Orbits Of Objects Research Articles

Uncertainty quantification techniques for data-driven space weather modeling: thermospheric density application

Machine learning (ML) has been applied to space weather problems with increasing frequency in recent years, driven by an influx of in-situ measurements and a desire to improve modeling and forecasting capabilities throughout the field. Space weather originates from solar perturbations and is comprised of the resulting complex variations they cause within the numerous systems between the Sun and Earth. These systems are often tightly coupled and not well understood. This creates a need for skillful models with knowledge about the confidence of their predictions. One example of such a dynamical system highly impacted by space weather is the thermosphere, the neutral region of Earth’s upper atmosphere. Our inability to forecast it has severe repercussions in the context of satellite drag and computation of probability of collision between two space objects in low Earth orbit (LEO) for decision making in space operations. Even with (assumed) perfect forecast of model drivers, our incomplete knowledge of the system results in often inaccurate thermospheric neutral mass density predictions. Continuing efforts are being made to improve model accuracy, but density models rarely provide estimates of confidence in predictions. In this work, we propose two techniques to develop nonlinear ML regression models to predict thermospheric density while providing robust and reliable uncertainty estimates: Monte Carlo (MC) dropout and direct prediction of the probability distribution, both using the negative logarithm of predictive density (NLPD) loss function. We show the performance capabilities for models trained on both local and global datasets. We show that the NLPD loss provides similar results for both techniques but the direct probability distribution prediction method has a much lower computational cost. For the global model regressed on the Space Environment Technologies High Accuracy Satellite Drag Model (HASDM) density database, we achieve errors of approximately 11% on independent test data with well-calibrated uncertainty estimates. Using an in-situ CHAllenging Minisatellite Payload (CHAMP) density dataset, models developed using both techniques provide test error on the order of 13%. The CHAMP models—on validation and test data—are within 2% of perfect calibration for the twenty prediction intervals tested. We show that this model can also be used to obtain global density predictions with uncertainties at a given epoch.

Is the Black-widow Pulsar PSR J1555–2908 in a Hierarchical Triple System?

The 559 Hz black-widow pulsar PSR J1555−2908, originally discovered in radio, is also a bright gamma-ray pulsar. Timing its pulsations using 12 yr of Fermi-Large Area Telescope gamma-ray data reveals long-term variations in its spin frequency that are much larger than is observed from other millisecond pulsars. While this variability in the pulsar rotation rate could be intrinsic “timing noise,” here we consider an alternative explanation: the variations arise from the presence of a very-low-mass third object in a wide multiyear orbit around the neutron star and its low-mass companion. With current data, this hierarchical-triple-system model describes the pulsar’s rotation slightly more accurately than the best-fitting timing noise model. Future observations will show if this alternative explanation is correct.

Optical observations of the artificial objects at the Lviv Astronomical Observatory

Space debris is becoming an increasing threat to near space services, including satellite communications, the launching of new satellites, as well as navigation and timekeeping programs. It affects even observations of the Earth. As space around us becomes more congested, the need to track space objects and provide information about space activities is becoming increasingly critical and urgent in helping to prevent collisions or damage caused by space debris. Among the methods of tracking artificial objects are optical methods, which can provide information about the position of the selected object (positional observations), distance to the object (laser observations), as well as about the behavior of the object in orbit and its shape (photometric observations). The Astronomical Observatory of Lviv National University is equipped with a special hardware complex and software for the implementation of observations of artificial objects and can provide relevant information.

Analysis of the orbital evolution of space debris using a solar sail and natural forces

