Small Satellites
CubeSats are small satellites with a nominal size of 10 x 10 x 10 cm. This size is referred to as "1U"; these tiny satellites can also be build in 2U, 3U, 6U, or 12U sizes. Their great advantage lies in their small size, and thus lower development cost, but also the strict form factor, which means these spacecraft can be deployed into space from a standardized deployer. Furthermore, they are typically launched as "secondary payloads", where the primary is a larger spacecraft mission, and so the launch costs are minimal compared to dedicated launches. With this lower cost comes a higher acceptance of risk, so CubeSats are often built with extremely low cost using commercial off-the-shelf (COTS) parts, and built in just a few years or even months.
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What started as an educational tool - giving students the opportunity to build their own spacecraft! - has evolved into a legitimate tool for cutting-edge science. With shrinking and more reliable electronics components, and new innovations in spacecraft components, CubeSats have become legitimate "small satellites", rather than just toy projects. In recent years, scientists have come to see their potential to form low-cost constellations of spacecraft - an idea all but impossible with larger, expensive spacecraft. As an example, the THEMIS mission included a constellation of five "medium-class explorer" (MIDEX) spacecraft at a total cost of $173 million. The QB50 constellation, by comparison, launched a constellation of 50 CubeSats at a cost of $100k-$500k each.
Our Work
The LAIR Lab is currently involved in four CubeSats missions. All of our CubeSats have one thing in common: their primary objective is space science, but they accomplish their science goals through novel engineering solutions. Here they are in chronological order:
The VLF Wave and Precipitation Mapper (VPM) is an Air Force Research Laboratory (AFRL) mission that will launch in Spring 2019. Beginning at Stanford and then at CU Boulder, we designed and built the main payload for this CubeSat, a two-channel VLF receiver that will measure the electric and magnetic components of VLF (1-30 kHz) electromagnetic waves in low-Earth orbit. Among its science objectives, VPM will provide a global map of VLF waves in space, most of which originate from either lightning or Navy VLF transmitters on the ground.
VPM advanced the state of CubeSat electronics by conducting all of the signal processing in an FPGA. Using an FPGA, we can calculate real-time Fourier transforms of the incoming VLF signals, thereby reducing the data volume to an amount that can be transmitted to the ground. Without this data reduction, the receiver records over 30 GB per day!
The VLF Wave and Precipitation Mapper (VPM) is an Air Force Research Laboratory (AFRL) mission that will launch in Spring 2019. Beginning at Stanford and then at CU Boulder, we designed and built the main payload for this CubeSat, a two-channel VLF receiver that will measure the electric and magnetic components of VLF (1-30 kHz) electromagnetic waves in low-Earth orbit. Among its science objectives, VPM will provide a global map of VLF waves in space, most of which originate from either lightning or Navy VLF transmitters on the ground.
VPM advanced the state of CubeSat electronics by conducting all of the signal processing in an FPGA. Using an FPGA, we can calculate real-time Fourier transforms of the incoming VLF signals, thereby reducing the data volume to an amount that can be transmitted to the ground. Without this data reduction, the receiver records over 30 GB per day!
Left: VLF Wave and Particle Precipitation Mapper (VPM) CubeSat, developed at Stanford University from 2012-2015 and at CU Boulder since 2015, in collaboration with the Air Force Research Laboratory. The payload includes a magnetic field search coil and an electric field antenna. The CubeSat launched to 500 km circular orbit in February 2020. |
The Compact Spaceborne Magnetic Observatory (COSMO) is a 3U CubeSat with a simple, straightforward mission: measure the Earth's magnetic field. But beneath the surface, this simple-sounding measurement is actually very difficult. We need to measure the magnetic field with an accuracy of one part in 100,000; we need to measure three vector components of the field, while also knowing the spacecraft orientation (attitude) to within a few arcseconds; and we need the spacecraft to be "magnetically clean", i.e. it should not produce any excess noise. For this last reason, we need to design the CubeSat bus from the ground up, ensuring we take all precautions to avoid excess noise.
The design of COSMO began in summer 2018 and will continue over the next few years. So far, we have a preliminary design of the spacecraft and have selected many of the key components. We are working with colleagues in the Mechanical Engineering department to design a compact, low-noise magnetometer that can make the required measurements. Students interested in working on this project can look to our Graduate Projects curriculum, ASEN 5018/6028-013.
