Electron Losses and Fields Investigation

Summary

Elfin is a 3U CubeSat out of UCLA's Institute of Geophysics and Planetary Physics (IGPP) and Earth Planetary and Space Sciences Department (EPSS). The project was funded by NSF, NASA, and AFRL. Early Elfin design and development work was primarily run by student volunteers across many departments at UCLA. The satellite's primary payloads are a fluxgate magnetometer and two energetic particle detectors, all built by EPSS staff.

Science!

Electrons get trapped in Earth's Van Allen radiation belts and bounce between reflection points. Occasionally, these electrons will precipitate out of the radiation belts and can collide with atmospheric particles, creating the auroral effect. The precipitating electrons can also interrupt communications or damage electronics in their path. The loss mechanism by which these electrons precipitate is not well understood.

Elfin is designed to measure the pitch angle and energy of these precipitating electrons near the loss cone. The CubeSat form-factor and design allows Elfin to fly at a lower orbit than similar missions in the past. Elfin can accept higher risk and a shorter lifetime than larger and more traditional missions. Additionally, the satellite is spin-stabilized to allow the instruments multiple views.

Role

I worked on Elfin for several years at UCLA. I started on the ground-segment communications, continued work on space-segment communications, helped test solar-panel design, and oversaw student engineering in a student chief engineer role.

Ground-Segment Communications

Elfin is using the VHF and UHF amateur bands for TT&C and primary science. The split-band operation allows a full-duplex link and should enable emergency commands even in the case of a stuck transmitter.

Elfin will use an earth station on the roof of Knudsen Hall at UCLA. The station has a phased yagi array on a RAS rotor. We initially had plans for geographically diverse earth stations, but the plans got descoped due to limited budget and student time.

Space-Segment Communications

The CubeSat uses two V-dipoles angled away from the satellite body on one of the ends. They're set at a 45° angle to decrease coupling with the magnetometer's stacer boom. The antenna elements are beryllium copper strips embedded in fiberglass tape (made by LoadPath). The fiberglass is spooled up into the "tunacan" area that fits inside the deployer's primary spring.

The onboard radio is a Helium-100 derivative from Astro Dev. Again, here the full duplex and split-band operation were driving factors.

Solar Panel Testing

Initially we experimented with Triangular Advanced Solar Cells (TASCs). These are very small form factor so they could be densely packed onto the spacecraft body, but they would also be painstaking to apply manually. We built a rough estimate of a reflow oven using Sparkfun's Reflow Toaster Controller. Our initial testing wasn't very promising; many of the light solar cells had moved around or popped up and soldered at odd angles.

Unfortunately, Spectrolab decided to retire the TASCs for the time being. We decided to change to UTJ cells because of TASC availability, the unsuccessful testing, and some changes to the panel layout that made the TASC packing factor less beneficial to Elfin.

We applied the UTJ cells in a more conventional manner: using sheets of double-sided Kapton tape. Unfortunately, the university had limited stock of the more expensive UTJ cells and wanted to move them onto a different revision of the solar panel after they'd been applied to the first.

We broke a few cells before finding a method that worked fairly well. We left the panels in a heated isopropyl alcohol bath overnight to weaken the adhesive, then used unscented dental floss to separate them from the panels. Even after the alcohol bath, some adhesive remained; it was easy to accidentally break cells. Still, we did recover over half the cells from panels, and they would have been worthless otherwise.

Project Status

After I graduated, the project got funding for a second copy to fly at the same time and collect additional data just after the first (phased slightly apart in the same orbit). The second mission was named Elfin-Star.

Elfin and Elfin-Star are set to launch on a Delta II rocket out of Vandenberg Air Force Base on 2018-09-15. The primary payload is ICESat-2.

AFRL's UNP

UNP hosts reviews with deliverables to make sure the missions and schools they are funding are on-track and working in a good direction. They brought in industry advisors as reviewers and had each school present.

I presented to some of the reviews as one of the student leaders. The reviews forced external deadlines on us, which was particularly healthy for a student project (where it can be difficult for the satellite project to compete for time with other obligations). It was a great learning experience, and the Program Office's emphasis on student learning is great.

Resources

Elfin

The website explains more and is likely more up to date than my information. Significant development work has occurred since I graduated.

AFRL UNP

Air Force Research Lab runs an educational program to help universities design, build, and launch small satellites. Elfin was a member of the 8th round (NS-8) of the program.

ELaNa

ELaNa is a NASA-run program to help launch CubeSats. They buy ride-share payload space on primary missions and award grants to universities.

Klofas's CubeSat List

Bryan Klofas keeps a fairly comprehensive and up-to-date table of CubeSat comms systems launched. It's useful both for seeing what others have done and for validating ground systems or aiding other missions.

SatNOGS

SatNOGS is an open source ground station project trying to build a global network of amateur receiver stations. Elfin didn't participate in SatNOGS while I was there (the project was still a bit young), but I appreciate what they're doing and look forward to seeing their continuing journey.