NASA's Class-D Missions Offer Lessons for Larger Science Missions

SAN FRANCISCO – As a group, NASA’s low-cost science missions have improved significantly.

“There were lessons learned over the years that helped,” said Charles Norton, NASA Jet Propulsion Laboratory deputy chief technologist. “In the beginning there were a lot of failures. The community bootstrapped itself to become successful.”

In fact, low-cost, risk-tolerant Class-D small satellite missions, which cost no more than $150 million, “have done transformative science,” said Florence Tan, NASA Science Mission Directorate deputy chief technologist.

TEMPEST-D and RAINCube, for example, cubesats ejected from the International Space Station minutes apart in 2018, provided data for the first near-real-time 3D model of storm evolution, Norton said. (TEMPEST-D stands for Temporal Experiment for Storms and Tropical Systems – Demonstration. RAINCube is short for Radar in a Cubesat.)

Given the success of recent Class-D missions, NASA’s Science Mission Directorate assembled a group of experts to find out whether any lessons could be applied to large missions.

“We took a step back and said, ‘Let’s consider this an experiment,’” said Carolyn Mercer, NASA Science Mission Directorate chief technologist. “I’m glad we did because there’s a lot that can be learned.”

The study, “Small Missions, Big Lessons,” presented in July at the AIAA ASCEND conference in Las Vegas, identified secrets to the success of recent Class D missions that could be applied to large science missions. Science Mission Directorate leaders were briefed on the study in August.

The study recommends establishing small, cross-disciplinary teams.

“There’s a lot of swift and open communications that comes as a result of having these teams,” Norton said. “In general, all members have a broad system-wide awareness of all aspects of the mission That helps enable rapid decision making and it tends to improve the level of accountability.”

Because of limited resources, “small missions are more effective in using people on an as-needed basis rather than maintaining a standing army,” Mercer said. “Big missions have lots of subsystems and we need a lot of people. At least in that class, our practice has been if we need those people ever during the course of the mission, we are going to keep them on that mission for the entire course of the development.”

The study suggests limiting requirements to those that add value.  

“Typically, with much larger missions, you have a checklist mentality,” Norton said. “Rather than trying to remove a requirement, you do whatever is necessary for the checklist. One of the recommendations is to look at establishing leaner requirements, even for Class C missions, for example, based upon the tailored lines of the small missions.”

“We have COTS parts that have already flown,” Tan said. “In such cases, is there a way to reduce requirements for documentation for those parts?”

The NASA Engineering and Safety Center has recommended establishing a Parts Evaluation and Assessment Laboratory (PEAL) with subject-matter experts who could provide guidance on parts selection and acceptance.

Even if that organization existed, mission managers would continue to inspect parts and perform component-level integrated tests. But PEAL could help by evaluating the “performance characteristics of parts for spaceflight missions,” Norton said.

For Class-D missions, managers tend to identify risks and work to mitigate them on a daily basis. By contrast, managers of large missions often spend a lot of time considering developmental risks.

When small missions identify a problem but fail to pinpoint the root cause, they may be able to mitigate risk during the operational phase of the mission. “Sometimes that’s allowed us to move ahead with integration and launch to maintain our schedule and our cost profile without having to risk mission success,” Norton said.

For Class D missions, review boards “are typically small and there’s not a gotcha mentality,” Mercer said. “The reviewers are there to help that mission succeed while still being independent. They share experience and guidance.”

Reviewers for large missions “sometimes focus more on compliance,” Mercer said. Support-based review boards could provide “more informal expertise and build trust within the project.”

Class-D missions “identify tailored documents that are truly needed,” Mercer said. “Larger missions create documentation that’s oftentimes not referenced. Who is reading it?”

Excessive documentation requirements can have unintended consequences like prompting developers to “stop work for up to four months before a lifecycle review so that they can freeze all the designs so that they can make sure that all the documentation is consistent,” Mercer said.

SMD smallsat science missions “routinely acquire high-quality science data at greatly reduced cost,” the report concludes. By adopting some practices of the smallsat missions, larger science missions may be able “to reduce costs while maintaining the quality.”