May 26 – Faster Than A Speeding Bullet

Today’s factismal: The fastest humans ever were the crew of the Apollo 10 moon mission, which rocketed back to Earth at an astounding 24,791 mph!

The problem with going into space is that you eventually have to come back. And the farther that you come back from, the faster you fly on re-entry. This happens because gravity is what physicists call a “conservative force”. That doesn’t have anything to do with how physicists vote; instead, it means that when you surrender to gravity, you get back all of the energy you put into fighting it with rockets.

The plan for the Apollo 10 mission (Image courtesy NASA)

The plan for the Apollo 10 mission
(Image courtesy NASA)

Perhaps the most extreme example of this was the Apollo 10 moon mission, crewed by Thomas Stafford, John Young, and Eugene Cernan. This was to be the last mission before an actual landing, and so it would test every system. The crew would go into lunar orbit, fly the lander to within nine miles of the lunar surface (Stafford would later say that it was so close he could almost touch it), and then rendezvous with the command capsule before heading back to Earth. To get back to Earth, all they had to do was break free of the Moon’s gravity and then fall all the way back.

The Apollo 11 capsule re-enters the Earth's atmosphere (Image courtesy Honeysuckle Creek tracking station)

The Apollo 11 capsule re-enters the Earth’s atmosphere
(Image courtesy Honeysuckle Creek tracking station)

And fall they did. Slowly at first, and then moving faster and faster. By the end of their fall, they were moving at 24,791 mph. To put that into perspective, they flashed across a distance equal to the width of the conterminous US every seven minutes and one equal to the circumference of the Earth in an hour. Looked at another way, they were moving as fast as the meteor that exploded over Russia earlier this year.

And that’s where you come in. You see, aeronautical engineers are interested in meteors because they happen to move through the atmosphere at the same speed that a returning spacecraft does, but are a lot less expensive to experiment on (because Mama Nature gives them to us for free). So they’d love to hear about any fireballs that you see. To report them, head on over to the American Meteor Society’s website. It is fun and free!
http://www.amsmeteors.org/members/fireball/report-a-fireball

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