Talk:Orbital mechanics

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Disputed[edit]

This page claims that Newtonian mechanics is the primary method, and that relativistic effects only need to be considered close to the sun. NASA began using JPL's Double Precision Orbit Determination Program (DPODP) in 1968 and relativistic corrections have been applied for lunar and planetary missions since 1968. In 1991 the IAU began the migration to a relativistic coordinate system and finalized the migration in 2000. Many if not most Earth orbits are also currently calculated with relativistic corrections or methods due to inaccuracies resulting from Earth oblateness and the Lunar perturbation. Voyager would have lacked the fuel to accomplish the grand tour using only Newtonian Mechanics and some critical functions like Doppler tracking absolutely require relativistic corrections. As the ephemera and flight paths currently require using relativity as current measurement sensitivities are well past the limits of Newtonian Mechanics the claims on this page should be addressed by a subject matter expert.

[1] [2] [3] Gdahlm (talk) 22:40, 7 June 2017 (UTC)

  • RE: Disputed by Gdahlm

The factual dispute seems on thin grounds based on current version which states " 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 (such as orbits close to the Sun)." This statement is correct, in my opinion. (No I am not a subject matter expert, but yes, one of my various degrees is in physics.) The article does not (presently) say that "relativistic effects only need to be considered close to the sun", which would indeed, imo, be incorrect.

Additionally, the article does indeed, correctly in my opinion, claim Newtonian physics is primarily used in this field, true at least for teaching the subject at the graduate physics level. But why rely on me when all you need do is check the work of Richard Battin [yes, THAT Physics Professor of MIT Richard Battin, Author and professor of the textbook ASTRODYNAMICS who is also well known for his namesake method of solving the Lambert Problem, and who must be regarded (if anyone is) as an authority on subject]. Battin's book is all about Newtonian physics, beginning with the two-body problem. Relativity is not ignored, it is simply put in perspective as correction to be made where high accuracy is needed, such as hitting a 10 meter target circle on the surface of Mars from an Earth launch, which is admittedly harder than bulls-eyeing womprats on Tatooine, which womprat kills would only hypothetically require Newtonian accuracy, or alternatively the keen eye of a Skywalker. Thus the factual dispute must fall and should be removed.

The article claim of subject matter (describing the scope of ideas covered by the field of "Astrodynamics") also appears reasonable and credible, even if some of the distinctions seem a little artificial. This is not and should not be taken as a definition of astrodymaics, but as an attempt to describe the subject matter, and in that it does a fair job, I say.

Proper references would be nice, of course, and these exist and should be added.

Someone who knows how should remove the disputed tag on the article. CumuloEpsilon (talk) 23:12, 20 September 2017 (UTC)

  • Wikipedia is not scientific journal and to provide an understanding to a layman of the idea of orbital mechanics, it's not necessary to get into relativistic effects except to note that, in certain high-precision situations, it may be necessary to take relativistic effects into account. This is already noted in the current revision (801704828, Sept 21 2017) so I'm removing the disputed tag. GaidinBDJ (talk) 04:02, 22 September 2017 (UTC)

References

  1. ^ Joseph H. Yuen. [https://descanso.jpl.nasa.gov/monograph/series2/Descanso2_all.pdf
  2. ^ The IAU 2000 resolutions for astrometry, celestial mechanics and metrology in the relativistic framework: explanatory supplement [https://arxiv.org/abs/astro-ph/0303376
  3. ^ Mathematical formulation of the Double-Precision Orbit Determination Program (DPODP). [1]

Differences[edit]

How do astrodynamics differ from orbital mechanics, celestial mechanics, and the like? There is also astrometry, and I am unsure how these fields differ/related to one another. — Preceding unsigned comment added by 64.134.140.53 (talk) 03:06, 28 November 2012 (UTC)

From PNA/Physics (historical)[edit]

Astrodynamics#Historical_approaches: needs to be re-written. Just throwing in names of famous scientists in history is useless. -- PFHLai 23:04, 2004 Oct 22 (UTC)

Yep. That's why this article has a todo list. --Doradus 19:54, 26 September 2006 (UTC)

Orbital mechanics[edit]

Orbital mechanics redirects here, but surely it would be better off redirecting to celestial mechanics? It seems more likely to me that somebody researching it would want to know about orbits in general, not just artificial ones. JulesH 11:24, 26 September 2006 (UTC)

Neat little law:[edit]

This is something about orbits I read a little while back, that might be appropriate in this article:

In order to slow down, you speed up; to speed up, you slow down.

Slowing down puts you into a lower orbit, which is faster in relation to a point on the surface of the body you are orbiting around. Speeding up puts you into a higher orbit, which is slower in relation to the aforementioned point.

