public void CreatePlayer(AControlDevice new_player_device)
    {
        GameObject     new_player = Instantiate(player_prefab, Vector3.zero, Quaternion.identity, null);
        PlayerIdentity identity   = new_player.GetComponent <PlayerIdentity>();

        identity.Configure(0, new_player_device, Color.blue);

        GameObject new_ship = Instantiate(
            ship_prefab, Vector3.zero, Quaternion.identity, new_player.transform
            );

        ShipCore core = new_ship.GetComponent <ShipCore>();

        core.BoardPlayer(identity);  // enabled systems.

        // TODO: put this somewhere else.
        core.Mount(Item.ion_drive);
    }