绕地球旋转的彗星

Question

I'm trying to make a simple game. Tell me how to make object (comet) fly and rotate around orbit of another object (planet). I could only make the comet turn and fly toward the planet, but it is necessary that when a certain distance is reached, the comet starts to rotate around the planet's orbit.

IMAGE

this.mesh.translateZ(this.speed);

if (this.target.position.distanceTo(this.mesh.position) >= 100) {
    let targetQuaternion = new THREE.Quaternion();
    let rotationMatrix = new THREE.Matrix4();
    rotationMatrix.lookAt(this.mesh.position, this.target.position, this.mesh.up);
    targetQuaternion.setFromRotationMatrix(rotationMatrix);

    if (!this.mesh.quaternion.equals(targetQuaternion)) {
        let step = 0.01;
        this.mesh.quaternion.rotateTowards(targetQuaternion, step);
    }
} else {
    //how to make a comet(this.mesh) fly around the orbit of the planet(this.target)?
}

Answer 1

The simplest way to make one object orbit another is to utilize parent-child relationships. If you add a child to an object it shares a transformation, so when the parent is rotated the child is rotated with it - and when the child has a large translation offset, it effectively "orbits" the parent.

Very simple example of this:

init() {
    this.planet = new Mesh(new SphereBufferGeometry(100))
    this.satellite = new Mesh(new SphereBufferGeometry(5))
    this.satelliteCenter = new Object3D()

    this.satellite.position.set(1000,0,0)
    this.satelliteCenter.add(this.satellite)

    this.scene.add(this.planet)
    this.scene.add(this.satelliteCenter)
}

update() {
    this.satelliteCenter.rotateY(Math.PI / 2000) // one full revolution every 1000 frames
}