Since the launch of the first artificial satellite around the Earth up to the present date, various non-functional objects are orbiting the Earth, such as deactivated satellites, satellite components, rocket bodies, among others. These objects can collide with operational satellites or other debris, generating a cloud of smaller particles. Space agencies are concerned about the current scenario of the space environment. If we continue as we are the number of objects in orbit will make it difficult to operate safely in the space environment. So space exploration may become unsustainable (ESA (2020)). In this work, the orbital evolution of these objects that are located in the geostationary orbit (GEO) is analyzed. In the mathematical model we consider the main disturbing forces, such as the direct solar radiation pressure (SRP), the perturbation of the third body (Sun and Moon) and the Earth oblateness. The SRP is the most relevant perturbation for objects with larger area-mass ratio. Knowing this, the possibility of using a solar sail is considered to help to clean the space environment. The main natural environmental perturbations that act in the orbit of the debris are considered in the dynamics. Such forces acting in the solar sail can force the growth of the eccentricity of these objects in the GEO orbit. Several authors have presented models of the solar radiation pressure considering the single-averaged model. But, doing a literature research, we found that the authors consider the Earth around the Sun in a circular and inclined orbit. Our contribution to the SRP model is in developing a different approach from other authors, where we consider the Sun in an elliptical and inclined orbit, which is valid for other bodies in the solar system when the eccentricity cannot be neglected. The expression of the SRP is developed up to the second order. We found that the first-order term is much superior to the second-order term, so the quadrupole term can be neglected. Another contribution is the approach to identify the initial conditions of the perigee argument (g) and the longitude of the ascending node (h), where some values of the (g,h) plane contribute to amplify the eccentricity growth. In the numerical simulations we consider real data from space debris removed from the site Stuff in Space. The solar sail helps to clean up the space environment using a propulsion system that uses the Sun itself, a clean and abundant energy source, unlike chemical propellants, to contribute to the sustainability of space exploration.

Space Debris Mitigation Using Drag Augmentation Device: A Review

Abstract: The commercialization of space has resulted in a significant increase in the frequency of spacecraft, which is adding to the already large number of objects in orbit. Therefore, future and present missions are at risk from space debris. Most of these spacecraft in orbit have very limited means of mitigation control systems. As a result, certain international regulations are imposed to obtain a license for a spacecraft for launch purposes. The necessity of a feasible debris mitigation technique enables future space missions to be safe and sustainable. This review sheds light on the drag augmentation devices such as dragsail, which can provide an effective means for accelerating the deorbiting process during the EOL phase, making space safe and sustainable without the risk of space debris. Keywords: Dragsail, Ballistic coefficient, Deorbit duration, Space debris, Low Earth Orbit

Active Control Loop of the BOROWIEC SLR Space Debris Tracking System.

The task of tracking cooperative satellites equipped with laser retroreflectors, by means of Satellite Laser Ranging (SLR), is an issue well described in the literature. The follow-up movement of the ground-based transceiver telescope behind an orbital object is based on the positional ephemeris data. The problem of controlling the follow-up motion of the telescope’s mount mostly in the configuration in this case boils down to the interpolation of the positional ephemeris data of the orbital object, which is the information input vector for the motion control system of the orthogonal and non-coupled axes of the propulsion system. In the case of tracking and determining the position of uncooperative objects (not equipped with retroreflectors), for which we can include rocket bodies and fragmentary elements, the task of keeping track of them becomes complex. The positional uncertainty of the ephemeris of uncooperative objects obtained mainly by means of survey radar acquisition requires the use of innovative solutions and complex control systems that enable the effective implementation of the tracking process. This paper presents innovative methods for the active control loop used in the SLR technique, consisting of dynamic motion corrections based on the passive optical acquisition with object recognition and analysis of the photon trace scattered from an orbital object.

Initial Orbit Determination Method for Low Earth Orbit Objects Using Too-Short Arc Based on Bistatic Radar

The problem of initial orbit determination (IOD) for low Earth orbit (LEO) objects using bistatic radar too-short arc (TSA) observations is addressed. For TSA observations, the traditional IOD methods suffer low accuracy. For LEO objects with stable attitude, the high order kinematic parameters can be obtained from the time derivatives of the radar echo phase. In this paper, we propose an analytical IOD method using bistatic radar TSA observations, which contain the position measurements (bistatic range, azimuth angle, and elevation angle) and the high order kinematic measurements (bistatic velocity, acceleration, and jerk). As the undetermined target state variables constitute a complex system of equations that can only be solved iteratively, we define an auxiliary coordinate system based on the bistatic geometry to help reduce the equations to one unary quartic equation. Further, we derive closed-form expressions of the orbital state. The performance of the proposed method is evaluated using linearization approximations. Numerical simulations are carried out for several typical LEO observation scenarios to demonstrate the performance of the proposed method.

