Gravity Tractor Research Articles

Dynamics and control of sun-facing diffractive solar sails in displaced orbit for asteroid deflection

A gravity tractor spacecraft propelled by a diffractive sail tracking a displaced orbit offers a potential option for deflecting near-Earth asteroids. This study delves into the preliminary dynamics, evaluates the deflection capabilities, and investigates the stability and control of the diffractive sail on the displaced orbit near the asteroid. Unlike reflective sails, diffractive solar sails generate tangential radiation pressure force, offering multiple advantages. These include the elimination of tilt attitude requirements, no offset angle restrictions from the target asteroid's flight direction, and superior deflection performance with an equivalent area-to-mass ratio when the diffraction angle surpasses 50deg. To maintain position, a controllable diffractive sail model using spatial light modulators, coupled with a feedback control law, is proposed. This control design stabilizes the periodic displaced orbit without necessitating tilt attitude adjustments towards the sun, as validated by our numerical simulations.

A study on unveiling the secrets of exoplanet hunting

Exoplanets are celestial bodies outside our solar system, orbiting stars other than our sun. They come in various sizes, compositions, and distances from their host stars. Scientists detect exoplanets by observing the dimming of a star's light as a planet passes in front of it (transit method), measuring the gravitational tug a planet exerts on its star (radial velocity method), or directly capturing their images. Studying exoplanets is a captivating area of astronomy that unveils our universe's vast array of planetary systems. Researchers delve into these distant worlds to explore their atmospheres, structures, and potential habitability, aiming to gather insights into the likelihood of life existing beyond our solar system. This paper addresses the challenges of distinguishing exoplanet signals from stellar activity, instrumental noise, and other astrophysical phenomena. It discusses the role of data-driven approaches, machine learning, and advanced statistical analyses in enhancing the reliability and accuracy of exoplanet detections after applying KNN.

The research on near-Earth objects(NEOs) and its possible protectionary methods

Recent year, as technologies and research have unprecedently grow in a fast speed, humans exploration toward outer space become enormous. Several private space exploration and aerospace manufacture corporations, such as SpaceX, have come into public which symbolize the development of human society and start to reshape the human civilization. Near Earth Objects(Neos) or Potential Hazard Asteroids(PHAs) have gradually focused by scientists. With the emerging of Neos observations, it has become vigilant that Neos impact to human civilization is obviously destructive refer to the distinction dinosaur. Neo impact technologies and strategies are tremendously vital in resort of continuing human civilization. This paper presents the time frame of launching of satellite and space station and their function of exploration and the information about near earth objects including its feature and propose several possible solutions toward Neos for short time scales and long times scales including nuclear explosive devices, kinetic impactor, asteroid gravity tractor and asteroid laser ablation. These methods have been list with their advantages and disadvantages and evaluation will be taken from the prospective of successful rate, time, efficiency and cost.

Mass-Optimized Gravity Tractor for Asteroid Deflection

A method for asteroid deflection that makes use of a spacecraft moving back and forth on a segment of a Keplerian orbit about the asteroid is studied with the aim of optimizing the initial gross mass of the spacecraft. The corresponding optimization problem is formulated as a discrete nonlinear optimal control problem where the parameters of the orbit segment are the control variables. A hypothetical asteroid deflection problem is solved numerically using the method of dynamic programming, and it is shown that a gravity tractor can be obtained that is significantly more efficient in terms of deflection attained per unit mass of the spacecraft, as compared to similar gravity tractors in the literature. It is further shown using a numerical approach that the results may be applied to a slowly rotating asteroid that is assumed to have an ellipsoidal shape.

Intelligent selection of NEO deflection strategies under uncertainty

This paper presents an Intelligent Decision Support System (IDSS) that can automatically assess the suitable robust deflection strategies to respond to a Near Earth Objects (NEO) impact scenario. The input to the IDSS is the warning time, the orbital parameters and mass of the NEO and the corresponding uncertainties. The output is the deflection strategies that are more likely to offer a successful deflection. Both aleatory and epistemic uncertainties on ephemerides and physical properties of the NEO are considered.The training data set is produced by generating thousands of virtual impactors, sampled from the current distribution of NEO. For each virtual impactor we perform a robust optimisation, under mixed aleatory/epistemic uncertainties, of the deflection scenario with different deflection strategies. The robust performance indices is considered by the deflection effectiveness, which is quantified by Probability of Collision post deflection. The IDSS is based on a combination Dempster-Shafer theory of evidence and a Random Forest classifier that is trained on the data set of virtual impactors and deflection scenarios. Five deflection strategies are modelled and included in the IDSS: Nuclear Explosion, Kinetic Impactor, Laser Ablation, Gravity Tractor and Ion Beam Shepherd. Simulation results suggest that the proposed decision support system can quickly provide robust decisions on which deflection strategies are to be chosen to respond to a NEO impact scenario. Once trained the IDSS does not require re-running expensive simulations to make decisions on which deflection strategies are to be used and is, therefore, suitable for the rapid pre-screening or reassessment of deflection options.

