Space warfare has been a staple of science fiction for decades, but real-world fears were checked by a 1967 Outer Space Treaty, which banned the use of nuclear weapons there. But the treaty didn’t ban the use of conventional weapons in space, and Russia began its first anti-satellite weapons program in 1961, according to leading expert Brian Weeden of the Secure World Foundation. After the Cold War ended, fears eased about space conflict.

A wake-up call came with China’s 2007 test of an anti-satellite missile that destroyed a Chinese target in space (creating more than 3,000 dangerous fragments). The Chinese have now conducted a total of eight tests of satellite-killer rockets, Weeden says. Russia, too, has resumed similar tests. The United States is also thought to have what amount to anti-satellite rockets in the “midcourse” leg of its missile-defense system.

Rocket attacks against satellites worry the Pentagon less these days than electronic ones. Satellites could use jammers to sabotage other satellites. Ground systems can already create electronic bubbles that block GPS signals. The Russians used this technology to disable a Ukrainian drone in 2014, according to a report by the Organization for Security and Cooperation in Europe, cited by Weeden.