Electric propulsion using C.sub.60 molecules

Fullerene propellants, which are stable carbon cage structures composed of even numbers of carbon atoms in the range of about 32 to 200 atoms, particularly a combination of conveniently obtainable C.sub.60 and C.sub.70, may be carried in solid form in a spacecraft, sublimated to produce the appropriate molecular propellant such as C.sub.60 or C.sub.70, which may then be ionized by DC discharge or RF radiation to efficiently produce specific impulses in the range above 1000 lbf -s/lbm

The development of HISPEC for Keck and MODHIS for TMT: science cases and predicted sensitivities

HISPEC is a new, high-resolution near-infrared spectrograph being designed for the W.M. Keck II telescope. By offering single-shot, R=100,000 between 0.98 - 2.5 um, HISPEC will enable spectroscopy of transiting and non-transiting exoplanets in close orbits, direct high-contrast detection and spectroscopy of spatially separated substellar companions, and exoplanet dynamical mass and orbit measurements using precision radial velocity monitoring calibrated with a suite of state-of-the-art absolute and relative wavelength references. MODHIS is the counterpart to HISPEC for the Thirty Meter Telescope and is being developed in parallel with similar scientific goals. In this proceeding, we provide a brief overview of the current design of both instruments, and the requirements for the two spectrographs as guided by the scientific goals for each. We then outline the current science case for HISPEC and MODHIS, with focuses on the science enabled for exoplanet discovery and characterization. We also provide updated sensitivity curves for both instruments, in terms of both signal-to-noise ratio and predicted radial velocity precision.Comment: 25 pages, 9 figures. To appear in the Proceedings of SPIE: Techniques and Instrumentation for Detection of Exoplanets XI, vol. 12680 (2023

Characterization of fullerenes for electrostatic propulsion applications

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. [...], also known as Buckminsterfullerene, possesses a remarkable resilience, high mass, and low ionization potential which indicate that it could make an excellent ion engine propellant. The development of an efficient, reliable [...] ion thruster for space flight requires a knowledge of many of the properties of this new molecule. The research described here focusses on the determination of some of these properties and their effects on the behavior of [...] in a plasma environment. Investigations of fullerene thermal stability, polarizability, electron-impact ionization and fragmentation phenomena, vibrational spectra, and plasma discharges are reported. The electron-impact ionization and fragmentation experiments were conducted using a time-of-flight mass spectrometer. Ionization efficiency curves for the production of both [...] and [...] ions were obtained, and appearance potentials of [...] eV for [...] and [...]eV for [...] and [...], respectively were identifed. Fullerene cracking patterns showed only even-numbered fragments, and only at electron energies above 70 eV. Multiply charged fullerene ions through [...] were observed, revealing the remarkable resistance of [...] to coulomb explosion. Experiments to determine the polarizability of [...] using a Mach-Zehnder interferometer and the Clausius-Mossotti relation were performed. The data yielded a polarizability value near [...]. Although previous experiments performed by other researchers with filament cathode discharge chambers successfully demonstrated the production of [...] plasma at a minimum discharge voltage of 22 V, difficulty with severe erosion of the tungsten filament cathode was encountered. Also, decomposition of the fullerenes at temperatures above 1073 K was observed. In light of these observations, the thermal stability of a fullerene mix was examined. Decay constants were obtained and used to find an Arrhenius plot for the thermal decomposition. The Arrhenius activation energy was found to be [...] kJ/mol. The disintegration of [...] occurs at significantly lower temperatures than those predicted by molecular dynamics simulations. A mechanism for fullerene disintegration different than [...] elimination, possibly involving ring-rearrangement in the fullerene cage, may be responsible. Because the determination of the purity of fullerene samples is vital when investigating their degradation at elevated temperatures, a study of fullerene contaminants and adsorbates using Fourier Transform Infrared (FTIR) spectroscopy was conducted. For solid fullerene samples, Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy was employed. Features in the 2350, 2330, and 1540 [...] region of the spectrum were found to be intrinisic to [...] and did not result from CO2 or O2 contamination. By increasing the CO2 content of solid [...], new features could be observed at 2377, 2330 and 2316 [...]. The peak observed at 1539 [...] in the solid vanished when fullerenes were placed in solution, but reappeared when the sample was dried under N2. The strength of this peak may be due to a Fermi resonance or crystal field effect, both of which could be destroyed by solvent interactions in solution. To avoid the presence of high temperature metal surfaces, a RF discharge chamber was constructed to maintain a fullerene plasma inductively, eliminating the presence of hot electrode surfaces. A xenon plasma was successfully generated in the thruster. The maximum extractable beam current was approximately 45 mA. Ion production cost for a pure xenon plasma was 1400 eV/ion. When [...] vapor was added to the xenon plasma, the discharge quenched when the ratio of [...] molecules to xenon atoms exceeded 1:16. A pure fullerene RF discharge could not be initiated. The cause of this phenomenon can be found in the electron attachment cross section of [...] this cross section is very large for electron energies up to 14 eV. It would be necessary to maintain an electron temperature of 10 eV or greater for positive fullerene ion production rates to exceed that of negative ion production rates. In summary, this research has been an investigation of some fundamental properties of [...] relevant to fullerene ion thruster development. It was found that although fragmentation by electron impact of [...] does not pose a significant problem, the thermal stability of fullerenes is not as great as had been anticipated. As a result, use of conventional hollow cathode configurations in fullerene ion thrusters is precluded. A RF fullerene ion thruster configuration was pursued instead, but proved difficult to operate because electron attachment cross sections for [...] remain large up to 14 eV electron energy. Therefore, the use of other ionization mechanisms may prove more successful for fullerene ion thruster development, and should be pursued in future work

