零重力世界中的速度递减

我试图在Box2D中创建一个围绕静态物体旋转的动态物体。 我有一个零重力的世界 DistanceJoint

我做错什么了吗?是应该在每一步重新创建线速度,还是我可以将这项工作委托给Box2D?

以下是相关代码:

// positions of both bodies

Vector2 planetPosition = new Vector2(x1 / Physics.RATIO, y1 / Physics.RATIO);
Vector2 satellitePosition = new Vector2(x2 / Physics.RATIO, y2 / Physics.RATIO);


// creating static body

BodyDef planetBodyDef = new BodyDef();
planetBodyDef.type = BodyType.StaticBody;
planetBodyDef.position.set(planetPosition);
planetBodyDef.angularDamping = 0;
planetBodyDef.linearDamping = 0;

planetBody = _world.createBody(planetBodyDef);

CircleShape planetShapeDef = new CircleShape();
planetShapeDef.setRadius(40);

FixtureDef planetFixtureDef = new FixtureDef();
planetFixtureDef.shape = planetShapeDef;
planetFixtureDef.density = 0.7f;
planetFixtureDef.friction = 0;

planetBody.createFixture(planetFixtureDef);

// creating dynamic body

BodyDef satelliteBodyDef = new BodyDef();
satelliteBodyDef.type = BodyType.DynamicBody;
satelliteBodyDef.position.set(satellitePosition);
satelliteBodyDef.linearDamping = 0;
satelliteBodyDef.angularDamping = 0;

satelliteBody = _world.createBody(satelliteBodyDef);

CircleShape satelliteShapeDef = new CircleShape();
satelliteShapeDef.setRadius(10);

FixtureDef satelliteFixtureDef = new FixtureDef();
satelliteFixtureDef.shape = satelliteShapeDef;
satelliteFixtureDef.density = 0.7f;
satelliteFixtureDef.friction = 0;

satelliteBody.createFixture(satelliteFixtureDef);

// create DistanceJoint between bodies

DistanceJointDef jointDef = new DistanceJointDef();        
jointDef.initialize(satelliteBody, planetBody, satellitePosition, planetPosition);
jointDef.collideConnected = false;
jointDef.dampingRatio = 0;

_world.createJoint(jointDef);

// set initial velocity

satelliteBody.setLinearVelocity(new Vector2(0, 30.0f)); // orthogonal to the joint