Space, Telecommunication, Astronomy, & Radiation Lab

Telemetry Fault-Detection Algorithms: Applications for Spacecraft Monitoring and Space Environment Sensing

2025-02-11T19:58:16Z

Telemetry Fault-Detection Algorithms: Applications for Spacecraft Monitoring and Space Environment Sensing Carlton, Ashley; Morgan, Rachel; Lohmeyer, Whitney; Cahoy, Kerri Algorithms have been developed that identify unusual behavior in satellite health telemetry. Telemetry from solid-state power amplifiers and amplifier thermistors from 32 geostationary Earth orbit communications satellites from 1991 to 2015 are examined. Transient event detection and change-point event detection techniques that use a sliding window-based median are used, statistically evaluating the telemetry stream compared to the local norm. This approach allows application of the algorithms to any spacecraft platform because there is no reliance in the algorithms on satellite- or component-specific parameters, and it does not require a priori knowledge about the data distribution. Individual telemetry data streams are analyzed with the event detection algorithms, resulting in a compiled list of unusual events for each satellite. This approach identifies up to six events of up to six events that affect 51 of 53 telemetry streams at once, indicative of a spacecraft system-level event. In two satellites, the same top event date (4 December 2008) occurs over more than 10 years of telemetry from both satellites. Of the five spacecraft with known maneuvers, the algorithms identify the maneuvers in all cases. Event dates are compared to known operational activities, space weather events, and available anomaly lists to assess the use of event detection algorithms for spacecraft monitoring and sensing of the space environment.

Design of the Deformable Mirror Demonstration CubeSat (DeMi)

2025-02-11T20:02:40Z

Design of the Deformable Mirror Demonstration CubeSat (DeMi) Douglas, Ewan; Allan, Gregory; Barnes, Derek; Figura, Joseph S.; Haughwout, Christian A.; Gubner, Jennifer N.; Knoedler, Alex A.; LeClair, Sarah; Murphy, Thomas J; Nikolaos, Skouloudis; Merk, John; Opperman, Roedolph A.; Cahoy, Kerri L. The Deformable Mirror Demonstration Mission (DeMi) was recently selected by DARPA to demonstrate in-space operation of a wavefront sensor and Microelectromechanical system (MEMS) deformable mirror (DM) payload on a 6U CubeSat. Space telescopes designed to make high-contrast observations using internal coronagraphs for direct characterization of exoplanets require the use of high-actuator density deformable mirrors. These DMs can correct image plane aberrations and speckles caused by imperfections, thermal distortions, and diffraction in the telescope and optics that would otherwise corrupt the wavefront and allow leaking starlight to contaminate coronagraphic images. DeMi is provide on-orbit demonstration and performance characterization of a MEMS deformable mirror and closed loop wavefront sensing. The DeMi payload has two operational modes, one mode that images an internal light source and another mode which uses an external aperture to images stars. Both the internal and external modes include image plane and pupil plane wavefront sensing. The objectives of the internal measurement of the 140-actuator MEMS DM actuator displacement are characterization of the mirror performance and demonstration of closed-loop correction of aberrations in the optical path. Using the external aperture to observe stars of magnitude 2 or brighter, assuming 3-axis stability with less than 0.1 degree of attitude knowledge and jitter below 10 arcsec RMSE, per observation, DeMi will also demonstrate closed loop wavefront control on an astrophysical target. We present an updated payload design, results from simulations and laboratory optical prototyping, as well as present our design for accommodating high-voltage multichannel drive electronics for the DM on a CubeSat.

Using the Galileo Solid-State Imaging Instrument as a Sensor of Jovian Energetic Electrons

2019-04-11T00:14:00Z

Using the Galileo Solid-State Imaging Instrument as a Sensor of Jovian Energetic Electrons Carlton, Ashley; de Soria-Santacruz Pich, Maria; Kim, Wousik; Jun, Insoo; Cahoy, Kerri We quantitatively describe the Jovian energetic electron environment using the Solid State Imager (SSI) on the Galileo spacecraft. We post-process raw SSI images by removing the target object and dark current to obtain frames only with the radiation contribution. The camera settings (gain state, filter, etc.) are used to compute the energy deposited in each pixel, which corresponds to the intensity of the observed radiation hits (the actual measurements are expressed with the digital number (DN), from which the energy deposited can be computed). Histograms of the number of pixels versus energy deposited by incident particles from processed SSI images are compared with the results from 3D Monte Carlo transport simulations of the SSI using Geant4. We use Geant4 to simulate the response of the SSI instrument to mono-energetic electron environments from 1 to 100 MeV. We fit the modeled instrument response to the SSI data using a linear combination of the simulated mono-energetic histograms to match the SSI observations. We then estimate the spectra of the energetic electron environment at Jupiter, or we estimate the integral flux when there is lower confidence in the spectra fits. We validate the SSI results by comparing the environment predictions to the observations from the Energetic Particle Detector (EPD) on the Galileo spacecraft, examining the electron differential fluxes from 10’s of keV to 11 MeV. For higher energies (up to 31.0 MeV), we compare our findings with the NASA GIRE model, which is based on measurements from the Pioneer spacecraft. This approach could be applied to other sets of imaging data in energetic electron environments, such as from star trackers in geostationary Earth orbits.

Laser Beacon Tracking for High-Accuracy Attitude Determination

2025-02-11T20:02:40Z

Laser Beacon Tracking for High-Accuracy Attitude Determination Nguyen, Tam; Cahoy, Kerri CubeSat pointing capabilities have greatly improved in the past few years, paving the way for more sophisticated science and technology demonstration missions. Advances in attitude determination have led to the development of several CubeSat-sized attitude sensors capable of achieving fine attitude knowledge,most of which utilize natural light sources as references, such as in the case of star trackers and sun sensors. However, inertial-based attitude sensors often limit ground tracking capability of the satellite due to high ephemeris uncertainty of most CubeSats. Laser beacon tracking directly measures of the satellite’s attitude relative to a ground station or target, eliminating attitude errors induced in the coordinate frame conversion process. In addition, the use of a narrow-band artificial light source allows filtering techniques to be implemented, reducing the probability of false positives. In this paper, we present the development of a low-cost CubeSat-sized laser beacon camera along with detailed simulation development and results to demonstrate the attitude sensing performance of the module. The end-to-end simulation includes a laser link radiometry model, hardware model, atmospheric scintillation model, and sky radiance model at the beacon wavelength. Simulation results show that the laser beacon camera is capable of achieving an attitude accuracy of less than 0.1 mrad with a fade probability of less than 1% during daytime under most sky conditions for a satellite above 20-deg elevation in low-Earth orbit.

