def aspcapStar_url(location_id, file_, url_header=None):
    """ aspcapStar url generator
    which in principle is able to generate file path

    Parameters
    ----------
    location_id: int
        for 'apo1m', it's 1
        for 'apo25m', it's like PLATE
    file_: string
        FILE
    url_header: string
        if None|'sas', it's set to be
        "https://data.sdss.org/sas/dr13/apogee/spectro/redux/%s/stars/l30e/l30e.2"%version

    Returns
    -------
    url: string
    the url of apStar file

    Note
    ----
    version: string
        currently it's 'r6' @20161031
    """
    if url_header is None or url_header is 'sas':
        url_header = (
            'https://data.sdss.org/sas/dr13/apogee/spectro/redux/r6/stars/l30e/l30e.2'
            )
    url_header = url_header.strip()
    file_ = file_.strip()
    try:
        url = '%s/%s/%s' % (url_header, location_id, file_)
    except:
        raise ValueError('@Cham: This is not an option!')
    return url
