Editing Nuclear electromagnetic pulse (section)

===Weapon altitude===
[[File: High altitude EMP.gif|right|333px|thumb|How the peak EMP on the ground varies with the weapon yield and burst altitude. The yield here is the prompt [[gamma ray]] output measured in kilotons. This varies from 0.115 to 0.5% of the total weapon yield, depending on weapon design. The 1.4 Mt total yield 1962 [[Starfish Prime]] test had a gamma output of 0.1%, hence 1.4 kt of prompt gamma rays (the '''blue''' '[[ionization|pre-ionisation]]' curve applies to certain types of [[nuclear weapon design|thermonuclear weapons]], for which [[gamma ray|gamma]] and [[X-ray]]s from the primary fission stage ionize the atmosphere and make it electrically conductive before the main pulse from the thermonuclear stage. The pre-ionisation in some situations can literally short out part of the final EMP, by allowing a conduction current to immediately oppose the Compton current of electrons).<ref>Louis W. Seiler, Jr. [https://apps.dtic.mil/sti/pdfs/ADA009208.pdf ''A Calculational Model for High Altitude EMP''] {{Webarchive|url=https://web.archive.org/web/20170429000435/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA009208 |date=2017-04-29}}. Air Force Institute of Technology. Report ADA009208. pp. 33, 36. March 1975</ref>{{r|Glasstone_1977}}]]

According to an internet primer published by the [[Federation of American Scientists]]:<ref name="fas">{{cite web |title=Federation of American Scientists. "Nuclear Weapon EMP Effects" |url=https://fas.org/nuke/intro/nuke/emp.htm |access-date=2016-06-04 |url-status=dead |archive-url=https://web.archive.org/web/20150101064654/https://fas.org/nuke/intro/nuke/emp.htm |archive-date=2015-01-01}}</ref>

: A high-altitude nuclear detonation produces an immediate [[flux]] of gamma rays from the nuclear reactions within the device. These [[photon]]s in turn produce high energy free electrons by Compton scattering at altitudes between (roughly) 20 and 40 km. These electrons are then trapped in the Earth's magnetic field, giving rise to an [[oscillating]] electric current. This current is asymmetric in general and gives rise to a rapidly rising radiated electromagnetic field called an electromagnetic pulse (EMP). Because the electrons are trapped essentially simultaneously, a very large electromagnetic source radiates [[coherence (physics)|coherently]].

: The pulse can easily span continent-sized areas, and this radiation can affect systems on land, sea, and air. ... A large device detonated at 400–500 km (250 to 312 miles) over [[Kansas]] would affect all of the continental U.S. The signal from such an event extends to the visual horizon as seen from the burst point.

Thus, for equipment to be affected, the weapon needs to be above the [[line-of-sight propagation|visual horizon]].<ref name="fas"/>

The altitude indicated above is greater than that of the [[International Space Station]] and many [[low Earth orbit]] satellites. Large weapons could have a dramatic impact on [[satellite]] operations and communications such as occurred during Operation Fishbowl. The damaging effects on orbiting satellites are usually due to factors other than EMP. In the [[Starfish Prime]] nuclear test, most damage was to the satellites' solar panels while passing through radiation belts created by the explosion.<ref>{{cite web |last=Hess |first=Wilmot N. |title=The Effects of High Altitude Explosions |publisher=[[National Aeronautics and Space Administration]] |date=September 1964 |id=NASA TN D-2402 |url=https://www.futurescience.com/emp/Hess-Wilmot.pdf |access-date=2015-05-13 |url-status=live |archive-url=https://ghostarchive.org/archive/20221009/http://www.futurescience.com/emp/Hess-Wilmot.pdf |archive-date=2022-10-09}}</ref>

For detonations within the atmosphere, the situation is more complex. Within the range of gamma ray deposition, simple laws no longer hold as the air is ionized and there are other EMP effects, such as a radial electric field due to the separation of [[Compton electron]]s from air molecules, together with other complex phenomena. For a surface burst, absorption of gamma rays by air would limit the range of gamma-ray deposition to approximately {{convert|10|mi|order=flip||}}, while for a burst in the lower-density air at high altitudes, the range of deposition would be far greater.{{citation needed|date=August 2016}}