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Future direct imaging missions such as HabEx and LUVOIR aim to catalog and characterize Earth-mass analogs around nearby stars. The exoplanet yield of these missions will be dependent on the frequency of Earth-like planets, and potentially the a priori knowledge of which stars specifically host suitable planetary systems. Ground or space based radial velocity surveys can potentially perform the pre-selection of targets and assist in the optimization of observation times, as opposed to an uninformed direct imaging survey. In this paper, we present our framework for simulating future radial velocity surveys of nearby stars in support of direct imaging missions. We generate lists of exposure times, observation time-series, and radial velocity time-series given a direct imaging target list. We generate simulated surveys for a proposed set of telescopes and precise radial velocity spectrographs spanning a set of plausible global-network architectures that may be considered for next generation extremely precise radial velocity surveys. We also develop figures of merit for observation frequency and planet detection sensitivity, and compare these across architectures. From these, we draw conclusions, given our stated assumptions and caveats, to optimize the yield of future radial velocity surveys in support of direct imaging missions. We find that all of our considered surveys obtain sufficient numbers of precise observations to meet the minimum theoretical white noise detection sensitivity for Earth-mass habitable zone planets, with margin to explore systematic effects due to stellar activity and correlated noise., Comment: Submitted to AAS Journals; under revision

Spectral shaping is critical to many fields of science. In astronomy for example, the detection of exoplanets via the Doppler effect hinges on the ability to calibrate a high resolution spectrograph. Laser frequency combs can be used for this, but the wildly varying intensity across the spectrum can make it impossible to optimally utilize the entire comb, leading to a reduced overall precision of calibration. To circumvent this, astronomical applications of laser frequency combs rely on a bulk optic setup which can flatten the output spectrum before sending it to the spectrograph. Such flatteners require complex and expensive optical elements like spatial light modulators and have non-negligible bench top footprints. Here we present an alternative in the form of an all-photonic spectral shaper that can be used to flatten the spectrum of a laser frequency comb. The device consists of a circuit etched into a silicon nitride wafer that supports an arrayed-waveguide grating to disperse the light over hundreds of nanometers in wavelength, followed by Mach-Zehnder interferometers to control the amplitude of each channel, thermo-optic phase modulators to phase the channels and a second arrayed-waveguide grating to recombine the spectrum. The demonstrator device operates from 1400 to 1800 nm (covering the astronomical H band), with twenty 20 nm wide channels. The device allows for nearly 40 dBs of dynamic modulation of the spectrum via the Mach-Zehnders , which is greater than that offered by most spatial light modulators. With a superluminescent diode, we reduced the static spectral variation to ~3 dB, limited by the properties of the components used in the circuit and on a laser frequency comb we managed to reduce the modulation to 5 dBs, sufficient for astronomical applications., Comment: 15 pages, 10 figures. arXiv admin note: substantial text overlap with arXiv:2209.09455

Pulsed pumping of a silica microcavity is used to generate single-soliton microcombs with conversion efficiency of 54%. Analytical expressions are developed by the Lagrangian approach and applied to model the results.

Generation of mid-infrared combs (3.3 micron band) with GigaHertz line spacing is demonstrated by interleaved difference-frequency-generation. The method, applied to a 22 GHz repetition-rate microcomb, is useful for spectral densification of sparse microcomb spectra.

With their compact size and semiconductor-chip-based operation, frequency microcombs can be an invaluable light source for gas spectrcoscopy. However, the generation of mid-infrared (mid-IR) frequency combs with gigahertz line spacing as required to resolve many gas spectra represents a significant challenge for these devices. Here, a technique referred to as interleaved difference-frequency generation (iDFG) is introduced that densifies the spectral line spacing upon conversion of near-IR comb light into the mid-IR light. A soliton microcomb is used as both a comb light source and microwave oscillator in a demonstration, and the spectrum of methane is measured to illustrate how the resulting mid-IR comb avoids spectral undersampling. Beyond demonstration of the iDFG technique, this work represents an important feasibility step towards more compact and potentially chip-based mid-IR gas spectroscopy modules.

