3

Technology Considerations

POTENTIAL TECHNOLOGICAL CONCERNS DURING THE SOLAR MAXIMUM

Satellite Drag

The solar extreme ultraviolet (EUV) output is the primary factor contributing to the decay of satellite and space debris orbits due to frictional interaction with the upper atmosphere (“drag”). As the solar EUV emission increases with solar activity, its absorption heats the upper atmosphere and increases the densities of atoms and molecules at a satellite's altitude. Proxies such as the radio emission at 10.7 cm are currently used by satellite operators in commercial enterprises and national agencies to analyze and predict changes in the upper atmosphere and the resulting orbital evolution. These proxies have not proven very effective in making accurate predictions, owing to additional increases in satellite drag from flare and auroral zone heating of the atmosphere.

Orbital decay can cause loss of contact and special problems for space facilities such as the Hubble Space Telescope, which will require “boosts” to maintain altitude; it can also result in aborted missions. In addition, the ever-increasing collection of space debris1 that must be tracked can be redistributed by increased drag. Although understanding of the sources of solar EUV radiation has improved dramatically since the last solar maximum, the new models of EUV behavior are based on observations that have not been tested through a solar maximum, when the number and intensity of transient contributions greatly increase.2 The contribution of variable auroral zone heating to drag is similarly difficult to characterize. Meanwhile, the demand for information on satellite drag grows with each passing solar cycle, driven by the increased use of space-based communications and navigation systems and the necessity of long-term planning for spacecraft in low-altitude orbits.

Radio and Communications Interference

A solar maximum affects radio communications in several ways. Most directly, enhanced radio output from the Sun degrades the effective sensitivity of receiver systems linking to satellites near the Earth-Sun line. Historically, the dominant effect has been on long-range, short-wave communication, which depends on radio-wave reflection from the bottom of the ionosphere. Enhanced EUV and soft x-ray emissions change the electron density and gradients in the ionosphere, directly and profoundly affecting this reflection. The effects of enhanced irregularities that often accompany ionospheric disturbances are also of growing importance. The resulting increased scattering of satellite-to-ground ultrahigh-frequency (UHF) transmission, or scintillation, can seriously interfere with direct satellite communication links. Similarly, the variability in propagation conditions degrades the performance of global positioning system (GPS) receivers, very low frequency (VLF) communications systems, and over-the-horizon radars. These effects are of particular concern in the high-latitude regions of auroral activity, but

1  

Aeronautics and Space Engineering Board, National Research Council, Protecting the Space Station from Meteoroids and Orbital Debris, National Academy Press, Washington, D.C., 1997.

2  

Board on Global Change, National Research Council, Solar Influences on Global Change, National Academy Press, Washington, D.C., 1994.



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Readiness for the Upcoming Solar Maximum 3 Technology Considerations POTENTIAL TECHNOLOGICAL CONCERNS DURING THE SOLAR MAXIMUM Satellite Drag The solar extreme ultraviolet (EUV) output is the primary factor contributing to the decay of satellite and space debris orbits due to frictional interaction with the upper atmosphere (“drag”). As the solar EUV emission increases with solar activity, its absorption heats the upper atmosphere and increases the densities of atoms and molecules at a satellite's altitude. Proxies such as the radio emission at 10.7 cm are currently used by satellite operators in commercial enterprises and national agencies to analyze and predict changes in the upper atmosphere and the resulting orbital evolution. These proxies have not proven very effective in making accurate predictions, owing to additional increases in satellite drag from flare and auroral zone heating of the atmosphere. Orbital decay can cause loss of contact and special problems for space facilities such as the Hubble Space Telescope, which will require “boosts” to maintain altitude; it can also result in aborted missions. In addition, the ever-increasing collection of space debris1 that must be tracked can be redistributed by increased drag. Although understanding of the sources of solar EUV radiation has improved dramatically since the last solar maximum, the new models of EUV behavior are based on observations that have not been tested through a solar maximum, when the number and intensity of transient contributions greatly increase.2 The contribution of variable auroral zone heating to drag is similarly difficult to characterize. Meanwhile, the demand for information on satellite drag grows with each passing solar cycle, driven by the increased use of space-based communications and navigation systems and the necessity of long-term planning for spacecraft in low-altitude orbits. Radio and Communications Interference A solar maximum affects radio communications in several ways. Most directly, enhanced radio output from the Sun degrades the effective sensitivity of receiver systems linking to satellites near the Earth-Sun line. Historically, the dominant effect has been on long-range, short-wave communication, which depends on radio-wave reflection from the bottom of the ionosphere. Enhanced EUV and soft x-ray emissions change the electron density and gradients in the ionosphere, directly and profoundly affecting this reflection. The effects of enhanced irregularities that often accompany ionospheric disturbances are also of growing importance. The resulting increased scattering of satellite-to-ground ultrahigh-frequency (UHF) transmission, or scintillation, can seriously interfere with direct satellite communication links. Similarly, the variability in propagation conditions degrades the performance of global positioning system (GPS) receivers, very low frequency (VLF) communications systems, and over-the-horizon radars. These effects are of particular concern in the high-latitude regions of auroral activity, but 1   Aeronautics and Space Engineering Board, National Research Council, Protecting the Space Station from Meteoroids and Orbital Debris, National Academy Press, Washington, D.C., 1997. 2   Board on Global Change, National Research Council, Solar Influences on Global Change, National Academy Press, Washington, D.C., 1994.

