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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. Outline. Introduction
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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
Outline • Introduction • Definitions • Problem • Objectives • Motivation • Analysis • EOP • Space Weather • STK Files • Summary
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
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
Objectives • Analyze currently available data • Recommend best option for splicing data • Discuss setup of data files • Available on CelesTrak website • STK compatible
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
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
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
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
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
EOP Parameters - Historical Leap Seconds
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
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
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
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
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
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
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
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
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
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)
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
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
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
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
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
Comparison of Conversions • Techniques – Interpolate, Iterate, Splines • Between approaches (left) • To exact values (right)
Splining technique closure Note small scales
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
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
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
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
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/