ICON satellite to study boundary between Earth's atmosphere, space

Inside the outermost layer of Earth's atmosphere, billions of negatively charged electrons bounce freely for long periods of time before being tamed by positive ions. The layer, the ionosphere, and its highly variable plasma waves can disrupt GPS signals and other radio-wave-based communication systems.

To better understand the ionosphere and pinpoint the forces responsible for its variability, scientists at NASA are sending a specially equipped satellite into space to observe the enigmatic layer.

The Ionospheric Connection Explorer, or ICON, developed by a team of scientists and engineers at the University of California, Berkeley, will be carried into space this week by Northrop Grumman's Pegasus XL rocket.

"ICON is built specifically to understand the connection between conditions at the boundary of space, at approximately 60 miles altitude, and how the ionosphere above responds," Thomas Immel, principal investigator on the ICON mission and a researcher at Berkeley's Space Sciences Laboratory, told UPI. "The mission design includes an orbit that strongly favors this kind of investigation."

How the ionosphere works

Scientists have long struggled to accurately model the behavior of the ionized plasma, which travels along rapidly shifting geomagnetic field lines.

During the day, as the sun's energy heats the upper atmosphere, gas molecules become ionized. Upwellings of ionized gas create dense bands of particles running on either side of the magnetic equator.

"Basic models of the ionosphere predict that there should be a regular rise and fall of this portion of the atmosphere as the Earth rotates from day to night, independent of longitude," according to the Space Sciences Laboratory.

But observations of the ionosphere have shown the layer's ionized particles and plasma waves behave and are distributed in unexpected ways -- ways not explained by current models. Analysis suggests the layer's idiosyncrasies aren't triggered by changes in solar activity.

"The ionosphere can vary a lot from one day to the next," Immel said. "It is not clear why, so it is nearly impossible to predict."

By more accurately modeling and forecasting the behavior of the ionosphere, engineers could better protect the signals of navigational and communication satellite systems from disruption. To improve their models, scientists need to determine what drives the ionosphere's dynamism, the terrestrial weather below or the space weather above.

"We think that the key is in the connection between the ionosphere and the energy in the atmosphere far below and we are built to resolve this," Immel said. "If the atmosphere below really is 'in charge,' then one can start to investigate how the atmosphere below plays a role in plasma storms around Earth, and how these storms driven by the sun are influenced by the Earth's weather itself."

ICON's mission and scientific payload

ICON will orbit Earth at a 27-degree inclination and at an altitude of some 360 miles -- a position that will allow its instruments to continuously image the atmosphere-space boundary, from roughly 60 to 250 miles above Earth's surface.

The scientific payload, which is mounted on an Orbital ATK LEOStar-2 spacecraft, features four instruments tasked with observing the ionosphere and measuring the characteristics of the surrounding space environment.

The Michelson Interferometer for Global High-resolution Thermospheric Imaging instrument will measure the temperature and speed of the neutral atmosphere, which is driven by weather patterns lower in Earth's atmosphere.

The Ion Velocity Meter will track the speed and movements of the ionosphere's charged particles. The instrument's measurements will help scientists isolate the influence of high altitude winds and the electromagnetic fields on the charged particles.

The Extreme Ultra-Violet instrument will help scientists model the daytime ionosphere by collecting images of oxygen glowing in the upper atmosphere.

"This helps track the response of the space environment to weather in the lower atmosphere," according to NASA.

The fourth instrument, the Far Ultra-Violet instrument, will image the upper atmosphere in the far end of the ultraviolet spectrum. The instrument will help scientists measure the density of the ionosphere at night, measurements that help researchers figure out how the ionosphere is impacted by weather in the lower atmosphere.

Scientists had to design and build the payload in such a way that all four instruments can function properly at the same time.

"The instruments first have to be designed not to interfere with each other -- self-compatibility -- which we have done," Immel said. "Then you have to make sure that the instruments do not interfere with the spacecraft and vice versa. We did that too."

If the instruments perform as expected, scientists will soon have the measurements they need to determine the effects of terrestrial weather on ionospheric variability, as well as understand how energy and momentum from the lower atmosphere influences the space environment.

"Understanding what drives variations in the ionosphere is important so that we can better predict what types of signal distortions we may expect and where, as well as ways to design systems that are more robust against these effects," according to the Space Sciences Laboratory.

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