Sub-L1 Monitors: What Science Discoveries Do We Need before Operational Settings

Sub-L1 monitors have been discussed for several decades to provide advance warning of incoming transients (coronal mass ejections - CMEs-, corotating interaction regions -CIRs-, solar energetic particles -SEPs-) before they impact L1 and Earth's magnetosphere. A number of orbits have been proposed, including Venus-like, distant retrograde orbits and pearl-like. However, before launching such a mission for operations, numerous science discoveries must be made. This includes: how CME, shock, SEP, and CIR properties vary at intermediate separations (0.01-0.1 AU) from the Sun-Earth line, how these transients evolve radially during the span of a few hours before impacting Earth, etc. Gaining such knowledge is necessary to design an appropriate sub-L1 space weather mission. Here, we discuss the remaining science questions that must be first answered as well as various possible instrumentation and mission design to make these scientific discoveries in advance of sub-L1 monitor.