This project is a collaboration between a space science Principal Investigator (PI) at SRI International and an engineering PI at University of Michigan. The objective of this three-year cross-disciplinary team effort is to build and operate a tiny, so-called CubeSat, spacecraft carrying a UHF radar receiver payload. Launch of the satellite will be as a secondary on a Department of Defense launch scheduled for December 2009. The satellite will be operated in coordination with the AMISR incoherent scatter radar from the ground to investigate the radio aurora from field-aligned irregularities in the high-latitude ionosphere. The primary scientific objective of the Radio Aurora Explorer (RAE) mission is to understand the microphysics of plasma instabilities that lead to field-aligned irregularities (FAI) of electron density in the polar lower (80-300 km) ionosphere. The RAE mission is specifically designed to remotely measure, with extremely high angular resolution (~0.5 degree), the wave spectrum of ~1 m scale FAI as a function of altitude, in particular measuring the magnetic field alignment of the irregularities. Due to the magnetic field geometry at high latitudes this bi-static (ground radar to satellite) configuration, in which a narrow radar beam is scattered off the FAI and then observed by the CubeSat receiver, is the only way to perform these measurements. Better understanding of ionospheric irregularities and their role in ionospheric dynamics is an important space weather research objective because plasma structures in the ionosphere can have an adverse effect on communications via satellite, HF and VHF radio and as well as an adverse effect on navigation, tracking, and positioning. The project has a very strong educational component; it relies on extensive undergraduate and graduate student involvement through all aspects of the mission. The new, largely unproven technology involved in cubesat missions, inherently makes the project associated with significant risks. On the other hand, however, the project has tremendous potential to be transformational not only within its own research area but also for the larger field of space science and atmospheric research as well as within aerospace engineering and education.
The Radio Aurora Explorer (or RAX) is the first CubeSat mission sponsored by the National Science Foundation to study space weather. RAX is a joint venture between the University of Michigan and SRI International. Itsprimary mission objective is to study large plasma formations in the ionosphere, the highest region of our atmosphere. These plasma instabilities are known to spawn magnetic field-aligned irregularities (FAI), or dense plasma clouds known to disrupt communication between Earth and orbiting spacecraft. To study FAI, the RAX mission will utilize a large incoherent scatter radar in Poker Flats, Alaska (known as PFISR). PFISR will transmit powerful radio signals into the plasma instabilities that will be scattered into space. During that time, the RAX spacecraft will be orbiting overhead and recording the scatter signals with an onboard receiver. These signal recordings will be processed by an onboard computer and transmitted back to our ground stations where scientists will analyze them. The goal of this one-year science mission is to enhance our understanding of FAI formation so that short-term forecast models can be generated. This will aid spacecraft operators with planning their mission operations around periods of expected communication disruption. The objective of the RAX mission is to understand the microphysics that lead to the formation of magnetic field-aligned plasma irregularities (FAI), an anomaly known to disrupt communications with orbiting spacecraft. The RAX mission is specifically designed to remotely measure, with extremely high angular resolution, the 3-D k-spectrum (spatial Fourier transform) of ~1 m scale FAI as a function of altitude, in particular measuring the magnetic field alignment of the irregularities. 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 spacecraft will measure "radio aurora", or the Bragg scattering from FAI that are illuminated with a narrow beam incoherent scatter radar (ISR) on the ground. This remote sensing method is based on the powerful mathematical relation that the radio aurora intensity is proportional to the irregularity k-spectrum evaluated at the Bragg wave number. The proposed ground-to-space bistatic radar experiment highly resolves the k-spectrum, which means that the sensed volume of plasma is homogeneous and that the received signal contains a pure content of wave vectors, which are important for accurate analysis of wave growth and damping. Moreover, each experiment will be tagged with the convection electric field Ec, a principal driver of the irregularities, which will be measured (besides altitude profiles of plasma density and temperatures) by the ISR immediately before and after each experiment. The RAX mission is a unique opportunity to quantify plasma processes in a homogeneously resolved volume of plasma with the driving force and the effect measured effectively simultaneously. Two RAX satellites have launched; RAX-1 in November 2010 and RAX-2 in October 2011. RAX-1 demonstrated tha the radar system worked as predicted however the satellite ceased operation prematurely due to a flaw in the solar panels. RAX-2 has continued the science measurements and detected the first ever FAI at this scale. The results are preliminary and in the process of study and publication.
