The BBC is reporting that the last mirror segment has been machined for the upcoming James Webb Space Telescope (JWST), scheduled for launch in 2013 (image credit: NASA). JWST is a huge infrared telescope — the mirror is so big (6.5 m / 21.3 ft in diameter) that it can’t fit in any launch vehicle, and so has to be built in segments and essentially unfolded once in space. Unfortunately, as is sometimes the case, a really good article is marred by a bad headline — “Telescope mirror nears completion.”
In reality, while the progress is encouraging, the mirror is a LONG way from completion. The mirror will consist of 18 hexagonal elements made from beryllium — a very light (and also, FWIW, very toxic) metal. What’s been accomplished so far (with the mirror) has been the production of the basic mirror segments — in amateur astronomy parlance, the mirror “blanks.” The detailed work of grinding and polishing the segments to their final shapes is now fully under way. This is all cutting edge (no pun intended) work, so kudos to all concerned.
Now why, you might ask, is this brute being built? It’s not really as a successor to (or replacement for) Hubble, since Hubble primarily works in visible wavelengths of light. JWST will be an infrared telescope, essentially capturing images of temperature. So in a sense, it’ll be the successor to the current Spitzer space telescope. Infrared astronomy has a number of advantages over visual astronomy, in particular the fact that many items of interest aren’t terribly bright in optical wavelengths — but almost everything gives off heat. JWST’s goals are grouped into four main themes:
- Identify the first bright objects that formed in the early Universe
- Determine how galaxies and dark matter evolved to the present day
- Understand the birth of stars and protoplanetary systems
- Study the physical and chemical properties of solar systems
An infrared telescope is ideal for all these studies, and infrared astronomy needs cold conditions. So, the JWST optics will be cooled to just a few tens of degrees above absolute zero once it’s in space. To pull this off, the bulk of the telescope will spend its working life hiding from the Sun, behind a thermal shield (the multi-layered thing in the above picture) the size of a tennis court.
I’ll describe the mission in more detail as things progress, but in the meantime, make sure to check out the JWST home page.
Update: the official Goddard Space Flight Center press release on this milestone is here.