The Defense Department will study the possibility of space weapons — perhaps particle beams, ray guns, space lasers, or orbiting missiles — that could intercept enemy missiles coming off the launch pad, according to a senior administration official who briefed reporters on the Missile Defense Review, due out on Thursday. But the Pentagon will forgo actually developing them, for now. It’s part of the Trump administration’s effort to “expand the scope of what we’re postured to defend against,” the official said.

Much has changed since the Pentagon’s last attempt to publicly frame the state of missile defense and the way forward: 2010’s Ballistic Missile Defense Review.

The new review is a response “to an environment in which we have not just ballistic missile threats but also cruise missile threats and novel types of weapons like hypersonics” — from China, Russia, and even elsewhere, the official said.

The study might last six months or so, according to sources who spoke to Defense News.

The review will also discuss prospects for using SM3 IIA missiles, of the sort on Aegis-class destroyers, as ICBM interceptors, with testing to occur in 2020. So far, the SM3 IIA has tested well against mid-range missiles that pose a regional threat (think Guam.) The review will also look to build on previous experimentation showing that the F-35 Joint Strike Fighter could be an ICBM interceptor during the missile's boost phase.

It will also reportedly highlight the potential use of directed energy weapons on drones for the same purpose.

Michael Griffin, the defense undersecretary for research and engineering, has pushed to expand U.S. missile defenses to confront growing Chinese and Russian capabilities and has suggested that the United States should look to directed energy, including laser, weapons in space as one potential solution to shoot down rockets during the critical boost phase, as they are just lifting off.

These new weapons would be partially cued by a planned constellation of sensor satellites in low Earth orbit that will keep tabs on Russian, North Korean, or Chinese mobile missiles — part of the “space-based sensor layer” that is to be in place by 2023 under a program backed by U.S. Strategic Command’s Air Force Gen. John Hyten.

The official said the review calls more study of space-based weapons, but would “not direct the fielding of anything or development of anything specific. It’s an area we are studying but not one we have made a concrete decision.”

Kingston Reif, who leads disarmament and threat-reduction policy at the Arms Control Association, said the call for more study on space-based lasers underlines how controversial such space-based interceptors are.

“DoD had a year to study this and couldn't come to an agreement! Further study should lead to the same inescapable conclusion: space-based interceptors would be unaffordable, unworkable, and massively destabilizing.”

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But Griffin believes they could work. “Honestly, a space-based interceptor to go after ballistic missiles in the boost phase is a relatively easy … challenge,” he told reporters on Capitol Hill in September. “If I use an entirely reasonable number based on experience of $20,000 per kilogram delivered via [a fractional bombardment system] to low orbit and, if I say I would be content with a layer of a thousand interceptors, which seems to me like a lot, and each of them weighs a metric ton – 1,000 kilograms — then the entire cost of that would be $20 billion, We’ve paid a lot more and gotten a lot less in the Defense Department over the years.”

At the same event, John Rood, the defense undersecretary for policy, sounded a more cautious tone.

“We’ve been looking at that question to see what the appropriate response would be,” Rood said, calling boost phase intercept “very attractive. That’s a reason we are looking at this capability.”

Trey Obering, who led the Missile Defense Agency as a three-star general, said in November that the cost was negligible compared to the price of the Ground-based Midcourse Defense system, the 44 interceptor rockets in Alaska and California that provides the nation’s first line of defense against ICBMs.

But while the GMD system might conceivably be expanded to ward off a relatively small North Korean missile salvo, experts say there’s no conceivable way to build, buy, and deploy enough interceptors to shield the United States from hundreds or thousands of Chinese and Russian ICBMs.

Obering, now an executive vice president with Booz Allen Hamilton, concedes the point. “We spent over $30 billion over 10 years on that and we got 44 shots to that.” He's now advocating lasers as a solution.

“Imagine if you were able to put up a laser that would achieve boost phase defense? … If you were to put up a constellation of lasers and reflectors, there, you’re taking multiple shots per laser and not just one shot,” he said. “It will be expensive to develop these and to field these. But the life-cycle cost will go down dramatically because we’ll be taking out multiple missiles with a single laser system.”

At a CSIS event in November, Griffin said that it would take a megawatt-class laser to kill an enemy missile from space.

Said Obering, “I believe that is in within the range of the doable in the next five years if we apply resources to it," with diode-pumped solid-state lasers, which amplify light energy by sending it through a crystal, ruby, or other solid.

The next day, speaking at the Defense One summit, Griffin concurred.

But critics aren’t convinced. In December, experts with the Union of Concerned Scientists wrote that such a system would be “exorbitantly expensive, easy to overwhelm or defeat, and politically destabilizing.” Citing a 2012 report by the National Academies of Science, they rejected the notion that a constellation would be relatively cheap.

“A system with an ‘austere,’ or simple, capability to counter a few North Korean missiles, for example, would cost at least $300 billion. But even that amount of money would not produce an effective defense. Its interceptor constellation would be vulnerable to an attack by anti-satellite weapons and could be overwhelmed by a salvo of missile launches,” they wrote.