Starfish Prime, EMPs, NEMPs and HEMPs explained

Image: US Government, Public domain

An electromagnetic pulse (EMP), also sometimes called a transient electromagnetic disturbance, is a short burst of electromagnetic energy. Such a pulse’s origination may be a natural occurrence or man-made and can occur as a radiated, electric or magnetic field or a conducted electric current, depending on the source.

Starfish Prime was a high-altitude nuclear test conducted by the United States on July 9, 1962, a joint effort of the Atomic Energy Commission (AEC) and the Defense Atomic Support Agency. The Defense Atomic Support Agency apparently became the Defense Nuclear Agency in 1971.

A Thor rocket carrying a W49 thermonuclear warhead (manufactured by Los Alamos Scientific Laboratory) and a Mk. 2 reentry vehicle was launched from Johnston Island in the Pacific Ocean. The explosion took place 250 miles (400 km) above a point 19 miles (31 km) southwest of Johnston Island. It was one of five tests conducted by the USA in outer space as defined by the Fédération Aéronautique Internationale (FAI). It produced a yield equivalent to 1.4 megatonnes of TNT. It was the largest man-made nuclear explosion in outer space.

On July 9, 1962, the Starfish Prime test was successfully detonated at an altitude of 400 kilometres (250 mi). The actual weapon yield was in the range of 1.4 to 1.45 megatons. The nuclear warhead detonated 13 minutes and 41 seconds after liftoff of the Thor missile from Johnston Island.

Starfish Prime caused an electromagnetic pulse (EMP), which was far larger than expected, so much larger that it drove much of the instrumentation off scale, causing great difficulty in getting accurate measurements. The Starfish Prime electromagnetic pulse also made those effects known to the public by causing electrical damage in Hawaii, about 1,445 kilometres (898 mi) away from the detonation point, knocking out about 300 streetlights, setting off numerous burglar alarms and damaging a telephone company microwave link. The EMP damage to the microwave link shut down telephone calls from Kauai to the other Hawaiian islands. (Wikipedia)

The electromagnetic pulse (EMP) damage of the Starfish Prime test was quickly repaired because of the ruggedness (compared to today) of Hawaii’s electrical and electronic infrastructure in 1962 and the relatively small magnitude of the Starfish Prime EMP in Hawaii and the relatively small amount of damage led some scientists to believe, in the early days of EMP research, that the problem might not be significant.

While some of the energetic beta particles followed the Earth’s magnetic field and illuminated the sky, other high-energy electrons became trapped and formed radiation belts around the earth. The weaponeers became quite worried when three satellites in low Earth orbit were disabled, although scientists were initially skeptical that electrons caused the damage. The half-life of the energetic electrons was only a few days. At the time it was not known that solar and cosmic particle fluxes varied by a factor 10, and energies could exceed 1 MeV.

These man-made radiation belts eventually crippled one-third of all satellites in low Earth orbit. Seven satellites failed over the months following the test, as radiation damaged their solar arrays or electronics, including the first commercial relay communication satellite, Telstar, as well as the United Kingdom’s first satellite, Ariel 1.

Subsequent calculations showed that if the Starfish Prime warhead had been detonated over the northern continental United States, the magnitude of the EMP would have been much larger because of the greater strength of the Earth’s magnetic field over the United States, as well as its different orientation at high latitudes. These new calculations, combined with the accelerating reliance on EMP-sensitive microelectronics, heightened awareness that EMP could be a significant problem.

The military pressed on. And now, in their terminology, a nuclear warhead detonated hundreds of kilometers above the Earth’s surface is known as a high-altitude electromagnetic pulse (HEMP) device. Effects of a HEMP device depend on such factors as the altitude of the detonation, energy yield, gamma ray output, interactions with the Earth’s magnetic field and electromagnetic shielding of targets but the most likely outcome is a massive erosion of communications capabilities for a prolonged period of time. Nuclear explosions create a characteristic pulse of electromagnetic radiation called a nuclear EMP or NEMP.

We know that an EMP, whether military or from a freak sunburst, is very likely to fry all electrics that are exposed to the EMP pulse, or flash. So to be properly prepared, you need to be able to shield your communications devices like your cell phone (for when the towers are back up), your shortwave emergency radio (emergency government communications) your CB radio (to talk to friends) and your Ham radio (for serious long-distance information exchanges.)

Defend Your Communications System

Large items

A Faraday cage or Faraday shield is an enclosure formed by conductive material or by a mesh of such material. Such an enclosure blocks external static and non-static electric fields by channeling electricity through the mesh, providing constant voltage on all sides of the enclosure. Since the difference in voltage is the measure of electrical potential, no current flows through the space. Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836. Here are some methods that implement his principles.

Small items.
Put your cellphone in a non-conductive paper bag. Seal completely. Wrap in aluminum foil. Place in Ziplock bag. Repeat.

metal trash binsEmergency
Get an old-fashioned metal trash can with tight metal lid, line completely with Styrofoam or cardboard. Place electrical object inside making sure not to touch anything metal.

Place your phones and radio in to a microwave oven, close door and hope it has a good seal.


Advance planning – Build a Faraday Cage

Faraday boxFind a large metal box of some sort – an old filing cabinet is a good option. Whatever you use has to be metal on every surface or it won’t work. Put insulated packing material inside the metal box. Place the items you want to protect for an emergency inside the box. Make sure they’re protected from the sides of the box by the packing material. Close the box. Cover any gaps in the container’s metal sides with copper mesh. And solder the mesh in place.