Space is so intrinsic to how advanced militaries fight on the ground that an attack on a satellite need no longer signal the opening shot in a nuclear apocalypse. As a result, “deterrence in space is less certain than it was during the Cold War,” says Todd Harrison, who heads the Aerospace Security Project at CSIS, a think tank in Washington, DC. Non-state actors, as well as more minor powers like North Korea and Iran, are also gaining access to weapons that can bloody the noses of much larger nations in space.

Spoofing: Impersonating adversaries’ satellites is usually trickier than jamming a signal, but easier than taking over the satellites—with similar effects.

That doesn’t necessarily mean blowing up satellites. Less aggressive methods typically involve cyberattacks to interfere with the data flows between satellites and the ground stations. Some hackers are thought to have done this already.

For example, in 2008, a cyberattack on a ground station in Norway let someone cause 12 minutes of interference with NASA’s Landsat satellites. Later that year, hackers gained access to NASA’s Terra Earth observation satellite and did everything but issue commands. It’s not clear if they could have done so but chose not to. Nor is it clear who was behind the attack, although some commentators at the time pointed the finger at China. Experts warn that hackers could shut off a satellite’s communications, rendering it useless. Or they could permanently damage it by burning off all its propellant or pointing its imaging sensor at the sun to burn it out.

Another common mode of attack is to jam or spoof satellite signals. There is nothing fancy about this: it’s easier than hacking, and all the gear required is commercially available.

Jammers, often mounted on the back of trucks, operate at the same frequency as GPS or other satellite communication systems to block their signals. “They basically throw a bubble around the jammer where the satellite signals don’t work,” says Brian Weeden, a space policy expert also at the Secure World Foundation. Jamming can interfere with the command signal going from the base station to the satellite, or it can mess with the signal before it reaches the end users.

Jammers: Many satellites were built without special concern for jamming, so their signals can easily be overwhelmed by malicious broadcasts.

There are strong suspicions that Russia has been jamming GPS signals during NATO exercises in Norway and Finland, and using similar tactics in other conflicts. “Russia is absolutely attacking space systems using jammers throughout the Ukraine,” says Weeden. Jamming is hard to distinguish from unintentional interference, making attribution difficult (the US military regularly jams its own communications satellites by accident). A recent report from the US Defense Intelligence Agency (DIA) claims that China is now developing jammers that can target a wide range of frequencies, including military communication bands. North Korea is believed to have bought jammers from Russia, and insurgent groups in Iraq and Afghanistan have been known to use them too.

Spoofing, meanwhile, puts out a fake signal that tricks GPS or other satellite receivers on the ground. Again, it’s surprisingly easy. In the summer of 2013, some students at the University of Texas used a briefcase-sized device to spoof a GPS signal and cause an $80 million private yacht to veer hundreds of meters off course in the Mediterranean. Their exploit wasn’t detected (they later announced it themselves). Russia also seems to use spoofing as a way of protecting critical infrastructure—or maybe even President Vladimir Putin himself as he moves around, keeping him safe from potential drone assassinations by hiding his location.

As well as being hard to pin on anyone, jamming and spoofing can sow doubt in an enemy’s mind about whether they can trust their own equipment when needed. The processes can also be switched off at any time, which makes attribution even harder.

But sometimes, someone might want to cripple a satellite. That’s where lasers come in.

No nation can yet put lasers in space that literally shoot down satellites. Generating enough power for such lasers is hard, whether one uses electricity or chemicals.

Lasers: Blowing up a satellite with a laser is hard, but temporarily blinding its sensors is a lot easier. This may already be happening.

However, high-powered lasers could in theory be fired from ground stations or mounted on aircraft. All the major space powers have put research funding into such weapons. There’s no evidence that anyone has yet used lasers to destroy targets in space, though aircraft-borne lasers have been tested against missiles within the atmosphere. The DIA report suggests that China will have a ground-based laser that can destroy a satellite’s optical sensors in low Earth orbit as early as next year (and that will, by the mid-2020s, be capable of damaging the structure of the satellite). Generally, the intention with lasers is not to blast a satellite out of the sky but to overwhelm its image sensor so it can’t photograph sensitive locations. The damage can be temporary, unless the laser is powerful enough to make it permanent.

