We present the optical requirement-driven observational constraints of the Remote Occulter, an orbiting starshade designed to work with ground-based telescopes to produce visible-band images and spectra of temperate planets around Sun-like stars. We then utilize these constraints to develop and present numerical simulations of time-dependent observable sky regions along with each region’s nightly available exposure duration and show that nearly the entire sky could be observed for up to 8 h a night. We further examine how changes introduced to our established constraints will impact such observational windows and discuss their implications, setting the ground for upcoming studies aiming to further investigate the Remote Occulter mission capabilities and architecture.
Launching a starshade to rendezvous with the Nancy Grace Roman Space Telescope (Roman) would provide the first opportunity to directly image the habitable zones (HZs) of nearby sunlike stars in the coming decade. A report on the science and feasibility of such a mission was recently submitted to NASA as a probe study concept. The driving objective of the concept is to determine whether Earth-like exoplanets exist in the HZs of the nearest sunlike stars and have biosignature gases in their atmospheres. With the sensitivity provided by this telescope, it is possible to measure the brightness of zodiacal dust disks around the nearest sunlike stars and establish how their population compares with our own. In addition, known gas-giant exoplanets can be targeted to measure their atmospheric metallicity and thereby determine if the correlation with planet mass follows the trend observed in the Solar System and hinted at by exoplanet transit spectroscopy data. We provide the details of the calculations used to estimate the sensitivity of Roman with a starshade and describe the publicly available Python-based source code used to make these calculations. Given the fixed capability of Roman and the constrained observing windows inherent for the starshade, we calculate the sensitivity of the combined observatory to detect these three types of targets, and we present an overall observing strategy that enables us to achieve these objectives.
NASA is developing starshade technology to Technology Readiness Level 5 within a directed activity called S5. The objective of S5 is to mature starshade technology to the level that exoplanet imaging missions, such as Starshade Rendezvous and HabEx, can begin the formulation phase. This paper outlines the S5 activity as a whole, to show how it closes all starshade technology gaps in a mutually consistent way. It serves as a companion paper to several other papers in this special section that report progress in specific starshade technologies.
Starshades are a leading technology to enable the detection and spectroscopic characterization of Earth-like exoplanets. We report on optical experiments of sub-scale starshades that advance critical starlight suppression technologies in preparation for the next generation of space telescopes. These experiments were conducted at the Princeton starshade testbed, an 80-m long enclosure testing 1/1000’th scale starshades at a flight-like Fresnel number. We demonstrate 10 − 10 contrast at the starshade’s geometric inner working angle (IWA) across 10% of the visible spectrum, with an average contrast at the IWA of 2 × 10 − 10 and contrast floor of 2 × 10 − 11. In addition to these high-contrast demonstrations, we validate diffraction models to better than 35% accuracy through tests of intentionally flawed starshades. Overall, this suite of experiments reveals a deviation from scalar diffraction theory due to light propagating through narrow gaps between the starshade petals. We provide a model that accurately captures this effect at contrast levels below 10 − 10. The results of these experiments demonstrate that there are no optical impediments to building a starshade that provides sufficient contrast to detect Earth-like exoplanets. This work also sets an upper limit on the effect of unknowns in the diffraction model used to predict starshade performance and set tolerances on the starshade manufacture.
