Download Orbitz!

Overview

My project is called Orbitz, because it simulates the orbits of various planets, moons, and stars around each other. My original idea was that it should be basically a gravitational sandbox, where one can create and play with solar systems of various configurations. You might think of it as a game, where the challenge lies not in defeating another player or some artificial intelligence, but in defeating physics itself.

Back to real life...I ended up running out of time, so I didn't get to implement all of the features I wanted to. I didn't get to do atmospheric effects, any sort of GUI to allow you to add/delete/modify objects mid-simulation, lighting, collisions, or saving/loading simulation state. I fully plan to implement these during the summer, and maybe Zoe will let me post the updated binaries for you to play with!

Features:

• mouse-controllable orbiting camera mode (rotation)
• motion-based camera modes
• texture-mapped planets, moons, and stars
• physically-based object properties (velocity, mass, position, radius, angular velocity); objects modeled using spheres
• time-based animation/calculation of object motion (not frame-based)
• orbit history tracking
• real gravitational model (Newton’s Law of Gravitation)
• skybox around the solar system, textured with an image of the Milky Way

Physics Model:

Orbitz uses Newton's Law of Gravitation to determine the net gravitational force on an object (and from that, its acceleration), affecting the object's velocity (and thus trajectory).

Newton's Law of Gravity (vector form) is expressed as the following:

where G is the gravitational constant, m is the mass of the object being pulled, m_p is the mass of the object doing the pulling, and r is the vector from m's center of mass to m_p's center of mass. For this version of the Orbitz program, G has been hard-coded as 1.0 (but will be adjustable in future versions).

Orbitz uses GLUT's idle function and the Windows high-performance timer to simulate motion. Each time the idle function is called, it uses Windows' high-performance timer to determine the period of time that has elapsed since the last time the idle function was called. The application then calculates the instantaneous accelerations of each object, and simulates the progression of the elapsed time by updating all objects' velocities and positions. There is a threshold for the elapsed time above which the simulation will divide the time interval into smaller intervals (each less than the threshold) and will simulate each small interval instead.

Instructions:

Key Commands:

• SPACE - toggles the simulation's paused state
• T - steps the simulation a few steps
• Z - zooms the camera out
• X - zooms the camera in
• N - snaps the camera to the next target
• C - clears all objects' orbit histories
• M - toggles display of objects' motion vectors
• P - snaps the camera to the previous target
• S - toggles drawing of all objects' orbit histories
• . - increases the simulation's time scale
• , - decreases the simulation's time scale
• H - prints this helpful information

There are five camera modes:

• Look At -- the camera is targeted on an object, and the user can freely rotate the camera around by clicking and dragging with the LEFT mouse button
• Look At Object In Velocity -- the camera is targeted on an object, and always looks TOWARDS the direction the object is traveling
• Look At Object In Acceleration -- the camera is targeted on an object, and always looks TOWARDS the direction the object is accelerating (the direction it is being pulled by the gravitational forces from all the other objects)
• Look At Object Anti Velocity -- the camera is targeted on an object, and always looks FROM the direction the object is traveling (think of it as the front)
• Look At Object Anti Acceleration -- the camera is targeted on an object, and always looks FROM the direction the object is accelerating

To zoom, you can also use your mouse's SCROLL WHEEL. Scroll UP to zoom IN, and DOWN to zoom OUT.

Screenshots:

Resources:

• J.H.T.'s Planetary Pixel Emporium -- sun and planetary texture maps
• CalTech Jet Propulsion Laboratory -- starmap texture
• Björn Jónsson's Planetary Texture Maps -- Callisto texture map
• NeHe's OpenGL Tutorials -- Lesson 39: Introduction to Physical Simulations