4 themis MSC LEO

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Information about 4 themis MSC LEO
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Published on January 16, 2008

Author: Carmina

Source: authorstream.com

Slide1:  THEMIS Launch and Early Orbit Flight Profile:  Flight Profile Mission Profile:  Mission Profile 81 Probe Separation:  Probe Separation Confirmation of Probe A Separation via TDRS West: 2007/049 00:14:00 UTC First TDRS Contact via Blind Acquisition Forward Link: 1.000 kbps Return Link: 1.024 kbps Initial Acquisition via GN:  Initial Acquisition via GN Initial Acquisition via Ground Network Insertion Attitude Was Difficult for Ground Network Coverage Probes Were Oriented with Antennas Pointing Away from Ground Stations (Known Before Launch) All Telemetry Links Appeared Weaker Than Expected Initial Concerns of Continuing Degradation Were Dispersed Later Overall Drop in Signal Level Plus Variations with Spin Phase Causes for Lower Than Expected Performance RF Power Dissipation Within Antenna (20% instead of 10%) Ripple in Antenna Patterns as Function of Antenna Look Angles Spin Phase and Elevation Angle Relative to Spin Plane Magnitude of Ripple Determined by Characterizing Telemetry Link Performance as Function of Probe Attitude and Range Ground Stations Had Difficulties to Lock on Weak Signals Equipment Characteristics and Configuration Does Not Match Assumptions Used to Develop Telemetry Link Budgets Initial Acquisition – Cont.:  Initial Acquisition – Cont. Predicted Spacecraft Antenna Aspect Angle (Top Panel) and Resulting Telemetry Link Margin (Bottom Panel) Based on Nominal Insertion Attitude Initial BGS View Period Data Rate 4K 01:00:00 – 13:00:00 MET Initial Acquisition – Cont.:  Initial Acquisition – Cont. Recorded Signal Strength from Initial BGS Passes with THEMIS B, C, D, E, A Intermittent RF and Data Lock on THEMIS B Only Recorded Signal Strength from Second BGS Pass with THEMIS A Solid RF and Data Lock Power & Thermal Issues:  Power & Thermal Issues Power & Thermal Issues Insertion Attitude Caused Concerns Spin Axis to Sun Angle: 45 - 50 deg Solar Panels Generate More Power Than Expected Shunts in Power System Cannot Dissipate Energy When Top Solar Panel Illuminated Turned on Catalyst Bed Heaters for Mitigation Prior to IDPU Power-on Battery Overvoltage Protection (OVP) Trips Detected OVP Trip First on THEMIS A during Separation Event Pass Team Was Concerned that Battery Overcharging Might Occur OVP Trips Turn All Digital Shunts On, Removing Power from Solar Array Strings 1, 2 and 3 Until Battery Voltage Drops to 32.2 V High Antenna Temperature (>70 C) When Transmitter Turned On Transmitter Operations Limited Due to Antenna Heating Up, Especially Near Perigee Vector Delivery:  Vector Delivery Vector Delivery from Boeing UCB Received Post-launch AAM Vector Based on Measured Performance of LV Second Stage and Predicted Performance of Third Stage Very Close Agreement with Pre-launch Predicts USSPACECOM Provided TLEs that Appeared to Match the AAM Orbital Period Expected Orbital Period Was 1999 ± 180 min (3-σ) Achieved Orbital Period Was 1884 min (1999 - 115 min) (OD Solution Provided by GSFC/FDF on 20-Feb-2007) Insertion Orbit:  Insertion Orbit Successful Initial Set of Round-robin State-of-health via BGS Insertion Orbit:  Insertion Orbit First Negative Acquisition at Apogee via HBK Insertion Orbit:  Insertion Orbit Difference Between Predictive and Definitive Insertion Orbits Spacecraft Emergency:  Spacecraft Emergency Declared Spacecraft Emergency Declared Spacecraft Emergency at 2007/050 03:30:00 UTC No Communications with Any Probe for 17 hours Concerns with Power and Thermal Issues in Insertion Attitude Additional Assets Brought Online GSFC/FDF Generated Acquisition Vectors for DSN Stations GSFC/FDF Generated First Valid OD Solution Initial Two-way Doppler Tracking Data Were Sparse Since Both BGS and WGS Had Difficulties to Lock onto Weak Signals Used Crude Angle Data from WGS to Enhance Tracking Data Set Probes Reacquired via HBK After 28 Hours Confirmed Good State of Health of All Five Probes Continued to Shadow Track with DSN Stations for Another Day DSS 46 (Madrid), DSS 66 (Canberra) and DSS 27 (Goldstone) Emergency Terminated at 2007/051 11:45:00 UTC First Orbit Solution:  First Orbit Solution Post-launch Orbit Configuration – Dispersed at L + 6.5 d

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