, and estimating the achievable performance of next generation exoplanet hunting Doppler spectrometers. For these instruments, no single source of instrumental error is expected to set the overall measurement floor. Rather, the overall instrumental measurement precision is set by the contribution of many individual error sources. We use a combination of numerical simulations, educated estimates based on published materials, extrapolations of physical models, results from laboratory measurements of spectroscopic subsystems, and informed upper limits for a variety of error sources to identify likely sources of systematic error and construct our global instrument performance error budget. While natively focused on the performance of the NEID instrument, this modular performance budget is immediately adaptable to a number of current and future instruments. Such an approach is an important step in charting a path towards improving Doppler measurement precisions to the levels necessary for discovering Earth-like planets.

PISCES: an integral field spectrograph to advance high contrast imaging technologies

We present a novel optical integral field spectrograph (IFS) called the Prototype Imaging Spectrograph for Coronagraphic Exoplanet Studies (PISCES), which will be a facility class instrument within the NASA Exoplanet Exploration Programs High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory. Integral field spectroscopy is ideal for imaging faint exoplanets: it enables spectral characterization of exoplanet atmospheres and can improve contrast by providing chromatic measurements of the target stars point-spread function (PSF). PISCES at the HCIT will be the first IFS to demonstrate imaging spectroscopy in the 10-9 contrast regime required for characterizing exoplanets imaged in scattered light. It is directly relevant as a prototype for IFS science instruments that could fly with the AFTA Coronagraph, the Exoplanet Probe missions currently under study, and/or the ATLAST mission concept. We present the instrument requirements, a baseline design for PISCES, a simulation of its performance, a solution to mitigate spectral crosstalk, experimental verification of our simulator, and the final vacuum compatible opto-mechanical design. PISCES will be assembled and tested at the Goddard Space Flight Center (GSFC), and subsequently delivered and integrated into the HCIT facility. Testing at HCIT will verify the performance of PISCES and its ability to meet the requirements of a space mission, will enable investigations into broadband wavefront control using the IFS as an image plane sensor, and will allow tests of contrast enhancement via multiwavelength differential imaging post-processing. Together with wavefront control and starlight suppression, PISCES is thus a key element for maturing the overall integrated system for a future coronagraphic space mission. PISCES is scheduled to receive first light in the HCIT in 2015.

Comparative Concepts for ATLAST Optical Designs

The ATALST (Advanced Technology for Large Aperture Space Telescopes) effort has presented several design incarnations. Here we will compare the design and performance of the 9.2m segmented, the 8m monolithic on-axis and 8m x 6m off-axis concepts.

The Optical Telescope Element Simulator for the James Webb Space Telescope

The James Webb Space Telescope Observatory will consist of three flight elements: (1) the Optical Telescope Element (OTE), (2) the Integrated Science Instrument Module Element (ISIM), and (3) the Spacecraft Element. The ISIM element consists of a composite bench structure that uses kinematic mounts to interface to each of the optical benches of the three science instruments and the guider. The ISIM is also kinematically mounted to the telescope primary mirror structure. An enclosure surrounds the ISIM structure, isolates the ISIM region thermally from the other thermal regions of the Observatory, and serves as a radiator for the science instruments and guider. Cryogenic optical testing of the ISIM Structure and the Science Instruments will be conducted at Goddard Space Flight Center using an optical telescope simulator that is being developed by a team from Ball Aerospace and Goddard Space Flight Center, and other local contractors. This simulator will be used to verify the performance of the ISIM element before delivery to the Northup Grumman team for integration with the OTE. In this paper, we describe the O OTE Sim TE Simulator (OSIM) and provide a brief overview of the optical test program. ulator