LOGAN, Utah — A NASA effort to combine the low-cost/high-speed benefits of the commercial cubesat/smallsat industry with the reliability requirements of high-value missions illustrates how far the cubesat industry still needs to go, according to a NASA official leading the effort.
Michael Johnson, chief technologist at the engineering directorate at NASA’s Goddard Space Flight Center, said NASA’s Dillingr 6u-cubesat, set for launch to the International Space Station this month aboard a SpaceX Falcon 9 rocket and Dragon capsule, is a case study in the clash between load-and-go cubesat missions and the demands for reliability.
Addressing the 31st AIAA/USU Conference on Small Satellites here Aug. 6, Johnson said the Dillingr project, originally set to launch in early 2016, was “painful.”
“We received components that out of the box did not work. We received components that, if it got to a certain temperature, would cease working.
“We received components where the data sheets did not agree with them. We received components with all kinds of issues — fingerprints in places where fingerprints should not be for a spaceflight system,” Johnson said.
For NASA and other U.S. government agencies —but also for certain commercial missions now accessible by cubesats — quantifying reliability is a must. It is becoming clear that smallsats can do many things previously thought to be the exclusive preserve of much larger spacecraft.
Run-and-gun “Fly/Retry” model has its limits
But these missions cannot adopt the “Fly/Retry” ethos that characterizes many commercial and university smallsat programs. “Fail early and often” is one of the phrases often heard in Silicon Valley.
But what works in that context will not work for government missions or commercial missions that need to launch many satellites in a short time period and cannot afford a high failure rate.
“Historically it was assumed that if you are flying a cubesat/smallsat mission, there would be high risk,” Johnson said. “There was a “Fly/Retry philosophy.
“With great probability it will not work the first time — the mission success rate for first-time missions is on the order of 60% or so and increases to maybe 80-90% the second time. So Fly/Retry works very well, if you can do that.
“If we are going to Mars, we cannot do Fly/Retry. You have to have confidence that it’s going to work when we get there. If you are going to a distant asteroid, you cannot do Fly/Retry,” Johnson said.
The Inter-Agency Small Satellite Reliability Initiative, launched in mid-2016, is designed to solve this problem to benefit all agencies using satellites.
“This is not just NASA. There are other government agencies that have missions of national importance They have had challenges selling [cubesat missions] to their stakeholders because their stakeholders think cubesats are toy sats.”
The initiative has attracted wide interest from commercial small-satellite companies, especially since NASA is determined not to correct the current cubesat design weaknesses by simply doing the work itself.
We could do it ourselves, but we want industry to do it
“It is industry that is going to get us many of the systems that we want to fly,” Johnson said. “We at Goddard, at JPL, at Los Alamos, Lincoln Laboratory, we can build these systems ourselves…. that will get us the level of reliability that we want.
“But we don’t want to do that. We want to be able to approach our colleagues from industry, tell them what we need, and procure it. We want to build only what we have to build, and buy what we can buy. That is the focus of this Smallsat Reliability Initiative. The approach is to make things better, not to break what’s working in the cubesat community.”