如何在Box2D中多次创建相同的主体？

Question

下面的代码是一个在屏幕上从右向左移动的单个小行星。我想要的是创建一个在时间间隔后创建的无限数量的这些。我该怎么做？

//ASTEROID

    ballD.type = BodyType.DynamicBody;

    //random location for asteroid
    int aLoc = (int) (aLocation * 15);
    float x = 260;
    switch(aLoc)
    {
    case 0:
        ballD.position.set(x, -110);
        break;
    case 1:
        ballD.position.set(x, -95);
        break;
    case 2:
        ballD.position.set(x, -80);
        break;
    case 3:
        ballD.position.set(x, -65);
        break;
    case 4:
        ballD.position.set(x, -50);
        break;
    case 5:
        ballD.position.set(x, -35);
        break;
    case 6:
        ballD.position.set(x, -20);
        break;
    case 7:
        ballD.position.set(x, -5);
        break;
    case 8:
        ballD.position.set(x, 10);
        break;
    case 9:
        ballD.position.set(x, 25);
        break;
    case 10:
        ballD.position.set(x, 40);
        break;
    case 11:
        ballD.position.set(x, 55);
        break;
    case 12:
        ballD.position.set(x, 70);
        break;
    case 13:
        ballD.position.set(x, 85);
        break;
    default:
        ballD.position.set(x, 0);
    }

    PolygonShape asteroid = new PolygonShape();
    asteroid.setAsBox(10f, 10);

    //asteroid definition
    fDef.shape = asteroid;
    fDef.density = .5f;
    fDef.friction = .25f;
    fDef.restitution = .75f;

    a = world.createBody(ballD);
    a.createFixture(fDef);

   //asteroid image
    aSprite = new Sprite(new Texture("img/asteroid-icon.png"));
    aSprite.setSize(10f * 4, 10f * 4);
    aSprite.setOrigin(aSprite.getWidth() / 2, aSprite.getHeight() / 2);
    a.setUserData(aSprite);

    asteroid.dispose();