That’s where NASA’s Sun Coronal Ejection Tracker (SunCET) comes in. Jointly led by the Johns Hopkins Applied Physics Laboratory and the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, SunCET will capture the first complete acceleration sequences of CMEs, from their beginnings in the lower part of the Sun’s atmosphere to at least four solar radii — roughly 432,700 miles (696,200 kilometers) — from the solar surface.

CMEs are enormous clouds of entangled magnetic fields and hot, charged atoms and electrons called plasma that burst from the Sun’s blazing atmosphere — the corona — at speeds of up to almost 1,900 miles per second (3,000 kilometers per second). Each month, roughly 100 of these explosions blast billions of tons of particles with 10 times the energy of the asteroid impact that wiped out the dinosaurs. Consequently, CMEs are critical drivers of severe space weather with significant implications for Earth. Those directed at the planet can interrupt GPS signals, lethally threaten astronauts and — most importantly — knock out the electrical power grid on the ground.

Beyond their practical implications for an increasingly technological society, CMEs also provide a rare opportunity to study the mechanics of plasma acceleration in a regime that researchers just cannot reproduce in the laboratory. In the standard model of a CME’s configuration in the solar corona, the CME creates a growing flux rope, which overlying magnetic fields resist. As a result, CMEs can only escape from the corona by accelerating to overcome the overlying magnetic field, making them a natural probe of the Sun’s surrounding magnetic field. Despite decades of observations using dozens of spacecraft and ground-based observatories collectively known as the Heliophysics System Observatory (HSO), however, scientists are still missing data from a critical part of the picture: the middle corona, the region where CMEs undergo much of their acceleration. Because of the region’s rapidly diminishing brightness, spacecraft have been unable to completely image CMEs as they grow and accelerate, meaning scientists are only able to hypothesize about the forces at work.

SunCET uses a specially developed camera sensor capable of capturing complete images and videos of a CME through its entire acceleration profile, from the lower part of the Sun’s atmosphere, or corona, through the middle corona roughly 432,700 miles (696,200 kilometers) from the solar surface.

The spacecraft relies on the wide field of view of a compact Ritchey-Chrétien telescope. The telescope is largely based on the DRACO telescope that enabled NASA’s DART mission to accomplish the world’s first planetary defense test mission. Unlike DRACO’s mirror, however, SunCET’s has coatings that reflect EUV light, similar to those on other mission instruments used to observe the Sun, such as the Extreme Ultraviolet Imager (EUVI) on NASA’s Solar Terrestrial Relations Observatory (STEREO) mission and the Extreme ultraviolet Imaging Telescope (EIT) on the NASA-European Space Agency Solar and Heliospheric Observatory (SOHO) mission.

Given that the Sun is roughly ten thousand to a billion times brighter than its surrounding atmosphere, most of these previous solar imagers either focused on just the solar disk or blocked it out with coronagraphs to concentrate on the corona. In doing so, however, they missed the exact region where CME acceleration occurs. Multiple research groups have tried using post-processing techniques to merge coronagraph and EUV images, but the process has been challenging and the methods riddled with caveats because of the way images were captured.

SunCET’s camera overcomes these obstacles by using a new simultaneous high-dynamic-range (or SHDR) algorithm. The system uses the camera’s compact spectral imager electronics system to independently read out rows of pixels on the detector. This capability allows it to create composite images of the bright solar disk with the very faint solar corona. The algorithm programs a circular region near the center of the sensor to take short exposures of the bright solar disk (baseline value of 0.035 seconds) while simultaneously taking long exposures (baseline value of 15 seconds) of the dim corona across the rest of the pixels.

The spacecraft’s onboard computer then takes the median across several sequential exposures — a process dubbed image-stack median, using a baseline of 3-4 images for long-exposure pixels and 10 images for short-exposure pixels — to return a final image: a complete view of an erupting CME. The onboard processes take only a minute to complete, and the final composite image is then compressed and stored in an onboard flash memory.