Racing high over the Sahara at 5 miles per second, protected from the desert’s parched endlessness and soaking in its sere beauty, I saw Khartoum, the city where the White and Blue Nile rivers meet. I turned my head left and followed the river downstream to Cairo and the Mediterranean. Twisting weightlessly back to my right, I could pick out sunlight glinting off the waters of Lake Tana and Lake Victoria, the Nile’s headwaters. Explorers from the early Greeks to Queen Victoria’s David Livingstone had toiled and failed to find what I could see at a glance. Impressive on its own—even more so since I had been over Winnipeg, on the edge of the Canadian prairies, just 20 minutes earlier.

Circling Earth so fast makes you think. When you look out the window of a space­ship, you see entire countries, vast swaths of continents. One turn of the head covers what once took thousands of years to traverse at ground level. Historians and archaeologists estimate that human beings started migrating from Africa to Asia about 70,000 years ago, and to Australia 20,000 years after that. We went to the New World of the Americas about 30,000 years ago. All told, from the first dissatisfied teenager’s steps away from home, it took about 50,000 years to walk to the far corners of the planet.

Technology helped us pick up the pace. By the 1870s, new railways across the US and India and the opening of the Suez Canal made it seem completely plau­sible that the fictional Phileas Fogg and his valet could circle the world in 80 days. In 1911, Roald Amundsen reached the farthest end of Earth and stood atop the South Pole; 50 years later, the Soviet Union sent Yuri Gagarin around that same world in a ­little more than 80 minutes. And since November 2000, astronauts on the International Space Station have circled our planet 16 times a day—that’s about 75,000 times around and counting.

This past year I was aboard the ISS for 2,336 of those orbits.

It was remarkable to see from space how predictable ­people are. Our homes and towns are almost all in places with moderate temperatures, and they generally have the same shape—a thinly occupied outer blob of suburb surrounding a densely populated core, all based around a ready source of water. It reminded me of the mold that grows under everybody’s sink. We infest our Earth in the most hospitable wet spots and live in the harsher places only when we have no other choice.

Also vis­ible from the ISS is the fact that all of the really good spots are taken. In our 70,000 years of wandering, our ancestors have had a look at pretty much everyplace on Earth, and the first arrivals in the best locations put down roots. Now those spots are full; living anywhere else requires modification of the local environment. And that takes energy. The farther we get from the heat/water sweet spot, the more energy it takes.

The communities and countries best at using energy to optimize a micro­climate for human life are also the ones whose ­people have the longest average lifespans. Canada, Sweden, and Iceland—places with inhospitable winter weather—are front-­runners in sustaining human health and life. They have no choice but to use what energy they have in the most efficient manner. Like the careful, constant nurturing of mushrooms in a hothouse, the right application of technology and stability can lead to the greatest yield.

Earth has never fed as many ­people as it does today. From orbit, the ­gingham-quilt patterns of farms all across eastern Europe and the massive grain fields of the world’s steppes and prairies are clearly laid out. Vast fields for supply connect to roads and railways for transportation, all leading to dense hubs of consumption in the cities. When the sun is just right, you can even see the wakes of ocean-going ships imperturbably hauling bulk goods between continents.

The space station, high above, is a microcosm—an international collection of people living in a finite area with finite resources, just like the planet below. Power comes from a blend of fossil fuels and renewable energy. Air, food, and water come in limited quantities. Like Earth, the ISS is subject to unpredictable outside forces—solar flares, meteor impacts, technical breakdowns, budget cycles, and international tensions. And in both locations, lives are in the balance. Make a small mistake and people are inconvenienced, capability is lost. Make a big one and ­people die.

The ISS is the largest spaceship that human beings have ever built. With its vast golden solar arrays and gleaming white radiators, it’s bigger across than an NFL football field, and it gracefully carries a leviathan mass of nearly a million pounds. Yet the ISS sustains only six astronauts. The delicate balance of power generation, atmospheric control, laboratory space, psychological environment, water puri­fication, and food supply were all exquisitely shaped for just half a dozen people.

