What is Orbiter Space Flight Simulator?

[Ulysees]

Newton's Laws: (from memory)
1. An object at rest remains at rest, or an object in motion stays in linear constant motion unless acted upon by a force.

2. F=ma
3. For every action, there is an equal but opposite reaction.

We're talking about Newton's law of gravity, not Newton's laws of motion.

But there's no reason you can't integrate an ellipsoid, or any other shape, without going beyond Newton's laws.

I've done this for a living. It's another thing we're talking about here (whether Newton's law can be used exactly in anything but point masses and equivalent spherical shells)

 

[D H]

You said "wrong" below this:

Well don't forget Newton's law of gravity only makes sense for point masses.

Wrong.

That is because what you wrote is wrong.

I've done this for a living. It's another thing we're talking about here (whether Newton's law can be used exactly in anything but point masses and equivalent spherical shells)

I gave the exact answer in post #58. Whether that integral is computable in closed form or has to be approximated numerically is a different question. The integral is the exact answer to the acceleration due to gravity. BTW, this is exactly what I do for a living (one of the things I do for a living). Moreover, NASA has many people at JPL and Goddard working on developing high-precision gravity models. Until recently they used ephemeris data from satellites that had some other primary objective as the basis for these gravity models. NASA and ESA together are now flying an expensive pair of satellites whose sole objective is developing even higher-precision gravity models of the Earth. Do you think they would this just for fun?

 

[tony873004]

If you're referring to F=GMm/d^2, then yes, this works only for point masses. But throw a double integral symbol in front of it, with the limits of integration describing your desired shape, and you can do any shape you want. You're still applying the point mass formula GMm / d^2 (or one M for acceleration) to each differential element. And if you want something that is not uniform in density, and you have your density function, then write it the way DH did.

 

[Ulysees]

NASA and ESA together are now flying an expensive pair of satellites whose sole objective is developing even higher-precision gravity models of the Earth. Do you think they would this just for fun?

Certainly not, but we were talking about the formation of a solar system from dust, and you are introducing ellipsoids. Don't you think they're from another application?

 

[Ulysees]

throw a double integral symbol in front of it, with the limits of integration describing your desired shape, and you can do any shape you want.

Not in the context of dust forming proto-planets in order to test Titius bode.

Even if an analytical formula came out from integration, you still can't use it in this context.

 

[tony873004]

Not in the context of dust forming proto-planets in order to test Titius bode.

I agree with you. You're not going to be using Newton's laws of gravity for dust. Objects need to be a few km wide before their gravity is significant enough to consider. I don't think it's fully understood yet, what happens prior to this point.

And that's one of many reasons why my program will have a difficult time helping you verify TB. My program is GM/d^2 inserted into an endless loop.

 

[Ulysees]

Why don't you post a copy of your program in case anyone wants to play with it. Or have you already?

 

[Ulysees]

Objects need to be a few km wide before their gravity is significant enough to consider.

Well you'd start with thick "dust" then, wouldn't you. Like that simulation of the formation of the moon from a collision of a large object with Earth: both objects turn into thick "dust" at places.

 

[D H]

Ulysses, please stop with the Titus-Bode law. It is numerology. No causal mechanism, and debunked by Neptune.

 

[Ulysees]

Red cars cost more to insure in the UK. Insurance companies do not seek a cause why red cars have higher statistics for accidents. They just use the result and charge more.

So if you do not know a cause for an observed statistical trend, that does not mean no cause exists. It just means you don't know a cause yet. In trials of new drugs they give a license if the drug gives results that are "statistically significant", and they have equations for deciding if a result is

a. statistically significant (and therefore caused by the drug) or

b. not significant (and therefore just chance), and the drug is rejected.

So refusing to even simulate the formation of planets roughly in search of ANY statistical pattern (if it exists it should appear after many repeats), refusing to even test is not a scientific approach, it is dogmatic thinking that has no place in science.

 

[D H]

We have now observed other solar systems. In several of these systems, the large gas giants orbit very close to their parent star. The Titus-Bode Law does not explain this phenomenon. In our solar system, the Titus-Bode law predicts a planet between Mars and Jupiter. No planet exists there; just a bunch of asteroids that collectively mass far less than any planet and that could not have formed into a planet because of the disruptive influence of Jupiter. The Titus-Bode Law does not explain this phenomenon. Neptune is also a member of our solar system, and it completely defies the Titus-Bode law.

Falsifiability and falsification are cornerstones of the scientific method. Scientific theories can never be proven true, but they can be proven false by one well-confirmed piece of falsifying evidence. Several scientific hypotheses to explain some phenomena have fallen by the wayside because of evidence against them. The Titus-Bode law is one such rejected hypothesis. It is now viewed as little more than numerology. The analogy to the insurance industry is a false analogy because science operates with the scientific method while the insurance industry does not. The medical industry operates on the edge of the scientific method because of ethics, the complicated nature of drug interactions, and a host of other reasons. A single bad reaction or failed cure is not an adequate reason to reject a drug that does work in some people.

The existence of Neptune is more than enough to reject the Titus-Bode law in physics and astronomy. Please desist with this stuff on the Titus-Bode law.

 

[Aethelwulffe]

Back to the subject of creating an orbital simulator, are any of you guys familiar with Orbiter? It is a free space-flight simulator. I myself am a pretty prolific add-on developer for it, having done some Mars mission stuff as well as some (well about 700 mb actually) SCI-FI add-ons for it. There is quite a great support community, and a lot of fun things to do with existing packages and add-ons, not to mention the SDK.
This software is being used in lots of space flight simulations for education, as well as a rendering engine for video presentations of space missions. Best of all, it is FREE, has a HUGE in-depth API and SDK, as well as tons of support from lots and lots of top-notch developers that all contribute for free and make their works free to the public, as well as help set up simulations in classrooms all over the world. If nothing else, the global/local coordinate system and other elements would be a good thing to check out for someone starting their own project...though you would be a few million man-years behind that particular project which has been developed since 1999 or so.
Just google Orbiter Space Flight Simulator and check it out if you care to. It's no joke, and it's no cheezy bit of work.