ELFIN

Electron Losses and Fields Investigation (ELFIN) is a nanosatellite developed by University of California, Los Angeles (UCLA). ELFIN is a 3U+ CubeSat designed to study space weather, specifically, the loss of relativistic electrons in the radiation belts. ELFIN was a participant in the Air Force Research Lab's University Nanosatellite Program and is currently funded by NASA's Low Cost Access to Space program and the National Science Foundation.

ELFIN carries a fluxgate magnetometer as well as two energetic particle detectors: one for ions and one for electrons and aims to understand the loss mechanisms of relativistic "killer" electrons by providing pitch angle resolved energetic particle measurements. The principal investigator of the project is Vassilis Angelopoulos.

<!-- == Subsystems ==

Attitude Determination & Control

 * The ELFIN Attitude Determination & Control (ADCS) designs, implements, and tests the various mechanisms that are used to control and acquire the orientation of ELFIN in space.


 * The determination is primarily concerned with sensors that can process telemetry data which can be used to acquire knowledge of the satellite's current attitude at any given time. The term attitude is used as the Cube-Sat's rotation with respect to a set inertial frame. On the spacecraft, the coarse sun sensor, horizon crossing indicator, and magnetoresistive magnetometer are used as an on-board attitude determination. To get further resolution, ELFIN also uses the fine sun sensor and fluxgate magnetometer. The data from the telemetry can be analyzed on the ground with the various instrument-processing techniques, through various breakout boards, and algorithms. The ADCS subsystem is primarily responsible for developing and testing the various techniques that will process the telemetry data in order to develop ELFIN's current attitude.


 * Attitude control, meanwhile, is the process of calculating and actuating the data in order to maintain the specific orientation requirements that allow the Cube-Sat to keep its attitude. The subsystem is working on developing an algorithm that will take the data, using both science pointing requirements and engineering power requirements, and use various instrument-analyzing machines to control the orientation. The testing is done in software-only simulations, such as MATLAB, as well as having a series of hardware-based tests. In the end, the commands will ultimately run on an on-board micro-controller that takes in the sensor data as parameters. The data will then be used to identify the needed input and output voltage that will drive the torquer coils.

Command & Data Handling

 * The Command and Data Handling (CNDH) subsystem focuses on monitoring the satellite, collecting data, and processing commands by using the Flight Computer, the Watchdog, the ADCS Main PIC, and the Power PIC.


 * The Flight Computer is responsible for the main principle tasks of the Cube-Sat by being able to read and write data as well as being able to configure the settings needed. The Flight Computer routes the commands and data between various components in order to control the satellite while working with the Watchdog. The Watchdog is used as a layer of redundancy and for security, as it monitors, with the help from various safeguards, and adjusts the Flight Computer in order to prevent corruption from happening to either PIC.


 * The subsystem focuses on running the programs through algorithms in order to minimize the space taken by the instrument data. The members of the team program various data structures that hold the administrative and housekeeping data until the Flight Computer needs them. The data includes information from the ADCS and Power PIC boards, as the two PICs relay information about the health of the spacecraft.

Communications

 * ELFIN is a 20rpm spinner that has a roughly orbit-normal spin axis, as needed by the science requirements. The antennas are positioned in between the spin axis and the spin plane in order to alleviate the spin's fading in all directions and orientations. The subsystem deals with using amateur radios that will allow the members of the team to beacon globally. Currently, the team uses ab AstroDev radio that provides a 19,200 baud GFSK AX.25 UI downlink.

Link Budgets

 * By using the uplink and downlink budgets, the team is able to use the beacons in order to receive a typical OSCAR station. The downlink antenna is a bent dipole which, for testing purposes and simulations, is set to 436.5 MHz. For the uplink antenna, the antenna is also a bent dipole but it is tuned to 144.4 MHz. The two antennas are made up of bistable fiberglass tape springs with embedded beryllium copper strips. The tape springs are not held in their secondary stable state, which allows them to provide their own kick force. Currently, the team members are working on testing the antennas and communicating to radio through various emulators.

Payload

 * Elfin's payload has a fluxgate magnetometer and two energy particle detectors (EPD), all of which are being developed in-house by UCLA staff members. The student subsystem is primarily responsible for designing and testing the systems that will protect the scientific instruments. Since ELFIN spins at a rate of 20 revolutions per minute, the energy particle detectors will be frequently exposed to the intense direct sunlight. As a result, the EPD is heavily shielded from the resulting influx of protons found on the aperture. If too much sunlight is focused on the particle detectors, the surrounding instruments may temporarily desensitize the EPD. Currently, the subsystem team has been working on refining the aperture designs and ground software for ELFIN's Fine Sun Sensor. The data from the Fine Sun Sensor will be processed by the ADCS sensors.

Power
ELFIN's power subsystem deals with both the hardware and software of the spacecraft. The entire electric power system is essentially a network of electrical components that are used to supply, transmit, and consume electric power. The system deals with sending the specific voltage and current requirements at certain, crucial times to the ADCS, command and data handling boards, actuators, and radios.

Staff
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Launch
ELFIN and ELFIN* are part of NASA's ELaNa-18. ELFIN launched with ICESat-2 in September 2018 from Vandenberg Air Force Base. They are tracked with norad cat-id of 43617 (ELFIN A) and 43616 (ELFIN B).

ELFIN-L
ELFIN-L is a collaboration mission between UCLA and Moscow State University. The Institute of Geophysics and Planetary Physics (IGPP) at UCLA delivered the ELFIN instruments for the Lomonosov Russian University Satellite. The satellite launched on 28 April 2016.

ELFIN-STAR
Electron Losses and Fields Investigation with Spatio Temporal Ambiguity Resolution (ELFIN-STAR or ELFIN*) option was awarded and executed in November 2017, which adds an identical CubeSat to the launch. This allows two measurements to be made over the same location in orbit which can determine if electron loss mechanisms are varying spatially or temporally. The satellites, ELFIN-A and ELFIN-B launched on 15 September 2018.