If we ever want to go farther from Earth—to an asteroid, let’s say, or Mars—we’ll need to design a ship that is far more efficient. The complexity and risk of hauling into orbit all that metal, more than 150,000 pounds of stuff for each passenger, could never be cost-­effective for traveling great distances. The ISS is wondrous as a first great international outpost in orbit. But it is not a model for something we could use to go elsewhere, to truly leave home.

Why? The basic limitation is power. Everything we do on the ISS, from firing the thrusters to heating the coffee, requires energy. Rather than dealing with the cost and complexity of hauling fuel up from Earth, the designers chose solar power. It’s ­simple technology: direct line of sight to the sun, predictable eclipsing when Earth is in the way. The eight solar arrays generate 84 kilowatts of electricity.

The space station, high above, is a microcosm—an international collection of people living in a finite area with finite resources, just like the planet below.

But nothing’s perfect. Huge solar panels are delicate; one tore during deployment and had to be stitched back together by hand during an emergency spacewalk. Keeping the lights on in the shadow of Earth requires big, reliable batteries, whose power converters require careful cooling with gigantic radiators that con­duct waste heat into the cold of space. High voltage and current are a danger, especially in weightlessness, where water can collect anywhere and metal objects can float onto exposed contacts.

In fact, the problems of building a better spacecraft and reducing the use of fossil fuels here on Earth both have the same solution: a compact, nonpolluting reliable source of energy. That would shrink spaceships to a much more reasonable size and expand the range of habitable places on Earth to the entire planet. OPEC and oil sands would be anachronisms. The reasons for ­petroleum-based borders and wars would fade into history.

But we’re not close to having that technology. We have atomic power, but our efforts to harness it also create poisons. Human errors like those at Three Mile Island and Chernobyl, or natural disasters like the 2011 earthquake in Japan, overwhelm even our best safeguards and intentions. Perhaps physicists, armed with their vast par­ticle accelerators and computing power, will crack the potential of nuclear fusion. Or maybe they will ­stumble upon some other way to harness the power stored in each atom. But despite perpetual adolescent dreams of future scientific beauty, the reality is that for now we need to dance with the partners we have: fossil fuels, nuclear fission, and the wind, sun, water, and heat of Earth itself.

A pail of gas that you can carry with one hand can take you and your car 50 miles. But the costs of a rampant petroleum economy are vis­ible even from space. The gray smear of pollution across the world’s largest cities obscures them on all but the windiest days. The inequality of wealth and individual opportunity stands out in the indulgent man-made Palm and World islands of Dubai. The jarring scars of strip-­mining cut into the land.

Yet I am confident we will find answers. The same driving, restless intellect that created the problems can minimize and even reverse them. New standards aim to ­double automobile fuel economy by 2025. Battery technology for electric cars is making progress, as are power-distribution networks. Improvements in renewable energy sources make them an ever-more significant proportion of our energy supply. Wind-­powered seawater desalination plants are coming online.

While I was on the space station, I used Twitter to ask hundreds of thousands of people what they would like me to take a picture of. Resoundingly, the answer was “home.” Everyone, from all around the world, wanted to see their hometowns. I found that thought-provoking. After millennia of wandering and settling, we are still most curious about how we fit in and how our community looks in the context of the rest of the world. A curiosity of self-­awareness, now answerable by technology.

This is where the answers to our problems will start. ­People across the planet need to see and internalize an accurate global vision of place and individual account­ability—to recognize the problems that face us all and the technologies that exist to combat them. Our young ­people need to be able to look up, to look beyond the horizons of their forebears, and see the wisdom and opportunity that comes from a more universal sense of responsibility.

The International Space Station is a phenomenal laboratory, an unparalleled test bed for new invention and discovery. Yet I often thought, while silently gazing out the window at Earth, that the actual legacy of humanity’s attempts to step into space will be a better understanding of our current planet and how to take care of it.

It is not a perfect world, but it is ours. Sometimes you have to leave home to truly see it.

Chris Hadfield (@Cmdr_Hadfield) was an astronaut with NASA and the Canadian Space Agency. He is author of the new book An Astronaut’s Guide to Life on Earth.