I didn't imply you lack imagination in general, just imagination on this particular subject. Radiation is a separate matter. That speed is precisely where aero

I didn't imply you lack imagination in general, just imagination on this particular subject. Radiation is a separate matter. That speed is precisely where aerodynamics start to matter again, as you hit stray particles. You want your profile to be as narrow as possible, so you're hitting as few particles as possible. Ice helps absorb the impact of such particles. Note that Alastair Reynolds is an astronomer, so he did think this bit through somewhat.