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Hubble Replacement on Slow Track
iamlucky13 writes "The targeted launch date for the James Webb Space Telescope, an infrared space observatory currently nearing the completion of the design stage, has been pushed back 2 years to help deal with a price tag that has grown to $4.5 billion. This advanced telescope is designed to build upon the achievements of the Hubble after its retirement, peering into deep space with it's large 6.5 meter primary mirror from the L2 point 1.5 million kilometers from earth. As the highest priority science mission on NASA's agenda, a decision was made to spread the extra cost over additional budget cycles rather than compromise it's instrument package. Regardless, some of the lower priority missions may feel the impact of the JWST cost growth."
We don't tend to call JWST "the successor to HST" so much anymore, but of course, the moniker has stuck. That said, there is a fair amount of overlap between the two: HST gets out to 2.5 microns with NICMOS, while JWST will reach down to 0.6 microns with NIRCam and NIRSpec. Of course, with STIS dead on the HST now, it's UV capabilities are reduced.
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In the end, it's a question of scientific drivers: the US Decadal Report placed JWST first on its priority list because astronomers argued more strongly for the high-redshift/star&planet formation science that it can do than argued for a new UV-optical telescope. Sure, it'd be great to have full coverage at all wavelengths, but money is finite and hard choices have to be made.
Besides, one of the key reasons JWST doesn't press too hard on the short wavelength end is because of the whole new generation of ground-based ELTs which will compete very handsomely with JWST at below 2 microns. Ok, that's not the UV, but
On the budget overrun, well, as a European, I can't speak for NASA really, but most of the cost inflation so far has been there. The key elements which raised the budget by 1G$ this year were:
(A) Revised cost request from the contractors, Northrup Grumman Space Technologies (NGST, ironically), based on increased specifications. NASA generally lets contracts which allow cost growth like this, as true fixed-cost contracts would be completely unaffordable at the get go.
(B) A huge delay incurred by the former NASA administrator (O'Keefe) not signing off on the use of a European Ariane 5 launcher, at ESA expense. There was serious wrangling at the congressional and lobbyist level to dump this in favour of a US launcher (e.g. Delta Heavy), which led to long delays (and thus cost overruns) in interfacing NGST (the company) with Arianespace. One of the first things Mike Griffin did when he came in was to sign off on this, breaking the logjam. However, as Paul Geithner at NASA said in the parent article, this has yet to pass the highest levels of US government, so could yet bite our ass again. But it's hardly fair to lay this one on the JWST per se: it's way beyond our pay grade.
(C) The transition to full cost accounting at NASA Goddard, the prime centre for JWST. In this case, this was money that was always going to be spent at Goddard on roads, buildings, etc., but had not been posted directly on JWST's budget. Again, hardly JWST's fault per se, but makes us look bad again.
In the end, as you've worked on NGST/JWST, you'll know it's a really challenging mission. 4.5$G is a lot of money, but the project (at all levels) is working very, very hard to make this thing work and make it great scientific value for that money, whatever that really means in this game.