RAX-2 stopped transmitting beacons over the weekend and is not responsive to normal commands. The cease in normal operations happened mid-day on Saturday, April 20, and the cause of the issue is currently under investigation. Over the next few days, we will be recording the spectrum during passes and sending up some custom commands in an attempt to determine the cause.
RAX-2 has been operating on-orbit for 540 days, has completed its scientific goals, and has surpassed it’s planned one-year scientific mission. We’ll be posting updates on the status as we investigate over the next few weeks.
Since our last update about radar experiments (January), RAX-2 has completed 6 experiments with the incoherent scatter radars in Poker Flat, Alaska, and Resolute, Canada. Although space weather conditions were active during some of the experiments, no FAI backscatter has been detected. The RTI plots from the two most recent experiments are shown below (expt 1031 completed March 16 and expt 1032 completed April 14). Since the space weather was active, we’ve been downloading raw samples from expt 1031 for analysis of the scintillation of the direct radar pulses.
Results from experiment 1032, completed with PFISR on April 14.
Results from experiment 1031, completed with PFISR on March 16.
If you’re an amateur radio operator tracking RAX-2, you may have noticed that the GS client stopped working after a recent Java update. We have fixed the bug, and the updated version of the GS client works with Java 1.6 and 1.7. You can download the updated ground station client from the Beacon Decoding Software page.
A paper on the design and implementation of the GPS subsystem on the RAX satellites is now available in the journal Acta Astronautica. We hope that this paper is helpful for other small satellite developers. The publication details and abstract are given below, and a complete list of papers on MXL research and spacecraft is available on the MXL website.
S.C. Spangelo, M.W. Bennett, D.C. Meinzer, A.T. Klesh, J.A. Arlas, J.W. Cutler, Design and Implementation of the GPS Subsystem for the Radio Aurora Explorer, Acta Astronautica, Volume 87, June-July 2013, Pages 127-138, ISSN 0094-5765, 10.1016/j.actaastro.2012.12.009
Abstract: This paper presents the design and implementation of the Global Positioning System (GPS) subsystem for the Radio Aurora eXplorer (RAX) CubeSat. The GPS subsystem provides accurate temporal and spatial information necessary to satisfy the science objectives of the RAX mission. There are many challenges in the successful design and implementation of a GPS subsystem for a CubeSat-based mission, including power, size, mass, and financial constraints. This paper presents an approach for selecting and testing the individual and integrated GPS subsystem components, including the receiver, antenna, low noise amplifier, and supporting circuitry. The procedures to numerically evaluate the GPS link budget and test the subsystem components at various stages of system integration are described. Performance results for simulated tests in the terrestrial and orbital environments are provided, including start-up times, carrier-to-noise ratios, and orbital position accuracy. Preliminary on-orbit GPS results from the RAX-1 and RAX-2 spacecraft are presented to validate the design process and pre-flight simulations. Overall, this paper provides a systematic approach to aid future satellite designers in implementing and verifying GPS subsystems for resource-constrained small satellites.
