If you want to build a rocket capable of escaping the earth's atmosphere and gravitational field, you need to be able to propel it a very long way, fast. Inherently this takes a great deal of fuel that needs to be safely stored and transported on board particularly on the long-term missions of the future.
Future space exploration - composite materials are likely to play a big part...
Highly explosive fuels / propellants must be carefully stored, preserved and available for use during initial blast-off and throughout the mission to go far beyond low-earth orbit and further into space.
NASA's preferred fuels of choice are Cryogenic propellants, explosive gases chilled to extremely cold temperatures and then condensed into highly combustible liquids. Cryogenic propellants are notoriously difficult to store and transport and NASA has continuously worked on a range of technologies to maximize the efficient storage and on-board delivery of these fuels.
Not only do cryogenic fuels need to be maintained at extreme temperatures, they are also under a great deal of pressure. This presents an interesting challenge for the Nasa scientists and engineers to overcome.
Traditionally, Cryogenic propellant tanks have been fabricated out of state-of-the-art metals but these are often very costly to manufacture and are potentially heavy vessels in order to cope with the levels of pressure they are required to retain.
However, recently NASA has announced another major Milestone in space technology with the successful testing of a new large scale composite pressurized cryogenic propellant tank. The 2.4meter diameter propellant tank fabricated from composite materials was successfully pressure tested at NASA's Marshall Space Flight Center in Huntsville, Alabama.
Watch this short video on NASA's cryogenic tank manufacturing, development and testing program.
The main aims of this 'game changing' development program are to provide a substantial decrease in tank weight and cost. However, NASA doesn't aim small, they are looking for up to a 30% reduction in tank weight and a 25% cost saving compared with the latest metallic tanks.
The ultimate goal is to enable NASA to go further and explore for longer. The sort of efficiency savings the new composite propellant tanks could offer will enable future NASA missions to reach new destinations.
Part of NASA's Space Technology Mission Directorate, the composite cryogenic storage tank project forms a critical path of the program designed to innovate, develop, manufacture, test and ultimately fly new technology for potential use in future missions. To learn more about NASA's Space Technology Directorate - have a look at - http://www.nasa.gov/spacetech
What does this succesful test mean for the future of space travel?
"These successful tests mark an important milestone on the path to demonstrating the composite cryogenic tanks needed to accomplish our next generation of deep space missions,"
said Michael Gazarik, NASA's associate administrator for space technology at NASA Headquarters in Washington.
"This investment in game changing space technology will help enable NASA's exploration of deep space while directly benefiting American industrial capability in the manufacturing and use of composites."
Image 1. NASA Technicians move the insulated, 2.4m diameter tank to their Hydrogen Cold Flow Test Facility - (Image Credit: NASA/MSFC/David Olive)
This latest test regime is one big step for composite materials, proving the potential for composite materials to dramatically improve the performance and range of future space missions. Composite materials could also offer impressive cost reductions, thus allowing for the development of technologies in other areas.
The insulated composite tank tested (shown below) was built by Boeing at their Tukwila, Washington and delivered in late 2012. Then began a series of inspections and tests to ascertain whether the composite material tank was capable and suitable for the storage of liquid hydrogen at cryogenic temperatures.
By cooling the tank down to -423 F and conducting a series of 20 high pressure cycles (reaching as much as 135psi) NASA researchers have been carefully developing future designs and specifications for future generations of larger composite vessels for cryogenic propellants.
Image Credit: NASA/MSFC/David Olive
Built by Boeing at their Developmental Center in Tukwila, the composite structure has been created using the latest automated fiber placement methods - ensuring a highly consistent fiber network to minimize irregularities in material structure and properties.
Image Credit: Boeing
Talking about the next stage of development, NASA's Cryogenic Tank Project Manager, John Vickers explains:
"The 18-foot (5.5-meter) tank will be one of the largest composite propellant tanks ever built and will incorporate design features and manufacturing processes applicable to a 27.5-foot (8.4-meter) tank, the size of metal tanks found in today's large launch vehicles."
This next 5.5m test tank, is currently under construction at Boeing's facility using the latest composite manufacturing tools and technologies. In the picture below you can see a robot precisely laying composite fibers for the inner wall structure of one of the composite test tanks.
Image Credit: Boeing
So why composites?
"The Composite Cryogenic Propellant Tank project will develop and ground demonstrate large-scale composite cryogenic propellant tanks applicable to heavy-lift launch vehicles, propellant depots, and future lander systems."
The primary objective of the Composite Cryotank Technologies and Demonstration (CCTD) program is to develop and test composite materials and to mature the technology readiness for use in space applications. The project focuses on a range of factors from the development of advanced composite materials to the structural concepts (joints / fasteners etc.) that often add extra weight to pressurized vessels (typically a weaker section in the design of a vessel).
Employing the latest out-of-autoclave manufacturing methods, Boeing and NASA are working together to design and test the composite vessels for their structural integrity, permeability and micro-cracking under the extreme conditions required for the storage of Cryogenic propellants for long range space exploration.
One of the biggest hurdles of the project is to ensure that the Cryogenic propellants are stored without leakage and composites are capable of providing an innovative solution.
In order to contain the liquid hydrogen propellant the composite laminate used in the manufacture of the test tanks is a unique combination of both thick and thin plies.
Then onto the next big test, maintaining structural integrity of the vessel at high pressure. To minimize the risk of structural damage throughout the manufacturing process, once the shell of the tank has been cured, engineers then apply a specialized structural health monitoring system that will alert the engineers if any damage should occur during the rest of the manufacturing process.
Key Areas of the Development Program
NASA engineers are working on a number of innovative key areas of composite design and manufacturing to make composite Cryogenic Tanks a viable reality for space exploration, including:
Shear Peak Reduction Structures - softening strip Y joints
Innovative Structural Health Monitoring Systems - designed to a 5,000 microstrain limit
High laydown rate AFP manufacturing systems
Ventable and purgeable sandwich structure design
Impermeable hybrid laminates - composite composites