Future Spaceplanes shall enable intercontinental travel at very high speeds, travelling on a sub-orbital trajectory, journey times from the UK to Australia could be cut from the current duration of around 20 hours to as little as two hours. Engineers are developing space launch systems intended to place satellites in low Earth orbit, and even to transport people to the edge of space.
Hypersonic manned and unmanned planes, missiles and weapons are also being developed to provide revolutionary military capability like prompt global strike, launch on demand, satellite servicing and antisatellite missions. Systems that operate at hypersonic speeds offer the potential for military operations from longer ranges with shorter response times and enhanced effectiveness compared to current military systems. Such systems could provide significant payoff for future U.S. operations, particularly as adversaries’ capabilities advance.
NASA categorizes speeds between Mach 5 ( 6125 kilometers per hour) to 10 Machs as Hypersonic. Aerodynamic drag roughly scales with the square of airspeed; double the speed, and the drag goes up four times. Streamlined shapes have partly overcome this problem, but the solution then, as it is now, is more thrust.
However development of reusable aircraft that can reach hypersonic speeds—Mach 5 (approximately 3,300 miles per hour/5,300 kilometers per hour) and above has been riddled with two intertwined, seemingly intractable challenges: The top speed of traditional jet-turbine engines maxes out at roughly Mach 2.5, while hypersonic engines such as scramjets cannot provide effective thrust at speeds much below Mach 3.5. This gap in capability means that any air-breathing hypersonic vehicles developed today would use disposable rockets for one-time boosts up to operating speed, limiting the vehicles’ usefulness.
Therefore countries are experimenting with new concepts and developing next generation engine technologies for hypersonic flight.
New concepts and next generation engine technologies for hypersonic flight.
The European LAPCAT-II program continues advancing the development of a hypersonic civil transport. The program includes a Mach 5 airliner powered by a precooled air-turbo ramjet, and a Mach 8 airplane powered by a ramjet engine, both fueled by LH2. This four-year program is co-funded by the European Commission under the theme of air transportation. It involves 16 partners representing six European member states.
Reaction Engines have come up with the concept Skylon spaceplane to demonstrate how its SABRE engine could make space access much easier . It’s an unpiloted, reusable vehicle that would be capable of transporting 15 tonnes of cargo into space. Reaction Engines is hoping to start test flights of Skylon in 2019.
Orbital Access Ltd announced December 7, 2016 that it has been awarded a £250,000 grant by the UK Space Agency to technically and commercially evaluate a roadmap for UK small space payload launchers. The project, coined FSPLUK, aims to define an initial commercially viable launch system able to be brought to service by 2020 leading to a fully re-usable system for services to start in 2030. The project focusses on horizontal take-off launch systems to exploit the UK’s forthcoming spaceport. The FSPLUK project team led by Orbital Access comprises BAE SYSTEMS, Reaction Engines, Fluid Gravity Engineering, the Universities of Glasgow and Strathclyde, Surrey Satellite Technologies, Clyde Space and the STFC.
According to multiple reports, Russia is expected to begin production soon of its 3M22 Zircon, a hypersonic missile that will travel 4,600 miles per hour — five times the speed of sound — and will have a range of 250 miles. The missile employs revolutionary scramjet technology to reach its hypersonic speeds whereby propulsion is created by forcing air from the atmosphere into its combustor where it mixes with on-board fuel – rather than carry both fuel and oxidizer like traditional rockets. This makes it lighter, and therefore much faster. “It uses no fans, rotating turbines or moving parts – just an inlet where air is compressed and a combustor where the air is mixed with fuel. Fewer moving parts also means less chance of mechanical failure. “The Zircon … would be capable of destroying the world’s most advanced warships and aircraft carriers in one strike and could be put into action by 2020.
ISRO (Indian Space Research Organisation) has successfully test-fired its Scramjet Rocket Engine On 28 August 2016, a breakthrough technology in air-breathing propulsion. The Scramjet engine designed by ISRO uses Hydrogen as fuel. Says ISRO, “Air-Breathing systems become much lighter and more efficient leading to reduced overall costs.” India is the fourth country to demonstrate the flight testing of Scramjet Engine.
Orlando Carvalho, head of Lockheed’s aeronautics division, said the U.S. government’s current plan was to manufacture and deploy a hypersonic weapon, before moving on to develop and deploy a hypersonic aircraft, Reuters reported. He added that the U.S. could make a hypersonic weapon by the 2020s, but a hypersonic aircraft like the SR-72 would be manufactured in the 2030s.
