NanoRacks-Evaluation of Gumstix Performance in Low-Earth Orbit (NanoRacks-Gumstix) - 02.22.17

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ISS Science for Everyone

Science Objectives for Everyone
Computers used in space must be designed to withstand radiation, and the lengthy testing process often means that space-based computers are two or three generations behind state-of-the-art computers on Earth. The NanoRacks-Evaluation of Gumstix Performance in Low-Earth Orbit (NanoRacks-Gumstix) investigation tests small computers called Gumstix modules, which are based on open-source software, as an alternative off-the-shelf option for use in space. The investigation studies whether the Gumstix microprocessors can withstand the radiation environment on board the International Space Station.
Science Results for Everyone
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The following content was provided by Kathleen Morse, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom:

Principal Investigator(s)
Kathleen Morse, Ph.D., Yosemite Space, Groveland, CA, United States

Co-Investigator(s)/Collaborator(s)
Information Pending

Developer(s)
Yosemite Space, CA, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
National Laboratory (NL)

Research Benefits
Space Exploration

ISS Expedition Duration
March 2016 - September 2016; April 2017 - September 2017

Expeditions Assigned
47/48,51/52

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • NanoRacks-Evaluation of Gumstix Performance in Low-Earth Orbit (NanoRacks-Gumstix) evaluates the Computer on Module technology performance in the low earth orbit space radiation environment.
  • NanoRacks-Gumstix determines the total number of soft errors, measures the Negated AND or NOT AND (flash reliability, occurrence of Logical Units (LUs), the occurrence of Single Event Functional Interruptions (SEFIs)) and the total time of operation for each module relative to the total time of the test.

Description

Traditionally, radiation hardened computers used in satellites and are typically 2 or 3 generations behind the state-of-the-art terrestrial processing technologies. NanoRacks-Evaluation of Gumstix Performance in Low-Earth Orbit (NanoRacks-Gumstix) investigates NanoRacls-Gumstix modules as an alternative commercial off-the-shelf (COTS) computer technology for space applications. NanoRacks-Gumstix modules are a Linux based computer with features found in modern computers and smart phones. They are small, low power, versatile and use current generation microprocessors. In addition, the NanoRacks-Gumstix software platform allows developers use use open source tools and libraries, which reduces development time. The NanoRacks-Gumstix module can be integrated into fault tolerant architectures and potentially enable computationally demanding, next generation space missions.
 
The NanoRacks-Gumstix module models chosen for the study are built on processors, which have feature sizes of 45 nm and 65 nm. Small feature sizes are known to have a total ionizing dose (TID) greater than 100 krad. However, these devices tend to be sensitive to single event effects (SEE), which include catastrophic and non-catastrophic latch-up (LU), single event upset (SEU) and single-event functional interrupt (SEFI). The proposed study characterizes SEE sensitivity, net operation time and general-purpose processor (GPP) performance during and after radiation exposure.
 
The research approach to evaluate NanoRacks-Gumstix modules for use in low-Earth orbit (LEO) involves ground-based testing and evaluation as well as six month space-based testing and post-flight evaluation. In addition, a ground-based control experiment runs in parallel to the space experiment. Prior to exposure, all NanoRacks-Gumstix modules undergo high-level functional analysis to characterize GPP stability, memory and peripherals. During radiation exposure, the four NanoRacks-Gumstix modules are connected to a watchdog. The watchdog circuit monitors the occurrence and frequency of LU and then cycles power to restore function to the affected module. The watchdog also monitors a heartbeat from each NanoRacks-Gumstix module and cycle power when no signal is received. The lack of signal can indicate an SEU or SEFI event. In addition, the watchdog records the net operation time for each module. During radiation exposure, each module runs custom software that determines the rate of soft errors and measures negative-AND gate (NAND) reliability. After exposure, the modules undergo high level functional testing for a second time so that any changes to the module performance, memory and peripherals can be observed.
 
High level functional analysis is performed on all modules before and after exposure to space and ground based tests. This includes low-level memory testing of the RAM and GPP stability evaluation at different clock speeds for a baseline task load. Pre and post exposure testing also includes tests to determine total number of soft errors and measures NAND reliability. These are the same tests that are performed during radiation exposure except that these are shorter in duration.
 
Low level testing counts the number of memory errors generated by the RAM on each module. The memory testing involves running diagnostic software that repeatedly writes known values to every memory address and reads those values back to look for mismatches. To evaluate processor stability with clock speed, the processor performs a given set of computationally demanding tasks at a given clock speed approved by the manufacturer. If the processor hangs, the time and the clock speed is noted. The module is then rebooted at a lower clock speed and retested. The CPU usage is recorded for each test. The operation of the peripheral interfaces for each NanoRacks-Gumstix module is tested. Peripherals include the USB (keyboard and mouse), video, WiFi and Bluetooth.
 
