Copyright 2009 Northrop Grumman Corporation

Climatology that Supports Deep Charging Assessments

J. Michael Bodeau

Technical Fellow Northrop Grumman Corporation

Space Weather Week April 28-May 1, 2009

Copyright 2009 Northrop Grumman Corporation

2

Industry Needs Long Duration Environments to Support Deep-Charging Assessments

• Spec Requested by Users: “Industry Users Group, Model Requirements Update: The Oracle has Spoken,” Working Group Meeting on New Standard Radiation Belt and Space Plasma Models for Spacecraft Engineering, Oct 2004 (Ref. 1)

Design Issue #1: Endurability/Wear-out due to mission

total dose

• Long-term average

• Long-term worst-case

• Flux energy spectra

Design Issue #2: Outages of rate-sensitive equipment

• Examples: processors, CCDs (charge coupled devices)

• Protons, electrons, heavy ions

• Worst case 5 min, 1 hr, 1 day, 1 week

Design Issue #3: Deep charging

• Falls between rate-sensitive (flux) and long-duration (fluence)

• Worst-case day, week, month, 3 months, 6 months electron flux spectra

• Access to historical flux data for anomaly resolution

• AE9/AP9 Development Spec only shows time averages to 1 week duration and less (Ref. 2)

• New environment model will have capability to generate longer term averages that meet industry needs (Ref. 3)

The Oracle Has Spoken!

Copyright 2009 Northrop Grumman Corporation

3

Traditional Focus on Short Term Peak Flux Is Based on Correlation with Anomalies

• Many spacecraft anomalies correlate with peaks in flux of energetic penetrating electrons

• 10-hr average, 24-hr average and 48-hr average fluxes have been used in these correlation studies

• NASA guidelines recommend limiting peak flux to a “safe” threshold, and provide a worst-case (several hour averaged) flux for GEO

Correlation Is Not Causation & Does Not Support Design

(Ref. 4)

(Ref. 5)

(Ref. 6)

Copyright 2009 Northrop Grumman Corporation

4

Deep Charging Is Similar to R-C Circuit…

threshold200kV/cm-100 exceeds field E if occurs ESD

)( and )(

discharge no assuming , state,steady At

constant dielectricby divided fluence /)(

leakagew/out capacitor into charge//)(

for and 0,0 uncharged,intially When

exp1exp)(

)0(

, ,

, , since

exp1exp/)()(

exp1exp)0()(

JtEIRtV

RCt

JttE

CQCIttV

RCtVE

tJtEtE

dtV

dV

E

Jd

IRAd

RAJI

RCd

AC

Ad

R

RCt

d

IR

RCt

d

VdtVtE

RCtIR

RCttVtV

or

or

oroo

ororo

coo

oror

o

c

e- e- e-

- - -

+++

E,J d

threshold200kV/cm-100 exceeds field E if occurs ESD

)( and )(

discharge no assuming , state,steady At

constant dielectricby divided fluence /)(

leakagew/out capacitor into charge//)(

for and 0,0 uncharged,intially When

exp1exp)(

)0(

, ,

, , since

exp1exp/)()(

exp1exp)0()(

JtEIRtV

RCt

JttE

CQCIttV

RCtVE

tJtEtE

dtV

dV

E

Jd

IRAd

RAJI

RCd

AC

Ad

R

RCt

d

IR

RCt

d

VdtVtE

RCtIR

RCttVtV

or

or

oroo

ororo

coo

oror

o

c

e- e- e-

- - -

+++

E,J d

e- e- e-

- - -

+++

E,J d

- - -

+++

E,J d

JQ(t) ,)(

for :SOLUTION STATE STEADY

constant dielectricby divided fluence /)(

t time toup fluence density Charge Jt Q(t)/Aq(t)

for :SOLUTION TIME EARLY

exp1exp)(

)(

exp1exp)(

, , where

exp1exp)0()(

0

JtE

t

JttE

t

tJtqA

tQtq

tJtEtE

RCd

AC

AdR

RCtIR

RCttVtV

or

or

or

o

oror

c

24 hour Averaged GOES >2MeV e- Flux in GEO 29-Jul-04, 9.25E+09

1E+04

1E+05

1E+06

1E+07

1E+08

1E+09

1E+10

2-J

un-8

7

1-J

un-8

8

1-J

un-8

9

1-J

un-9

0

1-J

un-9

1

31-M

ay-9

2

31-M

ay-9

3

31-M

ay-9

4

31-M

ay-9

5

30-M

ay-9

6

30-M

ay-9

7

30-M

ay-9

8

30-M

ay-9

9

29-M

ay-0

0

29-M

ay-0

1

29-M

ay-0

2

29-M

ay-0

3

28-M

ay-0

4

28-M

ay-0

5

28-M

ay-0

6

28-M

ay-0

7

27-M

ay-0

8

Av

e F

lux

[e

-/c

m^

2*d

ay

*s

r]

