A heliogyro is a rotating solar sail with the reflecting surface divided into a number of long and slender blades, which are stiffened by a spin-induced centrifugal force. Each blade can rotate ...around its own longitudinal axis so as to change the pitch angle and allow the thrust vector to be effectively controlled. The aim of this paper is to analyze the optimal heliocentric transfers of a Sun-facing heliogyro, that is, a heliogyro whose fundamental plane is always perpendicular to the Sun-spacecraft line. A simplified analytical model of the thrust and torque vectors provided by a Sun-facing heliogyro is illustrated, using the characteristic acceleration as a performance parameter. The proposed thrust vector model is then exploited to calculate the minimum flight times in a set of two-dimensional heliocentric transfers. Using an indirect method and a semi-analytical approach for trajectory optimization, some exemplary cases are discussed, such as circle-to-circle Earth-Mars and Earth-Venus transfers or a simplified mission to the asteroid 25143 Itokawa.
The use of advanced and highly engineered membrane films in solar sail design enables the thrust vector to achieve some specific characteristics that are capable of affecting the performance of a ...sail-based spacecraft trajectory in a transfer mission scenario. In this field, the recently proposed diffractive sail uses metamaterial films to coat the very thin sail membrane as a potential and effective (in some mission scenarios) alternative to the more common metallic reflective coating. The purpose of this work is to study the optimal guidance law, as a function of sail pitch angle, of a diffractive sailcraft with a Littrow transmission grating film in a typical two-dimensional heliocentric transfer. In particular, the optimal steering law is obtained through a classical indirect approach, depending on the characteristics of Lawden's primer vector, either in exact (by numerical simulation) or approximate (by analytical means) form. The performance of a diffractive sailcraft with a Littrow transmission grating film is then analyzed in a number of potential mission scenarios such as, for example, a phasing in a circular orbit, an interplanetary transfer between coplanar Keplerian trajectories, a circular orbit flip maneuver, and an escape from the Solar System. Simulation results indicate that this specific diffractive sailcraft is potentially capable of executing a typical solar sail-based mission scenario with a simple steering law.
The presence of plasma waves upstream from the Martian bow shock, with frequencies near the local proton cyclotron frequency in the spacecraft frame, constitutes, in principle, an indirect signature ...for the existence of planetary protons from the ionization of Martian exospheric hydrogen. In this study, we determine the "proton cyclotron wave” (PCW) occurrence rate between October 2014 and February 2020, based on Magnetometer and Solar Wind Ion Analyzer measurements from the Mars Atmosphere and Volatile EvolutioN mission. We characterize its dependence on several wave and solar wind (SW) properties, and solar longitude ranges. We confirm a previously reported long‐term trend with more PCWs near perihelion, likely associated with changes in exospheric hydrogen density. Furthermore, we report for the first time a decrease in median PCW amplitude for each consecutive Martian perihelion. Such variability cannot be attributed to differences in the distribution of SW conditions. This trend could be associated with changes in solar inputs, foreshock effects, and asymmetries due to the SW convective electric field influencing newborn protons. In addition, we observe PCWs more frequently for low to intermediate interplanetary magnetic field (IMF) cone angles, slower SW speeds, and higher SW proton densities. The IMF cone angle preference likely results from the trade‐off between associated linear wave growth rates, wave saturation energies, and pick‐up proton densities. Moreover, the dependencies on SW speed and density indicate the importance of the characteristic SW transit timescale and the charge exchange process coupling SW protons with the hydrogen exosphere.
Key Points
We confirm an annual periodicity of proton cyclotron wave occurrence rate upstream from the Martian bow shock between October 2014 and February 2020
We report a decrease in median wave amplitude for each consecutive Martian perihelion based on available sampling of the Martian upstream region
PCWs occur more frequently near perihelion for low to intermediate interplanetary magnetic field cone angles, slower solar wind speeds and higher solar wind densities
•A combinatorial method composed of analytical design and numerical optimization.•The multi-requirement optimization problem is simplified to single-objective one.•A self-adaptive decision variable ...region adjustment improves computational efficiency.•Optimal LISA formations for different deployment times are investigated.
Space-based gravitational wave (GW) detector such as the LISA (Laser Interferometer Space Antenna) mission requires high-precision and stability of the triangular formation. The dynamic environment of the detectors is complex, the science requirements for the formation are tight, and consequently, design and optimization of this high-standard formation with essentially many decision variables are very challenging. This paper studies the design and optimization of the stable initial formation of the heliocentric GW detector by taking the LISA as an example. The linearization method based on relative orbital elements is used for formation design in the two-body system. Three constraints are presented to reduce the number of decision variables to fourteen. The geometric features of the arm length and breathing angle of the triangular formation and the relative position of LISA to the Earth are analyzed and numerically verified in a high-fidelity dynamic model, from which the relationships of multiple requirements of LISA are studied, and a single index is summarized to simplify the optimization. Sobol sensitivity analysis is used to quantitatively evaluate the sensitivities of the decision variables to the cost function, with which a self-adaptive adjustment algorithm of the region of the variables is presented to improve the computational efficiency. The availability of the method to quickly and precisely find a stable initial formation in an extensive neighborhood of the nominal formation is verified by numerical simulation, where the best solution decreases about 47.54% of the arm length change from the requirement. This study shows that the initial formation should be deployed appropriately away from the Earth, and the gravitations of Venus and Jupiter should be utilized to maintain the formation stability.
