Responding to a critique

At the Baycon 2009 writer’s Workshop one of the points of feedback I received was on the orbital skydiving sequence that makes up the heart of Chapter one of Love and Loyalty. The person felt that orbital skydiving could never be a sport for anyone other than millionaires because of the costs of getting to orbit. That is true today, but I do not thin it will always be true. So as a thought experiment lets look at just the energy costs to lift a kilogram to orbit.

Getting to orbit, and for this post I am just talking about Low Earth Orbit (LEO) is primarily  composed of two factors, speed and altitude. Each of these has an energy cost that can be expressed in the lowest possible terms. For speed it is Ke=½MV², and for height it is Pe=mgh.

LEO orbital velocity is about 7800 m/s, there are factor for atmospheric drag and even something called gravity drag which add another 2000 m/s for a total of 9800 m/s required for LEO. So if we plug those values into the formula for Kinetic energy, Ke=½MV², Ke= 1/2(1)(9800)², or Ke=48,020,000 joules/kilogram.

For altitude we can plug in those number to get the energy cost to lift something to that height.  the low end of LEO is  160 kilometers or about 160000 meters. So the potential energy values are; Pe=(1)(9.8)(160000). [g= gravity for the earth that is 9.8 m/s²] or Pe=1,568,000 joules. Total cost in Joules 49,588,000 joules.

49 million joules sounds like a lot. It’s an awfully big number. the trouble is we have nothing to reference to, we don’t use joules in everyday life so the number has no weight to it. Gasoline, that we use everyday and it has an energy value in joules. It’s what moves our cars and ourselves around.

One gallon of gasoline has 130,000,000 joules of energy more than enough to life a kilogram to orbit twice over. Of course we can’t use a single gallon of gas to to get to orbit, not with today’s technology.  Still, with an drive that takes electric powers and converts it into motive force, and cheep electric power generation (hand waving for the first and fusion for the second) orbit is suddenly very cheap in term of cost.