Future Solar Missions Research Articles

Trajectory & maneuver design of the NEA Scout solar sail mission

The Near-Earth Asteroid Scout (NEA Scout) mission aimed to deliver a 6U CubeSat to a slow flyby of a Near Earth Asteroid using a solar sail as the primary propulsion system. NEA Scout was launched as a secondary payload aboard Artemis I, on November 16, 2022, but communication with the spacecraft was not achieved. This paper describes the target asteroid selection and the innovative trajectory and maneuver design for the NEA Scout mission, including cold gas maneuvers, multiple lunar flybys, solar sail thrusting, and design margins for solar sailing. The resulting trajectory design tools, solutions, and analyses are potentially applicable to future solar sail missions.

Broadband radiation pressure on a small period diffractive film.

The p-polarization component of radiation pressure force from an unpolarized blackbody light source is predicted by the use of a Maxwell equation solver for a right triangular prism grating of period 2 μm and refractive index 3.5. The transmitted and reflected angular scattering distributions are found to qualitatively agree with diffraction theory: At relatively short wavelengths the transmitted light is concentrated near the refraction angle, and reflected light is concentrated near the reflection angle. Owing to diffraction and multiple internal reflections, however, the spectral irradiance of transmitted and reflected light was found to significantly vary with wavelength. We found that the high value of the refractive index produced a large fraction of reflected light, thereby reducing the net transverse component of radiation pressure force. These results suggest that low index transmission gratings, anti-reflection coatings, optimized metasurface films, or reflection gratings should be explored for future solar sailing missions.

Selection of Three (Extreme)Ultraviolet Channels for Solar Satellite Missions by Deep Learning

Abstract We address the question of which combination of channels can best translate other channels in ultraviolet (UV) and extreme UV (EUV) observations. For this, we compare the image translations among the nine channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) using a deep-learning (DL) model based on conditional generative adversarial networks. In this study, we develop 170 DL models: 72 models for single-channel input, 56 models for double-channel input, and 42 models for triple-channel input. All models have a single-channel output. Then we evaluate the model results by pixel-to-pixel correlation coefficients (CCs) within the solar disk. Major results from this study are as follows. First, the model with 131 Å shows the best performance (average CC = 0.84) among single-channel models. Second, the model with 131 and 1600 Å shows the best translation (average CC = 0.95) among double-channel models. Third, among the triple-channel models with the highest average CC (0.97), the model with 131, 1600, and 304 Å is suggested in that the minimum CC (0.96) is the highest. Interestingly, they represent coronal, upper photospheric, and chromospheric channels, respectively. Our results may be used as a secondary perspective in addition to primary scientific purposes in selecting a few channels of an UV/EUV imaging instrument for future solar satellite missions.

Validation of the Alfvén Wave Solar Atmosphere Model (AWSoM) with Observations from the Low Corona to 1 au

Abstract We perform a validation study of the latest version of the Alfvén Wave Solar atmosphere Model (AWSoM) within the Space Weather Modeling Framework. To do so, we compare the simulation results of the model with a comprehensive suite of observations for Carrington rotations representative of the solar minimum conditions extending from the solar corona to the heliosphere up to the Earth. In the low corona (r < 1.25 ), we compare with EUV images from both Solar-Terrestrial Relations Observatory-A/EUVI and Solar Dynamics Observatory/Atmospheric Imaging Assembly and to three-dimensional (3D) tomographic reconstructions of the electron temperature and density based on these same data. We also compare the model to tomographic reconstructions of the electron density from Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph observations (2.55 < r < 6.0 ). In the heliosphere, we compare model predictions of solar wind speed with velocity reconstructions from InterPlanetary Scintillation observations. For comparison with observations near the Earth, we use OMNI data. Our results show that the improved AWSoM model performs well in quantitative agreement with the observations between the inner corona and 1 au. The model now reproduces the fast solar wind speed in the polar regions. Near the Earth, our model shows good agreement with observations of solar wind velocity, proton temperature, and density. AWSoM offers an extensive application to study the solar corona and larger heliosphere in concert with current and future solar missions as well as being well suited for space weather predictions.

