Tuesday, October 31, 2006

A week of decisons

"Reasonable people adapt themselves to the world. Unreasonable people attempt to adapt the world to themselves. All progress, therefore, depends on unreasonable people." - George Bernard Shaw.

I'm starting an effort at competing in the
Xprize Cup Lunar Lander Challenge.
It is a hard problem, not because any one part is hard but becuase there are many different parts that need to work together.

The basic technical requirement is that you build a rocket powered vehicle that can hover for 180 seconds. This basic physical fact is goverend by the rocket equation.

DV -- Delta V or change in velocity (DV needs to be > 1800 m/sec)
ISP -- a measuremnt of rocket engine efficency. It is the number of seconds that you can make one pound of thrust with one pound of propellant.
G is acceleration due to gravity. (9.81 m/sec^2)
ln is the natural log.
Mi is the Mass Initial. Or the weight of the vehicle including fuel at the beginning of the burn.
Mf is the Mass Final or the weight of the vehicle at the end of the burn. (the empty weight of the vehicle if you burn till its empty)
You can control some of these, specifically you want Mf or the empty weight of the vehicle to be as low as possible. You want the ISP of the engine to be as high as possible.
You get high ISP by running high rocket chamber pressures (but this makes tanks heavier)
Lots ot technical trade offs.

Beyond the mere technical decisions bussired in the rocket equation there are a host of decisons that are more mundane.

  • Where can you test a rocket?
  • What will the AST (government) let you test.
  • Do you build things in your shop or hire out to have part made.
  • What parts do you buy?
  • What parts do you design and build yourself?
  • What fuel do you use?
  • Whoose rocket design advice do you trust?
  • Do you buy an almost working design from a potential competitor?
  • Do you have the budget to be able to do this at all?
All of these questions need answers and a plan for resolution.
Drawing a rocket design on a CAD system is one thing. Getting it built with real valves and a real electronics is another.

In the comming days I will talk about all of these issues.