Last week, in my first post on humans in space, I talked about how many hours humans have spent in space. In this post, I want to talk about how far we have traveled beyond the confines of our atmosphere.

Human Space Density, in Miles

You can think in terms of how many miles we have traveled overall, or in terms of how far away we have gotten away from the Earth, before we turned around and came back. At first glance, they might seem to be the same thing, but this is definitely not the case. An astronaut might travel many millions of miles in low Earth orbit, but never get any farther away than a handful of miles above the upper reaches of Earth’s atmosphere. Or an astronaut might take a trip to the moon and back, with very little in the way of orbiting either body—in which case their distance travel and maximum “altitude,” or distance they get from the Earth, would be very nearly the same.

Here is a chart that provides information on both kinds of travel.

The maroon tells you how many miles our astronauts traveled in all, by year, and the blue tells you how many miles away from the Earth’s surface they reached during their missions (for that, I used the maximum distance traveled in each year). As you can see, the moon missions (that blue bump in the ’60s and early ’70s) stand out from the rest. The Apollo craft went much farther away from the Earth than any other space flights, before or since. For non-lunar missions, the average altitude was 179 miles, less than the distance from Houston to Dallas.

2001 was a banner year for space travel, when US space missions traveled a total of 233 million miles. That’s all the way to the sun and back, with enough left over to go to Mars. But our astronauts racked up all of those miles in low Earth orbit, never getting any farther from the Earth than about 250 miles.

The average distance missions travel, from the days of Mercury to the present day, is almost 10 million miles. For comparison, if you drive 10,000 miles per year on average, it would take you a thousand years to travel that far.

As you might guess, the International Space Station dragged the curve up all by itself, because astronauts spend months at a time on the ISS. The typical ISS mission lasts six months. An international team usually consists of three astronauts, who spend that half a year up there conducting experiments and maintaining the station. They’ve just added a new module to the ISS. The ISS has 15,000 cubic feet of living space. That’s about equivalent to a 2,100 square-foot home, down here.

By the way, some of my readers will note something odd about the above graph. The distances seem off. The 100-mile marker on the chart is the same distance from the 10-mile marker is the same length as the 10-mile marker is from zero. The thousand-mile marker is no farther from the 100-mile marker than the 100- is from the 1o-. What gives?

It’s a logarithmic scale. A log scale scrunches the data together, to allow you to compare data that spans a very large range. In this case, I wanted to get the low-Earth-orbit data onto the same graph as the millions-of-miles traveled data. It’s useful to be able to look at them together, but it can be misleading. Here is a chart showing the actual distances, without the log scale.

The image above shows you about 250,000 miles’ distance, to scale (I couldn’t fit Mars and the sun on there, and still show you anything meaningful with regard to the NASA missions. The old space-is-really-big thing). Notice how most space missions barely leave the atmosphere, as compared to how far it is, even just to our own moon.

Still, what an amazing thing it is, that we have reached beyond Earth’s atmosphere in such a substantive and sustained way.

I had hoped to post more information about the latest ISS mission, as a kind of bookend to my Mercury mission post last time. It has been the occasion of a couple of interesting milestones, including the first time a female space shuttle commander has transported a female ISS commander into orbit, and the fact that during this latest mission, the ISS astronauts added a new module to the space station. How cool is that?

But I have another business trip tomorrow and really need to get to bed. Perhaps I can include that as part of my next Look Up! post.

________________________

The same caveats apply regarding data accuracy as I spoke about last time. See the end of the prior post for more specifics.