Goddard Develops Risk-Based Approach to Using Inherited Components
Over the last seven years, Goddard Space Flight Center has experienced a massive increase in the use of inherited components, including flight-printed wiring assemblies.
An inherited component is one that either already exists or is built-to-print from an existing design. If these parts aren’t designed, manufactured, inspected, tested and delivered acceptably, they pose an elevated risk to missions.
“Five, seven years ago or so we started to see a trend of more and more of the hardware for many of our projects being inherited from previous designs,” explained Jesse Leitner, Goddard chief Safety and Mission Assurance (SMA) engineer.
These components, some of which are or include printed wiring assemblies with 100 or more modifications from the original design, were making their way into major flight projects such as MAVEN, GOES-R, JPSS, IRIS and OSIRIS-REx.
“This trend caused us a lot of grief,” explained Leitner. “One of the reasons is in some cases they were built to older or different design standards than we were used to. Before, there was a small quantity of this occurring, but then a larger volume started to encompass a large percentage of the hardware and software on a project, frequently violating some of our essential requirements.”
Developing a New Approach
Leitner explained that, at first, they tried to get manufacturers to change their methods for bringing in existing heritage designs in order to meet Goddard’s existing requirements, but that didn’t work.
“Telling vendors to do things a different way is not likely to get them to do it better,” said Leitner.
An area of particular interest was standard components, which are almost always Commercial Off-the-Shelf components such as inertial measurement units, star trackers, torquer bars and reaction wheels. NASA has flown such “standard components” on many spacecraft, as have other organizations. Because the vendor is developing the same thing for multiple customers, it is in their best economic interest to continue making it as they always had rather than customize it for NASA’s revised needs.
It turned out to be a moot point when Goddard realized that if developers and manufacturers tweaked their builds, it would actually increase the risk associated with these parts, as they would become untried pieces of hardware.
“Even if we perceive a lower risk by meeting our tried and true requirements, [we’re] often increasing the risk because [we’re] changing things about a product that was working fine,” said Leitner.
Prior to this realization, Goddard was focused almost entirely on a requirements-based approach, but it soon recognized the need to take a risk-based approach of looking at these items that wasn’t centered on a rigid view of meeting existing requirements.
“We developed a new approach for handling SMA for inherited and heritage items,” said Leitner. “This involved a more holistic view of the item that factors in not only what standards they used to produce the item [originally], but the prior history, its prior successes or anomalies, and also what has changed in the item relative to its prior use.”
Goddard started to use standard reliability techniques, both objective and subjective, to determine the risk associated with these heritage items, and in many cases found no elevated risk. The center documented this method in Goddard Space Flight Center Procedural Requirements (GPR) 8730.5, Safety and Mission Assurance Acceptance of Inherited and Build-to-Print Products.
Although the policy emphasizes the role of electronics, its application is all-encompassing, including mechanical systems. The focus of GPR 8730.5 is the use of a risk-based approach over a requirements-based one, which emphasizes the true risk of a part based on a variety of factors as opposed to rigid and seemingly arbitrary factors in existing requirements.
The policy also puts the onus back on NASA — rather than telling vendors how to do their jobs, this policy takes into consideration how vendors’ methods correlate to the agency’s projects and risk factors.
Lessons learned are another key aspect of the risk-based approach outlined in this policy. It’s vital that projects using heritage items refer back to past lessons learned related to the piece being used in order to avoid making the same missteps again.
To ensure lessons learned are referenced, Goddard has been developing Commodity Usage Guidelines documents, which are living documents that describe all of NASA’s experiences with each standard product or inherited item. These documents highlight which requirements were met during past uses, which were not met, anomalies, what was seen during inspections, experiences in the lab or on orbit, and so on.
“Lessons learned are an inherent element of this approach,” said Leitner
Implementing the Policy
After Leitner finished developing GPR 8730.5 with a broad team from the Safety and Mission Assurance Directorate (Code 300), it was time to implement it center-wide. The policy was implemented at Goddard in the last few months, and is working smoothly.
“We formed a position called the Standard Components Commodity Risk Assessment Engineer, or SCCRAE,” explained Leitner. “That person is responsible for gathering all the data, uniformly conducting things across the projects and learning from all the experiences of each project’s usage of these [heritage] items”
Even though the policy is working well, there are always challenges associated with change, especially after so many years of success.
“The biggest challenge was getting everyone to look at heritage components in an entirely different way,” said Leitner. “That really was the biggest thing because we were so driven by requirements in the past, getting people to take this risk-centric view and understand how to perform these types of risk assessments.”
To help employees adapt to the change, Goddard is continuing with training efforts to better educate everyone on risk and how to use it for everyday activities.
Although this Goddard-specific policy could be of use to any center facing a similar situation, Leitner explains that it’s Goddard’s particular type of work that drove them to develop it. Goddard has an unusually high number of spaceflight projects at any given time — as many as 20 at once — and many inherited items to process.
“That said, a lot of this philosophy can apply to many different types of NASA work, like the risk-based approach to accepting products instead of a requirements based approach,” said Leitner.
Furthermore, Leitner explained, this is simply one piece of a bigger transition for the center, and the agency, to risk-based SMA.