Chinese Hα Solar Explorer (CHASE) – a complementary space mission to the ASO-S

The Chinese Hα Solar Explorer (CHASE) is designed to test a newly developed satellite platform and conduct solar observations. The scientific payload of the satellite is an Hα imaging spectrograph (HIS), which can, for the first time, acquire full-disk spectroscopic solar observations in the Hα waveband. This paper briefly introduces CHASE/HIS including its scientific objectives, technical parameters, scientific application system, etc. The CHASE mission is scheduled to launch in 2021. It will complement the observations by on-orbit solar spacecraft (such as SDO, IRIS, STEREO and PSP), as well as future solar missions of the Solar Orbiter and Advanced Space-based Solar Observatory (ASO-S).

Boundary Detection in Three Dimensions With Application to the SMILE Mission: The Effect of Model‐Fitting Noise

AbstractThe magnetosheath and near‐Earth solar wind emit X‐rays due to charge‐exchange between the extended atmosphere and highly ionized particles in the solar wind. These emissions can be used to remotely sense the dynamic processes in this region. The Solar Wind Magnetosphere Ionosphere Link Explorer mission will carry out these measurements. In a previous paper, we looked at the effect of photon counting statistics on determining the location of the magnetopause and bow shock. In this paper we explore, through simulations, the more challenging question of orbital viewing geometry bias when the model and the emissions do not match each other exactly. Our simulations conclude that while care must be taken to avoid false minima in the fitting, there is very little to no orbital bias in extracting the position and large‐scale shape of the magnetopause and bow shocks from 2‐D X‐ray images from the future Solar Wind Magnetosphere Ionosphere Link Explorer mission.

The Sun: Our own backyard plasma laboratory.

The Sun's atmosphere increases in temperature from 6000 degrees at the surface to over a million degrees at heights of a few thousand kilometers. This surprising temperature increase is still an active area of scientific study, but is generally thought to be driven by the dynamics of the Sun's magnetic field. The combination of a 2-to-3 order of magnitude temperature range and a low plasma density makes the solar atmosphere perhaps the best natural laboratory for the study of ionized atoms. Atomic transitions at ultraviolet (UV) and X-ray wavelength regions generally show no optical depth effects, and the lines are not subject to the interstellar absorption that affects astronomical sources. Here I highlight the importance of atomic data to modeling UV and X-ray solar spectra, with a particular focus on the CHIANTI atomic database. Atomic data needs and problems are discussed and future solar mission concepts presented.

Extreme Ultraviolet Multilayer Nanostructures and Their Application to Solar Plasma Observations: A Review

The advent of nanoscale multilayer (ML) technology has led to great breakthroughs in many scientific and technological fields such as nano-manufacturing, bio-imaging, atto-physics, matter physics and solar physics. ML nanostructures are an enabling technology for the development of mirrors and reflective gratings having high efficiency at normal incidence in the extreme ultraviolet (EUV) range, a spectral region where conventional coatings show a negligible reflectance. In solar physics, ML mirrors have proved to be key elements for both imaging and spectroscopy space instruments, as they allow to make observations of EUV solar plasma emissions with spatial and spectral resolutions never reached before. ML-based instruments have been used in many of the major solar satellites and have flown in numerous sounding rocket experiments; moreover, in the last two decades many studies were performed in order to develop ML structures with increasingly better performance for future solar missions. In this paper, a review of the most promising ML nanostructures developed so far and applied to the observation of solar plasma emission lines is presented. After a brief recall of ML theory, a detailed discussion of the most promising material pairs and layer stack structures proposed and applied to past and current space missions will be presented; in particular, the review will focus on the ML structures having high efficiency in the 6 nm-35 nm wavelength range. Finally, the ML stability to low energy ion bombardment will be discussed.