Orbital dynamics of gravity tractor spacecraft employing artificial halo orbit

In this paper, the equations of motion for modeling a spacecraft near an earth-threatening asteroid are proposed and studied for deflecting the asteroid using a gravity tractor that effectively tows the asteroid with mutual gravity attraction. The motion of the spacecraft is expressed by separation distance between the two objects, two Eulerian angles expressing the attitude of the spacecraft–asteroid system, and their derivatives; it is assumed that the spacecraft and asteroid are connected with a variable-length gravity tether. The motion of the spacecraft in an artificial halo orbit (AHO) is investigated using the proposed equations. These equations are suitable for the investigation because the spacecraft in the AHO moves in a circular orbit at a constant angular velocity and distance from the asteroid. The results indicate that the AHO is unstable, and a linear quadratic regulator will be required to control the spacecraft. Numerical simulation results suggest that the AHO–AHO transfer can be realized by employing a control law that linearizes the proposed equations. The achievable deflection distance yielded by 1000 days of a towing mission is calculated for fictional Earth impactors; the results indicate that the proposed system is feasible for conducting long-term simulations.

Planetary defence systems – threat to survival?

ABSTRACT The article explains why Weaponisation of outer space may soon be inevitable and that development of space weapons is a serious issue, especially in regard to dealing with sensitive dual-use technology. At the same time, the Earth may be threatened by incoming asteroids and comets, which may endanger humankind’s existence. Hence, it is advisable to develop effective planetary defence systems. However, the article claims that discussed planetary defence technology – kinetic impactor, nuclear explosion, gravity tractor and space tug, laser, and solar collector – have far-reaching dual-use consequences with potential for their weaponisation. Thus, the article argues in favour of greater transparency and surveillance mechanisms for dual-use and arms control. Moreover, the private sector should be involved in discussion since it may be contributing to negotiation processes and can ensure secure research and development, as well as operability of sensitive planetary defence systems.

Assessment of Near-Earth Asteroid Deflection Techniques via Spherical Fuzzy Sets

Extensions of fuzzy sets to broader contexts constitute one of the leading areas of research in the context of problems in artificial intelligence. Their aim is to address decision-making problems in the real world whenever obtaining accurate and sufficient data is not a straightforward task. In this way, spherical fuzzy sets were recently introduced as a step beyond to modelize such problems more precisely on the basis of the human nature, thus expanding the space of membership levels, which are defined under imprecise circumstances. The main goal in this study is to apply the spherical fuzzy set version of Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS), a well-established multicriteria decision-making approach, in the context of planetary defense. As of the extraction of knowledge from a group of experts in the field of near-Earth asteroids, they rated four deflection technologies of asteroids (kinetic impactor, ion beam deflection, enhanced gravity tractor, and laser ablation) that had been previously assessed by means of the classical theory of fuzzy series. This way, a comparative study was carried out whose most significant results are the kinetic impactor being the most suitable alternative and the spherical fuzzy set version of the TOPSIS approach behaves more sensitively than the TOPSIS procedure for triangular fuzzy sets with regard to the information provided by our group of experts.

Магнитное буксирование астероидов с помощью космического аппарата, приводимого в движение солнечным парусом

The paper considers the possibility of changing the orbit of potentially dangerous asteroids using the concept of a spacecraft — a magnetic tractor. The described concept is based on the use of a superconducting electromagnet mounted on a spacecraft and a permanent neodymium magnet attached to the surface of an asteroid. The principle of operation of this type of vehicle is similar to the concept of a spacecraft — a gravitational tractor, however, the considered vehicle, in addition to the force of mutual gravitational interaction, uses the force of magnetic attraction as a tug. A solar sail is used as a propulsion system for the type of vehicles under consideration. Within the framework of the work, the analysis of the effectiveness of the use of spacecraft of this type was carried out by modeling the joint motion of the asteroid — spacecraft system for a long time using the example of the change in the orbit of the asteroid Apophis.