DARPA’s Advanced Full Range Engine (AFRE) Program Envisions Hybrid Propulsion System Paving the Way to Routine, Reusable Hypersonic Flight
Future U.S. military operations against peer/near-peer adversaries will be severely hampered by erosion in the availability of timely information from airborne ISR. Fielding of fifth generation aircraft equipped with capable air-to-air missiles, proliferation of highly capable Integrated Air Defense Systems (IADS), and other long-range defensive capabilities directly challenge the information superiority the U.S. has enjoyed with ISR capabilities provided by airborne platforms.
These platforms, developed for more permissive threat environments, are unable to access more contested battlespaces. With space also becoming contested, our unique ability to observe, orient, decide, and act (OODA) within an adversaries’ OODA loop is diminishing, sacrificing U.S. decisionmaking superiority. Without a survivable airborne ISR capability to complement space ISR capabilities, the effectiveness of future U.S. offensive strike operations may be limited, says DARPA.
To meet future requirements, DARPA envisions a survivable and affordable hypersonic regional ISR aircraft with the following attributes: Range greater than 1200 nm, Speed greater than Mac 5 and 60,000+ ft operation.
DARPA has launched its Advanced Full Range Engine (AFRE) program to develop one of the key enabling technologies for this envisioned future aircraft application. AFRE seeks to develop and demonstrate a new aircraft propulsion system that could operate over the full range of speeds required from low-speed takeoff through hypersonic flight.
“Instead of designing an entirely new kind of engine, we’re envisioning an inventive hybrid system that would combine and improve upon the best of off-the-shelf turbine and ramjet/scramjet technologies,” said Christopher Clay, DARPA program manager. “This won’t be the first time that ambitious engineers will attempt to combine turbine and ramjet technologies. But with recent advances in manufacturing methods, modeling, and other disciplines, we believe this potentially groundbreaking achievement may finally be within reach.”
DARPA believes that a dual flowpath engine such as a Turbine Based Combined Cycle (TBCC) system offers the best solution for a future hypersonic air vehicle. A TBCC system combines a turbine engine for low-speed operations with a dual mode ramjet (DMRJ) for high-speed operations via a common forward-facing air intake and rear-facing exhaust nozzle to release thrust. This design concept is enabled by advances made in the previous AFRL/DARPA funded X-51 scramjet engine flight demonstration program and the DARPA Falcon Combined-cycle Engine Technology (FaCET) program.
AFRE aims to develop critical technologies and culminate in ground-based testing of a full-scale, integrated technology demonstration system. If that testing is successful, further development of the AFRE technology would require flight testing in a potential follow-on demonstration program.
Lockheed close to the Breakthrough for its SR-72 drone development
Lockheed Martin Corp. said it was on the verge of a technological breakthrough that would allow its conceptual SR-72 hypersonic plane to reach six times the speed of sound, or Mach 6, according to reports. Marillyn Hewson, CEO of Lockheed, said that a hypersonic demonstrator aircraft the size of an F-22 stealth fighter could be built for less than $1 billion. The SR-72 will be a reconnaissance drone with strike capability.
The SR72 drone would fly at speeds of Mach 6.0, or 4,500 mph. That’s almost double the speed of the Lockheed SR-71 Blackbird, which made its first flight 50 years ago. The SR-71 still holds the record for being the fastest aircraft in the world. The SR-71 was so fast that it could actually out-fly missiles.
Lockheed Martin is working with Aerojet Rocketdyne to find a way to integrate a turbine engine, which would get the plane up to Mach 3, with a supersonic ramjet engine, or scramjet, to push it to Mach 6. The problem with hypersonic propulsion has always been the gap between the highest speed capabilities of a turbojet, from around Mach 2.2 to the lowest speed of a ramjet at Mach 4. Typical turbine engines cannot achieve high enough speeds for a ramjet to take over and continue accelerating.
NASA had funded a parametric design study to establish the viability of a Turbine Based Combined Cycle (TBCC) Propulsion system consisting of integrating several combinations of near-term turbine engine solutions and a very low Mach ignition Dual Mode RamJet (DMRJ) in the SR-72 vehicle concept.
NASA previously funded a Lockheed Martin study that found speeds up to Mach 7 could be achieved with a dual-mode engine combining turbine and ramjet technologies. The NASA-Lockheed study is looking at the possibility of a higher-speed turbine engine or a ramjet that can function in a turbine engine’s slower flight envelope; the DARPA HTV-3X had demonstrated a low-speed ramjet that could operate below Mach 3. Existing turbofan engines powering jet fighters and other experimental designs are being considered for modification. If the study is successful, NASA will fund a demonstrator to test the DMRJ in a flight research vehicle.
