Small Satellites for Space Weather Research

Transcription

1 SPACE WEATHER, VOL. 6, S05007, doi: /2008sw000392, 2008 Small Satellites for Space Weather Research Therese Moretto and Robert M. Robinson Published 23 May Citation: Moretto, T. and R. M. Robinson (2008), Small Satellites for Space Weather Research, Space Weather, 6, S05007, doi: /2008sw Recent advances in sensor and spacecraft technologies are making small satellites a cost-effective means to accomplish key research objectives in space weather. Small-satellite missions can complement existing or planned larger missions by filling gaps in time or coverage, or they can constitute stand-alone missions targeting specific, well-defined science and applications questions. Such missions would also play a crucial role in training the next generation of experimental space scientists, aerospace engineers, and space weather professionals. This article highlights some of the advancements that have been made in recent years that make small-satellite missions both feasible and cost-effective. Several new programs are under way that take advantage of the progress in sensor development, satellite platform design, and launch technology for small satellites. The time is right to integrate these emerging technologies to accomplish key science objectives, particularly in space weather. Throughout this article we use the term small satellite quite loosely to denote a wide range of satellite missions. No clear and universally agreed upon classification of satellites or satellite missions exists. Table 1 shows a rough classification that we shall use here for reference spanning from large satellites to picosatellites based on typical values for satellite mass, cost, and development time frame in each class. However, individual missions often span several classes when considering size, cost, or complexity. We focus here on missions in the microsatellite to picosatellite range. Division of Atmospheric Sciences sponsored a workshop in May 2007 to explore the possibilities and benefits of utilizing small-satellite missions to provide essential measurements for space weather research. In his keynote address at the workshop, the NASA Ames Research Center (ARC) director, Simon Pete Worden, stated his belief that significant science can be done with small satellites at the cost of a few million dollars per mission. He argued that the technology exists, as well as the launch opportunities, and asserted the feasibility and value of executing simple, focused missions of limited duration, in the 2- to 5-year range. Most of the workshop presentations, including Worden s, can be viewed at the meeting Web site, Formerly, the biggest obstacle to routine access to space was the cost of launching to orbit. Owing to the growing demand for low-cost access to space, government agencies and private industries have been striving to explore new technologies and strategies to reduce launch costs while keeping risk of launch failure low. One primary target of these efforts is providing launch opportunities for small satellites, which not only are more amenable to keeping costs low but also offer quicker turnaround times for end-to-end space missions. New launch opportunities include both dedicated flights on low-cost launch vehicles and ride-shares on larger missions. New Launch Opportunities In a recent report by the Assessment Committee for the National Space Weather Program (NSWP; see a key recommendation was for NSWP agencies to investigate the feasibility of using microsatellites with miniaturized sensors to provide cost-effective science and operational data sources for space weather applications. The U.S. National Science Foundation s (NSF) Copyright 2008 by the American Geophysical Union 1 of 5

