Game Development Reference
In-Depth Information
at temperatures below 90
K
(-297
o
F
). Commonly used fuels in liquid-cryogenic rocket engines
include liquid hydrogen and kerosene, although kerosene does not have to be kept at very low
temperatures. Cryogenic propellants provide better performance than solid propellants, but
the internal structure of a liquid-cryogenic rocket must be designed to deal with the very low
temperature requirements. One advantage of liquid-cryogenic rocket engines and liquid
rocket engines in general is that they can be throttled up or down to provide variable thrust.
Solid-Propellant Engines
Modern solid rocket engines are descendants of the very first rockets that used gunpowder as
the propellant. Solid rocket engines are simpler than liquid engines in that there are no fuel
pumps or propellant feed systems to worry about. The oxidizer and fuel are mixed together and
generally held in a casing made out of steel.
Solid rocket propellants can be quite exotic in their chemical makeup and can look nothing
like the gunpowder used of old. The Space Shuttle solid rocket boosters use a mixture of
ammonium perchlorate and powdered aluminum that has a consistency similar to a pencil
eraser. Unlike liquid rocket engines, solid rocket engines are generally not throttleable and
can't be shut down once they are ignited.
Liquid-Hypergolic Engines
Liquid-hypergolic engines use volatile propellants that ignite when they come in contact with
each other. There is no need to provide an ignition source. Because of their easy start and
restart capability, liquid-hypergolic engines are typically used to make small changes to the
attitude or position of a rocket or spacecraft once it is in outer space. Despite their volatile
nature, hypergolic propellants have a storage advantage over cryogenics in that they do not
need to be kept at ultra-low temperatures.
Hybrid Engines
A hybrid rocket engine is one that uses both liquid and solid fuels. Burt Rutan's privately built
SpaceShipOne rocket uses liquid nitrous oxide and a special type of rubber as the propellants
for the rocket engine.
Nuclear Engines
Nuclear rocket engines use a fission reaction to heat a reactor core to a very high temperature.
The propellant gas hydrogen is commonly used; it flows through the core and becomes super-
heated. The propellant gas exits the rocket nozzle at very high velocity. Nuclear engines can
achieve greater thrust for a given rate of propellant flow than liquid or solid rocket engines.
Exotic Engines
The great thing about being a game developer is that you can let your imagination run wild a
bit when you are creating a rocket simulation. Most of us are familiar with
Star Trek
and the
Warp Drive engines used to power the starships. You might also conceive of a rocket engine
driven by antimatter or by other exotic means. The key to using an exotic rocket engine in a
game simulation is coming up with an estimate of the thrust produced by the engine.