High-contrast imaging enabled by a starshade in formation flight with a space telescope can provide a near-term pathway to search for and characterize temperate and small planets of nearby stars. NASA’s Starshade Technology Development Activity to TRL5 (S5) is rapidly maturing the required technologies to the point at which starshades could be integrated into potential future missions. We reappraise the noise budget of starshade-enabled exoplanet imaging to incorporate the experimentally demonstrated optical performance of the starshade and its optical edge. Our analyses of stray light sources—including the leakage through micrometeoroid damage and the reflection of bright celestial bodies—indicate that sunlight scattered by the optical edge (i.e., the solar glint) is by far the dominant stray light. With telescope and observation parameters that approximately correspond to Starshade Rendezvous with Roman and Habitable Exoplanet Observatory (HabEx), we find that the dominating noise source is exozodiacal light for characterizing a temperate and Earth-sized planet around Sun-like and earlier stars and the solar glint for later-type stars. Further, reducing the brightness of solar glint by a factor of 10 with a coating would prevent it from becoming the dominant noise for both Roman and HabEx. With an instrument contrast of 10 − 10, the residual starlight is not a dominant noise, and increasing the contrast level by a factor 10 does not lead to any appreciable change in the expected science performance. If unbiased calibration of the background to the photon-noise limit can be achieved, Starshade Rendezvous with Roman could provide nearly photon-limited spectroscopy of temperate and Earth-sized planets of F, G, and K stars <4 parsecs away, and HabEx could extend this capability to many more stars <8 parsecs. Larger rocky planets around stars <8 parsecs would be within the reach of Roman. To achieve these capabilities, the exozodiacal light may need to be calibrated to a precision better than 2% and the solar glint to better than 5%. Our analysis shows that the expected temporal variability of the solar glint is unlikely to hinder the calibration, and the main challenge for background calibration likely comes from the unsmooth spatial distribution of exozodiacal dust in some stars. Taken together, these results validate the optical noise budget and technology milestones adopted by S5 against key science objectives and inform the priorities of future technology developments and science and industry community partnerships.
Starshades are a leading technology to detect and characterize Earth-like exoplanets. In this paper we report on optical experiments of sub-scale starshades that advance critical starlight suppression technologies in preparation for the next generation of space telescopes. These experiments were conducted at the Princeton starshade testbed, an 80 m long enclosure testing 1/1000th scale starshades at a flight-like Fresnel number. In this paper we summarize recent updates made to the starshade testbed and optical model. We present results from recent experiments testing two starshade masks with intentional perturbations built into their shape. One of the perturbed masks has three petals that are shifted radially outward by 7-11 microns and the other mask has two petals shifted radially outward plus two petal edge segments displaced from their nominal position. We show the model agrees with experiment to better than 25% accuracy. These results are placed into context with previous experiments on perturbed shapes and progress made towards satisfying a critical milestone in advancing starshade technology to TRL 5.
The Remote Occulter (Orbiting Starshade) is a proposed 100-meter class starshade working with a ground-based telescope, designed for visible-band imaging and spectroscopy of temperate planets around sun-like stars. With advanced adaptive optics and the largest telescopes like the 39 m ELT, it would enable the study of planetary systems and a wide variety of exoplanets. In this paper, we describe the geometrical constraints and establish which parts of the sky are observable.
We present an analysis of the Rayleigh scattering in the Princeton starshade testbed and show that it explains several notable features in the contrast images. The scattering is consistent with that expected due to air molecules and does not require airborne dust to explain. Rayleigh scattering limits the observable contrast at the ~ 1 × 10-11 level at the inner working angle in the contrast images, but it limits the observable suppression at ~ 10-9 level. We present a crude estimate of the level of scattering of starlight to be expected in a flight starshade due to zodiacal dust in the solar system and conclude that it is unlikely to be observable. We comment on whether Rayleigh scattering drives longer starshade testbeds to operate in vacuum.
Starshades are a leading technology to enable the direct detection and spectroscopic characterization of Earth-like exoplanets. Starshade starlight suppression technology is being advanced through sub-scale starshade demonstrations at the Princeton Starshade Testbed and we present here the successful completion of a technology milestone focused on the demonstration of high contrast at flight-required levels. We demonstrate 10-10 contrast at the inner working angle of a starshade with a flight-like Fresnel number at multiple wavelengths spanning a 10% bandpass. We show that while contrast at the inner working angle is limited by the presence of non-scalar diffraction as light propagates through narrow slits between the starshade petals, high contrast is still achieved over most of the image. Successful completion of this milestone verifies we can design a starshade capable of producing scientifically useful contrast levels.
