Spacecraft Separation Research Articles

Direct In‐Situ Estimates of Energy and Force Balance Associated With Magnetopause Reconnection

AbstractFundamental processes in plasmas act to convert energies into different forms, for example, electromagnetic, kinetic and thermal. Direct derivation from the Vlasov‐Maxwell equation yields sets of equations that describe the temporal evolution of magnetic, kinetic and internal energies in either the monofluid or multifluid frameworks. In this work, we focus on the main terms affecting the changes in kinetic energy. These are pressure‐gradient‐related terms and electromagnetic terms. The former account for plasma acceleration/deceleration from a pressure gradient, while the latter from an electric field. Although limited spatial and temporal deviations are expected, a statistical balance between these terms is fundamental to ensure the overall conservation of energy and momentum. We use in‐situ observations from the Magnetospheric MultiScale (MMS) mission to study the relationship between these terms. We perform a statistical analysis of those parameters in the context of magnetic reconnection by focusing on small‐scale Electron Diffusion Regions and large‐scale Flux Transfer Events. The analysis reveals a correlation between the two terms in the monofluid force balance, and in the ion force and energy balance. However, the expected relationship cannot be verified from electron measurements. Generally, the pressure‐gradient‐related terms are smaller than their electromagnetic counterparts. We perform an error analysis to quantify the expected underestimation of gradient values as a function of the spacecraft separation compared to the gradient scale. Our findings highlight that MMS is capable of capturing energy and force balance for the ion fluid, but that care should be taken for energy conversion terms based on electron pressure gradients.

Force-transmission characteristics of a cable-driven mechanism with high initial velocity for spacecraft separation in ground tests

Force-transmission characteristics of a cable-driven mechanism with high initial velocity for spacecraft separation in ground tests

ADRC-based compound control strategy for spacecraft multi-body separation

This paper proposes a compound control method for spacecraft multi-body separation which is based on active disturbance rejection control (ADRC), aiming to address the problems of decreased control accuracy and collisions caused by model uncertainty and vacuum plume disturbance. By comprehensively analyzing the positional relationship and attitude between each separator, the compound flight controller reconstructs the desired attitude of each separator based on artificial potential field method and realizes the tracking of the desired attitudes through ADRC. The closed-loop stability of the system is analyzed, and it is proved that the algorithm is stable in the sense of Lyapunov. The simulation results showed that the multi-body separation compound control strategy based ADRC has more advantages in robustness and security. This method is simple to implement, and it has value of reference and application in spacecraft multi-body separation.

Mesoscale Structure and Properties of the Terrestrial Magnetotail Plasma Sheet From the Magnetospheric Multiscale Mission

AbstractUsing Magnetospheric Multiscale mission (MMS) orbits in the Earth's magnetotail from 2017 to 2020, plasma conditions and the 3D spatial structure of inner‐magnetotail plasma environments (with a focus on the plasma sheet (PS)) are studied with different approaches. Threshold conditions for distinguishing the PS, PS boundary layers, and lobes are derived from the statistical properties of background plasma parameters. Our results support previous studies that employed similar methods using Cluster data. However, stronger currents are observed in both the lobes and PS, likely due to the smaller spacecraft separation (≲70 km) that can resolve thin electron‐scale currents. Threshold conditions are used together with magnetic field and electric field measurements to image the spatial structure of the PS. Results are in good agreement with a global neutral sheet model based on solar wind conditions and magnetospheric configurations. Furthermore, the Earth's dipole tilts toward the Sun around June solstice, which warps the magnetotail as much as ∼2–4 RE in Z geocentric solar magnetospheric. This warping effect is relaxed toward September equinox. Consequently, as MMS travels through the magnetotail from dawn to dusk during this period, there is an apparent dawn‐dusk asymmetry in plasma conditions between June and September. Kink‐like flapping waves and interplanetary magnetic field twisting are other mesoscale processes attributed with a few RE of flaring near the flanks. These findings reveal important insights into the mesoscale structure and dynamics of the magnetotail.

