The instrument complement suggested by the science definition team are straightforward in mounting, pointing, data rate, mass. The problem comes in supplying instrument power during dipping campaigns during long eclipse orbits. Body mounted arrays are very inefficient in use of cells but are required by science. The science requirement to disturb the plasma environment as little as possible rules out deployable, sun-pointing, panels. Body mounted arrays with 3-axis pointing makes thermal design more challenging.
Solar arrays have to be used as heat rejection surfaces.
It is possible to have the section of the spacecraft facing the earth not populated which leaves it open for a heat rejection surface. Circumferential heat pipes can be used to conduct heat to full circumference of the spacecraft. The ACS power load can be very high to counter aero-torques. Whether reaction wheels or momentum wheels are used they are likely to be torqued at high powers during perigee passage and, until the speed can be reduced by momentum unloading later in the orbit, they will continue to require relatively high power. Duty cycling of the instruments is the only option.