Currently there is a large, expensive auction on eBay for several hundred pieces of Marquardt concept art. The per-piece price of about ten bucks is pretty good, but the sum total is just a whole lot. Anyway, the auction listing provides a look at a *few* of the pieces, including one that depicts a “space sled.” This was a maneuver vehicle for a single astronaut, with much greater performance than the various maneuvering backpacks that had been designed over the decades. Instead of strapping it on, the pilot sits on it somewhat as if it was a motorcycle. The propellants are almost certainly cold gas (nitrogen) thrusters, which means specific impulse was really low. But it also made them very, very simple devices.
While Marquardt did some serious design work on space sleds, including building one that is currently on display at the USAF Museum in Dayton, it’s unclear how serious this one is. The space suit, after all, is pretty weak. There appear to be only two thrusters, both providing “forward” thrust; steering looks like it might have been by actually tilting the whole assembly. This would have provided only minimal thrust vectoring, and would have provided little to no pitch or roll control, and no braking thrust. My guess is that this was either the art department coming up with a concept on their own without much engineering input, or it was a very preliminary and perhaps unfinished piece.