Attachment R RPT 418 XO RPT 0042 Version 1.20.pdf

Effective Date: April 11, 2023 418-XO-RPT-0042 Responsible Organization: GeoXO/Code 418 Version 1.2 i

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The Radiation Environment for Electronic Devices on the Geostationary eXtended Observations (GeoXO) Series Satellites

Signature page

Prepared By:

Electronically approved by: 01/18/2022 Raymond L. Ladbury Date Author/Radiation Effects and Analysis Group NASA GSFC, Code 561

Reviewed By:

Electronically approved by: 01/18/2022

Megan E. Gorham Date GeoXO Flight Project, Systems Engineer NASA GSFC, Code 418

Approved By:

Electronically approved by: 11/03/2021

Steven W. Bidwell Date GeoXO Flight Project, Mission Systems Manager NASA GSFC, Code 418 ii

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TABLE OF CONTENTS

I. INTRODUCTION

II. RADIATION ENVIRONMENT

III. DESCRIPTION OF RADIATION EFFECTS

A. TOTAL IONIZING DOSE

B. DISPLACEMENT DAMAGE

C. SINGLE EVENT EFFECTS

D. RELEVANT SPACE RADIATION ENVIRONMENTS

IV. THE GEOXO MISSION

V. TOTAL DOSE AND DEGRADATION ANALYSIS

A. DEGRADATION ENVIRONMENTS

1. The Plasma Environment [3]

2. High Energy Particles – Spacecraft Incident Fluences

3. High Energy Particles – Shielded Fluences

B. TOTAL DOSE ESTIMATES

1. Top Level Ionizing Dose Estimates

2. Dose at Specific Spacecraft Locations

C. DISPLACEMENT DAMAGE ESTIMATES

VI. SINGLE EVENT EFFECTS ANALYSIS

A. HEAVY ION INDUCED SINGLE EVENT EFFECTS

1. Galactic Cosmic Rays

2. Solar Heavy Ions

B. PROTON INDUCED SINGLE EVENT EFFECTS

1. Trapped Protons

2. Solar Protons

VII. INSTRUMENT INTERFERENCE

VIII. SPACECRAFT CHARGING AND DISCHARGING

IX. SUMMARY

X. REFERENCES

APPENDICES

GLOSSARY

iii

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List of Figures

Figure 1. Projection of the solar activity during the GeoXO mission (Source: WDC-SILSO, Royal Observatory of Belgium, Brussels; forecasts based on cycles 21 and 22

Figure 2. Integral solar proton fluences for 15-year mission involving 11 solar active years are presented for 90% & 95% confidence levels

Figure 3. Bounding Integral electron fluences for all GeoXO missions (148°W Longitude)

Figure 4: Shielded integral solar proton fluences for 15 years with 11 solar active years (90% confidence level). The unshielded fluence from Figure 2 is included for reference

Figure 5: Shielded Integral Electron Fluences For 15 Year Mission (Worst Case). The unshielded fluence from Figure 3 is included for reference

Figure 6: Total ionizing dose for 15 year mission (worst case)

Figure 7: Equivalent particle fluences for mission Total Non-Ionizing Dose in Si for 15 year mission (worst case)

Figure 8: Equivalent particle fluences for mission Total Non-Ionizing Dose in GaAs for 15 year mission (worst case)

Figure 9: Integral LET spectra are shown for galactic cosmic ray ions hydrogen through uranium

Figure 10: Integral LET spectra are shown for hydrogen through uranium for the October 1989 solar particle event

Figure 11: Solar proton fluxes for single event effects evaluation

Figure 12: Hourly averages of solar proton fluxes for > 50 MeV protons for 1989

Figure 13: Hourly averages of solar proton fluxes for > 50 MeV protons for 1990

Figure 14: Hourly averages of solar proton fluxes for > 50 MeV protons for 1991

Figure 15: Daily integral electron levels for GeoXO iv

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List of Tables

Table 1. Radiation Effects in Geosynchronous

Table 2. Worst-Case Geosynchronous Plasma Environment

Table 3. Surface Coatings and Materials

Table A1: Spacecraft Incident Integral Solar Proton Fluences (#/cm2) for 15 Year Mission (11 Solar Active Years)

Table A2. Spacecraft Incident Integral Electron Fluences (#/cm2) for GeoXO Mission (Worst Case, 148°W)

Table A3. Integral Solar Proton Fluences (#/cm2) Behind Solid Sphere Aluminum Shields 15 Year Mission (11 Active Solar Years) – 90% Confidence Level

Table A4. Integral Electron Fluences (#/cm2) Behind Solid Sphere Aluminum Shields 15-Year Worst- Case Mission (15 Years At 148°W)

Table A5. Total Ionizing Dose (RadsSi) at the Center of Solid Al Spheres for 15-Year Worst-Case Mission (15 Years At 148W, 11 Active Years At 90% Confidence Level)

Table A6. Total Non-Ionizing Dose in Si (Equivalent Fluences) at Center of Solid Al Spheres for 15- Year WC Mission (15 Years At 148W, 11 Active Years At 90% Confidence Level)

Table A7. Total Non-Ionizing Dose in GaAs (Equivalent Fluences) at Center of Solid Al Spheres for 15-Year WC Mission (15 Years At 148W, 11 Active Years At 90% Confidence Level)

Table A8. Integral LET for Interplanetary Galactic Cosmic Rays (Z=1-92) 100 mils Aluminum Shielding

Table A9. Integral LET for the October 1989 Solar Particle Event (Z=1-92) 100 mils Aluminum Shielding

Table A10. Differential Fluxes from Solar Proton Events - 100 mils Aluminum Shielding, CREME96 .. 34

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I. INTRODUCTION

The purpose of this document is to define the radiation environment for the evaluation of degradation due to total ionizing and non-ionizing dose and of single event effects (SEEs) for the Geostationary eXtended Observations (GeoXO) instruments and spacecraft. The analysis took into account the radiation exposure for the nominal 15-year mission (10 years’ operating & 5 years on-orbit storage) at geosynchronous orbit.

Orbit: Geosynchronous, H = 35790/35790 km, 15-year Mission Requirement including 10 years of operation and up to 5 years of on-orbit storage. On-orbit locations are 75°W, 105°W, and 137°W longitude. The storage positions are 94°W and 92° W longitude. Checkout location is 88°W longitude.