CSMIR: An L-Band Clock Scan Microwave Interferometric Radiometer

Clock scan microwave interferometric radiometer (CSMIR) is a new concept of synthetic aperture radiometer. It has the potentials of being applied to the future Solar Polar Orbit and Geostationary Earth Orbit missions due to the advantages of having a simple and deployable array structure, easy calibration, and flexible visibility sampling. This paper discusses the development of an L-band CSMIR prototype, presents the achievements in hardware design, calibration method, and overall performance tests through outdoor experiments. The experimental results demonstrate the effectiveness of this new concept although some systematic errors and imperfections still exist. Some lessons learned from this prototype are discussed which are helpful to improve the performance in the future.

JPEG2000 Image Compression on Solar EUV Images

For future solar missions as well as ground-based telescopes, efficient ways to return and process data have become increasingly important. Solar Orbiter, e.g., which is the next ESA/NASA mission to explore the Sun and the heliosphere, is a deep-space mission, which implies a limited telemetry rate that makes efficient onboard data compression a necessity to achieve the mission science goals. Missions like the Solar Dynamics Observatory (SDO) and future ground-based telescopes such as the Daniel K. Inouye Solar Telescope, on the other hand, face the challenge of making petabyte-sized solar data archives accessible to the solar community. New image compression standards address these challenges by implementing efficient and flexible compression algorithms that can be tailored to user requirements. We analyse solar images from the Atmospheric Imaging Assembly (AIA) instrument onboard SDO to study the effect of lossy JPEG2000 (from the Joint Photographic Experts Group 2000) image compression at different bit rates. To assess the quality of compressed images, we use the mean structural similarity (MSSIM) index as well as the widely used peak signal-to-noise ratio (PSNR) as metrics and compare the two in the context of solar EUV images. In addition, we perform tests to validate the scientific use of the lossily compressed images by analysing examples of an on-disk and off-limb coronal-loop oscillation time-series observed by AIA/SDO.

Chromospheric polarimetry through multiline observations of the 850-nm spectral region

Future solar missions and ground-based telescopes aim to understand the magnetism of the solar chromosphere. We performed a supporting study in Quintero Noda et al. (2016) focused on the infrared Ca II 8542 A line and we concluded that is one of the best candidates because it is sensitive to a large range of atmospheric heights, from the photosphere to the middle chromosphere. However, we believe that it is worth to try improving the results produced by this line observing additional spectral lines. In that regard, we examined the neighbour solar spectrum looking for spectral lines that could increase the sensitivity to the atmospheric parameters. Interestingly, we discovered several photospheric lines that greatly improve the photospheric sensitivity to the magnetic field vector. Moreover, they are located close to a second chromospheric line that also belongs to the Ca II infrared triplet, i.e. the Ca II 8498 A line, and enhances the sensitivity to the atmospheric parameters at chromospheric layers. We conclude that the lines in the vicinity of the Ca II 8542 A line not only increase its sensitivity to the atmospheric parameters at all layers, but also they constitute an excellent spectral window for chromospheric polarimetry.

Testing and simulation of silicon photomultiplier readouts for scintillators in high-energy astronomy and solar physics

Space-based gamma-ray detectors for high-energy astronomy and solar physics face severe constraints on mass, volume, and power, and must endure harsh launch conditions and operating environments. Historically, such instruments have usually been based on scintillator materials due to their relatively low cost, inherent ruggedness, high stopping power, and radiation hardness. New scintillator materials, such as LaBr3:Ce, feature improved energy and timing performance, making them attractive for future astronomy and solar physics space missions in an era of tightly constrained budgets. Despite this promise, the use of scintillators in space remains constrained by the volume, mass, power, and fragility of the associated light readout device, typically a vacuum photomultiplier tube (PMT). In recent years, silicon photomultipliers (SiPMs) have emerged as promising alternative light readout devices that offer gains and quantum efficiencies similar to those of PMTs, but with greatly reduced mass and volume, high ruggedness, low voltage requirements, and no sensitivity to magnetic fields. In order for SiPMs to replace PMTs in space-based instruments, however, it must be shown that they can provide comparable performance, and that their inherent temperature sensitivity can be corrected for. To this end, we have performed extensive testing and modeling of a small gamma-ray spectrometer composed of a 6mm×6mm SiPM coupled to a 6mm×6mm ×10mm LaBr3:Ce crystal. A custom readout board monitors the temperature and adjusts the bias voltage to compensate for gain variations. We record an energy resolution of 5.7% (FWHM) at 662keV at room temperature. We have also performed simulations of the scintillation process and optical light collection using Geant4, and of the SiPM response using the GosSiP package. The simulated energy resolution is in good agreement with the data from 22keV to 662keV. Above ~1MeV, however, the measured energy resolution is systematically worse than the simulations. This discrepancy is likely due to the high input impedance of the readout board front-end electronics, which introduces a non-linear saturation effect in the SiPM for large light pulses. Analysis of the simulations indicates several additional steps that must be taken to optimize the energy resolution of SiPM-based scintillator detectors.

