US President Barack Obama has signed legislation that, by striking a single word from longstanding US nuclear defence policy, could heighten tensions with Russia and China and launch the country on an expensive effort to build space-based defence systems. The National Defence Authorisation Act, a year-end policy bill encompassing virtually every aspect of the US military, contained two provisions with potentially momentous consequences. One struck the word “limited” from language describing the mission of the country’s homeland missile defence system. The system is said to be designed to thwart a small-scale attack by a non-superpower such as North Korea or Iran. A related provision calls for the Pentagon to start “research, development, test and evaluation” of space-based systems for missile defence. Together, the provisions signal that the US will seek to use advanced technology to defeat both small-scale and large-scale nuclear attacks. It defies the laws of physics and is not based on science of any kind L. David Montague, retired president of missile systems for Lockheed That could unsettle the decades-old balance of power among the major nuclear states. Huge bipartisan majorities in both houses of Congress approved the policy changes over the past month, with virtually no public debate. Although the White House had earlier criticised the changes, it stopped short of threatening a veto. On Friday, Obama signed the legislation. In a four-page signing statement, the president criticised various aspects of the bill, including the structure of a cybersecurity command and limits on administrative leave for employees, but said nothing about the changes in nuclear defence policy. Before Obama’s action, proponents and opponents of the policy changes agreed that they could have dramatic effects. Leading defence scientists said the idea that a space-based system could provide security against nuclear attack is a fantasy. “It defies the laws of physics and is not based on science of any kind,” said L. David Montague, a retired president of missile systems for Lockheed and co-chair of a National Academy of Sciences panel that studied missile defence technologies at the request of Congress. “Even if we darken the sky with hundreds or thousands of satellites and interceptors, there’s no way to ensure against a dedicated attack,” Montague said in an interview. “So it’s an opportunity to waste a prodigious amount of money.” He called the provisions passed by Congress “insanity, pure and simple.” Republican Congressman Trent Franks, who introduced and shepherded the policy changes in the House, said he drew inspiration from former president Ronald Reagan’s Strategic Defence Initiative of the 1980s, which was intended to use lasers and other space-based weaponry to render nuclear weapons “impotent and obsolete.” Known as “Star Wars”, the initiative cost taxpayers US$30 billion, but no system was ever deployed. Franks said that striking the word “limited” from the homeland defence system’s mission, and at the same time pursuing a space-based system, would put the US on a path to better safeguard its security. He said the new approach would protect both US territory and surveillance satellites. “I hope that the day will come when we could have solid-state lasers in space that can defeat any missile attack,” said Franks, who represents suburbs north and west of Phoenix. “That day is a long ways off. But fortunately, it’s a little closer, and a little more certain, with the passage of these amendments.” Russia and China will use it as an excuse to do something that they want to do Philip E. Coyle III, former assistant secretary of defence The new policy Franks championed says America “should maintain and improve a robust layered missile defence system capable of defending the territory of the United States and its allies against the developing and increasingly complex ballistic missile threat”. A space-based defence system would hinge on annual congressional appropriations and decisions by the incoming Trump administration. The National Academy study, released in 2012, concluded that even a bare-bones space-based system would cost about US$200 billion to put in place, and hundreds of billions to operate in subsequent years. Franks, asked whether the country could afford it, replied: “What is national security worth? It’s priceless.” Philip E. Coyle III, a former assistant secretary of defence who headed the Pentagon office responsible for testing and evaluating weapon systems, described the idea of a space-based nuclear shield as “a sham”. “To do this would cost just gazillions and gazillions,” Coyle said. “The technology isn’t at hand – nor is the money. It’s unfortunate from my point of view that the Congress doesn’t see that.” He added: “Both Russia and China will use it as an excuse to do something that they want to do.” The word “limited” has guided US policy since the National Missile Defence Act of 1999. The qualifier reflects, in part, the reality that intercepting and destroying incoming warheads is supremely difficult, and that it would be impractical to field enough interceptors to counter a large-scale attack. The current homeland anti-missile system – the Ground-based Midcourse Defence system, or GMD – relies on interceptors at Vandenberg Air Force Base in California and Fort Greely, Alaska. In flight tests, the system, which has cost taxpayers more than US$40 billion, has only managed to destroy mock enemy warheads about half the time. The first of Franks’ amendments – to eliminate “limited” from US policy – was approved in April by the House Armed Services Committee with no debate and without a recorded roll-call vote. At a committee hearing May 17, a senior Democrat on the panel, Congressman Jim Cooper of Tennessee, offered mild protest. “I think it was a mistake to mandate a poorly thought out, unaffordable and unrealistic missile defence policy, including plans for a space-based missile deterrent,” Cooper said. But neither Cooper nor any other House Democrat sought to overturn the provisions, and he was among those who voted to pass the overall bill the next day.