One idea from the dawn – or at least pre-noon hours – of the space age that I think might be worth considering for a comeback is the “Propulsive Lift Landing Aid for Entry Vehicles,” or “Propulsive Lift Concept for the Descent and Landing of Manned Entery Vehicles” which mysteriously but fortunately boils down to “PLAME.” Studied by General Dynamics around 1967, PLAME was a concept for using turbojet engines to provide vertical thrust for the landing of space capsules or small spaceplanes. The turbojets were big, and required further volume for their inlets and exhaust; but modern designs would make them smaller, lighter and more fuel efficient. The amount of fuel they’d need would be limited due to their short run time… and being turbojets, there’d be no need for oxidizer, just stock-standard jet fuel.
For future passenger/tourist space vehicles, I’d imagine that a system like this might be an effective way to provide a safe land-landing system. A single conical or biconic space capsule would be a cheaper and lighter vehicle than a wing-body or lifting body (with notably less crossrange, of course); a PLAME system would allow a capsule to not only land on the ground (rather than ocean splashdown), but also would make the capsule largely independent of runways. A PLAME-equipped capsule could land pretty much anywhere that something like a Harrier could land.
Of course, a rocket system could be used instead of a turbojet system. It might be interesting to compare the two for use in the *same* capsule. Design the capsule to use turbojets… and then remove the turbojets and place rockets in the inlet/exhaust duct. Use the ejector effect to increase the thrust of the rocket. Trade studies might just show that a pure rocket system would weigh less than a turbojet system.
A system like this would allow, say, SpaceX or some other firm to launch tourist space capsules from Florida, and recover the capsule right next to the launch site. This would not only speed up and simplify processing of the capsule for the next flight (a not inconsiderable concern), it would also get the tourists on their way that much faster and safer. After having just spent days or weeks in space, they might – or might not – be in the mood to bob around in the ocean waiting for pickup. With a PLAME-capsule, they could be back out and about within a minute or two of landing, just yards from the airport terminal.