Orbit Simulator by rodrivas78

Software description:

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Title: "Orbit Simulator"  

Platform: MSX 1

Author: Rodrigo Gonzales

Nick: rodrivas78

Language: "X-BASIC" aka "MSX-BASIC KUN" or "TURBO BASIC"

Category: "SCHAU"

 Files:

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ORBITSIM.BAS: BASIC file

Orbit Simulator.dsk: Disk image for emulator

read_me.txt: Description

screenshot.png

FIGURE_1.png: Resultant velocity explanation 

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With the Orbit Simulator you can, as the name implies, simulate  

orbital trajectories. For this you only need to change (on the 1st 

line) the initial velocity parameters of the "satellite", contained 

in the variables VX and VY. For a better understanding see FIGURE 1. 

You can also redefine the location of the star (attractor) by changing 

variables X and Y. And also the satellite's initial position in 

in PX and PY.

The simulator is not accurate, but you can play around discovering

interesting trajectories that form beautiful images.

Instructions:

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To stop the simulation and return to the BASIC promt, type 'q' (lower case).

Type LIST (or F4 key) to show the listing.

After changing any of the parameters, type RUN (or F5 key).

Physics:

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The simulator contains a (simplified) physics engine. 

It consists of an integrator (of position and velocity) that calculates

and updates the position of the satellite based on the velocity, 

acceleration* (stored respectively in vectors VX, VY, AX and AY) 

and time (T).

The integrator can be divided into two sections: one part calculates

the position and the other updates the speed (taking into account the 

acceleration), both using a time interval, defined in T.

Position calculation:

 Px = Px + Vx * T 

 Py = Py + Vy * T

Velocity calculation:

 Vy = Vy + Ay * T 

 Vx = Vx + Ax * T

*Gravity

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The satellite is always being accelerated towards the star. The closer the trajectory pass through it, the greater the acceleration applied to the satellite (gravitational slingshot).

Description of the variables:

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 X and Y = star initial position

 PX and PY = satellite start position  

 VX = velocity vector on the x-axis  

 VY = velocity vector on the y-axis

 AX and AY = Acceleration vectors

  

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Links:

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GitHub:

https://github.com/rodrivas78/MSX/tree/master/BASIC_10_Liners/Orbit_Simulator

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Acknowledgement:

Thanks to Flávio Martins Prado ("praduca") for revising the code, improving and updating the loader.

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 Rodrigo Gonzales