21.7 years of GOES >2MeV e- flux data

…But the Current Source Varies Orders of Magnitude on Time Scales

of Days to 11-yr Solar Cycle

GOES 24 hour averaged >2 MeV flux data courtesy of NOAA-Space Weather Prediction Center (Ref. 8)

(Ref. 7)

Copyright 2009 Northrop Grumman Corporation

5

ESD Risk Is Defined by Charge Accumulated Over Long-Time Scales

GOES >2MeV e- Integrated Charge Density

29-Jul-04,

9.3

1

10

100

1000

22

-Ju

n-8

7

22

-Ju

n-8

8

22

-Ju

n-8

9

22

-Ju

n-9

0

22

-Ju

n-9

1

22

-Ju

n-9

2

22

-Ju

n-9

3

22

-Ju

n-9

4

22

-Ju

n-9

5

22

-Ju

n-9

6

22

-Ju

n-9

7

22

-Ju

n-9

8

22

-Ju

n-9

9

22

-Ju

n-0

0

22

-Ju

n-0

1

22

-Ju

n-0

2

22

-Ju

n-0

3

22

-Ju

n-0

4

22

-Ju

n-0

5

22

-Ju

n-0

6

22

-Ju

n-0

7

22

-Ju

n-0

8

Ac

cu

mu

late

d C

ha

rge

De

ns

ity

[n

C/c

m^

2]

2.8 yr tau

~300 day tau

~100 day tau

~30 day tau

~10 day tau

1 day

Daily 24-hr GOES >2MeV fluence data integrated by

an RC circuit with time constant tau, then converted

to charge density; updated to 22 Feb 09

17-Apr-95

22

18-Apr-95

39

15-Oct-95

249

12-May-95

132

Q density responds

quickly to spikes in

e- flux for all time

constants

More charge density is left when next storm

begins, so Q density stair-steps to higher

peaks for longer time constant materials

19-Apr-95

67

15-Mar-95

6.2

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6

Worst Case Depends upon Material Constants and Frequency of Storms, Not Just Peak Flux

GOES >2MeV e- Integrated Charge Density

29-Jul-04,

9.3

1.E-01

1.E+00

1.E+01

1.E+02

1-J

an

-03

1-M

ar-

03

1-M

ay-0

3

1-J

ul-

03

1-S

ep

-03

1-N

ov-0

3

1-J

an

-04

1-M

ar-

04

1-M

ay-0

4

1-J

ul-

04

1-S

ep

-04

1-N

ov-0

4

1-J

an

-05

1-M

ar-

05

1-M

ay-0

5

1-J

ul-

05

1-S

ep

-05

1-N

ov-0

5

Ac

cu

mu

late

d C

ha

rge

De

ns

ity

[n

C/c

m^

2]

~300 day tau

~100 day tau

~30 day tau

~10 day tau

1 day

Daily 24-hr GOES >2MeV fluence data integrated by an RC

circuit with time constant tau, then converted to charge density

A single very high flux peak

can push up cumulative

charge to high levels

Multiple recurring flux peaks

can push up cumulative

charge to high levels

Worst-case charge density

is not always caused by

worst-case peak flux

Copyright 2009 Northrop Grumman Corporation

7

Exponentially Smoothed Flux Provides Worst Case(s) for Deep Charging Assessments

Exponentially Smoothed Time Averaged GOES >2MeV e- Flux

29-Jul-04,

9.25E+09

1.0E+06

1.0E+07

1.0E+08

1.0E+09

1.0E+10

22

-Ju

n-8

7

22

-Ju

n-8

8

22

-Ju

n-8

9

22

-Ju

n-9

0

22

-Ju

n-9

1

22

-Ju

n-9

2

22

-Ju

n-9

3

22

-Ju

n-9

4

22

-Ju

n-9

5

22

-Ju

n-9

6

22

-Ju

n-9

7

22

-Ju

n-9

8

22

-Ju

n-9

9

22

-Ju

n-0

0

22

-Ju

n-0

1

22

-Ju

n-0

2

22

-Ju

n-0

3

22

-Ju

n-0

4

22

-Ju

n-0

5

22

-Ju

n-0

6

22

-Ju

n-0

7

22

-Ju

n-0

8

Tim

e-A

ve

rag

ed

Flu

x [

e-/

cm

^2

*da

y*s

r]

1 day MA of 5 sec GOES data

~10 day tau

~30 day tau

~100 day tau

~300 day tau

2.8 yr tau

24-hr GOES >2MeV fluence data was integrated by an

RC circuit with time constant tau, then averaged by tau

to obtain an exponentially smoothed time-averaged flux

17-Apr-95

2.13E+09

18-Apr-95

1.26E+09

15-Oct-95

2.48E+08

14-Apr-95

4.90E+09

Longer RC time

constant results in

lower worst-case

time-averaged flux

19-Apr-95

6.46E+0812-May-95

4.26E+08

wc

cnr

n

nwc

cnc

n

n

n

m

m

mn

nn

J

Jq

qMaxJ

JJq

t

Jtqq

wc

0n

c

1

E

field statesteady case-worst

E

flux averaged timecase- worst theas

/ Use

over t fluence the

1

then ,Jat constant isflux if

exp

1)(

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8

Tests Show Electrical Time Constants of Years-Supports Need for Long-Term Averages

