It's probably just plasma burning as a fusion drive would have a wake that you could weaponise and sterilise planets with. They'd be banned near an inhabited world as their wake would be hundreds of km long and could destroy the biosphere from orbit.
In previous Elites, ships were driven mainly by hydrogen fusion thrusters - so fusing hydrogen into helium, with the associated mass deficit converted to heat / KE of the exhaust ejecta per e=mC^2, propelling the craft in the opposite direction per Newton's 3rd law. So, not particularly dangerous, but very, very powerful and enormous fun to fly. You could set out from an orbital station, point the nose down at the planet, open the throttles and seamlessly accelerate down to the surface in a few minutes, in real-time.
So-called military drives were powered by anti-matter, chiefly manufactured by the sinister Sirius Corporation, on its planet Lucifer in the Sirius system. According to lore, vast induction coils were wrapped around the rocky volcanic world, capturing EMFs induced from the planet's motion thru its host white dwarf's magnetic field, such were the energy requirements of producing the stuff, and its reaction products
did include radio-isotopes, although there were strict penalties on dumping, so you wouldn't get away with jettisoning it anywhere near a population center.
Military drives had no extra kick, just better power density, allowing more cargo space for other stuff. Again, you opened the throttles and your ship took off, and kept accelerating until you told it not to. So again, great fun to fly.
Obviously, Earth-like worlds have magnetospheres that safely filter out far, far,
unimaginably worse radiation - alpha, beta & gamma (just Google "oh my God!" particles)..
What a magnetosphere is going to be utterly useless against is the highly-focused gravity-wave recoils caused by any kind of Alcubierre drive, which absolutely
could destroy whole planets, in a mere instant.
Whole star systems, in fact.
Couple this with the fact that when i launch out of the station in my shiny new ED ship, point down at the planet and open the throttles, absolutely SFA happens... i mean it lurches forwards for a few seconds then sputters out, its dubious powers of free-flight utterly spent, to basically coast along at a paltry limp of a slow taxiing velocity...
the only way i'm getting this pathetic crate down to the surface before teatime is
by engaging the warp-drive, so jolly good luck to anyone who happens to be aligned anywhere along my deceleration vector..
As for the dodgy Chieftain design, given that it's probably been tabled a speed limit of a few hundred meters / sec, most of the engine bay might as well be full of undercarriage, or whatever else is so much more important than basic freedom of movement. Cheese, for instance. Unless it fell out, and hit someone with a dairy allergy. A tonne of Edam at 200 m/s could bring you right out in hives, i suppose. Still, i can't see they'd go so far as banning it..