Breakthrough research in heliophysics is enabled by research platforms of a variety of sizes and with a range of functions: billion-dollar-scale strategic missions with payloads up to 100 kg can enable a new set of measurements otherwise not accessible; however, as described in Part I of this report, there are opportunities for leading-edge research with $375 million medium-size Explorers; $150 million small Explorers with payloads of 20 kg; and CubeSats, at $1 million scale, with payloads of 1 kg. In addition to these space-based platforms, suborbital programs provide unique, relatively low-cost opportunities for research and technology demonstration. For example, sounding rockets provide the only means for in situ sampling in regions inaccessible to aircraft, balloons, or satellite platforms.1 Ground-based facilities offer an entirely different, but no less necessary, “platform” for solar and space physics research and long-term observations. Finally, there are unique opportunities for solar and space physics research to be carried out by instruments hosted on commercial and government space platforms that carry payloads for other purposes.
A diversity of approaches is required for achieving the top-level objective in solar and space physics—to create system-wide understanding—but the data from these platforms need to be integrated into distributed yet coordinated approaches that create the best system-wide understanding from the data, which may very well be collected by a variety of platforms.
This appendix reviews the platforms that are currently available to pursue research in solar and space physics and examines prospects for the coming decade. Its review is not comprehensive (and discussions of NASA spacecraft are left to Part I of this report); however, it does provide illustrative examples of the scientific utility of selected platforms. The appendix also describes examples of data integration in constellations and so-called heterogeneous facilities—a set of distributed measurements from a variety of measurement vantage points, integrated into a greater whole.
1 In particular, direct in situ sampling in the important region of the lower ionosphere/thermosphere and mesosphere below 120 km altitude is not possible with aircraft and balloons, which operate well below this height, or with satellites, which to avoid atmospheric drag must be placed in orbits at higher altitude. See, NASA, “NASA Sounding Rocket Science,” at http://rscience.gsfc.nasa.gov/srrov.html.
GROUND-BASED SOLAR MEASUREMENTS
Significant science results of the past decade were accomplished at ground-based facilities—probing solar processes from the interior through the solar surface to the chromosphere and corona. Existing ground-based optical platforms include the Mauna Loa Solar Observatory (operated by HAO), the Sacramento Peak Observatory, Kitt Peak Observatory, GONG, and SOLIS (operated by the National Solar Observatory), the Mees Solar Observatory (University of Hawaii), the Big Bear Solar Observatory (New Jersey Institute of Technology), the San Fernando Observatory (CSUN), and the Mt. Wilson 60-foot tower (USC) and Mt. Wilson 150-foot tower (UCLA). Existing ground-based radio platforms include the Owens Valley Radio Observatory (OVSA; operated by NJIT), the Long-Wavelength Array (New Mexico State University), and the Haystack Mountain Observatory (MIT).
The Advanced Technology Solar Telescope (ATST) will provide U.S. leadership in large-aperture, high-resolution, ground-based solar observations and will be a unique complement to space-borne and existing ground-based observations. Full-Sun measurements by existing synoptic facilities (e.g., GONG, SOLIS, and ISOON), and new initiatives such as the Coronal Solar Magnetism Observatory (COSMO) and the Frequency-Agile Solar Radiotelescope (FASR), have the potential to balance the narrow field of view captured by ATST and are essential for the study of transient phenomena.
A major science goal is to continue comparison of highly resolved observations with numerical models in order to critically define the physical nature of photospheric features such as sunspots, faculae, and cool molecular clouds. Another goal is to better understand the physical behavior of magnetic fields in the chromosphere and corona—both on small and large scales—in order to study the flow, storage, and eruption of energy and mass in these poorly understood regions. The recent, mostly unexpected, behavior of the solar cycle and solar scientists’ inability to predict its future course makes synoptic studies of the magnetic field and surface and interior mass flows that are related to the solar dynamo a high-priority goal. Ground-based observations are increasingly used in near-real-time data-driven models of the heliosphere and space weather. A goal is to improve the quality of these measurements and to extend them upward into the chromosphere and corona.
