Polarimeter to Unify the Corona and Heliosphere (PUNCH) is a future mission by NASA to study the unexplored region from the middle of the solar corona out to 1 AU from the Sun. PUNCH will consist of a constellation of four microsatellites that through continuous 3D deep-field imaging, will observe the corona and heliosphere as elements of a single, connected system. The four microsatellites were initially scheduled to be launched in October 2023, but they have since been moved to a launch in rideshare with SPHEREx,[3] scheduled for 27 February 2025.[1]
On 20 June 2019, NASA announced that PUNCH and TRACERS were the winning candidates to become the next missions in the agency's Small Explorer program (SMEX).[4]
The stated primary objective of PUNCH is "to fully discern the cross-scale physical processes, from microscale turbulence to the evolution of global-scale structures, that unify the solar corona and heliosphere".[5] In other words, the mission aims to understand how the solar corona becomes the solar wind.[6]
The two specific objectives are to understand how coronal structures become the ambient solar wind, and to understand the dynamic evolution of transient structures in the young solar wind.[5] The Principal Investigator, Craig Edward DeForest from Southwest Research Institute (SwRI), thinks that such closer study will also lead to a better understanding of the causes of solar weather events like coronal mass ejections (CMEs), which can damage satellites and disrupt electrical grids and power systems on Earth.[2][4]
The more we understand what drives space weather and its interaction with the Earth and lunar systems, the more we can mitigate its effects – including safeguarding astronauts and technology crucial to NASA's Artemis program to the Moon.[4]
Instruments
The mission configuration consists of a constellation of four observatories, each carrying one primary instrument.[7]
The Narrow Field Imager (NFI) sits on only one spacecraft, and is an externally occulted visible-light coronagraph.
The Wide Field Imagers (WFIs) are side-looking heliospheric imagers with planar-corral baffles that sit on the remaining 3 spacecraft.
The NFI spacecraft also carries a student-built instrument, the Student Thermal Energetic Activity Monitor (STEAM). STEAM is a solid-state X-ray spectrometer that views the entire Sun as a point source, to study the physics of coronal heating and solar flares.
The fields of view (FoV) of the 3 WFIs overlap slightly with each other and with the NFI, and the instruments' operation is synchronized. The instruments operate through polarized Thomson-scatter imaging of the transition from corona to heliosphere.[8] PUNCH integrates images from its constellation of small satellites into a global composite after each orbit, covering ~6 orders of magnitude dynamic range. Through a stream of these images, PUNCH achieves 3D feature localization and accurate deep field imaging.[9] The mission builds on Cyclone Global Navigation Satellite System (CYGNSS) experience with smallsat constellations.[10]
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