The radiation environment effects that must be considered and their level of severity for the GeoXO missions are listed in Table 1.

Table 1: Radiation Effects in Geosynchronous Effect Level of Severity Spacecraft Charging/Discharging Severe Single Event Effects Severe Total Ionizing Dose Moderate Displacement Damage Non-shielded (Solar Cells, Sensors) – Severe

Shielded (Optoelectronics, Shielded Sensors) – Moderate

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II. RADIATION ENVIRONMENT

The natural space radiation environment of concern for damage to spacecraft electronics is classified into two populations, 1) the transient particles which include protons and heavier ions of all of the elements of the periodic table, and 2) the trapped particles which include protons, electrons and heavier ions. The trapped electrons have energies up to 10 MeV and the trapped protons and heavier ions have energies up to 100s of MeV. The transient radiation consists of galactic cosmic ray particles and particles from solar events (coronal mass ejections and flares).

The cosmic rays have low-level fluxes with energies up to TeV. The solar eruptions periodically produce energetic protons, alpha particles, heavy ions, and electrons. The solar protons have energies up to 100’s of MeV and the heavier ions reach the GeV range. All particle fluxes are isotropic and omnidirectional to the first order.

Space also contains low energy plasma of electrons and protons with fluxes up to 1012 cm2/sec.

The plasmasphere environment and the low energy (< 0.1 MeV) component of the charged particles are a concern in the near-earth environment. In the outer regions of the magnetosphere and in interplanetary space, the plasma is associated with the solar wind. Because of its low energy, thin layers of material easily stop the plasma so it is not a hazard to most spacecraft electronics. However, it is damaging to surface materials and differentials in the plasma environment can contribute to spacecraft surface charging and discharging problems [1, 2].

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III. DESCRIPTION OF RADIATION EFFECTS

Radiation effects that are important to consider for instrument and spacecraft design fall roughly into three categories: degradation from total ionizing dose (TID), degradation from displacement damage, and single event effects (SEEs).

A. Total Ionizing Dose Total ionizing dose in electronics is a cumulative long term ionizing damage due to protons and electrons. It causes threshold shifts, leakage current and timing skews. The effect usually first appears as parametric degradation of the device and ultimately results in functional failure. It is possible to reduce TID with shielding material that absorbs most electrons and lower energy protons. As shielding is increased, shielding effectiveness decreases because of the difficulty in slowing down the higher energy protons. When a manufacturer advertises a part as “rad-hard”, he is almost always referring to its total ionizing dose characteristics. Rad-hard does not usually imply that the part is hard to non-ionizing dose or single event effects.

B. Displacement Damage Displacement damage is cumulative long-term non-ionizing damage due to protons, electrons, and neutrons. The particles produce defects in optical materials that result in charge transfer degradation. These defects affect the performance of optocouplers (often a component in power devices), solar cells, CCDs, and linear bipolar devices. The effectiveness of shielding depends on the location of the device. For example, cover glasses over solar cells reduce electron damage and proton damage by absorbing the low energy particles. Increasing shielding, however, is not usually effective for optoelectronic components because the high-energy protons penetrate the most feasible spacecraft electronic enclosures. For detectors in instruments it is necessary to understand the instrument geometry to determine the vulnerability to the environment.

C. Single Event Effects Single event effects (SEE) occur as a result of charge being generated along the path of primary or secondary ionizing particles, and then being collected on circuit nodes and disrupting normal circuit response. In most cases, SEE are caused by heavier ions. However, for some devices, protons can induce SEE—in some cases through direct ionization by the proton, or, more commonly, by ionization by secondary particles produced in collisions between the proton and a nucleus in the device material. Some single event effects are non-destructive as in the case of single event upsets (SEUs), single event transients (SETs), multiple bit errors (MBEs), single event hard errors (SHEs), etc. Single event effects can also be destructive as in the case of single event latchups (SELs), single event gate ruptures (SEGRs), and single event burnouts (SEBs).

The severity of the effect can range from noisy data to loss of the mission, depending on the type of effect and the criticality of the system in which it occurs. Shielding is not an effective mitigator for single event effects because they are induced by very penetrating high-energy particles. The preferred method for dealing with destructive failures is to use SEE-hard parts.

When SEE-hard parts are not available, latchup protection circuitry is sometimes used in conjunction with failure mode analysis. However, this approach should be adopted cautiously, as even SEL events that do not result in device destruction have been observed to cause latent

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D. Relevant Space Radiation Environments Total ionizing dose is caused primarily by protons and electrons trapped in the Van Allen belts and solar event protons. As electrons are slowed down, their interactions with orbital electrons of the shielding material produce a secondary photon radiation known as bremsstrahlung.

Generally, the dose due to galactic cosmic ray ions and proton secondaries is negligible in the presence of the other sources. For surface degradation, it is also important to include the effects of very low energy particles.

Single event effects can be induced by heavy ions (solar events and galactic cosmic rays) and, in some devices, protons (trapped and solar events) and neutrons. Displacement damage is primarily due to trapped and solar protons and neutrons that are produced by interactions of primary particles with the atmosphere and spacecraft materials.∗ For lightly shielded applications, such as solar arrays, displacement damage may also occur due to energetic trapped electrons. Spacecraft charging can occur on the surface of the spacecraft due to low energy electrons. Deep dielectric charging occurs when high-energy electrons penetrate the spacecraft and collect in dielectric materials.

∗ In avionics applications it is necessary to consider neutrons that are produced by interactions of primary particles with the atmosphere.

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IV. THE GEOXO MISSION

The GeoXO spacecraft will be launched out to a geosynchronous orbit via a trajectory that has not yet been defined. Once GeoXO is at its geosynchronous orbit, its mission requirement is 15 years, with 10 years operational at 75°W, 105°W, and 137°W longitude and 5 years parking at either 94°W or 92° W longitude. Because trapped electron fluxes increase in GEO as one moves to higher longitudes, and because the spacecraft will not be stationed at longitudes greater than 148°W, we define particle fluences and doses for the worst-case of 15 years at 148°W. Due to its lengthy timescale, the GeoXO mission will include satellites launched throughout the solar cycle.

