NASA is launching rockets from a remote Pacific island to study mysterious, high-altitude cloud-like structures that can disrupt critical communication systems. The mission, called Sporadic-E ElectroDynamics, or SEED, opens its three-week launch window from Kwajalein Atoll in the Marshall Islands on Friday, June 13.
The atmospheric features SEED is studying are known as Sporadic-E layers, and they create a host of problems for radio communications. When they are present, air traffic controllers and marine radio users may pick up signals from unusually distant regions, mistaking them for nearby sources. Military operators using radar to see beyond the horizon may detect false targets — nicknamed “ghosts” — or receive garbled signals that are tricky to decipher. Sporadic-E layers are constantly forming, moving, and dissipating, so these disruptions can be difficult to anticipate.
Sporadic-E layers form in the ionosphere, a layer of Earth’s atmosphere that stretches from about 40 to 600 miles (60 to 1,000 kilometers) above sea level. Home to the International Space Station and most Earth-orbiting satellites, the ionosphere is also where we see the greatest impacts of space weather. Primarily driven by the Sun, space weather causes myriad problems for our communications with satellites and between ground systems. A better understanding of the ionosphere is key to keeping critical infrastructure running smoothly.
The ionosphere is named for the charged particles, or ions, that reside there. Some of these ions come from meteors, which burn up in the atmosphere and leave traces of ionized iron, magnesium, calcium, sodium, and potassium suspended in the sky. These “heavy metals” are more massive than the ionosphere’s typical residents and tend to sink to lower altitudes, below 90 miles (140 kilometers). Occasionally, they clump together to create dense clusters known as Sporadic-E layers.
“These Sporadic-E layers are not visible to naked eye, and can only be seen by radars. In the radar plots, some layers appear like patchy and puffy clouds, while others spread out, similar to an overcast sky, which we call blanketing Sporadic-E layer” said Aroh Barjatya, the SEED mission’s principal investigator and a professor of engineering physics at Embry-Riddle Aeronautical University in Daytona Beach, Florida. The SEED team includes scientists from Embry-Riddle, Boston College in Massachusetts, and Clemson University in South Carolina.
“There’s a lot of interest in predicting these layers and understanding their dynamics because of how they interfere with communications,” Barjatya said.
Scientists can explain Sporadic-E layers when they form at midlatitudes but not when they appear close to Earth’s equator — such as near Kwajalein Atoll, where the SEED mission will launch.
In the Northern and Southern Hemispheres, Sporadic-E layers can be thought of as particle traffic jams.
Think of ions in the atmosphere as miniature cars traveling single file in lanes defined by Earth’s magnetic field lines. These lanes connect Earth end to end — emerging near the South Pole, bowing around the equator, and plunging back into the North Pole.
At Earth’s midlatitudes, the field lines angle toward the ground, descending through atmospheric layers with varying wind speeds and directions. As the ions pass through these layers, they experience wind shear — turbulent gusts that cause their orderly line to clump together. These particle pileups form Sporadic-E layers.
But near the magnetic equator, this explanation doesn’t work. There, Earth’s magnetic field lines run parallel to the surface and do not intersect atmospheric layers with differing winds, so Sporadic-E layers shouldn’t form. Yet, they do — though less frequently.
“We’re launching from the closest place NASA can to the magnetic equator,” Barjatya said, “to study the physics that existing theory doesn’t fully explain.”
To investigate, Barjatya developed SEED to study low-latitude Sporadic-E layers from the inside. The mission relies on sounding rockets — uncrewed suborbital spacecraft carrying scientific instruments. Their flights last only a few minutes but can be launched precisely at fleeting targets.
Beginning the night of June 13, Barjatya and his team will monitor ALTAIR (ARPA Long-Range Tracking and Instrumentation Radar), a high-powered, ground-based radar system at the launch site, for signs of developing Sporadic-E layers. When conditions are right, Barjatya will give the launch command. A few minutes later, the rocket will be in flight.
On ascent, the rocket will release colorful vapor tracers. Ground-based cameras will track the tracers to measure wind patterns in three dimensions. Once inside the Sporadic-E layer, the rocket will deploy four subpayloads — miniature detectors that will measure particle density and magnetic field strength at multiple points. The data will be transmitted back to the ground as the rocket descends.
On another night during the launch window, the team will launch a second, nearly identical rocket to collect additional data under potentially different conditions.
Barjatya and his team will use the data to improve computer models of the ionosphere, aiming to explain how Sporadic-E layers form so close to the equator.
“Sporadic-E layers are part of a much larger, more complicated physical system that is home to space-based assets we rely on every day,” Barjatya said. “This launch gets us closer to understanding another key piece of Earth’s interface to space.”
NASA’s Goddard Space Flight Center, Greenbelt, Md.