Bayesian time delay interferometry for orbiting LISA: Accounting for the time dependence of spacecraft separations

Bayesian time delay interferometry for orbiting LISA: Accounting for the time dependence of spacecraft separations

Особливості використання гуми як конструкційного матеріалу під час створення вузлів стикування систем термостатування

Explosive bolts are widely used as actuating devices in the spacecraft separation systems. Explosive bolt body is divided into parts as a result of engagement of the pyromixture placed inside. Activated explosive bolts have negative mechanical effect on the interface elements and sensitive electronic devices installed nearby owing to explosive behavior of the pyromixture combustion, generating shock front with high pressure and velocities, impacts and collisions of the structural units. Cumulative effect of the above factors on the separated objects is called pyroshock. For separation systems with increased requirements to external actions and cleanliness, authors developed a shear explosive bolt or pyrobolt, divided into parts, cutting the body walls in segments, which are set in motion by action of the pressure of gases, released as a result of pyrocartridge activation. The basic sources of pyroshock for these shear explosive bolts with segments are: combustion of pyromixture, internal impacts of structural units against the bolt body; cutting of body wall in segments, release of preliminary deformed interface after activation. Structural solutions are presented to reduce the pyroshock per each of the components. Vibration impulsive loading during pyromixture combustion is reduced by optimization of explosive quantity, finding its minimum to provide the reliable activation of the device. To reduce the impact on the explosive bolt elements and shock front interface the rubber gasket is installed in the path of shock wave distribution, partially disseminating and absorbing its kinetic energy. Damper, made of easily deformable aluminum alloy, is also installed to decrease the internal impact of the rod against the explosive bolt body. Functional testing of the device, using the pendulum suspension and measuring separation speed and vibration impulsive loading, showed that body parts of the shear explosive bolt with segments are separated without significant impact loads and discharge of high-temperature gases and debris, providing reliable separation of compartments and units without damaging the sensitive equipment. Obtained values of the mechanical momentum, I = 0,4÷0,7 N•s and shock load spectrum – g-load 1950 g at the frequency range up to 5000 Hz, meet the up-to-date requirements to pyrotechnical devices. Key words: explosive bolt, pyroshock, shock wave, pyrocartridge, high-temperature gases, damper.

Self-Docking Characteristics and Sliding Mode Control on Space Electromagnetic Docking Mechanism

Electromagnetic docking technology can realize the flexible docking and safe separation of spacecraft, and presents broad application prospects. However, an electromagnetic force with nonlinearity and uncertainty properties increases the difficulties of the electromagnetic docking control. In this work, the magnetic dipole far-field model of a single coil has been established by simplifying the electromagnetic docking device. Afterward, the electromagnetic force and electromagnetic torque models were obtained during space electromagnetic docking. The space electromagnetic docking dynamics model was established by analyzing the influences of disturbance force and disturbance torque caused by a geomagnetic field. According to the one-dimensional docking reference trajectory, the sliding mode variable structure controllers based on exponential reaching law were proposed and verified. The quasi-sliding mode control method has been adopted to solve the chattering problem in sliding mode variable structure control. The simulation results show that it is necessary to design and add an electromagnetic controller to achieve flexible docking. The sliding mode variable structure controller based on quasi sliding mode can realize one-dimensional electromagnetic flexible docking, and have made good tracking effect on the reference trajectory. Compared with the control method based on exponential reaching law, it can reduce the chattering phenomenon in the control process. The sliding mode variable structure control strategy based on quasi sliding mode presented good robustness. Therefore, it can provide theoretical guidance and control reference for the flexible docking process between electromagnetic satellites.

Observations of Waves and Structures by Frequency–Wavenumber Spectrum in Solar Wind Turbulence

A well-known shortcoming of single-spacecraft spectral analysis is that only the 1D wavenumber spectrum can be observed, assuming the characteristic wave propagation speed is much smaller than the solar wind flow speed. This limitation has motivated an extended debate about whether fluctuations observed in the solar wind are waves or structures. Multispacecraft analysis techniques can be used to calculate the wavevector independent of the observed frequency, thus allowing one to study the frequency–wavenumber spectrum of turbulence directly. The dispersion relation for waves can be identified, which distinguishes them from nonpropagating structures. We use magnetic field data from the four Magnetospheric Multiscale (MMS) spacecraft to measure the frequency–wavenumber spectrum of solar wind turbulence based on the k-filtering and phase differencing techniques. Both techniques have been used successfully in the past for the Earth’s magnetosphere, although applications to solar wind turbulence have been limited. We conclude that the solar wind turbulence intervals observed by MMS show features of nonpropagating structures that are associated with frequencies close to zero in the plasma rest frame. However, there is no clear evidence of propagating Alfvén waves that have a nonzero rest-frame frequency. The lack of waves may be due to instrument noise and spacecraft separation. Our results support the idea of turbulence dominated by quasi-2D structures.