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Readiness for the Upcoming Solar Maximum they can also be severe in near-equatorial regions, where convective overturning and enhanced electron densities in the ionosphere can amplify the scintillations. Satellite and Space Systems Hazards Transient populations of energetic (MeV) protons, which enhance the Van Allen belt radiation for weeks to months following the arrival of a fast CME, potentially can affect the operation of spacecraft, including spacecraft in the highly populated geosynchronous orbit. For example, protons of these energies are known to contribute to single-event upsets in spacecraft electronics.3 Transient population protons can also reach higher latitudes than the typical inner radiation belt protons and may pose an additional radiation hazard to the crew of the International Space Station (ISS). 4 Peak levels of extravehicular activity will occur during the construction phase of ISS, which coincides with the upcoming solar maximum. These energetic protons are not taken into account in models of inner-zone protons, which are based on data taken during the maxima of solar cycles 20 and 21 (which were relatively mild compared with the maxima of solar cycles 19 and 22). The current prediction for the upcoming (cycle 23) solar maximum is that its activity level will be comparable to that of the previous solar maximum in 1989-1991.5 The transient populations produced by CME-generated interplanetary shocks were discovered only at the last solar maximum (and rediscovered to have occurred in preceding solar cycles that had had scant documentation), and so there is little calibrated predictive capability for the upcoming solar maximum. Earlier limited spacecraft coverage (both upstream in the solar wind and within the appropriate radiation belt region of the magnetosphere) supplied few constraints for dynamic models. Power Grids On March 13, 1989, the Hydro-Quebec Power System experienced a catastrophic failure resulting from its interaction with geomagnetically induced currents (GICs). The cause was probably the arrival of an interplanetary disturbance produced by a CME days earlier on the Sun. Although the Hydro-Quebec incident was the greatest problem of its kind during the previous solar maximum, less severe geomagnetic storms in September 1989 and October 1991 also created power system anomalies. In the Hydro-Quebec case, geomagnetic fluctuations had apparently coupled electromagnetically into the system, producing transformer saturation at many sites and causing voltages in the system to exceed safety margins. Widespread power blackouts that accompany such events produce a variety of problems. Oak Ridge National Laboratory assessed the potential impact of a widespread blackout in the Northeast United States as a result of a slightly more severe March 1989-type storm event. Its estimate of the impact to 3   Space Studies Board, National Research Council, Space Weather: A Research Perspective, 1997. This report is not available in hard copy; it may be viewed on the World Wide Web at the following address:<http://www.nas.edu/ssb/cover.html>. 4   Space Studies Board, National Research Council, Radiation Hazards to Crews of Interplanetary Missions: Biological Issues and Research Strategies, National Academy Press, Washington, D.C., 1996. 5   J.A. Joselyn, J.B. Anderson, H. Coffey, K. Harvey, D. Hathaway, G. Heckman, E. Hildner, W. Mende, K. Schatten, R. Thompson, A.W.P. Thomson, and O.R. White, “Panel Achieves Consensus Prediction of Solar Cycle 23,” Eos, Trans. Am. Geophys. Union, 78:205, 211-212, 1997.

