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7 Future Solutions, Vulnerabilities, and Risks The workshop session titled âThe Future: Solutions or Vulnerabilities?â was intended to look into the future and evaluate how technical systems and their utilization are expected to evolve, and how this evolution affects their vulnerability to space weather. The technical infrastructure, enabling technologies, and space-based assets of the country are constantly changing.Â New electronic devices, new navigation systems, and new power grid systems are all evolving in response to improved technologies and increased requirements for efficiency and capability. Within this environment of innovation, designers will need to trade engineering solutions to mitigating space weather impacts against operational needs and space weather forecasting. This chapter addresses the evolution of current technologies and systems and their vulnerability to space weather, anticipated new technologies that may be more, or less, vulnerable to space weather than currently, and the estimation of future risks. Session panelists were asked to examine their industry with the understanding that we do not know the full range of possible space weather as demonstrated by the Carrington event of 1859, whose effects on Earthâs magnetic field were far greater 1 than those of any magnetic storm in the space era, and by the solar radio burst on December 6, 2006, which was 10 times more intense than any previous solar radio burst recorded over the past 50 years. The sessionâs speakers each received questions, tailored to their particular expertise, that can be generally summarized as follows: (1) How will current technologies and systems evolve and what will be their vulnerability to space weather? (2) Can new technologies be expected that will be vulnerable to space weather? and (3) Will engineering solutions that mitigate space weather effects be possible and practical in the future? The limitations of a workshop format allowed for a sampling of three technology infrastructure areas in this session. An analysis of electrical power systems was presented by John Kappenman of Metatech Corporation. Presentations on GPS and aviation systems were given by Thomas McHugh of the FAA and Christopher Hegarty of the MITRE Corporation. An analysis of satellite systems was presented by Ronald Polidan of Northrop Grum- man Corporation. In addition, a presentation on estimating future extremes of space weather by T. Paul OâBrien from the Aerospace Corporation was presented by Joseph Fennell and is covered in this section. These presenta- tions and the related workshop discussions are summarized below. In some cases the summarized material draws substantially from the abstracts of the presentations included in Appendix C. 76
FUTURE SOLUTIONS, VULNERABILITIES, AND RISKS 77 Power Grids Future Vulnerability Severe space weather has the potential to pose serious threats to the future North American electric power grid.2 Recently, Metatech Corporation carried out a study under the auspices of the Electromagnetic Pulse Com- mission and also for the Federal Emergency Management Agency (FEMA) to examine the potential impacts of severe geomagnetic storm events on the U.S. electric power grid. These assessments indicate that severe geomag- netic storms pose a risk for long-term outages to major portions of the North American grid. John Kappenman remarked that the analysis shows ânot only the potential for large-scale blackouts but, more troubling, . . . the potential for permanent damage that could lead to extraordinarily long restoration times.â While a severe storm is a low-frequency-of-occurrence event, it has the potential for long-duration catastrophic impacts to the power grid and its users. Impacts would be felt on interdependent infrastructures, with, for example, potable water distribu- tion affected within several hours; perishable foods and medications lost in about 12-24 hours; and immediate or eventual loss of heating/air conditioning, sewage disposal, phone service, transportation, fuel resupply, and so on. Kappenman stated that the effects on these interdependent infrastructures could persist for multiple years, with a potential for significant societal impacts and with economic costs that could be measurable in the several-trillion- dollars-per-year range. Electric power grids, a national critical infrastructure, continue to become more vulnerable to disruption from geomagnetic storms. For example, the evolution of open access on the transmission system has fostered the transport of large amounts of energy across the power system in order to maximize the economic benefit of delivering the lowest-cost energy to areas of demand. The magnitude of power transfers has grown, and the risk is that the increased level of transfers, coupled with multiple equipment failures, could worsen the impacts of a storm event. Kappenman stated that âmany of the things that we have done to increase operational efficiency and haul power long distances have inadvertently and unknowingly escalated the risks from geomagnetic storms.