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New development approaches, including launch vehicles and advances in sensors, computing, and software, have lowered the cost of entry into space, and have enabled a revolution in low-cost, high-risk Small Satellite (SmallSat) missions. To bring about a similar transformation in larger space telescopes, it is necessary to reconsider the full paradigm of space observatories. Here we will review the history of space telescope development and cost drivers, and describe an example conceptual design for a low cost 6.5 m optical telescope to enable new science when operated in space at room temperature. It uses a monolithic primary mirror of borosilicate glass, drawing on lessons and tools from decades of experience with ground-based observatories and instruments, as well as flagship space missions. It takes advantage, as do large launch vehicles, of increased computing power and space-worthy commercial electronics in low-cost active predictive control systems to maintain stability. We will describe an approach that incorporates science and trade study results that address driving requirements such as integration and testing costs, reliability, spacecraft jitter, and wavefront stability in this new risk-tolerant "LargeSat" context., Comment: Presented at SPIE, Optics+Photonics 2023, Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems IV in San Diego, CA, USA. Minor typos corrected and DOI added 2023 Oct 19th

From 2018 to 2020, the Scientific Balloon Roadmap Program Analysis Group (Balloon Roadmap PAG) served as an community-based, interdisciplinary forum for soliciting and coordinating community analysis and input in support of the NASA Scientific Balloon Program. The Balloon Roadmap PAG was tasked with articulating and prioritizing the key science drivers and needed capabilities of the Balloon Program for the next decade. Additionally, the Balloon Roadmap PAG was asked to evaluate the potential for achieving science goals and maturing technologies of the Science Mission Directorate, evaluate the Balloon Program goals towards community outreach, and asses commercial balloon launch opportunities. The culmination of this work has been a written report submitted to the NASA Astrophysics Division Director., Comment: 95 pages, 69 figures, prepared by the NASA Balloon Program Analysis Group for the NASA Astrophysics Division Director and the 2020 Astrophysics Decadal Survey

The Coronagraphic Debris Exoplanet Exploring Payload (CDEEP) is a Small-Sat mission concept for high contrast imaging of circumstellar disks. CDEEP is designed to observe disks in scattered light at visible wavelengths at a raw contrast level of 10^-7 per resolution element (10^-8 with post processing). This exceptional sensitivity will allow the imaging of transport dominated debris disks, quantifying the albedo, composition, and morphology of these low-surface brightness disks. CDEEP combines an off-axis telescope, microelectromechanical systems (MEMS) deformable mirror, and a vector vortex coronagraph (VVC). This system will require rigorous testing and characterization in a space environment. We report on the CDEEP mission concept, and the status of the vacuum-compatible CDEEP prototype testbed currently under development at the University of Arizona, including design development and the results of simulations to estimate performance., Comment: 17 pages, 12 figures, Published in proceedings of SPIE Astronomical Telescopes + Instrumentation 2020

Project Blue is designed to deliver a small coronagraphic space telescope mission to low-Earth orbit capable of detecting an Earth-like planet in the habitable zones of the Sun-like stars Alpha Centauri A and B within the next 4 years within a Mission of Opportunity budget envelope. The concept heavily leverages emerging commercial capabilities -- including the telescope optics, spacecraft bus and launch vehicle -- and emphasizes a public-private partnership approach., Comment: 5 pages; White paper submitted to the Exoplanet Science Strategy study of the National Academies of Sciences, Engineering and Medicine

A NASA sounding rocket for high-contrast imaging with a visible nulling coronagraph, the PICTURE payload, has made two suborbital attempts to observe the warm dust disk inferred around Epsilon Eridani. The first flight in 2011 demonstrated a 5 milliarcsecond fine pointing system in space. The reduced flight data from the second launch, on 25 November 2015, presented herein, demonstrate active sensing of wavefront phase in space. Despite several anomalies in flight, post-facto reduction phase stepping interferometer data provides insight into the wavefront sensing precision and the system stability for a portion of the pupil. These measurements show the actuation of a 32$\times$32-actuator microelectromechanical system deformable mirror. The wavefront sensor reached a median precision of 1.4 nanometers per pixel, with 95% of samples between 0.8 and 12.0 nanometers per pixel. The median system stability, including telescope and coronagraph wavefront errors other than tip, tilt, and piston, was 3.6 nanometers per pixel, with 95% of samples between 1.2 and 23.7 nanometers per pixel., Comment: 23 pages, 8 figures, JATIS accepted

Emission profiles of the resonantly scattered OII~83.4~nm triplet can in principle be used to estimate \(\mathrm{O}^+\) density profiles in the F2 region of the ionosphere. Given the emission source profile, solution of this inverse problem is possible, but requires significant computation. The traditional Feautrier solution to the radiative transfer problem requires many iterations to converge, making it time-consuming to compute. A Markov chain approach to the problem produces similar results by directly constructing a matrix that maps the source emission rate to an effective emission rate which includes scattering to all orders. The Markov chain approach presented here yields faster results and therefore can be used to perform the \(\mathrm{O}^+\) density retrieval with higher resolution than would otherwise be possible.

