The math of space travel

Over on my sci-fi blog, I have printed many of the predictions of Arthur C. Clarke. Some were from novels and stories, others from essays or public appearances where he was asked to look into the future of the next few decades. This week, I printed his prediction that Earth to Saturn would take about seven months, which in his book 2001: A Space Odyssey is done by a manned spacecraft. In reality, we have only sent unmanned craft anywhere farther than our own Moon and the Cassini-Huygens unmanned trip to Saturn took seven years.

Achieving what we consider high speeds in outer space is easier than it is here on Earth. The constraints of friction and gravity are reduced to nearly nothing, so a single burst of propulsion can get a very big result with very little slowing down over time because of drag.  One of the problems is slowing down, which will take another big burst of propulsion in the opposite direction.  One of the Apollo missions clocked speeds of 25,000 miles per hour. (For my non-Yankee readers, that's about 40,000 kilometers per hour.)

The thing is, in outer space 25,000 mph is not all that fast. To get to Saturn in seven months, you would have to average 150,000 mph.

And then there's interstellar travel, much, much farther away than any of our planets. At those distances, a million miles an hour is pathetically slow. The nearest star that isn't our Sun is about 3,000 years away at a million miles per hour.

Okay, so let's go a billion miles per hour!  Then it's less than three years.  Well, then we run into another problem that Einstein and others say is insurmountable and that's the speed of light, which is about 670 million miles per hour, or just over one billion kilometers per hour.

Weight has no meaning without gravity, but mass is real regardless. I would weigh less than a toddler on the moon, but I'd still be the same size, the same mass. The thing is, objects gain mass as they go faster, and one of Einstein's theories is that the speed of light is a barrier we can't get past, the increase in mass being so great that the amount of energy needed to go faster would be beyond the limits of anything in the universe. In most of our favorite outer space sci-fi movies and TV shows, there are some tricks that can be pulled to get around this barrier and go faster than light speed, but this is more fiction than science. William Shatner, the actor known best as Captain Kirk, is fond of saying Star Trek is science fiction and Star Wars science fantasy. But both of those fictional universes (and so many others) rely on space travel being possible because of faster than light speeds, a nut that we may never be able to crack.

(Sorry to be such a buzzkill. Happy Easter and enjoy the Games of Thrones season premiere this evening.)