Last month, PUNCH's four instruments opened their doors to capture 'first light' – the mission's very first images of the Sun's outer atmosphere and the surrounding space.
These early images confirm a crucial milestone: the RAL Space-built camera systems onboard PUNCH's four satellites are functioning exceptionally well. This is the first step in the mission's goal of revealing new details of how the solar atmosphere unfolds throughout our solar system.
Now that the instrument doors are open, as part of the mission's so-called commissioning phase, scientists from RAL Space are drawing on their experience from an earlier NASA solar mission, STEREO, to lead PUNCH's in-flight calibration. The team are working closely with mission leads at the Southwest Research Institute (SwRI).
“This process converts PUNCH data from raw instrument readings into real-world values – like how bright the various parts of the image are, and the location that we're looking at in the sky," explains Dr Jackie Davies, RAL Space head of heliospheric physics and UK science lead for PUNCH. “To do that, we use a set of what we call 'well-behaved stars' – stars with, for example, constant and well-measured brightness, like some of those we see in these first light images. Successful calibration will allow us to combine data from all four satellites so they can work together seamlessly as a single observatory."
The image below was taken by one of PUNCH's three Wide Field Imagers (WFIs) on 14 April. It demonstrates the wide field of view from the instrument and is marked with labelled constellations. As commissioning progresses, the team will be removing the star fields and other background light from all images to highlight the faint stream of solar wind as it travels towards Earth. Once commissioning is complete, PUNCH will provide the first-ever imagery of the solar wind and coronal mass ejections in polarised light, offering new insights for scientists studying space weather phenomena.
The first light image from one of the PUNCH WFIs taken on April 14, 2025. Credit: NASA/SwRI
PUNCH will make global, 3D observations of the inner solar system and the solar corona to learn how its mass and energy become the solar wind, a stream of charged particles blowing outward from the Sun in all directions. The mission will explore the evolution of space weather events such as coronal mass ejections, which can be disruptive to technology in orbit and on Earth.
Three of PUNCH's four suitcase-sized satellites carry a WFI instrument. The remaining one carries a Near Field Imager (NFI). The NFI is a coronagraph, which blocks out the bright light from the Sun to better see details in the Sun's corona. The WFIs are heliospheric imagers that view the very faint, outermost portion of the solar corona and the solar wind itself. Once the four satellites reach their target configuration, images from these instruments will be stitched together to create the wide view of the journey of the Sun's corona and solar wind to Earth.
The first light image taken by the PUNCH NFI demonstrates that the camera is in focus, working properly, and is able to capture deep-field images of the solar corona against the glare of the Sun. The instrument is not yet fully aligned with the Sun, leading to bright glints of sunlight, which are visible to the right of the Sun's location on the image. Credit: NASA/SwRI/NRL
Southwest Research Institute, based in San Antonio, Texas, leads the PUNCH mission and operates the four spacecraft from its facilities in Boulder, Colorado. The mission is managed by the Explorers Program Office at NASA Goddard Space Flight Center in Greenbelt, Maryland, for the Science Mission Directorate at NASA Headquarters in Washington.