51 Pegasi b: The planet that started the revolution of exoplanet research

To celebrate its 150 anniversary, Nature collected 10 extraordinary papers published on Nature in November, 2019. One of the papers is on the discovery of the 51 Peg b by Swiss astronomers Michel Mayor and Didier Queloz from University of Geneva. 51 Peg b was the first confirmed planet around a solar-type star other than our own Sun. Mayor and Queloz later won the Nobel Physics Prize in 2019 because they have “explored our cosmic neighbourhoods on the hunt for unknown planets. Their discoveries have forever changed our conceptions of the world.” The discovery was made using the radial velocity technique. A star and a planet orbit each other, and although not much, the star still shows a noticeable wobble due to the gravitational tug of the planet. By observing this wobble motion, scientists can infer the existence of a planet around the star and calculate its mass and distance from the host star. Mayor and Queloz started their planet survey using ELODIE spectrograph in the early 1990s at Haute-Provence Observatory. Through their survey, they found a strange object orbiting the star 51 Pegasi, with a similar mass of Jupiter, but about 7 times closer to its host star than Mercury is to our sun. This object was later named as 51 Pegasi b, and confirmed by other research teams around the world, including Marcy’s research team from America. This new discovery was a big challenge to the traditional models of planet formation. How could a Jupiter-like planet form so close to its host star? Revised planet formation theory suggests 51 Peg b initially formed like a Jupiter farther away from 51 Pegasi, and later migrated inwards towards the star due to interaction with other planets or interaction with the material in the gaseous planetary disk. Since the discovery of 51 Peg b, more than 4200 exoplanets have been confirmed so far, and many more yet coming. The main detection methods of exoplanets are radial velocity technique, transiting technique, microlensing, and direct imaging methods. Most of the planets known today are detected using radial velocity technique and transiting technique. A lot of these planet systems are quite different from our Solar system, which makes people wondering, is our Solar system unique in the Universe? As more and more planets are detected, astronomers keep revising the theory of planet formation to account for the new discoveries. Eventually we will figure out the position of our own solar system in the Univerise, and how planets form. In the present paper, we will first briefly review the discovery of the first confirmed exoplanet around a solar-type star, 51 Peg b by Mayor and Queloz in 1995. Then, we introduce the properties of this extraordinary planet system, and show how this planet system single handly changed our view of planet formation. We shall also introduce the impact of this discovery on the exoplanet community and astronomy community as a whole. In the end, we point out the important implications of the discovery of 51 Peg b.

Deflecting an Asteroid with a Low-Thrust Tangential Engine to the Orbit

In order to solve the problem of deflecting a dangerous asteroid from a collision orbit with the Earth, using a low-thrust engine directed tangentially to the trajectory is considered. The engine can be mounted on the asteroid or on a “gravity tractor.” The purpose of this study is to establish the fundamental possibility of steering away an asteroid to a safe distance over times of approximately a month and a year. This is acceptable since an asteroid with about a 100-m diameter is unlikely to strike immediately after its discovery. We limited ourselves to a model statement of the problem: the engine provides constant tangential acceleration. Previously, we transformed the respective Euler equations using the averaging method. Here, we solve them by the method of series in powers of “slow time” and demonstrate the adequacy of the solution on the time intervals of decades. It turns out that asteroids up to 55 m in diameter can be deflected in a year with an engine thrust of 1 N. With a thrust of 20 N, asteroids up to 50 m in diameter can be deflected in a month, and asteroids with a diameter of up to 150 m, in a year. Diverting larger asteroids requires more time or more powerful engines. The results are compared with the previously obtained similar data for the case of the transversal perturbing acceleration. The tangential traction leads to better results in all cases; however, both variants nearly coincide for orbits with eccentricities up to 0.4. The difference becomes significant at $$e > 0.5$$ .

Evaluation of NEA deflection techniques. A fuzzy Multi-Criteria Decision Making analysis for planetary defense

Current statistics on the flux of impactors on the Earth reveal that asteroids with a diameter larger than few hundreds of meters are unlikely to reach the Earth’s orbit, although their potential effects on the life of our planet could be quite catastrophic. The present article assesses a set consisting of four deflection approaches, namely: kinetic impactor, ion beam deflection, enhanced gravity tractor, and laser ablation to be applied to mitigate a hypothetic impact with an asteroid smaller than 250 meters in diameter. This size range corresponds to the most common impactors that occur in timescales of less than 100.000 years. With the current discovery rate for small asteroids, such a range of diameters could be of interest to assess a future impact forecast, and quantify our capacity to react in time. To achieve this, a set of eight criteria are used: build time; active deflection duration; asteroid rotation; asteroid composition; asteroid structure; asteroid shape; level of maturity of a NEA deflection technique; and mission risk. This assessment is carried out with a combination of Multi-Criteria Decision Making tools and fuzzy logic, which enables proper management of imprecise criteria. The valuable knowledge provided by a group of experts enabled the importance of each attribute and the evaluation of these NEA deflection techniques to be quantified. Our results suggest that the kinetic impactor is the best option to deflect mid-size NEAs, whereas for larger asteroids, enhanced gravity tractor, and laser ablation become to be more appropriate.

