[myblake]

The article does mention advances in supercapaciter design as one of the enabling technologies, but I suspect just charging the things requires a ton of power. Let's do some back of the envelope physics with what we know (and reasonable ball park guesses when we don't)!

It's traveling 4K mph or about 1800m/s, let's assume since its 24in long and largely tungsten it has a mass of around 60kg. 1/2 * mass * velocity ^2 means it needs 97.2 megajoules of power. That's about 4 seconds for a 25MW reactor, so I guess you're right something smaller could fire it less rapidly, though the one every 6 seconds they cite as desired would require that much power.