The threat of a nuclear missile strike on United States soil has felt more tangible over the past few years, thanks to North Korea's intercontinental ballistic missile testing and oscillating relationships between the two countries. Against that backdrop, President Donald Trump announced plans on Thursday for the next generation of missile defense on land, sea—and in space.

The Missile Defense Review describes creating capabilities to stop an array of long-range missiles, including those that are hypersonic, or travel faster than the speed of sound. The assessment also discusses more radical ideas, like capabilities that could neutralize a missile anywhere in the world during its initial ascent, space-based tracking and interception technologies, and even high-energy lasers mounted on "airborne platforms."

Anywhere, Any Time, Any Place

And while Trump described a comprehensive, airtight vision of missile defense in his remarks, analysts say the administration's actual report is more of a survey of all possible avenues, from realistic, incremental next steps to unlikely moon shots.

"It would be technically unachievable, and economically ruinous if you tried." Laura Grego, Union of Concerned Scientists

"Our goal is simple: to ensure that we can detect and destroy any missile launched against the United States—anywhere, any time, any place," Trump said in prepared remarks Thursday. But analysts agree that such guarantees are currently technologically impossible. In practice, the only realistic steps are those that build on existing technologies and infrastructure. Pursuing a broader array of the initiatives outlined in the report would be prohibitively expensive. Not to mention that the more the US discusses and pursues elaborate defenses, the more it may provoke rivals like China and Russia to respond by bolstering their offensive capabilities.

"My general take on this is that it’s very much a continuation and consistent with the Obama administration’s approach," says John Plumb, a senior engineer at Rand who served as the principal director for nuclear and missile defense policy at the Pentagon during the Obama administration. "It's a cost-unconstrained review, a no-stone-unturned approach. Fully funded, this would be a tremendous amount of money. But it will not be fully funded."

Among the more realistic proposals: an expansion of ground-based interceptors in Alaska to protect against short-range missiles. The Obama administration brought the number of these interceptors from 30 to 44; the Trump administration suggests a new total of 60. Developing defenses against cruise missiles—which enter the atmosphere for part of their flight—and ultrasonic missiles, as the review suggests, are also logical evolutions. Even developing sensor arrays in space to detect and track missiles, as sci-fi as it sounds, could potentially be achieved off of existing technology.

But in thinking about the next generation of antimissile technologies, it's important to keep in mind that current missile-defense systems aren't particularly reliable, especially against long-range weapons that travel at high speed. This is why tempting ideas like laser interceptors remain so far off. The Defense Department needs to make sure today's defenses work before it can focus on tomorrow's.

Sticker Shock

And then there's the cost. The US has worked to develop missile-defense capabilities in fits and starts for decades, particularly since the "Star Wars" antimissile proposals of the Reagan administration. Current defenses have already run up hundreds of billions of dollars in expense, and critics of this latest appraisal say that even tackling its more realistic aspects would be irresponsibly costly.

"The main significance of the review is that it changes the program from a limited, regional defense system to an unlimited, global defense system. That is simple to say—it is impossible to do," says John Tierney, the executive director of the Center for Arms Control and Non-Proliferation and a former member of the House of Representatives. "The track record and history of ballistic-missile defense in the Department of Defense is one of hype and promise followed by deployment of very limited capability. I expect we’re seeing that pattern repeat itself."