Aerospace companies are striving to reduce the cost of space travel, as much as they could. In fact, the very origin of Elon Musk’s SpaceX is based on his intention to make affordable rockets. Even though his vision is slowly getting clear, a group of engineers thinks they can reduce the cost even further. However, their prototype might sound paradoxical within the realm of Aerospace. But, before we get there, it is important to understand how a traditional rocket motor works. Along with that, we will see how it is different from that of a Jet Engine(this is really important!).
Traditional Rocket Motor
Traditional Rocket Motor or Engine will have fuel and oxidizer. Depending on the phase that they are stored in, there is Solid Rocket Motor and a Liquid Rocket Engine. In the case of a Solid Rocket Motor, both fuel and oxidizer are kept separately on either end of a combustion chamber. Hence, when a spark is initiated using a pyrotechnic plug, the fuel will burn in an oxidative atmosphere. As a result, the combustion gas is formed, which is then pushed out through the nozzle. Following Newton’s Third Law of Motion, this exhaust gas will cause the rocket to lift up. In the case of a Liquid Rocket Engine, instead of fuel and oxidizer stored in the solid phase, tanks are used to hold them. Generally, Liquid Engines are considered to be the safest engine for human spaceflight.
Jet or air-breathing Engine
Jet Engine is similar to Rocket Engines in terms of the working principle. It follows Newton’s Third Law, but the difference is its architecture. While rocket motors would need a separate oxidizer, Jet engines suck air from the atmosphere. Hence, you don’t need a separate oxidizer tank for Jet engines. But, their applications are fairly limited to places wherein there is enough oxygen in the atmosphere. For spaceflight, Rocket motors are essential. Because space is a vacuum. Generally, Jet engines are said to have higher efficiency when compared to rocket engines.
Air-breathing Rocket Motor: Fenris
“Fenris” engine is different from a traditional rocket motor and a jet engine. Essentially, “Fenris” is a Single Stage to Orbit(SSTO) rocket with an air-breathing engine. Being an air-breathing rocket motor, you don’t need an oxidizer tank for driving the “Fenris” engine – similar to a jet engine. But, at the same time, “Fenris” is akin to a rocket motor – it doesn’t have any limitations for altitude. Once the rocket starts its operation, it will take air from the atmosphere to use it as an oxidizer. In other words, “Fenris” is a prudent crossover of both jet engine and rocket motor.
Combining Jet Engine and Rocket Motor
“Fenris” will use the advantages of both the Jet engine and rocket motor. Like said before, “Fenris” doesn’t have an oxidizer tank, but can break out of our earth’s atmosphere. Recently, to bring clarity over this concept, Christopher Goyne explained how such an engine would work.
“The idea is to use air-breathing engines earlier in the launch to take advantage of efficiency gains from engines that don’t have to carry their own oxidizer,” says Goyne. “Once you get high enough in the atmosphere, you start to run out of the air for the air-breathing system and you can use the rocket for that final boost to orbit.”
Christopher Goyne is the director of the University of Virginia’s Aerospace Research Laboratory. In addition to that, he is also an expert in the realm of hypersonic flight.
How does it work?
“Fenris” engine is one of a kind technology. Hence, working is a bit unconventional. But, definitely worth knowing. So, “Fenris” will act as both a jet engine and a rocket motor. When it is within the earth’s atmosphere, it will make use of an air-breathing engine for thrust. Firstly, gasoline is filled as the fuel, and once the ignition starts the engine will start generating thrust. Subsequently, as if it travels at higher speed, the ramming effect will compress the air surrounding it, and will make it flow into the combustion chamber. Therefore, keeping a constant supply of oxygen when the combustion takes plus. After a while, the engine will enter a space wherein there is a lack of oxygen. In such cases, “Fenris” will switch to a rocket motor. It will burn like a rocket till it reaches its orbit.
Zero moving parts
One of the advantages of the “Fenris” engine is that it doesn’t have any moving parts. As a result, the mechanical efficiency will be high, since there is no frictional loss. Furthermore, this gives the engine a greater overall efficiency, when compared with the traditional one.
Now you must be wondering, how the air can flow without a moving part. The answer to it is the Tesla valve. Developed by the prodigal Serbian-American inventor, Nikola Tesla, the Tesla valve is a fixed-geometry passive check valve. It helps to maintain the flow of fluid or air through a passage in one direction, without any moving parts. The interior of this valve is provided with enlargements, buckets. Generally, when the air flows through this conduit, there is no resistance to its passage, other than surface friction. In fact, it is this surface friction that constitutes an almost impassable barrier to its flow in the opposite direction.
How will it reduce the cost of space travel?
“Fenris” is the brainchild of Aaron Davis, an investor, and an aerospace enthusiast. He believes that his rocket will cut the total requirement of oxidizer by 20%. This will not only decrease the size of the rocket but would also decrease its overall weight. In other words, the materials for building rockets would drop, as well as the cost of buying oxidizer would also shrink. As of now, Davis has spent $500,000 in developing the prototype. At one point, he lacked the funds required for running advanced simulations tests. But, that didn’t stop him. He built a physical prototype and tested it by himself.
“At the end of the day, you can make really pretty simulations and nobody’s going to believe you,” Davis says. “It was cheaper to just go out and test whether my idea was valid or not.”
Although it is ambitious to claim “Fenris” as a potential replacement for SpaceX’s reusable rockets, Davis’ engine is definitely an interesting one. But, it is important for the rocket to get patented, so that we would know more of its specifications.
Is it a practical engine?
Even though “Fenris” sounds attractive, it still needs some work. According to Adonios Karpetis, an Aerospace Engineer, “Fenris” would need to up its feasibility, if it is to be used for human spaceflight missions. “The one static fire test of the Fenris device took place at zero speed,” says Karpetis. “What will happen when the Fenris device becomes truly supersonic and the air is rushing into it through the inlet at high speeds? A simple guess would predict diminishing behavior, quickly reducing the 600 seconds specific impulse to some lesser value.” In addition to Adonios Karpetis, Professor of Aerospace Engineering, Dan Erwin, too, shared his concerns. “I am skeptical of the entire concept”, he said.
To sum up, whether or not it is practical, Davis and his “Fenris” engine have surely achieved something that many aerospace companies haven’t. We are talking about NASA and Rolls Royce. Prior to Davis’ work, both NASA and Rolls Royce stopped experimenting with this model after running into a financial burden. As a result, air-breathing rocket engines went extinct. But, fortunately, it is back. Needless to say, it is better and seems achievable. However, before we jump into any conclusions, it is important for us to wait until the model gets patented and sets its first flight.