Compared with space missions, ground-based facilities can be far larger, more flexible and exploratory, and longer-lived. Accordingly, emphasis is on achieving high spatial resolution (e.g., NST, ATST), making unique measurements of physical processes at long wavelengths (e.g., OVSA, FASR), and collecting sufficient light flux to make high-time-resolution, high-precision measurements of magnetic and velocity fields, long-term synoptic observations, and novel frontier observations of various kinds (e.g., COSMO).
GROUND-BASED ATMOSPHERE-IONOSPHERE MEASUREMENTS
Ionospheric modification is an incisive tool for probing the upper atmosphere from the ground and offers a means of performing repeatable experiments and obtaining reproducible results. Ionospheric modifications use powerful high-frequency transmitters to induce phenomena in ionospheric plasmas. Some of these phenomena give insights into complicated plasma physics processes that may occur elsewhere in nature but that are difficult or impossible to explore in the laboratory or numerically. Other processes provide diagnostics of naturally occurring ionospheric phenomena and of natural rate constants that are otherwise hard to quantify. Ionospheric modification experiments affect the propagation of radio signals passing through the modified volume, which is how the phenomenon was first discovered (i.e,. the radio Luxembourg effect). These experiments generate airglow and radio emissions, which can be observed from the ground; create field-aligned plasma density irregularities that can be interrogated by small coherent scatter radars; generate low-frequency radio signals, which have practical societal utility; accelerate
electrons, mimicking auroral processes; and modify plasma density and electron and ion temperatures and enhance the plasma and ion lines observed by incoherent scatter. Because of this, heaters are most productive when located close to incoherent scatter radars.
The Department of Defense (DOD) operates and maintains the world’s largest ionospheric modification facility, the High Frequency Active Auroral Research Program (HAARP), near Gakona, Alaska. HAARP, which became fully operational during the past decade, is powerful, modular, and flexible and is especially well suited for studying ionospheric modification phenomena under different beam-pointing, emission frequency, and modulation conditions. HAARP is not co-located with an incoherent scatter radar, however, and its potential has therefore not been fully realized, since the phenomena it creates cannot be fully diagnosed.
Another ionospheric modification facility is currently under construction at the site of the Arecibo Radio Observatory. While this facility will be modest in power compared to HAARP, its co-location with Arecibo, the world’s most sensitive incoherent scatter radar, raises the prospect of discovery science in the areas of artificial and naturally occurring ionospheric phenomena. The Arecibo heater came about through close collaboration between DOD and the National Science Foundation (NSF). The collaboration included community support and involvement from the beginning that will continue through the planning and execution of heating campaigns. The committee regards this kind of interagency cooperation as a model to be followed for the utilization of existing ionospheric modification facilities as well as the planning and development of new ones.
Another recent, important development is the emergence of Advanced Modular Incoherent Scatter Radar (AMISR)-class incoherent scatter radars, which were supported by the 2003 National Research Council (NRC) decadal survey, The Sun to the Earth and Beyond.2 These are ultrahigh-frequency phased-array radars that can be electrically steered from pulse to pulse. AMISR-class incoherent scatter radars are currently deployed near Poker Flat, Alaska, and Resolute Bay, Canada. The latter of these includes two full radar faces and came about through international collaboration with Canada. Plans are being developed to deploy at least one additional radar in Antarctica. These facilities represent the current state of the art in high-power, large-aperture radars used for aeronomy and space physics.
An important hallmark of AMISR-class radars is their portability. These radars have been designed to be disassembled, shipped, and reassembled. The permanent infrastructure required for an AMISR is modest compared to the relocatable components, and shipping costs are expected to be modest compared to production costs. The objective of relocation is to enable discovery science through temporary deployments in geophysically interesting or under-instrumented regions. Additional benefits can accrue when relocation brings an AMISR-class radar into collaborative arrangements with other scientific assets, such as optical instruments, rocket ranges, or other radars. For example, current plans call for the redeployment of the radar near Poker Flat, Alaska, to La Plata, Argentina, where it could support an investigation into magnetic conjugacy effects with Arecibo pertaining to natural and heater-induced ionospheric phenomena. This particular relocation would also entail extensive collaborations with Argentine universities, faculty, and students, which are very welcome.
