Thursday, June 26, 2008

Apple #325: How to Get to Outer Space

I was at a dinner party the other night, and I forget how this came up -- oh! I remember! I mentioned that it was finally explained to me, through some episode of Nova or something like that, that weather is actually the effect of Earth spinning through space. That is, the air that's rushing around our planet is outer space, which just happens to be within Earth's atmosphere. I said that knowing this made the volatility of weather make more sense to me. It's from outer space! Of course it's going to be fierce and crazy!

(No remarks, please, about the nerdiness that I bring to dinner parties. You don't know what else happens at these gatherings that I don't tell you about. Oh, the Parcheesi games . . .)

In response to my news about the weather coming from outer space, one member of the dinner party asked, "Where does space start, anyway?"

Looking back to Earth from a shuttle in outer space
(Photo from

There was much discussion about this. I said that it was outside the earth's atmosphere, but none of us knew how far above the earth's surface you have to go to get to space. We made lots of guesses and speculations: as far away as it is to drive from here to California? 300 miles? 1,000 miles?

The question itched at me, and I asked my host, who is a teacher, if she had any sort of science textbook on hand. I remembered, once upon a time in my grade school career, seeing a diagram that showed the various levels of the earth's atmosphere with arrows and measurements indicating how high up they were. Sadly, my host said she had no such book, but that if I wanted to, I could go get on yon internet and look it up. Like the absolute giddy nerd that I am, I ran up to her computer room and got to Googling.

I found the answer, shared it with my fellow dinner-eaters, and together we marveled at this fact:
  • Outer space is defined as starting 62 miles above the Earth's surface. This is not far.
  • If you could drive your car to outer space, and if you drove 60 miles an hour, it would take you just over an hour to get there.
  • Here's another perspective on it: most commercial airline jets fly at 36,000 feet. That's about 6.8 miles, or 1/10 of the distance to get to outer space.

This diagram shows lots of the stuff that's up in the air at their respective heights. On this diagram, space starts at the 100 km mark.
(Diagram from Kowoma's GPS Explained page)

  • That 62 mile marker is totally arbitrary, by the way. The unit of measurement that scientists use is kilometers, and 62 miles equals 100 kilometers. So some scientist at some point seems to have picked a nice round number for the place where space begins.
  • One scientist argues that the true beginning of space should be defined as the place where the Earth's gravitational pull no longer has any effect on you. The place, he argues, where your home can no longer draw you back to it.
  • The rough location where Earth's gravity wouldn't affect you is 13 million miles away (a.k.a. 21 million kilometers). Now that is outer space.

The view from where outer space starts, or 62 miles above the Earth's surface. Looks pretty outer-spacey to me. I mean, I wouldn't want to be out there all by myself.
(Photo from Space Today Online)

  • But okay, let's say you want to go to regular old 62-mile-away space. That's not that far, as we've established. So why don't people go there more often?
  • Because to get there, you have to overcome that pervasive and mysterious force that no one really understands: gravity. It's one thing to say you're going to get past Earth's gravitational pull. It's another thing to actually do it.
  • To get yourself up in the air, you have to use a force greater than the force that's pulling you down to the ground (32 feet per second per second). Think about how hard it is for you to jump very high. Think about what a big deal we all make of it when a basketball player can jump high enough to grab a basketball out of the air and dunk it into a basket. That's only a few feet. And we're trying to go 62 miles.
  • (By the way, the record for the highest slam dunk goes to Michael Wilson of the Harlem Globetrotters, who dunked the ball successfully into a 12-foot hoop. That's not even 1/27,000 of the distance we're shooting for here.)

The celebrated Michael Jordan, performing one of his signature slam dunks. The top of his hoop is only 10 feet high -- not even as high as the one dunked into by the world record holder.
(Photo from

  • To get outside the realm of the Earth's gravity, you have to go fast enough to overcome the force of gravity itself, multiplied by the mass of the Earth, divided by its radius.
  • Leaving out all the messy math, this works out to be 11.2 kilometers per second. That's also known as 7 miles per second, or 25 thousand miles per hour.
  • To reach 25,000 mph, you have to have a huge force propelling you up there.
  • But of course you can't shoot just your body up into space -- you would burn up on the way out of the atmosphere. So you've got to have the appropriate pressurized suit, and the oxygen tanks so you can breathe up there, and you'd better put it all in a vehicle of some sort. So you'll need to get yourself a rocket ship.

You can get your very own Apollo Moon Suit replica, built to replicate those worn by the astronauts on the Apollo missions, for a mere $2,460 from the Space Store. The suits are custom-made, so you get no returns, no discounts.

  • Assuming you're going to use the same sort of rockets that NASA uses, your rocket by itself won't weigh all that much, only about 165,000 pounds. When you add the necessary boosters, it goes up to about 428,000 pounds.
  • But generally speaking, the amount of fuel you need for your rocket is in a ratio of 36:1. So, when you add the amount of fuel you need to your rocket and the boosters, you get an entire package that weighs around 4.4 million pounds.
  • Then, because your fuel is going to burn up wicked-fast -- in about 8 minutes, actually -- you'd better bring enough fuel to generate 4.5 million pounds of thrust.
  • Different rockets are propelled by different types of fuel, depending on their destination (the moon, Mars, someplace else). One option is to use liquid hydrogen in one tank and liquid oxygen in the other. Then let these two things get together, but in a controlled way, and you have an explosion strong enough to propel that 4.4 million pounds of stuff 62 miles, and then some.

The space shuttle Discovery's first launch on July 4, 2006. All that fuel interacting and exploding is what makes those huge billowing clouds of smoke.
(Photo from NASA)

  • The whole feat is so difficult to accomplish that if you can get your rocket to make it even 50 miles up, NASA will give you astronaut status.

All that to go 62 miles up. I'm going to think about this the next time I'm driving 62 miles horizontally, more or less.

Oh, and if you want to go on to the moon, you've got another 238,732 miles to go. But maybe after that first 62, the rest is cake.

"How High is Space?" Space Today Online
Seth Shostak, "Gray area where space begins,", reprinted at, June 25, 2004
What is Space? Space I: Worksheet 9, Native Access to Engineering Programme, Concordia University, Montreal
Katrina C. Arabe, Ride a White Hot Rocket, Industrial Market Trends, August 4, 2004
NASA Facts Online, Propellants


  1. Hi, I'm a writer with Geotimes magazine. I'm looking for a diagram of Earth's atmosphere to illustrate one of my articles and I came across your lovely image. Do you have a high-resolution copy you'd be willing to let us use? You'd be given credit in the magazine. Please email me at

    Thanks! Mary Morton

  2. It can't get any better than this.


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