2 Figure 1. Measuring about 10 centimeters on each side, CubeSat picosatellites weigh at most 1 kilogram. One example that puts these new ideas into practice is the newly created Hawaii Space Flight Laboratory (HSFL) at the University of Hawai i, which is working on establishing a sustainable local integration and launch capability, with support from the Hawaii Space Grant Consortium in partnership with the Pacific Missile Range Facility and the Kauai Test Facility, located at Barking Sands, on the west coast of the island of Kauai. The launch vehicle is Sandia National Laboratories Super Strypi research rocket, which can carry 300 kilograms to low-earth orbit (LEO). The first two launches are planned for 2009 and 2010, as part of the Low Earth Orbit Nanosat Integrated Defense Autonomous System (LEONI- DAS) program. The purpose of LEONIDAS is to develop a test bed for small satellites created and launched out of Hawaii, with remote sensing experiments and small-satellite technology demonstrations as main focus areas. Payloads for LEONIDAS launches are expected to include microsatellites built by HSFL as well as additional microsatellites and nanosatellites still to be determined. Future plans for LEONIDAS and HSFL include missions/ launches at a sustained rate of at least one per year. Total recurring costs for these launches are expected to be of the order of $9 million, which can be divided among multiple payloads. Plans are to offer this launch service to other university and research customers, including launch opportunities for small secondary payloads at a highly competitive price. In a similar initiative, the U.S government has established the Minotaur rocket program utilizing Minuteman intercontinental ballistic missiles (ICBMs) as an inexpensive and responsive small-mission launch capability. The price for a Minotaur I launch, which can carry 500 kilograms to LEO, is of the order of $20 million. Recently, the U.S. Air Force TacSat 2 minisatellite, designed to help military commanders gain access to up-to-the-minute satellite data from satellites directly overhead, was launched on a Minotaur I from the NASA Wallops Flight Facility (Wallops Island, Va.) with NASA s smallest satellite to date (the GeneSat 1 nanosatellite, designed for biological research; see nasa.gov/centers/ames/missions/2007/genesat1.html) as a secondary payload. TacSat 3, with a mission similar to that of TacSat 2, will be launched in the same way in June 2008 together with NASA s second miniature biological space laboratory, GeneSat 2, and a set of three test CubeSat picosatellites (Figure 1; see next section for more information about CubeSat). The TacSat Minotaur launches are under the purview of the U.S. Department of Defense (DOD) Space Test Program (STP). The inclusion of secondary payloads on these launches is the result of dedicated efforts within the STP to utilize excess capacity on the launches they sponsor. It demonstrates strong commitment by the STP not only to fulfill DOD needs but also to offer excess launch capacity to serve other U.S. government needs for small research satellite payloads. Another recent initiative by the STP, aimed at boosting the utilization of excess capacity on large launch vehicles, is the development of the Evolved Expendable Launch Vehicle (EELV) Secondary Payload Adapter (ESPA). ESPA is a ring placed under an EELV primary payload that supports up to six 180-kilogram secondary spacecraft. The first mission to utilize ESPA was the Space Test Program 1 (STP 1), which launched on an Atlas V rocket in March 2007 from Cape Canaveral. The ESPA ring carried four military research satellites as a secondary payload, two of which are relevant to space weather (one will investigate the causes of communication outages in the upper atmosphere, and the other will investigate plasma irregularities in the upper atmosphere). The satellites were successfully delivered into two different low-earth orbits, thus proving the ESPA concept and design. The STP s goal is to include the ESPA ring on as many of its launches as possible, and it is collaborating with NASA on extending the use of ESPA on NASA EELV launches. Considerable progress in launch vehicle technology for small satellites has also been accomplished in the private sector. The Falcon 1 rocket, developed by the Space Exploration Technology Corporation (SpaceX), has the capacity to carry of the order of 500 kilograms into LEO. Launches are currently offered at a flat rate of $7 million from several launch sites. The company expects to be offering shared launches and launch opportunities for small secondary payloads in the near future. The big issue for ride-sharing, of course, is eliminating potential risk of damage to the primary payload. This requires careful planning and strong integration between payload developers and spacecraft integrators. Ride-sharing has been greatly simplified in recent years because of the development of standardized satellite platforms. 2 of 5

3 Satellite Platforms The development of flexible but standardized, proven spacecraft designs eliminates the need for much of the nonrecurring engineering work typically associated with mission design and implementation. Along with the provision of readily available, cheap commercial-off-the-shelf (COTS) components and subsystems, standardized spacecraft greatly reduce the costs of individual missions while at the same time, making it technically feasible for a much larger community, including student projects, to get involved with spacecraft missions. A recent initiative by the STP to move away from the one-of-a-kind spacecraft philosophy is the design of the Standard Interface Vehicle (SIV). The STP-SIV is designed as an ESPA-class prototype spacecraft to provide a cost-effective platform for utilizing ESPA launch opportunities. Similar concepts to provide fast, cost-effective satellite solutions are being pursued in the commercial arena by United Kingdom s Surrey Satellite Technology Ltd. (SSTL) and the United States s SpaceQuest, Ltd. The latter offers a so-called data-buy concept. In this scenario, scientific instruments are put into orbit by a vendor who provides a spacecraft, launches it, operates it, and collects the data returned by the instrument, while maintaining sole responsibility and ownership of the mission throughout. The vendor recovers the cost of the mission by providing access to the scientific data over the Internet at a predetermined price. Another promising concept is the GeoQuickRide program at NASA s Rapid Spacecraft Development Office at Goddard Space Flight Center. This program offers opportunities to fly scientific instrument packages on government and commercial geostationary satellites. With an estimated Figure 2. The Poly Picosatellite Orbital Deployer (P-POD). This platform can contain three tiny, free-flying CubeSat spacecraft. These CubeSats are launched separately, allowing them to orbit independent of the P-POD and each other. 20 launches per year of geostationary satellites, they constitute an immense potential resource that could be utilized: Most often, these missions are designed with excess capacity of space, mass, power, and data return rates, which means that the only major cost factor involves integrating the small satellite with the launch package. At present, however, vendors request of the order of $10 million per mission for this service, and as a result it has been done only a few times. The advent of cheaper alternatives for getting research and technology demonstration missions into space will undoubtedly bring this price down in the future. A similar approach is used in the Active Magnetosphere and Planetary Electrodynamics Response Experiment ( AMPERE) undertaken jointly by scientists at Johns Hopkins University Applied Physics Laboratory and the Boeing Service Company to develop a new observational space weather capability. Utilizing magnetometer measurements from the attitude control system on board the constellation of Iridium communications satellites, the project will provide near-realtime, global estimates of the electric currents flowing into and out of Earth s upper atmosphere. Perhaps the most promising standardized platform for low-cost, student satellite missions is the Poly Picosatellite Orbital Deployer (P-POD), developed at California Polytechnic Institute ( see Figure 2). The P-POD is a container for three stacked picosatellites named CubeSats, each measuring 10 centimeters on a side and weighing at most 1 kilogram (Figure 1). P-PODs are designed to accommodate the CubeSat physical layout and design guidelines, taking advantage of a standard, flight-proven deployment system. A thriving student satellite program has developed over the past 4 years based on this CubeSat standard. Through the establishment of standards and collaboration between university groups worldwide, the CubeSat program has aided the construction and launch of 32 student-built picosatellites since With few exceptions, these were all launched outside the United States. Of the order of 40 universities in the United States are involved in the CubeSat program, which has matured much faster than expected. CubeSat projects are usually done on very low budgets, with hardware costs as low as $50,000 and launch costs of a similar magnitude. The success of CubeSat in attracting and exciting students while producing innovation and new technology clearly illustrates the potential for small-satellite projects to play a crucially important role in educating engineering and science students and in doing real science at low cost ( Space Weather Research Using Small Satellites Small-satellite missions can provide valuable measurements that would help answer important outstanding science 3 of 5