We test the utility of the OII 83.4 nm emission feature as a measure of ionospheric parameters. Observed with the Remote Atmospheric and Ionospheric Detection System (RAIDS) Extreme Ultraviolet Spectrograph on the International Space Station (ISS), limb profiles of 83.4 nm emissions are compared to predicted dayglow emission profiles from a theoretical model incorporating ground-based electron density profiles measured by the Millstone Hill radar and parameterized by a best-fit Chapman-{\alpha} function. Observations and models are compared for periods of conjunction between Millstone Hill and the RAIDS fields-of-view. These RAIDS observations show distinct differences in topside morphology between two days, 15 January and 10 March 2010, closely matching the forward model morphology and demonstrating that 83.4 nm emission is sensitive to changes in the ionospheric density profile from the 340 km altitude of the ISS during solar minimum. We find no significant difference between 83.4 nm emission profiles modeled assuming a constant scale height Chapman-{\alpha} best-fit to the ISR measurements and those assuming varying scale height.

A NASA sounding rocket for high contrast imaging with a visible nulling coronagraph, the Planet Imaging Coronagraphic Technology Using a Reconfigurable Experimental Base (PICTURE-B) payload has made two suborbital attempts to observe the warm dust disk inferred around Epsilon Eridani. We present results from the November 2015 launch demonstrating active wavefront sensing in space with a piezoelectric mirror stage and a micromachine deformable mirror along with precision pointing and lightweight optics in space., Comment: Presented at SPIE Astronomical Telescopes + Instrumentation

Explorers have made breakthroughs in many fields of astrophysics. The science from both these missions contributed to three Nobel Prizes - Giacconi (2002), Mather, and Smoot (2006). Explorers have: marked the definitive beginning of precision cosmology, discovered that short gamma-ray bursts are caused by compact star mergers and have measured metalicity to redshifts z>6. NASA Explorers do cutting-edge science that cannot be done by facility-class instruments. The Explorer program provides a rapid response to changing science and technology, to enable cutting-edge science at moderate cost. Explorers also enable innovation, and engage & train scientists, managers and engineers, adding human capital to NASA and the nation. The astrophysics Explorer launch rate now being achieved is 1 per 3 years, and budget projections are in the $150M/year range for the next five years. A newly Vigorous Explorer Program should be created to: 1. Reach the long-stated goal of annual astrophysics launches; 2. Find additional launch options for Explorers and actively encourage cost savings in launchers and spacecraft, such as new commercial vehicles and innovative partnerships. 3. Mitigate risk via stronger technical development and sub-orbital programs, and through longer, more thorough, Phase A programs, potentially reducing the need for a 30% contingency; 4. Strive to protect the funding for missions that have reached Phase B, to prevent significant launch slips and cancellations, with a goal of 4 to 5 years from Phase B to launch; 5. Review the project management procedures and requirements to seek cost reductions, including the risk management strategy and the review and reporting process; 6. Review and possibly modify the cost caps for all Explorer classes to optimize scientific returns per dollar. [ABRIDGED], Comment: 18 pages, no figures. An Activities/Program White Paper submitted to the Astro2010 NAS/NRC Decadal Review of Astronomy and Astrophysics

Exo-C is NASAs first community study of a modest aperture space telescope designed for high contrast observations of exoplanetary systems. The mission will be capable of taking optical spectra of nearby exoplanets in reflected light, discovering previously undetected planets, and imaging structure in a large sample of circumstellar disks. It will obtain unique science results on planets down to super-Earth sizes and serve as a technology pathfinder toward an eventual flagship-class mission to find and characterize habitable Earth-like exoplanets. We present the mission/payload design and highlight steps to reduce mission cost/risk relative to previous mission concepts. Key elements are an unobscured telescope aperture, an internal coronagraph with deformable mirrors for precise wavefront control, and an orbit and observatory design chosen for high thermal stability. Exo-C has a similar telescope aperture, orbit, lifetime, and spacecraft bus requirements to the highly successful Kepler mission (which is our cost reference). The needed technology development is on-course for a possible mission start in 2017. This paper summarizes the study final report completed in January 2015. During 2015 NASA will make a decision on its potential development.