In March 1983, President Ronald Reagan delivered an Oval Office speech to announce his Strategic Defense Initiative — or as it was dubbed by critics, “Star Wars.” He proposed a space-based missile defense program that would have placed infrastructure featuring high-powered lasers, beams of atomic particles, and rocket interceptors in orbit to shoot down enemy missiles before they reached the United States.

The program, infeasible from the start, never came to fruition. That was for the best, because it would have only incentivized the Soviet Union to simply build more missiles to overwhelm U.S. defenses. In other words: a much bigger arms race.

More than three decades later, most security experts consider the idea a dangerous relic of the past, but some members of Congress have chosen nostalgia over reason. In the recent defense authorization bill signed into law by President Trump, the Pentagon is ordered to “develop a space-based ballistic missile intercept layer” even though senior military officials have rightly opposed the idea.

The opposition is warranted. Because military satellites carrying space-based interceptors would be enormously expensive and operationally unviable, and would result in unintended strategic consequences, Congress should refuse to fund the program.

How much would it cost? While the estimates vary, experts have consistently found the costs for space-based missile defense interceptor systems to be prohibitive. For example, a 2004 report issued by the nonpartisan Congressional Budget Office estimated that the cost to acquire a limited kinetic space-based system, launch the parts into orbit, and operate them for 20 years could reach almost $80 billion in 2004 dollars (more than $100 billion today).

In 2012, the National Academy of Sciences assessed that a program larger than CBO assumed, but still “austere,” would have a life-cycle cost of at least $300 billion in 2010 dollars (about $350 billion today), or 10 times more expensive than other missile defense options they examined. A more extensive program would further burden taxpayers and either way, they concluded, the cost “would probably prove unaffordable.”

To put these numbers in perspective, NASA’s entire annual budget is about $20 billion. At a minimum, such a space-based missile defense system would brutally siphon funds from higher priority Pentagon programs.

Would it work? The existing ground-based national missile defense program, at a total cost of about $70 billion, has yet to demonstrate reliable effectiveness. In 18 tests of the system, it has destroyed the target missile only nine times — a 50 percent rate of success. In the last five tests, the interceptor has worked successfully just twice. This poor record is despite the tests being highly scripted for success. In these tests, critical information is provided to the defense that would not be known in battle. Making matters worse, the system has never been tested against realistic enemy decoys and countermeasures that can “fool” the radars and interceptors. If the tests were operationally realistic, the failure rate would be even higher.

Despite the failed record, Michael Griffin, the Undersecretary of Defense for Research and Engineering, has argued that a much more advanced space-based missile defense system would be “a relatively easy technological challenge.” He’s wrong. Space-based interceptors have unique, impractical limitations that exacerbate the challenges of missile defense.

To be close enough for boost-phase intercept, the interceptor satellites must travel in a low-earth orbit. But in low-earth orbit, the interceptor satellites pass over target sites on the ground so quickly that they don’t remain in position long enough to reach a boosting enemy missile. For this reason, a 2003 study by the American Physical Society concluded that a system of space-based interceptors designed to defeat boosting enemy missiles “would require a fleet of a thousand or more orbiting satellites just to intercept a single missile.”

What would be the unintended consequences? In 1972, President Richard Nixon signed the Anti-Ballistic Missile Treaty with Soviet leader Leonid Brezhnev, which strictly limited each side’s missile defense programs. The idea was simple: If one side deployed systems that aimed to intercept the other’s nuclear missiles, the other would be incentivized to build more offensive missiles to defeat them and vice versa — exactly the opposite of what either nation wanted. The result, both sides understood, would be an unsustainable arms race with increased risks of nuclear war.

Unfortunately, President George W. Bush withdrew the U.S. from the treaty in 2002, laying the groundwork for a new kind of conflict with Moscow. Russian President Vladimir Putin has specifically cited U.S. missile defenses as the primary motivation for building new Russian nuclear delivery systems. China has improved its capabilities for the same reason.

Space-based missile defenses would motivate U.S. adversaries to increase their nuclear arsenals and expand their anti-satellite capabilities to neutralize the new space infrastructure.

Along with President Trump’s proposal for a new Space Force, this type of system could become an unwitting step towards the weaponization of space. While Russia, China, and the United States have experimented with anti-satellite weapons, no nation has deployed attack weapons in space. The deployment of space-based interceptors for missile defense could lead to a dangerous war in space — the consequences of which are nearly unimaginable.

Ultimately, congressional appropriators hold the prerogative to fund this new proposal for space-based interceptors. Considering the financial and strategic implications, they would be wise to ignore 35 years of false promises and focus on supporting initiatives that will actually protect this nation.