1. Using EOP and Space Weather Data for Satellite Operations
David A. Vallado and T. S. Kelso
Analytical Graphics Inc.
Center for Space Standards and Innovation
Paper USR S7.3, Presented at the 6th US Russian Space Surveillance Workshop, St. Petersburg, Russia, August 22-26, 2005

2. Outline Introduction Analysis STK Files Summary Definitions Problem
Objectives
Motivation
Analysis
EOP
Space Weather
STK Files
Summary

3. Definitions Earth Orientation Parameters (EOP) Space Weather Data
Assist transformation between Celestial and Terrestrial Coordinate Frames
Celestial – GCRF (generic ECI)
Terrestrial – ITRF (generic ECEF)
UT1, LOD, xp, yp, AT
Space Weather Data
Incoming solar radiation effects the atmosphere
Geomagnetic
kp, ap
Eight 3-hourly and daily averages
Solar radiation
F10.7
Daily values
Affects upper atmospheric temperature and density
Large factor in determining atmospheric drag effect on satellite orbits

4. Problem EOP and space weather data needed to support tasks
Mission Design
Fuel budgets
Lifetime maneuver / orbit box planning
Real-time Operations
Few days into the future
Mission planning a few months ahead
Anomaly resolution a few months in the past
Available data is “chaotic” at best
Mix of predicted and observed values
Post processing data often takes a month or more
No synchronized update schedule for all parameters
Need seamless file of data to accomplish each mission task

5. Objectives Analyze currently available data
Recommend best option for splicing data
Discuss setup of data files
Available on CelesTrak website
STK compatible

6. Summary of EOP Data Files
IERS
EOPC04.62-now
(DUT1, xp, yp,, LOD, , , X, Y)
1962
00:00
USNO
Finals.daily, Finals2000a.daily
(DUT1, xp, yp,, , , X, Y)
-3 months
+ 90 days
USNO
Finals.all, Finals2000a.all (DUT1, xp, yp)
1973
+ 1 year
NGA
EOPPyddd.txt
(DUT1, xp, yp)
00:00
Sunday
23:59
Saturday
14:28
PAST
Current Time, T
FUTURE

7. Summary of Space Weather Data Files
00:00
-1 month
00:00
1 month
Current Year
00:00
yyyy.vm
(daily F10.7, daily and 3 hrly kp, ap)
Quar_dgd.txt (3 hrly kp, daily ap)
Quar_dsd.txt (daily F10.7)
- 3 months
45df.txt
(daily F10.7, ap)
+ 45 days
Predict.txt
(monthly F10.7)
- 6 months
+ 6 year
14:28
PAST
FUTURE
Current Time, T

8. I. EOP Data

9. Analyses Series are recomputed Comparisons Useful IERS USNO
Twice weekly
Some smoothing due to use of Vondrak algorithm
Removes high-frequency noise
USNO
Weekly ?
Comparisons Useful
Within Organizations
Bulletin A and B
, 
X , Y
Between Organizations
USNO, IERS, NGA
Note that axes scales and units are not constant

10. Analysis USNO Bltn A and Bltn B values Reasonably consistent , 
Bull B values only from Jan 1, 1989
Reasonably consistent
Bltn B dpsi some anomalies
Sep 1999

11. Analysis USNO Bltn A and Bltn B values Values before 1990
X , Y
Values from 1973
Values before 1990
Additional variations
Bltn B some anomalies
Sep-Oct 1999

12. Comparisons Between Organizations
USNO (Bltn A and Bltn B) and IERS (EOPC04)
Before 1984
Larger variations
FK5 instituted
Before 1997
Smaller variations
Update to Equation of the equinoxes
Note last few values
See next slide

13. Comparisons (Cont) Between Organizations
USNO (Bltn A and Bltn B) and IERS (EOPC04)
Last few days appear to differ (IERS and USNO)
On Feb 22 for xp
IERS
USNO
On May 5 for xp
IERS
USNO
IERS Delta =
USNO delta =

14. Comparisons (FK5 Corrections)
Between Organizations
USNO (Bltn A and Bltn B) and IERS (EOPC04)
Data availability
Bltn B values only after Jan 1, 1989
Each appear to have noise

15. Comparisons (IAU 2000 Corrections)
Between Organizations
USNO (Bltn A and Bltn B) and IERS (EOPC04)
Data availability
EOPCO4 Values after Jan 1, 1984
Bltn B appears to better follow EOPC04

