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RESEARCH POSTER PRESENTATION DESIGN © 2012
www.PosterPresentations.com
INTRODUCTION
What is the problem?
The ISS SpaceCube Experiment Mini (ISEM) is designed to
increase computing power on board the International
Space Station. Its field programmable gate arrays (FPGAs)
occasionally experience upsets known as single-event
upsets (SEUs), which are caused by a single particle hitting
sensitive electronics and freeing an embedded particle.
METHODS
1.* Upsets from 2014 (solar maximum) and 2017 (near
solar minimum) were located using ISS Tracker (Figure 1).
2. The SAA was simulated using the AE9/AP9/SPM
Radiation Environment Model (Figure 2).
3. The proportion of upsets likely caused by the SAA was
estimated (Table 2).
4. Space weather analysis was conducted to determine
whether an SEP event, radiation belt enhancement (RBE),
or geomagnetic storm (GST) was a plausible cause of each
upset that did not occur in the SAA.
5.** The proportion of upsets sufficiently close in time to
each space weather event was compared to the proportion
of the entire year that was sufficiently close in time to
each space weather event (Table 3).
6.** The temporal distribution of the upsets was tested for
uniformity (Figure 3).
* Solar maximum and (near) solar minimum were used to
distinguish between various space weather events.
** Steps 5 and 6 were only done for 2014 because 2017 did
not have enough upset data for reliable analysis.
RESULTS CONCLUSIONS
The proportion of upsets that occur in the SAA is
significantly higher than the proportion of time that the
ISS spends in the SAA. As a result, there is clear evidence
that the SAA causes upsets. We can estimate that
roughly 23% of all ISEM upsets and roughly 71% of ISEM
upsets that occur in the vicinity of the SAA are caused
by the SAA.
The lack of significant correlation between enhanced
space weather activity and ISEM upsets casts doubt on
the hypothesis that any of the space weather events
studied here (SEPs, GSTs, and RBEs) cause the upsets.
The temporal distribution of the upsets outside the
SAA fits a Poisson distribution reasonably well,
suggesting that uniform random or essentially random
processes, such as GCRs, cause many of the upsets.
There was very little difference between the numbers of
upsets per FPGA in 2014 and 2017. This is not enough to
discredit the hypothesis that GCRs are a significant
cause of the upsets, but it is surprising, as the frequency
of GCRs, while roughly constant in the short run, varies
significantly over the solar cycle.
A significant limitation of this analysis is the very small
amount of data: the only available upsets were 62
upsets from one FPGA in 2017 and 190 upsets from three
FPGAs in 2014.
REFERENCES
Galactic Cosmic Rays. (2012, May 11). Retrieved July 16, 2018, from
https://helios.gsfc.nasa.gov/gcr.html
Ginet, G.P., et al. (2013). AE9, AP9 and SPM: New Models for Specifying the
Trapped Energetic Particle and Space Plasma Environment. In: Fox, N.,
Burch, J.L. (Eds.), The Van Allen Probes Mission. Springer, Boston, MA.
I.S.S. Tracker. (n.d.). Retrieved July 18, 2018, from
http://www.isstracker.com/historical
Mewaldt, R. A., Davis, A. J., Lave, K. A., et al. 2010, ApJL, 723, L1
Primary Cosmic Rays. (n.d.). Retrieved July 16, 2018, from
http://cosmic.lbl.gov/SKliewer/Cosmic_Rays/Primary.htm
SpaceCube: A Family of Reconfigurable Hybrid On-Board Science Data
Processors. (2017, April 4). Retrieved July 2, 2018, from
https://spacecube.nasa.gov/
Zheng, Y. (2018). Space Weather Impacts on Satellites/Space Assets
[PowerPoint slides]. Retrieved from
https://ccmc.gsfc.nasa.gov/RoR_WWW/SWREDI/2018/REDI2018_template_
SWx_Impacts_Sat_final_f.pdf
ACKNOWLEDGMENTS
Sujay would like to thank Dr. Yihua Zheng for her mentorship and the staff
of the Community Coordinated Modeling Center (CCMC) for introducing him
to the field of space weather. He would also like to thank the Catholic
University of America (CUA) for its support through the Science and
Engineering Summer Internship (SESI) program. Finally, he would like to
thank Thomas Flatley for supplying and clarifying the ISEM upset data and
fellow forecasting intern Keyan Gootkin for helping him plot the SAA.
1Massachusetts Institute of Technology (MIT), 2NASA GSFC Code 674
Sujay Kazi1, Yihua Zheng2
Analysis of ISS SpaceCube Experiment Mini Upsets
Figure 1: A map of the 62 upsets that occurred on one FPGA of the SpaceCube experiment in 2017. The 10 upsets that occurred over South America and the 4 upsets that occurred over the south Atlantic ocean are likely caused by the SAA, while the others have less predictable causes.
Figure 2: A map of the flux intensity of the trapped particles at the height of the ISS orbit (about 400 km). The flux is close to zero everywhere other than the SAA because the inner radiation belt is well above the ISS orbit altitude everywhere else on the planet.
Figure 3: The year 2014 was split into 73 segments of 5 days each, and the frequency of the number of upsets outside the SAA in each period was tested against a Poisson distribution.
FURTHER RESEARCH
Future analysis would include a much greater amount of
upset data from many years and more information
regarding the nature and severity of each upset.
In particular, examining the frequency of upsets over
several years could be a way to test the hypothesis that
GCRs are a significant cause of the upsets.
Table 2: The numbers and proportions of upsets that occurred in the vicinity of the SAA in 2014 and 2017 were used to estimate what fraction of upsets are likely caused by the SAA.
Why should we care? Space weather can affect anything we send into space. For
instance, SEPs are a hypothesized cause for the loss of
contact with STEREO-B (a satellite launched in 2006 to help
provide a full view of the Sun) in October 2014, and
astronauts staying on the ISS for extended periods of time
have had cases of cancer caused by high-energy radiation.
Understanding the levels of threat various space weather
phenomena pose to electronics and people in space will be
necessary for future space missions, such as the James
Webb Space Telescope and a future trip to Mars.
What are the suspects? SEUs tend to be caused by space weather events including
solar energetic particles (SEPs) and galactic cosmic rays
(GCRs), as well as more static presences such as the South
Atlantic Anomaly (SAA), a region where the inner radiation
belt crosses the altitude of the ISS due to the shape of the
Earth’s magnetic field. These are shown below in Table 1:
Table 3: The proportion of 2014 upsets in the temporal vicinity of a GST, SEP event, or RBE is shown to be not significantly greater than the proportion of the whole year of 2014 in the temporal vicinity of each of these events. This means that it is plausible that these upsets had other causes and were close to these events simply by chance.