Electron-astrophysics in the solar wind: plasma physics at F-Class, lessons learned and things to do.

ESA F-Class missions offer a new opportunity to do space science with smaller, cheaper spacecraft. The mission format presents a tough challenge for plasma physics missions, can we make simple, small and cost-effective spacecraft for a topic that will make breakthrough discoveries? This presentation will discuss the past two proposals of the Debye mission, the lessons learned and the challenges ahead to make a similar mission feasible. Debye addresses a grand-challenge problem at the forefront of physics: to understand how energy is transported and transformed in plasmas. The smallest characteristic scales, at which electron dynamics determines the behaviour of energy, are the next frontier in space and astrophysical plasma research. Debye will be the first electron-astrophysics mission. Electron-kinetic processes operate at very small scales (< 10 km) but define the behaviour of the plasma at system-size scales. Debye will use the solar wind as a natural plasma laboratory to measure these electron-scale processes. Understanding the heating, acceleration, thermalisation, and heat flux of electrons is fundamental to our understanding of the dynamics and thermodynamics of plasmas throughout the Universe and thus to the entire field of astrophysics. Debye will answer the fundamental science question "How are electrons heated in astrophysical plasmas?" The mission will make the highest-resolution measurements of electrons ever made in space in terms of energy, angle, time, and space, coupled with two-point high-cadence field measurements to identify the plasma fluctuations responsible for electron energisation. This mission concept will provide ground-breaking and transformative physics results since the combination of rapid particle and field measurements over distances of less than 10 km is completely unprecedented. We believe Debye is a fast, feasible, and focussed mission, tailored to achieve these science objectives, but there are some technical challenges that are assessed to be problematic, how can we address data transmission, formation flying, the cost of multi-item payloads and multi-spacecraft missions?