by Karim Sultan

Created on: January 29, 2009

When one thinks of a spacecraft, images of star destroyers from Star Wars, the Enterprise from Star Trek, and the Discovery One from 2001: A Space Odyssey may come to mind. A contemporary view includes NASA's space shuttles and the Russian Soyuz series. But early satellites such as Voyager (USA), Sputnik (Russia) and Anik A1 (Canada) were also considered spacecrafts in their day. For the purpose of this article, we'll take a look at the requirements of a modern day manned spacecraft, capable of achieving launch from a planetary body as well as space travel.

Fuel

In order for a spacecraft to launch, it must be capable of generating enough thrust to overcome the planetary gravity well and achieve escape velocity. Although aerodynamics is important while in the atmosphere, they are meaningless once the spacecraft is in space. Airplanes achieve flight based on the movement of air over their wings; at high altitudes they require more thrust due to air density and every airplane has a maximum ceiling. A rocket can provide the thrust required for a spacecraft, but requires considerable fuel. Early fuels were often dangerous; the Saturn rocket series used an extremely volatile liquid oxygen fuel source. Later advances in the Titan rocket program lead to a binary fuel, which ignited when nitrogen tetroxide and hydrazine were combined. This fuel source was toxic and expensive, and lead to liquid hydrogen and the eventual development of refined petroleum (RP-1).

The main concerns with fuel are threefold: the mass of the propellant, the volume of the propellant, and the specific impulse of the propellant. The complex equation constantly being juggled by rocket scientists is what is the best fuel choice based on mission parameters, payload mass and budget restrictions. A highly effective fuel source such as liquid hydrogen is expensive and requires tremendous amounts of room in booster rockets, while RP-1, although less efficient in terms of specific impulse, is seven times denser.

The choice of fuel affects cost and ultimately available payload. A reusable spacecraft design usually incorporates booster rockets for launch, which separate as exhausted, and rely on the spacecraft being able to reenter the atmosphere by its own means. Propellant needs to be reserved for maneuvering while travelling in space; any design would need to accommodate extra fuel (and its mass) for this task. Launching again from a foreign planetary body (such as Mars) would require establishing a fuel

• 1
• 2
• 3
• Next Page >>