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Readiness for the Upcoming Solar Maximum the gross domestic product alone put total economic costs in the $3 billion to $6 billion range,6 which is comparable to the damage caused by a major natural disaster such as Hurricane Hugo. The Northeast, in fact, was found to be particularly vulnerable to GICs. Protections can be installed, but it is impossible to completely protect an extensive power grid from GIC effects. However, evasive measures (such as rerouting the distribution) can be taken if there is sufficient warning and the power industry is prepared to respond.7 EXISTING RESOURCES The United States, together with its European and Japanese partners, has succeeded in placing instrumentation in space and on the ground that is capable of tracing the course of a solar event from the Sun to its effects on the geospace environment and beyond. These space-and ground-based facilities include key elements outlined in Table 1, Table 2, and Table 3. Instruments on UARS are continuing a two-decade time-series of space-based measurements of the solar constant.8 However, neither the UARS measurements nor those currently being considered as part of the EOS or National Polar-orbiting Environmental Satellite System (NPOESS) programs can elucidate the souce(s) of solar irradiance variability. Images in various spectral lines and bands obtained on SOHO have already revealed the wealth of different features on the Sun and hint at their control by solar magnetism. Assuming the continued operation of UARS and its solar irradiance monitor, we will have the opportunity to observe simultaneously how different solar features evolve with the changes in the solar magnetic field and affect the total irradiance. These observations will finally allow us to identify the sources of solar irradiance variations across a large part of the solar spectrum. With SOHO, Yohkoh, Winf, IMP-8, and ACE, researchers can begin to distinguish among the varying causes and effects of flares and CMEs as the frequencies of both increase with increasing sunspot number. Using helioseismology techniques on SOHO and from complementary ground-based observatories such as the Global Oscillations Network Group (GONG), we can also begin to understand how the solar dynamo produces the diversity of solar features that affect life on Earth: sunspots, faculae and the active network that make the solar constant a variable; flares with their complex sunspot region connection and their many energetic 6   Hurricane Hugo struck the Carolinas in 1989, causing an estimated $5 billion in property damage, according to the Federal Emergency Management Agency (FEMA). See “FEMA/City to Fund Charleston Storm System Upgrade,” News: FEMA News Room, Aug. 6, 1996. The damage estimates for a magnetic storm are taken from P.R. Barnes and J.W. Van Dyke, “Potential Economic Costs from Geomagnetic Storms,” Geomagnetic Storm Cycle 22: Power System Problems on the Horizon: Special Panel Session Report, Institute of Electrical and Electronic Engineers Power Engineering Society (IEEE PES) Summer Meeting, Transmission and Distribution Committee of the IEEE PES, June 17, 1990, Minneapolis, Minnesota. 7   John G. Kappenman, Lawrence J. Zanetti, and William A. Radasky, “Geomagnetic Storm Forecasts and the Power Industry,” Eos, Trans. Am. Geophys. Union, January 28, 1997. 8   As this report was being completed, NASA announced the opportunity to conduct a Total Solar Irradiance Mission (TSIM) as part of the Earth Observing System program. TSIM is planned to continue the precise total solar irradiance data record measured by NASA-funded spaceborne instruments since 1979. A December 2001 launch is planned.

