RadSat-g (RadSat-g) - 08.08.18

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Computers operating in space must withstand a harsh radiation environment, which may sometimes cause system failures. Designed to detect and withstand the harmful effects of space radiation, RadSat-g houses and tests a novel computer investigation while orbiting in low-Earth orbit.
Science Results for Everyone
Information Pending

The following content was provided by Brock LaMeres, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details


Principal Investigator(s)
Brock LaMeres, Ph.D., Montana State University, Bozeman, MT, United States

David Klumpar, Ph.D., Montana State University (Space Science and Engineering Lab), Bozeman, MT, United States

Montana State University, Bozeman, MT, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Technology Demonstration Office (TDO)

Research Benefits
Information Pending

ISS Expedition Duration
February 2018 - August 2018

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • Computers operating in space must withstand a harsh radiation environment, which may cause system failures.
  • The primary failure mechanism known as single event effects (SEEs) in modern integrated circuits is due to high energy, ionizing radiation. SEEs are difficult to reproduce on the surface of the Earth due to the protective nature of the atmosphere and magnetosphere, thus RadSat-g, a CubeSat demonstration, is an ideal platform.
  • Single event effects are relatively infrequent (1-2 per day) in low-Earth orbit, so a long-term mission (6 months) is needed to collect meaningful reliability information on how they affect technology.
  • RadSat-g uses new ways of detecting SEEs and mitigating their effects, allowing the investigation to continue functioning in the harsh space environment.
  • The CubeSat avionics work to support the investigation by suppling power and data storage. The CubeSat creates its own power rails from the power supplied by the CubeSat batteries. The CubeSat also redundantly stores its own data as well as sending it to the avionics for storage and downlink.
  • The CubeSat’s radio performs communication with a ground station to upload commands and to download data.


The technology in RadSat-g improves the state-of-the-art space computing by deploying a novel single event effect (SEE) fault mitigation architecture on a commercial Field Programmable Gate Array (FPGA). Using a commercial FPGA fabricated in a process node of 45 nm yields an acceptable level of total ionizing dose (TID) immunity inherently through minimal feature sizes (approximately 400 krad). The use of a modern commercial FPGA also provides a significant increase in computational performance and power efficiency compared to custom, radiation hardened processors that use radiation hardened by design (RHBD) or radiation hardened by process (RHBP) techniques. The use of a commercial FPGA produces a tremendous reduction in cost by avoiding using low-volume, custom, radiation-hardened parts. The novel SEE mitigation architecture improves reliability beyond the existing SEE fault mitigation deployed on FPGA (i.e., triple modular redundancy (TMR) + memory configuration scrubbing) in order to deliver a platform that addresses all of NASA’s priorities for next generation space computers.
The SEE fault mitigation approach in this project extends TMR+ Scrubbing by including spare circuitry to enhance the operation of TMR and a spatially aware approach to improve traditional scrubbing. The approach to providing reliability involves breaking a commercial FPGA fabric into redundant tiles, each with the characteristics that fully contain the circuit of interest and also be individually reprogrammed using partial reconfiguration. For our system, each tile contains a Xilinx MicroBlaze™ soft processor (32-bit RISC architecture provided by Xilinx). At any given time, three of the tiles run in TMR with the rest of the tiles reserved as spares. The TMR voter is able to detect faults in the active triad by voting on the tile outputs. A configuration memory scrubber continually runs in the background and is able to detect faults in the configuration memory of both the active and inactive tiles. In the event of a fault in the active triad, (either detected by the TMR voter or scrubber), the damaged tile is replaced with a known good spare and foreground TMR operation continues. The damaged tile is repaired in the background by reinitializing its configuration memory through partial reconfiguration. This approach mitigates single event upsets (SEUs) in the FPGA circuit fabric in addition to single event functional interrupts (SEFIs) in the configuration memory. The advantage of this approach is that foreground operation may continue while the faulted tile is repaired and reintroduced into the system in the background. Since bringing on a spare tile takes significantly less time than performing background repair via partial reconfiguration of the damaged tile, the system availability is increased. This approach has been implemented on a Artix-7 FPGA with 9 MicroBlaze™ soft processors.
The payload is operated and supported by an avionics hardware stack that contains previous flight heritage. A power board governs solar cell operation, fixed power point tracking and battery charging. The power board also regulates multiple power rails that are used by the avionics systems. A Lithium L1 radio controls the uplink/downlink of commands and data to and from a ground station. An interface board controls commands sent to the payload as well as logging the payloads data. A passive magnet based attitude control system is used to provide longer orbital lifetime.

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Space Applications
Computers are extremely prevalent in space systems, making it important to have a reliable, low-cost computer while providing increased computation. Communications and autonomous systems benefit from the increased computation and radiation tolerance, allowing these systems to process data faster while experiencing less faults. This technology requires less shielding, freeing up mass of different technologies and creating more payload space during launch.

Earth Applications
Flexible, reliable, radiation-tolerant computers are imperative in system-critical applications and data analysis such as nuclear monitoring and power grid management on Earth.

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Operational Requirements and Protocols
NanoRacks CubeSats are delivered to the ISS already integrated within a NanoRacks CubeSat Deployer (NRCSD). A crew member transfers each NRCSD from the launch vehicle to the JEM. Visual inspection for damage to each NRCSD is performed. When CubeSat deployment operations begin, the NRCSDs are unpacked, mounted on the JAXA Multi-Purpose Experiment Platform (MPEP) and placed on the JEM airlock slide table for transfer outside the ISS. A crew member operates the JEM Remote Manipulating System (JRMS) – to grapple and position for deployment. CubeSats are deployed when JAXA ground controllers command a specific NRCSD.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Related Websites
Montana State University, LaMeres’ Research Overview

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Exploded CAD model showing the avionics, payload and structure of RadSat-g. Image courtesy of Matt Johnson.

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Rendering of RadSat-g in orbit around Earth. Image courtesy of Matt Johnson.

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