Permanent Human Settlement of the Earth, Space and Ocean Frontiers

Monday, April 10, 2006

Nuclear Space Travel

The first thing I learned as a US Navy Navigator was that you never sailed across the globe on a straight line (according to flat maps). Since the globe is a circle, the shortest distance between two points is a curve on that sphere. The same lesson is true in space travel. Since we are all traveling around the sun at a pretty good clip, when we launch our spacecraft away from earth, we have to launch in a curve to account for the orbit the spacecraft will be taking around the sun. As a rule, the slower the craft, the more pronounced is the circle. If you want to stretch the line out and make the trip shorter, you have to speed up.

Sorry about the space navigation lesson, but it is necessary to understand this part of the story. When we launched New Horizons to Pluto on January 19th, we launched the fastest spacecraft ever sent from earth. It passed the moon’s orbit in 9 hours, compared to the manned Apollo mission’s four days. This weekend, traveling at its amazing speed, it already passed the orbit of Mars (even though Mars was nowhere around when it crossed). That’s an unheard of rate. Normally, it takes a spacecraft around 270 days to make it out that far. New Horizons made it in just 79 days!

This is an important point. If we plan on manned launches to Mars, it would be awfully nice it make it out in 79 days. We shorten the mission and greatly reduce the risk to the crew. So why don't we then? Alas – unless we build nuclear rockets, we will not be able to. Why? Because the New Horizons weighed in at just 1000 pounds and we used the biggest rocket we had. The laws of physics absolutely prevent us from launching a much heavier manned craft on such a trajectory. Hence, we have to get busy and build the nuke ships that will make Mars travel reasonably practical.

Shown is the NASA Prometheus nuclear spacecraft concept.