The Brazilian Air Force (FAB, per its Portuguese acronym) is developing an unmanned prototype of a hypersonic propulsion aircraft with a supersonic combustion engine. This strategic FAB project, dubbed Prohiper, will revolutionize the nation’s space vehicle propulsion.
Strictly speaking, hypersonic propulsion – which is any kind of aerospace propulsion that keeps a vehicle in flight in the earth’s atmosphere at speeds greater than or equal to five times the speed of sound (Mach 5) – was developed several years ago by the Institute for Advanced Studies (IEAv, per its Portuguese acronym) in the state of São Paulo in most of its space probe vehicles and in its satellite launch vehicle. The difference with Prohiper is that the hypersonic propulsion is achieved through Supersonic Combustion Ramjet or “SCRamjet” engine that uses the atmosphere as an oxidizer, carrying only fuel on the vehicle. When used together, both technologies are given the name Hypersonic Airbreathing Propulsion.
Hypersonic propulsion is conventionally achieved through solid-propellant rocket engines, with aerial vehicles carrying the fuel (alcohol, hydrogen, or kerosene) and the oxidizer (generally oxygen) inside. The SCRamjet engine uses air to burn the fuel.
“The main advantage is that it reduces the total weight of the vehicle that is being launched. That makes for a heavier useful payload that can be carried by the launch vehicle. And since the vehicle is not carrying the oxidizer next to it inside, it becomes safer, and the weight reduction increases its efficiency,” explained Lieutenant Norton Assis, hypersonic researcher, in a promotional video for the project sent by FAB. “For instance, an engine using that fuel technology is capable of making a trip from Congonhas [in São Paulo] to New York in approximately one hour, as it is able to reach a speed of 12,000 kilometers per hour, or what amounts to 10 times the speed of sound.”
The first prototype to demonstrate this technology, dubbed 14-X, exists in a model resembling a delta wing format nearly 80 centimeters in length. The 14-X is just beginning testing in IEAv’s Professor Henry T. Nagamatsu Laboratory of Aerothermodynamics and Hypersonics, home to the largest wind tunnel in Latin America.
“IEAv has been conducting lab tests of key components of these engines, also called SCRamjets, such as the air intake and the combustor chamber,” said Major Tiago Cavalcanti Rolim, the engineer in charge of the Prohiper 14-X Project and head of the Experimentation Subdivision of IEAv’s Aerothermodynamics and Hypersonics Department. “The aim is to understand certain aspects of hypersonic and supersonic combustion flows, monitoring key properties such as pressure and temperature and establishing cause-and-effect relationships,” he said.
Maj. Rolim explained that launch vehicles currently in use are equipped with conventional propulsion systems that can carry a useful payload of about 4 percent of their weight. Thanks to the absence of oxygen tanks, the 14-X technology allow for a useful payload of up to 15 percent, relative to the weight of the aircraft.
“In fact, approximately 65 percent of the weight of these vehicles at the moment of launch corresponds to the weight of the oxygen stored in them,” explained Maj. Rolim. “As a way of mitigating that situation, new technologies have been researched with the purpose of increasing the proportion of useful payload and, as a result, reducing costs. Thus, there is a consensus in the scientific community that this new aerospace propulsion system may be used as a stage on space vehicles.”
Brazil at the forefront of space engineering
In the space industry, where stringent fuel restrictions for launching useful payloads into orbit demand an ongoing reduction in launch vehicle size, weight, and fuel consumption, Prohiper places Brazil in league with the few select powers that are testing this technology. Maj. Rolim said that in recent decades the research and development of the airbreathing supersonic propulsion technology demonstrators have increased at various research centers around the world. One of the countries that stand out in the development of this technology is the United States. He cites American projects HIFiRE, which is being developed through a collaboration between the U.S. Department of Defense and Australia’s Defence Science and Technology Group, and HYPER-X, whose research began in 1996 with flight records already set.
“The main motivation for this project is for our folks to be able to provide the FAB with a defense product over a 10-year timeline that will allow us to make flights into space as cheaply as possible, carrying more useful payload into space,” stated Israel Rêgo, head of IEAv’s Aerothermodynamics and Hypersonics Laboratory. The Brazilian Air Force intends to begin flight testing the 14-X technology demonstrator by 2020. “Today, we want to get out of the laboratory and make the leap to the flight-qualification phase for these new technologies,” Rêgo said.