June 26, 2019 – NASA has selected Southwest Research Institute (SwRI) to lead the Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission, a landmark Small Explorers Program mission that will image beyond the Sun’s outer corona. PUNCH is being led by Dr. Craig DeForest at the Southwest Research institute in Boulder, Colorado.
PUNCH will consist of a constellation of four suitcase-sized microsatellites that will orbit the Earth while focusing on the Sun’s outer atmosphere, the corona, and how it generates solar wind. PUNCH will image and track the solar wind as it leaves the Sun, transitions to interplanetary space and streams through the solar system. By studying this interplanetary medium, researchers hope to gain a better understanding of how solar events impact Earth’s atmosphere and magnetic field.
“The vacuum of space between the planets is not completely empty – it is actually filled with a tenuous, hypersonic ‘solar wind’ that streams out from the corona and affects spacecraft and planets – including our own,” said PUNCH Principal Investigator Dr. Craig DeForest, a scientist and program director in SwRI’s Space Science and Engineering Division. “PUNCH will observe the ‘no-man’s land’ between the outer solar corona and the solar wind, giving us our first clear images of the entire system connecting the Sun and Earth.”
The spacecraft will track coronal mass ejections (CMEs) in 3D as they erupt from the corona out into interplanetary space. CMEs cause some “space weather” events that affect Earth, and can threaten astronauts, damage satellites, black out power grids, and disrupt communication and GPS signals.
“Most of what we know about the space weather delivered by the solar wind comes from direct sampling by spacecraft embedded in it,” said PUNCH Project Scientist Dr. Sarah Gibson, acting director of the High Altitude Observatory (HAO), also in Boulder, Colorado. “This is like understanding global weather patterns based on detailed measurements from a few individual weather stations on the ground. PUNCH is more like a weather satellite that can image and track a complete storm system as it evolves across an entire region.”
The four spacecraft will fly in a distributed formation spread around the globe, operating in sync to produce polarized images of the entire solar system every few minutes. From low earth orbit, the vantage point will give researchers an unprecedented wide view of the solar wind in three dimensions.
Each of the PUNCH spacecraft carries a specialized camera to capture faint glimmers of sunlight reflected by free electrons in interplanetary space. The U.S. Naval Research Laboratory will provide a Narrow Field Imager for one of the spacecraft that will capture the outer corona itself; the other spacecraft will carry SwRI-developed Wide Field Imagers (WFIs). Dark baffles enable the WFIs to photograph space weather effects that are over a thousand times fainter than the Milky Way, despite flying in direct sunlight.
“Photographing the sky in polarized light is the secret sauce of the mission,” DeForest said. “When sunlight bounces off electrons, it becomes polarized. That polarization effect lets us measure how solar wind features move and evolve in three dimensions, instead of just a 2D image plane. PUNCH is the first mission with the sensitivity and polarization capability to routinely track solar wind features in 3D.”
The PUNCH mission is part of NASA’s Heliophysics Small Explorers Program, which seeks to find small, low cost initiatives to study the universe. Including launch costs, PUNCH is being funded for no more than $165 million. PUNCH is scheduled to launch on a Pegasus rocket as early as 2022.