LOGAN, Utah — As cubesats move from technology demonstrations and university projects to operational missions for companies and government agencies, ensuring those spacecraft are sufficiently reliable is a growing issue for the industry.
In an Aug. 6 presentation at the 31st Annual Conference on Small Satellites here, Michael Johnson, chief technologist for the applied engineering and technology directorate of NASA’s Goddard Space Flight Center, warned that despite increasing interest in cubesats and other smallsats at the agency to perform various missions, a lack of assurance about their reliability would keep NASA from pursuing them for some applications.
“Because we cannot quantify the mission confidence of cubesat subsystems, we can’t use them for certain types of missions,” he said.
Such missions, he said, include science investigations where it’s not feasible to quickly refly another spacecraft should the first one fail. Examples he provided ranged from cubesats that deploy from a larger spacecraft for studies of the surface of Jupiter’s icy moon Europa to constellations of such satellites that provide space weather observations from other locations in the Earth’s orbit around the sun.
Those applications clash with what he called the “fly/re-try” philosophy of cubesat development, where developers have accepted a higher risk of failure by using less reliable components or reduced testing, knowing they can simply try again should the first spacecraft fail. That approach works if it’s easy to rebuild a spacecraft and launch it again, but less appropriate for some more advanced applications where reflights aren’t feasible or otherwise desirable.
“If you’re going to Mars, you can’t do fly/re-try,” Johnson said. “You have to have confidence that it’s going to work when you get there.”
Hence, he said, the interest in improving the reliability of cubesat systems. His experience with one recent mission, Dellingr, illustrated the problem. Dellingr is a six-unit cubesat developed at Goddard to carry a set of heliophysics payloads that will launch later this month on a cargo mission to the International Space Station. Johnson said the Goddard team planned to develop the spacecraft using commercially-available components, much like many other cubesats.
“It was painful,” he recalled. “We received components that, out of the box, did not work. We received components that, when they got to a certain temperature, they would cease working. We received components where the data sheets did not agree with them. We received components with all kinds of issues.”
That experience, he said, illustrates the reliability problems that cause many cubesat missions to fail. “There’s some work that we have to do to raise the community from where it is to where we think it needs to be if we’re going to fly some of these mission concepts.”
A related issue to the reliability of spacecraft components is testing of cubesats prior to launch. Such spacecraft don’t traditionally go though the same thorough level of mission assurance testing that larger and more expensive spacecraft go through, which raises the risk that an undetected issue with the spacecraft will cause it to fail after launch.
That testing is often limited because of constraints with launches of small satellites as secondary payloads on larger rockets. “Launch is a huge driver in our business for reliability,” said Barbara Braun of the Aerospace Corporation, who supports the Air Force’s Space Test Program, during a cubesat mission success panel session Aug. 7. “Missing that launch or delaying that launch is not an option for them. So what happens? The testing gets cut short.”
David Voss of the Air Force Research Lab said that, based on his experience working with student and other small satellites, he recommends a core set of tests of spacecraft power, communications and other essential systems. “No matter how fast we go, or how slow we go, we do a version of those tests,” he said on the panel.
Johnson, as part of NASA’s new Small Spacecraft Virtual Institute established earlier this year, is working on a reliability initiative to determine the best ways to improve reliability for such spacecraft. The institute has also created a database, called Spacecraft Parts On Orbit Now (SPOON), to list small spacecraft components that have flown to help developers identify the best components for their missions.
Johnson, who was also on the Aug. 7 panel, said that these new efforts weren’t meant to apply the same rigorous mission assurance procedures used on larger and more expensive spacecraft to cubesats. “Some of the things that we’ve done over the last 50 years I think we can throw away and do some brand new things,” he said. “Some things we can hold on to.”