The NEID spectrometer is an optical (380-930 nm), fiber-fed, precision Doppler spectrometer currently in de- velopment for the WIYN 3.5 m telescope at Kitt Peak National Observatory as part of the NN-EXPLORE partnership. Designed to achieve a radial velocity precision of < 30 cm/s, NEID will be sensitive enough to detect terrestrial-mass exoplanets around low-mass stars. Light from the target stars is focused by the telescope to a bent Cassegrain port at the edge of the primary mirror mechanical support. The specialized NEID “Port Adapter” system is mounted at this bent Cassegrain port and is responsible for delivering the incident light from the telescope to the NEID fibers. In order to provide stable, high-quality images to the science instrument, the Port Adapter houses several sub-components designed to acquire the target stars, correct for atmospheric dis- persion, stabilize the light onto the science fibers, and calibrate the spectrometer by injecting known wavelength sources such as a laser frequency comb. Here we provide an overview of the overall opto-mechanical design and system requirements of the Port Adapter. We also describe the development of system error budgets and test plans to meet those requirements.
The presence of large amounts of dust in the habitable zones of nearby stars is a significant obstacle for future exo-Earth imaging missions. We executed the HOSTS (Hunt for Observable Signatures of Terrestrial Systems) survey to determine the typical amount of such exozodiacal dust around a sample of nearby main sequence stars. The majority of the data have been analyzed and we present here an update of our ongoing work. Nulling interferometry in N band was used to suppress the bright stellar light and to detect faint, extended circumstellar dust emission. We present an overview of the latest results from our ongoing work. We find seven new N band excesses in addition to the high confidence confirmation of three that were previously known. We find the first detections around Sun-like stars and around stars without previously known circumstellar dust. Our overall detection rate is 23%. The inferred occurrence rate is comparable for early type and Sun-like stars, but decreases from 71+11 -20% for stars with previously detected mid- to far-infrared excess to 11+9 -4% for stars without such excess, confirming earlier results at high confidence. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal luminosity function of the dust, we find upper limits on the median dust level around all stars without previously known mid to far infrared excess of 11.5 zodis at 95% confidence level. The corresponding upper limit for Sun-like stars is 16 zodis. An LBTI vetted target list of Sun-like stars for exo-Earth imaging would have a corresponding limit of 7.5 zodis. We provide important new insights into the occurrence rate and typical levels of habitable zone dust around main sequence stars. Exploiting the full range of capabilities of the LBTI provides a critical opportunity for the detailed characterization of a sample of exozodiacal dust disks to understand the origin, distribution, and properties of the dust.
NEID is a new extreme precision Doppler spectrometer for the WIYN telescope. It is fiber fed and employs a classical white pupil Echelle configuration. NEID has a fiber aperture of only 0.92” on sky in high-resolution mode, and its tight radial velocity error budget resulted in very stringent stability requirements for the input illumination of the spectrograph optics. Consequently, the demands on the fiber injection are challenging. In this paper, we describe the layout and optical design of the injection module, including a broadband, high image quality relay and a high-performance atmospheric dispersion corrector (ADC) across the bandwidth of 380 – 930 nm.
LIGO (Laser Interferometer Gravitational-wave Observatory) is a trio of sensitive Michelson interferometers designed to detect extremely relativistic astrophysical processes by the ripples they produce in spacetime. For best sensitivity, these interferometers are kilometers long, contain nearly unstable cavities, and operate at high optical power, making them uniquely susceptible to thermal aberrations and radiation-pressure-derived instabilities. We describe the LIGO
interferometers, and their high power lasers and input optics, and described how thermal aberrations have been successfully controlled using adaptive corrective heating. The Advanced LIGO detectors, an upgrade to LIGO planned for installation in the year 2010, will operate with even higher optical power. We detail the additional challenges in construction and thermal compensation for Advanced LIGO, and detail how radiation-pressure derived instabilities influence the design, operation, and sensitivity ofAdvanced LIGO.