2009 October 17
A while back an interesting paper appeared on astro- ph, the astrophysics preprint server: “Large Instrument Development for Radio Astronomy“, by J. R. Fisher and others who appear to be radio engineers at the National Radio Astronomy Observatory. It’s a whitepaper submitted to the Astro2010 decadal review and I think it’s fair to summarize it as a shot at the Square Kilometer Array concept.
The whitepaper doesn’t explicitly name the SKA but that’s clearly what it’s about. The basic argument is of the “let’s not be hasty” form — it takes time to develop new technologies, combining multiple scientific goals in one observatory is difficult, the costs of complex designs can quickly get out of hand, and so on. The SKA concept, which envisions serious progress in many areas of radio astronomical engineering and pretty much aspires to be the Greatest Radio Telescope For Everyone Evar as well as By Far The Most Expensive Radio Telescope Evar certainly calls for lots of new technologies and a complex design.
I’m sympathetic to pretty much all of their arguments. Building the largest radio telescope ever with new, incompletely-understood technology would, I think, be a really bad idea. From what I’ve seen, “all-in-wonder” designs for any technological system are usually a red flag — flexibility almost always comes at the cost of clean, simple, and correct functionality for any particular purpose. World-class hardware and software engineering is hard and takes time.
That being said, their arguments are the same ones that are always used to discourage innovations. “Oh, it’s risky, it’ll take a long time, we understand the existing stuff so much better.” These arguments are often valid, but technology wouldn’t be much fun if they were always heeded. Of course, “fun” shouldn’t be the operative word when you’re talking about a multi-billion-dollar investment. But in the case of the SKA, there’s no way to build the telescope without requiring some innovation. In the terminology of the whitepaper, it’s just a question of how much risk you’ve retired before you start building it.
In the particular case of the SKA, I’m not sure what I think. One thing is the fact that there’s a long development path leading to the SKA itself — pathfinders and prototypes and precursors, oh my. A lot of work is already happening to build and test the kinds of systems that would be involved in the SKA. It’s not as if ground is going to be broken on the final thing before a detailed design has been worked out and thought through. There won’t be any prototype fully-functioning observatories with thousands of antennas, but I think the basic issues involved in scaling up a large array to a huge array are low-risk: a lot of the requirements are parallelizable, and if you understand a good-sized batch of antennas well, you can understand how a much larger batch is going to behave.
On the other hand, a project as big as the SKA tends to develop its own inertia. If, after another decade of work, there’s trouble on all of the engineering fronts, no one’s going to want to (or even be able to?) just abort the whole project. For small R&D projects, you can say, “OK, it didn’t work, that’s good to know,” but when you’re planning to spend a few billion dollars, the plug just doesn’t get pulled. And in that case, you could be spending lots of money on a telescope that will be merely OK when that money could have been spent on several projects that would have each been great.
Maybe it’s best to think of the SKA like a space mission. Space missions are expensive and risky, so you always see that they deploy pretty unexciting telescope technologies; they get their science leverage from whatever application-specific advantage is provided by being in space. The SKA is also expensive and risky since the upfront capital investment will be so large. So in all probability it will likewise deploy technology that will be boring by the time SKA construction starts; this is OK since the SKA gets its science leverage by being really huge. In this case, the question is, is it possible to deploy boring technology in the SKA model? I think so, since the key pieces are the antennas, feeds, and communications links — those are the things that you really, really don’t want to have to replace en masse. And those are eminently testable in smaller configurations. So hooray, the SKA will work out fine! Good thing we figured that out.