Look Up!

[Ed.: Today’s post is by MJ Locke, but due to minor technical difficulties it appears under my name.]

Foreword: For several months during 2007, I collected data for a series of graphics-focused posts on space exploration. I wondered how far we humans have penetrated into space, in the years since our first vehicles rose above the layers of our world’s atmosphere.

Next Saturday, May 5, 2012, we will reach the fifty-first anniversary of the first U.S. launch of an astronaut into space. This is a revisit to a series of posts I put up then. I’ve updated the dates, but all of my analytical data is five years old.

Mercury Redstone 3

On May 5, 1961, 37-year-old Alan Shepard climbed into a tiny capsule atop a liquid-fueled rocket. He rode it up from Cape Canaveral, Florida to an altitude of 116 miles: about forty miles above the upper reaches of the atmosphere. He experienced six gees (six times Earth’s gravitational pull) during liftoff, stayed aloft about 15 and a half minutes, and then splashed down in the waters of the Gulf Stream.



I was very young then, a preschooler, but even so I remember my excitement, and also fear, as I watched the news footage. I recall watching the wind from the helicopter’s blades stirring up the waves that splashed against the capsule as it righted itself.

I can only imagine what it must have felt like, soaring up so high. Not to mention how it felt, coming down.

I remember seeking a glimpse of his face through the little portal, and the thrill I felt when the divers helped him emerge and climb into the sling.

President Kennedy was there, for that first launch.


Since that time, the US has launched over 170 piloted missions, and many, many robotic missions. Our astronauts have spent months at a time in the International Space Station, working in cooperation with people from a variety of other nations to do scientific and engineering research.

We have fifty-one years of human-piloted space exploration under our belt*. Alan Shepard and Mercury-Redstone 3 set the stage for everything that came after that.

Human Space Density, in Hours

What does that really mean, though? How far have we travelled in space, to date? How long have we lived there?

Here is a graph showing how many hours humans (only US astronauts, so far; see note below) have spent above the level of the atmosphere.

I’m counting the upper edge of the atmosphere as about 76 miles up, though you will find many different estimates–and in fact, it changes over time, with fluctuations in the solar wind and other factors, including global warming impacts. But 76 miles is a good average number for our purposes.

So how much time are we talking about, really? For comparison, the average American work-year is about 2,000 hours. A year has about 8,900 hours, all told.

As you can see in the chart above, after a promising start with Mercury, Gemini, and Apollo, the US manned space program languished, when SkyLab drew to a close. It wasn’t until 1981 that the space shuttle program re-energized space exploration. The hours really started racking up once the International Space Station was completed. You can also see the effect of the Challenger (1986) disaster. The Columbia re-entry breakup (2003) is not as easy to see, but it is the cause of the dip in 2003-2004. In fact, it slowed the pace of NASA shuttle missions through the remainder of its run.

If you were to add up all the hours every NASA astronaut has spent in space since our first manned mission, that’s almost 31 years. As of 2007, humans had spent nearly half a lifetime’s worth of time outside Earth’s atmosphere (A good deal more than that, in fact, if you include other nations’ efforts. I couldn’t find the data for them).

Granted, that’s a pittance, compared to how many people live beneath the atmosphere. (In fact, it surprised me. I thought it would be more.) But it’s a start.

As you can see from the chart above, the US has had seven major piloted space programs since we launched Alan Shepard into space.

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, as if they had been traveling in a straight line away from Earth. The blue tells you how many miles away from the Earth’s surface they actually reached during their missions. In both cases, I used the annual miles traveled by US astronauts.

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.

The maroon shows that 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 10-. 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 even begin to 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 effect). Notice how most space missions barely leave the atmosphere, and notice how far it is, even just to our own moon.

The End of the US Space Era? Or a Pause?

Right now, our space exploration efforts seem becalmed. The fifty years between Shepard’s launch and the final voyage of the space shuttle Atlantis may have been our high-water mark, with regard to space travel. I’d be very sad if that were the case. I prefer to be optimistic, however. NASA’s rover, Curiosity, is nearing Mars. A variety of visionaries and entrepreneurs are seeking ways to commercialize space travel—everything from asteroid mining to space tourism, telecommunications, and spaceports in the New Mexican desert. New exoplanets are being discovered by the day now. Perhaps our robotic probes and astronomic surveys will reveal clues of life beyond our world, which might inspire us once again to reach upward again, and seek to escape the confines of Earth’s gravity. I hope so.

We have barely passed beyond the membrane of our atmosphere. Is there life on other worlds? What wonders lie in store out there? I hope that we will continue to find in us the spirit of our ancestors, and to continue to reach beyond our atmosphere, to explore and even someday perhaps settle on other worlds.

Notes: Let me haul out the usual caveats. I pulled the graphical data together primarily from NASA’s mission data pages, with Wikipedia as a secondary source (in particular for the International Space Station). About five percent of the data (in particular, maximum altitude and distance traveled) was not readily available online, in which case I SWAG’d^ it, based on data from other missions. In other words, there is slop in the data. Don’t use it for your doctoral thesis, or to calculate whether you have enough oxygen to survive till the rescue team arrives. Also, I only have information on US astronauts.

* Van Allen belt, that is.

^ Scientific Wild Assed Guess. It’s tethered to real numbers to some degree, but it definitely floats around in the ether to some degree, too.

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