Nanotechnology Challenges for Future Space ... - ACS Publications

Chapter 4

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Nanotechnology Challenges for Future Space Weather Forecasting Networks 1,

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Rainer A. Dressier *, Gregory P. Ginet , Skip Williams , Brian Hunt , Shouleh Nikzad , Thomas M. Stephen , and Shashi P. Karna 2

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Air Force Research Laboratory, Space Vehicles Directorate, 29 Randolph Road, Hanscom Air Force Base, MA 01731 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 Department of Physics and Astronomy, University of Denver, Denver, CO 80208 Army Research Laboratory, Aberdeen Proving Ground, MD 21005-5066 2

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This chapter provides an overview of space weather and articulates the need for an affordable space weather forecasting network as communication and navigation become increasingly reliant on spacebased systems. Space weather forecasting efforts face a number of technological challenges to provide global specification of the nearEarth and solar space environment. Nanotechnology is seen to play a pivotal role in technically enabling such an effort and in making it affordable. Concepts of future nano-structured energetic particle sensors are presented.

Introduction We live in a world that increasingly relies on uninterrupted global communications and space-based navigation systems. Trans-ionospheric transmission depends on the health of communications satellites and the electrical properties of the ionosphere. Both can be seriously compromised by space weather, which refers to space environmental 46

© 2005 American Chemical Society

In Defense Applications of Nanomaterials; Miziolek, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.


47 conditions as influenced by solar activity and, to a lesser degree, by cosmic radiation and interplanetary dust, such as cometary and asteroidal debris. The solar eruptions that result in the most prominent space weather effects experienced in Earth's surroundings have numerous detrimental consequences affecting both the civilian and military communities. Among the hazards associated with space weather are erroneous data transmissions, such as global positioning system (GPS) inaccuracies, total communication outages, power grid failures, satellite hardware degradation, and changes in the neutral density of the thermosphere, which alter spacecraft orbits. The commercial impact is real, as demonstrated by an exceptionally strong solar proton event on July 14, 2000 ("Bastille Day" event) that rendered a Japanese scientific satellite useless and disrupted instruments on many other satellites. It is, therefore, not a surprise that the space-weather threats to our current and future means of existence are increasingly recognized as a research and development priority by many industrialized nations. From a national defense point of view, the relevance of space weather and the associated space situational awareness is well understood and space weather is a core mission area of the Air Force Weather Agency and Air Force Space Command. Forecasting space-weather events is daunting since specifying the space environment involves precise knowledge of the conditions of the surface of the sun, the solar radiative and particle outflow, the interplanetary medium, and the Earth's magnetosphere, thermosphere and ionosphere, all of which are strongly coupled. Given the task at hand and the pervasive impacts of space weather, a multi-agency National Space Weather Program (NSWP) was generated with involvement of the Department of Defense, the Department of Commerce (i.e., NOAA), the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), and the Federal Aviation Administration (FAA). A successful effort in forecasting the moments in time and global positions of space weather effects must involve a comprehensive effort combining space-monitoring, realtime data processing, and analysis based on physical space weather models. Currently, one of the main impediments to accurate forecasting is the serious lack of relevant data, due to the extended temporal and spatial ranges involved and the high cost of space instrumentation. Many proposals exist addressing these issues, involving both remote sensing approaches and in-situ sensors distributed on clusters of miniaturized satellites. At the current state of aerospace technology, the cost of a network of satellites that provides global coverage and continuous monitoring of vital parameters of both the Earth's space environment and solar activity would be prohibitive. The reduction of launch costs through miniaturization of both spacecraft and sensor technology must, therefore, be a high priority in attaining the objectives of the NSWP. There is a general consensus that nanoscience and technology will play a fundamental role in enabling a future space weather network. The purpose of the present chapter is to identify some of the fundamental scientific questions that need to be addressed to pave the way for generation-after-next space-weather sensors. The identification of the underlying science undoubtedly requires breeding novel sensor concepts. This could be regarded as a premature effort, as nanoscience is still in its infancy. Our primary objective, however, is to portray space weather as an important and attractive technology driver for future government-sponsored nanoscience.