Active Polarimetric Measurements for Identification and Characterization of Space Debris

2025-02-11T19:58:16Z

Active Polarimetric Measurements for Identification and Characterization of Space Debris Pasqual, M. C.; Cahoy, K. L. A bench-top polarimeter ( λ = 1064 nm) is used to measure the polarimetric Bidirectional Reflectance Distribution Function (BRDF) of several common spacecraft materials in both bistatic and monostatic geometries. The Mueller matrix and polarimetric properties of each material were estimated as a function of the illumination and viewing angles. The findings expand upon previous research suggesting that active polarimetry may be useful for the remote characterization and identification of space debris.

Laser-Guide-Star Satellite for Ground-Based Adaptive Optics Imaging of Geosynchronous Satellites

2025-02-11T19:58:16Z

Laser-Guide-Star Satellite for Ground-Based Adaptive Optics Imaging of Geosynchronous Satellites Marlow, Weston; Carlton, Ashley; Hyosang, Yoon; Clark, James; Haughwout, Christian; Cahoy, Kerri; Males, Jared; Close, Laird; Morzinski, Katie In this study, the feasibility and utility of using a maneuverable nanosatellite laser guide star from a geostationary equatorial orbit have been assessed to enable ground-based, adaptive optics imaging of geosynchronous satellites with next-generation extremely large telescopes. The concept for a satellite guide star was first discussed in the literature by Greenaway and Clark in the early 1990s ("PHAROS: An Agile Satellite-Borne Laser Guidestar," Proceedings of SPIE, Vol. 2120, 1994, pp. 206-210), and expanded upon by Albert in 2012 ("Satellite-Mounted Light Sources as Photometric Calibration Standards for Ground-Based Telescopes," Astronomical Journal, Vol. 143, No. 1, 2012, p. 8). With a satellite-based laser as an adaptive optics guide star, the source laser does not need to scatter, and is well above atmospheric turbulence. When viewed from the ground through a turbulent atmosphere, the angular size of the satellite guide star is much smaller than a backscattered source. Advances in small-satellite technology and capability allowed the revisiting of the concept on a 6U CubeSat, measuring 10×20×30 cm. It is shown that a system that uses a satellite-based laser transmitter can be relatively low power (~1 W transmit power) and operated intermittently. Although the preliminary analysis indicates that a single satellite guide star cannot be used for observing multiple astronomical targets, it will only require a little propellant to relocate within the geosynchronous belt. Results of a design study on the feasibility of a small-satellite guide star have been presented, and the potential benefits to astronomical imaging and to the larger space situational awareness community have been highlighted.

Assessment of Radiometer Calibration With GPS Radio Occultation for the MiRaTA CubeSat Mission

2025-02-11T19:58:15Z

Assessment of Radiometer Calibration With GPS Radio Occultation for the MiRaTA CubeSat Mission Marinan, A. D.; Cahoy, K. L.; Bishop, R. L.; Lui, S. S.; Bardeen, J. R.; Mulligan, T.; Blackwell, W. J.; Leslie, R. V.; Osaretin, I. A.; Shields, M. The microwave radiometer technology acceleration (MiRaTA) is a 3U CubeSat mission sponsored by the NASA Earth Science Technology Office. The science payload on MiRaTA consists of a triband microwave radiometer and global positioning system (GPS) radio occultation (GPSRO) sensor. The microwave radiometer takes measurements of all-weather temperature (V-band, 50-57 GHz), water vapor (G-band, 175-191 GHz), and cloud ice (G-band, 205 GHz) to provide observations used to improve weather forecasting. The Aerospace Corporation's GPSRO experiment, called the compact total electron content and atmospheric GPS sensor (CTAGS), measures profiles of temperature and pressure in the upper troposphere/lower stratosphere (~20 km) and electron density in the ionosphere (over 100 km). The MiRaTA mission will validate new technologies in both passive microwave radiometry and GPSRO: 1) new ultracompact and low-power technology for multichannel and multiband passive microwave radiometers, 2) the application of a commercial off-the-shelf GPS receiver and custom patch antenna array technology to obtain neutral atmospheric GPSRO retrieval from a nanosatellite, and 3) a new approach to space-borne microwave radiometer calibration using adjacent GPSRO measurements. In this paper, we focus on objective 3, developing operational models to meet a mission goal of 100 concurrent radiometer and GPSRO measurements, and estimating the temperature measurement precision for the CTAGS instrument based on thermal noise Based on an analysis of thermal noise of the CTAGS instrument, the expected temperature retrieval precision is between 0.17 and 1.4 K, which supports the improvement of radiometric calibration to 0.25 K.

Interpolation Method for Update with Out-of-Sequence Measurements: The Augmented Fixed-Lag Smoother

2025-02-11T19:58:15Z

Interpolation Method for Update with Out-of-Sequence Measurements: The Augmented Fixed-Lag Smoother Yoon, Hyosang; Sternberg, D. C.; Cahoy, Kerri In this study, the authors propose a novel method to handle OOSMs in Kalman filtering. The proposed method, called the augmented fixed-lag smoother (AFLS), is based on the fixed-lag smoother (FLS) formulation, which has been shown to be optimal [10]. We generate the OOSM node from the two adjacent nodes, plug the generated estimations into the state vector and the covariance matrix, and update the filter with OOSMs using the FLS update equation. This approach gives a generalized solution that can handle any number of OOSMs. We also extend the AFLS algorithm to nonlinear system, called the extended AFLS (EAFLS), and give an application example on a satellite-tracking problem.

Interplanetary space weather effects on Lunar Reconnaissance Orbiter avalanche photodiode performance.

2025-02-11T19:58:16Z

Interplanetary space weather effects on Lunar Reconnaissance Orbiter avalanche photodiode performance. Clements, E. B.; Carlton, A. K.; Joyce, C. J.; Schwadron, N. A.; Spence, H. E.; Sun, X.; Cahoy, K. Space weather is a major concern for radiation-sensitive space systems, particularly for interplanetary missions, which operate outside of the protection of Earth's magnetic field. We examine and quantify the effects of space weather on silicon avalanche photodiodes (SiAPDs), which are used for interplanetary laser altimeters and communications systems and can be sensitive to even low levels of radiation (less than 50 cGy). While ground-based radiation testing has been performed on avalanche photodiode (APDs) for space missions, in-space measurements of SiAPD response to interplanetary space weather have not been previously reported. We compare noise data from the Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA) SiAPDs with radiation measurements from the onboard Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument. We did not find any evidence to support radiation as the cause of changes in detector threshold voltage during radiation storms, both for transient detector noise and long-term average detector noise, suggesting that the approximately 1.3 cm thick shielding (a combination of titanium and beryllium) of the LOLA detectors is sufficient for SiAPDs on interplanetary missions with radiation environments similar to what the LRO experienced (559 cGy of radiation over 4 years).