NSF also sponsored an NRC study on a distributed array of small instruments (DASI),3 which could have major impact for future measurements. Due to the near omnipresence of wireless or phone connectivity, sensors can be distributed and worked as an integrated whole. The instruments in question could include ground-based imagers, optical interferometers, and spectrometers, magnetometers, radio beacon
2 National Research Council, The Sun to the Earth and Beyond—A Decadal Research Strategy in Solar and Space Physics, The National Academies Press, Washington, D.C., 2003.
3 National Research Council, Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop, The National Academies Press, Washington, D.C., 2006.
and Global Positioning System (GPS) receivers, ionosondes, coherent scatter radars, and other small, relatively inexpensive devices. Broadly interpreted, the instruments could also include small satellites, sounding rockets, and balloons. The arrays could be assembled on an ad hoc basis for campaigns of short or intermediate duration. Instruments could be rotated in and out of service, possibly in a rotation in the EarthScope model. Instruments could possibly be checked in and out of central reserves in the way that seismometers are currently within the Earth sciences. Arrays of instruments could furthermore be anchored by large, class-I facilities (incoherent scatter radars, wind-temperature lidars, and so on, as needed).
Among such measurements, there has been much progress in lidar measurements. A giant leap forward in understanding of meteorological influences and neutral-plasma interactions on the atmosphere-ionosphere-magnetosphere (AIM) system can be achieved if neutral wind, temperature, and mass density measurements can be obtained simultaneously at subscale-height altitude resolution from the lower atmosphere to the mid-thermosphere (~200 km altitude). Beyond providing the first continuous measurements of Earth’s thermal and wind structure from the lower atmosphere to the mid-thermosphere, this measurement capability would enable new discoveries in understanding wave-mean flow interactions, gravity wave propagation into the thermosphere, mesosphere turbulence, secondary wave generation in the thermosphere, eddy diffusivity, wave fluxes of momentum, heat, and constituents, and heating and cooling processes. In addition, these areas of study would significantly advance models, as many of these physical processes are presently parameterized in numerical simulations. For example, eddy diffusivity in the mesosphere is a parameter that is poorly characterized and parameterized in models but is absolutely crucial to understanding and modeling the chemistry and thermal balance of the mesosphere and thermosphere.
Combining such a neutral gas measurement capability with existing altitude-resolved plasma measurements provided by the incoherent scatter radar technique, along with other complementary instrumentation, would further broaden the potential for scientific discovery in areas of ion-neutral thermal and momentum exchange, Hall and Pedersen conductivity behavior, neutral wind effects on current flow and dissipation, neutral wind dynamo processes, and ion-neutral chemical interactions.
HOSTED PAYLOADS ON COMMERCIAL AND GOVERNMENT PLATFORMS
There are opportunities to leverage distributed systems for commercial and government use by adding sensors and finding secondary uses of data from these systems, in the context of breakthrough science investigations of solar and space physics.
As a prime example for secondary data use, the International GNSS Service (IGS) has been very successful in creating a leveraged global network of GPS/GNSS (Global Navigation Satellite Systems) receivers that provides excellent science data to the geophysics community without unduly taxing the resources of any single country or agency. The AIM community has been leveraging this global network to great success. The AIM community would benefit from adopting a proactive approach to the evolving and growing global GNSS network. The community should develop a leadership role in coordinating GNSS networks for AIM science, following the IGS model of leveraging an international effort across multiple institutions. Activities could include developing standards for data access; facilitating institutional hosting of GNSS receivers for AIM science; and providing scientific leadership in the use of global GNSS networks for AIM science.
