Talk:Orbital mechanics

Disputed

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.

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)

As well as I know it, GR was needed for GPS, not because of the orbits, but because they depend on very accurate (atomic) clocks. Gah4 (talk) 23:19, 15 June 2022 (UTC)

References

Differences

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)

Orbital mechanics

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)

I disagree. Orbital mechanics is more specific to, as you note, artificial ones. Gah4 (talk) 04:48, 19 March 2021 (UTC)

Diagram request

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)

Please don't include animations which cannot be stopped. That triggers migraines for me if I read while the animation is playing. It may have a similar (but more serious) effect on epileptics. — Preceding unsigned comment added by Hetware (talk • contribs) 20:41, 5 March 2023 (UTC)

Clarification on orientation

"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

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

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)

when

When was the change from using analytical solutions to numerical solutions? It seems that in the early days, even though it seems strange now, NASA used analytical solutions, that is analytical geometry. Gah4 (talk) 04:53, 19 March 2021 (UTC)

delta-v

There is a recent change from delta-v. As well as I know it, delta-v (spelled out and spoken) is the usual term, but I am not sure enough, and didn't check and references, to change it. Gah4 (talk) 23:21, 15 June 2022 (UTC)

Calculating orbits with the Conley-Zehnder index & the Floer number

The following article is at the edge of my comprehension. I thought I would post it here so that someone more knowledgeable about the subject would figure a way how to weave it into this article.

• Sloman, Leila (2024-04-15). "Geometers Engineer New Tools to Wrangle Spacecraft Orbits". Quanta Magazine. Retrieved 2024-04-22.

Peaceray (talk) 07:11, 22 April 2024 (UTC)