Implementation and validation of a CubeSat laser transmitter

2025-02-11T19:58:16Z

Implementation and validation of a CubeSat laser transmitter Kingsbury, R. W.; Caplan, D. O.; Cahoy, K. L. The paper presents implementation and validation results for a CubeSat-scale laser transmitter. The master oscillator power amplifier (MOPA) design produces a 1550 nm, 200mW average power optical signal through the use of a directly modulated laser diode and a commercial fiber amplifier. The prototype design produces high-fidelity M-ary pulse position modulated (PPM) waveforms (M=8 to 128), targeting data rates > 10 Mbit/s while meeting a constraining 8W power allocation. We also present the implementation of an avalanche photodiode (APD) receiver with measured transmitter-to-receiver performance within 3 dB of theory. Via loopback, the compact receiver design can provide built-in self-test and calibration capabilities, and supports incremental on-orbit testing of the design.

Atmospheric characterization of cold exoplanets with a 1.5-m space coronagraph

2025-02-11T20:02:40Z

Atmospheric characterization of cold exoplanets with a 1.5-m space coronagraph Maire, A. -L.; Galicher, R.; Boccaletti, A.; Baudoz, P.; Schneider, J.; Cahoy, K.; Stam, D.; Traub, W. Several small space coronagraphs have been proposed to characterize cold exoplanets in reflected light. Studies have mainly focused on technical feasibility because of the huge star/planet flux ratio to achieve in the close-in stellar environment (108-1010 at 0.2'). However, the main interest of such instruments, the analysis of planet properties, has remained highly unexplored so far. We performed numerical simulations to assess the ability of a small space coronagraph to retrieve spectra of mature Jupiters, Neptunes and super-Earths under realistic assumptions. We describe our assumptions: exoplanetary atmosphere models, instrument numerical simulation and observing conditions. Then, we define a criterion and use it to determine the required exposure times to measure several planet parameters from their spectra (separation, metallicity, cloud and surface coverages) for particular cases. Finally, we attempt to define a parameter space of the potential targets. In the case of a solar-type star, we show that a small coronagraph can characterize the spectral properties of a 2-AU Jupiter up to 10 pc and the cloud and surface coverage of super-Earths in the habitable zone for a few stars within 4-5 pc. Potentially, SPICES could perform analysis of a hypothetical Earth-size planet around α Cen A and B.

Trapped photoelectrons during spacecraft charging in sunlight

2025-02-11T19:58:15Z

Trapped photoelectrons during spacecraft charging in sunlight Cahoy, K.; Lai, S. T. For a dielectric spacecraft charging in sunlight, the potentials are different on the sunlit and dark sides. Differential charging of spacecraft surfaces can trap low-energy electrons by means of potential wells and barriers. The low-energy electrons are mostly photoelectrons and secondary electrons. Motivated by the recent interest in trapped photoelectrons measured by the Van Allen Probes in the radiation belts, we calculate the extent of the trapped photoelectron area and the potential barrier as a function of the dipole strength and sun angle using the monopole- dipole model. We find that the dipole strength is an important parameter in controlling the behavior of the potential wells and barriers. The usual inequality, 1/2 ≤ A ≤ 1 where A is the dipole strength, used in the monopole-dipole model can be relaxed and amended for finite sun angles. We then use a simple method to estimate the density of the trapped low-energy electrons in these areas. In sunlight charging, the low-energy electron population around the spacecraft is enhanced by the photoelectrons trapped inside the potential barrier.

Direct imaging of exoEarths embedded in clumpy debris disks

2025-02-11T20:02:40Z

Direct imaging of exoEarths embedded in clumpy debris disks Defrere, D.; Stark, C.; Cahoy, K.; Beerer, I. The inner solar system, where the terrestrial planets formed and evolve, is populated by small grains of dust produced by collisions of asteroids and outgassing comets. At visible and infrared wavelengths, this dust cloud is in fact the most luminous component in the solar system after the Sun itself and the Earth may appear similar to a clump of zodiacal dust to an external observer. Hence, the presence of large amounts of dust in the habitable zone around nearby main-sequence stars is considered as a major hurdle toward the direct imaging of exoEarths with future dedicated space-based telescopes. In that context, we address in this paper the detectability of exoEarths embedded in structured debris disks with future space-based visible coronagraphs and mid-infrared interferometers. Using a collisional grooming algorithm, we produce models of dust clouds that simultaneously and self-consistently handle dust grain dynamics, including resonant interactions with planets, and grain-grain collisions. Considering various viewing geometries, we also derive limiting dust densities that can be tolerated around nearby main-sequence stars in order to ensure the characterization of exoEarths with future direct imaging missions.

Combining laser frequency combs and iodine cell calibration techniques for Doppler detection of exoplanets

2025-02-11T20:02:40Z

Combining laser frequency combs and iodine cell calibration techniques for Doppler detection of exoplanets Cahoy, K.; Fischer, D.; Spronck, J.; Demille, D. Exoplanets can be detected from a time series of stellar spectra by looking for small, periodic shifts in the absorption features that are consistent with Doppler shifts caused by the presence of an exoplanet, or multiple exoplanets, in the system. While hundreds of large exoplanets have already been discovered with the Doppler technique (also called radial velocity), our goal is to improve the measurement precision so that many Earth-like planets can be detected. The smaller mass and longer period of true Earth analogues require the ability to detect a reflex velocity of ~10 cm/s over long time periods. Currently, typical astronomical spectrographs calibrate using either Iodine absorptive cells or Thorium Argon lamps and achieve ~10 m/s precision, with the most stable spectrographs pushing down to ~2 m/s. High velocity precision is currently achieved at HARPS by controlling the thermal and pressure environment of the spectrograph. These environmental controls increase the cost of the spectrograph, and it is not feasible to simply retrofit existing spectrometers. We propose a fiber-fed high precision spectrograph design that combines the existing ~5000-6000 A Iodine calibration system with a high-precision Laser Frequency Comb (LFC) system from ~6000-7000 A that just meets the redward side of the Iodine lines. The scientific motivation for such a system includes: a 1000 A span in the red is currently achievable with LFC systems, combining the two calibration methods increases the wavelength range by a factor of two, and moving redward decreases the 'noise' from starspots. The proposed LFC system design employs a fiber laser, tunable serial Fabry-Perot cavity filters to match the resolution of the LFC system to that of standard astronomical spectrographs, and terminal ultrasonic vibration of the multimode fiber for a stable point spread function.

