DARPA begins work on the ‘Ouija’ project, which will use satellites to examine radio frequencies in the Earth’s atmosphere

The United States military aims to deploy satellites to understand more how radio transmissions behave in the earth’s atmosphere. The Defense Advanced Research Projects Agency (DARPA) has launched Ouija, a program that will track high-frequency radio waves in the ionosphere using sensors on “low-orbiting satellites.” For one component of the project, DARPA has issued a request for proposals, and a second request for proposals will be issued at a later date.

The ionosphere is well known for being the region of the atmosphere where auroras can be seen depending on the Earth’s magnetic field and solar activity. The Ouija mission will focus on an area of the ionosphere between 125 and 185 miles (300 and 400 kilometers) in altitude, much beyond the International Space Station’s orbit, which circles our earth at a typical height of 400 km (250 miles).

In an April 22 statement, DARPA officials claimed that understanding how radio waves operate in this environment will be critical in assisting future warfighters. Because of the high density of the charged particles (mostly electrons) that can modify the route of radio transmissions, the propagation of the signal in the ionosphere is highly unpredictable.

According to Britannica, the word “ionosphere” originally appeared in the 1920s, and by the 1950s, organizations like the Institute of Radio Engineers had recognized the atmospheric zone’s impact on radio waves. Satellite investigations of this region began soon after the first satellite launch in 1957 and continue today.

The necessity to define the parameters impacting long-range radio transmission prompted most of the early studies on the ionosphere, according to Britannica. Solar activity as well as the 11-year solar cycle can change the density of the ionosphere, making it much more difficult to predict how radio communications in this region would be affected. The sun, which is scheduled to reach the end of its cycle in 2025, has already produced a number of X-class and big flares in recent times.

In two technical areas, DARPA intends to contribute to ionosphere research. The first is by launching numerous small satellites into orbit and utilizing the Ouija scientific payload to “probe electron density directly and indirectly through radio occultation utilizing navigation satellites.” Proposals are presently being accepted in this study area.

The necessity for an HF (high-frequency) mission payload featuring a wide frequency range and minimal noise was recognized by DARPA. However, because HF antennas customized for such operations tend to be lengthy, designing its antenna is going to be problematic. Longer antennas are more difficult to install in space and can cause drag in the atmosphere. The second technical area is an electron density model that will be validated using on-orbit data in the future. DARPA stated that it would share more information about their plans in this area at a later time.

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