By Ashley Penton
Did you ever watch a NASA launch on TV when you were a kid? I missed the Apollo generation and man walking on the moon, but I watched the Space Shuttle launch on TV repeatedly. Every time was just like the first: the anticipation, the excitement, the wonder. I felt this way even on the very last Shuttle launch, which I watched as an adult at work while working on NASA’s new launch vehicle. It is still almost overwhelming to just imagine all the possibilities of what is out there in space, in worlds beyond ours.
As humans, we have a natural curiosity and a need to understand the things we see. The only way to understand these things beyond Earth is to go there… on a rocket ship! While there are certainly other applications for propulsion (travel, military, hobbyists), curiosity about space is my driving factor. The idea of launching people, probes, satellites, etc. into space to visit, study, and observe the universe around us is exciting.
The broader concept of propulsion includes both liquid and solid systems as well as everything in between (yes, there are things in between). The liquid systems are complex engines with pumps, injectors, and nozzles. They are characterized by the fuel and oxidizer they use along with their size and thrust profile (which is determined by the detailed designs of the injector, nozzle, etc.). Most people only see the big picture: such as seeing a “Space Shuttle”, rather than a launch vehicle with three liquid engines fed by an external tank, and two solid rocket boosters on its sides. The RS-25 engine is that engine that worked to launch the shuttle into space time and time again. Liquid systems are reusable with minimal refurbishment. Also, a big benefit is that a liquid engine can be throttled back, or even stopped and restarted as needed. This allows for a more precise design of the thrust while planning whatever task is needing to be accomplished. While more complexity can lead to more failure mechanisms, it also produces an amazing machine that takes in only a couple of chemicals and returns a large quantity of thrust.
Solid rockets, on the other hand, are usually considered to be the big, dumb, jock of the rocket world. They use a cured solid propellant that already contains the fuel and the oxidizer in it. With large amounts of thrust produced from a relatively simple system (adding to reliability), these rockets are great to add a boost to a larger vehicle and/or to perform a task where the rocket will not be recovered. Aside from some structural components solid rockets are not reusable anyway. While the thrust profile can be tailored with the grain design (the pattern of the hole in the middle of the propellant), once started there are limited options for stopping it on demand, and no ability to start it up again if you do manage to stop it. Despite that, there is an elegance to a system that is both so simple and so powerful.
Other propulsion systems include hybrids, gels, and castables… none of which I have worked with much, but all seem really cool too!
With my education in chemistry, mathematics, and aerospace engineering, of course I would develop an affinity for propulsion. But my love of rockets comes from the wonder of the power and magnitude of a man-made system to lift not just experiments and probes, but even people into space. We weren’t going to get there any other way; we had to blaze our own trail! While the likelihood that I’ll ever make it to space is slim, it still thrills me every time I see an astronaut or payload launched to the International Space Station, or another probe/rover launched on its way to the Mars surface. Like most rocket folks, I honestly think everyone should be as fascinated by propulsion, and the things it allows us as a species to do, as I am.