CubeSat deformable mirror demonstration

2025-02-11T20:02:40Z

CubeSat deformable mirror demonstration Cahoy, K.; Marinan, A.; Kerr, C.; Cheng, K.; Jamil, S. The goal of the CubeSat Deformable Mirror Demonstration (DeMi) is to characterize the performance of a small deformable mirror over a year in low-Earth orbit. Small form factor deformable mirrors are a key technology needed to correct optical system aberrations in high contrast, high dynamic range space telescope applications such as space-based coronagraphic direct imaging of exoplanets. They can also improve distortions and reduce bit error rates for space-based laser communication systems. While follow-on missions can take advantage of this general 3U CubeSat platform to test the on-orbit performance of several different types of deformable mirrors, this first design accommodates a 32-actuator Boston Micromachines MEMS deformable mirror.

Planetary Imaging Concept Testbed Using a Recoverable Experiment-Coronagraph (PICTURE C)

2025-02-11T19:58:16Z

Planetary Imaging Concept Testbed Using a Recoverable Experiment-Coronagraph (PICTURE C) Cook, T.; Cahoy, K.; Chakrabarti, S.; Douglas, E.; Finn, S. C.; Kuchner, M.; Lewis, N.; Marinan, A.; Martel, J.; Mawet, D.; Mazin, B.; Meeker, S. R.; Mendillo, C.; Serabyn, G.; Stuchlik, D.; Swain, M. An exoplanet mission based on a high-altitude balloon is a next logical step in humanity's quest to explore Earthlike planets in Earthlike orbits orbiting Sunlike stars. The mission described here is capable of spectrally imaging debris disks and exozodiacal light around a number of stars spanning a range of infrared excesses, stellar types, and ages. The mission is designed to characterize the background near those stars, to study the disks themselves, and to look for planets in those systems. The background light scattered and emitted from the disk is a key uncertainty in the mission design of any exoplanet direct imaging mission, thus, its characterization is critically important for future imaging of exoplanets.

Effect of Longitude-Dependent Cloud Coverage on Exoplanet Visible Wavelength Reflected-Light Phase Curves

2025-02-11T19:58:16Z

Effect of Longitude-Dependent Cloud Coverage on Exoplanet Visible Wavelength Reflected-Light Phase Curves Webber, M. W.; Lewis, N. K.; Marley, M.; Morley, C.; Fortney, J. J.; Cahoy, K. We use a planetary albedo model to investigate variations in visible wavelength phase curves of exoplanets. Thermal and cloud properties for these exoplanets are derived using one-dimensional radiative-convective and cloud simulations. The presence of clouds on these exoplanets significantly alters their planetary albedo spectra. We confirm that non-uniform cloud coverage on the dayside of tidally locked exoplanets will manifest as changes to the magnitude and shift of the phase curve. In this work, we first investigate a test case of our model using a Jupiter-like planet, at temperatures consistent to 2.0 AU insolation from a solar type star, to consider the effect of H2O clouds. We then extend our application of the model to the exoplanet Kepler-7b and consider the effect of varying cloud species, sedimentation efficiency, particle size, and cloud altitude. We show that, depending on the observational filter, the largest possible shift of the phase curve maximum will be similar to 2 degrees-10 degrees for a Jupiter-like planet, and up to similar to 30 degrees (similar to 0.08 in fractional orbital phase) for hot-Jupiter exoplanets at visible wavelengths as a function of dayside cloud distribution with a uniformly averaged thermal profile. The models presented in this work can be adapted for a variety of planetary cases at visible wavelengths to include variations in planet-star separation, gravity, metallicity, and source-observer geometry. Finally, we tailor our model for comparison with, and confirmation of, the recent optical phase-curve observations of Kepler-7b with the Kepler space telescope. The average planetary albedo can vary between 0.1 and 0.6 for the 1300 cloud scenarios that were compared to the observations. Many of these cases cannot produce a high enough albedo to match the observations. We observe that smaller particle size and increasing cloud altitude have a strong effect on increasing albedo. In particular, we show that a set of models where Kepler-7b has roughly half of its dayside covered in small-particle clouds high in the atmosphere, made of bright minerals like MgSiO3 and Mg2SiO4, provide the best fits to the observed offset and magnitude of the phase-curve, whereas Fe clouds are found to be too dark to fit the observations.

Response of geostationary communications satellite solid-state power amplifiers to high-energy electron fluence.

2025-02-11T19:58:16Z

Response of geostationary communications satellite solid-state power amplifiers to high-energy electron fluence. Lohmeyer, Whitney; Carlton, Ashley; Wong, Frankie; Bodeau, Michael; Kennedy, Andrew; Cahoy, Kerri The key components in communications satellite payloads are the high-power amplifiers that amplify the received signal so that it can be accurately transmitted to the intended end user. In this study, we examine 26 amplifier anomalies and quantify the high-energy electron environment for periods of time prior to the anomalies. Building on the work of Lohmeyer and Cahoy (2013), we find that anomalies occur at a rate higher than just by chance when the >2 MeV electron fluence accumulated over 14 and 21 days is elevated. To try to understand “why,” we model the amplifier subsystem to assess whether the dielectric material in the radio frequency (RF) coaxial cables, which are the most exposed part of the system, is liable to experience electrical breakdown due to internal charging. We find that the accumulated electric field over the 14 and 21 days leading up to the anomalies is high enough to cause the dielectric material in the coax to breakdown. We also find that the accumulated voltages reached are high enough to compromise components in the amplifier system, for example, the direct current (DC) blocking capacitor. An electron beam test using a representative coaxial cable terminated in a blocking capacitor showed that discharges could occur with peak voltages and energies sufficient to damage active RF semiconductor devices.

Quantifying the average and the likelihood of increases in space weather indices and in situ measurements during Solar Cycles 20–23

2025-02-11T19:58:16Z

Quantifying the average and the likelihood of increases in space weather indices and in situ measurements during Solar Cycles 20–23 Lohmeyer, Whitney Q.; Pang, Anthony; Cahoy, Kerry; Shprits, Yuri It is known that space weather harshly affects spacecraft performance, yet spacecraft operations and understanding the cause of anomalies can be challenging due to the complexity of environmental metrics. In this work, we analyse five metrics and in-situ measurements (Kp, Dst, and AE index, and high-energy proton and electron flux) throughout Solar Cycles 20–23 (1964 to 2008), and provide a baseline for the environment during the phases of the solar cycles (maximum, minimum, declining or ascending). We define increased activity as activity greater than two median absolute deviations (MADs) above the average activity for each phase. MAD is used, rather than standard deviation, because it is more resilient to outliers. The average and MAD values are tabulated in Table 3 to Table 6. We determine the probability that increased activity occurs 3, 14 or 30 days before a random day to distinguish between increased/quiet activities and to aid in correlating intensifications of the environment and anomalous satellite performance.

