Single-event upset in geostationary transfer orbit during solar-activity maximum period measured by the Tsubasa satellite

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    well with those of trapped protons. The peak SEU rate appears around L = 1.4. The transition point from SEUs caused by trapped pro-tons to those caused by galactic cosmic rays is around L = 2.6. During the experiment period, increased SEU count was sometimes

    Recently, SEUs are not considered to lead to serious situ-ations in spacecraft system because a SEU is a bit upset

    areas in the geomagnetosphere in order to understand thecharacteristics of SEU occurrence and its relation to the

    environment on spacecraft system, and was operated inGTO during solar-activity maximum period. This paper

    of bus-system components in space. The Tsubasa satellitewas launched into GTO, where on board experiments wereconducted in the more severe radiation environment ofGTO rather than in geostationary orbit (GEO) or lowearth orbit (LEO). The Tsubasa satellite had been operatedfrom February 2002 until September 2003, corresponding

    * Corresponding author.E-mail address: (H. Koshiishi).

    Available online at

    Advances in Space Research 42in CPUs and/or memories that induces software errors,and can be restored by automatic correction, software re-upload, or power reset. However, SEUs still require atten-tion in both the development and the operation phase ofspacecraft since high-energy particles often increase rapidlydue to solar and geomagnetic events, or a single high-energy particle often causes multiple-bit upsets (e.g., Swift,2000). In these cases, simultaneous SEUs may lead to seri-ous situations in spacecraft system.

    Thus, it is still important to monitor SEUs over wide

    reports SEU occurrence related to the space radiation envi-ronment measured by the Tsubasa satellite.

    2. Measurement

    The objective of the Tsubasa satellite (Mission Demon-stration Test Satellite-1: MDS-1) developed by the JapanAerospace Exploration Agency (JAXA) is to verify thefunctions of commercial parts and the new technologiesdetected due to solar and geomagnetic events outside the inner radiation belt. 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

    Keywords: Space radiation environment; Single-event upset; Geostationary transfer orbit

    1. Introduction

    A single-event upset (SEU) is a type of spacecraft anom-alies that is caused by a single high-energy particle in semi-conductor electronic devices (e.g., Robinson, 1989).

    space radiation environment. A few experiments have beenconducted over wide areas in the geomagnetosphere suchas in geostationary transfer orbit (GTO) (Violet and Fred-erickson, 1993). The Tsubasa satellite was specicallydeveloped for researching the eects of the space radiationSingle-event upset in geostasolar-activity maximum period m

    H. Koshiishi *, H. M

    Japan Aerospace Exploration Agency,

    Received 31 October 2006; received in revised for


    This paper reports single-event upset (SEU) occurrence related ting solar-activity maximum period measured by the Tsubasa satelthat they are mainly caused by trapped protons. Thus, the spatial0273-1177/$34.00 2007 COSPAR. Published by Elsevier Ltd. All rights resedoi:10.1016/j.asr.2007.11.02613 September 2007; accepted 20 November 2007

    e space radiation environment in geostationary transfer orbit dur-. Most SEUs are measured in the inner radiation belt, indicatingtribution and the temporal variation of the SEU count correlateonary transfer orbit duringasured by the Tsubasa satellite

    tsumoto, T. Goka

    (2008) 15001503rved.

  • collection were stable. Table 1 lists the major characteris-

    also observed especially on 21 April 2002 and 24 August2002, which were due to solar ares (see Solar-GeophysicalData) and halo-type coronal mass ejections (see SOHOLASCO CME CATALOG) occurring on the same days.

    Fig. 1. The Lt diagram of the proton ux with energy range of 2143 MeV from March 2002 to May 2003. Precipitations of protonsobserved on 21 April 2002 and 24 August 2002 due to solar ares andhalo-type coronal mass ejections are marked with 1 and 2,respectively.

    pace Research 42 (2008) 15001503 1501tics of the Tsubasa satellite.The Space Environment Data Acquisition Equipment

    (SEDA) is on board the Tsubasa satellite to observe thespace radiation environment and to measure the spacecraftanomalies due to them (Koshiishi et al., 2002). The StandardDoseMonitor (SDOM) of the SEDA observes protons withenergy range of 0.9210 MeV in 12 bins in every 8 s (Greenet al., 2004). The Heavy Ion Telescope (HIT) of the SEDAobserves heavy ions (heliumiron) with energy range of18179 MeV/nucleon (Matsumoto et al., 2005).