Orbiting planets induce a weak radial velocity (RV) shift in the host star that provides a powerful method of planet detection. Importantly, the RV technique provides information about the exoplanet mass, which is unavailable with the complementary technique of transit photometry. However, RV detection of an Earth-like planet in the ‘habitable zone’1 requires extreme spectroscopic precision that is only possible using a laser frequency comb (LFC)2. Conventional LFCs require complex filtering steps to be compatible with astronomical spectrographs, but a new chip-based microresonator device, the Kerr soliton microcomb3–8, is an ideal match for astronomical spectrograph resolution and can eliminate these filtering steps. Here, we demonstrate an atomic/molecular line-referenced soliton microcomb as a first in-the-field demonstration of microcombs for calibration of astronomical spectrographs. These devices can ultimately provide LFC systems that would occupy only a few cubic centimetres9,10, thereby greatly expanding implementation of these technologies into remote and mobile environments beyond the research lab.

We present the results of two 2.3 micron near-infrared radial velocity surveys to detect exoplanets around 36 nearby and young M dwarfs. We use the CSHELL spectrograph (R ~46,000) at the NASA InfraRed Telescope Facility, combined with an isotopic methane absorption gas cell for common optical path relative wavelength calibration. We have developed a sophisticated RV forward modeling code that accounts for fringing and other instrumental artifacts present in the spectra. With a spectral grasp of only 5 nm, we are able to reach long-term radial velocity dispersions of ~20-30 m/s on our survey targets., To appear in "Young Stars and Planets Near the Sun", Proceedings of IAU Symposium No. 314 (Cambridge University Press), J.H. Kastner, B. Stelzer, S.A. Metchev, eds

An important technique for discovering and characterizing planets beyond our solar system relies upon measurement of weak Doppler shifts in the spectra of host stars induced by the influence of orbiting planets. A recent advance has been the introduction of optical frequency combs as frequency references. Frequency combs produce a series of equally spaced reference frequencies and they offer extreme accuracy and spectral grasp that can potentially revolutionize exoplanet detection. Here we demonstrate a laser frequency comb using an alternate comb generation method based on electro-optical modulation, with the comb centre wavelength stabilized to a molecular or atomic reference. In contrast to mode-locked combs, the line spacing is readily resolvable using typical astronomical grating spectrographs. Built using commercial off-the-shelf components, the instrument is relatively simple and reliable. Proof of concept experiments operated at near-infrared wavelengths were carried out at the NASA Infrared Telescope Facility and the Keck-II telescope., Laser frequency combs emit a spectrum of equally spaced peaks that can provide precise frequency references useful for astronomy. Here, the authors demonstrate a frequency comb using electro-optical modulation, which has a line spacing that is resolvable using grating spectrographs unlike the mode-locking approach.

Experiments to characterize fullerene decomposition at temperatures above 973 K were conducted by spectroscopic analysis of samples heated in vacuo. The thermal decomposition can be described by first-order kinetics with an activation energy of 266±9 kJ/mol and a preexponential factor of 1.24×10^(9) s^-1. Though scanning electron micrographs display structures with a distinctly faceted appearance, x-ray diffraction, Raman spectroscopy, and transmission-electron microscopy all show that the material is composed of amorphous carbon and graphite, indicating that pyrolysis of the fullerite occurs without destroying crystal facets.

An evaluation is made of the potential benefits of C60 molecules as a basis for ion propulsion. Because C60 is storable, its use may result in a larger usable propellant fraction than previous methods of cluster ion propulsion. C60 may also relax such engineering constraints as grid spacing, which restrict the performance of noble gas ion propulsion. The behavior of C60 in a plasma discharge environment, as well as various electron impact cross sections of the molecule, will greatly afftect the feasibility of the concept.

