A minimum of 3 (north,equat,south) x 2 (dawn, dusk) positions. Limb observation from the night side also possible with lesser conflicts with nadir surface observations with the main goal to monitor plume spatial structure (high solar phase angle). High phase angle constraints are the most meaningful for plume observations Synergy with JANUS.
any rule that is used to schedule the observation: repetition rules, continuous (plasma instruments), one-off, every orbit, every day, etc