Pre and post exposure testing takes place at Yosemite Space using available computer facilities located in Groveland, CA. The principal investigator and software engineer consultant are on hand to perform tests and analysis. Dr. John Samson serves as a technical consultant. He evaluates test plans and results remotely at Honeywell Aerospace. The goal for both ground and space testing is to determine the total number of soft errors, measure NAND reliability, the occurrence of LUs, and the total time of operation for each module. The NanoRacks External Platform provides an optimal environment for LEO radiation studies since it offers minimal to no radiation shielding and exposure to space for up to 6 months.
 
To check for soft errors, each module's processor runs custom software to perform predetermined mathematical calculations with known inputs and outputs, also known as golden standard comparisons. The results of these calculations are periodically summarized time stamped, and downlinked to be analyzed in semi-real time. The results are written to an external SDHC micro memory card, which uses Error Correcting Code (ECC) circuitry to detect and correct transfer errors. A soft error is expected to show up as a miscalculation. The number of golden standard miscomparisons determines the computational correctness number. Once the assembly is returned from space, the contents of the memory cards from each module is examined to determine the total soft error rate for each module as well as the total operational time of the modules during flight.
 
To detect possible future failures and to evaluate NAND reliability, a cyclical redundancy check (CRC) is executed for the duration of the space experiment and ground testing. A future failure can be caused by a SEU that causes a flipped bit on the portion of the NAND that contains the operating kernel or critical system files. If not corrected, this can cause the whole systems to hang temporarily or permanently at some point in the future. In the event that a corrupted file is found by the CRC, the discrepancy will be recorded and written to an external SDHC micro memory card. In the event that the program hangs or the processors hang, the watchdog cycles power to the module.
 
A radiation hardened, LU immune watchdog circuit detects the occurrence of LU and the occurrence of a potential SEU or SEFI in each NanoRacks-Gumstix module. In addition, it records the event and then cycle power to the module to enable recovery. To detect LU, the watchdog is also programmed to detect irregularities in current draw for each module using current monitoring circuitries. Each current monitor consists of a shunt resistor in series with the supply line of a NanoRacks-Gumstix module and an instrumentation amplifier amplifying the small voltage drop through the shunt and forwarding the signal to an analog input of the watchdog microcontroller. The output voltage of the instrumentation amplifier is equivalent to the current draw of the monitored NanoRacks-Gumstix module. The watchdog is also programmed to expect periodic heartbeat from each module. If the watchdog circuit does not receive a signal in a specified amount of time, the watchdog records the absence of signal and then resets power to the module and therefore restores the operation of the module. Metal–oxide–semiconductor field-effect transistor (MOSFET) components act like switches and cycle power to the NanoRacks-Gumstix module. The absence of signal could be caused by a SEU or SEFI event. The events are recorded in the watchdog removable memory. The data is downlinked from the watchdog to the International Space Station (ISS). In addition, each NanoRacks-Gumstix module is able to downlink data regarding soft errors and NAND reliability through the NanoRAcks-Gumstix communication. Each of the NanoRacks-Gumstix communications ports is routed to the watchdog. The watchdog communications port contains information from all four NanoRacks-Gumstix modules and the watchdog.
 
TID and proton fluencies for one day of testing at Crocker Nuclear Laboratories cyclotron exceeds six months in LEO by orders of magnitude. The goals of ground-based tests are to characterize LU in NanoRacks-Gumstix and verify that the watchdog can protect them from catastrophic failure while in space.
 
A control experiment is conducted in a radiation-free environment over the same time as the space experiment. This uses the prototype watchdog circuit and runs similar tests as the ground based radiation experiment and the space experiment. The total number of soft errors, the NAND reliability, the frequency of LU and SEFI and the net operation time of each module is recorded. The control experiment takes place at Yosemite Space in Groveland, CA using available facilities.

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Applications

Space Applications
The microprocessors that power today’s computers are very sensitive to cosmic rays, which are more prevalent in space. High-energy particles from the sun and other cosmic sources can interfere with processors and cause malfunctions or loss of data, known as single event effects. This investigation studies the radiation tolerance of a small commercially available computer called a Gumstix module, which has capabilities found in modern computers and smart phones. The devices use processors with very small gaps between transistors, which enables tiny computers but also makes the processors vulnerable to errors caused by cosmic rays. The investigation uses a watchdog circuit that keeps track of any radiation-related errors during a six-month stay on the exterior of the ISS.

Earth Applications
Tiny, powerful microprocessors power today’s smartphones and computers, but the same processors are not widely used in space because they may not be able to withstand the extreme temperature and radiation environments. This investigation tests whether one small computer called a Gumstix module can withstand the harsh radiation of space, and whether it could be used in future spacecraft. Miniature spacecraft using Gumstix could conduct communications and remote sensing research, lowering the cost of access to space and benefiting people on Earth.

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Operations

Operational Requirements and Protocols
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Decadal Survey Recommendations

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Results/More Information

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Related Websites
Yosemite Space

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Imagery

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The NanoRacks-Gumstix flight board. Image courtesy of Yosemite Space.

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Flight Boards including the NanoRacks-Gumstix Board and External Watchdog. Image courtesy of Yosemite Space.

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NanoRacks-Gumstix Radiograph from ground based radiation testing. Image courtesy of Yosemite Space.

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