One of the smaller line items in the Missile Defense Agency’s $9.9 billion budget request for 2019 is also one of the most interesting: $66 million to keep developing a laser that can be mounted on a drone and used to destroy enemy missiles on the launch pad — or shortly after takeoff.

That amount includes $61 million to continue the laser-on-a-drone program, called the Low Power Laser Demonstrator, or LPLD, and $5 million to scale up its laser to sufficient destructive power.

Why does a low-power laser cost $61 million but scaling it up to sufficient power only cost $5 million? The answer lies in recent innovations in solid-state fiber lasers. Unlike highly volatile chemical lasers or less powerful solid-state bulk lasers, solid-state fiber lasers use the same sort of fiber-optic technology that forms the backbone of the information economy. Adding more power has become a matter of just adding more fiber.

Last fall, Lockheed Martin, Boeing, and General Atomics all received contracts for the program’s first phase; each will present its own solution to the Pentagon in the months ahead. The military will pick one winner to continue; the goal is to have something ready for testing by 2020.

So the LPLD appears to be on track. But the MDA's budget proposal — about $2 billion greater than the 2018 request — reflects a past year of ups and downs, as well as the work ahead to overcome broad skepticism and setbacks that have some calling U.S. missile defense a paper tiger.

MDA is seeking $852 million to integrate the SM-3 IIA interceptor missile onto Aegis-equipped destroyers. The hope is that these will allow the U.S. to defend sites like Guam, Japan, and possibly Hawaii from North Korean attacks. In February 2017, the Pentagon announced that they had successfully tested the new missiles. But just weeks ago, the agency announced that the most recent test of the SM-3 IIA had failed.

They said little else about that flub, until today.

“What we were testing there was something called ‘engage on remote.’ That part of it required a lot of steps to get there in terms of queuing and tracking. Notification and the launch of the SM-3 IIA missile. All of that went as planned. What occurred was, after the launch of the SM-3 IIA missile, there was an anomaly. At this time, we are still looking,” Gary Pennett, who directs MDA operations, told reporters during a Pentagon briefing on Monday. The agency has convened a failure review board, he said. But the problem isn’t big enough to ground the entire effort. “It was isolated pretty much to the interceptor.”

That’s good news because it means that all the other components—from the satellites that pick up the heat signature of the target missile, to the radars at sea that chart its trajectory, to the launch controls to the boosters on the rocket itself—performed as they were supposed to.

MDA officials anticipate that they will procure the SM-3 IIA by the end of the year for deployment to Poland's land-based, Aegis-controlled missile defense battery. That assumes the review goes well and they can fix the problem that caused the last failure. “We will not fly another missile until we understand what failed on that missile,” Pennett said. “It may be something relatively straightforward. We will understand what is wrong with it before we put it on contract.”

The MDA budget also alludes to the agency’s future anxieties, including next-generation hypersonic missiles. The agency is asking for $120 million to begin inventing defenses against them.

There’s also $926.4 million for Ground-Based Midcourse Defense interceptors in Alaska. The agency will procure and dig silos for 20 more on top of the 40 in the ground now. (Silo building and emplacement is an additional $524 million.) These are essentially the country’s last real line of defense against missiles that might strike the continental United States. Their job is to hit the incoming missile in space, at the missile’s apex. Their record, historically, is spotty at best. But the Pentagon successfully tested its newest seekers for GMD interceptor in May.