4 questions in space weather. Table 2 provides a list of instruments amenable to launch on small satellites. The table indicates the science topics that each instrument would help address and its readiness in a general sense for being flown on small satellites. Readiness is classified as immediate, meaning that such instruments are already suitable for small-spacecraft missions; near-term, indicating that such measurements are likely to be possible from small satellites within the next 5 years; or later, indicating that these measurements are not expected to be possible within 5 years. The readiness estimates consider the smallness of instruments along with their potential to achieve low enough power and data rate requirements. Table 2 clearly demonstrates the great potential for small satellites to have a significant impact in all areas of space weather science. Educational Benefits of Small Satellites A number of successful programs have offered lowcost access to space, including Skylab, Getaway Specials, and Hitchhiker, all supported by NASA between 1973 and Among other accomplishments, these programs have helped attract young engineers into the space industry and contributed to the continuing strength of the U.S. aerospace enterprise. Obviously, there is no substitute for a hands-on approach to learning the skills and experience needed to succeed in the aerospace industry. This realization is also the motivation behind a number of recent initiatives within the DOD; for example, the U.S. Air Force Office of Scientific Research (AFOSR) has supported the FalconSat program at the Air Force Academy. Under the motto Learn Space by Doing Space, the goal of this program is to have students design, construct, test, launch, and operate a new microsatellite or nanosatellite every 2 3 years. Since the start of the program in 2000, more than 200 cadets have graduated with real satellite experience. The third satellite in the program, the microsatellite FalconSat 3, was successfully launched in March 2007 as one of the satellites of the STP 1 mission. One objective of this satellite is to investigate ionospheric irregularities. A similar initiative aimed at the broader civilian academic community is the AFOSR s University Nanosat program. With a mandate to create a space cadre of highly trained U.S. university students, the program supports hands-on teaching of systems engineering through design, assembly, integration, test, launch, and in-orbit operation of studentbuilt satellites. The concept is that every other year, about 10 university proposals are selected to receive $110,000 to design and build a satellite over 2 years. So far, the program has led to one mission launch: Two spacecraft of the Three Corner Sat mission, designed to demonstrate stereoscopic imaging, formation flying, and innovative command and data handling, were launched in December However, because 4 of 5

5 of a sensor glitch on board the launch vehicle, the satellites were placed in a lower-than-expected orbit. This caused mission lifetime to run out before science goals were met. Currently, the third mission of the program, NanoSat 3 (designed to demonstrate autonomous high-precision real-time relative navigation using innovative GPS technologies), is in storage awaiting launch in December 2009, and the fourth mission (also aimed at improving navigation accuracy and demonstrating controlled formation flying) is expected to be ready for delivery (i.e., ready for launch) before the end of A New Opportunity Space-based measurements from small satellites have great potential to advance discovery and understanding of space weather. Advances in sensor technology and burgeoning launch opportunities are making small-satellite missions more cost-effective. Scientific satellite missions in the $1 10 million range (including launch costs) are possible, and such missions can help fill important observational gaps. Thus, it is important that the cost of missions be kept as low as possible to avoid getting trapped by risk aversion leading to spiraling programmatic complexities and costs. Equally important, such missions play a crucial role in training the next generation of experimental space scientists and aerospace engineers. Effective training of the next generation of aerospace experts has been hampered by the length of time required to plan and execute large space missions. A small-satellite mission that can be designed, built, flown, and operated in 3 4 years is ideal for student participation, permitting them to experience all aspects of the end-to-end mission process. The natural fascination students have for space exploration will be strengthened by the opportunity to see the scientific output of their small-satellite research projects. Regular access to space, provided by small satellites, will maintain creativity and innovation in space science and aerospace engineering and keep a general widespread interest in space. Furthermore, small satellites will inspire the development of new experimental methods and technology. The space weather community will benefit greatly through this new technology. Therese Moretto is a space weather scientist and program director at the U.S. National Science Foundation, located in Arlington, Va. Robert M. Robinson is a space weather scientist and program director at the U.S. National Science Foundation, located in Arlington, Va. 5 of 5