Solar-Lander

a small java orbit-sim project using the libGDX framework with a controllable lander

Keybinds

WASD : Movement
V (HOLD) : Show Force Vectors of Lander(redundant, see bottom boxes)
Space (HOLD) : Show Hitboxes
Z (HOLD) : -10x Zoom Out
X (HOLD) : -100x Zoom Out

How it Works

Physics

The program uses primarily uses two physics equations to determine orbits and velocities

(1). The Law of Gravitation: F = G * (m1 * m2) / r^2

• F is the gravitational force between the two objects/planets
• G is the universal gravitational constant, 6.674 x 10^-11
• m1 and m2 are the masses of the two objects
• r is the distance between the center of mass for each object.\

(2). Orbital Velocity: V = SQRT((G * M) / R)

• V is the orbital velocity
• G is the universal gravitational constant, 6.674 x 10^-11
• M is the mass of the central body(assuming orbiting body has insignificant mass in comparison)
• R is the distance between the center of mass for each object.

Code

Generation

• the program starts by generating an array of solarObjects solarSystem[]
• solarSystem[0] is reserved for the central body / sun
• other planets are generated with random radii [700 - 200] and corresponding mass based on (4/3) * pi * (radius)
• then it gets assigned a random position between [10,000 , 0] and [10,000 , 10,000]
• if the planet fails orbitCheck() (it overlaps another planet) it gets new properties
• planets are assigned a starting velocity based on equation (2)
  • by default the starting velocity puts them into a perfect circular orbit

Game-Loop

• position and velocity changes are calculated for both lander and solarSystem[]
• the main viewport extendView is updated and the lander sprite are rendered with a SpriteBatch
• planets and other objects are rendered using a ShapeRender object on extendView
• the ui/labels are then updated and rendered on viewport screenView
• the minimap viewport miniView is updated and has the scaled down system rendered within