Stability of EUV multilayer coatings to low energy alpha particles bombardment

Future solar missions will investigate the Sun from very close distances and optical components are constantly exposed to low energy ions irradiation. In this work we present the results of a new experiment related to low energy alpha particles bombardments on Mo/Si multilayer optical coatings. Different multilayer samples, with and without a protecting capping layer, have been exposed to low energy alpha particles (4keV), fixing the ions fluency and varying the time of exposure in order to change the total dose accumulated. The experimental parameters have been selected considering the potential application of the coatings to future solar missions. Results show that the physical processes occurred at the uppermost interfaces can strongly damage the structure.

Automated interplanetary shock detection and its application to Wind observations

We present an automated two‐step detection algorithm for identification of interplanetary (IP) shocks regardless their type in a real‐time data stream. This algorithm is aimed for implementation on board the future Solar Orbiter mission for triggering the transmission of the high‐resolution data to the Earth. The first step of the algorithm is based on a determination of a quality factor, Q indicating abrupt changes of plasma parameters (proton density and bulk velocity) and magnetic field strength. We test two sets of weighting coefficients for Q determination and propose the second step consisting of three additional constraints that increase the effectiveness of the algorithm. We checked the algorithm using Wind (at 1 AU) and Helios (at distances from 0.29 to 1 AU) data and compared obtained results with already existing lists of IP shocks. The efficiency of the presented algorithm for the Wind shock lists varies from 60% to 84% for two Q thresholds. The final shock candidate list provided by the presented algorithm contains the real IP shocks, as well as different discontinuities. The detection rate of the IP shocks equals to 64% and 29% for two Q thresholds. The algorithm detected all IP shocks associated with the solar wind transient structures triggering intense (Dst<−100 nT) geomagnetic storms.

Synchronized observations by using the STEREO and the largest ground-based decametre radio telescope

We consider the approach to simultaneous (synchronous) solar observations of radio emission by using the STEREO-WAVES instruments (frequency range 0.125–16 MHz) and the largest ground-based low-frequency radio telescope. We illustrate it by the UTR-2 radio telescope implementation (10–30 MHz). The antenna system of the radio telescope is a T-shape-like array of broadband dipoles and is located near the village Grakovo in the Kharkiv region (Ukraine). The third observation point on the ground in addition to two space-based ones improves the space-mission performance capabilities for the determination of radio-emission source directivity. The observational results from the high sensitivity antenna UTR-2 are particularly useful for analysis of STEREO data in the condition of weak event appearances during solar activity minima. In order to improve the accuracy of flux density measurements, we also provide simultaneous observations with a large part of the UTR-2 radio telescope array and its single dipole close to the STEREO-WAVES antennas in sensitivity. This concept has been studied by comparing the STEREO data with ground-based records from 2007–2011 and shown to be effective. The capabilities will be useful in the implementation of new instruments (LOFAR, LWA, MWA, etc.) and during the future Solar Orbiter mission.

