# What is Astrodynamics: Definition and 12 Discussions

Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft. The motion of these objects is usually calculated from Newton's laws of motion and law of universal gravitation. Orbital mechanics is a core discipline within space-mission design and control.
Celestial mechanics treats more broadly the orbital dynamics of systems under the influence of gravity, including both spacecraft and natural astronomical bodies such as star systems, planets, moons, and comets. Orbital mechanics focuses on spacecraft trajectories, including orbital maneuvers, orbital plane changes, and interplanetary transfers, and is used by mission planners to predict the results of propulsive maneuvers.
General relativity is a more exact theory than Newton's laws for calculating orbits, and is sometimes necessary for greater accuracy or in high-gravity situations (e.g. orbits near the Sun).

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1. ### I If Jupiter had a 5th large moon until "recently", would we know?

Hi! I'm fascinated by the apparent "concentration" of the four large Galilean moons in a barely 1.5 million km "strip", and the vast, "empty" distance to the next moons (moonlets?) Out of a purely aesthetic sense of horror vacui, :wink: I've always wondered if there was at least another Jovian...
2. ### I Astrodynamics Question: Derivation of Sp. Orbital Energy?

So this should be coming easily, but for some reason I can't seem to grasp why or how this is being done: So say we have equation: 0 = a + (μ/r3) r , where μ = G(M+m) or ≈ GM and M >> m. According to this book, the first step to finding ξ, the Specific Mechanical/Orbital Energy they dot...
3. ### Got an astrophysics/ astrodynamics question....

How would a solar system need to be set up to provide a life bearing world, standard 1 g, with the surface area of Jupiter with a standard day / night 24 hour cycle?
4. ### MATLAB Solving Orbital Motion Equations with RK4 Using MATLAB

I'm trying to plot the solutions of the second order differential equation d^2R/dt^2 = GM/R^2 + Lz^2/R^3. I'm reducing this to a system of first order ODEs and then using RK4 to solve this system. My code is given by function RK4system() Tsim = 10...
5. ### Basic Astrodynamics: Understanding Total Energy

Using the well established classical equation to determine the sum of kinetic and potential energies of a satellite at two different altitudes, the result is a lower total energy at the higher altitude. Since the speed is less and the height is greater I think I understand this result. Yet I...
6. ### Satellite Access from state vectors

I've been trying to figure out how to calculate if a satellite is in view of a ground station (and above a certain elevation) using just position vectors for both satellite and ground station. Does anyone know of an equation, algorithm, etc. that does this? Thanks
7. ### Center of mass - cant find error in derivation

First of all, I am sorry if this is in the wrong subforum; I'm not sure if astrodynamics should be under astronomy. The post is also fairly long. My problem is that in my derivation of the center of mass of a binary system, I get a conflicting result for the distances of the center of mass to...
8. ### Keplar's First Law: Explaining Orbit and Eccentricity

I know that Keplar's First law is true, but it doesn't occur to me why do stars orbit the center of gravity. Is there a proof for that, or a way for me to visualise why? Also, to measure the eccentricity of the orbit, e^2=1+(2E(L^2))/(GM(m^2)). How did they derive this equation?
9. ### I want to pour a Sol sized bucked of water on the sun

So I don't feel as freaked out as I did before reading the Tips sticky about making sure every bit of science is plausible. I would like to try and keep it believable for the immersion though. http://gizmodo.com/could-the-sun-be-extinguished-by-a-bucket-of-water-just-1669914928 It all started...
10. ### Attempting writing. Looking for brains to pick for accuracy.

Hi I am a want to be writer that has high hopes publishing before I am 70, maybe. lol I have a short story idea that is slowly turning into a small novel and even if it never publishes I would like to keep junk science out of it. I am not sure where to post the thread for it or if this is the...
11. ### Difference between orbital mechanics and astrodynamics ?

Hello all. The title of this thread sums up my question - what is the difference between orbital mechanics and astrodynamics ? Or is there a difference at all ? I have sometimes seen different uses of the terms, for example, on many sites I see " astrodynamics or orbital mechanics is ... " ...
12. ### Astrodynamics, mean anomaly related problem

Homework Statement For an elliptic movement, calculate the mean value for a period of \left( \frac{a}{r} \right)^k , with k = 1,2,3,4,5 and being a the major radius. i.e. calculate \frac{1}{2 \pi} \int_0^{2 \pi} \left( \frac{a}{r} \right)^k dl, being l the mean anomaly. 2...