Out of This World
Spacecraft and Component Performance Soars with ASTM Committee E21
With the recent landing of the Mars rover Curiosity and the amazing pictures it has begun transmitting back to earth, the U.S. National Aeronautics and Space Administration has been much in the news. It so happens that NASA and other builders of materials intended to go up in space rely on the standards of ASTM International Committee E21 on Space Simulation and Applications of Space Technology.
Space may be the "final frontier" - as viewers were reminded through numerous episodes of the original Star Trek television series - but it is a frontier defined technologically here on earth. Almost from the start of the space era, critical aspects of technology related to space flight such as decontamination, re-entry to the earth's atmosphere, and a host of other topics have been defined and shaped through the efforts of ASTM International Committee E21 on Space Simulation and Applications of Space Technology, which organized in 1963.
Committee E21 still conducts its standards development meetings in conjunction with other technical societies such as the Institute of Environmental Sciences and Technology, and the committee co-sponsors the IEST Space Simulation Conference. With a current membership of approximately 35, E21 has jurisdiction over 56 standards and has four technical subcommittees that maintain these standards.
In keeping with the consensus-based nature of ASTM, E21 has brought together participants from industry and government, and it has influenced practice globally as well as in North America. Its work has continued to be critical, up to and including the recent landing of the Mars rover Curiosity on one of our nearest planetary neighbors.
Challenges Unlike Any Others
The space environment is radically different than here on earth, notes Nikki Lowrey, senior contamination control engineer at Jacobs Technology Inc., Tullahoma, Tenn., the advanced technology division of Jacobs Engineering. Lowrey says spacecraft are high precision instruments in which there is no opportunity to effect repair once they are launched. "Simulation and testing are vital to the success of government, military and private space systems," says Lowrey. "Contamination control is also essential to assure performance."
Overall, Lowrey explains, the activities pursued by Committee E21 are focused on establishing standard practices and test methods to assist manufacturers of spacecraft and their components to assure that the system will perform as intended in the harsh environments of space - as well as during launch and re-entry, where applicable. A key to this is the development of standards for the simulation of these environments in ground test chambers, which generate materials performance data to use in analytical modeling and to help with the prediction of in-orbit spacecraft performance, she explains.
"Testing of materials in simulated space environments is costly and time-consuming. Standardization of test methods allows users to share and compare data. E21 standards are also used by government agencies and contractors to communicate requirements to component manufacturers for contamination control and environmental survivability," Lowrey says.
For example, ASTM standard E595, Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment, is a centerpiece of E21. According to Lowrey, E595 is the internationally recognized test method for screening of nonmetals for use in the vacuum environment of space. Testing in accordance with E595 is required for all NASA spacecraft, per NASA-STD-6016 Standard Materials and Processes Requirements for Spacecraft, Section 220.127.116.11, and the standard is referenced for the screening of materials in ISO 15388 Space Systems - Contamination and Cleanliness Control, she notes. E595 materials outgassing data is also shared across the aerospace industry via the NASA Materials and Processes Technical Information System, or MAPTIS, database. "Subcommittee E21.05 on Contamination performs periodic round robins on this test method with high participation rates and has established a solid basis of statistical precision for this test method," says Lowrey.
Another area of focus is contamination, a problem that can dramatically shorten the life of spacecraft and interfere with performance, says Lowrey. For example, she notes, particles that would fall to earth in a terrestrial environment will float in space, interfering with sensors and mechanisms. Similarly, films and fingerprints will darken in the ultraviolet of space, degrading optics and thermal control surfaces. To avoid these problems, spacecraft are manufactured in clean rooms with attention to both particles and film contaminants. An initiative of E21.05 over the past 25 years has been to develop a complete set of standards to guide the manufacturers of spacecraft components. Lowrey says these standards help to broaden the base of suppliers that have the necessary understanding and capability to provide qualified spacecraft components.
"Data from flight experiments such as NASA's Long Duration Exposure Facility and the Materials International Space Station Experiment are used to validate standards for ground simulation such as ASTM E2089, Practices for Ground Laboratory Atomic Oxygen Interaction Evaluation of Materials for Space Applications," she adds.
Standards Promote Information Sharing
The value of ASTM International's space standards efforts is also acknowledged by Jack Sanders, contamination control specialist at ATK Space Systems in Beltsville, Md. The company manufactures a variety of space-related items, ranging from the giant solid rocket boosters once used on the space shuttle to instruments used within satellites. Customers include both government agencies and commercial space operators.
