Arecibo Diaries: Traveling on a High-Tech Ship of Discovery
Apr. 22, 2003
by Seth Shostak - Senior Astronomer
The guts of any SETI experiment lie coiled within its digital signal processors. Deep inside these unimposing aluminum boxes, herds of electrons shuttle back and forth at the command of circuitry and software, sorting the incoming cosmic static by frequency, and hunting for the faint, slowly varying tone of distant transmitters.
For more than a decade, Project Phoenix has used digital signal processors originally built for NASAs SETI search the one that was halted in 1993. Sure, weve improved these devices a great deal, but in the digital world, a hardware design thats a dozen years old is museum fodder.
The world has turned. The old processor, known to its pals as the Targeted Search System (TSS), is still around, hunkered down in a tractor-trailer container parked outside the observing room. There was so much electronics in this baby that the trailer required 38 kilowatts of full-time air conditioning just to keep the chips cool and calculating. But we use something different now a new, modular system that is rather straightforwardly called the New Search System (NSS).
The NSS takes up a small fraction of the space of the old signal processor, which means it fits nicely in the Observatorys computer room, saving the cost of those 38 kilowatts. And yes, it does what the old system did, but the NSS has a radically different architecture, as the computer jocks would say. You can grasp the architecture by considering a simple analog Swedish automobile manufacture. Instead of using a single assembly line which is vulnerable to complete failure at any point small teams of stalwart Swedes build complete cars from start to finish.
The teams of the NSS are called PDMs, or Programmable Detection Modules (the careful reader will note the copious appearance of acronyms in this article. Such is the consequence of engineers natural desire for economy of communication, or EOC.) Each PDM handles about 2 MHz of the microwave band, splitting incoming cosmic static into several million channels, and searching for signals that appear in those channels.
So whats the big deal?
Well, the NSS is more than just a replacement for the old system (which, in addition to constant cooling, also required a lot of maintenance.) Its considerably more reliable and reliability is important when youre on the telescope, and every minute is precious. When a PDM fails, scrutiny of the heavens proceeds with the other PDMs. The chance of catastrophic failure that would stop observing is reduced.
As an astronomer who actually sits in front of the glowing ensemble of screens that control the telescope, I experience first-hand the advantages of the NSS. This is far more than a hardware upgrade: the software has also been rewritten. I can now quickly look at incoming signals that are being checked out. Do they look like satellites, or radar, or? Whats their strength? Their drift rate? Autopilot is nice, but to really get the feel of the craft, you have to poke and pull at the controls.
This is the most complex project Ive ever worked on, says Tom Kilsdonk, a tall, soft-spoken software developer whos been crafting code for the NSS for five years. Ive got to say that its really exciting to see a plan come together.
Mike Davis, Director of SETI Projects for the SETI Institute, and a former Director of the Arecibo Observatory, is less restrained. This is impressive as hell, he says. It shows the real benefits of an object-oriented programming approach.
Not having visited hell yet, I cannot fully gauge Davis comparison. But seeing signals pour down the flat panel monitors of the NSS I feel as if Im taking the con on a high-tech ship of discovery.