def _get_spacecraftid(spid):
    """
    Normalizes Landsat SPACECRAFT_ID fields

    'Landsat_8' -> 'L8', 'Landsat5' -> 'L5' etc
    """
    if spid.upper().startswith("LANDSAT"):
        return spid[0].upper() + spid[-1]
    else:
        return spid