Исследование выносливости сплава АМг6 при циклическом объемном температурном деформировании

Theoretical studies of the endurance of an aviation alloy of AMg6 type during its long-term cyclic volumetric temperature deformation beyond the limits of Hooke's law have been carried out. A technique has been developed for assessing the endurance of aviation alloys in cyclic volumetric temperature deformation taking into account the presence of cavities (cracks) based on bringing the cyclic volumetric temperature deformation conditions to the conditions of standard mechanical testing of samples. According to the developed method, a preliminary assessment of the endurance of the aviation alloy of AMg6 type with a workhardened and annealed surface is carried out using the available limited base of empirical data obtained on the basis of standard mechanical tests of experimental samples. The effect of the initial length of a crack in experimental samples on the endurance of the experimental samples, at which its uncontrolled growth is possible during cyclic volumetric temperature deformation, is assessed. A comparative analysis of the calculated endurance of the experimental samples with the actual endurance of the structural material (hard worked alloy AMg6) of a real orbital object such as the «Zarya» module of the international space station shows a discrepancy of no more than 12,5 %.

Relativistic hydrodynamical simulations of the effects of the stellar wind and the orbit on high-mass microquasar jets

ABSTRACT High-mass microquasar jets, produced in an accreting compact object in orbit around a massive star, must cross a region filled with stellar wind. The combined effects of the wind and orbital motion can strongly affect the jet properties on binary scales and beyond. The study of such effects can shed light on how high-mass microquasar jets propagate and terminate in the interstellar medium. We study for the first time, using relativistic hydrodynamical simulations, the combined impact of the stellar wind and orbital motion on the properties of high-mass microquasar jets on binary scales and beyond. We have performed 3-dimensional relativistic hydrodynamic simulations, using the PLUTO code, of a microquasar scenario in which a strong weakly relativistic wind from a star interacts with a relativistic jet under the effect of the binary orbital motion. The parameters of the orbit are chosen such that the results can provide insight on the jet-wind interaction in compact systems like for instance Cyg X-1 or Cyg X-3. The wind and jet momentum rates are set to values that may be realistic for these sources and lead to moderate jet bending, which together with the close orbit and jet instabilities could trigger significant jet precession and disruption. For high-mass microquasars with orbit size a ∼ 0.1 AU, and (relativistic) jet power $L_j\sim 10^{37}(\dot{M}_w/10^{-6}\, {\rm M}_\odot \, {\rm yr}^{-1})$ erg s−1, where $\dot{M}_w$ is the stellar wind mass rate, the combined effects of the stellar wind and orbital motion can induce relativistic jet disruption on scales ∼1 AU.

Space debris in low earth orbits region: Formation and reduction process analysis in past decade

The paper considers main features of spacecraft launch traffic, break-up events in orbit, re-entry of space objects from low Earth orbits region (altitude up to 2000 km above the Earth's surface) for the period from 2010 to mid-2021. Conclusions are drawn regarding to main regularities of processes of increasing and decreasing the number of space objects in orbit. Statistical models for predicting space debris based on analyzed data have been developed.

MONITORING THE ARTIFICIAL SPACE OBJECTS WITH UKRAINIAN NETWORK OF OPTICAL STATIONS

The article describes the successes and challenges of the Ukrainian network of optical stations (UMOS) in recent years in the field of astrometric observations of artificial space objects both in low-Earth orbit (LEO) and geostationary Earth orbit (GEO). UMOS was established in 2012 as a joint partnership of organizations interested in satellite observations for scientific purposes and practical near Earth space monitoring. The main purpose of the UMOS has been (and still is) to combine scientific and technical means with regular optical (positional and / or non-positional) observation. The short list of equipment of the UMOS members are given in the tables. The programs for observations, used methods and obtained results are described in the paper. In conclusion, the advantages of observations of artificial space objects by means of a network are summarized. The experience of UMOS and main results obtained by UMOS can be considered as the first step to create the SSA system of Ukraine.