SCIENTIFIC POTENTIAL OF DECIGO PATHFINDER AND TESTING GR WITH SPACE-BORNE GRAVITATIONAL WAVE INTERFEROMETERS

Deci-Hertz Interferometer Gravitational Wave Observatory (DECIGO) Pathfinder (DPF) has an ability to detect gravitational waves (GWs) from galactic intermediate mass black hole binaries. If the signal is detected, it would be possible to determine parameters of the binary components. Furthermore, by using future space-borne GW interferometers, it would be possible to test alternative theories of gravity in the strong field regime. In this review paper, we first explain how the detectors like DPF and DECIGO/BBO work and discuss the expected event rates. Then, we review how the observed gravitational waveforms from precessing compact binaries with slightly eccentric orbits can be calculated both in general relativity and in alternative theories of gravity. For the latter, we focus on Brans–Dicke (BD) and massive gravity (MG) theories. After reviewing these theories, we show the results of the parameter estimation with DPF using the Fisher analysis. We also discuss a possible joint search of DPF and ground-based interferometers. Then, we show the results of testing alternative theories of gravity using future space-borne interferometers. DECIGO/BBO would be able to place 4–5 orders of magnitude stronger constraint on BD theory than the solar system experiment. This is still 1–2 orders of magnitude stronger than the future solar system mission such as ASTROD I. On the other hand, LISA should be able to put four orders of magnitude more stringent constraint on the mass of the graviton than the current solar system bound. DPF may be able to place comparable constraint on the MG theories as the solar system bound. We also discuss the prospects of using eLISA and ASTROD-GW in testing alternative theories of gravity. The bounds using eLISA are similar to the LISA ones, but ASTROD-GW performs the best in constraining MG theories among all the GW detectors considered in this paper.

SoFAST: Automated Flare Detection with the PROBA2/SWAP EUV Imager

The Sun Watcher with Active Pixels and Image Processing (SWAP) EUV imager onboard PROBA2 provides a non-stop stream of coronal extreme-ultraviolet (EUV) images at a cadence of typically 130 seconds. These images show the solar drivers of space-weather, such as flares and erupting filaments. We have developed a software tool that automatically processes the images and localises and identifies flares. On one hand, the output of this software tool is intended as a service to the Space Weather Segment of ESA’s Space Situational Awareness (SSA) program. On the other hand, we consider the PROBA2/SWAP images as a model for the data from the Extreme Ultraviolet Imager (EUI) instrument prepared for the future Solar Orbiter mission, where onboard intelligence is required for prioritising data within the challenging telemetry quota. In this article we present the concept of the software, the first statistics on its effectiveness and the online display in real time of its results. Our results indicate that it is not only possible to detect EUV flares automatically in an acquired dataset, but that quantifying a range of EUV dynamics is also possible. The method is based on thresholding of macropixelled image sequences. The robustness and simplicity of the algorithm is a clear advantage for future onboard use.

A study of the guidance method for the Small Solar Power Sail Demonstrator, IKAROS

We present the guidance approach for the Small Solar Power Sail Demonstrator, IKAROS. This approach will be used for future solar sail missions. First, we show the range of orbital controllability, which is severely restricted by the attitude constraint from the power and communication. Second, we also present the adaptive guidance method, in which guidance parameters are updated based on the estimation of the spacecraft's parameters such as the area and reflectivity coefficient of the sail. Finally, we evaluate the guidance approach performance by comparing to flight data of IKAROS.

Stability of extreme ultraviolet multilayer coatings to low energy proton bombardment

In this work we present results of an new experiment related to low energy protons bombardments on nano-structured optical coatings. Multilayer structures protected by different capping layers have been fabricated and exposed to low energy protons (1 keV). The experimental parameters have been selected considering the potential application of the coatings to solar mission instrumentation. Future solar missions will investigate the Sun from very close distances and optical components are constantly exposed to low energy ion particles irradiation. The experiment was repeated fixing the proton flux while varying the total dose accumulated. Results show that physical processes occurred at the uppermost interfaces can strongly damage the structure.

Capped Mo/Si multilayers with improved performance at 304 nm for future solar missions

Novel capping layer structures have been deposited on periodic Mo/Si multilayers to optimize reflectance at 30.4 nm. Design, deposition and characterization of such coatings are presented. Most of the structures proposed show improved performance with respect to standard Mo/Si multilayers and are stable over time. Reflectance at 121.6 nm and in the visible spectral range have been also tested to explore the applicability of such coatings to the Multi Element Telescope for Imaging and Spectroscopy (METIS) instrument, a coronagraph being developed for the ESA Solar Orbiter platform.