Okay, so this isn’t quite happening in space yet, but I so very much want it to: a nuclear thermal pulse rocket!
No, it’s not like Orion, not at all, but it is edging into outright torch territory. Atomic Rockets’ explanation is science-heavy, but it boils down to this: most NTR designs can have either a high specific impulse, or a high (ish, solid-cores aren’t exactly all that thrusty) thrust, not both. This thing finds a way to have its cake and eat it by abusing a quirk of its reactor design to either kick out amazing amounts of thrust with the customary high Isp that nuclear thermals have, or keep the low thrust but increase its Isp to the sort of values you normally see in ion/plasma engines or fission-fragment rockets, both of which are very efficient but have basically no thrust to speak of. Either option can allow for a rocket which can merrily ignore the horrors of transfer windows and jet around wherever it wants, like a proper spaceship. It’s also fairly safe by nuclear rocket standards.