Гравитационное буксирование астероидов космическими аппаратами с солнечным парусом в качестве движительной установки

The paper considers the possibility of changing the orbit of potentially dangerous aste-roids using a gravity tractor. The concept of using spacecrafts equipped with a solar sail for gravitational towing is described. The analysis of this type spacecraft effectiveness is carried out on the example of changing the orbit of the Apophis asteroid. Software and mathematical support for modeling the joint motion of the asteroid-spacecraft system has been developed. The model was used to assess the impact of spacecraft with design features on the asteroid’s orbit over a long period of time. Several variants of the spacecraft configuration with different weight and sail design are considered. A comparative analysis of the results of using solar sail vehicles with similar vehicles using low-thrust jet engines is carried out.

Diversion of an Asteroid Using a Transversal Thruster

The diversion of a hazardous asteroid on a collisional trajectory with the Earth using a transversal thruster is considered. The thruster could be either mounted on the asteroid or used as a “gravitational tractor”. The aim of the study is to establish the fundamental possibility (or impossibility) of diverting an asteroid to a safe distance over a time of order months or years. This is acceptable, since the impact of an asteroid with a diameter of order 100 m on the Earth just after its discovery is very improbable. A model formulation of the problem in which the thruster provides a constant transversal acceleration of the asteroid is used. The corresponding Euler-type equations are transformed using the method of previous averaging. These equations are solved using the method of “slow time” power series, and the adequacy of the solutions over time scales of decades is demonstrated. An asteroid up to 55 m in diameter can be deflected over a year using a 1 N thruster. Asteroids with diameters up to 50 m can be diverted over a month, and with diameters up to 150 m over a year, using a 20 N thruster. Moving larger asteroids requires more time or more powerful engines.

Seeing is Believing

A black hole is an object with an extreme gravitational tug from which no light can escape. The nature of their strong gravity causes any material coming within the influence of its event horizon to be lost forever. The radiation from the hot disk of matter encircling the black hole opens the possibility to image these elusive objects, as it is impossible otherwise. Here, the first-ever image of the shadow of the supermassive black hole in a nearby galaxy, M87, is reported based on the observations by the Event Horizon Telescope.

Three-dimensional simulations of neutrino-driven core-collapse supernovae from low-mass single and binary star progenitors

We present a suite of seven 3D supernova simulations of non-rotating low-mass progenitors using multi-group neutrino transport. Our simulations cover single star progenitors with zero-age main sequence masses between $9.6 M_\odot$ and $12.5 M_\odot$ and (ultra)stripped-envelope progenitors with initial helium core masses between $2.8 M_\odot$ and $3.5 M_\odot$. We find explosion energies between $0.1\,\mathrm{Bethe}$ and $0.4\,\mathrm{Bethe}$, which are still rising by the end of the simulations. Although less energetic than typical events, our models are compatible with observations of less energetic explosions of low-mass progenitors. In six of our models, the mass outflow rate already exceeds the accretion rate onto the proto-neutron star, and the mass and angular momentum of the compact remnant have closely approached their final value, barring the possibility of later fallback. While the proto-neutron star is still accelerated by the gravitational tug of the asymmetric ejecta, the acceleration can be extrapolated to obtain estimates for the final kick velocity. We obtain gravitational neutron star masses between $1.22 M_\odot$ and $1.44 M_\odot$, kick velocities between $11\, \mathrm{km}\, \mathrm{s}^{-1}$ and $695\, \mathrm{km}\, \mathrm{s}^{-1}$, and spin periods from $20\, \mathrm{ms}$ to $2.7\,\mathrm{s}$, which suggests that typical neutron star birth properties can be naturally obtained in the neutrino-driven paradigm. We find a loose correlation between the explosion energy and the kick velocity. There is no indication of spin-kick alignment, but a correlation between the kick velocity and the neutron star angular momentum, which needs to be investigated further as a potential point of tension between models and observations.