For this reason, it is prudent to assume that the mission will occur during worst-case environmental conditions. In terms of TID, displacement damage and spacecraft charging threats, this is the active phase of the solar cycle. In terms of single-event effects, the appropriate galactic cosmic ray (GCR) environment to assume is that for solar minimum, since GCR fluxes are slightly higher for this portion of the solar cycle. During the active phase of the sun, the likelihood that the spacecraft will be exposed to particles from solar events (either solar flare or coronal mass ejections) increases significantly. Based on an average 11-year solar cycle, the GeoXO mission will encounter 11 years of solar active conditions. Figure 1 shows a projection of the solar cycle during the GeoXO mission, based on the solar activity data of solar cycles 21 and 22. The geosynchronous radiation environment encountered by the GeoXO will consist of protons, electrons and heavier ions from solar events, galactic cosmic ray heavy ions, and solar wind plasma consisting of low energy protons, electrons, and heavier ions.

Figure 1: Projection of the solar activity during the GeoXO mission (Source: WDC-SILSO, Royal

Observatory of Belgium, Brussels; forecasts based on cycles 21 and 22)

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V. TOTAL DOSE AND DEGRADATION ANALYSIS

The total ionizing dose accumulation causes performance degradation and failure on a variety of active semiconductor electronic devices, from transistors to memories, processors and power converters, etc. It can also cause darkening of optical materials due to color-center formation.

Non-ionizing energy loss in materials (atomic displacement damage) causes degradation of solar cells, optoelectronics, and detectors. The low energy particles also contribute to the erosion of surfaces and degradation of materials.

A. Degradation Environments In geosynchronous orbits low energy particles (< 40 keV) from the solar wind plasma contribute to the degradation of surface materials. The higher energy particles trapped in the Van Allen belts and from high-energy solar events can penetrate solar cell cover glasses and solar array substrate structures and, therefore, are responsible for solar cell degradation. Microelectronics components are also susceptible to high-energy particles even though they are usually inside box enclosures.

1. The Plasma Environment [3] The geosynchronous environment will charge spacecraft exterior surfaces. Since different materials are used and since sunlight can illuminate only one side at a time, there will always be some differential charging as well as absolute charging. The effect of this surface charging on the performance of spacecraft must be evaluated in terms of malfunctions, upsets and failures.

Surface charging could disrupt environmental measurements on scientific spacecraft where control of electrostatic fields is required. For this reason, material selection to minimize differential charging is recommended. If the charging analysis indicates differential potentials of less than 500V, there should be no spacecraft discharge problems. However, if predicted potentials on materials exceeds 500V, the NASA Charging Analyzer Program (NASCAP) can be used. The worst-case geosynchronous plasma environment is given in Table 2 and can be used as input to the NASCAP program.

Table 2: Worst-Case Geosynchronous Plasma Environment Electron number density, NE, cm-3 1.12 Electron temperature, TE, eV 1.2x104 Ion number density, NI, cm-3 2.36x10-1 Ion temperature, TI, eV 2.95x104

Surface charging also increases contamination. The contaminants are attracted back to charged surfaces and deposit on them. This changes the surface characteristics. Altered surface optical properties result in higher temperatures. Changes in secondary and photoelectron yields result in altered charging characteristics. Deposition of the dielectric contaminants can also reduce surface conductivity. If severe discharges were to occur on the surfaces, the materials can be damaged which can change their thermal control performance. Table 3 lists the acceptable and unacceptable surface coatings and materials for spacecraft use.

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Table 3: Surface Coatings and Materials Acceptable Material/Coating Unacceptable Material/Coating

Paint(carbon black) Anodize GSFC NS43 paint(yellow) Fiberglass material Indium tin oxide Paint(white) Zinc ortho-titanate paint(white) Mylar(uncoated) Alodyne Teflon(uncoated) Kapton(uncoated) Silica cloth Quartz and glass surfaces (if possible, to avoid)

2. High Energy Particles – Spacecraft Incident Fluences

The spacecraft incident proton fluence levels given in this document are most often used for standard solar cell analyses that take into account the cover glass thickness of the cell. There are two possible sources of high-energy particles: trapped electrons encountered in the geosynchronous orbit and protons from solar events that can occur anytime during the 15 years of the mission. The proton fluence levels are also used to determine displacement damage effects, however, most analysis methods require that the surface incident particles be transported through the materials surrounding the sensitive components. The proton fluences behind nominal aluminum shield thicknesses are given in Section V.A.3.

The trapped particle fluxes were estimated with NASA’s AP-8 [4] model for protons and AE-8 [5] model for electrons. The models come in solar minimum and maximum versions. The uncertainty factors defined for the models are a factor of 2 for the AP-8 and 2 to 5 for the AE-8.

These uncertainty factors apply to long-term averages expected over a 6-month mission duration.

Daily values can fluctuate by two to three orders of magnitude depending on the level of activity on the sun and within the magnetosphere.

The solar proton levels can now be estimated from the new Emission of Solar Proton (ESP) model [6]. Previously, estimates of solar proton levels were obtained from models [7, 8] that were largely empirical in nature, making it difficult to add data to the model from more recent solar cycles. The ESP model is based on satellite data from solar cycles 20, 21, and 22. The distribution of the fluences for the events is obtained from maximum entropy theory, and design limits in the worst-case models are obtained from extreme value theory. The solar proton predictions are not linear over time; therefore, the levels given in this document may be invalid if extrapolated for longer mission durations.

Total integral solar proton fluences were estimated for a 15-year mission with 11 of those years being solar active years. Table A1 gives the proton fluence levels as a function of particle energy for 90% & 95% confidence levels for a 15-year mission involving 11 solar active years.

Table A2 gives the electron fluence levels as a function of particle energy for the worst-case mission/longitude (15 years at 148°W). Figure 2 is a plot of the data contained in Table A1 and Figure 3 is a plot of the data contained in Table A2. The energies are in units of >MeV and the fluences are in units of particles/cm2. These values do not include a design margin.

