Why isn’t Russia blocking GPS in Ukraine?

THE PATTERN of craters across Antonovsky bridge in Kherson, a city in southern Ukraine, illustrates the power of a precision strike. The bridge, one of only two main routes into or out of the city across the Dnipro river, was rendered impassable on July 27th by Ukrainian soldiers, who are fighting to retake Kherson from Russian forces. They used a handful of missiles fired from an American-supplied HIMARS launcher, which relies on global positioning system (GPS) signals to find their target. GPS is a powerful tool of war, but it can often be rendered useless by the enemy. What could Russia do to prevent more strikes of this kind?

The NavStar Global Positioning System was developed by America’s air force in the 1970s. It was the first system to provide portable, accurate navigation anywhere on earth. The receiver picks up precise time signals from several satellites and calculates its position by triangulation. GPS-guided munitions have almost completely replaced unguided bombs in America’s arsenal. Many other weapons, from missiles to artillery shells, are also GPS-enabled. Much of Ukraine’s older Russian-made weaponry is not so advanced. But America and other backers are providing GPS-guided rockets and artillery shells. The technology is expensive but almost guarantees a hit, assuming the target is stationary and its location is known.

But GPS can be vulnerable. The satellites that power it are around 20,000 kilometres from Earth, but their transmitters are no more powerful than a car’s headlight. Their weak signals can be drowned out by radio transmitters operating on the same wavelengths. Some are harder to jam than others. Military GPS receivers may use “M-code”, a military-only signal. Some receivers have electronic filters to separate signals from noise, and directional antennas to pick up only signals from satellites. American weapons, such as HIMARS rockets, also have back-up inertial guidance, which measures acceleration and uses it to extrapolate distance and direction of travel. This kicks in if GPS fails to guide the missile.