The Radio Aurora Explorer – a Bistatic Radar Mission to Measure Space Weather Phenomenon

SSC10-II-4 The Radio Aurora Explorer – A Bistatic Radar Mission to Measure Space Weather Phenomenon James Cutler, Matthew Bennett, Andrew Klesh University of Michigan 1320 Beal Avenue, Ann Arbor, MI, 48109; 734-647-8223 jwcutler, mattwb, aklesh @umich.edu Hasan Bahcivan, Rick Doe SRI International Engineering & Systems Division, 333 Ravenswood Avenue, Menlo Park, CA 94025; 650-859-2165 hasan.bahcivan, [email protected] ABSTRACT In this paper, we describe the Radio Aurora Explorer (RAX) and its space weather mission. RAX is a satellite mission funded by the National Science Foundation (NSF) to study space weather, and is a joint effort between SRI International and the University of Michigan. The primary mission objective is to study plasma instabilities that lead to magnetic field-aligned irregularities (FAI) of electron density in the lower polar thermosphere (80-400 km). These irregularities are known to disrupt trans-ionospheric communication and navigation signals. The RAX mission will use a network of existing ground radars that will scatter signals off the FAI to be measured by a receiver on the RAX spacecraft. The satellite is a 3kg CubeSat with a scheduled launch in late 2010. RAX is the first of the NSF-sponsored satellites to be manifested for a launch and represents a path forging activity for similar science missions conducted on nanosatellite vehicles. INTRODUCTION deployment of sensors in space, for focused The Radio Aurora Explorer (RAX) is the first science missions that target a specific space of several nanosatellites commissioned by the weather phenomenon, and for increased multi- National Science Foundation (NSF) to study point measurements of space plasma and extend our knowledge of space weather. parameters through coordinated and distribute In 2008, NSF hosted a workshop to explore satellites. Also, due to their low-cost, the potential use of a specific nanosatellite innovative missions with higher-risk are form factor, the CubeSat [1], for novel space acceptable and encouraged [2]. Proposals to weather missions. Despite their obvious the NSF program included science missions to limitations in mass (less than 4 kg) and size investigate upper-atmospheric, ionospheric, (less than 10x10x30 cm ) these small satellites magnetospheric, and solar space weather offer potential advantages that compliment research. Currently, the NSF funds six their larger forerunners. They provide the missions. RAX is the first of these missions opportunity for fast implementation and with a scheduled launch in late 2010. Cutler 1 24th Annual AIAA/USU Conference on Small Satellites The RAX space weather investigation seeks to project management, scientific analysis, and better understand the distribution and genesis community outreach. The RAX mission has of naturally occurring ionospheric already engaged K-12 students in high-altitude irregularities by deploying the first known balloon field tests of critical RAX position and ground- to-space bistatic coherent-scatter timing subsystems. By selecting to transmit radar system. Plasma irregularities are telemetry data in the 70 cm amateur radio naturally occurring ionospheric structures that band and widespread propagation of can significantly degrade the performance of modulation formats, RAX will engage a satellite-based communication and navigation global community in tracking health, status, systems. As our economy and society and science data streams on-orbit. becomes increasingly dependent on GPS and space-based communication, commerce and In the remainder of this paper, we provide an human safety can be threatened by even overview of the RAX mission. We summarize momentary system outages. the scientific background and objectives, and describe our scientific method for The RAX mission overcomes the limitations measurements. We then discuss the RAX of existing measurements by using a novel bi- satellite design and conclude with a summary static radar experimental configuration. The of mission status. ground-to-space bi-static geometry enables high horizontal and altitudinal resolution SCIENCE OVERVIEW measurements of the auroral FAI. The high RAX is a plasma-sensing ultra-high frequency resolution is achieved through two factors: (1) (UHF) radar mission developed in response to the radar illuminating the irregularities has a NSF’s 2008 CubeSat-based Science Missions narrow beam width, which is typical of all for Space Weather and Atmospheric Research. incoherent scatter radars (ISR), and (2) the The RAX mission goals are to better radar-to-irregularity distance is short because understand the genesis and distribution of the radar can be pointed at high elevation naturally occurring ionospheric irregularities angles (as opposed to a monostatic radar [6]. Deploying the first known ground-to- pointed at very low elevation to meet the space bistatic coherent-scatter radar system, perpendicularity condition). the RAX mission will coordinate a network of megawatt-class ground-based radar Beyond science and technology, RAX has a observatories with an on-orbit CubeSat radar strong commitment to post-secondary and K- receiver to yield a unique scattering geometry 12 outreach. The RAX PIs hope to create a (Figure 1) for characterizing the climatology new class of opportunities for student space and evolution of meter-scale ionospheric physics experimentalists by inviting graduate structures—features inaccessible to ground- and undergraduate students to participate in a based observation [5]. These globally series of orbital radar experiment workshops, observed ionospheric irregularities, driven by a once-in-an-academic-lifetime opportunity to the interaction of naturally occurring strong influence mission science execution. Through electric fields and ionospheric plasma fabrication, testing, operations, analysis, and gradients, result from a chaotic interplay of discovery, the RAX mission will involve as solar magnetic and ultraviolet forcing of many as 200 students, providing them with a Earth’s upper atmosphere. broad skill set including engineering design, Cutler 2 24th Annual AIAA/USU Conference on Small Satellites SRI INTERNATIONAL PROPOSAL EXU-10-079 15 APRIL 2010 of meter-scale ionospheric structures —features inaccessible to ground-based observation. These globally observed ionospheric irregularities, driven by interaction of naturally occurring strong electric fields and ionospheric plasma gradients, result from a chaotic interplay of solar magnetic and ultraviolet forcing of Earth’s upper CubeSat Form Factor atmosphere. First, all satellites in this NSF program are The RAX mission will investigate ionospheric irregularities CubeSats, and therefore RAX must conform to gain insight into several candidate causal mechanisms to the CubeSat standard [3]. Cal Poly and (plasma instabilities), only a few of which have been Stanford University developed the standard observed by ground-based research radars. By gauging the which defines several structural features of the global spatial distribution of these ionospheric irregularities satellite. The mission was allotted a 3U and their causal geophysical drivers, the RAX mission will satellite, nominally with a volume of advance the state of space weather forecast. 10x10x30 cm and less than 3 kg. Thus, the An in-depth discussion of RAX measurement of ionospheric science mission was crafted to utilize this Figure 2. RAX ground-to-space resource-constrained satellite. irregularities is included in co-investigator Dr. Hasan Figure 1 – Schematicbistatic drawinggeometry. of the RAX mission Bahcivan’s 2008 NSF submission, CubeSat-based Ground- radar geometry. A ground radar transmits radar Launch Manifest to-Space Bistatic Radar Experiment—Radio Aurora Explorer (Appendixpulses towards III -irregularities2) and his that are aligned with follow-on experimental study in the Journal of Geophysical Researchthe Earth’s (A magneticppendix field. III- The irregularities scatter The second constraint (and also an these signals towards space. RAX will receive 3). A detailed technical description of RAX spacecraft payload and bus subsystems is opportunity) was a manifested launch these signals, process them onboard, and downlink opportunity on a US Air Force Space Test presented in Section 6; discussion of operational considerationsdata is providedto the science in operationsSection centers. 7. Program launch, STP-26, for the RAX mission. At program inception, the launch The RAX mission will investigate ionospheric date was scheduled for December 2009 and irregularities to gain insight into several 2 RELEVANCE AND BENEFITS TO NASA the orbital parameters were a 650 km circular candidate causal mechanisms (plasma orbit at an inclination of 72 degrees. This instabilities), only a few of which have been Science resulted in two distinct sub-constraints. observed by ground-based research radars. By RAX addresses the fundamental nature of ionospheric plasma irregularities in the Design, build, test, and delivery of the RAX gauging the global spatial distribution of these Earth's thermosphere. These irregularities are the basis of a natural space-weather mission had to be done in less than 12 months. ionospheric irregularities and their causal phenomenon that can compromise the operation of communication and navigation Also, at an altitude of 650 km, assessment of geophysical drivers, the RAX mission will satellites—with potentially disastrous consequences for both commerce and safety. de-orbit properties was a prime driver for the advance the state of space weather

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