â This trend sug- gests that even more severe impacts can occur in the future from large storms. Kappenman noted that, at the same time, no design codes have been adopted to reduce geomagnetically induced current (GIC) flows in the power grid during a storm. Operational procedures used now by U.S. power grid operators have been developed largely from experiences with recent storms, including the March 1989 event. These procedures are generally designed to boost operational reserves and do not prevent or reduce GIC flows in the network. For large storms (or increasing dB/dt levels) both observations and simulations indicate that as the intensity of the disturbance increases, the relative levels of GICs and related power system impacts will also increase proportionately. Under these scenarios, the scale and speed of problems that could occur on exposed power grids have the potential to impact power system operators in ways they have not previously experienced. Therefore, as storm environments reach higher inten- sity levels, it becomes more likely that these events will precipitate widespread blackouts in exposed power grid infrastructures. The possible extent of a power system collapse from a 4800 nT/min geomagnetic storm (centered at 50Â° geomagnetic latitude) is shown in Figure 7.1. Such dB/dt levelsâ10 times those experienced during the March 1989 stormâwere reached during the great magnetic storm of May 14-15, 1921. The least understood aspect of this threat is the permanent damage to power grid assets and how that will impede the restoration process. Transformer damage is the most likely outcome, although other key assets on the grid are also at risk. In particular, transformers experience excessive levels of internal heating brought on by stray flux when GICs cause a transformerâs magnetic core to saturate and to spill flux outside the normal core steel magnetic circuit. Kappenman stated that previous well-documented cases have involved heating failures that caused melting and burn-through of large-amperage copper windings and leads in these transformers. These multi-ton apparatus generally cannot be repaired in the field, and if damaged in this manner, they need to be replaced with new units, which have manufacture lead times of 12 months or more. In addition, each transformer design can contain numerous subtle design variations that complicate the calculation of how and at what density the stray flux can impinge on internal structures in the transformer. Therefore the ability to assess existing transformer vulnerability or even to design new transformers that can tolerate saturated operation is not readily achievable.
78 SEVERE SPACE WEATHER EVENTSâUNDERSTANDING SOCIETAL AND ECONOMIC IMPACTS FIGURE 7.1â Scenario showing effects of a 4800 nT/min geomagnetic field disturbance at 50Â° geomagnetic latitude scenario. 7.1 and C.3a Kappenman.eps The regions outlined are susceptible to system collapse due to the effects of the GIC disturbance; the impacts would be of unprecedented scale and involve populations in excess of 130 million. SOURCE: J. Kappenman, Metatech Corp., âThe Future: Solutions or Vulnerabilities?,â presentation to the space weather workshop, May 23, 2008. The experience from recent space weather events suggests a threatening outcome for todayâs infrastructure from historically large storms that are yet to occur. Recent analysis by Metatech estimates that more than 300 large EHV transformers would be exposed to levels of GIC sufficiently high to place these units at risk of failure or permanent damage requiring replacement. Figure 7.2 shows an estimate of percent loss of EHV transformer capacity by state for a 4800 nT/min threat environment such as might occur during a storm of the magnitude of the May 1921 event. Such large-scale damage would likely lead to prolonged restoration and long-term shortages of supply to the affected regions. In summary, present U.S. grid operational procedures are based largely on limited experience, generally do not reduce GIC flows, and are unlikely to be adequate for historically large disturbance events. Historically large storms have a potential to cause power grid blackouts and transformer damage of unprecedented proportions, long-term blackouts, and lengthy restoration times, and chronic shortages for multiple years are possible. As Kappenman summed up, âAn event that could incapacitate the network for a long time could be one of the largest natural disasters that we could face.