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Learning MatLab - Plotting an Orbit

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I'm trying to write a Matlab (well.. octave) code to plot the tradjectory of a satellite in orbit.

 

Unfortunately it just keeps drawing a diagonal line, but I can't for the life of me work out why it wont do any type of "proper" orbit.

 

I think it's nearly there as if I "drop" the satelite (no tangental velocity) it does a sort of 1D elipse.

 

I've attatched the file anyway (renamed .m to .txt as uploader didn't like) if somebody could have a look I would be very appreciative.

 

 

I'm using the following to work out trajectories (given in question);

 

[Math]

r(t + \delta t) = 2r(t) - r(t-\delta t) + \delta t^2 * F(t)/m...............and.......

\\

\\

v = 1/(2 \delta t)*x(t+\delta t) - x(t-\delta t))

[/Math]

 

F, r, and v are 3D vectors for the Force, posion and velocity respectively.

 

I'm plotting the x and z values of r(x,y,z)- to try and generate a loop, elipse etc of a 2D orbit.

Orbit2.txt

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OK turns out it is working... sort of. My point was being sucked into the black hole and then the programme got upset and decided to spit it out creating a massive line that dwarfed the orbit before being "sucked in".

 

However- the orbits still seem a little odd though- the origin of the black hole (0,0) is far too close to the elipse IMO.

 

If somebody could take a look it'd be really good.

 

I've attatched some pics and the altered code for a reasonable orbit. If you want to change the "starting velocties" change r and/ or rOld, in units of about 100- there is not explicit starting velocity that changes the tradjectory (it is effectively (r-rOld)/dt).

 

You can increase the "length" of the orbit it is showing by changing t.

Orbit2 (2).txt

Launch into Elipse.jpg

Launch into escape.jpg

Launch into wierd orbit then escape.jpg

Precessional Elipse.jpg

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