Can anyone think of a place to put this?

Phædrus 12:01, 20 March 2007 (UTC)

I'm not sure it's that useful. It's barely even true. If you slow down, you slow down; there's nothing magical about orbits that makes this false. However, it is true that if you slow down at one point in an orbit, you do often end up in an orbit with a shorter period and a higher top speed, which is kind of interesting. --Doradus 18:56, 19 April 2007 (UTC)
I added a "Rules of thumb" section which I hope covers this general idea in a less confusing way. -- Beland (talk) 01:49, 21 January 2008 (UTC)

Phraedrus: You are incorrect, your speed is dependent on your semi major axis and speeding up puts you in a larger orbit which means you are going slower, simple derivation from Kepler's equations.

This article needs a lot of help[edit]

Well, folks, this is the article that taught me I'm no good at writing large articles from scratch. I'll be happy to contribute any way I can, but three years after I had first intended to revamp this article, I haven't done much. If someone else wants to give it ago, they'll have my full support. --Doradus 19:02, 19 April 2007 (UTC)

Not every one is a physicist, please write out your equations in full, like this, force = mass*distance/time squared, Newtons. Force of gravitational attraction = G*M*m/r^2, Newtons. Energy = force*distance, hence [G*M*m/r^2]*r = G*M*m/r joules. and your energy/mass = G*M/r, joules per kg. velocity v = r/t =[2*G*M/r]^1/2 = {2*[r^3/m*t^2]*M}/r, m/s, since f^2=1/t^2, then velocity, r/t = frequency*wave length = f*{r*[2*M/m]^1/2}, m/s. Since hf = mc^2, joules, then mass, m = h*f/c^2, kg, substituting for mass gives us, v=f*r[2*[h*f(M)/c^2]*[1/h*f/C^2]]^1/2, m/s. which contracts to, v=r*[2*f*f(M)]^1/2, m/s, where f(M) is the frequency of the wave between mass M and the test mass, see www.QuantumMatter.com.--79.68.156.33 23:57, 3 November 2007 (UTC)

Duplication?[edit]

Is the "Application" subsection of Kepler's Laws partly redundant with the "Position as a function of time" section of Kepler's laws of planetary motion? Not sure where this material belongs or in what form. -- Beland (talk) 19:22, 6 August 2008 (UTC)

Diagram request[edit]

I was asked to clarify this request. Suggestions of things that might be illustrated or animated:

  • A sequence showing initial orbit, transfer orbit, and final orbit.
  • Docking maneuver
  • Lower orbits = faster movement
  • Equal areas in equal times

-- Beland (talk) 19:22, 6 August 2008 (UTC)

Clarification on orientation[edit]

"Without applying torque (such as using thrusters or reaction wheels) a satellite will maintain the same orientation with respect to the fixed stars."

This seems incorrect. It seems like it should state that a satellite will maintain the same angular rotation rate with respect to the fixed stars. Certainly communications satellites can not require a constant expenditure of fuel or increasingly fast reaction wheels to aim their antennae at the planet they orbit.Three d dave (talk) 20:32, 6 April 2015 (UTC)

Somebody is missing the point, or I do not understand Newton[edit]

I am having problems with understanding space, vacuum, and atmosphere. That is aerodynamics versus astrodynamics!

If somebody is wrong or everybody is wrong, or we need the story, or I am a skeptic. I wonder if being a skeptic and self publishing a book is a post modern given free humans rights! Well not in some countries.

Well don't throw at me a whack of equations, as basics is enough.

Cheers. — Preceding unsigned comment added by 75.155.223.49 (talk) 19:05, 27 November 2018 (UTC)

Do you have a specific question relevant to this article that could be answered better in it?--agr (talk) 20:41, 27 November 2018 (UTC)

Confusing rules of thumb[edit]

Some of the statements in the Rules of thumb section are rather confusing:

  • Orbits are elliptical, with the heavier body at one focus of the ellipse. Special case of this is a circular orbit (a circle is a special case of ellipse) with the planet at the center.
What planet?
  • Thus one cannot move from one circular orbit to another with only one brief application of thrust.
How long is brief?
  • From a circular orbit, thrust applied in a direction opposite to the satellite's motion changes orbit to elliptical;
But all orbits are elliptical...

Apart from the lack of citations, the wording in this section is ambiguous and confusing. Could somebody with more knowledge of the subject clarify matters. I think it's a good thing to have this section, but it's not really serving its purpose with the current wording. Thanks Davidelit (Talk) 01:02, 17 July 2019 (UTC)