Where can I buy one?
Posted by aogSaturday, 17 January 2004 at 22:31 TrackBack Ping URL

Via Instantman is a report on paraffin as a rocket fuel. It’s used in what is called “hybrid” motor where a solid fuel is burned in combination with a liquid or gaseous oxidizer.

One form of this has been in use in model rocketry for a while. In that form, the solid is cellulose and the fluid is nitrous oxide. As might be expected in these days, the primary motivator was coping with federal regulations.

The new work with paraffin may be very interesting, depending on what the net thrust (or specific impulse (aka Isp) is. But it’s important to remember that specific impulse isn’t the only consideration for rocket fuels. Transport and handling costs aren’t insignificant. There’s also the size of the space ship. Although the oxygen/hydrogen reaction has a very high Isp (which was why it was used for the Saturn rockets) it also has a high cost. The density of even liquid hydrogen is low so that one needs huge cyrogenic camps to hold it. The weight of those tanks has the effect of lowering the effective Isp of the system. This is where hybrid motors shine. The tank to hold paraffin needs no (heavy) cryogenic support and it can be far smaller because of the much higher density.

It is here we see the real failure of NASA. Because it’s the government, they will always go for the top end, highest performance choices despite their drawbacks in practice. This stems from the lack of business realities in a government agency. Unfortunately, at this point in time it is precisely that kind of concern that is the primary economic impediment to space flight.

P.S. As a side note one need only look at SpaceShip One project which has been designed, built, and made multiple test flights for about $2 million. Does any reader seriously think NASA could even put out just the RFP for something like this for less than $2 million?