Using EOP and Space Weather Data for Satellite Operations

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 AAS 05-406, Presented at the AAS Astrodynamics Specialist Conference, Lake Tahoe CA August 7-11, 2005

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

3. Definitions • Earth Orientation Parameters (EOP) • 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. Motivation • So What? • With analytical theories (i.e. SGP4), it mattered little • TEME example • AFSPC still uses two-line element set data in TEME (never officially defined!) • Time sometimes assumed to be UTC • No polar motion, no ECI/ECEF distinctions • SGP4 only approximated atmospheric drag • No use of solar indices • No rigorous application of force models • With numerical techniques, EOP and space weather are required inputs • Integrate in inertial • Apply forces in fixed • If you use incorrect values of • EOP • A few meters • Space Weather • 1s to 1000s of kilometers

7. EOP Data Sources • 1. General Directory: • http://hpiers.obspm.fr/eoppc/eop/eopc04 • *Current data (Current year to date) – updated Daily (~1400 UTC) • http://hpiers.obspm.fr/eoppc/eop/eopc04/eopc04.05 • http://hpiers.obspm.fr/eoppc/eop/eopc04/eopc04_IAU2000.05 • Historical data (1962 to date) – updated Daily (~1400 UTC) • http://hpiers.obspm.fr/eoppc/eop/eopc04/eopc04.62-now • http://hpiers.obspm.fr/eoppc/eop/eopc04/eopc04_IAU2000.62-now • 2. General Directory: • http://maia.usno.navy.mil/ • Current data (t-3 months-date + 90 days) – updated Daily (~1705 UTC) • http://maia.usno.navy.mil/ser7/finals.daily • http://maia.usno.navy.mil/ser7/finals2000A.daily • Historical data (1973 to date + 1 year) – updated Weekly (Thursday) • http://maia.usno.navy.mil/ser7/finals.all • http://maia.usno.navy.mil/ser7/finals2000A.all • 3. General Directory: • http://earth-info.nima.mil/GandG/sathtml/eopp.html • Current data – updated Weekly (Thursday) • Coefficients effective for the following week starting Sunday. • Multiple files, 5 is last digit of year, 255 is the day of the year in the example below • ftp://164.214.2.65/pub/gig/pedata/2005EOPP/EOPP5255.TXT * Not necessarily needed for processing, use 62-now files

8. 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) 23:59 Saturday 00:00 Sunday 14:28 PAST FUTURE Current Time, T

9. Space Weather Data – Current • 1. General Directory: • ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/INDICES/KP_AP/ • Current data – updated Monthly (~22nd – 24th) • Each month is a .vx where x is the month (1-12). When the year is complete, it’s simply 2005 • ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/INDICES/KP_AP/2005.v1 • Data assembled from 1950 to 2005 (atmosall.txt) • Numerous omissions exist in the data (above file is linearly interpolated) • Current data—updated daily • Includes observed F10.7 daily values • ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SOLAR_RADIO/FLUX/DAILYPLT.OBS • 2. General Directory: • http://www.sel.noaa.gov/Data/index.html • Current data – updated 3-Hourly • http://www.sel.noaa.gov/ftpdir/indices/quar_DGD.txt • Current data – updated Daily (~0230 UTC) • http://www.sel.noaa.gov/ftpdir/indices/quar_DSD.txt • Predicted data – updated Daily (~2114 UTC) • No 3hrly values • http://www.sel.noaa.gov/ftpdir/latest/45DF.txt • Predicted data – updated Monthly (~3rd of the month) • Includes f10.7 monthly values predicted for about 2 years into the future • Also has some old data which [depending on the access time] is overcome by actual measurements • http://www.sel.noaa.gov/ftpdir/weekly/Predict.txt

10. 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

11. I. EOP Data

12. EOP Parameters - Historical Leap Seconds

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

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

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

16. 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

17. 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 • 0.035728 IERS • 0.03383 USNO • On May 5 for xp • 0.035699 IERS • 0.035491 USNO • IERS Delta = 0.000029 • USNO delta = -0.031661

18. 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

19. 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

20. 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

21. 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

22. 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 • USNO Predicted Bulletin A • 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)

23. II. Space Weather Data

24. Space Weather • Tracked for many years • 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

25. 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: • 1-1000 km ephemeris differences are possible • Unable to determine if from data interpretation or model differences

26. 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 = 145 + 75*COS{ 0.001696 t – 0.35*SIN(π + 0.001696 t )} • t is the number of days from Jan 1, 1981

27. Historical and Polynomial Trend

28. Schatten Predictions

29. Statistics Comparisons Combined Results 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

30. Observed / Adjusted values

31. 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

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

33. Splining technique closure Note small scales

34. III. File Setup

35. File Setup • Proceeding can be complex and time consuming • CSSI (Dr. Kelso) has done the work for you! • http://celestrak.com/SpaceData • Files updated every 3 hours • STK compatible • Ability to generate custom-sized datasets • Smaller data sets may perform better on some more limited installations • Naming indicates start date • Schedule • EOP and Space weather files ready today • Operational in next STK release

36. Files • C:\Program Files\AGI\STK 6.0\DynamicEarthData • EOP Files • EOP1962-01-01.txt (New STK File) • EOP1973-01-02Old.txt (Existing STK file) • Space Weather Files • Atmos1957-01-01.txt (New STK File) • Atmos1957-01-01Old.txt (Existing STK File) • Shorter files also available for about the last 5 years

37. 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

38. 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

39. 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: http://celestrak.com/SpaceData/