Radio Aurora eXplorer (RAX) is a Cubesat-based ground-to-space radar experiment for the studies of ionospheric plasma turbulence. The mission is funded by the NSF small satellite Program for space weather and atmospheric science program that started in 2008. Five megawatt-class UHF mid- and high-latitude incoherent scatter radars (whose primary operations are ground-based ionospheric measurement) are utilized to illuminate the plasma turbulence to be measured by RAX as coherent radar scatter. The principal science objective is to make common volume radar measurements of coherent and incoherent scatter radar returns to determine the ionospheric turbulence response to magnetospheric forcing. Prediction of the plasma turbulence is important for space weather because the plasma turbulence in the form of meter-scale field-aligned irregularities (FAI) (1) impacts trans-ionospheric navigation and communication signals by scattering or scintillation; (2) creates a layer of anomalous resistivity on the magnetosphere-ionosphere current circuit impacting the energetics of the upper atmosphere, which may result in, for example, unpredictable satellite drag.

RAX I was launched in November 2010 via STP aboard a Minotaur-4 vehicle from Kodiak, Alaska. Following a successful launch, all systems performed nominally with the exception of the failure of one of the four solar panels. A ground-to-space radar experiment using the Poker Flat Incoherent Scatter Radar (PFISR) was successfully carried out three weeks after launch. However, the remaining spacecraft solar panels gradually degraded resulting in mission termination in early 2011.

The functioning of the rest of the spacecraft was demonstrated by the flawless conduct of the first science experiment. The RAX team precisely computed and prepared the spacecraft conjunctions and the ground-radar transmissions with a precision of 1 s. During the 300 s raw radar data acquisition experiment, the payload collected 1.2 GB of snapshot radar data. The instrument data processing unit processed the radar signals to a basic science product, a gray-scale map of range-time intensity (RTI) of 50 KB in size. The spacecraft operations team of University of Michigan downlinked the data overnight in several passes and passed the data to science operations team of SRI International who decoded the spacecraft data and carried out the initial analysis and made the results available for a major scientific meeting in the morning. During the initial check-out payload noise measurements conducted over the Indian ocean in eclipse showing noise levels of -113 dBm, well within expectations. Furthermore, the payload data was clear of any interference over the Indian ocean test. The RTI plot of the first experiment, however, shows some level of interference mainly caused by a nearby defense radar. We have found that that the entire RAX trajectory during that first experiment was fully within the view of that radar. Although the interference level is of some concern, we have identified ways to avoid it, such as choosing conjunctions outside the illumination zone of the defense radar.

In February 2011, a solar panel anomaly panel was formed to address the solar panel problem experienced on RAX I. The design flaw was identified and RAX2 incorporates this fix plus several minor enhancements. Additional sun sensors were added to increase our attitude determination knowledge. Also, modifications were made to the power system to reduce RFI and thereby lower the noise floor of RAX2.

RAX II spacecraft is to be launched through NASA on a Delta rocket to a polar elliptical (400-800 km) orbit in late October. The new orbit, in contrast to the 650 km circular 72 degree RAX I orbit, provides additional experimental opportunities including (1) joint experiments with Resolute incoherent scatter radar and EISCAT Svalbard radar at higher radar elevation angles, (2) closer proximity to F region natural or man-made plasma turbulence (both resulting in increased sensitivity and resolution), and (3) a larger number of experimental conjunctions with polar radars due to high inclination orbit.