30-05-2012, 11:06 AM
High-Altitude Electromagnetic Pulse (HEMP)
High.docx (Size: 260.2 KB / Downloads: 30)
A nuclear burst detonated in space over the United States would create a high-altitude electromagnetic pulse (HEMP) that could cause the functional collapse of the electrical power grid. As a result, major infrastructures such as communications, transportation, financial services, emergency services, energy distribution, food and water could also be disrupted or extremely impaired.
The United States Congress formed a Commission in 2003 to examine the impact of nuclear weapon generated electromagnetic pulse (EMP) on the United States. The work performed by the EMP Commission has been groundbreaking in terms of studying the impact of HEMP on the civil infrastructure of the United States. They initiated a comprehensive research program and clearly identified the threat and general mitigation strategies. In 2007 they are meeting again to check on the progress of government and industry bodies with regard to their recommendations. Unfortunately, it is not clear whether action will be taken by those responsible to deal with this problem. In addition, the proposed legislation to reestablish the EMP Commission for a period of four years, until the year 2010, long enough for the Commission to help implement its 3-5 year plan for neutralizing the catastrophic EMP threat, has not yet been approved. We should remember that while the threat may be of low probability, the impact on the United States could be devastating. In fact the Commission makes the point that by doing nothing, we may be inviting attack.
For those who are interested in this subject, it is important to read the EMP Commission Report and to evaluate for yourselves whether actions could be taken in areas of your expertise to remedy the current situation. It is also critical that those in Congress understand the importance of protecting our infrastructure from this serious threat.
This article reviews the public information available concerning HEMP and its likely effects on commercial systems. Much of the technical information described in this article is found in the EMP Commission Report [1] and in the standardization work of Subcommittee 77C of the International Electrotechnical Commission (IEC) [2].
Background
The high-altitude electromagnetic pulse (HEMP) is defined as a series of electromagnetic waveforms that are generated from a nuclear detonation at altitudes above 30 km and propagate to the Earth’s surface. While the existence of HEMP has been known since the early 1960s, improvements in the understanding of the HEMP and increases in the susceptibility of electronics to HEMP over the years has raised new issues for commercial equipment and systems that are part of the civil infrastructure. In addition, an important new study by the Congressional EMP Commission published in 2004 [1], clearly indicates that the U.S. infrastructure is vulnerable to the possibility of even a single high-altitude nuclear burst. With the end of the Cold War, the possibility of a massive nuclear exchange has diminished, while the possibility of a limited attack by a terrorist group has increased. This means that the future target of HEMP may well be the civil infrastructure of the United States as opposed to military systems, which have considered the HEMP threat for many years.
The U.S. Congressional EMP Commission
The United States Congress formed a Commission in 2003 to examine the impact of nuclear weapon generated electromagnetic pulse (EMP) on the United States. The term EMP was understood for the purposes of the study to cover the electromagnetic fields generated from a high-altitude burst, which is more narrowly defined as HEMP. The Commission is chaired by Dr. William R. Graham and consists of nine members with broad experience in areas of military and commercial systems and electronics. It was chartered to:
1. Assess the EMP threat to the United States including the nature and magnitude of EMP threats within the next 15 years from all potentially hostile states or non-state actors.
2. Evaluate the vulnerability of U.S. military and especially civilian systems.
3. Determine the capability of the U.S. to repair and recover from damage to military and civilian systems.
4. Examine the feasibility and cost of EMP hardening select military and civilian systems.
5. Recommend protection steps the U.S. should take.
In order to begin their study, the Commission examined the HEMP research performed in the past (mainly for military purposes) and paid particular attention to the results of several high-altitude nuclear tests performed by the United States and the Soviet Union in 1962. In addition the Commission directed new research to evaluate the possible impact of the HEMP waveform on present-day commercial equipment and systems that are part of the infrastructure. With these new research findings, the Commission drew conclusions concerning the seriousness of the threat and recommended broad mitigation measures for the future. Some important results from their study are summarized in this article.
High-altitude Nuclear Tests Performed in 1962
On the evening of July 9, 1962 [1] the United States performed a high-altitude nuclear test known as Starfish; it was publicized in advance and was observed by the public in Honolulu, Hawaii. The U.S. government indicated that the device had a yield of 1.4 MT and was detonated at an altitude of 400 km; this was at a distance of 800 nautical miles (~1400 km) from Hawaii. The EMP Commission Report contains one of the photographs that were taken at the time [1]. While there were no noticeable direct impacts to individuals on the ground (no blast, shock, radiation, etc.) some electrical systems were still affected by the electromagnetic fields. Reports included the facts that some streetlights were extinguished, microwave communications were disrupted, and burglar alarms had sounded. While these system effects were not very dramatic in 1962, it is clear that the level of technology used in electronic equipment has changed significantly over the years: from analog to digital, with operating frequencies increasing from megahertz to gigahertz, and with the operating voltages of chips reaching ever lower levels. These changes have increased the probability of malfunction of 2007 commercial equipment to the HEMP threat.
The HEMP Time Waveform
At this point it is important for the reader to understand that HEMP is not described as a single pulse, but rather as a series of waveforms covering times from nanoseconds to hundreds of seconds. After years of research it has been determined that three main waveforms are generated due to different nuclear generation and atmospheric mechanisms. The description of the mechanisms is beyond the scope of this article, but readers with an interest are referred to other papers [5, 6]. Figure 2 illustrates the three main waveforms of interest as defined by the IEC [7]. The early-time waveform is referred to in the figure as E1, the intermediate-time waveform is referred to as E2 and the late-time waveform is known as E3. The reader should note that the pulse widths of these three waveforms are ~100 ns, 1 ms, and 10s of seconds, respectively. The peak values shown in Figure 2 are 50 kV/m, 100 V, and 40 V/km, respectively.