Invariant Manifolds in Celestial Mechanics

Chapter 68 - George David Birkhoff, Dynamical systems (1927)

The evolution of the solar system is an interesting dynamical problem in celestial mechanics. Computer simulations have shown that planetary bodies in multiple-body systems become unstable after a long time. In this thesis, through numerical simulations, we investigate the stability of the Earth in a binary star system. In the Sun, Earth, and Jupiter three-body system, we treat Jupiter as the second star (Star 2) and we simulate the Earth's orbit over many orbital periods. In our program, we generate the positions, velocities, accelerations, and other orbital elements of each body using Newton's laws of motion. We explore four types of simulations including when the system is run with the usual locations and masses, when the mass of Star 2 is changed at the position of Jupiter, when the stars have equal mass and the location of Star 2 is changed, and when the position and mass of Star 2 changed. We plot the position coordinates of the Earth and determine when the Earth exhibits unpredictable or erratic behaviors.

: Formulas from Lambert's problem in celestial mechanics are presented for use in a computer program to calculate velocity requirements for rapid intercept of an earth satellite by a rocket fired from the earth or from an orbit about the earth. The rocket is assumed to receive an impulsive velocity at launch and the effect of impulsive midcourse corrections are considered. The effects of the earth rotation are included is the rocket is fired from the earth, but those due to the earth's atmosphere are ignored. The rocket and target satellite are assumed to be moving in conic section in the earth's gravitational field.

In the following paper we tried to apply the Lie-formalism to the regularized restricted three body problem. It will be shown that this algorithm leads to a very simple structure program which is also fast.

On certain determinants connected with a problem in celestial mechanics

We present an algorithm to compute the incomplete elliptic integral of a general form. The algorithm efficiently evaluates some linear combinations of incomplete elliptic integrals of all kinds to a high precision. Some numerical examples are given as illustrations. This enables us to numerically calculate the values and the partial derivatives of incomplete elliptic integrals of all kinds, which are essential when dealing with many problems in celestial mechanics, including the analytic solution of the torque-free rotational motion of a rigid body around its barycenter.

Application of Lie-Series to Regularized Problems in Celestial Mechanics

The purpose of this series of lecture notes is to give an outline of the basic tools required to show the occurrence of chaotic motions in the simplest non--integrable problems in Celestial Mechanics, such as the circular restricted planar 3--body problem. No formal proofs will be given here; they can be found in the references given for each section. Section 1 describes the linear and local theory of ordinary differential equations in the neighbourhood of a fixed point; the problems arising in the embedding of invariant stable and unstable manifolds are also discussed. Section 2 is about periodic orbits; the subjects discussed include variational equations, surfaces of section, the continuation of periodic orbits in the restricted 3--body problem, and bifurcation of hyperbolic periodic orbits from resonant periodic orbits. Section 3 covers fundamental models of resonance, the global behaviour of separatrices, and their intersections; all this allows to give at least an outline of the proof of the fundamental result --presented by Poincaré in his book Les méthodes nouvelles de la mécanique céleste-- by which homoclinic points must necessarily occur in the restricted problem. A short conclusion underscores the fact --shown in a rigorous vay much later-- that this in turn implies that chaos in the strongest possible sense occurs in the restricted problem, and is an essential feature of every non--integrable system, even very simple ones with only two degrees of freedom. I apologize for reporting here my lectures in a very short format, almost without comments in between the formulas and statements of the main results; my understanding of the purpose of this notes is that they should serve as a reminder of the existence of many subjects to be studied, rather than a complete presentation which could not be contained in this format.

