Re: Orbital simulator alogorithms

From: Hop David (hopspageHATESSPAaMmM_at_tabletoptelephone.com)
Date: 09/25/04 

To: sci-space-tech@moderators.isc.org
Date: Sat, 25 Sep 2004 11:05:05 -0700

Jim McCauley wrote:
> "Hop David" <hopspageHATESSPAaMmM@tabletoptelephone.com> wrote in message
> news:41531C4A.5010801@tabletoptelephone.com...
>
>>I'm trying to model orbits with Lunar perturbations in Microsoft Excel
>
>
> This does not really answer the question, but I am reminded of an algorithm
> for simple orbits developed by some middle-school students of mine about
> twenty years ago. They had challenged themselves to create a program in the
> Logo computer language to cause the graphical "turtle" to behave like a
> satellite in orbit. Here is what they came up with:
>
> 1. Remember three things:
> a. the direction you're pointed in now
> b. the "sideways speed" you're traveling at now
> c. the position you occupy now.
> 2. Point toward the earth.
> 3. Fall for a distance determined by the influence of the inverse
> square law at your current altitude.
> 4. Turn in the direction you remembered from Step 1.
> 5. Go forward the amount of the "sideways speed" from Step 1.
> 6. Remember where you are right now.
> 7. Jump back to your position at Step 1.
> 8. Point toward the position you remembered at Step 6.
> 9. Jump back to the position you remembered at Step 6.
> 10. Go back to Step 1.
>
> Essentially, it's vector addition carried out in a sequence of steps.
>
> Provided that the values for planetary mass and satellite speed are chosen
> with care, the small line segments produced by this algorithm approximate an
> orbital ellipse quite nicely. The algorithm and the Logo program in which
> it is realized are comprehensible by students as young as third grade.
>
>
> Jim McCauley
>
>

I remember having a blast playing with Logo. Haven't seen that program
for a long time. 

-- 
Hop David
http://clowder.net/hop/index.html

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