Space and Physics
PUBLISHED
The Earth's ionosphere – the upper part of the atmosphere where solar radiation separates electrons from atoms to leave a mess of electrically charged particles – is well known for interfering with radio waves. The Defense Advanced Research Projects Agency, better known as DARPA, has launched a program to explore how and why this happens. Being DARPA, the work has military applications, but it could also provide insight into a poorly understood part of our planet's surroundings, and counterparts on other planets.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.In the days when international news came by shortwave radio, interference from the ionosphere was a constant problem, particularly when solar flares added a burst of high-energy charged particles to the mix. That's become less of a problem for ordinary citizens in the Internet Age, but the military still needs to bounce messages off the ionosphere to get them to airplanes or soldiers fighting in distant lands, and communication with satellites passes through the same zone.
Most exploration of the ionosphere has been done using ground-based instruments, but DARPA is keen to change that by using sensors on low-orbiting satellites. Presumably in a reference to the spooky effects ionosphere interference can have on TV signals or the polar sky they've called it the "Ouija" program. Or perhaps whoever named it was bored.
“Ouija will augment ground-based measurements with in-situ measurements from space, in very low-Earth orbit (VLEO), to develop and validate accurate, near real-time HF propagation predictions,” said Ouija program manager Jeff Rogers in a statement. “The VLEO altitude regime, approximately 200-300 km (120-180 miles) above Earth, is of particular interest due to its information-rich environment where ionospheric electron density is at a maximum. Fine-grained knowledge of the spatial-temporal characteristics of electron density at these altitudes is required for accurate HF propagation prediction.”
DARPA is seeking bids (closing next week, so you'd probably better have yours underway) to build, launch and operate satellites to study the ionosphere. Rather than put all their eggs in one basket, the plan is for Ouija's instruments to be spread across multiple satellites, which will measure the ever-changing density of electrons in the ionosphere.
“The [High Frequency] mission payload will require a high sensitivity, high dynamic range, low noise HF measurement subsystem,” Rogers said. “The antenna for this subsystem is a particular challenge, as efficient HF antennas that operate at the lower end of the frequency band are long, presenting deployment and space vehicle drag challenges.”
A second component to the program has yet to seek bids, but will aim to develop high resolution measures of electron density using VLEO satellites.