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3. High Energy Particles – Shielded Fluences Evaluation of non-ionizing energy loss damage requires the use of shielded fluence levels. For this analysis nominal shielding thicknesses of 50, 100, 200, and 350 mils of aluminum were used for a generic solid sphere geometry. The spacecraft incident, solar proton estimates for the 90% confidence level for 15-year mission duration with 11 year solar active years were transported through the shield thickness to obtain fluence estimates behind the shielding. Table A3 gives the degraded proton energy spectra. The spectra are plotted in Figure 4. The electron fluence estimates behind these shielding thicknesses for the 15-year worst-case mission (15 years at 148°W) are given in Table A4 and plotted in Figure 5. It can be seen from the figures that even though the shielding absorbs low energy particles, the low energy range of the spectrum is filled in by the higher energy particles as they are degraded by passing through the material.

Figure 4: Shielded integral solar proton fluences for 15 years with 11 solar active years (90% confidence level). The unshielded fluence from Figure 2 is included for reference.

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Figure 5: Shielded Integral Electron Fluences For 15 Year Mission (Worst Case). The unshielded fluence from Figure 3 is included for reference.

B. Total Dose Estimates

1. Top Level Ionizing Dose Estimates Doses are calculated from the surface incident integral fluences as a function of aluminum shield thickness for a simple geometry. The geometry model used for spacecraft applications is the solid sphere. The solid sphere doses represent an upper boundary for the dose inside an actual spacecraft and are used as a top-level requirement. In cases where the amount of shielding surrounding a sensitive location is difficult to estimate, a more detailed analysis of the geometry of the spacecraft structure may be necessary to evaluate the expected dose levels. This is done by modeling the electronic boxes or instruments and the spacecraft structure. The amount of shielding surrounding selected sensitive locations is estimated using solid angle sectoring and 3-dimensional ray tracing. Doses obtained by sectoring methods must be verified for 5-10% of the sensitive locations with full Monte Carlo simulations of particle trajectories through the structure for many histories.

Table A5 and Figure 6 give the top-level total ionizing dose results for the worst-case 15-year GeoXO mission (15 years at 148°W). The solar proton doses were calculated using 11 solar active years and a 90% confidence level. The doses (rads silicon) are calculated here as a function of aluminum shield thickness for solid spheres. A minimum design for twice the expected dose is recommended.

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Figure 6: Total ionizing dose for 15 year mission (worst case).

2. Dose at Specific Spacecraft Locations In cases where parts cannot meet the top level design requirement and a “harder” part cannot be substituted, it is often beneficial to employ more accurate methods of determining the dose exposure for some spacecraft components to qualify the parts. One such method for calculating total dose, solid angle sectoring/3-dimensional ray tracing, is accomplished in three steps:

1) Model the spacecraft structure:

-develop a 3-D model of the spacecraft structures and components -develop a material library -define sensitive locations

2) Model the radiation environment:

-define the spacecraft incident radiation environment -develop a particle attenuation model using theoretical shielding configurations (similar to dose-depth curves).

3) Obtain results for each sensitive location:

-divide the structural model into solid angle sectors -ray trace through the sectors to calculate the material mass distribution -use the ray trace results to calculate total doses from the particle attenuation model.

Once the basic structural model has been defined, total doses can be obtained for any location in the spacecraft in a short time (in comparison to Monte Carlo methods). The value of dose

To verify the correct version of this document, please contact the GeoXO Series Configuration Management Office mitigation measures can be accurately evaluated by adding the changes to the model and recalculating the total dose. For spacecraft with strict weight budgets, the 3-D ray trace method, the total dose design requirement can be defined at a box or instrument level avoiding unnecessary use of expensive or increasingly unavailable radiation hardened parts.

As the design of the GeoXO evolves, it may become necessary to estimate the doses at specific locations in the spacecraft or instruments. Often the dose requirement can be met by modeling the surrounding electronic box only or by modeling only the instrument.

C. Displacement Damage Estimates Long-term damage due to atomic displacements (displacement damage) degrades solar cells, optoelectronics, imaging devices such as CCDs, and some bipolar technologies. The displacement damage is caused by exposure of the components to protons, neutrons and electrons. In the geosynchronous environment, the threat ranges from moderate to severe depending on the amount of shielding surrounding the components. Sensors that are fully exposed to the space environment are especially susceptible.

Displacement damage is evaluated by combining the shielded proton energy spectra given in Section V.A.3 for the material and the results of laboratory irradiation of the devices sensitive to atomic displacement damage. The level of the hazard is highly dependent on the device type and can be process specific. For the GeoXO mission, it is important to keep in mind that some optoelectronic devices experience enough damage during one large solar proton event to cause the device to fail. It is necessary that the parts list screening for radiation also include a check for devices that are susceptible to displacement damage. For convenience, we have estimated equivalent damage fluences based on NIEL equivalence in Si and GaAs for 1-MeV, 10-MeV, 50-MeV and 63-MeV protons and for 1-MeV neutrons. Table A6 gives equivalent particle fluences for these particles/energies assuming damage follows Non-Ionizing Energy Loss (NIEL) in Si, with Figure 7 presenting the same information graphically. Similarly, Table A7 presents equivalent fluence for III-V materials, assuming damage follows NIEL in GaAs (not universally true), with Figure 8 presenting the results graphically.

This document does not address solar array degradation due to the space radiation environment.

However, JPL Publication 96-9 titled “GaAs Solar Cell Radiation Handbook” [9], dated July 1, 1996, contains useful material that can be used by the spacecraft contractor as a guide when preparing his solar array degradation model.

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Figure 7: Equivalent particle fluences for mission Total Non-Ionizing Dose in Si for 15 year mission (worst case).

c Figure 8: Equivalent particle fluences for mission Total Non-Ionizing Dose in GaAs for 15 year mission (worst case).

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1. Trapped Protons At geosynchronous orbit, the trapped protons have energies < 2 MeV. Therefore, they are not a significant factor in producing interference or damage in microelectronics.

2. Solar Protons Protons from solar events will also be a single event effects hazard for the GeoXO spacecraft.

These enhanced levels of protons could occur anytime during the 15-year mission but are most likely during the portion of the mission that occurs during the active phase of the solar cycle. As with the solar heavy ion LET spectra, solar proton fluxes are averaged over worst day, worst week, and the peak of the October 1989 solar event. The proton flux averages for a nominal 100 mils of shielding are given in Table A10 and are shown in Figure 11.

Figure 11: Solar proton fluxes for single event effects evaluation.

