The Sun Radio Interferometer Space Experiment (SunRISE) Mission Overview

The Sun Radio Interferometer Space Experiment (SunRISE) will reveal aspects of how solar energetic particles (SEPs) are accelerated at Coronal Mass Ejections (CMEs) and how SEPs are released into interplanetary space. SunRISE is a constellation of small spacecraft operating as a radio interferometer to produce a synthetic aperture. As the first low radio frequency interferometer in space, SunRISE will provide spatially and temporally resolved observations of decametric-hectometric (DH, < 15 MHz) radio bursts that cannot be observed on Earth due to ionospheric absorption. DH radio bursts are produced by electrons energized near expanding CMEs (Type II) and released by solar flares into space (Type III). SunRISE will image and track the locations of DH Type II radio bursts, relative to the structures of expanding CMEs, with the aim of constraining the acceleration mechanism relevant for producing SEPs. SunRISE will image and track the locations of DH Type III radio bursts, with the aim of tracing the magnetic field topology from active regions into interplanetary space. Six small spacecraft, of a 6U form factor, will fly in a supersynchronous geosynchronous Earth orbit (GEO) within about 10 km of each other, in a passive formation, forming a very long baseline interferometer (VLBI) observatory. Key aspects that enable this mission concept are that only position knowledge of the spacecraft is required, not active control, and that the architecture involves a modest amount of on-board processing coupled with significant ground-based processing for navigation, position determination, and science analysis and operations. The SunRISE leverages more than 50 years of development in VLBI techniques and mission-enabling advances in software-defined radios, GPS navigation and timing, and small spacecraft technologies that have been developed and flown over the past few years on DARPA High Frequency Research (DHFR) and the Community Initiative for Continuing Earth Radio Occultation (CICERO) missions. The SunRISE mission began Phase B (Formulation) in 2020 June, with a planned review to assess readiness to proceed to Phase C (Development) in 2021Q2. This paper presents a summary of the SunRISE mission and its current status. Complementary abstracts are presented by J. Kasper, A. Romero-Wolf, and A. Hegedus.