NASA has identified key technologies that would advance air-breathing launch propulsion systems during validation flight tests and would lead to the design of a staged air-breathing launch vehicle. These technology investments include the development of Mach 4+ turbines for turbine-based combined cycles, long-duration Mach 7+ scramjet operation, stable mode transitions of rocket-based and turbine-based combined cycle vehicles, an integrated air collection and enrichment system, and detonation wave engine operation.
Reaction Engine’s Synergetic Air-Breathing Rocket Engine (Sabre)
BAE is planning to invest £20.6 million ($31.8 million) in a 20% stake of Reaction Engines, a UK-based engineering firm which has developed what it calls “breakthrough” aerospace engine technology, SABRE, which stands for Synergetic Air-Breathing Rocket Engine, is designBed to enable aircraft to operate from a standstill on the runway to hypersonic flight in the atmosphere, and then transition to rocket mode for spaceflight.
A Synergetic Air-Breathing Rocket Engine (Sabre) fitted jet can fly five times the speed of sound, or Mach 5, and reach any place in the world within just four hours. Along with hypersonic air travel, a reusable space plane that takes off and lands like an aircraft is “one of the concepts that could be made possible by this engine.” “What we’re developing here is a revolutionary new form of propulsion, and it’s designed for low-cost space access and hypersonic air travel,” explained Reaction Engines’ Managing Director, Mark Thomas.
The design comprises a single combined cycle rocket engine with two modes of operation. The air breathing mode combines a turbo-compressor with a lightweight air precooler positioned just behind the inlet cone. Previous attempts to build single stage to orbit propulsion systems have been hampered by the weight of an on-board oxidizer, such as liquid oxygen, that is needed by conventional rocket engines. Reaction Engines’ idea was to design a device that could use the oxygen already present in the atmosphere through combustion like an ordinary jet engine.
Head of Advanced Manufacturing, Simon Hanks, said SABRE is the first engine in the world to successfully build an on-board oxidizer that uses the oxygen in the atmosphere via its pre-cooler technology. This rapidly cools the incoming airstream in the blink of an eye.
There are three core building blocks to the SABRE engine, the pre-cooler, the engine core and the thrust chamber. Each of these systems can be developed and validated using ground based demonstrations which saves cost and time relative to flight test, a design feature that benefitted the development of the propeller and jet engine, We plan to demonstrate each of these independently over the next four years, beginning with a high temperature test of the pre cooler in 2017.
At high speeds this precooler cools the hot, ram-compressed air leading to an unusually high pressure ratio within the engine. The compressed air is subsequently fed into the rocket combustion chamber where it is ignited with stored liquid hydrogen. The high pressure ratio allows the engine to continue to provide high thrust at very high speeds and altitudes. The low temperature of the air permits light alloy construction to be employed which gives a very lightweight engine—essential for reaching orbit.
The technology behind Sabre includes ultra-lightweight heat exchangers to cool very hot air streams. Its cooling system uses several thin pipes, which are arranged in a swirl pattern. These pipes are filled with condensed helium, which extracts heat from the air and cools it from more than 1,832 degrees Fahrenheit (1,000 degrees Celsius) down to minus 238 F (minus 150 C) in one one-hundredth of a second. The oxygen in the chilled air will become liquid in the process.
The US Air Force Research lab has started working on the engine’s precooler. The AFRL precooler test program, which is called Durable Pre-cooling Heat Exchangers for High Mach Flight, consists of three phases, the last of which could involve test flights.
He added that the state-of-the-art high vacuum furnace at their headquarters in Oxfordshire is being used to fuse together the complex matrices that make up their pre-cooler module. “We’re using here some technology to high-vacuum braise a much larger version of this (pre-cooler module) together. We’re operating at about one ten-billionth of an atmosphere at very high temperatures approaching a thousand degrees to achieve this joining process, which is very much unique to Reaction Engines.”We’re about to start building a significant new UK test site to test critical subsystems and aim to test a fully integrated engine core in 2020.
“The biggest issue that the guys have had to wrestle with is how you cope with extremely high temperatures that come into the engine when you’re doing hypersonic speeds; so more than five times the speed of sound, 4,000 miles-per-hour. The temperature coming in at the front of the engine is a thousand degrees centigrade. And you have to be able to cool that air very rapidly to be able to do anything useful with it,” said Thomas.
Once built, their technology will allow SABRE-powered vehicles to save carrying hundreds of tons of on-board oxidant on their way to orbit, and negate the need for first-stage rockets that are jettisoned once the oxidant is used up. The company says this could lead to a ten-fold saving in the cost of sending a craft into space, which currently costs about 100 million dollars.BAE’s statement says that SABRE can also “transition” to a rocket mode, allowing spaceflight at speeds up to orbital velocity — or 25 times the speed of sound.
