To Mars with Standards
NASA’s unmanned Space Launch System is scheduled to lift off in 2018 on its first step to a subsequent manned mission to Mars in the 2030s.
A recent milestone in the Mission to Mars is the completed welding on the SLS’s core stage liquid hydrogen tank. The tank stands more than 40 metres tall, and according to NASA, is the largest cryogenic fuel tank for a rocket in the world.
The system’s hydrogen tank, together with another tank for liquid oxygen, will hold a total of 2,770 cubic metres of the fuel, and send the advanced launch vehicle into deep space.
And, as has been true for many missions, SLS and its Orion Multi-Purpose Crew Vehicle will burst from the Earth’s atmosphere and enter deep space with the support of countless engineering standards, including those from ASTM.
“The new era of the space race has arrived, with an increased need to standardize design, test, and operation procedures in support of these missions,” says Paul Gill, manager of NASA’s Technical Standards Program, Huntsville, Alabama.
For liftoff, the liquid hydrogen and oxygen of the Space Launch System will be converted into gases in a combustion chamber, where they will be ignited and then propel the rocket into space. S. Eddie Davis, of the Materials and Processes Laboratory at the NASA Marshall Flight Center in Huntsville, Alabama, leads a group that has worked to vet the launch system oxygen tank materials and to help prevent the possibility of fire.
To minimize the fire hazard, materials are tested with ASTM standards. “We use all of the ASTM standards for oxygen, and there are a lot of them,” says Davis.
These are the standards from ASTM’s committee on compatibility and sensitivity of materials in oxygen enriched atmospheres (G04), including the test method for determining the combustion behavior of metallic materials in oxygen-enriched atmospheres (G124).
“Doing G124 testing is critical,” says Davis. G124 is the primary test method used to qualify a material for use in a NASA oxygen system. NASA scientists use it to compare how different metallic materials burn.
Davis and Stephen Peralta, project manager at NASA White Sands Test Facility in New Mexico, single out other standards from Committee G04 as useful to NASA investigations. For example, D2512 helps in measuring the threshold impact sensitivity of a material with liquid oxygen. And there’s the G86 test, which determines the sensitivity of materials to mechanical impact in liquid and gaseous oxygen. “These two test methods are invaluable to the selection of materials that may experience an impact in an oxygen system, such as the impact of a valve closing,” Davis says.
Peralta also highlights G88, Guide for Designing Systems for Oxygen Service. “G88 captures a lot of knowledge in the community with respect to oxygen systems and puts it in a place where it can be referenced,” he says.
And there’s an ASTM manual — Manual 36, Safe Use of Oxygen and Oxygen Systems: Handbook for Design, Operation, and Maintenance — that guides safe oxygen system design, storage, handling, and usage. Committee G04 sponsors the manual, which is in the process of being revised. This manual is used extensively by NASA.
There are particular concerns with oxygen and materials compatibility for the Mars and other deep space missions. “For future missions like Mars, of long duration, you wish you could get there in a day, but that’s not going to happen,” says Davis. “You’re going to have to carry oxygen for long periods of time, especially under high pressure.” And the safest material for the application needs to be used.
Peralta oversees the maintenance of a guide for evaluating the compatibility of nonmetallic materials for oxygen service (G63). Jess Waller, Ph.D., a project leader at the NASA White Sands Test Facility, Las Cruces, New Mexico, oversees a practice for evaluating the age resistance of polymeric materials in oxygen enriched atmospheres (G114), using methods from ASTM’s committees on rubber (D11) and plastics (D20).
NASA is also investigating the possibility of using composite materials for rocket propulsion tanks, either alone or in combination with metals, for a lighter weight assembly. Here too G124 will help determine whether that’s a good approach or not.
When Committee E21 on Space Simulation and Applications of Space Technology organized in 1963, ASTM’s magazine, Materials Research and Standards, noted that its first meeting convened with a sense of “urgency and immediacy.” MR&S reported that “Recent space probe failures have been costly to the United States in both time and money. Failure of an instrumented space probe is expensive, but failure of a manned space vehicle would be a disaster.” NASA was part of the work from the start, with representatives serving as chairs of two of the group’s new subcommittees.
Today, E21 standards continue to be an integral part of space simulation testing. Such testing predicts performance in space and helps ensure that spacecraft are ready for the environment out of this world. NASA spacecraft, for example, must be tested with E595, an internationally recognized method for screening nonmetals for use in the vacuum of space.
Other E21 groups focus on contamination and thermal protection, both critical for safety and performance. The subcommittee on contamination oversees 35 standards that describe how to discover, sample, and measure contamination, which can have a negative impact on sensors and other equipment. The E21.07 subcommittee maintains 15 standards that address thermal protection materials for space applications. And just this year, E21.08 published a method for measuring heat flux, which is crucial to choosing materials with the needed thermal exposure conditions.
