“SIMPLY PUT, these tests are dangerous, and we will not conduct them.” So said Kamala Harris, America’s vice-president, in a speech on April 18th at Vandenberg Air Force Base in California. Ms Harris was announcing an American ban on full-fledged testing of “direct-ascent anti-satellite missiles”—ground-launched weapons designed to blow up satellites in orbit.

Four countries—America, China, India and Russia—have conducted such tests, most recently Russia in November last year. The danger Ms Harris fears is not so much the weapons themselves, but the mess they create. Space is already full of junk: empty rocket stages, flecks of paint, nuts and bolts, toothbrushes dropped by careless astronauts and the like. It can stay aloft for decades. At orbital speeds, even small items can cause damage. The International Space Station (ISS) has to dodge bits of junk roughly once a year. In June 2021 debris punched a jagged hole in one of its robotic arms.

Anti-satellite missiles, designed to blow satellites to smithereens, make the problem far worse. A typical test might generate over 100,000 pieces of debris, says Marlon Sorge at the Aerospace Corporation, a non-profit organisation based in California. Ms Harris noted that after a Chinese test conducted in 2007, more than 2,500 chunks of debris big enough to track remain in orbit. There will be an unknown but much larger number of smaller bits.

Meanwhile the number of satellites in orbit is rising fast. SpaceX, an American firm, has permission to launch around 12,000 satellites for its Starlink orbital-internet service, more than have been launched since the Space Age began in 1957. Others firms such as Planet and Maxar, which provide orbital imagery, run fleets of their own. Armies rely on satellites for communication, weather forecasting and even to provide early warning in the event of a nuclear attack.

In the worst case, a combination of more clutter and more things to hit could begin a slow-motion chain reaction, in which each collision produces more debris, making future collisions more likely. This Kessler syndrome—named after the NASA scientist who first modelled the phenomenon in 1978—could leave important orbits unusable for decades.

Since that would be bad for everyone, Ms Harris hopes that other countries might copy America’s policy. Perhaps. The timing of the initiative is inauspicious, to put it mildly. Alongside $2.5bn in weapons shipments, America is thought to be supplying intelligence, including from satellites, to Ukraine’s army, to help that country fight Russia’s invasion. Russian officials have complained about SpaceX’s shipments of satellite terminals to Ukraine’s armed forces.

And although space debris is bad for everyone, it is worse for some than others. More than half of all active satellites are American, meaning that other countries would have less to lose if parts of Earth’s orbit became too dangerous to use.

But there are reasons for optimism, too. America’s self-imposed ban is only on “destructive” missile tests, so nations that followed suit would not have to give up their orbital weaponry entirely. Other methods of disabling satellites are being investigated, from blinding or jamming them to grabbing them with other satellites. And, says Robin Dickey, another analyst at the Aerospace Corporation, Ms Harris’s speech seems to be focused more on building “norms of responsible behaviour” than formal arms-control agreements—leaving other countries free to adopt bans without international pressure.

Such norms, it would seem, already have power. Countries that conduct anti-satellite tests are tellingly defensive about them. America justified one in 2008 on the dubious grounds that the targeted satellite, which was out of control, contained hundreds of kilograms of hazardous rocket fuel. After an Indian test in 2019, the country’s foreign ministry claimed that, by deliberately choosing a target in a relatively low orbit, the resulting debris would “decay and fall back onto the Earth within weeks”. The battle, in other words, may be half-won already. ■

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