Lasers need to be aimed very precisely, and to work well they require complex adaptive optics to make up for atmospheric disturbances, much as some large ground-based telescopes do. Yet there is some evidence, all unconfirmed and eminently deniable, that they are already being used. In 2006, US officials claimed that China was aiming lasers at US imaging satellites passing over Chinese territory.

“It’s happening all the time at this low level,” says Harrison. “It’s more gray-zone aggression. Countries are pushing the limits of accepted behavior and challenging norms. They’re staying below the threshold of conflict.”

In November 2016, the Commercial Spaceflight Center at AGI, an aerospace firm, noticed something strange. Shortly after it was launched, a Chinese satellite, supposedly designed to test high-performance solar cells and new propellants, began approaching a number of other Chinese communications satellites, staying in orbit near them before moving on. It got within a few miles of one—dangerously close in space terms. It paid visits to others in 2017 and 2018. Another Chinese satellite, launched last December, released a second object once it reached geostationary orbit that seemed to be under independent control.

The suspicion is that China is practicing for something known as a co-orbital attack, in which an object is sent into orbit near a target satellite, maneuvers itself into position, and then waits for an order. Such exercises could have less aggressive purposes—inspecting other satellites or repairing or disposing of them, perhaps. But co-orbiting might also be used to jam or snoop on enemy satellites’ data, or even to attack them physically.

Russia, too, has been playing about in geostationary orbit. One of its satellites, Olymp-K, began moving about regularly, at one point getting in between two Intelsat commercial satellites. Another time, it got so close to a French-Italian military satellite that the French government called it an act of “espionage.” The US, similarly, has tested a number of small satellites that can maneuver around in space.

As the dominant player in space for decades, the US now has the most to lose. The DIA report points out that both China and Russia reorganized their militaries to give space warfare a far more central role. (President Donald Trump’s revival of the idea of a Space Force, while much ridiculed, may boost its importance in military thinking.) And there are fears among the US military that the US has lost its edge. “Russia and China are making advances in developing counterspace systems faster than we are protecting our satellites, which makes us increasingly vulnerable to attacks in space,” Harrison says.

In response, the US military is starting to make satellites tougher to find and attack. For instance, the NTS-3, a new experimental GPS satellite scheduled for launch in 2022, will have programmable, steerable antennas that can broadcast at higher power to counter jamming. It’s designed to remain accurate even if it loses its connection with ground controllers, and to detect efforts to jam its signal.

Another solution is not just to make single satellites more resilient, but to use constellations in which any one satellite is not that important. That’s the thinking behind Blackjack, a new DARPA program to create a cheap network of military communications satellites in low Earth orbit.

Co-orbital attack: Refueling and fixing satellites sound like good ideas. But if you can loiter close to a satellite, you can threaten it with a surprise attack.

Such constellations could also be used to control nuclear weapons, said General John Hyten, the head of US Strategic Command, at the National Space Symposium in April. Instead of relying on hardened communications links, he said, nuclear command and control needs to have “a near infinite number of pathways that go through every element of space: hardened military space, commercial space, different kinds of links … so that the adversary can never figure out how the message is getting through.”

The 1967 Outer Space Treaty prohibits weapons of mass destruction in space or on “celestial bodies” like the moon. It also forbids “military bases, installations and fortifications” on celestial bodies, though not in Earth orbit. The major spacefaring nations ratified the treaty long ago, but the ambitions of the treaty to codify peaceful uses of space seem increasingly distant, as hawkish rhetoric and actions grow more common.

The UN has tried for decades to get nations to agree not to “weaponize” space. Representatives from more than 25 countries met at a closed meeting in Geneva in March to discuss a new treaty. “The underlying difficulty in breaking the impasse is the continued distrust between major powers,” says Hitoshi Nasu, a space lawyer based at the University of Exeter in the UK, who is working with colleagues to write a guide on how international law applies to space.

But much as in the days of the Cold War, the only way to stop a conflict in space is to signal strongly that you are willing and able to carry one out, says Harrison: “Today, we are not adequately prepared for such a conflict, and our lack of preparation undermines deterrence and makes conflict in space more likely.”