An example of a successfully hosted payload is the Two Wide-Angle Imaging Neutral-Atom Spectrometer (TWINS) instrument, which provides stereoscopic imaging of the magnetosphere from twin platforms hosted on DOD spacecraft. TWINS is in a Molniya orbit with 63.4 degree inclination and 7.2 Earth radius (RE) apogee, which is ideal for its imaging objectives. Also, the Los Alamos National Laboratory geosynchronous Earth orbit satellites have been providing important particle measurements for decades.
A very cost-effective approach to creating a robust, long-term data set to meet AIM system science objectives is to host GPS remote sensing instruments on research and operational satellites deployed by NASA and the National Oceanic and Atmospheric Administration. GPS deployed on commercial satellites and constellations is another viable option. GPS is relatively simple to host because (1) it is passive (low electromagnetic emissions); (2) it operates autonomously; and (3) it is self-calibrating. The committee supports coordination with the Technology and Innovation Working Group to develop a new generation of space-borne GPS receivers that can perform high-quality ionospheric measurements with low mass and power (~1-2 kg, 1-2 W). Another technology development option is technology transfer to commercial providers of navigation receivers to add an ionospheric measurement capability. Such receivers can acquire ionospheric measurements of reasonable quality on a non-interference basis because they perform the operational navigation function.
Science objectives relevant for NASA require other orbits, but hosted opportunities are currently and increasingly available in a variety of orbits and even provide an opportunity for carrying out constellation missions that would be prohibitive in cost if dedicated spacecraft were utilized. For example, the Iridium NEXT constellation will replace the current Iridium communications satellites and will consist of 72 low-Earth-orbit (LEO) satellites (66 + 6 on-orbit spares). The orbits are nearly polar (86.4 degree inclination) at an altitude of 780 km, which is ideal for studies of particle precipitation or total electron content maps, for example. Each satellite can support up to 50 kg, 50 W average (200 W peak), and a 1-Mbps peak data rate. Several studies are underway to investigate the feasibility of placing science payloads on some or all of the Iridium NEXT satellites. For example, scientists at Johns Hopkins University’s Applied Physics Laboratory have organized a grassroots effort for the GEOscan project, which would place several different types of instruments on the satellites and would also provide the infrastructure for some CubeSats. The constellation would provide continuous coverage over the entire Earth, allowing for high-time-resolution studies on a global scale. Despite the fact that this constellation provides an unprecedented opportunity that will possibly never happen again, it is not clear whether there is sufficient time for GEOscan or something similar to materialize, since the first Iridium launch will occur in 2015. This illustrates the importance of NASA or NSF developing a capability to respond quickly to similar kinds of opportunities.
In addition to LEO opportunities, there are also many geostationary Earth orbit (GEO)-hosted opportunities. GEO communications satellites, such as StarBus, are launched 2 to 3 times a year and typically have excess capacity for 100 kg, up to 300 W, and downlink rates up to 70 Mbps. They can provide pointing control of 0.1 degrees and have greater than 5-year lifetimes. This is particularly important because it is difficult to get an orbit slot in GEO. GEO sits at the outer edge of the radiation belts and the inner edge of the plasma sheet and is thus perfectly situated for investigations of the link between substorm injections and the energization of particles in the inner magnetosphere. It is also the location of many commercial and government assets. Thus the ability to understand the space weather environment is very important.