Orbital and Nasa 3D printed scramjet engine part survives critical wind tunnel tests
Orbital ATK has successfully tested a 3D printed hypersonic engine combustor at Nasa Langley Research Centre in Virginia. The breakthrough could lead to planes that can travel 3,425mph (5,500km/h) – 4.5 times the speed of sound.
The combustor was created through a manufacturing process known as powder bed fusion (PBF). In this, a layer of metal alloy powder is printed and a laser fuses areas of together based on the pattern fed into the machine by a software program.
As each layer is fused, a second is printed until the final product is complete. Any additional powder is removed and the product is polished. The combustor was successfully put through a range of hypersonic flight conditions over the course of 20 days, including one of the longest duration propulsion wind tunnel tests ever recorded.
Orbital says one of the most challenging parts of the propulsion system, scramjet combustion. This houses and maintains stable combustion within an extremely volatile environment.
ISRO successfully tests Scramjet engine
In its release, ISRO said that important flight events, such as burn out of booster rocket stage, ignition of the second stage solid rocket, functioning of Scramjet engines for 5 seconds followed by burn out of the second stage took place exactly as planned. After a flight of 5 minutes, the vehicle touched down in the Bay of Bengal.
ISRO’s Advanced Technology Vehicle (ATV), which is an advanced sounding rocket, was the solid rocket booster used for today’s test of Scramjet engines at supersonic conditions. ATV carrying Scramjet engines weighed 3277 kg at lift-off. ATV is a two stage spin stabilised launcher with identical solid motors as the first as well as the second stage (booster and sustainer). The twin Scramjet engines were mounted on the back of the second stage. Once the second stage reached the desired conditions for engine “Start-up”, necessary actions were initiated to ignite the Scramjet engines and they functioned for about 5 seconds. Today’s ATV flight operations were based on a pre-programmed sequence.
Some of the technological challenges handled by ISRO during the development of Scramjet engine include the design and development of hypersonic engine air intake, development of materials withstanding very high temperatures, supersonic combustor or mixing of very high speed air (velocity around 1.5 km/s) with fuel, computational tools to simulate hypersonic flow, ensuring performance and operability of the engine across a wide range of flight speeds, proper thermal management and ground testing of the engines.
The development of this high-technology system will go a big way in meeting India’s futuristic space transportation needs.
Basically, turbofan engines are only really efficient up to around Mach 2.5. Ramjets can then take you to around Mach 4, but then they too lose their efficiency. For future, reusable space transportation systems, as well as for hypersonic flight vehicles, scramjet propulsion system is very likely to offer an economic alternative to classical, expendable and hence expensive rocket driven systems and is one of the key technologies for hypersonic flight.
Scramjets are ‘airbreathing’ aircraft because rather than carrying both fuel and the oxygen needed to provide acceleration, they carry only hydrogen fuel and ‘pull’ the oxygen needed to burn it from the atmosphere. Air is forced into the front of the engine and as hydrogen is injected into the airstream, the gases are compressed causing the temperature to rise and ignition to occur. This generates huge amounts of thrust and enables the jet to travel at speeds far in excess of the 1,350mph top speed of Concorde.
A scramjet (supersonic combustion ramjet) is a variation of a ramjet with the distinction being that the combustion process takes place supersonically. At higher speeds, it is necessary to combust supersonically to maximize the efficiency of the combustion process and to avoid the losses induced by a final normal shock.
Also like a ramjet, there are few or no moving parts, making the scramjet geometrically quite simple. At full scale, to get to their initial scramjet operating velocity of Mach 4, or some 3000 mph, scramjets need some other propulsion system to initially accelerate the vehicle.
The most practical concept at the moment is the turbine-based combined cycle, says Chris Goyne, Professor of Mechanical and Aerospace Engineering and Director of the Aerospace Research Laboratory at the University of Virginia in Charlottesville, So, in this case, he says, a gas turbine or a turbojet engine used to takeoff on the runway and accelerate up to the scramjet takeover speed.
The absolute upper limit for hypersonic flight is about Mach 15, Goyne says, but scramjet tech will be developed around a paradigm of Mach 5 or 6.
Cruising altitude for a hypersonic aircraft from LAX to Sydney or Los Angeles to Singapore would be about 100,000 ft., about twice that of the Concorde “If you fly too low, there’s a lot of air density friction and the aircraft gets too hot,” said Chris Goyne, “Too high, you start to run out of oxygen. The sweet spot altitude is 100,000 ft. or so.”
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