Capt. Edward H. Lundquist, U.S. Navy (Ret.): You have referred to futuristic directed-energy weapons as having “bottomless magazines.” What does that mean?

Rear Adm. Nevin P. Carr, Jr.: We call them “bottomless” because they’re deeper, but, really, your fuel tank becomes a magazine-limiter. In the case of directed-energy weapons, refueling becomes rearming, so it can be a very effective weapon, but it changes lots of other things about the equation, such as logistics. If we no longer have to buy and produce missiles and ship them around the country by truck or by rail to ships that then transport them to other ships, we will have very deep magazines and be very self-sufficient. One of the hallmarks of the U.S. Navy has always been the ability to sustain ourselves for a long period of time, and this just makes it even better. However, I don’t see directed-energy weapons and electromagnetic railguns replacing conventional weapons, especially in the near future. They’re going to supplement those weapons. There will be tactical situations sometimes that are optimized for one or another. We’re not going to flip a switch tomorrow and have everything be laser sharp. It’s going to be a long, long time.

What are the research and development challenges to make a practical system?
We have prototype efforts under way for both free-electron laser [FEL] and railgun. Each effort is an investment of more than $100 million. The FELs are being built by a Boeing-led team out at Los Alamos National Lab in Los Alamos, N.M., and that effort is aimed at producing a 100-kilowatt direct-energy beam using a linear accelerator, or FEL. That would be a stepping stone on the way to a megawatt energy beam because the only way you’re going to get megawatt directed energy is with chemical lasers or FEL, and chemical lasers are just not suitable for shipboard use.

An FEL requires a linear accelerator  – the one at Stanford University is 2 miles long. How are we going to fit something that big inside a ship?

It doesn’t have to be 2 miles long. The Stanford facility exists to do things other than produce a free-electron beam. There’s a linear accelerator about the size of a football field that we have been experimenting with at the Jefferson National Lab in Newport News, Va. Clearly, that’s still too big, but there are linear accelerators as large as a table. The trick is to get the accelerator small, robust, and protected enough so that it can move around on a ship at sea and produce the power level that we want. Our belief is that we can get that volume down to 50 feet, and the width of a destroyer is about 50 feet, just to put it in perspective. That’s still a large volume, but it’s something you could build a ship around.

So what do we need to do to get there?
We need to continue to explore the many things that go into shrinking the size of the linear accelerator to producing the electrons with the “gun,” as it’s called. It actually emits the electrons. The optics are very important. With the FEL, once you produce this beam you can tune the wavelength to find the most favorable propagation windows within the atmosphere and optimize your laser. That’s one of the drawbacks of a solid-state laser: It’s a fixed-width single wavelength, which is a function of the lasing medium. Changing the wavelength of your beam is just the first part. You now must have optics that can steer that changing beam around, so you have to be able to adapt your mirrors. That’s a science all in its own. There are many moving parts.

We also have an FEL facility at the Naval Postgraduate School in Monterey, Calif., that we obtained from Stanford. That’s a very important part of this whole effort, because that’s the only place where we have young naval officers in uniform experimenting with this technology and learning about it. They’re the ones who are going to become senior naval officers who develop tactics and concepts of operations. Today’s young people are digital natives, and we’re digital immigrants. They’ll be the directed-energy natives of tomorrow. They understand it from the inside.

What about railguns?
The project is being executed extremely well. They’re hitting every project milestone. We had the world record shot at 32 megajoules [MJ] in December 2010. We’re going to plateau at 32 MJ for a while. That is where I want to focus our efforts to get the first prototype available in the fiscal year 2017 timeframe.

When you say “prototype,” you’re talking about something that could go on a ship?
It’s something you could design into the front end of a ship or place on a large ship that could host it. One of the main challenges with railgun, in addition to understanding what’s going on inside the barrel at the very high velocities and high temperatures, is getting the power density up so we can get the size down. Just like you talked about the size challenge we had with the linear accelerator, right now the rail gun you’ve seen down at Dahlgren, Va., takes a garage full of capacitors. The size of the power supply necessary to achieve these shots has steadily shrunk. That has been a concerted part of our effort. It’s tracking right down parametrically toward the region that we need to get it to so we can fit in the front end of a ship.

Railgun is like directed energy: It’s flexible, it’s scalable, you can dial the velocities you want for the tactical scenario, and it’s multi-mission. It’s a long-range critical strike weapon, but it also can be surface-strike, and we’re very interested in its application to air defense.

This article first appeared in the Defense, Spring 2011 Edition.