Today was the first day of the ELSA Conference. Talks focused on the status of Gaia hardware and software, with a lot of concentration on the expected effects of radiation damage to the CCDs and strategies for dealing with that. There were many great contributions; a few facts that stuck in my mind are the following:
Prusti (ESA) emphasized the point that the intermediate or preliminary catalog released in 2015 will only be slightly less good than the final catalog of 2020, if all goes well. He argued that Gaia should release preliminary catalogs since surveys like SDSS have prepared the astronomical community for non-permanent and non-final and buggy catalogs. I agree.
Charvet (EADS) showed the spacecraft design and assembly. It is made from silicon carbide, not metal, for rigidity and stability. Apparently this makes fabrication much more difficult. The mirrors are silvered, polished silicon carbide, attached to a silicon carbide skeleton. The machining of the parts is good to a few microns and there is an on-board interferometer that continuously measures the internal distances relevant to the
basic angle (between the two lines of sight) at the picometer level. It also has an on-board atomic clock. He strongly implied that this is the most challenging thing anyone at EADS has worked on.
van Leeuwen (Cambridge) spoke about spacecraft spin and attitude. He showed that his re-reduction of the Hipparcos catalog (published in book form) came from permitting the spacecraft to be jerked or
clanked by configurational changes (related to temperature changes?). He found 1600 such events in the time-stream and when he modeled them, the systematic errors in the data set went down by a factor of five. I commented after his talk that the real message from his talk was not about spacecraft attitude but about the fact that it was possible to re-analyze the raw data stream. The Gaia position seems to be that raw data will be preserved and that re-analyses will be permitted, as long as they don't cost the Consortium anything. That's fine with me.
O'Mullane (ESA) gave a romp through the computer facilities and made some nice points about databases (customizability and the associated customer service is everything). He does not consider it crucial to go with open-source, in part because there is an abstraction layer between the software and the database, so change of vendor is (relatively) cheap. He then went on to say how good his experience has been with Amazon EC2, which doesn't surprise me, although he impressed me (and the crowd) by noting that while it takes months for ESA to buy him a computer, he can try out the very same device on EC2 in five minutes. That's not insignificant. From a straight-up money point of view, he is right that EC2 beats any owned hardware, unless you really can task it 24-7-365.