The determination of the motion of N point-like masses subject to their mutual gravitational forces is the fundamental problem in celestial mechanics, with important astrophysical applications, including the dynamics of planetary and satellite systems and the evolution of stellar systems (ranging from multiple stars to stellar clusters and galaxies). From the perspective of theoretical physics, this has always been a core problem in gravitation theory; through observations of the motion of celestial bodies it can be tested, quantitatively validated, or even disproved. However, even for N as small as 3, it is impossible to find general solutions in terms of simple analytical functions (as for the two-body problem). A great variety of orbits are possible and it can be shown that only particular initial conditions give rise to periodic behaviour. Even the perturbative techniques worked out in Ch. 12 can be successfully applied only in the particular case of hierarchical systems, where the attraction of one body prevails (see Sec. 15.1). As a consequence, the general gravitational N-body problem has been studied by two alternative methods which can yield only partial results, but are in some way complementary. The first is numerical integration, starting from given initial conditions. In this way the motion can be determined in detail, but only for a limited span of time (due to both limitations in computer time and accumulation of numerical errors; see Sec. 15.1); in addition, it is often impossible to determine the region of phase space where a property of the numerically determined orbits holds. The second method is the search for general constraints or criteria regarding qualitative features of the motion, such as its periodic character, its stability and its geometrical and topological properties. KeywordsEquilibrium PointSolar SystemOrbital PlaneTest MassTidal ForceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The dynamics of the spin–spin problem in Celestial Mechanics

Large Language Models (LLMs) can solve some undergraduate-level to graduate-level physics textbook problems and are proficient at coding. Combining these two capabilities could one day enable AI systems to simulate and predict the physical world. We present an evaluation of state-of-the-art (SOTA) LLMs on PhD-level to research-level computational physics problems. We condition LLM generation on the use of well-documented and widely-used packages to elicit coding capabilities in the physics and astrophysics domains. We contribute ∼50 original and challenging problems in celestial mechanics (with REBOUND), stellar physics (with MESA), 1D fluid dynamics (with Dedalus) and non-linear dynamics (with SciPy). Since our problems do not admit unique solutions, we evaluate LLM performance on several soft metrics: counts of lines that contain different types of errors (coding, physics, necessity and sufficiency) as well as a more educational’ Pass-Fail metric focused on capturing the salient physical ingredients of the problem at hand. As expected, today's SOTA LLM (GPT4) zero-shot fails most of our problems, although about 40% of the solutions could plausibly get a passing grade. About 70%–90% of the code lines produced are necessary, sufficient and correct (coding & physics). Physics and coding errors are the most common, with some unnecessary or insufficient lines. We observe significant variations across problem class and difficulty. We identify several failure modes of GPT4 in the computational physics domain, such as poor physical units handling, poor code versioning, tendency to hallucinate plausible sub-modules, lack of physical justification for global run parameters (e.g., simulation time, or upper-lower bounds for parametric exploration) and inability to define steady-state or stopping conditions reliably. Our reconnaissance work provides a snapshot of current computational capabilities in classical physics and points to obvious improvement targets if AI systems are ever to reach a basic level of autonomy in physics simulation capabilities.

In order to apply a parametric method to a minimum time control problem in celestial mechanics, a sensitivity analysis is performed. The analysis is continuous in the sense that it is done in the infinite dimensional control setting. The resulting sufficient second order condition is evaluated by means of automatic differentiation, while the associated sensitivity derivative is computed by continuous reverse differentiation. The numerical results are given for several examples of orbit transfer, also illustrating the advantages of automatic differentiation over finite differences for the computation of gradients on the discretized problem.

The purpose of this paper is to show that the explosion and fragmentation of the nucleus of a galaxy may produce circumstances theoretically resembling a generalization of a Restricted Problem in Celestial Mechanics.

We prove the existence of half-entire parabolic solutions, asymptotic to a prescribed central configuration, for the equation \begin{equation*} \ddot{x} = \nabla U(x) + \nabla W(t,x), \qquad x \in \mathbb{R}^{d}, \end{equation*} where $d \geq 2$, $U$ is a positive and positively homogeneous potential with homogeneity degree $-\alpha$ with $\alpha\in\mathopen{]}0,2\mathclose{[}$, and $W$ is a (possibly time-dependent) lower order term, for $\vert x \vert \to +\infty$, with respect to $U$. The proof relies on a perturbative argument, after an appropriate formulation of the problem in a suitable functional space. Applications to several problems of Celestial Mechanics (including the $N$-centre problem, the $N$-body problem and the restricted $(N+H)$-body problem) are given.

Explore the restricted three-body problem in three dimensions—a classic problem in celestial mechanics—by varying the initial positions and velocities of a particle moving around two fixed masses, whose masses are and .