In the current era of space exploration, the name of the game is “cost-effective.” By reducing the costs associated with individual launches, space agencies and private aerospace companies (aka. NewSpace) are ensuring that access to space is greater. And when it comes to the cost of launches, the single-greatest expense is that of propellant. To put it simply, breaking free to Earth’s gravity takes a lot of rocket fuel!
To address this, researchers at the University of Washington recently developed a mathematical model that describes the workings of a new launch mechanism: the rotating detonation engine (RDE). This lightweight design offers greater fuel-efficiency and is less complicated to construct. However, it comes with the rather large trade-off of being too unpredictable to be put into service right now.
If new rocket engines being developed by the European Space Agency (ESA) are successful, they could revolutionize rocket technology and change the way we get to space. The engine, called the Synergistic Air-Breathing Rocket Engine (SABRE), is designed to use atmospheric air in the early flight stages, before switching to conventional rocket mode for the final ascent to space. If all goes well, this new air-breathing rocket could be ready for test firings in about four years.
Conventional rockets have to carry an on-board oxidizer such as liquid oxygen, which is combined with fuel in the rocket’s combustion chamber. This means rockets can require in excess of 250 tons of liquid oxygen in order to function. Once this oxygen is consumed in the first stages, these used up stages are discarded, creating massive waste and expense. (Companies like SpaceX and Blue Origin are developing re-usable rockets to help circumvent this problem, but they’re still conventional rockets.)
Conventional rockets carry their own oxygen because its temperature and pressure can be controlled. This guarantees the performance of the rocket, but requires complicated systems to do so. SABRE will eliminate the need for carrying most on-board oxygen, but this is not easy to do.
SABRE’s challenge is to compress the atmospheric oxygen to about 140 atmospheres before introducing it into the engine’s combustion chambers. But compressing the oxygen to that degree raises its temperature so much that it would melt the engines. The solution to that is to cool the air with a pre-cooling heat exchanger, to the point where it’s almost a liquid. At that point, a turbine based on standard jet engine technology can compress the air to the required operating temperature.
This means that while SABRE is in Earth’s atmosphere, it uses air to burn its hydrogen fuel, rather than liquid oxygen. This gives it an 8 x improvement in propellant consumption. Once SABRE has reached about 25 km in altitude, where the air is thinner, it switches modes and operates as a standard rocket. By the time it switches modes, it’s already about 20% of the way into Earth orbit.
Like a lot of engineering challenges, understanding what needs to be done is not the hard part. Actually developing these technologies is extremely difficult, even though many people just assume engineers will be successful. The key for Reaction Engines Ltd, the company developing SABRE, is to develop the light weight heat exchangers at the heart of the engine.
Heat exchangers are common in industry, but these heat exchangers have to cool incoming air from 1000 Celsius to -150 Celsius in less than 1/100th of a second, and they have to do it while preventing frost from forming. They are extremely light, at about 100 times lighter than current technology, which will allow them to be used in aerospace for the first time. Some of the lightness factor of these new heat exchanges stems from the wall thickness of the tubing, which is less than 30 microns. That’s less than the thickness of a human hair.
Reaction Engines Limited says that these heat exchangers will have the same impact on aerospace propulsion systems that silicone chips had on computing.
A new funding agreement with the ESA will provide Reaction Engines with 10 million Euros for continued development of SABRE. This will add to the 50 million Pounds that the UK Space Agency has already contributed. That 50 million Pound investment was the result of a favorable viability review of SABRE that the ESA performed in 2010.
IN 2012, the pre-cooler and the heat exchangers were tested. After that came more R&D, including the development of altitude-compensating rocket nozzles, thrust chamber cooling, and air intakes.
Now that the feasibility of SABRE has been strengthened, Reaction Engines wants to build a ground demonstrator engine by 2020. If the continued development of SABRE goes well, and if testing by 2020 is successful, then these Air Breathing rocket engines will be in a position to truly revolutionize access to space.
In ESA’s words, “ESA are confident that a ground test of a sub-scale engine can be successfully performed to demonstrate the flight regime and cycle and will be a critical milestone in the development of this program and a major breakthrough in propulsion worldwide.”
The technology, which sounds straight out of a science-fiction movie, has enough reality to it for the United Kingdom government to offer $90.62 million (£60 million), in stages, to a company looking to develop the engine.
Skylon isn’t flight-ready yet, but so far the project did pass a United Kingdom Space Agency technical assessment. If completed, the UK Space Agency says Skylon is just one of many vehicles that could use this engine, which is called Sabre.
“The unique engine is designed to extract the oxygen it needs for low atmosphere flight from the air itself, paving the way for a new generation of spaceplanes which would be lighter, reusable and able to take off and launch from conventional airport runways,” the agency stated.
The money, stated Reaction Engines founder Alan Bond, will fund “the next phase in the development of its engine and heat management technology.” More specifically, this is what the company plans to use the funds for:
– Engine technical design work;
– Improving lightweight heat exchanger technology and manufacturing;
– Performing wind tunnel and flight testing of engine components;
– Doing a “ground demonstration” of the engine.
If all stays to schedule, Reaction Engines expects a Sabre prototype will be ready in 2017, with flight tests commencing in 2020.
The major goal of Sabre is to use hot air entering the engine to obtain the required oxygen for operations, rather than carrying the gas separately on board. The engine is supposed to switch to a “rocket mode” at 26,000 feet in altitude.
“This advantage enables a spaceplane to fly lighter from the outset and to make a single leap to orbit, rather than using and dumping propellant stages on the ascent – as is the case with current expendable rockets,” the UK Space Agency stated.
Reaction Engines promises Skylon would give “reliable access to space” through carrying payloads of up to 15 tonnes, but at only 2% of the cost of more conventional launch vehicles — namely, rockets. It remains to be seen if they will achieve that cost goal, but the funding is welcome news nonetheless for the company.
That’s a lot of power under one roof! For the first time in… well, ever… all fifteen Space Shuttle Main Engines (SSMEs) are together inside NASA’s Engine Shop at Kennedy Space Center. They will be prepped for shipment to Stennis Space Center in Mississippi where they’ll become part of the propulsion used on NASA’s next generation heavy-lift rocket: the Space Launch System.
The engines, built by Pratt & Whitney Rocketdyne, are each 14 feet (4.2 meters) long & 7.5 feet (2.3 meters) in diameter at the end of its nozzle, and weighs approximately 7,000 lbs (3175 kg).
Each engine is capable of generating a force of nearly 400,000 pounds (lbf) of thrust at liftoff, and consumes 350 gallons (1,340 liters) of fuel per second. They are engineered to burn liquid hydrogen and liquid oxygen, creating exhaust composed primarily of water vapor.
The engines will be incorporated into the Space Launch System (SLS), which is designed to carry the Orion Multi-Purpose Crew Vehicle – also currently in development – as well as serve as backup for commercial and international transportation to the ISS. By utilizing current technology and adapting it for future needs, NASA will be able to make the next leap in human spaceflight and space exploration – while getting the most “bang” out of the taxpayers’ bucks.
“NASA has been making steady progress toward realizing the president’s goal of deep space exploration, while doing so in a more affordable way. We have been driving down the costs on the Space Launch System and Orion contracts by adopting new ways of doing business and project hundreds of millions of dollars of savings each year.”
– NASA Deputy Administrator Lori Garver
While it’s sad to see these amazing machines removed from the shuttles, it’s good to know that they still have plenty of life left in them and will soon once again be able to take people into orbit and beyond!