48 It is clear that this chapter cannot cover all aspects of space weather sensors that will benefit from nanotechnology and lead to improved forecasting systems. The importance of nanoelectronics in future sensors will only be marginally addressed. The reader is referred to the chapter of this volume by Kama et al. Although electromagnetic radiation is an important component of space weather, we prefer not to discuss optical nanosensors since efforts are already widespread in characterizing the optical response of nanomaterials. In the following section, we provide a brief introduction to the space environment and space weather, and discuss current forecasting methodologiesfroma space-vehicle perspective. We then review the current state of micro-particle sensor technology followed by a delineation of scientific challenges posed in defining specific nanostructured sensors. Unlike research on optical properties and chemical reactivity or catalytic activity of nano-structures, essentially no efforts are known to us that investigate the response of nano-structured surfaces and materials to hyperthermal particles (i.e., ions, neutrals and electrons). We hope we can seduce a number of leaders of the field to study these interactions.

Overview of Space Weather In this section, we provide a brief overview of the individual domains that govern space weather. For a more extensive treatise we recommend the Handbook of Geophysics and the Space Environment (/) distributed in CD-ROM form by the Air Force Research Laboratory Battlespace Environment Division at Hanscom AFB, MA. Fig. 1 provides a schematic representation of the domains of space weather. While the preponderance of the solar energy affecting Earth is in electromagnetic form, space weather effects are induced by both the radiative and corpuscular components of solar output. The latter is referred to as the solar wind, consisting mostly of protons (-95%), alpha particles, and electrons that propagate at average velocities of 450 km s" away from die sun. Since the solar wind consists almost entirely of charged particles, the interaction between the fast moving plasma and the solar magnetic field causes the solar wind to pull the solar magnetic field awayfromthe sun, producing the interplanetary magnetic field (IMF). The IMF plays an important role in particle transport through the interplanetary medium, and, more importantly, in the interaction of the solar wind with the terrestrial plasma. Solar radiative and particle output, also summarized as solar activity, are highly variable on both short and long timescales. Sporadic large releases of energy, such as solarflaresand coronal mass ejections (CMEs), can cause dramatic bursts of UV, EUV, and X-ray radiation and "gusts" of high density, more energetic solar wind. Solar flares are sudden releases of energy over the entire electromagnetic spectrum When a solar flare is observed on the sun, it is already too late for satellite operators to conduct protective measures. Protection from solar flares must involve the observation of characteristic signatures on the solar surface, in the solar wind properties, and in coronal electromagnetic radiation that point towards the onset of a flare. Given the approximate solar rotational period of 26 days, long-time forecasting requires observations on the 1


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EARTH Figure J. Schematic of the Sun-Earth Connection. The thin lines signify magneticfieldlines. backside of the sun. Missions involving clusters of satellites orbiting the sun are currently being discussed for this purpose. Coronal mass ejections or solar prominences are large releases of solar mass. The total mass released can exceed 10 kg, with ejection velocities up to 2,000 km/s. The observation of a coronal mass ejection normally precedes its impact on Earth by 2 to 3 days. Precise knowledge of the location, direction, speed of ejection, and solar and interplanetary magnetic field configurations are necessary to make forecasts of the moment of terrestrial impact. Thefrequencyof energetic solar events such as flares and coronal mass ejections is strongly correlated with the number of sunspots observed on the photosphere. Sunspot numbers have been counted since the 16 century and exhibit a periodic trend with an average period of 11.4 years. Fig. 2 displays the recent solar cycle indicating that, as this chapter is being written, we have just passed a solar maximum. Whereas knowledge of the moment of impact of a coronal mass ejection on Earth can be gleanedfromsolar and solar wind properties, as iterated above, prediction of the magnitude and precise location of space weather effects on Earth requires a comprehensive understanding of the response of Earth's plasma and neutral particle envelope to solar wind changes. If it weren't for the Earth's magnetic field, Earth's atmosphere would be directly exposed to the high energy particles of the solar wind, and life as we know it would not be possible. The interaction between the terrestrial and the solar wind magnetic fields and associated plasmas causes the solar wind to be diverted around our planet, thus sheltering us from a direct impact. The region of magnetized plasma surrounding Earth is referred to as the magnetosphere. The magnetic field lines of the magnetosphere are not shaped like those of a magnetic 13

