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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."
$4.5 billion? That's far too expensive. I mean, we could keep our troups in Iraq for almost another month for that kind of money! What are they thinking, wasting it on a stupid big telescope.
While the launch slip will help NASA avoid big cash infusions on the program in the near term, Geithner conceded it will not save money in the long term. In fact, he said, about half of the $1 billion in cost growth is now attributable to the two-year delay.
They admit the total cost will be greater, but as funding is dished out on an annual (? periodic) basis, NASA can spread out the slice of funds that the JWST will take over a couple of funding rounds, so that the impact on other projects is lessened.
IAAA (I am an astronomer) and I work on the JWST project from the European Space Agency side (JWST is a joint NASA, ESA, and Canadian Space Agency project).
While it's true that ground-based telescopes with adaptive optics can compete (or beat) the spatial resolution that JWST will deliver, JWST's image quality should be extremely stable across a fairly large field of view, which will deliver more precise measurements. Just as importantly though, at L2, JWST will be very cold (roughly 50 Kelvin or -223C) and thus will detect almost no background emission from the telescope. On the ground, the warm telescope and atmosphere lead to a very bright infrared background against which it's really difficult to see very faint sources.
As a result, JWST will be able to detect and analyse the first galaxies as they formed in the Universe at high redshift and very low-mass stars and planets being born in the Milky Way. At key wavelengths between 2.5 and 20 micrometres, the JWST will be more sensitive than even 30-50 metre diameter ground-based telescopes for imaging.
In the end, JWST and the next generation of extremely large telescopes (ELTs) on the ground will be highly complementary, much as Hubble and the Keck were: JWST will find the very faintest sources in surveys and determine their statistical properties, while the ELTs will take follow-up high-resolution spectroscopy for detailed characterisation of individual sources.
As for L2, there's at least one astronomical satellite (WMAP) there already, with more (e.g. ESA's Herschel) to come before JWST. But don't worry: it's a big place. As for us spending the money on other pet astro projects, err, nope, we're not. JWST involves some very challenging technology and that stuff is just very expensive. Finally, on the issue of flight hardware, we do actually have some of it done: the 18 hexagonal segments of the primary mirror (made out of beryllium) have been fabricated and are now being machined and polished.
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.
The problem with the whole Moon idea is that you will have to build the telescope here on Earth first, then launch it into space in order to get to the Moon. Since space itself is actually preferable to the Moon (i.e. no gravity, no dust, no retro-rockets needed to land, etc.), why not just leave it in space?
It's true that the Moon would act as a shield for radio wavelengths,m but it wouldn't achieve much for optical-IR telescopes really: the ultimate limit to sensitivity is the zodiacal light in the solar system, which you'd see just as much of from the Moon as from near-Earth space. Get the telescope out beyond Jupiter and things get way better.
As for the 1km aperture, well, interferometry is one way to go, since you can hope to get the resolving power of the very long baseline, if not the collecting area. Ground- and space-based optical/IR interferometers are improving / under development and may eventually reach 1km baselines, while 30-50m filled aperture ground-based telescopes will likely be with us within a decade or so.
Finally, all large professional telescopes use mirrors, not lenses: mirrors can be supported against gravity from behind, whereas lenses sag.