This paper presents the findings from a study to evaluate the feasibility of a radioisotope power system (RPS) combined with active cooling to enable a long-duration Venus surface mission. On-board power with active cooling technology featured prominently in both the National Research Council's Decadal Survey and in the 2006 NASA Solar System Exploration Roadmap as mission enabling for the exploration of Venus. Power and cooling system options were reviewed and the most promising concepts were modeled to develop an assessment tool for Venus mission planners considering a variety of future potential missions to Venus, including a Venus Mobile Explorer (either a balloon or rover concept), a long-lived Venus static lander, or a Venus Geophysical Network. The concepts modeled were based on the integration of General Purpose Heat Source (GPHS) modules with different types of Stirling cycle heat engines for power conversion and cooling. Unlike prior investigations which reported on single point design concepts, this assessment tool allows the user to generate either a point design or parametric curves of approximate power and cooling system mass, power level, and number of GPHS modules needed for a “black box” payload housed in a spherical pressure vessel. Input variables include altitude, pressure vessel diameter, payload temperature, and payload power on Venus. Users may also specify the number and type of pressure vessel windows, use of phase-change material for additional (time-dependent) payload cooling, and amount of (rechargeable) battery power for peak power demand operations. Parameter sets that would enable a Venus surface mission with fewer than 16 GPHS modules were identified. Thus, the study provides guidance for design practices that might enable a long-duration Venus surface mission with an attainable quantity of 238Pu, and with achievable operating parameters.

NASA is considering missions to explore near-interstellar space (40 - 250 Astronomical Units) early in the next decade as the first step toward a vigorous interstellar exploration program. A key enabling technology for such an ambitious science and exploration effort is a propulsion system capable of providing fast trip times, yet which has low enough mass to allow for the use of inexpensive launch vehicles. Advanced propulsion technologies that might support the First interstellar precursor mission by the end of the first decade of the new millennium include solar sails and nuclear electric propulsion. Solar sails and electric propulsion are two technology areas that may hold promise for the next generation of interstellar precursor missions as well - perhaps a thousand astronomical units traveled in a professional lifetime. Future missions to far beyond the Heliosphere will require the development of propulsion technologies that are only at the conceptual stage today. For years, the scientific community has been interested in solar sail and electric propulsion technologies to support robotic exploration of the solar system. Progress in thin-film materials fabrication and handling, and advancement in technologies that may enable the deployment of large sails in space are only now maturing to the point where ambitious interstellar precursor missions using sails can be considered. Xenon ion propulsion is now being demonstrated for planetary exploration by the Deep Space 1 mission. The primary issues for the adaptation of electric propulsion to interstellar precursor applications include the development of low specific mass nuclear power systems, engine lifetime, and high power operation. Recent studies of interstellar precursor mission scenarios that use these propulsion systems will be described, and the range of application of each technology will be explored.

This paper describes an evaluation of various propulsion options for robotic interstellar rendezvous missions to stars ranging from 4.5 Light Years (L.Y.) with a 10-year trip time, to 40 L.Y. with a 100-year trip time. Concepts considered included advanced electric propulsion, nuclear (fission, fusion, antimatter) propulsion, beamed energy (e.g., light sails, MagSails) propulsion, electromagnetic catapults, in-situ propellant production concepts (e.g., the interstellar ramjet), and hybrid systems (e.g., antimatter-catalyzed fission/ fusion). The various candidate propulsion options were evaluated using three screening criteria. First, is it possible for the candidate system to achieve the required AV, which can be as much as 0.6 c for a fast, 4.5-L.Y. mission. Second, does the propulsion systems require an extensive, mission-unique supporting infrastructure. Finally, the technology readiness levels of the various subsystem technologies of the propulsion concept are reviewed. This screening process resulted in the selection of beamed energy sail, matter-antimatter, and fusion ramjet concepts as the most promising candidates. Potential mission performance and near-term technology goals of these concepts were then evaluated.

