List of mirror URLs for IERS download

Both of the USNO hosts (maia.usno.navy.mil, toshi.nofs.navy.mil) for retrieving the IERS Bulletin A dataset are flaky. Instead of a primary URL specified by the configuration setting utils.iers.iers_auto_url and mirror URL by utils.iers.iers_auto_url_mirror, I suggest a single list of URLs.

Here is what I propose for backward compatibility:

• Understand both iers_auto_url and iers_auto_url_mirror to be either a string or a list of strings.
• Construct the list of URLs to try by concatenating all of the URLs from iers_auto_url and iers_auto_url_mirror and removing duplicates.
• Deprecate the iers_auto_url_mirror configuration setting for removal in a future release.

Here is a possible default URL list:

• http://maia.usno.navy.mil/ser7/finals2000A.all
• http://toshi.nofs.navy.mil/ser7/finals2000A.all
• ftp://cddis.gsfc.nasa.gov/pub/products/iers/finals2000A.all
• https://datacenter.iers.org/data/9/finals2000A.all

[bhazelton]

I’m not sure if this is the right thread, but there’s a big red warning on both http://maia.usno.navy.mil/ and http://toshi.nofs.navy.mil/ saying that they will be down for maintenance from Oct. 24 2019 until April 30 2020 (6 months!). Is the community already aware of this?

[lpsinger]

@pllim, no, it’s still really flaky. Our project (growth-astro/growth-too-marshal) has to download the IERS files in its CI tests, and even with the https URL, it’s failing more often than it is succeeding. I think that we really do need a list of fallback URLs. Also, astroplan needs to be able to use the fallbacks.