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1 10 100 1000

Energy (MeV)

Pa rti cl es

/c m 2 /s

/M eV

Average Over Peak

Average Over Worst Day

Average Over Worst Week

Values Do Not Include Design Margin

Differential Solar Proton Event Fluxes at 1 AU 100 mils Aluminum Shielding, CREME96

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VII. INSTRUMENT INTERFERENCE

The particle background causes increased noise levels in instruments and other electronics. This can be a concern if low noise levels are required for instrument observations, for example. The particle background of concern in GEO comes from galactic cosmic rays, trapped electrons, and solar particle events. The galactic cosmic ray background is fairly steady and varies slowly with the solar cycle. The trapped electron environment is very volatile at GEO altitudes and the electron fluxes can vary by several orders of magnitude over periods as short as a month. Solar particle events typically last from days to weeks. The particle fluxes during these events vary continuously with time and can reach values that are comparable to trapped electron fluxes.

Both long-term and worst-case estimates of these particle fluxes are given in Table 4 for a nominal shielding of 100 mils of aluminum.

Table 4: Long-term and worst-case particle fluxes in GEO behind 100 mils of aluminum shielding

Radiation: Long-term flux (#/cm2/s): Worst-case flux (#/cm2/s):

galactic cosmic rays 2.5 4.6 trapped electrons 6.7 x 104 1.3 x 106 solar particle events --- 2.0 x 105

No long-term flux is included for solar particle events because the events occur over short periods of time compared to the length of the mission. Such a long-term flux would have little relevance for the viewing and data collection activities on GeoXO. However, particle interference during solar events is of particular concern because it can impact the observation times of instruments. To present a more realistic picture of the solar particle event flux variations, solar proton flux data from the GOES Space Environment Monitor (SEM) of are presented in Figures 12-14. The elemental composition of a solar particle event consists of about 95% protons, on average. These figures represent the hourly average flux of >50 MeV protons as a function of time for the years 1989, 1990 and 1991. This was a very active period during the solar maximum phase of the last complete solar cycle, #22. Note that the scale for flux in these figures is logarithmic.

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Figure 12: Hourly averages of solar proton fluxes for > 50 MeV protons for 1989.

Figure 13: Hourly averages of solar proton fluxes for > 50 MeV protons for 1990.

0 50 100 150 200 250 300 350

Hourly Average of Solar Proton Flux > 50 MeV for 1989 Fl ux

M eV P ar tic le s/ cm ^2

/s ec

Day of Year GOES Space Env ironment Monitor Data

0 50 100 150 200 250 300 350

Hourly Average of Solar Proton Flux > 50 MeV for 1990

Fl ux

M eV

P ar tic le s/ cm

^2 /s ec

Day of Year GOES Space Env ironment Monitor Data

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Figure 14: Hourly averages of solar proton fluxes for > 50 MeV protons for 1991.

0 50 100 150 200 250 300 350

Hourly Average of Solar Proton Flux > 50 MeV for 1991 Fl ux

M eV P ar tic le s/ cm ^2

/s ec

Day of Year

GOES Space Env ironment Monitor Data

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VIII. SPACECRAFT CHARGING AND DISCHARGING

Surface charging and deep dielectric charging must also be evaluated for the GeoXO mission.

The spacecraft can accumulate high levels of electron build-up on its surfaces (low energy electrons) and in the dielectrics (high-energy electrons). The particle accumulation profiles must be analyzed for possible surface and deep dielectric charging effects. The average electron accumulation profiles on a daily basis are shown in Figure 15. However, it should be remembered that these are long-term, average fluxes predicted by the AE8 Model and that on a given day the electron flux may be substantially higher. Measurements made on the GOES satellites indicate that daily flux levels can exceed those predicted by AE8 by a factor of about

20. When the transfer trajectory for the GeoXO spacecraft is defined, it also needs to be evaluated for levels of charging environments. The transfer trajectory will likely have a higher charging environment than at geostationary because of possible trajectory passes through more intense regions of the outer zone electron belt. Guidelines for controlling surface charging effects are given in reference [3] and guidelines for controlling deep dielectric charging are given in reference [11].

Figure 15: Daily integral electron levels for GeoXO.

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IX. SUMMARY

A top-level radiation environment specification was presented for the GeoXO mission.

Although the environment is considered “moderate”, the environment poses challenges to mission designers because of its highly variable nature caused by activity on the sun.

Spacecraft and instrument designers must be made aware that some newer technologies and commercial-off-the-shelf (COTS) devices are very soft to radiation effects. COTS devices that lose functionality at 5 krads of dose are not uncommon. Also, one extremely large solar proton event can cause enough displacement damage degradation in some opt coupler devices to cause failure. Increasingly, single event effects require careful part selection and mitigation schemes.

With its full exposure to galactic cosmic heavy ions and particles from solar events, GeoXO must have a carefully planned radiation engineering program.

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X. REFERENCES

[1] A. Holmes-Siedle and L. Adams, Handbook of Radiation Effects, p. 16, Oxford University Press, Oxford, 1993.

[2] A. R. Frederickson, “Upsets Related to Spacecraft Charging,” IEEE Trans. on Nucl. Science, Vol.

43, No. 2, pp. 426-441, April 1996.

[3] C.K. Purvis, H.B. Garrett, A.C. Wittlesey and N.J. Stevens, “Design Guidelines for Assessing and Controlling Spacecraft Charging Effects”, NASA Technical Paper 2361, Sept. 1984.

[4] D. M. Sawyer and J. I. Vette, “AP-8 Trapped Proton Environment,” NSSDC/WDC-A-R&S 76-

06, NASA/Goddard Space Flight Center, Greenbelt, MD, December 1991.

[5] J. I. Vette, “The AE-8 Trapped Electron Model Environment,” NSSDC/WDC-A-R&S 91-24, NASA/Goddard Space Flight Center, Greenbelt, MD, November 1991.

[6] M. A. Xapsos, J. L. Barth, E. G. Stassinopoulos, G. P. Summers, E.A. Burke, G. B. Gee, “Model for Prediction of Solar Proton Events”, to be published in Proceedings of the 1999 Space Environment and Effects Workshop, Farnborough, UK.