Simulation and Uncertainty Quantification of Electron Beams in Active Spacecraft Charging Scenarios

Novel active sensing methods have been recently proposed to measure the electrostatic potential of noncooperative objects in geosynchronous equatorial orbit and deep space. Such approaches make use of electron beams to excite the emission of secondary electrons and X-rays and infer properties of the emitting surface. However, the detectability of secondary electrons is severely complicated in the presence of complex charged bodies, making computationally efficient simulation frameworks necessary for in situ potential estimation. The purpose of this paper is twofold: firstly, to introduce and test a quasi-analytical, uncoupled, and computationally efficient electron beam expansion and deflection model for active charging applications; and secondly, to characterize the uncertainty in the beam–target intersection properties, which condition the measurement of secondary electrons. The results show that a combination of secondary electrons and X-ray methods is highly desirable to yield a robust and accurate measure of the potential of a target spacecraft.

Influence of Sustainable Development of Space Activities on Earth Ecology

In the age of New Space, faces the global problem of orbit space constraint. Sustainable development of space activities will be possible only when space users implement technologies and practices suitable to avoid accumulating objects in orbit. Artificial debris in orbital space has reached catastrophic proportions. This harm the Earth’s ecology leading to increased steps to transform a planet that is unsuitable for life. Based on the fractal analysis, the graphic interpretation of the components of SWOT-analysis of development of the rocket and space industry is built. It is found that the weak side and threat to the activities of the aerospace industry is the insufficient funding of implemented projects and inefficient distribution of finances between its components: science and production. It is proposed to use blockchain technology as an effective tool for the cybersecurity of space objects. The ecological risks from space activities that affect the Earth’s ecology are analyzed. It is proven that the prevention of severe environmental consequences and minimization of the negative impact of the above threats require the introduction of environmental management systems in space activities.

Extreme mass-ratio inspirals around a spinning horizonless compact object

Extreme mass-ratio inspirals (EMRIs) detectable by the Laser Interferometer Space Antenna are unique probes of the nature of supermassive compact objects. We compute the gravitational-wave signal emitted by a stellar-mass compact object in a circular equatorial orbit around a Kerr-like horizonless supermassive object defined by an effective radius and a reflectivity coefficient. The Teukolsky equations are solved consistently with suitable (frequency-dependent) boundary conditions, and the modified energy and angular-momentum fluxes are used to evolve the orbital parameters adiabatically. The gravitational fluxes have resonances corresponding to the low-frequency quasinormal modes of the central object, which can contribute significantly to the gravitational-wave phase. Overall, the absence of a classical event horizon in the central object can affect the gravitational-wave signal dramatically, with deviations even larger than those previously estimated by a model-independent analysis of the tidal heating. We estimate that EMRIs could potentially place the most stringent constraint on the reflectivity of supermassive compact objects at the remarkable level of $\mathcal{O}({10}^{\ensuremath{-}6})%$ and would allow one to constrain various models which are not ruled out by the ergoregion instability. In particular, an EMRI detection could allow one to rule out (or provide evidence for) signatures of quantum black-hole horizons with Boltzmann reflectivity. Our results provide motivation for performing rigorous parameter estimation to assess the detectability of these effects.

Short-Arc Association and Orbit Determination for New GEO Objects with Space-Based Optical Surveillance

For Geosynchronous Earth Orbit (GEO) objects, space-based optical surveillance has advantages over regional ground surveillance in terms of both the timeliness and space coverage. However, space-based optical surveillance may only collect sparse and short orbit arcs, and thus make the autonomous arc association and orbit determination a challenge for new GEO objects without a priori orbit information. In this paper, a three-step approach tackling these two critical problems is proposed. First, under the near-circular orbit assumption, a multi-point optimal initial orbit determination (IOD) method is developed to improve the IOD convergence rate and the accuracy of the IOD solution with angles-only observations over a short arc. Second, the Lambert equation is applied to associate two independent short arcs in an attempt to improve accuracy of the single-arc IOD semi-major axis (SMA) with the use of virtual ranges between the optical sensor and GEO object. The key idea in the second step is to generate accurate ranges at observation epochs, which, along with the real angle data, are then used to achieve much improved SMA accuracy. The third step is basically the repeated application of the second step to three or more arcs. The high success rate of arc associations and accurate orbit determination using the proposed approach are demonstrated with simulated space-based angle data over short arcs, each being only 3 min. The results show that the proposed approach is able to determine the orbit of a new GEO at a three-dimensional accuracy of about 15 km from about 10 arcs, each having a length of about 3 min, thus achieving reliable cataloguing of uncatalogued GEO objects. The IOD and two-arc association methods are also tested with the real ground-based observations for both GEO and LEO objects of near-circular orbits, further validating the effectiveness of the proposed methods.