Simulations for Planning Next-generation Exoplanet Radial Velocity Surveys

Future direct imaging missions similar to the HabEx and LUVOIR mission concepts 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 supporting 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. While our detection rates and mass-sensitivity are optimistic, we have margin to explore systematic effects due to stellar activity and correlated noise in future work

The planet formation imager

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

The planet formation imager

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.</p

2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments

Photonic technologies offer numerous functionalities that can be used to realize astrophotonic instruments. The most spectacular example to date is the ESO Gravity instrument at the Very Large Telescope in Chile that combines the light-gathering power of four 8-m telescopes through a complex photonic interferometer. Fully integrated astrophotonic devices offer critical advantages for instrument development, including extreme miniaturization when operating at the diffraction-limit, plus integration, superior thermal and mechanical stabilization owing to the small footprint, and high replicability offering significant cost savings. Numerous astrophotonic technologies have been developed to address shortcomings of conventional instruments to date, including the development of photonic lanterns to convert from multimode inputs to single mode outputs, complex aperiodic fiber Bragg gratings to filter OH emission from the atmosphere, beam combiners enabling long baseline interferometry with for example, ESO Gravity, and laser frequency combs for high precision spectral calibration of spectrometers. Despite these successes, the facility implementation of photonic solutions in astronomical instrumentation is currently limited because of 1) low throughputs from coupling to fibers, coupling fibers to chips, propagation and bend losses, device losses, etc., 2) difficulties with scaling to large channel count devices needed for large bandwidths and high resolutions, and 3) efficient integration of photonics with detectors. In this roadmap, we identify 23 key areas that need further development. We outline the challenges and advances needed across those areas covering design tools, simulation capabilities, fabrication processes, the need for entirely new components, integration and hybridization and the characterization of devices. To realize these advances the astrophotonics community will have to work cooperatively with industrial partners who have more advanced manufacturing capabilities. With the advances described herein, multi-functional integrated instruments will be realized leading to novel observing capabilities for both ground and space based platforms, enabling new scientific studies and discoveries