NASA’s Sounding Rocket Program provides regular, inexpensive access to near-Earth space for a broad range of space science disciplines, including solar, geospace, and astrophysics research missions. The program has been extremely successful throughout its history, consistently providing high science return for the funding invested. Scientific payloads launched on sounding rockets provide the only means to gather data along nearly vertical profiles and are the only platforms capable of in situ sampling of the mesosphere and lower ionosphere regions (40-150 km altitude), which constitute Earth’s critical interface region between the atmosphere and space. The obtained data rates can sometimes exceed those of satellites by orders of magnitude. The rocket program is also used to provide timely calibration and correlative
data for several of NASA’s larger satellite scientific missions and enables new instrument concepts to be developed and tested in space. Another critical attribute of the Sounding Rocket Program is that it provides training for scores of university graduate students, many of whom are now among the nation’s leaders in the field of space research. The program can uniquely carry out this training because other programs are too risk averse or span too long a period of time for a graduate student to be involved from start to finish. Although new instruments have been developed within the rocket program, the emphasis for mission selection in the past 10 to 15 years continues to be governed primarily by science and the promise of closure of critical science questions. It is conceivable that a percentage of rocket flights could be dedicated to technology development as their main objective. A new NASA-developed capability, the High Altitude Sounding Rocket with apogees of ~3,000 km, providing approximately 40 minutes of observing time above 100 km, which is significantly longer than the 5- to 10-minute typical mission-duration periods of apogees of 200-1000 km, would have a huge impact on the utility of rockets for science and technology development. Such rockets would also include approximately 1-meter-diameter experiment sections, which are significantly larger than current payload diameters (40-50 cm). These new platforms would enable significantly longer observing times for solar missions that track developing features on the solar disk, as well as enable direct penetration of the cusp and auroral acceleration regions and also the inner radiation belt, by geospace missions.
High-altitude balloon experiments have a rich history in solar and space physics. Balloons continue to offer a unique science platform, and, like sounding rockets, they provide opportunities for instrument development and program management that are essential in the training of the next generation of scientists and engineers. Investigations using balloons are contributing to fundamental research advances across the discipline areas that constitute solar and space physics, with observations that range from gamma-ray solar flares to particle precipitation to large-scale magnetospheric electric fields.
In solar physics, balloons offer a low-cost method for carrying heavy payloads high above the atmosphere. Such missions have led to scientific discoveries and are an ideal platform for developing and testing new spacecraft instrumentation. For example, in the 1980s, hard-X-ray microflares and superhot flare plasmas were discovered during missions using balloon-based X-ray instruments. Balloon missions (e.g., HEIDI, HIREGS) were also essential for the development of the RHESSI (Ramaty High Energy Solar Spectroscopic Imager) small Explorer that has operated for nearly a decade.
Balloons have also made important contributions to understanding both auroral and radiation belt particle precipitation. For example, electron microbursts were discovered with balloons,4 and it is now recognized that microbursts are an important loss mechanism for the radiation belts and may be an ideal test case for studying nonlinear wave-particle interactions. Balloons also offer a unique platform for precipitation studies that is complementary to spacecraft measurements. The BARREL (Balloon Array for RBSP Relativistic Electron Precipitation) project will fly 40 small (~20 kg) balloon payloads during two Antarctic campaigns in 2013 and 2014 to provide a global view of electron precipitation during the RBSP (renamed Van Allen Probes) mission and be able to distinguish complex temporal and spatial variations.
The Ultra Long Duration Balloon (ULDB) program remains critical for solar research; X-ray, gamma-ray, and neutron instruments are generally very heavy due to the amount of power required to stop high-energy photons and the long observing window required to catch rare large gamma-ray flares.
4 K.A. Anderson and D.W. Milton, Balloon observations of X rays in the auroral zone 3: High time resolution studies, Journal of Geophysical Research 69(21):4457-4479, doi:10.1029/JZ069i021p04457, 1964.
Balloons remain the cheapest and most effective method for carrying large (>1,000 kg) payloads to the edge of space. The increased availability of the ULDB program provides a critical enhancement of capability for a variety of science disciplines.
VERY SMALL SPACECRAFT
Through March 2011 55 CubeSats had been launched worldwide. CubeSats are distinguished by their conformance to a size standard that allows them to be carried into orbit within a generic dispenser/carrier, the so-called P-POD. The P-POD fully encapsulates the CubeSats, providing a high level of protection for the launch vehicle and any primary payload. Owing to its simplicity and ease of adaptability to a wide variety of launch vehicles, the P-POD has been qualified for flight and utilized on a number of launch vehicles. To date, all CubeSats launched have conformed to size requirements of the standard 3-U P-POD, which accommodates up to three CubeSats measuring 10 × 10 × 10 cm.