• New (Ref. 9) and old (Ref. 10) test data show electrical decay time constants > 1 yr for some materials

Need W-C Flux Exponentially Smoothed Over Time Scales Matching Material Electrical Decay Time Constants

Approx time constant

Rho

[-cm]

Tau

(r=1) [days]

W-C Cum. Charge Density [nC/cm

2]

W-C Tau Averaged Flux [e-/cm

2-sr-day]

~3 3 E+18 3.07 13.4 4.34 E+09

~10 1 E+19 10.25 22.0 2.13 E+09

~30 3 E+19 30.74 38.8 1.26 E+09

~100 1 E+20 102.5 66.6 6.46 E+08

~300 3 E+20 307.4 132 4.26 E+08

2.8 yrs 1 E+21 1025 249 2.42 E+08

5.6 yrs 2 E+21 2050 342 1.66 E+08

(Ref. 10)

(Ref. 10)

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9

Good Radiation Models Enable More Credible ESD Risk Assessments

• From AE9/AP9 we expect to find (and thank you for it): 1. “Clean” environment data sets over a wide range of energies spanning at least one solar

cycle and preferably two 2. Data sets integrated and exponentially smoothed over time periods of 1 week, 1 month, 3

month, 6 months, 1 year, 2 years, 3 years 3. Worst-case accumulated charge density and exponentially smoothed flux for the above

averaging time periods (or the means to compute them from the data sets)

• Satellite manufacturers will need to: 1. Transport external environment into the spacecraft to define internal charging risk (NASA

Handbook 4002, discusses ways to do this) 2. Establish time constant of materials & pick appropriate W-C environment

•NASA materials data base (another NASA/LWS supported effort - thank you) •Other historical test data •New tests using advanced non-contacting probe test methods

• NASA Handbook 4002 will need to be updated to reflect new definition of worst-case environment, and available material time constants

• Some pieces of the puzzle are still missing • Adjustments for temperature (activation energy) and aging in space (change with time in

vacuum and dose) are TBD at this time

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10

References:

1. “Industry Users Group, Model Requirements Update: The Oracle has Spoken,” Working Group Meeting on New Standard Radiation Belt and Space Plasma Models for Spacecraft Engineering, Oct 2004, College Park, MD, available at http://lwsscience.gsfc.nasa.gov/RB_meeting1004.htm

2. “AE9/AP9: New Radiation Specification Models-Update,” Ginet and O’Brien, 9 Sep 2008 available at http://lws-set.gsfc.nasa.gov/RadSpecsForum.htm

3. Personal Communication with P. O’Brien.

4. AME switch anomaly plot is from: “Conclusive Evidence for Internal Dielectric Charging Anomalies on Geosynchronous Communications Spacecraft,” Wrenn, Journal of Spacecraft and Rockets, Vol. 32, No. 3, May-June 1995, pp.514-520

5. Star Tracker anomaly plot is from: “Thick Dielectric Charging on High Altitude Spacecraft,” Vampola, J. Electrostatics, 20 (1987) 21-30. This paper is essentially identical to a previous publication: “Thick Dielectric Charging on High Altitude Spacecraft”, Vampola, Report SD-TR-86-46, July 25, 1986 (DTIC access number AD-A171 078, approved for public release, unlimited distribution).

6. CRRES pulse per orbit data is from: “Spacecraft Anomalies on the CRRES Satellite Correlated With the Environment and Insulator Samples,” Violet and Fredrickson, IEEE Transactions on Nuclear Science, Vol. 40, No. 6, December 1993, pp.1512-1520.

7. The 1-D circuit model for deep charging is widely used. For instance, see Appendix E of “Avoiding Problems Caused by Spacecraft On-Orbit Internal Charging Effects,” NASA-HDBK-4002, Feb 17, 1999; also Figure 2 of “Internal Charging and Secondary Effects,” Romero and Levy, The Behavior of Systems in the Space Environment, Ed. R. N. DeWitt et al., 1993 Kluwer Academic Publishers, p565ff.

8. GOES 24-hr averaged >2 MeV flux data courtesy of NOAA-Space Weather Prediction Center: http://www.swpc.noaa.gov/ftpmenu/indices/old_indices.html

9. Recent test results that also show very long time constants can be found in “Charge Storage Measurements of Resistivity for Dielectric Samples from the CRRES Internal Discharge Monitor,” Green, Frederickson and Dennison, 9th Spacecraft Charging Technology Conference, Tsukuba, Japan, April 2005 and the references it contains

10. The example plots showing extremely long (>1year) electrical decay time constants are from “Physical Principles of Electrets,” Sessler, Chapter 2 of Electrets: Topics in Applied Physics, 2nd edition, Volume 33, Springer Verlag, 1987

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