update_up_vector(player:object, planet:mesh)
{
    up_vector = normalize(planet.up);
    reference_point = ray_trace (object.old_position, -up_vector, planet);
    movement = object.position - object.old_position;
    movement_clamped = movement - up_vector * dot (movement, up_vector);
    reference_point += movement_clamped;
    reference_point = ray_trace (reference_point, -up_vector, planet);
    player.up = normal_vector(mesh, reference_point);
}