â Solutions for the Future Given the potentially enormous implications of power system threats due to space weather, major emphasis focuses on preventing storm-related catastrophic failure. Trends have been in place for several decades that have
FUTURE SOLUTIONS, VULNERABILITIES, AND RISKS 79 ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ 40%ï¿½ ï¿½ 97% ï¿½ ï¿½ï¿½ ï¿½ 39% 30% ï¿½ ï¿½ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ 7% 24% ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ 23% ï¿½ ï¿½ ï¿½ï¿½ 72% ï¿½ 34% ï¿½ 47% ï¿½ï¿½ ï¿½ï¿½ ï¿½ 32% ï¿½ï¿½ ï¿½ï¿½ ï¿½ 12% ï¿½ ï¿½ 36%ï¿½ ï¿½ ï¿½ 33% ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ 26% ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ 35% ï¿½ ï¿½ 9% ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ 55% ï¿½ ï¿½ ï¿½ ï¿½ï¿½ï¿½ ï¿½ ï¿½ 11% ï¿½ ï¿½ ï¿½ ï¿½ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ 15% ï¿½ ï¿½ï¿½ï¿½ï¿½ ï¿½ï¿½ ï¿½ï¿½ ï¿½ 6% 24% ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ 82% 19% 18% ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ 30% ï¿½ ï¿½ï¿½ ï¿½ ï¿½ï¿½ ï¿½ ï¿½ 19% ï¿½ 55% 7% ï¿½ 27% ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ 47% ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ï¿½ ï¿½ ï¿½ 17% ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ 17% ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ï¿½ ï¿½ 37% ï¿½ 6%ï¿½ ï¿½ 38% ï¿½ï¿½ 1% 7% ï¿½ ï¿½ ï¿½ 75% ï¿½ ï¿½ ï¿½ ï¿½ ï¿½ 8% ï¿½ 21% ï¿½ 7.2 and C.3b Kappenman.eps FIGURE 7.2â A map showing the at-risk EHV transformer capacity (estimated at ~365 large transformers) by state for a 4800 nT/min geomagnetic field disturbance at 50Â° geomagnetic latitude. Regions with high percentages of at-risk capacity could experience long-duration outages that could extend multiple years. SOURCE: J. Kappenman, Metatech Corp., âThe Future: Solutions or Vulnerabilities?,â presentation to the space weather workshop, May 23, 2008. acted to inadvertently escalate the risks from space weather to this critical infrastructure. Kappenman stated that procedures based on K-index-style alerts provide very poor descriptions of the impulsive disturbance environ- ments and lead to uncertainties about the adequacy and efficacy of operational procedures during large storms. He offered several solutions for the future. With respect to the entire grid, remedial measures to reduce GIC levels are needed and are cost-effective. The installation of supplemental transformer neutral ground resistors to reduce GIC flows is relatively inexpensive, has low engineering trade-offs, and can produce 60-70 percent reductions of GIC levels for storms of all sizes. Additional research work is already under way by the EMP Commission in this area. Kappenman noted that improved situational awareness for power grid operators is needed and is readily available (i.e., with an emphasis on disturbance environments/GIC levels instead of ambiguous K/G indices). In addition, regional system operators require initial and continuing training to understand their assigned roles and responsibilities in protecting the power system during solar events using new tools. Economic and societal costs attributable to impacts of geomagnetic storms could be of unprecedented levels. For example, consider the following cost estimates: â¢ August 14, 2003, Northeast blackout: $4 billion to $10 billion, 3 â¢ Hurricane Katrina: $81 billion to $125 billion,4,5 â¢ Future severe geomagnetic storm scenario: $1 trillion to $2 trillion in the first year, and â¢ Depending on damage, full recovery could take 4 to 10 years.6