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Readiness for the Upcoming Solar Maximum TABLE 1 Options for Current and Future Solar-Focus Research Facilities Facility/Spacecraft Mission Type Products ACE NASA Explorer in halo orbit at L1, launched on August 25, 1997 Real-time monitoring of the composition, density, velocity, temperature, and magnetic fields of the solar wind CGRO NASA Compton Gamma-Ray Observatory Monitoring of the highest-energy emissions from the Sun Flare Genesis NASA balloon program Solar vector magnetogram GOES NOAA satellite in geosynchronous orbit that carries geospace and Earth-monitoring (primarily weather-related) instrumentation Carries solar x-ray flux monitors that warn of flares; also carries instruments for in situ particle and magnetic field measurements; GOES-M will include a solar x-ray imager that will take real-time images of solar activity every minute GONG Worldwide network of ground-based helioseismology observatories run by the National Solar Observatory Structure and dynamics of the solar interior HESSIa NASA SMEX planned for mid-2000 launch Simultaneous, high-resolution imaging and spectroscopy of solar flares from 3-keV x-rays to 20-MeV gamma rays with high time resolution to expslore during solar maximum the basic physics of particle acceleration and energy release in solar flares IMP-8 NASA Interplanetary Monitoring Platform mission launched in 1973 Nearly continuous density, velocity, temperature, energetic particle, and magnetic field data on the solar wind and the magnetospheric response to it in a high (30 RE [Earth radius]) near-equatorial orbit. Plasma, magnetic field, and energetic particle data from a near-circular 35 RE, 12-day orbit. Approximately two-thirds of each orbit is in the solar wind. Annual data coverage in the 70% range in recent years; increased coverage in 1998 anticipated SEON NOAA and USAF network of ground-based optical and radio observatories Continuous solar optical and radio observations SOHO NASA/ESA mission launched in 1995 Structure of the solar interior, the surface magnetic fields, the inner corona, CMEs, and the solar wind a Nasa's selection of HESSI for its Small Explorer line occurred after completion of the final draft of this report; therefore, this mission is not discussed in the text. In a brief report published in January 1997 (Space Studies Board, National Research Council, An Assessment of the Solar and Space Physics Aspects of NASA's Space Science Enterprise Strategic Plan, National Academy Press, Washington, D.C.), the committees recommended that NASA develop a strategy to launch HESSI in time for the upcomming solar maximum.

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Readiness for the Upcoming Solar Maximum TRACE NASA SMEX to be launched in March 1998 High-resolution EUV/UV imager with the capability of following the structure of the solar magnetic field into the corona UARS NASA mission launched in 1991 Solar variability at UV wavelengths and atmospheric effects Ulysses ESA/NASA mission launched in 1991 into an orbit out of the ecliptic plane Sampling of the plasma conditions in the solar wind Voyager 1 & 2 NASA planetary flyby missions, carrying out the most distant exploration of the solar system Currently sampling conditions in the heliosphere beyond Pluto's orbit with particle and field sensors Wind NASA mission launched in 1994; part of ISTP/GGS program Solar wind density, velocity, temperature, energetic particles, magnetic fields, and waves Yohkoh Japanese (ISAS) and U.S. (NASA) mission launched in 1991 Solar activity via soft x-ray (5-50 Å) and hard x-ray imaging (10-100 keV) and spectroscopy of coronal activity

