Room with a View

July 2003 - Ad Astra Magazine

You wake up after a particularly restful sleep. In your dream, you were floating. After opening your eyes, you look around -- This isn't like any hotel room that you've ever seen. You climb out of bed, try to stand up, and find yourself coming off of the floor in 1/3^rd gravity. Whoops! Now you remember where you are - over a hundred miles above anywhere you've been before; you're in space.

As the human race has progressed in our march outwards into space, we have used several different methods of getting there. Initially, multi-stage rockets were used to launch the craft into orbit. The Saturn V rocket, for example, ended up being 99% fuel to push its own weight and the remaining 1% payload. In order to do this, several stages were used, with each one dropping off after expending its fuel. Once in orbit, the final stage would ignite, sending the cargo towards the Moon.

One such fuel tank has had an alternate use; in this case a space station. After the final Apollo missions were cancelled, a surplus upper stage of a Saturn rocket was modified. Instead of an upper stage fueled for sending the command and lunar modules towards the Moon, the stage was retrofitted as a space station called Skylab. This space lab was successful, having several separate crews performing tests throughout in the spacious interior.

Where previous launch vehicles were only used once, the Space Shuttle was designed to be reusable, returning to Earth in order to be later launched again. The concept of re-using some of the launch sections was also looked at. Since it would have been extremely difficult to have the Shuttle providing the main thrust required to lift off, a plan arose where it would be augmented by an external source. This source became the Solid Rocket Boosters (SRB's). After launch, these boosters would provide the required thrust to reach a sufficient altitude with the required speed. When the fuel was almost gone, these boosters were designed to separate from the launch assembly and parachute back to Earth. After separation, the Shuttle would then provide itself with the remaining thrust to reach the orbit desired. However, in order to do this, as well as provide additional lift during liftoff, much more fuel than could be carried within the orbiter itself would be required. This is where the idea of the External Tank (ET) came in.