[7] E. G. Stassinopoulos, “SOLPRO: A Computer Code to Calculate Probabilistic Energetic Solar

Flare Protons,” NSSDC 74-11, NASA/Goddard Space Flight Center, Greenbelt, MD, April 1975.

[8] J. Feynman, T. P. Armstrong, L. Dao-Gibner, and S. Silverman, “New Interplanetary Proton

Fluence Model,” J. Spacecraft, Vol. 27 No. 24, pp 403-410, July-August 1990.

[9] Anspaugh, B.E., “GaAs Solar Cell Radiation Handbook”, JPL Publication 96-9, July 1, 1996.

[10] A. J. Tylka, J. H. Adams, Jr., P. R. Boberg, W. F. Dietrich, E.O. Flueckiger, E.L. Petersen, M.A.

Shea, D.F. Smart, and E.C. Smith, “CREME96: A Revision of the Cosmic Ray Effects on Micro- Electronics Code: to be published in IEEE Trans. On Nuc. Sci., December 1997.

[11] “Avoiding Problems Caused by Spacecraft On-Orbit Internal Charging Effects”, NASA

Technical Handbook NASA-HDBK-4002, Feb. 1999.

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APPENDICES

Table A1 Spacecraft Incident Integral Solar Proton Fluences (#/cm2) for 15 Year Mission (11 Solar Active

Years) Values Do Not Include Design Margins

Energy Confidence

>MeV 90% 95% 1 1.42E+12 1.60E+12 3 6.39E+11 7.85E+11 5 4.19E+11 5.43E+11 7 3.08E+11 4.14E+11

10 2.15E+11 3.01E+11 15 1.34E+11 1.98E+11 20 9.23E+10 1.42E+11 25 6.72E+10 1.06E+11 30 5.09E+10 8.21E+10 35 3.96E+10 6.52E+10 40 3.15E+10 5.28E+10 45 2.56E+10 4.33E+10 50 2.10E+10 3.62E+10 55 1.76E+10 3.04E+10 60 1.49E+10 2.59E+10 70 1.08E+10 1.91E+10 80 8.15E+09 1.46E+10 90 6.28E+09 1.13E+10 100 4.94E+09 8.98E+09 125 2.97E+09 5.42E+09 150 1.93E+09 3.51E+09 175 1.32E+09 2.39E+09 200 9.43E+08 1.72E+09 225 6.96E+08 1.27E+09 250 5.25E+08 9.57E+08 275 4.06E+08 7.38E+08 300 3.19E+08 5.80E+08

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Table A8 Integral LET for Interplanetary Galactic Cosmic Rays (Z=1-92)

100 mils Aluminum Shielding Values Do Not Include Design Margins

LET LET Fluence LET LET Fluence MeV*cm2/mg #/ cm2/day MeV* cm2/mg #/ cm2/day

Solar Minimum Solar Maximum 1.00E-03 4.25E+05 1.00E-03 1.54E+05 1.65E-03 4.24E+05 1.65E-03 1.54E+05 1.69E-03 3.29E+05 1.69E-03 1.07E+05 1.70E-03 3.04E+05 1.70E-03 9.42E+04 1.72E-03 2.84E+05 1.72E-03 8.46E+04 1.77E-03 2.54E+05 1.77E-03 7.02E+04 1.81E-03 2.30E+05 1.81E-03 5.98E+04 1.85E-03 2.12E+05 1.85E-03 5.20E+04 1.91E-03 1.90E+05 1.91E-03 4.34E+04 1.98E-03 1.72E+05 1.98E-03 3.75E+04 2.01E-03 1.67E+05 2.01E-03 3.59E+04 2.13E-03 1.46E+05 2.13E-03 3.05E+04 2.28E-03 1.27E+05 2.28E-03 2.69E+04 2.53E-03 1.07E+05 2.53E-03 2.39E+04 3.01E-03 8.29E+04 3.01E-03 2.11E+04 3.54E-03 6.87E+04 3.54E-03 1.98E+04 4.52E-03 5.55E+04 4.52E-03 1.88E+04 5.56E-03 4.90E+04 5.56E-03 1.83E+04 6.54E-03 4.58E+04 6.54E-03 1.82E+04 7.52E-03 2.76E+04 7.52E-03 7.46E+03 8.55E-03 2.13E+04 8.55E-03 5.04E+03 9.60E-03 1.75E+04 9.60E-03 3.97E+03 1.97E-02 7.02E+03 1.97E-02 1.88E+03 2.96E-02 5.07E+03 2.96E-02 1.63E+03 4.00E-02 4.33E+03 4.00E-02 1.55E+03 5.04E-02 3.81E+03 5.04E-02 1.43E+03 6.00E-02 3.50E+03 6.00E-02 1.36E+03 6.97E-02 2.91E+03 6.97E-02 1.08E+03 8.01E-02 2.66E+03 8.01E-02 1.01E+03 9.00E-02 2.40E+03 9.00E-02 9.12E+02 1.01E-01 2.23E+03 1.01E-01 8.74E+02 2.00E-01 9.84E+02 2.00E-01 3.59E+02 4.02E-01 4.33E+02 4.02E-01 1.52E+02

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Table A8 (Continued) Integral LET for Interplanetary Galactic Cosmic Rays (Z=1-92)

100 mils Aluminum Shielding Values Do Not Include Design Margins

LET LET Fluence LET LET Fluence MeV* cm2 /mg #/ cm2 /day MeV* cm2 /mg #/ cm2 /day