Orientation of the stream interface in CIRs

Corotating Interaction Regions (CIRs) are complex structures in the Heliosphere that arise from the interaction of fast and slow solar wind streams. The interface between fast and slow solar wind is called the stream interface, which often has considerable north-south tilt. We apply a sliding window correlation method on multi-spacecraft data in order to obtain the time delay between the spacecraft. Using these time delays and in-situ solar wind velocity measurements, we can shift the positions of two spacecraft, and, together with the position of the reference spacecraft, we can reconstruct the spatial orientation of the stream interface. We examined four CIRs from two different solar sources at the beginning of 2007 using ACE, WIND, and STEREO-A spacecraft data. The gradually increasing distance between STEREO-A and the other spacecraft provides an opportunity to determine the effects of spacecraft separation on the quality of the results. In three out of the four events, the determined planes generally follow the Parker spiral in the ecliptic, their off-ecliptic tilt is determined by the position of the source of the high-speed stream. For the fourth event, STEREO-A was probably too far away for this method to be successfully applied.

Field-aligned scale length of depleted structures associated with post-sunset equatorial plasma bubbles

In this study we make use of the Swarm counter-rotation constellation for estimating the typical scale length of the post-sunset equatorial plasma bubbles (EPBs) along fluxtubes. The close approaches between Swarm spacecraft near the equator occurred in September and October 2021, covering the magnetic local time from 19:00 to 23:00, which is favorable for the occurrence of EPBs. It is the first time to show the quasi-simultaneously samplings by Swarm A/C and B of the same fluxtube but at different altitude. The observations frequently reveal plasma density depletions only at one spacecraft altitude, confirming that EPBs extend only over finite parts of the fluxtube. Based on a statistical analysis of double and single EPB detections on the same fluxtube, our results imply the typical field-aligned scale length of the depletion structures associated with EPBs of the order of 550 km. Our detections are from the lower part of the depleted fluxtubes, and they coincide well with the latitudes of the equatorial ionization anomaly. In the upper part of the fluxtube near the magnetic equator, our estimation technique does not work well because of too large field-aligned spacecraft separation of the Swarm satellites.

Regioisomeric N–C functionalization of an asymmetric N-rich framework: a promising pathway to heat-resistant energetic materials

Energetic materials with high decomposition temperatures have wide applications in extreme environments such as spacecraft separation systems and drilling engineering.

DRAFT: A Method for Wave Analyses in Space Plasmas

In this study, we apply a method for wave analyses in space plasmas, to better understand the nature of plasma waves and turbulence. Such a method is based on four-spacecraft measurements of magnetic fields or electric fields; it calculates the phase velocity of each single-frequency wave by using the timing analysis, then divides the wave frequency by the phase velocity to obtain the wavevector, and finally solves the dispersion relation (ω–k relation) by considering all frequency channels, and thus is termed Dispersion RelAtion From Timing (DRAFT). Quantitatively, we define three parameters, match of amplitude (MOA), ratio of half-wavelength to spacecraft separation (λ/2R sc), and correlation coefficient (CC), to judge the reliability of this method. We illustrate the usage of this method and validate the efficiency of the three parameters by analyzing the Magnetospheric Multiscale data. We find that the DRAFT results are generally accurate under conditions MOA > 0.5, λ/2R sc > 1, CC > 0.8. As a support, we compare our method with the previous methods such as Means and singular value decomposition (SVD). We find that if the three criteria (MOA, λ/2R sc, CC) are satisfied, the DRAFT, Means, and SVD are consistent in resolving the wave normal angle. Such a comparison robustly validates the reliability and rationality of the DRAFT method. Using DRAFT, we successfully solve the dispersion relation of an Alfvén wave in Earth’s magnetosheath and obtain its three-dimensional K -spectrum. Our method should be useful to study the low-frequency waves and weak turbulence in space plasmas.

New Insights into the First Two PSP Solar Encounters Enabled by Modeling Analysis with ADAPT-WSA

Parker Solar Probe's (PSP's) unique orbital path allows us to observe the solar wind closer to the Sun than ever before. Essential to advancing our knowledge of solar wind and energetic particle formation is identifying the sources of PSP observations. We report on results for the first two PSP solar encounters derived using the Wang–Sheeley–Arge (WSA) model driven by Air Force Data Assimilative Photospheric Flux Transport (ADAPT) model maps. We derive the coronal magnetic field and the 1 R ⊙ source regions of the PSP-observed solar wind. We validate our results with the solar wind speed and magnetic polarity observed at PSP. When modeling results are very reliable, we derive time series of model-derived spacecraft separation from the heliospheric current sheet, magnetic expansion factor, coronal hole boundary distance, and photospheric field strength along the field lines estimated to be connected to the spacecraft. We present new results for Encounter 1, which show time evolution of the far-side mid-latitude coronal hole that PSP corotates with. We discuss how this evolution coincides with solar wind speed, density, and temperature observed at the spacecraft. During Encounter 2, a new active region emerges on the solar far side, making it difficult to model. We show that ADAPT-WSA output agrees well with PSP observations once this active region rotates onto the near side, allowing us to reliably estimate the solar wind sources retrospectively for most of the encounter. We close with ways in which coronal modeling enables scientific interpretation of these encounters that would otherwise not have been possible.