Sanders became involved with Committee E21 in the late 1980s, focusing on ongoing space simulation efforts. At the time, he recalls, one of the "hot" issues being handled by Subcommittee E21.04 on Space Simulation Test Methods was defining a solar constant - an estimate of the amount of solar radiation to which a vehicle or component would be exposed in space. In order to accomplish that goal, that subcommittee had to devise test methods that could accurately measure solar output across the electromagnetic spectrum.
Sanders says because of the need to work with multiple customers and share technical data, "It is vital to have an easy way to communicate about design, testing and manufacturing requirements… The specifications produced by E21 have been extremely helpful because we all understand them," he says.
"People trust the standards because they know a wide variety of professionals in government and industry have reviewed them, and anybody in the world is welcome to use them," Sanders adds.
A longtime participant in standards making - currently chairman of E21.05 and past chairman of the main Committee E21 - Robert Moss, now a consultant based in Palo Alto, Calif., has seen space technology unfold almost from the start of the industry. "I have designed and built satellites and have been involved with all kinds of interesting projects over the years," he says. Among the more noteworthy projects on his curriculum vitae are the Pioneer 10 and 11 spacecraft (the first to leave the solar system) and the Mariner project, which transited the orbits of Mars and Venus.
"When Mariner went past Mars in 1965, I was working at the Jet Propulsion Laboratory, and I was able to take my two older daughters to the facility where we monitored the operation - we were among the first 10 or 12 human beings to see the images that were transmitted back of the Martian moon, Phobos!"
In all that work, says Moss, standards played an increasingly vital role. "There was a big push in the 1960s and into the 1970s because the space industry was expanding," he notes. Since then, although growth in the field has leveled off somewhat, the role of standards has become, if anything, more central.
"We have found in our subcommittee that clean room standards that are more generic and can't be easily applied to spacecraft - we have different issues to worry about," Moss says.
To achieve practically perfect cleanliness meant moving far beyond the standards of terrestrial medical or pharmaceutical facilities. Indeed, notes Moss, the committee has moved on to develop new documents that refine requirements for testing clean room products.
"We have continued to generate new documents, but the emphasis has shifted from some of the basic areas associated with space flight to more sophisticated issues such as avoiding biocontamination," says Moss. For example, in the case of the newest NASA Mars landing, as with all interplantetary missions, there is a vital need to make sure that the craft is completely scrubbed of anything living or, indeed, of organic material that could mislead researchers looking for indications of past or present life on the planet. "It would be puzzling if scientists discovered that Mars had E. coli," he says.
Moss says the committee's work, so specifically focused on space, has had limited influence elsewhere. However, says Moss, Subcommittee E21.05 has scheduled regular meetings with ASTM Committee G04 on Compatibility and Sensitivity of Materials in Oxygen Enriched Atmospheres, which focuses more on the clean rooms used by the semiconductor industry. "We work in parallel, and we try to coordinate our work and stay in touch," he explains.
Looking to the Future
Although standards continue to evolve, many of the most fundamental ones are based on tried and true technologies and techniques. For instance, explains Edward Martinez, chairman of Subcommittee E21.08 on Thermal Protection Materials and program manager for heat shield installation for the NASA Orion program, Moffett Field, Calif., "people think that because you are NASA or because you are going into space that you are using the newest, cutting-edge technology." In fact, says Martinez, it is mostly the opposite. The environments are so extreme that you must have something that is proven. "We often focus on very mature technology because it is something we can count on and we know how it will work." As an illustration, Martinez says his subcommittee created two new standards that were first published by ASTM in a monograph, "but it took about five years to turn them into working standards."
At NASA, Martinez is focused on the agency's next generation of spaceships with initial flight testing planned for 2014. His main focus is the ablative heat shield manufactured by Textron. "Standards fit within how we test things and integrate instruments into materials, what kind of instruments we use and how we evaluate components in ground testing prior to flight," he says.
As Orion progresses and as space technology continues to advance, standards will continue to play a critical role. "If the standards are correct and people follow them, nothing bad happens," says Moss. "On the other hand, if we had a standard that left out something and a satellite failed or blew up, that would be an example of something we did wrong - but as far as I know, the things we have done over the years through E21 have worked," says Moss.Alan R. Earls is a writer and author who covers business and technology topics for newspapers, magazines and websites. He is based near Boston, Mass.