My research is in plasma physics and propulsion with a focus on practical applications. To develop new technologies you have to push against the boundary of what is known, and that take times and usually happens in small incremental steps. In other words the new technology is only a little better than the current technology. For some things like computers and smartphones, a little better seems to sell, thus a new iphone every 6 months, even though they may not be a substantial improvement over the previous version. However in spacecrafts and propulsion, a little better isn’t good enough. The motto of propulsion has always been bigger, better, and faster engines. However in recent times an additional property has been added, cheaper. Now that seems to be at odds with the previous three. How do you get a bigger engine for less money?
Better and cheaper is usually an oxymoron for technology. To make something better, usually in performance, requires improvements in materials, science, coding, and so forth. All that of course takes time which costs money. Then if you have to use higher performance materials or components, those cost more money. Lets say you want a higher performance jet engine for airplanes. Maybe you run the engine faster or hotter to get more thrust. That requires higher strength materials to withstand the higher temperatures and stresses. If the engine runs faster, you may need more robust gears or shafts to transfer the force. Thus the engine is more expensive.
The exception to the rule where you can get cheaper and better, eventually, is when a paradigm shifting technology or process comes along. Computers are a prime example, or rather the production of computer chips. Computer used to run on vacuum tubes and punch cards and took and entire room. Then came the discovery of semi-conductor materials, transistors, and the methods to produce them. Now computers can fit on a desk. Now the technology to produce computer chips continues to advance to make smaller and smaller transistors. This allows you to put more and more transistors on a square inch of silicon. This not only allows you to increase the computer speed, but also means you can make lower performance chips using less material thus less money. Thus today the $100 tablet is much more powerful than the room sized computer of the 60’s.
So to get bigger, better, and cheaper you need a paradigm shifting new technology. In space and propulsion, those are harder to come by. We are currently push up against the theoretical limits of jet and rocket engines. There’s just not much more room to improve according to the laws of physics. So there’s not alot of impetus to develop new engines. New jet engines are still being developed not necessary for better performance, but to reduce emission and operating costs. Currently there is some rocket engine development occuring in the US. Aerojet and Orbital ATK are both spending their own money to develop a new liquid rocket engine, though it’s not going to be drastically better than the existing engines. The RS-25, better known as the Space Shuttle Main Engine, is the highest performaning rocket engine ever developed by humans. It is also horrendously complicated and expensive. The new engines are unlikely to try and meet or beat the SSME’s performance. So why is money being spent to develop a new engine that’s not going to better than the best we have? The answer is politics. The new engines are being developed to replace the Russian RD-180 which we currently buy from Russian to power the Delta and Atlas rockets. Given the recent tensions with Russia, Congress has decided giving money for rocket engines is bad. So this is a case of not better, not cheaper, but necessary due to non-technology issues.
In my mind, there are two contenters for paradigm shifting technology in propulsion: nuclear, and addition manufacturing (3D printing). Fusion propulsion has the potential to make interplanetary travel much faster and eventually cheaper. But the technology is still in its early stages and will be very expensive to develop. So fusion propulsion can satisfy the better desire. The cheaper part could be fullfillled by 3D printing. Additive manufacturing can greatly reduce the time and cost to produce components, which will make things cheaper. It also has the potential to make very complex components which may improve performance if designed correctly. Companies have already 3D printed small rocket engines or parts of rocket engines and shown the parts can survive the high temperatures and pressures. Initially 3D printed parts won’t have better performance than their conventional counterparts, and in some cases may have worse performance. But as the technology is further developed, 3D printed engines could also reach the better criteria.