VLF Propagation Mapper (VPM)
The Very-Low-Frequency Propagation Mapper (VPM) is a 6U CubeSat designed as a companion to the Demonstration and Science Experiments (DSX) mission developed by Air Force Research Laboratory. The primary goal of both missions is to investigate the propagation of Very-Low-Frequency (VLF) waves in the inner magnetosphere. These waves are responsible for accelerating electrons to relativistic energies during geomagnetic activity, dramatically enhancing the hazardous radiation belts, and also for scattering those electrons out of the radiation belts during recovery periods. The mechanisms by which electrons are accelerated and scattered are complicated and not completely understood.
DSX includes a powerful VLF transmitter onboard - the first ever VLF transmitter to fly in space. It will launch VLF waves from high altitude (6,000-12,000 km) at specific frequencies and in targeted directions. VPM, flying in low-Earth orbit at 500 km altitude, will "listen" for the VLF signals transmitted by DSX. If successful, VPM will be able to map the radiation pattern of the DSX transmitter and analyze the propagation path between the two spacecraft. |
Our Work
While at Stanford, our group was responsible for the design, development, and fabrication of the VLF receiver on VPM, called the micro-broadband receiver (uBBR). The receiver electronics include two analog receiver channels (one each for the magnetic and electric field components), a digital processing board, a dedicated power conditioning system, and a GPS receiver. The GPS receiver ensures accurate time-tagging of the recorded signals with 100 nanosecond timing precision. The digital board includes an FPGA, which processes the raw signals in real-time and creates user-selectable data products.
The uBBR was delivered to AFRL for integration into the CubeSat bus, which was designed at developed at AFRL. After successful integration and testing, the complete VPM spacecraft was launched to the International Space Station (400 km altitude) in December 2019 via the Cygnus resupply vehicle. In February 2020, the Cygnus left the ISS with VPM, and deployed it into a circular orbit at 500 km altitude. The spacecraft is currently in commissioning, and we expect to start receiving data very soon! |
References
- Su, Yi-Jiun, William R. Johnston, James Parker McCollough, and Patrick Roddy. "DSX Space Weather Experiments-Initial Results." In AGU Fall Meeting 2019. AGU, 2019.
- McCollough, James, Jay Albert, Michael Starks, William Johnston, and Yi-Jiun Su. "Active Experiments with the DSX Mission." In 42nd COSPAR Scientific Assembly, vol. 42. 2018.
- Johnston, William R., James McCollough, Michael Starks, and Jay Albert. "The Demonstration and Science Experiments (DSX) Mission." In 2015 AGU Fall Meeting. AGU, 2015.
- Inan, U., I. Linscott, R. A. Marshall, D. Lauben, M. J. Starks, and J. H. Doolittle. "The VLF Wave and Particle Precipitation Mapper (VPM) Cubesat Payload Suite." In AGU Fall Meeting Abstracts. 2012.