Before the GOP-controlled Congress spends billions of your tax dollars on new, highly controversial weapons in space, you might think it would seek the opinion of the Defense Department. But no. Strange as it may seem, Republicans are rushing ahead with space-based missile interceptors over the objections of the White House and before a Pentagon review on the subject has been completed.

It’s almost as if congressional leaders want to spend money on space weapons no matter whether the military wants them or if they even work.

This week Congress approved the development of missile interceptors in space as part of the 2019 National Defense Authorization Act, calling for a working prototype by 2022. Last year’s defense bill contained similar language, but specified that the project would only move ahead if endorsed by the Defense Department’s ongoing Missile Defense Review, which has yet to see the light of day.

Rather than wait for the Pentagon review, this year Congress acted without it. An amendment proposed by Sen. Ted Cruz, R-Texas, struck out the Pentagon review in the name of removing “the legal hurdle” to developing space weapons. The effect was to order up missile interceptors in space whether or not the Pentagon thinks it’s a good idea.

This gift from Congress has not been well-received. In June, the White House released a statement saying it “strongly objects” to the Cruz amendment as an “unfunded mandate,” and urged Congress to wait for the results of the ongoing review, calling any decision on development “premature at this point.”

Over at the Pentagon, Lt. Gen. Sam Greaves, who leads the Missile Defense Agency, warned that space-based interceptors would “require a significant change in national policy” and would be expensive. His predecessor, then- Vice Adm. James Syring, said in 2016, “I have serious concerns about the technical feasibility of interceptors in space, and I have serious concerns about the long-term affordability of a program like that.”

As futuristic as they may sound, spaced-based weapons are an old—and bad—idea. The Reagan administration tried and failed to develop a space-based laser as part of its Strategic Defense Initiative. Then the George H.W. Bush administration switched from lasers to kinetic kill vehicles with Brilliant Pebbles and, when that failed, came up with Global Protection Against Limited Strikes, or GPALS. Eerily similar to Congress’s current iteration, GPALS called for a scaled-down system to protect against limited ballistic missile threats from regional powers like Iraq, Iran, and North Korea.

But the false allure of space weapons only hides its immense technical and financial hurdles, not to mention its hugely destabilizing effects. A 2003 American Physical Society study showed that in order to have just one satellite-based interceptor on station above a launch site at any given time would require a network of at least 1,600 satellites (with a corresponding five- to ten-fold increase in American space-launch capacity). That number nearly matches all the active satellites in orbit today. And yet the system could easily be overwhelmed by an adversary launching multiple, inexpensive missiles at once.

Even a bare-bones system would be ridiculously costly. A 2012 National Research Council report determined that the total life-cycle cost of developing, building, launching, and maintaining an “austere and limited-capability network” of 650 satellites would be $300 billion.

In addition to spending hundreds of billions for a paper-thin system, Congress could also spook Russia and China into a dangerous arms race. Since the 1960s, rival powers have maintained a fragile norm against placing weapons in space. The deployment of space-based interceptors would irreparably destroy that precedent. Moreover, any interceptor that is able to target an enemy missile can also knock an enemy satellite out of the sky.

Against this capability, the claim that space-based interceptors have a purely defensive mission would ring hollow in Moscow and Beijing, who would be forced to deploy anti-satellite weapons of their own. This would greatly increase the likelihood of a shooting war in space, posing a grave risk to the satellites upon which the U.S. military (and civil society) depends. As the nation that is most dependent on satellites for military and civil communications, we have the most to lose from a space war.

None of this is inevitable, but the development of space weapons greases the skids for this dangerous outcome. The United States should recognize space-based interceptors for what they really are: infeasible, unaffordable, and utterly destabilizing. Congress should reject space weapons and save our money—and our satellites—instead.

At a minimum, Congress might want to check in with the Pentagon.