80 SEVERE SPACE WEATHER EVENTSâUNDERSTANDING SOCIETAL AND ECONOMIC IMPACTS Global Positioning Systems and Aviation Future Vulnerability The FAA is in the process of transitioning the National Airspace System to utilize space-based navigation as the primary means of navigation. This transition is part of an overall modernization of the National Airspace System to implement integrated Communications Navigation and Surveillance (CNS). CNS services required by the FAA for aviation are provided partially by the FAA and partially by private sector operators. One way of achiev- ing navigation is with GPS and augmentation systems. In his presentation, Thomas McHugh noted that the use of GPS for CNS is an evolving process with several different approaches, each offering advantages and challenges. Surveillance services are planned as part of the Automatic Detection and Surveillance-Broadcast system (ADS-B), and an integrated CNS service is planned through the Next Generation Air Transportation system (NextGen). CNS is vulnerable to space weather: accuracy and integrity can be lost for non-augmented single-frequency GPS users, and availability can be lost for augmented single-frequency GPS users. All GPS users are vulnerable to loss of availability during extreme events such as radio-frequency interference from solar radio bursts and loss of reception of many or all GPS signals due to scintillation. Additional threats to robust CNS include loss of high frequency for oceanic reporting and disruption of the national power and telecommunications infrastructure during an extreme event. As McHugh noted, âThe vulnerabilities to CNS are down in the ionosphere.â These vulner- abilities are mitigated by new signals and codes for the modernized GPS system, backup navigation systems, and autonomous navigation systems. Space weather vulnerabilities depend critically on the type of navigation employed, which can be divided into two broad categories, non-precision and precision. Non-precision navigation requirements are looser and apply in operations less vulnerable to space weather, whereas precision navigation requirements, used in landing and approach procedures, are strict, and the availability of navigation services is exchanged for safety. The ionosphere is the primary source of error for users of single-frequency non-augmented GPS, which uses the Klobuchar model7,8 to correct ionospheric ranging errors; frequently these corrections are in error. Since accuracy is degraded during even minor ionospheric events, this technology can be used only for non-precision applications. This technology is also vulnerable to scintillation, which causes temporary loss of GPS reception and affects the availability of Receiver Autonomous Integrity Monitoring (RAIM), which can be interrupted by the loss of even a small number of satellite signals. As discussed by McHugh, certification of aviation technology requires 10 â7 probability of not providing misleading information, and âit is extremely difficult to certify the ionosphere.â Augmented users are less vulnerable to minor and moderate ionospheric disturbances but still can be affected by scintillation, solar radio bursts, and major ionospheric disturbances. The primary source of augmentation over the continental United States, Alaska, and Hawaii is the Wide Area Augmentation System (WAAS). WAAS disables the use of precision navigation in areas affected by ionospheric disturbances and does so using internal detection of the disturbances so that safety is never compromised. When large areas of disturbance are detected, precision navigation is disabled for all areas until 8 hours after disturbances cease. During the October and November 2003 magnetic storms, WAAS was disabled throughout the service area for 30 hours, and similar impacts are expected during the next solar maximum. McHugh expects that for the next solar maximum there will be four or five storms that will lead to widespread outages and that there will be shorter, regional outages âfor probably the top 20 storms of the cycleââ Solutions for the Future The FAA approach to mitigating space weather impacts is in part to implement new GPS signals and codes and in part to maintain backup systems. Starting with the GPS Block IIF satellites, a new L5 civil GPS signal will be transmitted in an aviation-protected frequency band. The L5 signal along with the L1 civil signal allows GPS receivers to estimate and remove ionospheric errors, a capability that will mitigate the problems with the Klobuchar and SBAS (Satellite-based Augmentation Systems) thin shell models such as WAAS. In addition, the L5 signal design is more robust than the L1C/A signal and will help mitigate unintentional interference. Hegarty stated that