First results on a new PIAA coronagraph testbed at NASA Ames

2025-02-11T20:02:40Z

First results on a new PIAA coronagraph testbed at NASA Ames Belikov, R.; Pluzhnik, E.; Connelley, M. S.; Witteborn, F. C.; Lynch, D. H.; Cahoy, K. L.; Guyon, O.; Greene, T. P.; McKelvey, M. E. Direct imaging of extrasolar planets, and Earth-like planets in particular, is an exciting but difficult problem requiring a telescope imaging system with 1010 contrast at separations of 100 mas and less. Furthermore, the current NASA science budget may only allow for a small 1-2 m space telescope for this task, which puts strong demands on the performance of the imaging instrument. Fortunately, an efficient coronagraph called the Phase Induced Amplitude Apodization (PIAA) coronagraph has been maturing and may enable Earth-like planet imaging for such small telescopes. In this paper, we report on the latest results from a new testbed at NASA Ames focused on testing the PIAA coronagraph. This laboratory facility was built in 2008 and is designed to be flexible, operated in a highly stabilized air environment, and to complement existing efforts at NASA JPL. For our wavefront control we are focusing on using small Micro-Electro- Mechanical-System deformable mirrors (MEMS DMs), which promises to reduce the size of the beam and overall instrument, a consideration that becomes very important for small telescopes. At time of this writing, we are operating a refractive PIAA system and have achieved contrasts of about 1.2×10-7 in a dark zone from 2.0 to 4.8 λ/D (with 6.6×10-8 in selected regions). In this paper, we present these results, describe our methods, present an analysis of current limiting factors, and solutions to overcome them.

Radio science measurements of atmospheric refractivity with Mars Global Surveyor

2025-02-11T19:58:16Z

Radio science measurements of atmospheric refractivity with Mars Global Surveyor Cahoy, Kerri; Hinson, David; Tyler, G. Leonard Radio occultation experiments with Mars Global Surveyor measure the refractive index of the Martian atmosphere from the surface to ~250 km in geopotential height. Refractivity is proportional to neutral density at low altitudes and electron density at high altitudes, with a transition at ~75 km. We use weighted least squares to decompose zonal refractivity variations into amplitudes and phases for observed wave numbers k=1-4 over the entire altitude range and use the results to analyze atmospheric structure and dynamics. The data set consists of 147 refractivity profiles acquired in December 2000 at summer solstice in the Martian northern hemisphere. The measurements are at an essentially fixed local time (sunrise) and at latitudes from 67deg to 70degN. Thermal tides appear to be responsible for much of the observed ionospheric structure from 80 to 220 km. Tides modulate the neutral density, which in turn, controls the height at which the ionosphere forms. The resulting longitude-dependent vertical displacement of the ionosphere generates distinctive structure in the fitted amplitudes, particularly at k=3, within plusmn50 km of the electron density peak height. Our k=3 observations are consistent with an eastward propagating semidiurnal tide with zonal wave number 1. Relative to previous results, our analysis extends the characterization of tides to altitudes well above and below the electron density peak. In the neutral atmosphere, refractivity variations from the surface to 50 km appear to arise from stationary Rossby waves. Upon examining the full vertical range, stationary waves appear to dominate altitudes below ~75 km, and thermal tides dominate altitudes above this transition region.

Communication satellite power amplifiers: current and future SSPA and TWTA technologies

2025-02-11T19:58:16Z

Communication satellite power amplifiers: current and future SSPA and TWTA technologies Aniceto, Raichelle; Cahoy, Kerri; Lohmeyer, Whitney This study captures the state of current satellite transponder technology, specifically, solid-state power amplifiers (SSPAs) and traveling wave tube amplifiers (TWTAs), and describes expected future advances, including GaN SSPAs. The findings of five previous SSPA and TWTA studies, including the 1991 European Space and Technology Center study, the 1993 National Aeronautics and Space Administration study, and three Boeing studies conducted in 2005, 2008, and 2013, are tabulated and summarized. The results of these studies are then compared with new analyses of two validated sources of amplifier data: a commercially licensed database, Seradata's Spacetrak, and a publicly available database, Gunter's Space Page. The new analyses consider a total of 18,902 amplifiers (6428 TWTAs, 2158 SSPAs, and 10,316 unspecified amplifiers) onboard 565 communications satellites launched from 1982 to 2016. This new study contains the largest number of satellites and amplifiers to date and compares output power, redundancy, and bandwidth capabilities. We find an increase in output power from the 1993 study of >200% for Ku-band TWTAs and C-band SSPAs, and >1000% increase for C-band TWTAs. The ratio of operational to redundant amplifiers is 10 times higher for TWTAs than SSPAs, and the majority of amplifiers over the past 30 years operate with bandwidth less than 100 MHz. A second analysis is conducted using failure records and telemetry of 16 geostationary satellites equipped with 659 amplifiers: 535 SSPAs and 124 TWTAs. We find that <2% of TWTAs and 5% of SSPAs experience anomalies. Overall, this research was performed to update and clarify how the power and bandwidth needs and redundancy trends of the SatCom community have evolved over the past 30 years.

Radiometer Calibration Using Colocated GPS Radio Occultation Measurements

2025-02-11T19:58:16Z

Radiometer Calibration Using Colocated GPS Radio Occultation Measurements Cahoy, K. L.; Blackwell, W. J.; Bishop, R.; Cohen, B.; Crail, C.; Cucurull, L.; Dave, P.; DiLiberto, M.; Erickson, N.; Fish, C.; Ho, S. P.; Leslie, R. V.; Milstein, A. B.; Osaretin, I. A. We present a new high-fidelity method of calibrating a cross-track scanning microwave radiometer using Global Positioning System (GPS) radio occultation (GPSRO) measurements. The radiometer and GPSRO receiver periodically observe the same volume of atmosphere near the Earth's limb, and these overlapping measurements are used to calibrate the radiometer. Performance analyses show that absolute calibration accuracy better than 0.25 K is achievable for temperature sounding channels in the 50-60-GHz band for a total-power radiometer using a weakly coupled noise diode for frequent calibration and proximal GPSRO measurements for infrequent (approximately daily) calibration. The method requires GPSRO penetration depth only down to the stratosphere, thus permitting the use of a relatively small GPS antenna. Furthermore, only coarse spacecraft angular knowledge (approximately one degree rms) is required for the technique, as more precise angular knowledge can be retrieved directly from the combined radiometer and GPSRO data, assuming that the radiometer angular sampling is uniform. These features make the technique particularly well suited for implementation on a low-cost CubeSat hosting both radiometer and GPSRO receiver systems on the same spacecraft. We describe a validation platform for this calibration method, the Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat, currently in development for the National Aeronautics and Space Administration (NASA) Earth Science Technology Office. MiRaTA will fly a multiband radiometer and the Compact TEC/Atmosphere GPS Sensor in 2015.