Solar Minimum Solar Maximum 6.03E-01 2.90E+02 6.03E-01 1.10E+02 7.96E-01 2.23E+02 7.96E-01 8.84E+01 1.00E+00 1.79E+02 1.00E+00 7.22E+01 2.01E+00 3.39E+01 2.01E+00 5.88E+00 3.02E+00 1.43E+01 3.02E+00 2.03E+00 3.99E+00 7.76E+00 3.99E+00 1.02E+00 5.03E+00 4.59E+00 5.03E+00 5.81E-01 5.99E+00 3.07E+00 5.99E+00 3.80E-01 8.00E+00 1.55E+00 8.00E+00 1.90E-01 1.01E+01 9.00E-01 1.01E+01 1.10E-01 1.11E+01 7.17E-01 1.11E+01 8.75E-02 1.20E+01 5.76E-01 1.20E+01 7.04E-02 1.30E+01 4.67E-01 1.30E+01 5.71E-02 1.40E+01 3.85E-01 1.40E+01 4.72E-02 1.50E+01 3.16E-01 1.50E+01 3.88E-02 1.60E+01 2.61E-01 1.60E+01 3.20E-02 1.70E+01 2.20E-01 1.70E+01 2.71E-02 1.80E+01 1.85E-01 1.80E+01 2.27E-02 1.91E+01 1.54E-01 1.91E+01 1.89E-02 2.00E+01 1.30E-01 2.00E+01 1.60E-02 2.49E+01 4.45E-02 2.49E+01 5.50E-03 3.00E+01 6.27E-04 3.00E+01 8.18E-05 3.49E+01 6.86E-05 3.49E+01 1.06E-05 4.01E+01 4.18E-05 4.01E+01 6.50E-06 4.50E+01 2.83E-05 4.50E+01 4.42E-06 5.00E+01 2.00E-05 5.00E+01 3.13E-06 5.06E+01 1.92E-05 5.06E+01 3.00E-06 5.55E+01 1.34E-05 5.55E+01 2.11E-06 6.02E+01 9.38E-06 6.02E+01 1.49E-06 6.53E+01 6.32E-06 6.53E+01 1.01E-06 7.00E+01 4.40E-06 7.00E+01 7.01E-07 7.50E+01 2.83E-06 7.50E+01 4.52E-07 8.04E+01 1.65E-06 8.04E+01 2.63E-07 8.52E+01 7.71E-07 8.52E+01 1.23E-07 9.03E+01 1.94E-07 9.03E+01 3.10E-08 9.57E+01 2.88E-08 9.57E+01 4.60E-09 1.00E+02 1.19E-08 1.00E+02 1.89E-09 1.01E+02 5.27E-09 1.01E+02 8.41E-10 1.03E+02 2.54E-09 1.03E+02 4.05E-10

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Table A9 Integral LET for the October 1989 Solar Particle Event (Z=1-92)

100 mils Aluminum Shielding Values Do Not Include Design Margins

LET LET Fluence LET Fluence LET Fluence MeV*cm2/mg #/cm2/s #/cm2/s #/cm2/s

Average Over Peak Average Over Worst Day Average Over Worst Week 1.00E-03 1.93E+05 5.21E+04 1.15E+04 2.01E-03 1.93E+05 5.21E+04 1.15E+04 3.01E-03 1.93E+05 5.20E+04 1.14E+04 4.02E-03 1.92E+05 5.17E+04 1.13E+04 5.01E-03 1.90E+05 5.11E+04 1.11E+04 6.03E-03 1.86E+05 5.02E+04 1.08E+04 7.02E-03 1.82E+05 4.90E+04 1.05E+04 7.97E-03 1.77E+05 4.76E+04 1.01E+04 8.95E-03 1.71E+05 4.60E+04 9.68E+03 1.01E-02 1.64E+05 4.40E+04 9.19E+03 1.99E-02 9.60E+04 2.55E+04 5.07E+03 2.99E-02 5.39E+04 1.43E+04 2.78E+03 4.00E-02 3.23E+04 8.56E+03 1.65E+03 4.98E-02 2.11E+04 5.59E+03 1.07E+03 6.00E-02 1.45E+04 3.84E+03 7.33E+02 6.97E-02 1.06E+04 2.81E+03 5.34E+02 8.01E-02 7.91E+03 2.09E+03 3.96E+02 9.00E-02 6.16E+03 1.63E+03 3.08E+02 9.99E-02 4.90E+03 1.29E+03 2.44E+02 2.00E-01 9.50E+02 2.51E+02 4.67E+01 3.01E-01 3.15E+02 8.31E+01 1.53E+01 4.02E-01 1.25E+02 3.32E+01 6.08E+00 5.01E-01 3.82E+01 1.01E+01 1.80E+00 6.03E-01 1.86E+01 4.94E+00 8.78E-01 7.01E-01 1.35E+01 3.58E+00 6.52E-01 8.05E-01 9.85E+00 2.62E+00 4.91E-01 9.04E-01 7.55E+00 2.02E+00 3.87E-01 1.00E+00 5.88E+00 1.57E+00 3.10E-01 2.01E+00 7.49E-01 2.06E-01 5.99E-02 3.02E+00 4.11E-01 1.13E-01 3.33E-02 3.99E+00 2.64E-01 7.29E-02 2.14E-02 5.03E+00 1.74E-01 4.80E-02 1.42E-02 6.06E+00 1.21E-01 3.36E-02 9.92E-03 7.04E+00 8.68E-02 2.40E-02 7.11E-03 8.00E+00 6.39E-02 1.77E-02 5.26E-03 8.99E+00 5.04E-02 1.40E-02 4.13E-03 1.01E+01 3.85E-02 1.07E-02 3.15E-03 2.00E+01 5.75E-03 1.60E-03 4.63E-04 2.52E+01 2.14E-03 5.95E-04 1.72E-04

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Table A9 (Continued) Integral LET for the October 1989 Solar Particle Event (Z=1-92)

100 mils Aluminum Shielding Values Do Not Include Design Margins

LET LET Fluence LET Fluence LET Fluence MeV*cm2/mg #/cm2/s #/cm2/s #/cm2/s

Average Over Peak Average Over Worst Day Average Over Worst Week 3.00E+01 1.83E-05 5.10E-06 1.55E-06 3.53E+01 7.23E-07 2.01E-07 7.14E-08 4.01E+01 3.26E-07 9.08E-08 3.43E-08 4.50E+01 1.95E-07 5.44E-08 2.12E-08 5.00E+01 1.36E-07 3.78E-08 1.48E-08 5.55E+01 8.43E-08 2.35E-08 9.31E-09 6.02E+01 4.92E-08 1.37E-08 5.58E-09 6.53E+01 3.28E-08 9.12E-09 3.75E-09 7.00E+01 2.49E-08 6.92E-09 2.84E-09 7.50E+01 1.80E-08 5.00E-09 2.04E-09 8.04E+01 1.20E-08 3.34E-09 1.36E-09 8.52E+01 6.69E-09 1.86E-09 7.56E-10 9.03E+01 2.03E-09 5.64E-10 2.29E-10 9.46E+01 1.33E-10 3.71E-11 1.51E-11 1.00E+02 5.01E-11 1.39E-11 5.66E-12 1.01E+02 2.22E-11 6.19E-12 2.51E-12 1.03E+02 1.07E-11 2.99E-12 1.21E-12