The scientific utility of very small satellites is being demonstrated through NSF’s CubeSat-based Science Missions for Space Weather and Atmospheric Research Program. Seven scientific CubeSat missions have been competitively selected (through July 2011) from many more proposals submitted to the NSF program through its first three solicitations. The missions (FireFly, RAX, FIREBIRD, CINEMA, CSSWE, DICE, and CADRE) will pursue science goals, including studies of lightning-induced terrestrial gamma rays; electromagnetic emissions near ionospheric radar beams; mechanisms responsible for relativistic electron microbursts; energetic radiation belt electrons; electrons, ions, and neutral atoms in the ionosphere; ion-neutral coupling in the ionosphere; and the atmospheric density response in the thermosphere to extreme forcing. The NSF CubeSat program is substantially oversubscribed.
Technological gains in miniature, low-power, highly integrated electronics, microelectromechanical system devices, and other nanoscale manufacturing techniques have enabled revolutionary approaches to experimental space science that have not widely been put into practice by the heliophysics community. Small, low-cost satellites provide opportunities not typically available to traditional, large spacecraft. Low-cost “expendable” spacecraft may be deployed into regions where satellite lifetimes are constrained but where important, yet not well characterized, science linkages take place. The lower ionosphere well below 300 km and reaching down into the thermosphere at even lower altitudes is an important coupling region between the upper atmosphere and the ionosphere, yet atmospheric drag severely limits satellite lifetime against orbital decay at these altitudes. The solar chromosphere is another poorly characterized coupling region where harsh environments limit satellite lifetime. The science return per dollar to perform in situ measurements in these types of regimes, to conduct even limited lifetime measurements, is enhanced by low-cost platforms. Constellation missions, described elsewhere in this report, composed of dozens of science platforms are enabled by low-cost satellites that can be launched in large numbers from a single launch vehicle or from a number of launch vehicles as secondary or rideshare payloads at very low launch costs. Very small instrument-carrying satellites, e.g., with total mass-to-orbit in the range of 1 to 20 kg, can accommodate instruments of great utility for heliophysics. Their utility for collecting unique science measurements is greatly enhanced when they are deployed as swarms or into unique environments. Continuing technological developments will lead to even more capable spacecraft with space, weight, and power (SWAP) resources capable of supporting payload complements even more sophisticated than those permitted by the present-day 3-U CubeSats. Already, a number of organizations have developed prototype 6-U deployers and satellites that have significantly enhanced SWAP resources compared to the 3-U standard.
Launch opportunities for conforming CubeSats are becoming commonplace. The NASA Launch Services Program’s Educational Launch of Nanosatellites (ELaNa) program for educational satellites has been established and is well underway, providing launch manifesting for CubeSats. The first ELaNa CubeSats
were launched in March 2011 as secondary payloads on the ill-fated Glory launch, and several other ELaNa follow-on missions are in the launch queue. To date 35 satellite projects have been selected for manifesting as secondary payloads under the ELaNa program. A new call for proposals was announced (July 2011) that entertains flight opportunity proposals for 6-U CubeSats, in addition to the traditional 1-U, 2-U, and 3-U form factors. Launch opportunities in the future are expected to increase, especially for certain orbits. Two large spacecraft are under development that will resupply the International Space Station (ISS)—the Dragon spacecraft of Space-X (Space Exploration Technologies Corporation) and the Cygnus spacecraft of Orbital Sciences Corporation. Both Space-X and Orbital have initiated programs to carry CubeSats on these ISS resupply missions. Indeed, the ISS itself could be used to store and launch on demand any number of CubeSats. Such a capability would allow quick responses to geophysically interesting events, or, for example, the measured deployment of CubeSats to form a thermosphere constellation. The feasibility of launching CubeSat-like satellites from the ISS has been demonstrated multiple times through the micro-electromechanical systems-based PicoSat Inspector program for the Aerospace Corporation.