Wavefront control in space with MEMS deformable mirrors for exoplanet direct imaging

2025-02-11T19:58:16Z

Wavefront control in space with MEMS deformable mirrors for exoplanet direct imaging Cahoy, K. L.; Marinan, A. D.; Novak, B.; Kerr, C.; Nguyen, T.; Webber, M.; Falkenburg, G.; Barg, A. To meet the high contrast requirement of 1 x 10(-10) to image an Earth-like planet around a sun-like star, space telescopes equipped with coronagraphs require wavefront control systems. Deformable mirrors (DMs) are a key element of a wavefront control system, as they correct for imperfections, thermal distortions, and diffraction that would otherwise corrupt the wavefront and ruin the contrast. The goal of the CubeSat DM technology demonstration mission is to test the ability of a microelectromechanical system (MEMS) DM to perform wavefront control on-orbit on a nanosatellite platform. We consider two approaches for an MEMS DM technology demonstration payload that will fit within the mass, power, and volume constraints of a CubeSat: (1) a Michelson interferometer and (2) a Shack-Hartmann wavefront sensor. We clarify the constraints on the payload based on the resources required for supporting CubeSat subsystems drawn from subsystems that we have developed for a different CubeSat flight project. We discuss results from payload laboratory prototypes and their utility in defining mission requirements.

Space weather radiation effects on geostationary satellite solid-state power amplifiers

2025-02-11T19:58:16Z

Space weather radiation effects on geostationary satellite solid-state power amplifiers Lohmeyer, W. Q.; Cahoy, K. L. In order to understand and mitigate the effects of space weather on the performance of geostationary (GEO) communications satellites, we analyze 16 years of archived telemetry data from Inmarsat, the UK-based telecommunications company. We compare 665,112 operational hours of housekeeping telemetry from two generations of satellites, designated as Fleet A and Fleet B. Each generation experienced 13 solid-state power amplifier (SSPA) anomalies for a total of 26 anomalies from 1996 to 2012. We compare telemetry from the Inmarsat anomalies with space weather observations, including data from the OMNI2 database, Geostationary Operational Environmental Satellites, the Advanced Composition Explorer Satellite, and Los Alamos National Laboratory (LANL) GEO observations; the evolution of the sunspot number; and the Kp index. Most SSPA anomalies for Fleet A occur as solar activity declines; Fleet B has not yet experienced a full solar cycle. For both fleets, the average value of Kp remained <2 over time periods of 2 days, 3 days, and 2 weeks around the time of anomaly, which suggests that the anomalies occurred at times of relatively quiet geomagnetic activity and that they were probably not solely caused by surface charging. From 1996 to 2009, the average of the 1.8-3.5MeV electron flux was 1.98 #/(cm(2)s st keV). Five of the 26 anomalies, unfortunately, do not have corresponding science observations (specifically, electron flux data in the LANL data set), so part of this study focuses on the 21 anomalies when science observations were available. Six out of 21 anomalies experienced a high-energy electron flux greater than 1.5 standard deviations above the mean of the log(10) of the flux between 7 and 14days prior to the anomaly. By contrast, a Monte Carlo simulation finds that on average, only 2.8 out of 21 (13%) of randomly assigned anomalies occur between 7 and 14days after an electron flux greater than 1.5 standard deviations above the mean. Our observations suggest that internal charging from either past elevated radiation belt fluxes or some conditions related to relativistic electron enhancements (either causally or accidentally) is most likely responsible for the SSPA anomalies. We next consider the timing of these anomalies with respect to the local time (LT) and season. Anomalies occur at all LT sectors with 46% (Fleet A) and 38.5% (Fleet B) in the midnight to dawn sector and 54% (Fleet A) and 46% (Fleet B) in the local noon to dusk sector. From the local time distribution, surface charging does not appear to be the sole causative agent of the anomalies. Understanding the connection between the space weather conditions and anomalies on subsystems and specific components on identical and similar geostationary communications satellites for periods of time longer than a solar cycle will help guide design improvements and provide insight on their operation during space weather events.

Mars atmospheric CO2 condensation above the north and south poles as revealed by radio occultation, climate sounder, and laser ranging observations

2025-02-11T19:58:15Z

Mars atmospheric CO2 condensation above the north and south poles as revealed by radio occultation, climate sounder, and laser ranging observations Cahoy, Kerri; Zuber, Maria; Hu, R. Y. We study the condensation of CO2 in Mars' atmosphere using temperature profiles retrieved from radio occultation measurements from Mars Global Surveyor (MGS) as well as the climate sounding instrument onboard the Mars Reconnaissance Orbiter (MRO), and detection of reflective clouds by the MGS Mars Orbiter Laser Altimeter (MOLA). We find 11 events in 1999 where MGS temperature profiles indicate CO2 condensation and MOLA simultaneously detects reflective clouds. We thus provide causal evidence that MOLA non-ground returns are associated with CO2 condensation, which strongly indicates their nature being CO2 clouds. The MGS and MRO temperature profiles together reveal the seasonal expansion and shrinking of the area and the vertical extent of atmospheric saturation. The occurrence rate of atmospheric saturation is maximized at high latitudes in the middle of winter. The atmospheric saturation in the northern polar region exhibits more intense seasonal variation than in the southern polar region. In particular, a shrinking of saturation area and thickness from LS similar to 270 degrees to similar to 300 degrees in 2007 is found; this is probably related to a planet-encircling dust storm. Furthermore, we integrate the condensation area and the condensation occurrence rate to estimate cumulative masses of CO2 condensates deposited onto the northern and southern seasonal polar caps. The precipitation flux is approximated by the particle settling flux which is estimated using the impulse responses of MOLA filter channels. With our approach, the total atmospheric condensation mass can be estimated from these observational data sets with average particle size as the only free parameter. By comparison with the seasonal polar cap masses inferred from the time-varying gravity of Mars, our estimates indicate that the average condensate particle radius is 8-22 mu m in the northern hemisphere and 4-13 mu m in the southern hemisphere. Our multi-instrument data analysis provides new constraints on modeling the global climate of Mars.