16. Coefficient Approach NGA provides coefficients
Continuous representation of
UT1, xp, yp
Lacks LOD, , , X , Y
Generally smaller order effects
Long-term behavior of EOP coefficients
xp, yp reasonable to use past the end of a data file
UT1 not recommended past about a month

17. Comparisons – Long Term
EOPC04 to NGA Coefficients
One year different epochs are shown
Notice variability
Runoff for UT1, xp
Current week is valid (highlighted)
Note 0.04 s ≈ 280m at 7 km/s

18. EOP – How to Splice Together
EOPC04
Use 62-now file
Up to current day
Recomputed frequently
USNO Predicted Bulletin A
Use .daily file
Daily values (t-3 months to t+3 months)
Updated daily
Use .all file
1 year predictions
Data availability
Use last known file of each if any are not available
Values are “acceptable” for short periods of time (~week)

19. II. Space Weather Data

20. Space Weather Tracked for many years Older data
Data to the 1930s
Older data
Has numerous missing dates
Physically a zero means little here!
Corrected in our files
Quality flag set to 4 as an indicator
Includes seasonal/solar cycle variations
Observed and adjusted to 1.0 AU values
DRAO and Lenhart values
Atmospheric models use both

21. Sensitivity Results Atmospheric Drag (see Vallado AAS 05-199)
Large variations
Changing the atmospheric model
Changing how the input data is interpreted
F10.7 at 2000 UTC
Last 81-day average F10.7 vs. the central 81-day average
Using step functions for the atmospheric parameters vs interpolation
Many others
Point to take away:
km ephemeris differences are possible
Unable to determine if from data interpretation or model differences

22. Space Weather – Predictions
Lots of Variability
Constant F10.7
Not very accurate
Never use 0.0!
Schatten
Varies with each solar cycle
Polynomial Trend (Vallado 2004, 535)
Matches several solar cycles
F10.7 = *COS{ t – 0.35*SIN(π t )}
t is the number of days from Jan 1, 1981

23. Historical and Polynomial Trend

24. Schatten Predictions

25. Statistics Comparisons
Combined Results
Avg Deviation
Standard Deviation
Ctr 81-day – Daily F10.7
15.00
21.99
Last 81-day – Daily F10.7
17.17
24.92
Trend 81-day – Daily F10.7
20.79
29.88
Monthly Trend – Monthly F10.7
15.33
21.85
Individual Results
Variability ‘same’ between
81-day averages and daily values
Monthly trend and monthly averages
Predicted (3-day, 45-day and 2 year) solar flux values

26. Observed / Adjusted values

27. kp – ap Conversions Rigorously defined
1940 – Chapman and Bartels – Geomagnetism
Discrete values
Values exist that are not in the discrete values
Finding 3-hourly ap values for the last month
Finding kp values from predicted ap values
Some Interpolation clearly required
Approaches
Linear Interpolation
Iteration
Spline

28. Comparison of Conversions
Techniques – Interpolate, Iterate, Splines
Between approaches (left)
To exact values (right)

29. III. File Setup

30. File Setup Proceeding can be complex and time consuming
CSSI (Dr. Kelso) has done the work for you!
Files updated every 3 hours
STK compatible
Naming indicates start date
Schedule
EOP and Space weather files ready today
Operational in next STK release

31. Additional Information
Common changes for both files
All ASCII text
Start dates can be set to a time before the current date
Naming convention permits quick determination
Set an end date
Observed and predicted sections consistent
Spacing minimized (file size)
Maintain free-field read capability
Indicate number of data points

32. Additional Information
Specifics
EOP
Add day, month, year to data
Switch to predominantly IERS EOP-C04 data from USNO Bltn A data
Data now available from 1962 instead of 1973
Removed data for errors in xp, yp, and UT1
Added LOD, , 
Added AT, X, Y into one file
Last values set to zero
Include automatic leap second introduction
Space Weather
Data from 1957 to date (more is possible)
Added centered 81 day in addition to last 81 day average values, observed and adjusted
Spliced past, current, and predicted data
New structure for predicted data
Monthly and Daily sections
Trend values for long term prediction possible

33. Conclusions EOP and Space Weather data Not high visibility
However, large variations in numerical results
Ap/kp conversion
Recommend using Cubic Spline approach
Predicted solar flux values
Polynomial trend available for long term use
Reasonable statistics to existing Schatten files
Your single source for consolidated values available: