If you mean humans, the money was a factor but only part of it. Apollo was based on a step by step approach. They took risks, yes, but careful calculated risks and they did shorter then longer trips to Earth orbit, then around the Moon and even with Apollo 10 did a test landing all the way to the surface, but not actually landing and returned to Earth, which turned up a problem that would probably have lead to the death of the astronauts if they had landed.

So the main problem with Mars is that there are no more stepping stones between the Moon two days away and Mars, six months away and about two years round trip to get back. Some asteroids are closer, but they are

• Not that exciting as a destination for humans -
• Any individual asteroid typically can be visited easily only once per decade

Anyway - as far as I know they didn’t have plans to visit asteroids. The ideas to build a Stanford Torus in LEO were based on getting materials from the Moon rather than asteroids.

So, what do you do next after the Moon, but before Mars? Nothing really, not any dramatic destination anyway. No destination to excite the public imagination with the political support they had for the Moon and all the different “firsts” they could do on the way to a lunar landing such as first human to see the far side of the Moon, first to leave LEO, first view of Earth from deep space, Earth rise over the Moon, first humans to see an eclipse of the sun by the Earth, first time humans saw the craters of the Moon close up from orbit etc. It would have been a long haul of many uninteresting missions (at least as far as the general public was concerned) before the final mission to Mars, if you wanted to do it safely as for the Moon.

It’s a huge step up from the Moon to Mars. You can only go every 2 years, even now (it may become more flexible eventually using “ballistic transfer”) and certainly back then. You can go to the Moon at any time of the year. You can’t take a “lifeboat” with you to Mars. The lunar missions had some redundancy with the lunar module (apart from Apollo 8) and that saved the lives of the Apollo 13 crew. If they had an Apollo 13 type accident that happened as a mission set out for Mars, they would have to last out for two years before they can get back to Earth again.

Before Apollo, there were early ideas to send humans to the Moon with a big rocket, very quickly. They could have got there years earlier that way. They even had the idea of landing someone there before they had developed the technology to get them back again, and then to keep them supplied by sending missions from Earth with food, air etc until they figured out a way to get them back. With the idea that if they did that they could save a year or two over the time it takes to land the first human on the Moon. Early on, early 1960s era, they were ambitious and thought they could do everything really quickly like that.

But NASA decided on a more cautious step by step approach. And just as well they did. Surely a mission like that would have ended in disaster and tragedy, as they didn’t appreciate how challenging it was going to be to make reliable hardware to go to the Moon without accidents.

Experiences like Apollo 1 and Apollo 13 and indeed the Apollo 10 incident underscored the wisdom of this step by step approach.

So after that - it’s not surprising that they didn’t have much stomach for a mission to Mars and even if someone had written the check for them to do it, I don’t think they’d have done a mission to Mars back then. It’s like the early idea to send a big rocket quickly to the Moon unable to return to Earth - enthusiasts making plans, but not too likely it would be implemented. It’s not that NASA has become more cautious. They always were careful and cautious, back then too, taking huge risks, but careful calculated risks, and rightly so I think. A Mars mission would have been a step too far.

I think it is a good thing that they didn’t actually. Romantic and exciting as a human mission to Mars might be, it also runs the risk of muddying the science of Mars by introducing Earth life, and indeed depending what is there, it could even make present day life on Mars extinct, if it is, for instance, a less evolved early form of life. Given Mars’ history that’s a reasonable hypothesis for what might be there based on what we know so far.

It could also be more highly evolved than Earth life e.g. because of the harsh conditions early on, if it stimulated very rapid evolution, eukaryotes already there 3 billion years ago - those who optimistically search for easily recognizable fossils in Curiosity images are hoping that Mars life is at least 2.5 billion years advanced over Earth life evolutionarily. And there’s the possibility of life on Mars that is harmful to the biosphere of Earth. And - it would not necessarily show up as problems suffered by the human crew. For instance if it was a form of microbe that takes over from some key component of our biosphere or it is just harmful not to humans but to some other animals or plants on Earth, then you wouldn’t notice anything until they got back to Earth, and it got into our biosphere. Maybe even evolved a bit, as microbes can quite quickly, to adapt to some challenge on Earth, then causes a problem.

Back then then they would not have been able to take precautions against such a risk. They just didn’t know enough microbiology, with many advances since then. The precautions for the lunar missions would have done nothing at all to protect Earth. And also as for the Moon probably it wouldn’t have been taken that seriously either - for Apollo 11 the first opportunity for infecting our oceans happening as soon as they opened the hatch when the command module landed in the sea when Apollo 11 returned. They did that because of a problem with the crane meant to lift Apollo 11 out of the sea. Rather than leave the astronauts to get seasick as they fixed the problem, with the world watching also, they decided to airlift divers over and get the crew out - in decontamination garments, but just got out of the module into an open boat with the module door wide open so any dust could get into the ocean. But even without that, and other slips, their precautions were not up to the standards needed to keep microbes out of the Earth’s biosphere, as we now know.

They didn’t know about many of the extremophiles we know about, it was before the archaea were recognized as a separate domain of life (that was in 1977), before the discovery of ultramicrobacteria or about the risks from GTAs, how easily genetic capabilities can be transferred via horizontal gene transfer and many other things. And every Mars Sample Return study so far has used new science to say that we have to increase the level of precuations over the previous ones. First the ultramicrobacteria. Then the GTAs and also the theoretical studies suggesting that it’s theoretically possible to have life with cells only 50 nm in diameter if it has only one biopolymer and no proteins (like “RNA world” life). Nowadays you are required to contain particles even as small as a few tens of nanometers in diameter for a sample return if there is any risk of returning life to Earth that’s non native to Earth.

Luckily the Apollo 11 precautions were not needed. But what if the Moon had had life, and it was hazardous to us? It could be, say, a photosynthetic lifeform that out competed our plankton and was inedible (because of its different biochemistry), maybe didn’t produce oxygen or produced some other chemical that resembles our biochemicals but not exactly and so is poisonous, or any number of ways it could be problematical. Well that would have been it, it would have got into our oceans at that point.

I can imagine that perhaps in the vastness of our universe there are places where there are planets like Earth with intelligent species living on them, and then other planets or moons nearby with life on them also, and the intelligent species when they develop space travel, then bring back life by accident. And perhaps in most of the cases no harm is done, or it is a minor nuisance, like problem species of plants returned from another continent, but in a few cases the life brought back may severely degrade their biosphere and perhaps in a very few cases, especially if done as early as Apollo when their technology isn’t very sophisticated, perhaps they go extinct.

Also now we can explore Mars remotely from Earth, especially once we get broadband communications in the 2020s, we could download a complete 3D multi-gigabyte landscape about our rovers as they travel over Mars dozens of times a day. Then explore those landscapes in 3D, look at nearby rocks right down to microscopic detail.

Later on can do that with humans in orbit around Mars, explore via telepresence. I think that’s far better than humans with present day technology, but they couldn’t have considered that as a possibility back in the 1970s as they didn’t have telepresence technology at all, and the idea of a multigigabyte digital image returned from Mars would have seemed absurd.

For more about that see my OK to Touch Mars? Europa? Enceladus? Or a Tale of Missteps?