The Interaction between the LEO Satellite Constellation and the Space Debris Environment

The wide application of satellite constellations in the field of space-based global communications and remote sensing has led to a substantial increase in small-satellite launch plans, a sharp increase in the density of space objects in low-Earth orbit (LEO), and a reduction in available orbit and frequency resources. This will further aggravate the trend of deterioration of the space debris environment. Taking the Starlink constellation as an example, this paper describes the influence of the constellation from the environmental debris flux of the satellite, the evaluation of the number of evasion maneuvers, the change of risk level, the success rate of post mission disposal (PMD) and the growth rate of space objects. The simulation results show that the collision risk of the Starlink constellation is related to the orbital parameters, and the higher success rate of post-mission disposal (PMD) can reduce the collision risk of the constellation. The large constellations increases the growth rate of space objects, and even if all the satellites are disposed of after the mission, the impact of constellations on the space environment can not be offset.

Review on strategies of space-based optical space situational awareness

Space-based optical (SBO) space surveillance has attracted widespread interest in the last two decades due to its considerable value in space situation awareness (SSA). SBO observation strategy, which is related to the performance of space surveillance, is the top-level design in SSA missions reviewed. The recognized real programs about SBO SAA proposed by the institutions in the U.S., Canada, Europe, etc., are summarized firstly, from which an insight of the development trend of SBO SAA can be obtained. According to the aim of the SBO SSA, the missions can be divided into general surveillance and space object tracking. Thus, there are two major categories for SBO SSA strategies. Existing general surveillance strategies for observing low earth orbit (LEO) objects and beyond-LEO objects are summarized and compared in terms of coverage rate, revisit time, visibility period, and image processing. Then, the SBO space object tracking strategies, which has experienced from tracking an object with a single satellite to tracking an object with multiple satellites cooperatively, are also summarized. Finally, this paper looks into the development trend in the future and points out several problems that challenges the SBO SSA.

Deterrence by Debris: The Downside to Cleaning up Space

Current calls to remove orbital debris come from nearly every corner, including governments, militaries, private corporations, and the scientific community. While debris poses a clear threat to space operations, and while this threat will continue to grow over time, too little energy has been spent considering the second-order effects of developing the ability to remove orbital debris. An unintended consequence of debris removal is that it would weaken one of the elements of deterrence that prevent self-interested states from engaging in more frequent kinetic antisatellite tests or taking hostile actions against orbital objects. This article examines the issue of orbital debris, connects the existence of debris to deterrence, and then offers some solutions to mitigate the weakening of deterrence in the event that debris removal becomes a reality.

Fringe visibility errors resulting from dual object imaging for stellar interferometers.

Practical stellar interferometry for space domain awareness is challenged by the relative motions of orbital objects and telescope arrays that require array phasing using guide stars. An orbital object's image sensitivity to the location and brightness of the guide star is problematic, possibly resulting in a degraded resolution or loss of image content when both objects fall within the interferometer's field of view. We characterized an orbital object's visibility using visibility contrast to noise ratios (CNRΔv) as a performance metric for orbital object image quality. Experimental validations included orbital object visibility measurements for dual binary pinholes that were scaled in size and brightness individually to match expected interferometer data collection scenarios. We show agreement in CNRΔv results, indicating resolvable orbital object signals during periods of collection when signal contributions from both the orbital object and guide star are present. Expanding presented results to imaging interferometers, we discuss how dual object imaging could degrade performance under the scenarios examined.

A Globally Averaged Thermospheric Density Data Set Derived From Two‐Line Orbital Element Sets and Special Perturbations State Vectors

AbstractWe describe a long‐term data set of global average thermospheric mass density derived from orbit data on ∼7,700 objects in low Earth orbit, via the effect of atmospheric drag. The data cover the years 1967–2019 and altitudes 250–575 km, and the temporal resolution is 3–4 days for most years. The data set is an extension and revision of a previous version. The most important change is the use of more precise orbit data: special perturbation state vectors are now used starting in 2001, instead of mean Keplerian orbital elements. The data are suitable for climatological studies of thermospheric variations and trends, and for space weather studies on time scales longer than 3 days.