Atmospheric characterization of cold exoplanets using a 1.5-m coronagraphic space telescope

2025-02-11T19:58:16Z

Atmospheric characterization of cold exoplanets using a 1.5-m coronagraphic space telescope Maire, Anne-Lise; Galicher, Raphael; Boccaletti, Anthony; Baudoz, Pierre; Schneider, Jean; Stam, Daphne; Cahoy, Kerri; Traub, Wes High-contrast imaging is currently the only available technique for the study of the thermodynamical and compositional properties of exoplanets in long-period orbits, comparable to the range from Venus to Jupiter. The SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) project is a coronagraphic space telescope dedicated to the spectropolarimetric analysis of gaseous and icy giant planets as well as super-Earths at visible wavelengths. So far, studies for high-contrast imaging instruments have mainly focused on technical feasibility because of the challenging planet/star flux ratio of 10-8-10-10 required at short separations (200 mas or so) to image cold exoplanets. However, the main interest of such instruments, namely the analysis of planet atmospheric/surface properties, has remained largely unexplored. Aims. The aim of this paper is to determine which planetary properties SPICES or an equivalent direct imaging mission can measure, considering realistic reflected planet spectra and instrument limitation. Methods. We use numerical simulations of the SPICES instrument concept and theoretical planet spectra to carry out this performance study. We also define a criterion on the signal-to-noise ratio of the measured spectrum to determine under which conditions SPICES can retrieve planetary physical properties. Results. We find that the characterization of the main planetary properties (identification of molecules, effect of metallicity, presence of clouds and type of surfaces) would require a median signal-to-noise ratio of at least 30. In the case of a solar-type star <10 pc, SPICES will be able to study Jupiters and Neptunes up to -5 and -2 AU respectively, because of the drastic flux decrease with separation. It would also analyze cloud and surface coverage of super-Earths of radius 2.5 Earth radii at 1 AU. Finally, we determine the potential targets in terms of planet separation, radius and distance for several stellar types. For a Sun analog, we show that SPICES could characterize Jupiters (M ≥ 30 Earth masses) as small as 0.5 Jupiter radii at ≤2 AU up to 10 pc, and super-Earths at 1-2 AU for the handful of stars that exist within 4-5 pc. Potentially, SPICES could perform analysis of a hypothetical Earth-size planet around a Cen A and B. However, these results depend on the planetary spectra we use, which are derived for a few planet parameters assuming a solar-type host star. Grids of model spectra are needed for a further performance analysis. Our results obtained for SPICES are also applicable to other small (1-2 m) coronagraphic space telescopes.

SPICES: spectro-polarimetric imaging and characterization of exoplanetary systems.

2025-02-11T19:58:16Z

SPICES: spectro-polarimetric imaging and characterization of exoplanetary systems. Boccaletti, Anthony; Schneider, Jean; Traub, Wes; Lagage, Pierre-Olivier; Stam, Daphne; Gratton, Raffaele; Trauger, John; Cahoy, Kerri; Snik, Frans; Baudoz, Pierre; Galicher, Raphael; Reess, Jean-Michel; Mawet, Dimitri; Augereau, Jean-Charles; Patience, Jenny; Kuchner, Marc; Wyatt, Mark; Pantin, Eric; Maire, Anne-Lise; Vérinaud, Christophe SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450-900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/2022, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5-10 AU) from nearby stars (<25 pc) with masses ranging from a few Jupiter masses to Super Earths (∼2 Earth radii, ∼10 M) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System.

Exoplanet Albedo Spectra and Colors as a Function of Planet Phase, Separation, and Metallicity

2025-02-11T19:58:16Z

Exoplanet Albedo Spectra and Colors as a Function of Planet Phase, Separation, and Metallicity Cahoy, Kerri; Marley, Mark; Fortney, Jonathan First generation space-based optical coronagraphic telescopes will obtain images of cool gas- and ice-giant exoplanets around nearby stars. Exoplanets lying at planet-star separations larger than about 1 AU—where an exoplanet can be resolved from its parent star—have spectra that are dominated by reflected light to beyond 1 μm and punctuated by molecular absorption features. Here, we consider how exoplanet albedo spectra and colors vary as a function of planet-star separation, metallicity, mass, and observed phase for Jupiter and Neptune analogs from 0.35 to 1 μm. We model Jupiter analogs with 1× and 3× the solar abundance of heavy elements, and Neptune analogs with 10× and 30× the solar abundance of heavy elements. Our model planets orbit a solar analog parent star at separations of 0.8 AU, 2 AU, 5 AU, and 10 AU. We use a radiative-convective model to compute temperature-pressure profiles. The giant exoplanets are found to be cloud-free at 0.8 AU, possess H2O clouds at 2 AU, and have both NH3 and H2O clouds at 5 AU and 10 AU. For each model planet we compute moderate resolution (R = λ/Δλ ~ 800) albedo spectra as a function of phase. We also consider low-resolution spectra and colors that are more consistent with the capabilities of early direct imaging capabilities. As expected, the presence and vertical structure of clouds strongly influence the albedo spectra since cloud particles not only affect optical depth but also have highly directional scattering properties. Observations at different phases also probe different volumes of atmosphere as the source-observer geometry changes. Because the images of the planets themselves will be unresolved, their phase will not necessarily be immediately obvious, and multiple observations will be needed to discriminate between the effects of planet-star separation, metallicity, and phase on the observed albedo spectra. We consider the range of these combined effects on spectra and colors. For example, we find that the spectral influence of clouds depends more on planet-star separation and hence atmospheric temperature than metallicity, and it is easier to discriminate between cloudy 1× and 3× Jupiters than between 10× and 30× Neptunes. In addition to alkalis and methane, our Jupiter models show H2O absorption features near 0.94 μm. While solar system giant planets are well separated by their broadband colors, we find that arbitrary giant exoplanets can have a large range of possible colors and that color alone cannot be relied upon to characterize planet types. We also predict that giant exoplanets receiving greater insolation than Jupiter will exhibit higher equator-to-pole temperature gradients than are found on Jupiter and thus may exhibit differing atmospheric dynamics. These results are useful for future interpretation of direct imaging exoplanet observations as well as for deriving requirements and designing filters for optical direct imaging instrumentation.

