As the agency looks at opportunities to use CubeSats in science and exploration missions, NASA’s Safety and Mission Assurance (SMA) community is working to address some of the SMA challenges associated with these small spacecraft.
The Appeal of CubeSats
CubeSats are class of small research spacecraft that may be as small as four inches on a side with a weight around three pounds. CubeSats, which often use commercial off-the-shelf parts, are cheaper and quicker to develop.
Whereas a traditional spacecraft could take seven to ten years to complete, CubeSats can be completed in a manner of months. Because of cost-effectiveness and speed in which CubeSats can be created, NASA is looking for new ways to utilize these small spacecraft for complex science research.
“Historically, CubeSats have been used as a training vehicle, a means of having students build something for space and seeing their specific CubeSat fly and get information,” said NASA Electronic Parts and Packaging (NEPP) Program Co-Manager Ken LaBel. “Now we’re entering a new regime. The question now becomes, how useful can we make these CubeSats?”
Challenges With CubeSats
CubeSats are much smaller than traditional spacecraft, with limitations on the size, volume and weight of onboard electronics, as well as the amount of power that can be consumed.
“Power becomes a big driver from the electronics side,” said LaBel. “We can no longer have solar arrays with batteries — we’re trying to do it on a much, much smaller scale — so power-efficient electronics are much more critical.”
In order to optimize power-efficiency with weight and volume, CubeSats frequently use commercial electronics — products that were not developed for space use. In addition, the smaller spacecraft have less mass and therefore less shielding from the radiation found in low-earth orbit.
Efforts have been made to assess and analyze the risk and reliability of these commercial parts. NEPP recently completed a study to survey the CubeSat supply chain and quantify and characterize the types of parts procured by NASA for CubeSat projects. The study found that the vast majority of CubeSat parts are industrial or automotive grade commercial parts.
Improving CubeSat Reliability
While CubeSats present challenges for design, the lower cost and shorter development times provide opportunities to evaluate new ideas in assurance, reliability improvement and testing.
“CubeSats need to have an assurance framework that is compatible with their development time and cost,” said Reliability and Maintainability (R&M) Program Manager John Evans.
In order to better prepare CubeSats for the demands of science research in low-earth orbit, OSMA’s R&M and NEPP programs are teaming up with Vanderbilt University to improve the reliability of commercial parts in CubeSats.
“The environmental information doesn’t change, it’s how you end up applying the information for your specific parts and design,” said LaBel. “We’re looking at how we can methodically assure reliability on a system level instead of a traditional part-by-part level.”
The Vanderbilt team is using Model-Based Mission Assurance concepts to address safe usage of these commercial parts by using a student-designed CubeSat, RadFX, as an exemplar. The project is still in its infancy, but the research provided will benefit the CubeSat community as a whole.
In addition, NEPP has hosted Professor Michael Swartwout of Saint Louis University at the last two annual Electronics Technology Workshops, where he presented on tracking the success and failure rates of all known CubeSat missions. Building upon these efforts, OSMA has placed a grant with Swartwout to try and determine what are the prevalent causes of failure or common threads to develop mission success.
NASA’s Goddard Space Flight Center’s (GSFC) Reliability and Risk Analysis Branch is supporting the effort by analyzing the Saint Louis University CubeSat database and performing reliability and risk analysis. Early results show that the reliability of these systems is improving and that mass of the designs impacts the reliability.
EEE Parts Database of CubeSat Projects and Kits CubeSat Data Analysis Goal Structuring Notation in a Radiation Hardening Assurance Case for COTS-Based Spacecraft