The European version of the Hubble Space Telescope archive, now served from ESA's Space Astronomy Centre (ESAC), has its roots back in the early 1980s. At the time, it was felt that European users of Hubble might be handicapped by the need to communicate with, or even physically travel to, STScI, the scientific operations centre of Hubble in Baltimore, Maryland, USA. And so in 1984, ESA and ESO cooperated to operate a Hubble information, utilities and data centre — the Space Telescope European Coordinating Facility (ST–ECF), based at the European Southern Observatory's Headquarters near Munich.
Prominent among its charges was to "provide an efficient means of archiving and cataloguing Space Telescope (ST) data and for retrieving and disseminating non-proprietary ST data". The advent of the web — the ST–ECF's website was registered as number 162 (!) or so — has done away with much of the need for a separate European centre, but the archive continues to be an invaluable resource.
This European archive has always been a dynamic twin of the primary brother at STScI — and not just a black and white copy. Out of necessity and circumstances it was both useful and possible to test and implement now self-evident features like on-the-fly calibration, thumbnails of images and spectra, visibility of all metadata, and web-based archive interfaces to name just a few — sometimes long before they could become part of the primary archive at STScI. The latter has always had much more demanding operational and science policy requirements on its shoulders, making swift changes more difficult.
The HST archive has been a powerful resource in the scientific exploitation of Hubble. One way to determine the scientific impact of an observatory or mission is to count the number of refereed publications that have been produced over the years (see figure above). As of January 2014, there are a total of 11 890 refereed publications based on Hubble data, 776 of which were in 2013 alone (note that this number is not yet "final", and may increase). Of these, more than half come solely from data in the HST archive. The European astronomical community, which makes up roughly one third of the community of Hubble users worldwide, is particularly prominent in exploiting the HST archive resource, as they have authored almost half of the publications based purely on archival data.
When the ST–ECF was closed in 2010, the HST archive was moved to its current home at the European Space Astronomy Centre (ESAC) near Madrid, Spain. It now lives among the collection of ESA space science mission archives. Preparatory work from 2008 to 2010 eased the transition, and also minimised the resources needed for operation and maintenance of the archive.
Since its official inauguration in July 2011, the HST archive at ESAC has served the community flawlessly — as did the original one from the ST–ECF. We see a user family of between 200 and 300 independent IP addresses; this is a bit less than during the ST–ECF's peak times, but at that time we were also handing out the then-new contributions to the Hubble Legacy Archive (HLA) — ACS-Grism spectra, for example. At present, the makeshift implementation of the relocation is being upgraded to a third generation user interface similar to that of XMM and Gaia. At the same time the operational machinery is now modelled in-line with the local standard. Both efforts will eliminate any special needs for maintenance and support.
Now the HST archive finds itself at ESAC, between the archives hosting the extremes of the wavelength range — XMM-Newton on the short (left) side, Herschel covering the infrared on the right, and Planck representing the far-right microwave edge. But rather than leaning back in comfort, we now want the archive to bring all these various components together under a single overarching interface that one might describe as a "multi-frequency science data exploration tool". As we move forward, we would like to hear from you, the HST archive users, on whether you have any ideas that you would like to share on how to best design such a multi-frequency space astronomy archive interface. As a user, what would be your top requirement to scientifically exploit such a facility?
ESA Senior Archive Scientist, ESAC
ESA HST Project Scientist, STScI
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