SwRI-led PUNCH spacecraft reach final milestone before launch

SwRI-led PUNCH spacecraft reach final milestone before launch
by Clarence Oxford
Los Angeles CA (SPX) Jan 23, 2025
Four compact spacecraft, designed and constructed by Southwest Research Institute (SwRI), have arrived at Vandenberg Space Force Base in California for final preparations ahead of their upcoming launch. NASA's Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission will share its ride to orbit 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 satellite constellation is slated for launch in late February 2025. The spacecraft will enter a polar orbit along the day-night line, maintaining continuous sunlight exposure and providing a clear view of the Sun and its surroundings.

Three of the satellites are equipped with Wide Field Imagers (WFI) developed by SwRI. These heliospheric imagers will capture views from 18 to 180 solar radii - approximately 45 degrees - away from the Sun in the sky. The WFIs employ an artificial "horizon" and advanced baffles to observe the faint outermost regions of the solar corona and the solar wind.

"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 explained. "The wide-field achromatic optics are based on the renowned Nagler eyepiece design used in terrestrial telescopes."

The fourth satellite carries a coronagraph, the Narrow Field Imager, developed by the U.S. Naval Research Laboratory. This instrument will provide continuous imaging of the Sun's corona.

Together, the four spacecraft will function as a "virtual instrument," synchronously capturing roughly a quarter of the sky centered on the Sun. Each satellite is also equipped with a camera, developed by RAL Space, to capture three raw images using polarizing filters every four minutes. Additionally, unpolarized calibration images will be taken every eight minutes.

"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 create a 3D map of the features they observe throughout the corona and inner solar system."

This new observational capability will allow researchers to accurately determine the trajectory and speed of coronal mass ejections as they move through the solar system. Current instruments are limited to observing the corona without capturing 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!"

The Small Explorers (SMEX) program supports frequent, cost-effective space missions for advanced heliophysics and astrophysics research. SwRI leads the PUNCH science mission and will operate the four spacecraft. The mission team includes the U.S. Naval Research Laboratory, responsible for the Narrow Field Imager, and RAL Space in Oxfordshire, England, which supplied the detector systems for the visible-light cameras.