An aircraft that takes off from a runway, travels to the very edge of Earth’s atmosphere, delivers its payload or even travels into space, then heads back to earth and lands on the same runway it took off from: it sounds like science fiction.
Fundamental to its design is the propulsion system that powers it from a horizontal runway launch right through to Earth orbit (up to 600 km). The Synergetic Air-Breathing Rocket Engine (SABRE) is a new type of rocket engine that incorporates elements of a jet engine into its design. The SABRE, and in particular its advanced heat-exchanger technology, provides a breakthrough in propulsion like that of the invention of the jet engine, which makes multi-stage launch vehicles a legacy technology.
REL’s pioneering engine technology offers greatly improved reliability, a tenfold reduction in cost, and responsive access to space. No longer will space missions take months or even years to plan. REL’s Skylon space plane can take off and land from a runway, which means that a space mission can be conducted as easily as a commercial flight.
Plans for the Skylon plane are still in their infancy but the technology that provides the incredible thrust to weight ratio required to accelerate the plane to Mach 5.5 inside the atmosphere and on to Mach 25 to break out of the atmosphere is already mature. Whilst conventional rocket engines require vast amounts of liquid oxygen as fuel, the SABRE engine takes advantage of the oxygen in the surrounding atmosphere, which reduces the required oxidizer by over 250 tonnes.
Once outside of the atmosphere, the rocket phase requires onboard oxygen. During take-off and initial ascent the SABRE engine runs in jet engine mode so it can use the oxygen from the air. Until REL’s breakthrough technology, this configuration was not possible. As the air intake speed increases, the air intake temperature also increases. By the time it is travelling at Mach 5.5 the air intake temperature is around 1000�C. At this temperature conventional jet engines cannot operate - materials begin to fail and the air cannot be effectively compressed.
REL’s solution to this problem is to super-cool the air from 1000�C to cryogenic temperatures (-150�C) in less than a hundredth of a second with a pre-cooler. Flight weight is the point at which a component’s performance justifies its weight. The pre-cooler required the development of a new generation of heat exchangers that can not only transfer 400 MW of heat, but can do it at flight weight (that is 100 x lighter than conventional heat exchangers). This miniaturisation of a heat exchanger can be compared to the miniaturisation of the electronic circuit board to the microchip.
Validation system implementation
The whole test system uses LabVIEW system design software and CompactDAQ measurement hardware. The modular nature of the platform helped easily customise the data acquisition system. Using a combination of analogue and digital modules to take in a range of signals including engine speed, air, and component temperatures, as well as the air pressure and flow throughout the system. The data acquisition system had to handle a wide range of signals, for example temperature varying from -196�C to 1000�C and pressure from vacuum to 250 bar.
For safety reasons, the technicians cannot be in close proximity to the test system during the test. Using flexible NI DAQmx drivers, acquisition devices could be used over a variety of communication buses with the same application programming interface. For the main pre-cooler diagnostics, a local 8-slot NI cDAQ-9188 chassis communicating via Ethernet was used and a 4-slot NI cDAQ-9174 chassis communicating over USB, was located within the control room, to interface with the plant control system. LabVIEW helped bring together all the different system components under one application. The LabVIEW Datalogging and supervisory control module provided seamless integration with a Mitsubishi PLC, which controlled the system and also helped the development of the SCADA UI.
Future of the project
The European Space Agency has evaluated the SABRE engines pre-cooler heat exchange on behalf of the United Kingdom Space Agency and has given official validation of the test results. Now that the pre-cooler has been successfully validated, we can reconfigure the testbed to test other sub-assemblies before we bring all the subsystems together into a full-size demonstration SABRE engine to commence ground testing.
With the flexibility of LabVIEW, all the existing components can be reused in the new system and software can be re-written to new requirements. Some of the signals can be reallocated and the system can be enhanced with additional hardware, which saves both time and the cost of buying a new system.
Skylon, with its SABRE engines, is on its route to true 21st century commercially viable access to space. They have successfully demonstrated the key enabling new technology, the pre-cooler, and work is escalating to take the development to the next stages of system integration testing. LabVIEW has been an integral development tool for the pre-cooler testing and will be used for further development test systems.
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