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Readiness for the Upcoming Solar Maximum TABLE 2 Options for Current and Future Geospace-Focus Spacecraft Spacecraft Mission Type Products Cluster To be launched in 2001 by ESA Four-spacecraft multipoint measurement of plasma, energetic particles, electric and magnetic fields and waves in high-latitude cusp, magnetopause boundary layer, and magnetosheath DMSP DOD's operational satellite system for weather and space environment data Space weather information in the form of auroral images and particles and fields environment data. DMSP satellites are placed in polar orbits (altitude approx. 850 km); they also provide traditional weather data Equator-S Project led by the Max-Planck-Institut für extraterrestrische Physik (MPE) in support of ISTP; successfully launched by ESA on December 2, 1997 Plasma, energetic particles, and magnetic field measurements from a highly eccentric orbit close to the equatorial plane (perigee ~500 km; apogee more than 60,000 km); orbit of Equator-S will allow radiation belt measurements that complement those of NASA's GGS program FAST NASA SMEX mission launched in 1996 to study in detail the plasma physics of Earth's auroral regions and the interaction of the solar wind with Earth's magnetosphere Measurements of magnetic and electric fields in the upper atmosphere, and particles' mass, charge, and velocity (to determine their origin). Provides high-time-resolution particle flux, density, electric and magnetic field, and wave measurements GEOTAIL Project of Japan's ISAS and NASA; designed and built by ISAS and launched on July 24, 1992 Dynamics of Earth's magnetotail over a wide range of distance, extending from the near-Earth region (8 RE) to the distant tail (about 200 RE). Characterizes plasma conditions (including particles, fields, and waves) in tail of the magnetosphere GOES NOAA satellite in geosynchronous orbit that carries geospace and Earth-monitoring (primarily weather-related) instrumentation Carries solar x-ray flux monitors that warn of flares; also carries instruments for in situ particle and magnetic field measurements. GOES-M will include a solar x-ray imager that will take real-time images of solar activity every minute IMAGE NASA MIDEX mission scheduled for launch in mid-January 2000 Will use neutral atom, UV, and radio imaging techniques to study the global response of Earth's magnetosphere to changes in the solar wind Interball Russian-led project: Interball Auroral Probe launched August 1996; Interball Tail Probe launched August 1995 Multipoint simultaneous measurements at different altitudes by two main satellites and two subsatellites, each launched into orbit as the passenger of its main satellite. Allows detailed study of the tail polar magnetosphere, magnetosheath and solar wind, spatial structures of individual space plasma processes, ambient plasma parameters, and cause-and-effect relationships

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Readiness for the Upcoming Solar Maximum Polar Launched February 24, 1996, as the second of two NASA spacecraft launched in the GGS initiative and part of the ISTP program Measure complete plasma, energetic particles and fields in the high-latitude polar regions, and energy input through the dayside cusp; determine characteristics of the auroral plasma acceleration outflow; provide global, multispectral, auroral images of the footprint of magnetospheric energy disposition into the ionosphere and upper atmosphere; and help determine the role of the ionosphere in substorm phenomena and in the overall magnetospheric energy balance SAMPEX Spacecraft launched by NASA into a high-inclination orbit in 1992 to study sources of the energetic particles in Earth's magnetosphere Measures energetic electrons and ion composition of particle populations from ~0.4 MeV/nucleon to hundreds of MeV/nucleon from a zenith-oriented satellite in a near polar orbit; payload combines some of the most sensitive particle sensors ever flown in space

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Readiness for the Upcoming Solar Maximum TABLE 3 Options for Current and Future Ionosphere/Upper Atmosphere-Focus Research Facilities Facility/Spacecraft Mission Type Products CANOPUS Canadian Space Agency project designed to be an integral part of the GGS mission, organized by NASA as part of the ISTP program A network of optical, magnetic, and radiowave instrumentation in western Canada for studying ionospheric currents and auroras over North America Jicamarca Radio Observatory Operated by Instituto Geophysico del Peru with assistance from NSF under a cooperative agreement with Cornell University Located in Jicamarca, Peru, a low-latitude NSF facility for study of the near-equatorial ionosphere's and atmosphere's characteristics Millstone Hill Operated by the NSF under a cooperative arrangement with the Massachusetts Institute of Technology Located northwest of Boston, Massachusetts. Can view the auroral and subauroral zone determining convection and other magnetospheric/ionospheric interactions National Astronomy and Ionosphere Center Arecibo Operated by Cornell University under a cooperative agreement with the National Science Foundation Located on the island of Puerto Rico; includes the world's most sensitive incoherent scatter radar. Measurements of ionospheric and upper atmospheric properties up to 3,000 km are made using radar as well as a variety of optical instruments Poker Flat Rocket Range Operated by the University of Alaska's Geophysical Institute under contract to NASA's Wallops Flight Facility, which is part of the Goddard Space Flight Center NASA rocket launch facility in Alaska with a supporting aeronomical observatory Polar Cap Observatory To be funded by NSF and operated by a joint U.S.-Canadian steering committee A large incoherent scatter radar facility to be erected in Canada at Resolute Bay, Northwest Territories, for the observation of the effects of solar storms and other space-related events on Earth' s environment. Operation is planned before the upcoming peak of solar activity Sondrestrom Facility Funded by the NSF Upper Atmospheric Facilities Program and operated and managed by SRI International. Part of a global network of incoherent scatter radars An incoherent scatter radar and associated optical, magnetic, and radiowave instrumentation located in Greenland for studying the high-latitude ionosphere

