PropCube 2 Satellite

Photo: Naval Research Lab

PropCube 2 is the third of three PropCube satellites developed by the Naval Postgraduate School (NPS), flying under the Propagation CubeSat series to study artificial ionization in Earth’s ionosphere. Developed by the NPS, the satellites use a commercial 1U CubeSat platform provided by Tyvak NanoSatellite Systems integrated with purpose-built sensors to measure ionospheric electron density and irregularities.

PropCubes 1 and 3, going by the nicknames of Flora and Merryweather, were launched into a 500 x 800-Kilometer, 64° orbit as secondary payloads on an Atlas V rocket in October 2015, riding alongside the classified NROL-55 satellite of the National Reconnaissance Office. PropCube 2 (Fauna) was originally planned to ride on a SpaceX mission in July 2015 for deployment into the 51.6° ISS orbit but was then moved to a high-inclination launch on a Falcon 9 before eventually moving back to an ISS-orbit deployment over two years after the original launch date.

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Image: Naval Research Lab
Image: NASA

Featuring UHF and S-Band receivers, the satellites are tasked with measuring total ionospheric electron content, plasma irregularities by their amplitude and phase scintillations, and artificial ionospheric disturbances introduced by sending stimulations into the upper atmosphere by means of high-power radio pulses. According to the PropCube Project, artificial stimulation will be provided by the Arecibo observatory in Puerto Rico, the Sura Ionospheric Heating Facility in Russia, and the HAARP facility in Alaska (High Frequency Active Auroral Research Program).

Radio stimulation can be used to actively shape the electron density in Earth’s ionosphere up to large ionospheric drops in electron density in the F-region beginning around 190 Kilometers in altitude. This could be useful for a number of applications including the military as Earth’s ionosphere is used for communications, over-the-horizon radars and the particle population in ionosphere can influence the accuracy of satellite navigation.

However, to exploit active ionospheric stimulation, information on what types of inputs yield which results and where plasma is displaced as the result of artificial ionospheric heating is needed.

The F-region reflects radio signals which is exploited by airplanes for air-to-ground communication, ships for sea-to-shore communication, over-the-horizon radar systems, military and governmental communication systems, shortwave radio broadcasting and amateur radio operators. The PropCubes will conduct in-situ and close-range observations in the ionospheric F-region while radio pulses are being deliberately targeted at the satellite’s location by a ground-based transmitter to artificially stimulate the ionosphere and create the interactions that are of interest to the mission.

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Image: Naval Research Lab

The PropCubes measure total electron content by differential group delay and track the effect of ionospheric heating on communications using different radio frequency bands. The primary goal of the PropCube missions is understanding the physics for the generation of artificial plasma clouds and how this can be exploited.

A number of techniques and theories exist on how artificial ionization can be achieved. One proven method is sending high-power radio waves into the ionosphere tuned to the electron gyro frequency, yielding an artificial ionization cloud of limited stability and duration. An improved technique developed by the Naval Research Lab is using ‘twisted beams’ tuned to the 2nd, 3rd, 4th, 5th or 6th electron cyclotron harmonic frequency at the desired altitude, also utilizing seed ionization clouds to reduce power requirements.

Having a satellite traverse the region of artificial ionization will allow an iterative process of properly tuning the emitted radio waves to create the desired results in the ionosphere such as long-lasting artificial ionization for the creation of new high-frequency reflection layers below 200 Kilometers to permit advanced over-the-horizon communications or the creation of plasma irregularities to distort trans-ionospheric radio signals to tamper with communications by foreign entities.