    The Single-event Upset Monitor (SUM) of the SEDAmeasures SEUs in the test samples of two commercial 64-Mbit DRAMs in every 128 s. The SUM writes a test datainto all address of the test samples, waits for 64 s, readsthe contents from all address, and compares the contentswith the test data. The SUM conducts the same procedureagain in next 64 s. If the SUM nds the dierence betweenthe contents and the test data in the rst 64 s, and does notnd the dierence at the same address in the second 64 s,the dierence is classied to a SEU. Otherwise, if theSUM nds the dierence in both successive 64 s, the dier-ence is regarded to be owing to hardware errors. The hex-byte data of 55 and AA are used as a test data oneafter another.

    3. Analysis and discussion

    The most eective energy range to cause SEUs in theto solar-activity maximum period. In this paper, the dataset obtained from March 2002 to May 2003 is used in anal-yses because, during this period, the operation and the data

    Table 1The major characteristics of the Tsubasa satellite

    Launch date 4 February 2002Experiment period 12 February 2002 to 24 September 2003Dimension 1.2 1.2 1.5 mWeight 480 kgOrbit perigee 500 kmOrbit apogee 36,000 kmOrbit inclination 28.5Orbit period 10 h 35 minAttitude control Spin stabilized 5 rpm

    H. Koshiishi et al. / Advances in Sdevices depends on the eective shield thickness of thespacecraft body and the materials around the devices.The proton data obtained by the SDOM is compared withthe SEU data obtained by the SUM, indicating that thespatial distribution of protons with energy range exceedingseveral tens MeV is consistent well with that of the SEUcount. This result suggests that the equivalent aluminumshield thickness around the test samples of the SUM isabout 1 cm (e.g., Holmes-Siedle and Adams, 1993).

    Fig. 1 illustrates the Lt diagram of the proton ux withenergy range of 2143 MeV obtained by the SDOM.Trapped protons in this energy range are observed mostlyin the L-shell below L = 2. Precipitations of protons wereFig. 2 depicts the magnetic-local-time (MLT) distributionof the proton ux. In the inner radiation belt, trapped pro-tons distribute almost uniformly against MLT. An asym-metry that appears in peak-ux range is mostly due tothe relation between the orbit of the Tsubasa satellite andFig. 2. The magnetic-local-time (MLT) distribution of the proton uxwith energy range of 2143 MeV from March 2002 to May 2003. Eachvalue is the largest ux at each location during the above period.Enhanced ux between 0 h and 6 h (MLT) and around 18 h (MLT)corresponding to precipitations of protons observed on 21 April 2002 and24 August 2002 are marked with 1 and 2, respectively.

  • pac1502 H. Koshiishi et al. / Advances in Sthe spatial distribution of trapped protons in the inner radi-ation belt, which is seen as a seasonal eect in Fig. 1. Out-side the inner radiation belt, two groups of enhancedproton ux were obtained along the orbit of the Tsubasasatellite, which corresponded to precipitations of protonsin Fig. 1. In these cases, the proton radiation environmentbecomes severe for a few orbit periods in GTO even outsidethe inner radiation belt.

    The Lt diagram of the SEU count obtained by theSUM is illustrated in Fig. 3. Most SEUs are measured inthe L-shell below L = 2, indicating that they are mainly

    Fig. 3. The Lt diagram of the single-event upset (SEU) count detected intwo 64-Mbit DRAMs from March 2002 to May 2003.

    Fig. 4. The magnetic-local-time (MLT) distribution of the single-eventupset (SEU) count detected in two 64-Mbit DRAMs from March 2002 toMay 2003. Each value is the largest count at each location during theabove period.caused by trapped protons. The temporal variation of theSEU count correlates well with that of trapped protonsin Fig. 1. SEUs measured outside the inner radiation beltare mainly caused by galactic cosmic rays (GCRs). TheSEU count outside the inner radiation belt is almost con-stant with time, except for increased SEU count associatedwith solar and geomagnetic events especially on 21 April2002, since the ux of GCRs is considered to be almostconstant during such a short experiment period as com-pared with an 11-year solar cycle period. The MLT distri-bution of the SEU count is depicted in Fig. 4. While theMLT distribution outside the inner radiation belt is almostuniform, the MLT distribution in the inner radiation beltshows an asymmetry in peak-count range, which followsthe asymmetry of the proton ux seen in Fig. 2.

    Fig. 5. The single-event upset (SEU) rate as a function of L in 0.1 stepdetected in two 64-Mbit DRAMs averaged from March 2002 to May2003. The proton ux with energy range of 86210 MeV and the heavy ioncount (heliumiron) averaged through the above period are also plotted.

    e Research 42 (2008) 15001503Fig. 5 plots the SEU rate as a function of L in 0.1 stepobtained by the SUM overlaid with the proton ux withenergy range of 86210 MeV obtained by the SDOM andthe heavy ion count (heliumiron) obtained by the HITaveraged through the experiment period. The peak SEUrate appears around L = 1.4