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Figure 2. Sunspot numbersfrom1955 to present depicting the recent solar cycle. dipole, but exhibit a long tail, the magnetotail, at the night side of our planet. This is a direct consequence of the interaction between the solar wind and Earth's magnetic field. The diversion of the solar wind occurs at the magnetopause which, at quiescent solar conditions, is situated at a distance of approximately 10 Earth radii (1 # = 6.4 x 10 km) where plasma densities are approximately 10 cm" . Coronal mass ejections can produce solar wind gusts that momentarily push the magnetopause to radii well below 6 thus exposing geosynchronous satellites, orbiting at an altitude of 36,000 km above the equator, to the direct solar wind. Fig. 1 depicts the approximate location of a geosynchronous orbit (GEO). Every so often, the solar wind and terrestrial magnetic fields couple in a way that allows energetic particles to penetrate the magnetosphere. Such magnetic reconnection events are still not understood well enough to predict the location and moment of their occurrence. These magnetic reconnection events are the source of aurorae and geomagnetic storms that can be so detrimental to satellites, communications, and terrestrial power grids. Aurorae are the low altitude signature of the Earth's plasma sheet, a layer of plasma extending from approximately 6 RE on the nightside down through the magnetotail. This plasma poses charging hazards to geosynchronous orbiting satellites. A region exists within the magnetosphere where energetic charged particles are trapped by the Earth's magnetic field. This region, normally within 4-7 R , has two overlapping components, the plasmasphere (Fig. 1) and the radiation belts. The radiation belts contain charged particles with energies ranging from 1 keV to hundreds 3

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51 of MeV. These trapped energetic particles are associated with the extraterrestrial ring current that counteracts the inherent magnetic field of Earth as observed on its surface. This current is intensified during a geomagnetic storm, resulting in important reductions of the geomagnetic field, similar to a barometric pressure drop during a tropospheric storm. The mechanism leading to a geomagnetic storm is currently hotly debated. A common sequence of events involves the diffusion of polar ionospheric ions (ionospheric upwelling) into the magnetotail region, where they are energized and injected into the radiation belts. The onset of a storm can be sensed by the change of ionic constituents in the ring current. During quiescent periods, the positive ion component of the ring current consists primarily of protons. During storms, 0 densities can exceed proton densities. 0 is the principal ion of the upper ionosphere. Solar activity and geomagnetic storms alter electron density profiles of the ionosphere and can cause significant heating of Earth's upper neutral atmosphere, the thermosphere. Ionospheric perturbations, such as ionospheric scintillation, result in variations in electromagnetic signal propagation paths. These types of perturbations reduce the accuracy of single-frequency GPS receivers and geo-location systems, cause high frequency (HF) communications outages, and generate clutter for space surveillance radar. +


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Space Weather Sensing Approaches Current efforts in specifying ionospheric scintillation involve mostly ground-based ionospheric sounding networks that provide forecasts of up to ~l/2 hour. Military operations, however, demand several hour forecasts. This requires a denser data set of the driving magnetospheric and solar wind parameters, as well as an improved understanding of the coupling between the ionosphere and magnetosphere. In the following we will focus primarily on the challenge for improved global specification of the magnetosphere and the solar wind. Several concepts are being put forward to provide global specification of magnetospheric and solar wind properties. They can be separated in two approaches: i) a distributed set of micro, nano, or picosatellites with in-situ sensors (per unofficial definition, micro, nano, and picosatellites have mass ranges of 10-100,1-10, and

Nanotechnology Challenges for Future Space ... - ACS Publications

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