Every significant rocket ever launched into space has used the same shape to direct the fire that comes out of the tail — it looks like a bell, and it's inefficient. For a rocket, small inefficiencies translate into greatly enlarged costs in sending stuff to space. Inefficiencies mean it's more expensive to launch the satellites that enable TV broadcasting, weather forecasting, GPS and other technologies that we use every day on Earth. One potentially better replacement for this bell-shaped nozzle is called an “aerospike," which is a concept that has existed since the 1950s, but that has yet to propel any rocket into orbit because of a lack of experimental data to support the decades of theory of its operation. Simply put, it seems that few people are experimenting with aerospikes because few people have before, leading to a cycle in which the development of the concept has stagnated and space companies are unwilling to take on the risk of building this “unproven" technology.
My senior thesis aimed to provide some of that experimental data and renew interest in the aerospike. I have designed two scaled-down rockets, one with the classic bell-shaped nozzle and one with an aerospike, and am using wind tunnels available on Princeton's campus to simulate their launch at twice the speed of sound. The data provided by these experiments will hopefully support the theory that aerospikes can operate more efficiently than bell nozzles and encourage other research and industry groups to use the aerospike on full-scale rockets.