•Feasible domain analysis for the heliocentric gravitational-wave detection configuration is performed.•A semi-analytical configuration uncertainty propagation method is proposed.•The bounds of the ...feasible domain are analytically derived.
Long-term stability is vital for a space-based gravitational-wave (GW) observatory, which can be affected by orbit insertion errors. To analyze the effects of orbit insertion errors on the configuration stability of a heliocentric GW observatory and find the feasible domain, a semi-analytical configuration uncertainty propagation-based analysis method is proposed in this paper. First, a state transition tensor (STT) technique is employed to propagate the orbit uncertainties of each spacecraft in the configuration. The semi-analytical configuration uncertainty propagation solution is then developed by combining the STT and a Tayler approximation to the stability index uncertainties with respect to the orbit uncertainties. Using an independently and identically distributed assumption, the stable sets at any specified epoch are analytically derived based on the semi-analytical solution. The feasible domain is obtained by intersecting the stable sets at different epochs. Finally, the proposed method is verified and applied to analyze the feasible domain of the Laser Interferometer Space Antenna (LISA) project. Accuracy analysis shows that the relative errors of the proposed semi-analytical configuration uncertainty propagation solution are less than 0.35% for a 10-years propagation. Feasible domain analysis results show that the standard deviations of the position and velocity insertion errors should be less than 45.22 km and 9.05 mm/s, respectively, to guarantee configuration stability. The proposed method could be useful for configuration design and stability analysis of a future heliocentric GW observatory mission.
The LISA (Laser Interferometer Space Antenna) mission has been selected by the European Space Agency’s Science Programme Committee as the third large-class mission of the Cosmic Vision Programme, ...addressing the science theme of the Gravitational Universe. With a planned launch date in 2034, LISA will be the first ever space-borne Gravitational Wave observatory, relying on laser interferometry between three spacecraft orbiting the Sun in a triangular formation. Airbus is currently leading an industrial Phase A system study on behalf of the European Space Agency. The paper will address the astrodynamics challenges associated with the LISA constellation design, driven by tight requirements on the geometric quality metrics of the near equilateral formation.
Abstract
A current sheet (CS) is the central structure in the disrupting magnetic configuration during solar eruptions. More than 90% of the free magnetic energy (the difference between the energy in ...the nonpotential magnetic field and that in the potential one) stored in the coronal magnetic field beforehand is converted into the heating and kinetic energy of the plasma, as well as accelerating charged particles, by magnetic reconnection occurring in the CS. However, the detailed physical properties and fine structures of the CS are still unknown, since there is no relevant information obtained via in situ detections. The Parker Solar Probe (PSP) may provide us with such information should it traverse a CS in an eruption. The perihelion of PSP’s final orbit is located at about 10 solar radii from the center of the Sun, so it can observe the CS at a very close distance, or even traverse the CS, which would provide us with a unique opportunity to look into the fine properties and structures of the CS, helping to reveal the detailed physics of large-scale reconnection that would have been impossible before. We evaluate the probability that PSP can traverse a CS, and examine the orbit of a PSP-like spacecraft that has the highest probability to traverse a CS.
We address the heliocentric in-orbit repositioning problem of an E-sail-based spacecraft that covers a circular parking orbit of given radius, with the assumption that the propulsive acceleration is ...directed along the Sun-spacecraft line. According to the recent literature, the analysis exploits the possibility of reducing the mathematical problem to the dynamics of an equivalent nonlinear oscillator with a single degree of freedom. The analytical expression of the spacecraft heliocentric trajectory, which is available in polar form when its motion is periodic, is used to obtain approximate relationships among the E-sail performance, the flight time, and the desired phasing angle. The approximate analytical model is validated through numerical simulations, whereas the last part of the paper discusses a comparison with the optimal in-orbit repositioning transfers available in the literature.
•The paper analyzes the heliocentric in-orbit repositioning of an E-sail.•A Sun-facing attitude is assumed in the analysis.•The problem is reduced to the dynamics of an equivalent nonlinear oscillator.•The paper proposes an analytical approximation of the E-sail trajectory.•A comparison with optimal results from the literature is discussed in detail.
We report a comprehensive study of Mars dayglow observations focusing on upper atmospheric structure and seasonal variability. We analyzed 744 vertical brightness profiles comprised of ∼109,300 ...spectra obtained with the Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite. The dayglow emission spectra show features similar to previous UV measurements at Mars. We find a significant drop in thermospheric scale height and temperature between LS = 218° and LS = 337–352°, attributed primarily to the decrease in solar activity and increase in heliocentric distance. We report the detection of a second, low‐altitude peak in the emission profile of OI 297.2 nm, confirmation of the prediction that the absorption of solar Lyman alpha emission is an important energy source there. The
CO2+ UV doublet peak intensity is well correlated with simultaneous observations of solar 17–22 nm irradiance at Mars.
Key Points
Significant drop in thermospheric temperature between two Martian seasons
Detection of second layer of OI 297.2 nm emission below 100 km
Strong correlation between observed mid‐UV dayglow and simultaneously measured EUV flux at Mars
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