I admit it: I'm an optimist. I wanted Elon Musk to show me a strong Mars plan with real finances and real life-support design. I was hoping he'd talked some of his billionaire friends into financing this Mars dream. I wanted the dream to be real.

Optimists, of course, are frequently disappointed, which is why we're often mistaken for cynics. And so, listening to Musk talk about a ticket to Mars that costs less than $200,000 — the median price of a house in America — I must say: I was disappointed. That number doesn’t square with what is likely to be the enormous cost of making Mars habitable for humans.

Optimists are frequently disappointed I should have realized earlier, when Musk was talking about restaurants in his spaceship, that this was not the plan I wanted. This was Wernher von Braun's "Man Will Conquer Space Soon," a series published in Collier's Weekly from 1952 to 1954 — a way to popularize space that was light on human safety concerns and heavy on rocket design. The point of von Braun's articles — which were not printed in scientific journals or even science-focused magazines, but rather in a well-read general interest publication — was to summon forth enthusiasm for space. Von Braun worked with Walt Disney, too: he wanted educational films that would be seen and understood by the masses, perhaps to inspire another generation of rocket scientists, or more simply, to convince taxpayers to fund his endeavors. He had, after all, joined the Nazi party to get funding for his rockets. (His V-2 rockets, which sometimes hit the UK in World War II, were developed with Nazi money and slave labor.)

So, Musk feted us with a well-produced, 4-minute video clip. He showed off his rocket designs, and talked wildly about how quickly we would get people to Mars, and how he wants to earn money to spend only on Mars. Musk appeared slightly delusional regarding the effects of radiation on the human body — a critical mistake for someone who wants humans to survive a trip to Mars on his spaceship — and wholly uninterested in food or habitat. Other people's problems, really; soft, messy biology problems. He teased, instead, the possibility of an interplanetary transport system, name-checking Enceladus and Europa.

The soft, messy biology problems are the critical problems Those soft, messy biology problems Musk is ignoring are the critical problems, the ones that are truly difficult for long-term Mars living. A rocket explosion is the exception rather than the rule these days. But space is tough on the human body. We evolved here, on Earth, and we rely on our habitat in ways that we still don't fully understand. Our circulatory system, our visual system, and our muscles all struggle in low gravity; we are vulnerable to radiation; we must eat, we must shit, we must breathe. Here, on Earth, the problems of eating, breathing, and shitting are all solved; there, whether in space, on Mars, or on any other planet, they are maddeningly difficult. How difficult? Well, figuring out agriculture the first time took our species a couple millennia — and that's on Earth, where the soil isn't poisoned by perchlorates.

Breathing, maintaining muscle mass in low gravity, making sure our circulatory systems work, avoiding radiation — these are all problems we, as a species, have barely encountered. About 500 humans have been to space; that's still hardly enough people for a well-powered clinical trial. And few people have spent long consecutive periods in space — Scott Kelly's year is an outlier.

Musk punted on the real problems, saying he just wants to build the railroad; someone else can figure out the rest. But these messy biology problems are the ones that matter for human transit and a permanent settlement. And they matter to his railroad, too: a train doesn’t work very well if its passengers arrive at their destination fatally sickened or dead.

A train doesn't work very well if its passengers arrive at their destination dead

Which brings us back to the real sticking point for Mars colonies: money. Solving these problems, which we do not understand well, is going to be expensive. Really expensive. Probably a lot more expensive than the rockets. I don't think Musk will struggle to find volunteers for a Mars mission — Mars One, which is even less serious, managed to get plenty — but figuring out how to develop the technology that will prevent people from dying in space or on Mars is going to be costly. That's why cost estimates for Mars programs tend to be in the hundreds-of-billions-to-trillions range. There's a substantial upfront cost for life-support systems, which will need to be very seriously tested before they are responsible for anyone's continued existence.

It’s also why a return to the Moon feels inevitable if we ever want to bring humans anywhere else in space. After all, we’ve only just figured out how to support a small group of people in the Antarctic — and that continent has both gravity and air. Building a Moon base would let us test life-support systems much closer to Earth, with the possibility of rescue in case of disaster. It would also allow for refueling on a place with far weaker gravity than Earth’s, which might make Mars flights easier as well.

All is not lost I love space, and I want space colonies — not as a back-up plan for Earth, as Musk does, but because I want humans to do something no other terrestrial species has ever done: live somewhere else. Not just visit there; live there. I have been waiting a very long time for a serious proposal for a base of operations on another space rock. I am still waiting.

But like the optimist I am, I must point out that all isn’t lost. After all, von Braun invented the Saturn V rocket that took the Apollo astronauts to the surface of the Moon. He did something even more significant than that: he coordinated the team that designed the rocket Jupiter-C, which launched the first US satellite. Though his concept of satellites wasn’t exactly right — von Braun was unaware of the role computers would come to play in modern life, and so his idea was for crewed satellites — we now have the internet on our phones thanks in part to his pioneering work.

Though the Mars plans may provide Musk with his motivation, his actual gift to human society may be something entirely different. His work with reusability has been astonishing, and the fuel plans he presented yesterday were inspired. If Musk is the father of space mining or sustainable rocketry, rather than the architect of life on Mars, that is still a remarkable thing. None of us, after all, ever know what our legacy will actually be.