FUTURE SOLUTIONS, VULNERABILITIES, AND RISKS 81 the L5 signal has a âdataless component, which will allow the signal to be tolerant to signal fades roughly 7 dBs stronger due perhaps to ionospheric scintillation than the CAâ code. The new L2 (discussed below) and L5 signals are expected to be operational by the 2016-2018 time frame. The second approach to mitigating space weather impacts is to maintain backup navigation systems indepen- dent of GPSâwhich is required even without space weather because of the threat from intentional interference. For the foreseeable future FAA policy is to maintain legacy backup systems for all GPS-based navigation. These backup systems generally are less capable than GPS-based systems. ADS-B and NextGen have analyzed potential backup systems such as eLORAN, DME/DME RNAV, and intertial navigation as likely candidates, but there was no clear conclusion. Fleet equipage and acceptance is a major factor in deciding which legacy or new systems will be maintained. In addition to the new L5 signal for the FAA, GPS and the larger Global Navigation Satellite System (GNSS) are being modernized in a process that will extend to at least 2020. Modernization requires launching new satellites that transmit the new signals and codes, resulting in an incre- mental process. Figure 7.3 shows the current and planned signals and codes. The original GPS satellites, Block I through Block IIR, transmit a C/A (coarse-acquisition) code at L1 (1575.24 MHz) and encrypted precise (P(Y)) codes at L1 and L2 (1227.6 MHz). The first step in GPS modernization began with Block IIR-M satellites in 2005, and 6 of these satellites (out of 30) are currently in operation. The Block IIR-M satellites add a new civilian code (L2C) on L2 and new encrypted military signals (M-code) on both L1 and L2. The advantage of the L2C code is C/A-code Block I/II/IIA/IIR P(Y)-code P(Y)-code (satellites launched up to 2004) C/A-code Block IIR-M L2C P(Y)-code P(Y)-code (2005- present) M -code M -code C/A-code Block IIF L2C (~2009â2013) P(Y)-code P(Y)-code L5 M -code M -code C/A-code Block III L2C L1C (1st launch ~2014) P(Y)-code P(Y)-code L5 M -code M -code frequency L5 L2 L1 (1176.45 MHz) (1227.6 MHz) (1575.42 MHz) FIGURE 7.3â The evolution of the GPS frequency plan to modernize the signal and codes.Â The upper panel shows the legacy signals.Â The next panel down shows the new civilian code L2C and Hegarty.epson L1 and L2.Â The third panel from the 7.3 same as C.2 the new M codes top shows the addition of the L5 safety-of-life signal, and the bottom panel shows the addition of the L1C signal. SOURCE: C. Hegarty, MITRE Corp., âThe Future: Solutions or Vulnerabilities?,â presentation to the space weather workshop, May 23, 2008.
82 SEVERE SPACE WEATHER EVENTSâUNDERSTANDING SOCIETAL AND ECONOMIC IMPACTS that civilian receivers can estimate ionospheric contributions to ranging errors and remove them. Following the II-RM satellites are the Block IIF satellites transmitting a new signal on L5 in 2009. Following the Block IIF satellites are the Block III satellites, which will introduce a new code on L1 called L1C. The sequence for fully populating the GPS constellation is L2C (2014), L5 (2016-2018), and L1C (2021). The primary advantage of transmitting a set of frequency diverse signals is the ability to remove ionospheric ranging errors, and this advantage is expected to make augmentation systems unnecessary. In addition, the new signals and codes will be more resistant to fades caused by scintillation or solar radio bursts. This advantage will be provided by transmitting with more power and by employing data-free pilot codes. Using the legacy L1C/A code as a reference, the L2C code has a 3-dB advantage, the L5 signal has a 7-dB advantage, and the L1C code has a 6-dB advantage. How successful these new signals and codes will be in mitigating space weather effects is an open question. As Hegarty noted, âIonospheric effects tend to be stronger at lower frequencies where the L2C and L5 signals are located.â Added robustness is expected, especially with respect to ionospheric gradients and ionospheric ranging errors. The added robustness with respect to the fading caused by scintillation and solar radio bursts is less clear, in part because these space weather phenomena are not adequately characterized and in part because the space weather impacts on the new signals and code have not been analyzed. Hegarty concluded, âI will leave it to the ionospheric physicist to tell us how much less likely [it is] that we will lose reception.