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Readiness for the Upcoming Solar Maximum SuperDARN International collaborative program for scientific investigation of the upper atmosphere, ionosphere, and magnetosphere; managed by an executive council consisting of the principal investigators A high-latitude network of high-frequency radars capable of imaging the two-dimensional, global-scale structure of electric fields and plasma convection in polar regions TIMED NASA space mission scheduled for launch in January 2000 using a Delta II launch vehicle The first of NASA's proposed solar-terrestrial probes— a line of spacecraft designed to investigate Sun-Earth connections; being designed to measure response of Earth's upper atmosphere to solar variability and to measure solar variability in the EUV wavelengths UARS NASA mission launched into space aboard the STS shuttle Discovery (STS-48) on September 12, 1991 Research satellite for monitoring physical and chemical processes in the stratosphere and lower mesophere. Also a monitor of solar radiative variability emissions that can directly affect Earth's atmosphere; and the separable but sometimes related CMEs that produce a panoply of interplanetary and geophysical effects, including geomagnetic storms.9 With SAMPEX, FAST, Polar, and Geotail, researchers can observe the geospace responses to these different solar stimuli, and (from the ground and suborbital platforms) the atmospheric and ionospheric consequences. Another technological development since the last solar activity cycle is the widespread availability of the World Wide Web (WWW). This Internet-based information system has completely revolutionized the way researchers access the latest information and tools, and analyze and exchange data. The importance of the Web and the advent of computers capable of the near-real-time global numerical simulation of space weather events cannot be overemphasized. Through these capabilities and modeling efforts such as those mentioned below, researchers are poised to acquire a physical understanding of Sun-Earth coupling at solar maximum that was never before possible. The upcoming solar maximum also provides opportunities to test and refine models and simulations of solar activity. The development of both models and computers capable of the near-real-time global magnetohyrodynamic simulation of a long-duration (i.e., >1 day) event was demonstrated for the January 6-11, 1997, magnetic cloud. A modular approach to developing a geospace general circulation model is under way as part of the NSF-sponsored Geospace Environment Modeling (GEM) program. Its purpose is to provide a modeling capability in support of the NSWP goals that can be benchmarked against the body of data collected from ISTP satellite and coordinated ground-based studies. The models are being tested against data 9   Space Studies Board, National Research Council, Space Weather: A Research Perspective, 1997. This report is not available in hard copy; it may be viewed on the World Wide Web at the following address: <http://www.nas.edu/ssb/cover.html>.

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Readiness for the Upcoming Solar Maximum from the solar minimum and the current rise toward maximum. The extreme events of solar maximum like those ensuing from the March 1989 and 1991 storm periods are expected to provide the most stringent tests for the model development, but only if the relevant spacecraft data are available to constrain the models. Having a full suite of solar and geospace instrumentation in place will also provide spinoffs in other disciplines of space science: Astronomers will have new insights into stellar magnetism and emissions, astrophysicists will find new analogies regarding particle sources and acceleration mechanisms in stellar environments, investigators in the Origins program will better understand the central stars in their extrasolar planetary systems and the effects of those stars on their surrounding planets, planetary scientists will have a basis for better modeling past Martian climate variability and for understanding how an active early Sun affected conditions on the surface of Mars (and Earth), and Earth scientists will have the information needed to physically model solar variability effects on our own planet. SUMMARY Researchers recognize that each solar cycle is unique in its impact on Earth's environment. Solar cycles 19 and 22 were extremely active, cycles 20 and 21 comparatively benign. We now have a unique capability to capitalize on whatever the Sun generates that will affect Earth 's environment during the maximum in solar cycle 23. The observations and the scientific results forthcoming from a concerted effort by the solar-terrestrial community will enhance the basic understanding of solar phenomena, which will in turn improve the predictability of environmental perturbations that affect Earth satellites, communications, power grid disruptions, and other aspects of technology that affect our lives.