AD Leonis: Radial Velocity Signal of Stellar Rotation or Spin–Orbit Resonance?

Abstract AD Leonis is a nearby magnetically active M dwarf. We find Doppler variability with a period of 2.23 days, as well as photometric signals: (1) a short-period signal, which is similar to the radial velocity signal, albeit with considerable variability; and (2) a long-term activity cycle of 4070 ± 120 days. We examine the short-term photometric signal in the available All-Sky Automated Survey and Microvariability and Oscillations of STars (MOST) photometry and find that the signal is not consistently present and varies considerably as a function of time. This signal undergoes a phase change of roughly 0.8 rad when considering the first and second halves of the MOST data set, which are separated in median time by 3.38 days. In contrast, the Doppler signal is stable in the combined High-Accuracy Radial velocity Planet Searcher and High Resolution Echelle Spectrometer radial velocities for over 4700 days and does not appear to vary in time in amplitude, phase, period, or as a function of extracted wavelength. We consider a variety of starspot scenarios and find it challenging to simultaneously explain the rapidly varying photometric signal and the stable radial velocity signal as being caused by starspots corotating on the stellar surface. This suggests that the origin of the Doppler periodicity might be the gravitational tug of a planet orbiting the star in spin–orbit resonance. For such a scenario and no spin–orbit misalignment, the measured indicates an inclination angle of 15.°5 ± 2.°5 and a planetary companion mass of 0.237 ± 0.047 M Jup.

The Deflector Selector: A machine learning framework for prioritizing hazardous object deflection technology development

Several technologies have been proposed for deflecting a hazardous Solar System object on a trajectory that would otherwise impact the Earth. The effectiveness of each technology depends on several characteristics of the given object, including its orbit and size. The distribution of these parameters in the likely population of Earth-impacting objects can thus determine which of the technologies are most likely to be useful in preventing a collision with the Earth. None of the proposed deflection technologies has been developed and fully tested in space. Developing every proposed technology is currently prohibitively expensive, so determining now which technologies are most likely to be effective would allow us to prioritize a subset of proposed deflection technologies for funding and development. We present a new model, the Deflector Selector, that takes as its input the characteristics of a hazardous object or population of such objects and predicts which technology would be able to perform a successful deflection. The model consists of a machine-learning algorithm trained on data produced by N-body integrations simulating the deflections. We describe the model and present the results of tests of the effectiveness of nuclear explosives, kinetic impactors, and gravity tractors on three simulated populations of hazardous objects.

A novel push-pull asteroid magnetic Tractor(MT)

The possibility of an asteroid striking the earth is well known. The chosen technique for diverting such an asteroid depends on the lead time measured from the determination that an asteroid has a large probability of colliding and the expected time of such a collision. There are a large number of possible deflection techniques that are available, each suited to different lead times. If the lead time is unpleasantly short, desperation measures such as using nuclear devices may apply. If the lead time is comfortably long, the heralded gravity tractor (GT) is a good option. It is capable of precisely and verifiably altering the orbit of a threatening asteroid. If the lead time happens to be somewhere between desperate and comfortable, it is not clear what option may be invoked. It is likely the most probable scenario to occur is one where the lead time is somewhere in between very short and very long. There is a plethora of different techniques in the literature, but some are so fanciful that their reliability would certainly be in question. There is a need for a new deflection technique that has the reliability and the precision of the gravity tractor but is able to produce larger deflection forces to handle much shorter lead times. This is the problem that this paper addresses. The proposed solution to this problem is a push-pull asteroid magnetic tractor(MT) that is shown to produce orders of magnitudes larger deflection forces and to accommodate much shorter lead times than the GT.

Statistical multi-criteria evaluation of non-nuclear asteroid deflection methods

In this paper we assess and compare the effectiveness of four classes of non-nuclear asteroid deflection methods applied to a wide range of virtual collision scenarios. We consider the kinetic impactor, laser ablation, the ion beaming technique and two variants of the gravity tractor. A simple but realistic model of each deflection method was integrated within a systematic approach to size the spacecraft and predict the achievable deflection for a given mission and a given maximum mass at launch. A sample of 100 synthetic asteroids was then created from the current distribution of NEAs and global optimisation methods were used to identify the optimal solution in each case according to two criteria: the minimum duration between the departure date and the time of virtual impact required to deflect the NEA by more than two Earth radii and the maximum miss-distance achieved within a total duration of 10 years. Our results provide an interesting insight into the range of applicability of individual deflection methods and argue the need to develop multiple methods in parallel for a global mitigation of all possible threats.