That wasn't Brackett's fault, Chandler famously said he didn't know who killed the chauffeur. Like many of his novels The Big Sleep was made by combining two or more of his short stories, and sometimes things didn't make sense.
It's been a long time since I read it... but the specifics of that part of the story:
> Back in Haven, Dougal's men used the acquired knowledge to build a primitive crewed spaceship, adopting a low-tech design of Robert Goddard—a rapid firing cannon using high-explosive shells detonating behind the ship to provide propulsion (but which might blow up the ship). Because the ship would not be airtight, only members of MacKinnie's company (who still had their space suits) could pilot it, and because it would only be able to carry a minimal payload, Graham (the lightest of the company) volunteered and was chosen as pilot. Before the launch, MacKinnie proposed to her, and she accepted. As soon as Prince Samual's World was unified, and in the presence of unsuspecting Imperial witnesses, Graham's ship was launched and achieved orbit, although it could not re-enter the atmosphere (meaning that the Imperials had to rescue Graham). King David then immediately requested that Prince Samual's World be admitted to the Second Empire as a self-governing world capable of crewed space travel, not as a colony.
Agreed, but to be pedantic, it applies to all momentum machines which carry its own "propellant", not "fuel".
For instance, in a NERVA rocket, the "fuel" is the uranium rods in the reactor, the "propellant" is the liquid hydrogen that is heated and shot out the exhaust bell.
Solar Sail, Laser Sail, Electric Sail, Magnetic Sail, Mini-magnetospheric plasma sail, MagBeam, Plasma Magnet Sail, Photon Drive, Bussard Ramjet, Ram-Augmented Interstellar Rocket.
Basically any spacecraft that does not carry its own propellant. Most of these have either pathetic thrust or are way beyond our current state-of-the-art.
I'm no expert but I think the answer is "No", due to other problems.
Distances are closer in Globular Clusters. Alas, those are "metal poor", so the only planets are gas giants like Jupiter.
Distances are closer in Open Galactic Clusters like the Pleiades. Unfortunately those cluster tend to disperse. By the time a space faring civilization has evolved, the stars are no longer close.
Distances are closer in the Galactic Core. Unfortunately that is a high radiation environment due to Sagitarius A* (the mega-black hole at the center of the galaxy_ and all the nebulae the hole is dragging in.
Short answer: places where the distance between stars is closer are unlikely to have space faring civilizations.
And about five minutes later, zillions of programmers would start writing similar apps, in hope of a big payday when Facebook shows up to buy them out.
