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CRRES MEP SEU Rates

We also tested the CREME/TRP/AP8MAX module by comparing with trapped-proton-induced SEU rates observed in the Micro-Electronics Package (MEP) aboard CRRES (Campbell 1991; Campbell et al. 1994). The comparisons are summarized in the table below. Apart from one device (93422, for which some authors have expressed reservations about the ground-test data), the calculations generally agree with the observed rates to within a factor of ~2 for the eight months prior to 24 March 1991. (We have made no attempt to analyze the post-March 1991 SEU rates.) Excluding the 93422, the ratio of calculated to observed SEU rates varied from device to device, with values ranging from ~0.8 to 2.4. For the ensemble of devices considered, the average value of the calculated to observed rates was 1.5.

A previous analysis (Petersen 1997) reported apparently better agreement between AP8MAX-based calculations and the observed CRRES/MEP SEU rates, with an average calculated-to-observed ratio of ~0.95. However, it is now acknowledged that those calculations were misleading, in that they failed to take into account details of the CRRES orbit.

In particular, those calculations set the argument of perigee and initial longitude of the ascending node to "default" values of zero. Moreover, these quantities underwent significant precession during the CRRES mission, largely due to the oblateness of the Earth. This precession, which was also inadequately accounted for in the Petersen (1997) calculations, significantly affected CRRES's sampling of the trapped proton belt. (The argument of perigee is especially important in this regard, since it controls the latitudes at which apogee and perigee are encountered.) In fact, by carefully tracking this orbital precession, it is possible to largely account for the ~monthly variation seen in the CRRES/MEP SEU rates, at least prior to the 24 March 1991 disturbance.

The calculations below included these details of the CRRES orbit. As shown in the table below, we re-evaluated the argument of perigee and the initial longitude of the ascending node on the first day of each month, by examining CRRES orbital data provided by the NASA SSCWeb. These revised orbital parameters were then input to the CREME software, to calculate monthly CRRES/MEP SEU rates.

(Note that the current CREME orbit generator does not automatically generate orbital precession. For this reason, orbital parameters must be re-evaluated, rather than simply running the orbit-averaging over a larger number of orbits. We verified that tracking the precession on even finer time scales did not significantly change the calculated results.)

CRRES/MEP Trapped Proton-Induced SEU RATES1

Launch to 23 March 1991 (Orbits 4-584)

Table 1
CRRES MEP
Device: 93422 93L422 82S212 92L44 21L47 2164 71681 6116
BLK: 1C 1B 1D 15 14 ? 23 24
Bendel Parameter(s)2: 17.66 16.40 16.60 20.33 20.48 A=3.5;B=4.03 24.06 25.02
Observed3 SEUs/kbit/day: 4.20 3.15 0.83 0.112 0.065 0.081 0.0053 0.0031
Start Date Argument of Perigee4 Initial Longitude Ascending Node4 CREME96/TRP Calculated SEU Rates (SEUs/kbit/day)5,6,7
08/01/90 205o 62o 0.67 1.95 1.64 0.087 0.078 0.111 0.0075 0.0043
09/01/90 229o 316o 0.85 2.49 2.09 0.110 0.100 0.141 0.0096 0.0054
10/01/90 252o 286o 1.01 2.94 2.47 0.131 0.118 0.168 0.0113 0.0064
11/01/90 276o 319o 1.05 3.07 2.58 0.137 0.123 0.175 0.0118 0.0067
12/01/90 299o 140o 0.93 2.72 2.28 0.121 0.109 0.154 0.0105 0.0059
01/01/91 323o 180o 0.75 2.18 1.83 0.097 0.087 0.123 0.0084 0.0048
02/01/91 347o 70o 0.60 1.76 1.48 0.078 0.070 0.100 0.0068 0.0039
03/01/91 9o 73o 0.58 1.70 1.43 0.076 0.068 0.097 0.0066 0.0037
Average Calculated Rate8 0.81 2.35 1.98 0.105 0.094 0.134 0.0090 0.0051
Ratio [Ave. Calc./Obs] 0.19 0.75 2.37 0.93 1.45 1.64 1.70 1.65

NOTES:

  1. Following Petersen (1997), trapped-proton induced SEUs are defined as those collected at L < 2. However, the reported rates are orbit-averaged, that is, evaluated using the time of the whole orbit, not just those portions located at L < 2.
  2. Bendel parameters taken from Petersen (1997), Table 1.
  3. Observed average SEU rates taken from Petersen (1997), Table 1.
  4. Argument of Perigee and Initial Longitude of Ascending Node deduced from SSCWeb orbital paths. Argument of Perigee starts at 205o on 1 August 1990 and precesses at a rate of 0.7713 deg/day. Initial longitude of ascending nodes was taken directly from the SSCWeb trajectory information.
  5. Shielding distribution as given by Smith (1994) for Device U25.
  6. Other orbital parameters (apogee, perigee, inclination, as given in following table) given by Campbell (1991).
  7. Calculated rates from the CREME/TRP software, with input parameters as follows:
Apogee 33582 km
Perigee 348 km
Inclination 18.2o
Argument of Perigee Variable, as shown above
Initial Longitude of Ascending Node Variable, as shown above
Initial Displacement from Ascending Node 0
Number of Orbits 75
Number of Steps per Orbit 200
Model AP8MAX
Shielding Device U25 Distribution
  • "Average Calculated Rate" is the average of the monthly rates.

The comparisons shown here confirm the "factor of two" uncertainty generally quoted for AP8-based orbit-averaged calculations. This conclusion may also be as much as can be expected, given the uncertainties in the CRRES/MEP ground-test data.

However, the following discrepancies are perhaps worth noting:

  1. According to Gussenhoven et al. (1996), direct measurements from the Proton Telescope (PROTEL) on CRRES showed trapped proton fluxes at ~15-80 MeV which typically exceeded those from AP8MAX by up to a factor of three. In this study of SEU rates, however, the observed SEU rates tend to be smaller than the AP8MAX predictions by a factor of ~1.5. This discrepancy may be related to the fact that higher-energy protons, which were beyond the range of the PROTEL measurements, primarily caused the MEP SEUs.
  2. Whereas the calculated SEU rates shown here are too high on average, low-altitude (<1000 km) doses and SEU rates are generally under-estimated by the AP8 models. This discrepancy may be related to the fact that most of the CRRES/MEP SEUs were observed at higher altitudes (~3000 km).

References:

  1. Campbell 1991: A.B. Campbell, "SEU Flight Data from the CRRES MEP", IEEE Transactions on Nuclear Science 38, no. 6, pp. 1647-1654, December 1991.
  2. Campbell et al. 1994: A.B. Campbell, P. McDonald, R. Gonyea, and M. Reeves, "Results from the CRRES MEP Experiment", IEEE Transactions on Nuclear Science 41, no. 3, pp. 432-437, June 1994.
  3. Gussenhoven 1996: M.S. Gussenhoven, E.G. Mullen, and D.H. Brautigam, "Improved Understanding of the Earth's Radiation Belts from the CRRES Satellite", IEEE Transactions on Nuclear Science 43, no. 2, pp. 353-368, April 1996.
  4. Petersen 1997: E.L. Petersen, "Predictions and Observations of SEU Rates in Space", IEEE Transactions on Nuclear Science 44, no. 6, pp. 2174-2187, December 1997.
  5. Smith 1994: E.C. Smith, "Effects of Realistic Satellite Shielding on SEE Rates", IEEE Transactions on Nuclear Science 41, no. 6, pp. 2396-2399, December 1994.
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