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The Climatology of Anthropogenic and Natural VLF wave Activity in Space (CANVAS) mission was recently (Spring 2019) selected for funding by NSF. CANVAS will measure VLF waves from low-Earth orbit, similar to VPM, but using five channels instead of two. With three magnetic field components and two electric field components, it is possible to determine the complete set of wave parameters, including the wave k-vector, Poynting vector, polarization, and medium index of refraction. And we'll get all of these parameters as a function of frequency. The goals is to map the transmission of VLF energy from the ground into space, injected by both lightning and VLF transmitters, and to use this energy to learn more about the D-region ionosphere.
CANVAS is in the early stages of development, and began detailed design as a Graduate Projects course in Fall 2019. The spacecraft will require advancement of our two-channel FPGA processing chain into a five-channel system; design of deployable electric field antennas; and incorporation of a novel carbon-fiber deployable boom for the three-axis search coil antenna. On top of that, we need to design the entire spacecraft bus, including the structure, radio, power systems, avionics, and attitude control system.
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The Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) mission is the crown jewel in our set of science CubeSats. AEPEX aims to image precipitation of energetic electrons from the radiation belts - one of the main loss mechanisms for radiation belt electrons - through their X-ray signatures. As energetic electrons collide with the atmosphere, they produce X-rays, many of which are backscattered into space. By imaging these X-rays, we can determine the flux of electrons precipitating, along with their energy spectrum, spatial extent, and temporal variation. but measuring "hard" X-rays, with energies above 50 keV, is difficult, and usually requires instruments with large mass. To get around this, we are designing an instrument that uses off-the-shelf X-ray detectors designed for security X-ray systems. These are compact and light, but the design of the X-ray optics is still quite complicated.
AEPEX was recently granted a "Phase A" award to further the design through a Concept Study. If this first phase is successful, the full mission implementation will begin in summer 2019. The development of AEPEX will require some novel design of instrument electronics and software, interfacing with the Blue Canyon XB spacecraft bus, and primarily design of the instrument itself. AEPEX is a unique opportunity that combines spacecraft and systems engineering, space science, electronics, and fundamental particle physics.
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References
- Sousa, A., R. A. Marshall, S. Ingram, J. Chang, C. Young, I. Linscott, and U. Inan (2016), A CubeSat Instrumentation Suite for the Study of VLF-Wave-Induced Electron Precipitation, J. Geophys. Res. Space Physics, submitted.
- Mason, J. P., T. N. Woods, A. Caspi, P. C. Chamberlin, C. Moore, A. Jones, R. Kohnert, X. Li, S. Palo, and S. C. Solomon (2015), Miniature X-Ray Solar Spectrometer (MinXSS) - A Science-Oriented, University 3U CubeSat, J. Spacecraft and Rockets, submitted.
- Marshall, R. A., M. Nicolls, E. Sanchez, N. G. Lehtinen, and J. Neilson (2014), Diagnostics of an artificial relativistic electron beam interacting with the atmosphere, J. Geophys. Res. Space Physics, 119, doi:10.1002/2014JA020427.
- Palo, S., D. O'Connor, E. DeVito, R. Kohnert, S. Schaire, S. Bundick, G. Crum, S. Altunc, and T. Winkert (2014), Expanding CubeSat Capabilities with a Low Cost Transceiver, 28th Annual AIAA/USU Conference on Small Satellites, paper SSC14-IX-1.
- Schiller, Q., D. Gerhardt, L. Blum, X. Li, and S. Palo (2014), Design and Scientific Return of a Miniaturized Particle Telescope Onboard the Colorado Student Space Weather Experiment (CSSWE) CubeSat, 2014 IEEE Aerospace Conference, 10.1109/AERO.2014.6836372.
- Puig-Suari, J., C. Turner, and W. Ahlgren (2001), Development of the Standard CubeSat Deployer and a CubeSat Class PicoSatellite, 2001 IEEE Aerospace Conference, 10.1109/AERO.2001.931726.
- Heidt, H., J. Puig-Suari, A. S. Moore, S. Nakasuka, and R. J. Twiggs (2000), CubeSat: A new Generation of Picosatellite for Education and Industry Low-Cost Space Experimentation, 14th USU Conference on Small Satellites, paper SSC00-V-5.