Henry Spencer wrote: > > On Sat, 8 Feb 2003, Randall Clague wrote: > > >There are things Hubble has been doing for a > > >decade that those ground-based telescopes will *never* do. > > > > I was trying to imagine what some of those things might be... Hubble > > Deep Field. No ground based telescope - correction, no Earth based > > telescope - can look at the same patch of sky for hours and hours and > > hours and hours without blinking. > > Yep. > > And Hubble works farther into the infrared, and much farther into the > ultraviolet, than any ground-based scope can. > > And it has a much darker sky background, which matters when working on > very faint objects. > > And it can point closer to the Sun, although its cautious operating > policies limit that. > > And it can observe rapid time variations without a lot of superimposed > atmospheric noise. > > And -- minor but not entirely insignificant -- it has a clear view of the > entire sky, something that is quite difficult to achieve from any single > point on Earth. > > And, finally, although its high resolution has been exceeded by adaptive > optics and interferometry on the ground, its high resolution comes with > many fewer ifs, ands, and buts. Adaptive optics requires either nearby > bright guide stars, or still-experimental laser guide stars. Imaging > interferometry can observe only bright sources, because you need a fair > number of photons per millisecond to detect interference fringes.
Which says that the repair mission was justified in terms of lead time and opportunity cost, however the dollar figures work out: even _if_ it would have been cheaper to build and launch a replacement unit rather than send up a repair crew, the time required to construct the replacement would have represented lost observing opportunities. (I've seen this assertion made about the Hubble but I'm not at at all sure that I believe it. Assuming that a shuttle launch would have been required for either a replacement telescope or a repair mission, would the cost and effort of constructing replacement hardware on the ground really have been less than what went into the on-orbit retrofit operation?) -dave w _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
