Recently I posted a remark in the comments section of an article on cutbacks at SpaceX, the private space launch company founded by Elon Musk, along the lines of “who didn’t see this coming.” Fans of SpaceX were not amused. The thought that human space travel is hard just doesn’t seem to register with some. And, at least among this group, there seems to be a critical mass convinced that humans colonizing Mars in the coming decades is well within our grasp with just a bit of the right special sauce.

I’m a lifelong enthusiast of the heavens. I spent my grade school years in Florida straining for glimpses of Mercury and Gemini rockets arcing over the Atlantic towards space. I’ve worked under NASA contracts several times in my career as a physicist. I’ve taught astronomy and astrophysics. I think that my bona fides in this area are reasonably as good as anyone’s.

Yet when I think about human travel in space three words come to mind: not so fast.

I’m a proponent of space exploration. But given the tremendous expense of sending humans into space compared to the low cost and huge bang for the buck in sending probes, it sure seems logical to me to ask what’s the justification. I can’t come up with a particularly scintillating answer to that by myself.

It’s instructive to understand what putting humans into space was originally about. It was not principally scientific exploration. The space race in the 1950s and ’60s was about the U.S. demonstrating to the Soviet Union that they could put into orbit all of the small satellites, dogs and other things they wanted — but when it came to the technology required to get people all the way to the Moon and back in one piece, we were the goods. The race to the Moon was the Cold War fought in the vacuum of space.

Not that the space race was without merit. Back in the 1960s, Mercury, Gemini and Apollo space missions dominated headlines and network TV. A generation of people like me were inspired to careers in science by space. I still remember riding my bicycle down Main Street in the town where I lived in 1969 and seeing a crowd gathered in front of an appliance store to watch the moon landing on the color televisions in the front window. It was cool almost beyond words. And it was, albeit briefly, a unifying event.

But somewhere after the first moon landing, we lost our way in terms of a clear reason for human space exploration. With the Cold War ending our original raison d’être went away — and was never replaced with any new, clearly articulated mission.

The entire space shuttle program, for instance, suffered from ill-defined goals and poor performance, resulting in a couple of needless catastrophes. In the end, the space shuttle was reduced to lofting science experiments for fifth graders into orbit — not exactly the most efficient use of a dearly expensive program.

In recent years NASA, a massive bureaucracy without a cogent mission if there every was one, has seemed content to keep its head down until required to nod approvingly when politicians get into trouble and need to jump-start their popularity with some plant the flag on Mars jingoism. I’m not saying that NASA is devoid of talent or lacks the capacity for useful work because none of that is true. But if you can explain to me what they are doing, in terms of human exploration of space, that justifies their budget I’m all ears.

The problem that NASA, SpaceX and everyone else who’s interested in sending humans to Mars and beyond has isn’t just finding the right special sauce — it’s fundamentally physical. The very nature of the universe imposes limitations on the speed of travel in space. Space is infinitely big, yet the maximum speed of travel within it is quite small. Even going someplace as close as Mars requires months each way at the highest imaginable speeds. And during this lengthy journey occupants of a spacecraft beyond Earth’s magnetosphere stand a good chance of encountering high, possibly lethal doses of radiation due to solar activity. That’s right. Put me in coach!

Contrast that with sending robotic probes around the solar system — something that has a demonstrable record of great success at very low cost. Robotic probes don’t really care about how long it takes to get where they are going and they don’t need food, water, extensive radiation shielding or an atmosphere to go along with them.

I heard a claim recently that humans need to go to Mars because they can do things in 15 minutes that it would be impossible for robots to do in anywhere near the same amount of time. That’s true if your only metric is surveying the landscape and figuring out where to best dig a hole. But when one calculates the expense of sending humans and the support they require very far into space with our current levels of technology, I’d argue that robots are much better at the job.

One day I hope that we do figure out how to travel to the stars. That’d be completely awesome. But I suspect that the secrets to efficient space travel are much more likely to be revealed in a lab right here on Earth than by traveling around in our solar system in crude, fragile spaceships without purpose.

Associated Press and Idaho Press Club award-winning columnist Martin Hackworth of Pocatello is a physicist, writer, consultant and retired Idaho State University faculty member who now spends his time happily raising three children, llama farming and riding mountain bikes and motorcycles.