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Table A10

Differential Fluxes from Solar Proton Events 100 mils Aluminum Shielding, CREME96

Note: Spectra were cut off at E =1 MeV and E=1000 MeV Values Do Not Include Design Margins

Energy Proton Flux Proton Flux Proton Flux MeV #/cm2/s #/cm2/s #/cm2/s

Average Over Peak Average Over Worst Day Average Over Worst Week

1.00 1.75E+03 4.62E+02 8.85E+01

2.00 2.68E+03 7.09E+02 1.36E+02

3.02 3.47E+03 9.17E+02 1.76E+02

4.04 4.11E+03 1.09E+03 2.09E+02

5.04 4.62E+03 1.22E+03 2.36E+02

6.03 5.03E+03 1.33E+03 2.58E+02

7.02 5.33E+03 1.41E+03 2.75E+02

8.06 5.56E+03 1.47E+03 2.88E+02

9.00 5.69E+03 1.51E+03 2.96E+02

10.05 5.76E+03 1.53E+03 3.01E+02

14.99 5.41E+03 1.44E+03 2.92E+02

20.03 4.50E+03 1.21E+03 2.52E+02

24.98 3.57E+03 9.65E+02 2.07E+02

30.31 2.73E+03 7.40E+02 1.64E+02

35.27 2.11E+03 5.75E+02 1.31E+02

40.49 1.61E+03 4.42E+02 1.04E+02

50.50 9.91E+02 2.73E+02 6.79E+01

60.43 6.33E+02 1.75E+02 4.58E+01

70.33 4.20E+02 1.17E+02 3.20E+01

79.63 2.94E+02 8.18E+01 2.33E+01

90.17 2.03E+02 5.65E+01 1.68E+01

100.69 1.44E+02 4.01E+01 1.24E+01

150.25 3.84E+01 1.06E+01 3.80E+00

200.77 1.39E+01 3.79E+00 1.50E+00

299.59 3.32E+00 8.62E-01 3.88E-01

400.31 1.16E+00 2.85E-01 1.39E-01

499.23 4.97E-01 1.16E-01 5.96E-02

605.64 2.07E-01 4.64E-02 2.54E-02

704.94 1.10E-01 2.48E-02 1.44E-02

798.17 6.61E-02 1.48E-02 9.03E-03

903.74 3.95E-02 8.88E-03 5.66E-03

995.41 2.65E-02 5.96E-03 3.94E-03

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GLOSSARY

Linear Energy Transfer (LET) - a measure of the energy deposited per unit path length as an energetic particle travels through a material. The common LET unit is MeV-cm2/mg of material (Si for MOS devices, etc.).

Multiple Bit Upset (MBU) - an event induced by a single energetic particle such as a cosmic ray or proton that causes multiple upsets or transients during its path through a device or system.

Single Event Burnout (SEB) - a condition that can cause device destruction due to a high current state in a power transistor.

Single Event Dielectric Rupture (SEDR) – a single-event effect in antifuse-type field programmable gate arrays that may result destruction of the dielectric and functional failure of the cell.

Single Event Effect (SEE) - any measurable effect to a circuit due to a strike by a single ion. Such effects include (but are not limited to) SEUs, SHEs, SELs, SEBs and SEGRs.

Single Event Gate Rupture (SEGR) - a single ion induced condition in power MOSFETs that may result in the formation of a conducting path in the gate oxide.

Single Event Latchup (SEL) - a condition that causes loss of device functionality due to a single event induced high current state. An SEL may or may not cause permanent device damage, but requires power strobing of the device to resume normal device operations.

Single Event Upset (SEU) - a permanent or transient change of state induced by an energetic particle such as a cosmic ray or proton in a device. This may occur in digital, analog, and optical components or may have effects in surrounding interface circuitry (a subset known as Single Event Transients (SETs)). These are “soft” errors in that a reset or rewriting of the device causes normal device behavior thereafter.

Single Hard Error (SHE) - an SEU that causes a permanent change to the operation of a device. An example is a stuck bit in a memory device.

Threshold LET (LETth) - the minimum LET to cause an effect at a particle fluence of 1x107 ions/cm2.

Total Ionizing Dose (TID) - the mean energy imparted by ionizing radiation to a sensitive device region divided by the mass of the region. This is typically given in units of rad(Si), where 1 rad(Si) = 100 erg deposited per gram of silicon.

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418-XO-RPT-0042 DCR

CCR #:X00038 Rev Title: 418-XO-RPT-0042: Baseline Radiation Environment Contract #: N/A GeoXO S/C Effectivity: All Instruments CCB Status: Approved Doc #: 418-R-RPT-0042 CCB Date: 01/18/2022 Doc Section: ALL Contract: Mod#: N/A DOORs Version: N/A Doc Change Date: Jan. 18, 2022 Doc Version: 1.0

CCR #:X00061 Rev Title: 418-XO-RPT-0042: Redline to Radiation Environment for Electronic Devices Contract #: N/A GeoXO S/C Effectivity: Systems Engineering CCB Status: Approved Doc #: 418-R-RPT-0042 CCB Date: 05/04/2022 Doc Section: Table A5 Contract: Mod#: N/A DOORs Version: N/A Doc Change Date: May 04, 2022 Doc Version: 1.1

CCR #:X00170 Rev Title: 418-XO-RPT-0042: update to the referenced report Contract #: 80GSFC22CA055 80GSFC22CA059 GeoXO S/C Effectivity: S/C CCB Status: Approved Doc #: 418-R-RPT-0042 CCB Date: 03/13/2023 Doc Section: Table A6 and Figure 6 Contract: Mod#: P0009; P00010 DOORs Version: N/A Doc Change Date: Apr. 11, 2023 Doc Version: 1.2

CM note: Modified the Effective Date header to April 11, 2023 since the SC contract is awarded. Additionally, this document is included in section LIST OF ATTACHMENTS of the SC contract and as a result, should not have an Expiration Date on the header.