Characterization of a semidiurnal eastward-propagating tide at high northern latitudes with Mars Global Surveyor electron density profiles

2025-02-11T19:58:16Z

Characterization of a semidiurnal eastward-propagating tide at high northern latitudes with Mars Global Surveyor electron density profiles Cahoy, Kerri; Hinson, David; Tyler, G. Leonard Apparent phase velocities of zonal structure, estimated from Mars Global Surveyor (MGS) electron density profiles, are used to identify and characterize SE1, the semidiurnal eastward-propagating tide with zonal wave number one, at high northern latitudes during the summer of Mars Year 26. SE1 shows impressive phase stability with altitude, season, and local time. SE1 maintains a presence at amplitudes between 5 and 15% of the zonal mean at 125 ± 10 km altitude for most of the summer season. Further analyses using MGS electron density profiles will contribute to the identification and characterization of nonmigrating tides in the upper atmosphere of Mars.

Physical characteristics and occurrence rates of meteoric plasma layers detected in the Martian ionosphere by the Mars Global Surveyor Radio Science Experiment

2025-02-11T19:58:16Z

Physical characteristics and occurrence rates of meteoric plasma layers detected in the Martian ionosphere by the Mars Global Surveyor Radio Science Experiment Withers, Paul; Mendillo, Michael; Hinson, David; Cahoy, Kerri Low-altitude plasma layers are present in 71 of 5600 electron density profiles from the Martian ionosphere obtained by the Mars Global Surveyor Radio Science experiment. These layers are produced by the ablation of meteoroids and subsequent ionization of meteoric atoms. The mean altitude of the meteoric layer is 91.7 +/- 4.8 km. The mean peak electron density in the meteoric layer is (1.33 +/- 0.25) x 10(10) m(-3). The mean width of the meteoric layer is 10.3 +/- 5.2 km. The occurrence rate of meteoric layers varies with season, solar zenith angle, and latitude. Seasonal variations in occurrence rate are particularly strong, often exceeding an order of magnitude. Meteoric layer altitude, peak electron density, and width are all positively correlated, with correlation coefficients of 0.3-0.4. Other correlation coefficients between the physical characteristics of meteoric layers and atmospheric or observational properties, such as scale height, solar zenith angle, and solar flux, have absolute values that are significantly smaller, indicating lack of correlation. The photochemical lifetime of plasma in meteoric layers is similar to 12 days and depends on altitude.

Nonlinear Optics for Frequency-Doubling in Nanosatellite Laser Communication

2025-02-11T20:02:40Z

Nonlinear Optics for Frequency-Doubling in Nanosatellite Laser Communication Clark, James; Cahoy, Kerri Free-space optical communication attracts interest due to its promise of higher data rates for similar size, weight, and power costs compared with radio systems. However, while satellite-to-ground optical communication has been tested from low Earth orbit and the Moon, intersatellite optical links are still an area of active research and development. Second-harmonic generation (SHG, or “frequency doubling”) with nonlinear optics may improve the link margins of laser systems that serve as crosslinks as well as downlinks. For example, the output of a 1550 nm laser could be doubled to 775 nm on command, allowing the satellite to use whichever wavelength is advantageous (e.g. improved detector and propagation properties), without spending the mass budget for an entire second laser system. Link-budget analysis suggests that a nanosatellite crosslink can gain 3-4 dB of link margin with a frequency-doubler. This improvement is largely driven by the reduction in beamwidth that comes with the higher frequency. It is not substantially greater than the improvement that comes with using the same narrower beamwidth at 1550 nm. However, SHG would allow a diffraction-limited system to use different beamwidths for beacon acquisition and communication without any moving parts.

Response of geostationary communications satellite solid-state power amplifiers to high-energy electron fluence

2025-02-11T19:58:16Z

Response of geostationary communications satellite solid-state power amplifiers to high-energy electron fluence Lohmeyer, Whitney; Carlton, Ashley; Wong, Frankie; Bodeau, Michael; Kennedy, Andrew; Cahoy, Kerri The key components in communications satellite payloads are the high-power amplifiers that amplify the received signal so that it can be accurately transmitted to the intended end user. In this study, we examine 26 amplifier anomalies and quantify the high-energy electron environment for periods of time prior to the anomalies. Building on the work of Lohmeyer and Cahoy (2013), we find that anomalies occur at a rate higher than just by chance when the >2 MeV electron fluence accumulated over 14 and 21 days is elevated. To try to understand “why,” we model the amplifier subsystem to assess whether the dielectric material in the radio frequency (RF) coaxial cables, which are the most exposed part of the system, is liable to experience electrical breakdown due to internal charging. We find that the accumulated electric field over the 14 and 21 days leading up to the anomalies is high enough to cause the dielectric material in the coax to breakdown. We also find that the accumulated voltages reached are high enough to compromise components in the amplifier system, for example, the direct current (DC) blocking capacitor. An electron beam test using a representative coaxial cable terminated in a blocking capacitor showed that discharges could occur with peak voltages and energies sufficient to damage active RF semiconductor devices.

End-to-end simulation of high-contrast imaging systems: methods and results for the PICTURE mission family

2025-02-11T20:02:40Z

End-to-end simulation of high-contrast imaging systems: methods and results for the PICTURE mission family Douglas, Ewan S.; Hewawasam, Kuravi; Mendillo, Christopher B.; Cahoy, Kerri L; Cook, Timothy A.; Finn, Susanna C. Finn; Howe, Glenn A.; Kuchner, Marc, J.; Lewis, Nikole K.; Marinan, Anne D.; Mawet, Dimitri; Chakrabarti, Supriya We describe a set of numerical approaches to modeling the performance of spaceflight high-contrast imaging payloads. Mission design for high-contrast imaging requires numerical wavefront error propagation to ensure accurate component specifications. For constructed instruments, wavelength and angle-dependent throughput and contrast models allow detailed simulations of science observations, allowing mission planners to select the most productive science targets. The PICTURE family of missions seek to quantify the optical brightness of scattered light from extrasolar debris disks via several high-contrast imaging techniques: sounding rocket (the Planet Imaging Concept Testbed Using a Rocket Experiment) and balloon flights of a visible nulling coronagraph, as well as a balloon flight of a vector vortex coronagraph (the Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph, PICTURE-C). The rocket mission employs an on-axis 0.5m Gregorian telescope, while the balloon flights will share an unobstructed off-axis 0.6m Gregorian. This work details the flexible approach to polychromatic, end-to-end physical optics simulations used for both the balloon vector vortex coronagraph and rocket visible nulling coronagraph missions. We show the preliminary PICTURE-C telescope and vector vortex coronagraph design will achieve 10−8 contrast without post-processing as limited by realistic optics, but not considering polarization or low-order errors. Simulated science observations of the predicted warm ring around Epsilon Eridani illustrate the performance of both missions.