PUNCH spacecraft make final pit stop before launch

Four small suitcase-sized spacecraft, designed and built by Southwest Research Institute, have made a final Earth-side pit stop at Vandenberg Space Force Base in California. NASA’s Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission is sharing a ride to space with the Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) observatory.

“The PUNCH mission will integrate our understanding of the sun’s corona, the outer atmosphere visible during total solar eclipses, with the ‘solar wind‘ that fills and defines the solar system,” said PUNCH Principal Investigator Dr. Craig DeForest of SwRI’s Solar System Science and Exploration Division. “Once the constellation is deployed, we’ll be able to routinely see and understand the solar wind itself, as it streams out from our star and washes over Earth.”

The PUNCH constellation of satellites is targeted to launch in late February 2025 into a polar orbit along the day-night line, so the spacecraft will remain in the sunlight with a clear view in all directions.

Three satellites will carry SwRI-developed Wide Field Imagers (WFI)—heliospheric imagers providing views from 18 to 180 solar radii, or 45 degrees, away from the sun in the sky. The WFIs use an artificial “horizon” and deep baffles to view the very faint outermost portion of the solar corona and the solar wind itself.

“The instrument reduces direct sunlight by over 16 orders of magnitude or a factor of 10 million billion—the ratio between the mass of a human and the mass of a cold virus,” DeForest said. “The wide-field achromatic optics are based on the famous Nagler eyepiece design used in terrestrial telescopes.”

One satellite carries a coronagraph, the Narrow Field Imager developed by the U.S. Naval Research Lab, that images the sun’s corona continuously.

All four spacecraft are synchronized to serve as a single “virtual instrument” to capture roughly a quarter of the sky, centered on the sun. Each spacecraft also includes a camera, developed by RAL Space, to collect three raw images, through three different polarizing filters, every four minutes. In addition, each spacecraft will produce a clear unpolarized image every eight minutes, for calibration purposes.

“When electron particles scatter sunlight, the waves of light become aligned in a particular way—this is polarized light,” DeForest said. “By measuring the light using polarizing filters similar to polarized sunglasses, PUNCH scientists can make a 3D map of the features they see throughout the corona and inner solar system.”

This new perspective will allow scientists to discern the exact trajectory and speed of coronal mass ejections as they move through the inner solar system, improving on current instruments that only measure the corona itself and cannot measure motion in three dimensions.

“The PUNCH team proved to be remarkably resilient as we successfully overcame a number of late-breaking challenges over the last several months to complete integration and environmental testing of the four observatories,” said PUNCH Project Manager Ronnie Killough. “I look forward to a successful launch.”