â Satellites Future Vulnerability Polidan commented that the satellite industry faces two distinct aspects of space weather phenomena in the future: measurement and impact. Space weather is the primary environmental factor in designing missions to be successful. Since spacecraft and instrument technologies continuously evolve, satellite manufacturers must stay abreast of how new technologies will survive in the harsh environment of space. Prior to the last 50 years in space, space weather events occurred that were much larger and would have been more damaging than anything expe- rienced since 1957. In 2001, the Rumsfeld Commission warned of the possibility of a âspace Pearl Harborââan attack on U.S. space assets by an adversary that would leave the country vulnerable. There is also a real and serious threat to satellites from major space weather events. Polidan noted that the industry âstarted wondering whether or not we should be a lot more concerned about unexpected space weather events that would produce not a space Pearl Harbor but a space Katrina, a storm that we should have been prepared for but were not, with effects that were much more damaging than they should have been.â Satellite systems will continue to be designed to operate through extremes of the space environment over their designed life. It is highly atypical to intentionally design a system likely to have a vulnerability to extremes of the space environment. Trying to operationally forecast specific instances of extremes of the space environment may be of limited value: either the threshold beyond which to expect a negative impact on any specific technological system is not known, or it is known because such an impact has occurred before and therefore is not unusual or very extreme. There are exceptions: e.g., human extravehicular activity and large-scale infrastructure based on GPS. In general, as discussed by the workshop participants, extremes are often not well understood, and sometimes designs fail to meet specifications. Solutions for the Future Polidan offered several possible solutions for the future. A new factor to be considered when developing future space weather measurement missions is the availability of lower-cost launches. While there are well-known efforts to develop lower-cost launch vehicles such as the Falcon family being developed by SpaceX, there are also other approaches to low-cost access to space that are less well known. For example, the Lunar CRater Observation and Sensing Satellite (LCROSS), currently being built by Northrop Grumman Space Technology for NASA Ames, is expected to launch in 2009 as a secondary payload with the Lunar Reconnaissance Orbiter (LRO). (The LCROSS
FUTURE SOLUTIONS, VULNERABILITIES, AND RISKS 83 mission objective is to guide the upper stage of the launch vehicle to an impact in a permanently shadowed lunar crater and analyze the ejecta for the presence of water. The LCROSS mission is not small; it has a wet mass of more than 800 kg and has significant on-board propulsion.) Northrop Grumman is examining LCROSS-based space weather mission concepts that utilize this secondary payload approach for access to space. This approach can offer much lower launch costs and provide a vehicle with enough propulsion to get it to an ideal location to perform space weather measurements. To mitigate some of the future effects of severe space weather, Polidan remarked that companies will look to new electronics technologies that are more tolerant of space radiation. âRadiation-hardened-by-designâ approaches may yield affordable space electronics that could help âweatherâ such storms. There are a variety of potential technologies in the marketplace to draw from to build future missions. Currently almost all of these technologies are in early stages of development and need both sustained technology development and rigorous testing in an appropriate space environment before they are ready for incorporation into a mission. Workshop participants discussed the prospect that new approaches and new technology on the horizon could make the next 50 years in space more affordable and more secure than the previous 50 years. The measurement of space weather phenomena and their impacts on space mission hardware are being considered by space mission providers. They are exploring new ways to assist the science community in acquiring the needed measurements. Polidan remarked that future solutions for the satellite industry depend on accurate space weather data, model- ing, and forecasts for the design of billion-dollar space systems, billion-dollar launch decisions, operations, and anomaly investigations. He concluded that the industry is âvery interested in working with the [space weather] community to understand space weather, to get the measurements, and to also assess how those events can impact our designs so we can provide very long-lived and viable spacecraft.