Oooh… even with a 1cm channel through a meter of shielding the radiation is kinda fierce… x20 channels is not as friendly a neighbor as I’d hoped for. To maintain the safety margin either closable ports w/ the added weight and complexity or use beam heating all the way and onboard propellant for the last stage… ouch… needs more MWe…
… but as the MHD units have to have beams anyhow for their work…
