I woke up today with ToughSF poasting Gradient Field Imploding Liner Fusion Propulsion System. This report is fairly recent, like 2018. I wasn't quite blogging Atomic Rockets content then but, soon.
The "field" here means magnets. The liner is of some metal that can crumple when subjected to the Tesla. This implode-the-liner-with-dekamagnets tech is not new. Here is something from 1976. Also given the heat of the fusion around there, they cannot use superconductors - not 1976 niobium, not 1986 ceramics, nothin' under 125 K. Which puts MR Lapointe at some engineering conundra. For instance he only has 30 Tesla to play with, which he's wrapping externally. 1 T, internal.
Luckily for him and his, "magneto-inertial" designs had been an active, uh, field of research up to 2018. And he doesn' t have to keep the plasma: we're going to spaaace. The drive works by pulse like an Orion; unlike Orion they have to start in space.
This is about where nerds start talking z-pinch (or ζ-). This report is talking θ-pinch.
To load up these interplanetary missions, the 2018 paper suggests a couple of SLS boosts to eject 260 "mt" off our well. "mt" looks like "metric tonnes" so I'd say "T" or "Mg". As of last Friday Elon can sell you a Starship with throwaway booster (supposedly 188 T); he might soon be able to rent you one as well (for 115 T). They'd allow assemblage in orbit, some of those T being sufficient fuel and orbiting Starship to push your fusion rocket out of Earth's hair.
Where we speak of specific-impulse (Isp) as usual the time-savings ramp up beyond Mars, like this takes 50-100 "mt" to Saturn in 200 days. In this context, 20 mt is a crewed mission. The report requires for the Earth-to-Saturn mission no less than 20000 s of Isp, which I take as a function of deltaV more than of distance.
Isp depends on what to use for the crumpling liner. Table 5 lists 32,200 s for Lithium (7.8 kN thrust), 17,145 s for Beryllium (14.45 kN). So lithium is how we, Earthlings and Venereans, get the direct lines to Saturn and beyond. Definitely going to have to construct the former in some anhydrous and anoxic environment like, uh, in space. Table 5 further calculates the energy required, for Mars: lithium to expend 165 MJ.
Asimov-approved beryllium would appear to work best where we don't care about longterm Isp. A three-month trip to Mars ain't that much better than a six-month. Here we're optimising for thrust and, it seems, for energy (153 MJ). Energy aside that looks better for anything as far as Jupiter; inner-planetary travel or Oberth toward the Sun will give us lots of that energy, as well. With the extra thrust comes more payload and, we must add, more payload affords more options for crew comfort. Like spinning the hab, protection from radiation, all of it.
Also, pipe dream here, if we had stations on Vesta or on Deimos, beryllium could probably hit up Saturn thence (and it might even be mineable on that differentiated silicon). Launch windows will be a bear out there however.