on the HDST

Some of the latest news about telescopes is the High Definition Space Telescope (HDST), proposed by the Association of Universities for Research in Astronomy (AURA) – the folks who run America’s national observatories. The HDST is, as currently drafted, an optical telescope (like the Hubble Space Telescope) with a 12-meter mirror made of folded segments (like the James Webb Space Telescope) that will unfold themselves (like the James Webb Space Telescope) as the telescope goes to position itself in an orbit beyond the Moon (like JWST). Basically, it’s currently envisioned as the James Webb Space Telescope, only bigger and without the need for cold temperatures.

I recently attended a meeting at the American Museum of Natural History announcing this telescope, and it does look impressive: 25x the resolution of Hubble (which is also the gain between DVD and Ultra HD resolution, which justifies their “High Definition” name*). It will also carry with it a starshade that will allow it to block out the light of stars and let it image earth-sized planets orbiting them. That second capability is claimed to be well out of reach for ground-based telescopes, and would provide our first chance of spectroscopically identifying life on other planets. Oxygen, for instance, is highly reactive. To have lots of it in the atmosphere rather than sitting on the ground as rust (like Mars) implies something is constantly replenishing the Oxygen. Something like plants with chlorophyll.

So, it all sounds amazing! And, it’s true; every time we build a bigger telescope we find things we didn’t even know to look for when we started. That’s been the constant history since the origins of the telescope.


This budget is initially expected to be $8-$9 billion dollars** – it’s already starting at the cost of JWST. And this is the James Webb Space Telescope that basically ate all of NASA’s astrophysics budget, and threatened to eat its planetary sciences and manned spaceflight money too before it was turned into a separate line item in NASA’s budget. There’s still some bad blood remaining in the astronomical community and in Congress after all the missions that were cancelled because (at least in part) JWST got too expensive. But now AURA wants to do all that again ON PURPOSE?

There are other things worth considering. Space telescopes don’t have to cost $9 billion dollars. GALEX, an ultraviolet telescope run by NASA and (toward the end) Caltech, cost $150 million (and presumably more to operate). The New Horizons mission to Pluto cost $700 million. I think it would be far better to fund 9 $1 billion missions to do a diverse and more specifically targeted amount of science, than putting it all in one giant do-everything mission.

Consider, also: While a 12-meter HDST telescope would positively dwarf the 2.4-meter Hubble Space Telescope and the 6.5-meter James Webb Space Telescope, as well as all currently operational telescopes on the Earth, we can expect that by the time it launches, at least one of the current super-telescope projects will have succeeded: the 39-meter European Extremely Large Telescope (E-ELT), the 24-meter Grand Magellan Telescope (GMT), or even the 30-meter Thirty Meter Telescope (catchy!). Their light-gathering power will far surpass the HDST, although the HDST will be able to stare at things for far longer, and not have to worry about clouds. As for the blurring effects of the Earth’s atmosphere, adaptive optics systems allow ground-based telescopes to see finer details than HST, and I would expect that trend to continue on into the future. You might not get the 1 part in 10 billion removal of starlight that the HDST proponents say is only possible from space, but that’s one thing, and I’m not yet convinced that that one thing is worth giving up all the other scientific pursuits.

Still, it’s not like increasing ground-based capabilities completely invalidate the HDST. The E-ELT is going to primarily be available for members of the European scientific community; the GMT for partners of the Carnegie Institutes, and the TMT for the US, Japan, and Canada. And that’s ultimately only four telescopes for the whole of the astronomical profession.

Finding signs of life on distant planets is undoubtedly a lofty goal that needs to be done, but if we try to spend $9 billion dollars on it, that’s ALL we will do for a decade. Of course, given the way the US Government budgets things, we might not GET to divide up the $9 billion dollars – we might have to use that $9 billion JWST budget line item or NASA loses it forever. In which case… game on! But I’m not convinced.

* Although you can bet that someone’s famous name would eventually be attached to it. Hubble was Edwin Hubble, the person who discovered that the Andromeda Galaxy really was a distant galaxy, prior to that name the telescope was simply “Space Telescope”. Spitzer was Lyman Spitzer, another highly influential astronomer and one of the main driving forces behind the (Hubble) Space telescope; the telescope that carries HIS name was originally called “Space Infrared Telescope Facility”, and you can occasionally still find references to “SIRTF” in materials related to the Spitzer Space Telescope. James Webb was the NASA administrator during the early parts of the Apollo project and is not related to this astronomer/singer-songwriter.

** The actual plan for HDST shows that they have learned from JWST’s enormous budgeting problems (going from $1.6 billion to $8.8 billion), and they have plans to avoid those mistakes.


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