Research activities in advanced propulsion concepts at the Jet Propulsion Laboratory are reviewed. The concepts, which include high power plasma thrusters such as lithium-fueled Lorentz-Force-Accelerators, MEMS-scale propulsion systems, in-situ propellant utilization techniques, fusion propulsion systems and methods of using antimatter, were selected for study because each offers the potential for either significantly enhancing space transportation capability or enabling bold, ambitious new missions. This has been shown through systems and missions evaluations - the essential tools for determining the benefits and performance drivers of an advanced concept Potential performance of a new concept traditionally has been compared with that of chemical propulsion. However, because of the growing acceptance of electric propulsion in both government and commercial sectors, concepts must now show a significant benefit relative to this technology as well. There is a range of maturity levels represented by the advanced concepts studied under this program, yet each concept faces feasibility issues. Our research is focused on addressing, one-by-one, the key feasibility issues of each concept. In addition to potentially addressing the propulsion needs of missions like those of the Human Exploration and Development of Space (HEDS) initiative, outer planet sample returns and orbiters, or other ambitious deep space endeavors, this research is aiding in fundamental scientific discoveries and developments in other technologies.

Consideration is given to one aspect of space nuclear power safety, namely, the radiation dose rate risk due to a reentered reactor. It is found that for nuclear-thermal propulsion NERVA vehicles, the minimum required altitude for initial basing and earth escape is 500 to 600 km; for final end-of-life storage, the required altitude is about 1000 km. For a 10-MWe nuclear-electric propulsion vehicle, the basing node is 800 km and the final end-of-life storage altitude is 1100 km. Radiation levels have been evaluated for both the SP-100 nuclear electric and the NERVA nuclear thermal reactors as a function of operating time, power level, and time after shutdown.

Various propulsion systems are considered for a split-mission piloted exploration of Mars in terms of reducing total initial mass in low earth orbit (IMLEO) as well as trip time. Aerobraked nuclear thermal propulsion (NTP), multimegawatt (MMW) nuclear electric propulsion (NEP), and MMW solar electric propulsion (SEP) are discussed and compared to a baseline aerobraked chemical propulsion system. NTP offers low IMLEO, MMW NEP allows both low IMLEO and a short trip time, and both nuclear systems offer better mission characteristics than the chemical system. The MMW SEP is concluded to be less efficient in spite of a lower IMLEO because of the system's higher specific mass and nonconstant power production. It is recommended that MMW NEP and SEP systems be considered for application to Mars cargo missions. The NEP system is concluded to be the most effective propulsion configuration for piloted Mars missions and lunar base missions.

Three types of electric thrusters currently under development at JPL have potential to support future missions which utilize multimegawatt nuclear electric propulsion. These electric thrusters are the electron bombardment ion thruster, the magnetoplasmadynamic (MPD) thruster, and the electron‐cyclotron‐resonance (ECR) thruster. The electron bombardment ion thruster is a relatively mature technology which has been developed for operation at kilowatt power levels but will require new development for application in the multimegawatt regime. The MPD engine represents a technology which may be very well suited to steady‐state multimegawatt applications but which has been limited to sub‐scale (100’s of kW) and pulsed (MW) testing thus far. The ECR plasma engine represents a class of very promising new concepts which are still in the basic research phase of development, but which may possess important fundamental advantages over other electric thruster technologies. In this paper, models of these thrusters are described and used to make projections of thruster specific mass, efficiency, and power handling capacity for operation in the multimegawatt regime.

The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H2O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality., Published in Experimental Astronomy as part of topical collection "Future of Optical-infrared Interferometry in Europe"

We employ an efficient 1550 nm resonant waveguide-type electro-optic comb generator with PM nonlinear fiber optics to generate 50 fs pulses and 500 nm broad super- continuum at 20 GHz.

We describe the contents and functionality of the NASA Exoplanet Archive, a database and tool set funded by NASA to support astronomers in the exoplanet community. The current content of the database includes interactive tables containing properties of all published exoplanets, Kepler planet candidates, threshold-crossing events, data validation reports and target stellar parameters, light curves from the Kepler and CoRoT missions and from several ground-based surveys, and spectra and radial velocity measurements from the literature. Tools provided to work with these data include a transit ephemeris predictor, both for single planets and for observing locations, light curve viewing and normalization utilities, and a periodogram and phased light curve service. The archive can be accessed at http://exoplanetarchive.ipac.caltech.edu., Comment: Accepted for publication in the Publications of the Astronomical Society of the Pacific, 4 figures