â Risk and Predicting Future Extremes As noted earlier, technological systems and especially satellites are designed to operate in or through the extremes of environmental impacts that may occur during the system lifetime. For the designer, therefore, predic- tion of specific space weather events is not useful. Instead, knowledge of climatology and especially the extremes within a climate record are required. Fennell noted that âengineers want to be able to design through extremesâ and an important aspect of space weather research is being able to predict extremes. Designers would like to know the probability of a damaging environmental parameter, such as MeV electron fluence, exceeding a set value. In some cases the damage may be accumulative, requiring knowledge of the long-term climate; in other cases it may be temporary, such as MeV electron fluence causing spacecraft charging. The designer then can trade cost and complexity against the probability or risk of losing a satellite as a result of space weather. Unfortunately, the NASA science programs that gather the data for characterizing the space climate are typically short term, and the space age itself has been too short a period for evaluating the possible risks. Of course many other fields of engineering, economics, and actuarial science would also like to be able to predict extremes. Fortunately, there is a class of functions that model extremes in distributions with large numbers of samples. These are extreme value functions (H(x)), which are probability density functions that estimate the likeli- hood of a single sample falling outside extreme minimum or extreme maximum limits (x). For example, given the history of daily rainfall in any given month, it is possible to predict with an extreme value function the probability of a daily rainfall exceeding any previous daily rainfall, or some other arbitrary value, in a future month.Â These functions are described in OâBrienâs abstract (see Appendix C), and for the class of functions describing a maxi- mum value, the value k describes the asymptotic behavior of H(x). For kÂ =Â â1, H(x) is bounded and an extreme possible value can be found. For â1Â <Â kÂ <Â 0, the slope of H is steep and low probabilities for extreme values can be determined. For the case of daily rainfall, if â1Â <Â kÂ <Â 0, there is a small probability that in a future month, a daily rainfall will exceed any previous daily rainfall. Extreme-value analysis has been applied to a variety of space weather phenomena with some success. For example, deep dielectric charging associated with the maximum fluence of 100s keV to MeV electrons, 9,10 single- event upsets associated with MeV protons,11 and total radiation dose12 have been analyzed with some success and consequence for satellite design.
84 SEVERE SPACE WEATHER EVENTSâUNDERSTANDING SOCIETAL AND ECONOMIC IMPACTS 10 0 â 10 â1 Âµ = 1.79 Â± 0.02 P[Dst<x] 10 â2 Ï = 0.26 Â± 0.01 K = â0.22 Â± 0.04 min obs. = â589 (14-Mar-1989) 10 â3 Estimated Dst Limit: â938 [â644,â1366] 10 â4 3 2 1 0 â10 â10 â10 10 Dst, nT FIGURE 7.4â The extreme value distribution function for Dst as estimated from 20-day blocks. Each data point represents a minimum Dst measured during an independent, historical 20-day period. It predicts that the probability of Dst being less than â938 nT in any future 20-day period is 10â4. SOURCE: OBrien.eps 7.4 T.P. OâBrien, Aerospace Corporation, âExtreme Events in Space Weather,â presentation to the space weather workshop, May 23, 2008. Perhaps more interesting is the application of extreme-value analysis to the Carrington event of 1859. In this case the parameter analyzed is 1-hour averages of Dst. Dst, the perturbation of the terrestrial magnetic field near the equator, is typically negative during magnetic storms. The extreme-value distribution function (H(x)) estimated from 1-hour averages of Dst organized into 20-day blocks is shown in Figure 7.4. This data set has k = â0.22. From this function the estimated lower limit to Dst is â938 nT. That is, in any 20-day block of data the probability of Dst exceeding (being less than) â938 nT is 10â4. Now compare this estimate of the minimum possible value of hourly averaged Dst with that estimated from Colaba (Bombay) magnetometer data during the Carrington event: â883 nT (Tsurutani et al., 2003; X. Li, personal communication).13 Of course, there are multiple assumptions implicit in the conclusion that the Carrington event was nearly the extreme possible. These include the geophysics of the data set in Figure 7.4 being the same as that which produced the Colaba magnetometer extreme value during the Carrington event. Fennell remarked that âwe many not be measuring what we would classically call Dst when you get down in this part of the probability distributions.