Satellites with bigger volumes than CubeSats, but still well below a standard Explorer size, could revolutionize research in AIM and other science disciplines. Because of their substantially smaller cost, such tiny Explorers could be built with a much higher risk-tolerance and could carry a small number of instruments, or novel low-weight sensors, into interesting locations of the space environment. Tiny Explorers would still be carried as secondary payloads and would share some commonalities. However, they would open a new set of opportunities for longer-duration measurements.
Constellations of measurement platforms of various sizes have the potential to take advantage of miniaturization technologies, enhanced computational capabilities, and autonomous systems, as well as novel system and network approaches. The value of many breakthrough solar and space physics constellations strongly depends on the number of elements in the system. With the advent of small CubeSats and tiny Explorers, novel means of investigations are enabled that have the potential to provide an unprecedented density of measurements in the upper atmosphere and elsewhere.
Illustrative Examples of Newly Enabled Constellations
Magnetosphere Radiation Belt Constellation
A 6- to 12-month database of continuous ultralow-frequency measurements of the azimuthal mode number spectrum would provide a critical missing piece of information for radiation belt modelers. A constellation of ~30 CubeSats equipped with fluxgate magnetometers in a circular orbit near the geomagnetic equatorial plane (e.g., geosynchronous) would be an ideal platform for such a radiation belt study.
Ionosphere-Magnetosphere Coupling Constellation
A constellation mission utilizing small satellites would radically improve understanding of the dynamics of the coupled thermosphere-ionosphere system. In order to achieve this goal, the following top-level requirements must be met:
1. Each satellite needs to be complemented with instrumentation that is capable of measuring both the neutral and ion state variables, such as density, temperature, and winds. There are a few different instru-
ment packages that are capable of achieving this requirement, with many of them small enough to fit on very small spacecraft.
2. Each satellite needs to pass through the auroral zone, since this is the primary science zone.
3. There must be enough satellites in a single orbital plane that the return time to a location is less than dynamical timescales within the system.
4. Multiple planes of satellites should be utilized to provide information on the longitudinal structure and the dynamics of the system.
Measurements from a diverse set of platforms—space missions, suborbital, ground-based, CubeSats, alternatives—can enhance the science of any single-point space missions. Examples of successfully demonstrated integration are THEMIS ground-based, BARREL and RBSP, and the rocket flights that were done during the CRRES mission.
A heterogeneous facility generalizes this integration concept into a comprehensive approach that encompasses all aspects of a mission, but it is applied to a variety of platforms that are integrated through operational means, data analysis, and dissemination to target science objectives in an integrated fashion. Heterogeneous facilities are particularly valuable to system science for understanding mesoscale and global-scale processes. Heterogeneous facilities would combine and coordinate measurement platforms that are developed through a variety of means and financial support.
Illustrative Example of Heterogeneous Facilities: A Storm-Based Campaign
The purpose of a storm-based heterogeneous facility would be to set up and operate a campaign over a given time period focused on a variety of assets, all deployed to understand geomagnetic storms. Global GPS networks have provided a synoptic view of ionospheric storms that emphasizes how different physical processes and regional features work in concert to create the “global ionospheric storm.” GPS networks operate continuously so that no special coordination is needed as part of a heterogeneous facility. However, significant questions regarding the physical processes causing the storm-time dynamics requires unraveling coordinated observations. A storm investigation would require that the GPS data be analyzed during an event in which coordinated observations from SuperDarn, NSF radars, and wind measurements are obtained. Mission data would play a role also. These facilities would be operated in a mode that optimizes their data for the particular science objectives being pursued. Mobile facilities could be located where they are most needed to investigate particular mesoscale features that are prominent during storms, such as storm-enhanced density or tongues of ionization. The scientific payoff is understanding the physical drivers of the ionospheric response that is captured by the GPS sensors. This campaign may also involve coordinated operation of some CubeSats and also balloon launches.