The Transmission of ULF Waves From the Solar Wind to the Magnetosphere: An Analysis of Some Critical Aspects

Several critical aspects may influence the analysis of the relationship between the solar wind (SW) and magnetospheric fluctuations, for example, the characteristics and frequency of SW fluctuations that are expected to impinge the magnetosphere may not be the same when they are observed by spacecraft located at different places in front of the magnetosphere; similarly, the choice of analytical methods adopted for the spectral analysis might influence the frequency estimate (as well as the wave identification itself) both in the SW and magnetosphere. Focusing our attention on these aspects, we present an analysis of SW compressional fluctuations (f ≈ 1–5 mHz), following two interplanetary shocks observed by two interplanetary spacecraft, regarded as two different situations in terms of spacecraft separation and distance from the magnetosphere. Our results show that some differences in the characteristics of SW fluctuations emerge when the same stream is observed at different places and confirm the critical role of analytical methods in determining fluctuation characteristics. We compared aspects of SW fluctuations with those of magnetospheric fluctuations following the sudden impulses due to the impact of interplanetary shocks. For this scope, we examined observations by two satellites at geostationary orbit and at several ground-based stations. We found that the magnetospheric fluctuations were related to compressional SW fluctuations approximately at the same frequencies, with no evidence for wave activity of internal origin or directly driven by the shock impact.

Analysis of Cable-Force Transmission Characteristics and Disturbing Force/Moment of High-Acceleration Cable-Driven Parallel Mechanism

During the landing process of a probe, the backshell separation stage is full of uncertainty and risk. To mitigate this, it is necessary to simulate spacecraft separation prior to launch to verify safety and performance. A high-acceleration cable-driven parallel mechanism is normally used to simulate the force state required for the backshell to separate. Unfortunately, little attention has been paid to research the cable force on the end-effector, especially under high acceleration. In this article, a dynamic model of the cable-force transmission is proposed. The influences of disturbing force/moment on the position and orientation of the end-effector and axial force are analyzed. Indices for evaluating the performance of the cable-force transmissions are proposed. The factors affecting the performance are also explored. Finally, the experimental results are used to verify the correctness of the proposed dynamic model. The deviation caused by the disturbing force/moment is basically consistent with the desired deviation. The increase in the disturbing force/moment correspondingly reduces the resultant force of the end-effector. A series of experiments provide guidance and a theoretical basis for a ground simulation experiment of spacecraft separation.

Spatial evolution of magnetic reconnection diffusion region structures with distance from the X-line

We report Magnetospheric Multiscale four-spacecraft observations of a thin reconnecting current sheet with weakly asymmetric inflow conditions and a guide field of approximately twice the reconnecting magnetic field. The event was observed at the interface of interlinked magnetic field lines at the flank magnetopause when the maximum spacecraft separation was 370 km and the spacecraft covered ∼1.7 ion inertial lengths (di) in the reconnection outflow direction. The ion-scale spacecraft separation made it possible to observe the transition from electron-only super ion-Alfvénic outflow near the electron diffusion region (EDR) to the emergence of sub-Alfvénic ion outflow in the ion diffusion region (IDR). The EDR to IDR evolution over a distance less than 2 di also shows the transition from a near-linear reconnecting magnetic field reversal to a more bifurcated current sheet as well as significant decreases in the parallel electric field and dissipation. Both the ion and electron heating in this diffusion region event were similar to the previously reported heating in the far downstream exhausts. The dimensionless reconnection rate, obtained four different ways, was in the range of 0.13–0.27. This event reveals the rapid spatial evolution of the plasma and electromagnetic fields through the EDR to IDR transition region.