â Additionally, the above conclusion assumes that the Sunâs variability is statistically unchanged over the time it has been observed and into the foreseeable future. Summary As society becomes more interconnected, and as its systems become more efficient and connected, with risk transferred among them, as noted by James Caverly in an earlier session of the workshop, space weather impacts on electric power grids, satellites, and GPS are going to affect almost every area of our lives. The challenge for society is understanding the true nature of the vulnerability now and in the future. A frequent theme throughout the workshop was the uncertainty in attempting to analyze future vulnerabilities. Uncertainty is introduced by the use of systems in ways not expected, or engineered for, by their designers. In some cases, the system providers may not even know who the users are. For example, the International GNSS Service
FUTURE SOLUTIONS, VULNERABILITIES, AND RISKS 85 (IGS) network is used for tsunami warnings and tracking ground movement during an earthquake. Yield mapping by farmers is another example of a high-precision, time-sensitive application of GPS. Even NASA depends on the IGS to point the antennas in the Deep Space Network. There also exist organizational challenges for the future; the privatization of systems introduces uncertainty. For example, La Porte noted that ENRON was able to game the power industry in ways the original designers never envisioned. Furthermore many systems are designed based on recent experience and not the potential for extreme events. As discussed throughout the workshop, the U.S. economy is highly dependent on electricity and wireless technology (for banking, energy, transportation, food, water, emergency services, and other necessities). Future systems and procedures will continue to cope not only with evolving user needs and new technological advances, but also with a variable space weather environment. NOTES â 1. Tsurutani, B.T., W.D. Gonzalez, G.S. Lakhina, and S. Alex, The extreme magnetic storm of 1Â-2 September 1859, J. Geophys. Res. 108(A7), 1268, 2003, doi:10.1029/2002JA009504. â 2. Graham, W., et al. Report of the Commission to Assess the Threat to the United States from Electromagnetic Pulse Attack, Volume 1, Executive Report, 2004, available at http://www.house.gov/hasc/openingstatementsandpressreleases/ 108thcongress/04-07-22emp.pdf. â 3. U.S.-Canada Power System Outage Task Force, Final Report on the August 14, 2003 Blackout in the United States and Canada: Causes and Recommendations, 2004. â 4. National Oceanic and Atmospheric Administration, The Deadliest, costliest, and most intense United States tropi- cal cyclones from 1851 to 2006, NOAA Technical Memorandum NSW TPC-5, April 2007, available at http://www.nhc.noaa. gov/pdf/NWS-TPC-5.pdf. â 5. USA Today, Katrina damage estimate hits $125B, September 9, 2005. â 6. Estimates derived by Metatech Corporation, presented by J. Kappenman at the space weather workshop, May 22, 2008. â 7. Klobuchar, J.A., Ionospheric effects on GPS, Chapter 12 in Global Positioning System: Theory and Applications, Vol. 1 (B.W. Parkinson and J.J. Spilker, Jr., eds.), American Institute of Astronautics and Aeronautics, Reston, Va., 1996. â 8. Navstar GPS Joint Program Office, Navstar GPS Space Segment/Navigation User Interfaces, Interface Specification, IS-GPS-200, Revision D, El Segundo, Calif., 2006, pp. 123-125. â 9. Fennell, J.F., H.C. Koons, M.W. Chen, and J.B. Blake, Internal charging: A preliminary environmental specification for satellites, IEEE Trans. Plasma Sci. 28(6), 2029-2036, 2000. 10. OâBrien, T.P., J.F. Fennell, J.L. Roeder, and G.D. Reeves, Extreme electron fluxes in the outer zone, Space Weather 5, S01001, 2007, doi:10.1029/2006SW000240. 11. Xapsos, M.A., C. Stauffer, T. Jordan, J.L. Barth, and R.A. Mewaldt, Model for cumulative solar heavy ion energy and linear energy transfer spectra, IEEE Trans. Nucl. Sci. 54(6), 1985-1989, 2007. 12. Thomsen, M.F., M.H. Denton, B. Lavraud, and M. Bodeau, Statistics of plasma fluxes at geosynchronous orbit over more than a full solar cycle, Space Weather 5, S03004, 2007, doi:10.1029/2006SW000257. 13. Tsurutani, B.T., W.D. Gonzalez, G.S. Lakhina, and S. Alex, The extreme magnetic storm of 1-Â2 September 1859, J. Geophys. Res. 108(A7), 1268, 2003, doi:10.1029/2002JA009504.