Sun radio interferometer space experiment (SunRISE): Tracking particle acceleration and transport in the inner heliosphere

The authors present a space-based array designed to localize and track the radio emission associated with coronal mass ejections (CMEs) from the Sun. Radio emission from CMEs is a direct tracer of the particle acceleration in the inner heliosphere and potential magnetic connections from the lower solar corona to the larger heliosphere. These questions are among those highlighted in the current Solar Decadal Servey, e.g., “Discover and characterize fundamental processes that occur both within the heliosphere and throughout the Universe.” Furthermore, CME radio emission is quite strong, such that only a relatively small number of antennas is required, and a small mission would make a fundamental advancement in our scientific understanding. Indeed, the current state-of-the-art for tracking CME radio emission is defined by single antennas (Wind/WAVES, Stereo/SWAVES) in which the tracking is accomplished by assuming a frequency-to-density mapping. This type of heliophysics mission has been studied several times in the past, but had so far been found to be cost prohibitive, due to the inherent complexity of building multiple spacecraft and flying them in constellation. However, with the increased popularity and success of CubeSat concepts, accompanied by the miniaturization of subsystem components, a range of missions are now being enabled at lower cost than ever before. The paper presents the science requirements for a Small Explorer (SMEX)-class (typically < ∼$100M, including all lifecycle costs) mission concept, and walks through the major features of the SunRISE mission study. SunRISE is composed of six 6U (where 1U is defined as a 10 by 10 by 10cm form-factor) CubeSats placed in an orbit slightly above the Geostationary Equatorial Orbit (GEO) to achieve the aforementioned science goals. The spacecraft fly in a passive formation, which allows them to form an interferometer while minimizing the impact on operations complexity. The paper provides an overview of the mission and spacecraft design, as well as the concept of operations for the mission. Finally, it discusses how the SunRISE mission concept could serve as a stepping stone in demonstrating space-based interferometry and enable more complex mission concepts in the future.