The day the United States detonated a nuclear bomb in space

Kathleen Norris and her brother drive up to Tripler Army Hospital, on a hill overlooking Pearl Harbor. She is still in high school. In an account published much later, she recalls the advice given to residents: find somewhere with a clear view. The test is scheduled for 11 p.m.

More than 1,300 kilometres away, on Johnston Atoll, a Thor rocket carries a nuclear bomb. Ships, aircraft and observation stations have been positioned across the Pacific to monitor the experiment. Its name is Starfish Prime.

The bomb detonates at an altitude of about 400 kilometres. In Honolulu, it is still July 8, 1962. By Universal Time, it is July 9.

Norris will remember a green flash, then a sky turning yellow and red before gradually darkening again. Photographs taken in Hawaii show the glow above the horizon. The explosion has happened in space, but people are watching from the islands. 1 2

The lights on Oahu

On the ground, streetlights go out.

On Oahu, the island where Honolulu stands, around thirty streetlighting circuits fail simultaneously. Part of the network is affected, more than a thousand kilometres from the bomb. The phenomenon has a name: an electromagnetic pulse, a brief disturbance capable of causing surges in electrical systems. 3

Effects of this kind are exactly what interest the military. Starfish Prime is part of a series of high-altitude tests investigating what nuclear explosions can do to communications and military equipment. 4

Another rocket

On July 10, a rocket lifts off from Florida with a very different mission. It carries Telstar 1, a communications satellite built by Bell Laboratories for AT&T.

Within hours of launch, television pictures cross the Atlantic: an American flag filmed in Maine is seen in France. The satellite also relays telephone calls and data. It works. 5

Telstar was not even in orbit when the bomb went off.

Another satellite, Ariel 1, was already there. On July 12, its transmissions start becoming erratic. Data arrive intermittently. Between transmissions, ground stations receive only a signal carrying no information, or nothing at all. An examination of its power supply points to the solar cells: they are producing less electricity. A technical report will link the deterioration to particles from Starfish. 6

The glow has faded, but particles released by the explosion remain trapped by Earth's magnetic field. They have joined regions that already hold naturally occurring energetic particles: the Van Allen belts. Satellites passing through them encounter this extra radiation. Their solar panels and electronic components can suffer damage on each passage. 7

Instruments aboard Telstar measure this environment while the satellite handles its communications work. Researchers will compare its exposure with the damage observed in its solar cells and experimental components. In late October, they also detect additional electrons from new Soviet tests. The space through which Telstar travels is still being altered from Earth. 8

Trying to reach it again

In November, Telstar starts having trouble responding to commands.

Engineers examine the circuits that receive and interpret instructions from the ground. Radiation has damaged some of their transistors. To try to recover the satellite, teams reproduce the problems in the laboratory and change the commands they transmit. They are trying to work around the failing components. 9

The satellite stays silent for part of the winter, then returns to service in January 1963. Communications work again for a few weeks. On February 21, they stop once more. This time, Telstar does not return. It was launched seven months earlier. 10

What remains in orbit

Above Earth, the remnants of the explosion still need watching. Satellites equipped to measure its effects are launched in the years that follow.

In Hawaii, Kathleen Norris had watched the sky turn dark again in less than an hour. Up there, traces of the explosion would remain detectable for up to eight years. 1 11