ta of figure 15 correspond to a particular data rate and the LET is for the InGaAs detector material. (LET) = To assess proton effects on the link at other data rates, we could analyze other data sets measured at other rates as we have for the 400 Mbps data set. However more general results can be obtained by inspecting figure 16, which plots cross section dependence on IV-34 optical power for 200, 400, and 1000 Mbps. The two data sets shown represent the high and low LET particles, namely He ions and high energy protons. Note that across the full optical power range and for these two extremes in particle LET, the cross section exhibits, to first order, a direct proportionality to data rate. This trend was noted in all of the detector BER data, and it is consistent with the arguments pertaining to clock rate dependence made earlier in this section. According to equation 3, a cross section that is proportional to data rate results in a BER which is independent of data rate. The cross section is represented by O, and is the particle flux. The on-orbit error rate in terms of errors per day, however, would be expected to scale linearly with error cross section. It would be up to the application as whether the BER or the error rate is the more important metric. #errors BER = Transmitted Data Rate By using the Weibull approximation we can describe the LET dependence of the proton-induced error cross section and then combine this response with the LET spectrum arising from direct ionization by protons in the detector material system. Then it is possible to exercise the conventional tools for heavy ion upset rate predictions to assess link BER performance in proton rich orbits. This general approach has been validated against flight data with excellent agreement [LaBe-97a, Mars-96, and references therein]. ETX75 InGaAs p-i-n Diode at 400 Mbps Optical Power -25 dBm -23 dBm -21 dBm -19 dBm -17 dBm -15 dBm LET in InGaAs (MeV cm 2 /g) Figure 15. Proton-induced bit error data depends on the effective particle LET, even though