The Dream of Spaceflight

Me and fellow member of team "Gagarin", at Space Camp (Huntsville, AL) circa 2001
This past Friday during a test flight over the Mojave desert the privately funded SpaceShipTwo crashed, killing one test pilot and severely injuring another. Combined with the destruction of a privately built Antares rocket during launch (thankfully nobody injured), it's been a hard week for the business of space.

Some worry these two accidents have been a damning setback to the dream. Here the dream I'm referring to is making space travel common, available to everyone. And to be clear, it's a LONG ways off... Currently it costs between $1 and $10 per lb to fly on commercial airlines (of course, we don't buy tickets by the lb, but its a round number). By comparison, launching something in to space is over 1000X more expensive, around $10,000 per lb. When private companies are able to make spaceflight an everyday reality, we'll be a lot closer to this dream.

Around 540 people have flown in space (and perhaps a few more if you believe militaries have flown secret missions). That's it! Fewer than 600 humans have ever left our world. Given that the World population is still increasing, I wondered:  Has the number of people who have flown in to space actually kept up with population growth?

In other words, even though it's insanely expensive to launch people, and very few have been fortunate enough to go, are we making any progress on the dream?


Here's a visual timeline of all (publicly known) humans ever launched into space, from Wikipedia:

The number of spaceflight missions per year (both crewed and not) reached its peak in the early 1960's. It's an encouraging sign the recent trend has reversed, and that the number of missions per year has continued to grow for the past decade.
From Wikipedia

An Increase of People

For reference, here's the growth of the World population since the beginning of the human spaceflight era according to the US Census Bureau. For spaceflight to become common place, we have to be launching new people faster than this curve.
World Population since 1957

I was able to grab some nicely formatted table containing the name of every known astronaut (and all other varieties of 'naut), as well as their first launch date. Here is the cumulative number of people who have flown in to space over time:
Number of people in space over time
This is such a neat graph! It has encoded in it so much of the history of human spaceflight. (Note this does not count the total number of times people have flown, since many astronauts have flown on multiple missions and are only counted once here.) See the slight flattening around 1967? That's because the US didn't fly any missions in 1967 after the tragic Apollo 1 fire. My parents were kids then.

You can see a steady linear growth in the number of space-people throughout the 1960's and 1970's, even after the Apollo missions to the Moon ended in 1972. The cumulative curve takes a sharp bend upwards in the early 1980's when the Space Shuttle program begins. I show up around this time as well.

This growth is ambitious, and by 1985 the US is launching more humans in to space than ever before (or since) per year. In 1986 there is another sobering bend in this curve. I was 3 years old when Challenger exploded. The Shuttle program endured, the cumulative curve began to grow again. There's a much smaller bend in the curve in 2003. I was in college when Columbia disintegrated during reentry.

I don't mention these accidents to make light of them, or to diminish the horrible tragedy of last Friday. Going into space is dangerous business. Even testing and training for it is dangerous. For spaceflight to become commonplace, it must be both affordable and safe. 

Are We Approaching The Dream?

So numerically speaking, the goal is to ensure this curve with the cumulative number of space travelers grows faster than the population. (I realize this is actually a huge over-simplification, and somewhat incorrect) Nevertheless, here is what dividing these curves looks like, that is [cumulative number of people traveled to space] / [world population] each year.

Thankfully this curve shows positive growth, though given the small numbers of space travelers it's not surprising. This graph says that overall we've been winning, that truly more of our species have been space travelers over time (a higher fraction). Maybe one day I'll be lucky enough to count myself among them.

The curve has slowed in recent years, and even dipped a little bit down as the Shuttle flights have ended. If you were to simply fit a straight line to this fraction over the past +50 years (and I did), you expect that we'll reach 1 in every 1000 humans to travel in space around the year..... 600,000 AD.

This linear fit is obviously (or hopefully) an absurd model for how we expect the fraction of space travelers to grow. Also, the world population will not continue to just grow without bound.
The fraction of humans traveling to space should begin to grow again once programs like Orion (or Dream Chaser) come online. Hopefully we see a steep increase with these new missions, like we saw in the early 1980's with the Shuttle. Private missions like SpaceShipTwo will help make this exponential growth a reality. And to paraphrase a well-known saying, exponential growth is the most powerful force in the Universe.

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