Standards for other ASTM committees are also useful. For example, the practice for stitches and seams (D6183), from the committee on textiles (D13), is used in spacesuit construction. D6183 shows what various stitches look like and how they join fabric layers in a seam. Choosing the right combination of stitch, seam, and thread type makes for durability and strength. The standard covers the general purpose of each. That way, sewn items will perform as expected.
Another example is a standard from the nondestructive testing committee (E07). The standard, for leak testing (E1066), is useful for locating and measuring gas leaks from parts or containers that hold explosive gases or liquids. Such systems could be refrigeration or fertilizer storage.
To improve the reliability and mission assurance of flat panel composite materials and components used in aerospace applications, a series of practices and a companion guide have been issued under the jurisdiction of E07. These standards capture the current best NDT practice for flat panel composites and replace NAS 999, and were initiated in the task group on nondestructive testing of aerospace materials, led by Waller, that resides in the E07 subcommittee on specialized NDT methods. These standards specifically call out current best practice for ultrasonic testing, shearography, IR flash thermography, acoustic emission, and radiologic testing of composites, sandwich core constructions, and repair patches. A companion guide (E2533) calling out general NDT guidance for inspection of polymer matrix composites is also available.
A recent push to develop NDT for more complex composite components recently culminated in the release of two guides for NDT of thin-walled metallic liners (E2982) and composite overwraps (E2981) in filament wound pressure vessels, also known as composite overwrapped pressure vessels. These guides are also products of the E07.10 Taskgroup on NDT of Aerospace Materials.
NASA — in collaboration with national and international colleagues drawn from government, industry, and academia — is looking to the future and the possibilities of additive manufacturing. Their initial focus is on metal parts used in aerospace applications that may have low or high structural margins, and which may also be fracture-critical. The agency is also looking at AM for both ground and space hardware applications. It could be used to make parts in space that are needed while in orbit or transit, to reduce weight, to increase mission reliability, and to make complicated “design-to-constraint” components with fewer parts, shorter lead time, less waste, and lower cost.It is well-known that NDT will play a key role in qualifying AM-manufactured parts for use in aerospace applications. To this end, Waller is leading an ASTM effort to develop an NDT guide for metallic AM parts in the task group on NDT of aerospace materials. The proposed standard (WK47031) will cover established and emerging methods to detect flaws and defects during and after manufacture. “We are working with the NDT subject matter experts in E07, and the additive manufacturing experts in ASTM Committee F42, to advance NDT best practice as applied to metal AM parts, thus helping to ensure their safe and reliable use in NASA’s flight applications,” says Waller. The work also fits into the AM standards development structure recently approved by the International Organization for Standardization (ISO) and ASTM.
“Until NDT qualification and certification procedures are implemented, use of AM parts in aerospace application will be impeded,” says Waller. “We also use NDT to monitor hardware performance over the service lifetime, thus ensuring the parts remain reliable and safe to use. //
NASA staff members and support contractors, who work across the United States, serve on diverse ASTM committees:
NASA’s involvement in ASTM standards development is not new.
ASTM members who work at NASA cite OMB circular, A-119, Federal Participation in the Development and Use of Voluntary Consensus Standards and in Conformity Assessment Activities, as shifting NASA’s approach to standards development. Before A-119, there were only NASA standards. The standards were specific to individual NASA centers, of which there are 10, with no central access point.
S. Eddie Davis, NASA Marshall Flight Center, Huntsville, Alabama, says that NASA needed to get involved in industry standards, and to work with other companies and government agencies involved in efforts similar to the agency. That way, everyone would benefit. OMB A-119 spurred that along.
Based at NASA’s Marshall Space Flight Center, Paul Gill manages the NASA Technical Standards Program; he is also chair of the NASA Engineering Standards Panel. Gill says, “It was costing a lot more money internally [before A-119], and we were consolidating our own standards to operate under one common standard across the agency.” Using standards available through other groups made sense.
NASA’s Technical Standards System today provides the agency with access to over 1.9 million standards, codes, regulations, and related documents.
Today, Gill says, the Technical Standards Program has successfully integrated the agency’s diverse standards products into one platform. And, additional usefulness comes from the application notes and lessons learned from those using the standards, which are included with the standards.
When needed, if there is no industry standard, NASA develops its own standards, with small working groups developing drafts that are eventually reviewed and approved by the entire agency.
From May 2015 to May 2016, ASTM standards represented the largest number of standards downloads through the NASA technical standards system, followed by SAE. Other referenced organizations for the same time include the American Society of Mechanical Engineers, the National Fire Protection Association, and the American Welding Society, among others.