Curlometer Technique and Applications

AbstractWe review the range of applications and use of the curlometer, initially developed to analyze Cluster multi‐spacecraft magnetic field data; but more recently adapted to other arrays of spacecraft flying in formation, such as MMS small‐scale, 4‐spacecraft configurations; THEMIS close constellations of 3–5 spacecraft, and Swarm 2–3 spacecraft configurations. Although magnetic gradients require knowledge of spacecraft separations and the magnetic field, the structure of the electric current density (for example, its relative spatial scale), and any temporal evolution, limits measurement accuracy. Nevertheless, in many magnetospheric regions the curlometer is reliable (within certain limits), particularly under conditions of time stationarity, or with supporting information on morphology (for example, when the geometry of the large scale structure is expected). A number of large‐scale regions have been covered, such as: the cross‐tail current sheet, ring current, the current layer at the magnetopause and field‐aligned currents. Transient and smaller scale current structures (e.g., reconnected flux tube or dipolarisation fronts) and energy transfer processes. The method is able to provide estimates of single components of the vector current density, even if there are only two or three satellites flying in formation, within the current region, as can be the case when there is a highly irregular spacecraft configuration. The computation of magnetic field gradients and topology in general includes magnetic rotation analysis and various least squares approaches, as well as the curlometer, and indeed the added inclusion of plasma measurements and the extension to larger arrays of spacecraft have recently been considered.

Bayesian time delay interferometry

Laser frequency noise (LFN) is the dominant source of noise expected in the Laser Interferometer Space Antenna (LISA) mission, at $\sim$7 orders of magnitude greater than the typical signal expected from gravitational waves (GWs). Time-delay interferometry (TDI) suppresses LFN to an acceptable level by linearly combining measurements from individual spacecraft delayed by durations that correspond to their relative separations. Knowledge of the delay durations is crucial for TDI effectiveness. The work reported here extends upon previous studies using data-driven methods for inferring the delays during the post-processing of raw phasemeter data, also known as TDI ranging (TDIR). Our TDIR analysis uses Bayesian methods designed to ultimately be included in the LISA data model as part of a "Global Fit" analysis pipeline. Including TDIR as part of the Global Fit produces GW inferences which are marginalized over uncertainty in the spacecraft separations and allows for independent estimation of the spacecraft orbits. We demonstrate Markov Chain Monte Carlo (MCMC) inferences of the six time-independent delays required in the rigidly rotating approximation of the spacecraft configuration (TDI 1.5) using simulated data. The MCMC uses fractional delay interpolation (FDI) to digitally delay the raw phase meter data, and we study the sensitivity of the analysis to the filter length. Varying levels of complexity in the noise covariance matrix are also examined. Delay estimations are found to result in LFN suppression well below the level of secondary noises and constraints on the armlengths to $\mathcal{O}(30)\ {\rm cm}$ over the ${\sim}2.5\ {\rm Gm}$ baseline.

Simulation analysis of liquid sloshing separation in spacecraft with tank based on SPH method

<p indent=0mm>The separation of spacecraft in orbit is based on multibody dynamics in a space microgravity environment, while liquid sloshing is studied based on complex nonlinear dynamics. In this study, the smoothed particle hydrodynamics (SPH) method was used to simulate liquid sloshing with a free surface in a spacecraft tank, and the separation dynamic model of the spacecraft and liquid fuel was established. Through the analysis of spacecraft separation dynamics and fluid–structure coupling dynamics, the problem of the influence of sloshing of the liquid in the fuel tank on spacecraft separation attitude was solved. The interference force and torque of liquid sloshing on the spacecraft can be obtained from the model fluid–structure coupling dynamics calculation. The separation attitude of spacecraft with liquid sloshing in the tank is different from that based on a rigid body assumption. The liquid levels affect the calculation results of spacecraft separation attitude, interference force, and torque. The analysis results provide a reference for the optimization design and separation safety design of the spring separation mechanism and improve the reliability of spacecraft attitude control design.

Cluster After 20 Years of Operations: Science Highlights and Technical Challenges

AbstractThe Cluster mission was the first constellation using four identical spacecraft to study Sun‐Earth connection plasma processes. Using four spacecraft in a tetrahedron shape, it could measure, for the first time, 3D quantities such as electrical currents, plasma gradients or divergence of the electron pressure tensor and 3D structures such as boundaries, surface waves or vortices. Launched in pairs in July and August 2000, on two Soyuz rockets from Baikonur, the four spacecraft have been collecting data continuously for more than 20 years. The mission faced many challenges during the years of operations as some spacecraft subsystems had a lifetime of a few years beyond the initial two‐year mission. The major one was to operate without functioning batteries and to successfully pass short and long eclipses, up to 3 h long, without damaging the on‐board computers and transmitters and without freezing the fuel. More than 1,000 eclipses have been successfully passed since 2010 using a specially made procedure which switches off the complete spacecraft before entering into eclipse and switches it on when the Sun is again illuminating the solar panels. During 20 years, many discoveries and science results have been published in more than 2,700 scientific papers. A few highlights are presented here, focusing on how varying the spacecraft separation was essential to achieve the science goals of the mission. The Cluster Science Data System and the Cluster archive allows public access to all science data as well as spacecraft ancillary data.