After WWII, everyone expected that we’d pretty soon have nuclear rocket planes, so that was the predicted massive increase in fuel efficiency. The problem is that nuclear reactors are a lot more dangerous to nearby humans than people thought back in the 50s. And while nuclear reactors might heat reaction mass to a higher temperature than chemical reactions do, you still have to shove the reaction mass out the back of the rocket. A fusion rocket might have a power source that can run forever, but you still have a limited supply of reaction mass to shove out the back, and once your reaction mass is gone you’re done.
So even a nuclear rocket has a fixed amount of delta-v that is known when the ship blasts off from your backyard heading for Ganymede. You can’t just turn on the rockets full-blast and zoom over there, you may have unlimited nuclear fuel for power but you’ve got limited hydrogen in your reaction tanks.
First of all, the “futurists” didn’t really have any actual expertise. They were just free-lance writers who submitted a manuscript to a publication like Mechanix Illustrated, who likely didn’t even subject it to any editorial review. Like today, the best way to get an article publishes is a) be a regular contributor on a wide range of subjects, and b) send in the glitzy-ditziest manuscript of the month, and c) make sure it lends itself to a lot of clip-art graphics.
Many of the predictions could easily be found to be impossible in any real sense. The prediction that people would be commuting to work in flying cars or 'copters made no allowance for a million of the damned things in the air space of a single city all simultaneously, none of them capable of making a sudden turn or stop in emergency or requiring parking space.
All it takes is one single fly in the ointment to spoil an entire panoply of predictions. In 1950, no-one could have predicted miniaturized circuitry, and everything they envisioned would have required vast arrays of vacuum tubes. So of course, they were wrong about everything made possible by transistors.
Nor did they understand how public attitudes like fear could get in the way of even something so obvious as nuclear power, which they did know about and assumed a prosperity from. Or the developmental setbacks from a manipulated financial infrastructure, crushing litigation, and intellectual property greed.
They also probably misunderstood the power of toys and entertainment to drive the development of new products, instead of health and well-being. Even Alexander Graham Bell expressed fear that his telephone would have its practical utility eroded by frivolous users having private personal conversations on finite phone lines.
Nuclear fusion or fission is not a source fuel .In theory a boat ,ship ,car,plane or spaceship that is nuclear fusion or fission could stay up for months or more before need to get more polonium or uranium. But there are some problems that have to overcome to make it a reality.
1 safety
2 accident / nuclear fallout
3 radioactive
4 building a small reactor to fit in boat ,ship ,car,plane or spaceship
5 radioactive wastes
A boat ,ship ,car,plane or spaceship accident could cause nuclear fallout over a city even over ocean the wind can blow it over to city.
So there many problems why we are not using nuclear fusion or fission .
And nuclear fusion is still in the research and development stage and yet to get good working nuclear fusion.
We still do not know how to build a reactor small enough to fit in a boat ,ship ,car,plane or spaceship.
We certainly do have nuclear reactors small enough to fit into boats. The US Navy has a whole fleet of nuclear powered submarines and aircraft carriers, we also used to have nuclear powered cruisers although those are decommissioned right now.
Also, I think one reason why subs and warships use nuclear power even though it is dangerous to do so is because several of them already carry nuclear weapons.
In the case of submarines, nuclear power provides capabilities that can’t be done any other way. For large aircraft carriers, extreme cruising range plus being able to devote the space that would otherwise be needed for fuel for aircraft fuel and ammunition.
You started off by including ships in your list of vessels that we purportedly “still do not know how to build a reactor small enough to fit in,” ignoring the fact that there have been hundreds of nuclear ships and submarines built since the advent of the USS Nautilus (SSN-571) over 60 years ago. Regarding safety, the U.S. Navy has never had a serious nuclear accident over this span of time.
As for smaller vessels, the nuclear-powered research submarine NR-1 (launched over 45 years ago) was only 400 tons displacement.
As for spacecraft, there have been many of these that have also been nuclear-powered, mainly using radioisotope thermoelectric generators (RTGs). RTGs have been used on spacecraft since the early 1960s. The USSR launched a number of low-powered fission reactors starting in 1967. More information here.
