30 March - 2 April 2009
ESA/ESOC
Darmstadt, Germany

• Conjunction processing becoming more important
  • Must do all on all
  • Two-line element (TLE) information of limited quality
• Search for additional observational data sources to replace TLE data
  • ISON

• Conjunction Operations
  • SOCRATES
    • Continuous operations since 2004
    • http://www.celestrak.com/SOCRATES/
  • SOCRATES-GEO
    • New effort in July 2008
    • Focuses on Geosynchronous Owner Operator satellites
• Observations
  • ISON
    • Cooperative scientific activities since 2001

• Measurement Times

• Filter Position Uncertainty
  • Initial TLE is not accurate enough

• Filter Residual Ratios
  • Using Improved initial estimate

• Smoother Position Uncertainty

• Position Consistency test

• Comparison to TLE’s
  • Smoother Ephemeris
  • Ephemeris of TLE-TLE
    • Epoch to epoch

• Process entire interval (August – Nov 2008)
  • Intelsat Data

• Process interval (August 2008)
  • ISON Data (with maneuvers)

• Compare Intelsat Reference Orbit to ISON Ephemeris with maneuvers

• Process interval (August 2008)
  • ISON Data (no maneuvers)

• Last TLE appeared in 1971
• ISON regular tracking
  • Interval Jan 2008 to 2009
  • Additional density of observations in Jan 2008 and Aug 2008
    • Analysis from each of these two time frames

• January 2008 start

• August 2008 start

• Coordinate Frames
  • J2000 isn’t always “J2000”
• Initial Orbit Determination
  • TLE
  • Numerical (LS)
  • Other
• Sensors
  • Type
    • Optical vs Radar/other
  • Location
  • How many sensors?

• Data
  • Number
    • Per pass
    • Where located in a pass
    • Total obs available
  • Quality
    • Calibration values
  • Format
    • Best to create a script reader for each one
    • We used ODTK and .geosc format
• Observational Corrections Included?
  • Ionosphere
  • Refraction
  • Other

• Used in multiple programs - Extended for AGI programs
• Limited precision
• Data Types
  • 10 = RtAsc-Decl
  • 12 = Space Based Rtasc-Decl
  • 71 = Az-el

• Optical Data is excellent data source (ISON)
  • Can replace TLE data
    • Generally km-level or less accuracy
  • Increases confidence in conjunction answers
    • Decreases unnecessary maneuvers
• Formats are important
  • Preserve precision
• Data is important
  • Type
  • Quality
  • Calibration
  • Etc.
• Initial effort complete
  • Mostly manual at this point, but could be automated rather easily

• Suggest a New format
  • Simplifies many existing difficulties
  • Interested in comments from the community

# this is intended to be a simple obs format
# the data is all space delimited so variable sizing (precision) is possible
# comment lines are preceded by the # symbol in the first col
# units are km and km/s and deg
Units = “km”
# obs are assumed to be earth fixed topocentric
# coordinate system is ITRF, ECI (Specify GCRF or J2000), or TEME
Coordinate System = “ITRF”
# 
# data types control how much information follows on each line:
# 0 range only
# 1 azimuth and elevation
# 2 range, azimuth and elevation
# 3 topocentric right ascension and declination
# 4 ephemeris values (xyz, xyz dot)
# 5
# 6
#  
#Typ  Sat #   Sen #   Yr    M D  hr min sec       value       value       value
 2       7734     932   1995  1 29 02 38 37.000      2047.5023400   60.4991    16.1932
 2       7734     932   1995  1 29 02 38 49.00010      1984.67700   62.143445    17.288761
 0       7734     932   1995  1 29 02 48 49.0001     12952.7540340  
 1       7734     932   1995  1 30 12  8  6.005010      255.1423545    47.42558661

• AGI format (relevant parameters)
  • Input ephemerides as observations
  • Coordinate system, is Earth Centered, Earth Fixed (ECEF, ITRF)
  • Data is space delimited
  • No velocity vector

• Used in multiple programs
  • Extended for AGI programs
• Permits Range, Doppler, Angles

• Used in multiple programs - Extended for AGI programs
• Types
  • 21 = Range
  • 34 = Range-rate