Analysis of Possible use of Non-Ramped Uplinks, using example of  Cassini Rhea Encounter   David Tyner NOPE 11 Jan 2006
<ul><li>Actual Rhea encounter used ramped predicts </li></ul><ul><ul><li>Uplinking used a time history of Doppler compensa...
<ul><li>Analysis of  Rhea encounter, if had used non-ramped Uplinking </li></ul><ul><ul><li>Uplinking starts using a singl...
<ul><li>Graphical Analysis if had used exactly same predicts, but had used non-ramped TSF technique (“BLF” at transfer bet...
XFR at T 0  = 2245z TSF 34  =   7174.510 MHz TSF 63   =   7174.660 MHz TR  MAX  = (150 Hz/s) * (3600 s/hr) =  540 kHz/hr “...
TR  MAX  = (150 Hz/s) * (3600 s/hr) =  540 kHz/hr “ Improved” Non-Ramped Uplink Transfer at Closest Approach  TSF 34  =   ...
 
XFR at T 0  = 2245z TSF 34  =   7174.535 MHz TR  MAX  = (150 Hz/s) * (3600 s/hr) =  540 kHz/hr XFR at T 0  = 0550z TSF 63 ...
TSF 34  =   7174.535 MHz TR  MAX  = (150 Hz/s) * (3600 s/hr) =  540 kHz/hr 2 nd  GDSCC PDX loaded to Restrict < 50 kHz “ B...
Windowed Non-Ramped Uplinks T 0 331 / 0230 0430 0630 0830 1030 1230 1430 1630 T 0 + OWLT =  T OWLT +2 +4 +6 +8 +10 +12 +14...
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Cassini at Saturn, use of windowed ramped uplink

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Cassini at Saturn, use of windowed ramped uplink

  1. 1. Analysis of Possible use of Non-Ramped Uplinks, using example of Cassini Rhea Encounter David Tyner NOPE 11 Jan 2006
  2. 2. <ul><li>Actual Rhea encounter used ramped predicts </li></ul><ul><ul><li>Uplinking used a time history of Doppler compensated XAs </li></ul></ul><ul><ul><li>Each Uplink Frequency in time, arrives at S/C at near to BLF </li></ul></ul><ul><ul><li>Provides Minimal Stress on S/C transponder PLL </li></ul></ul><ul><ul><li>Guarantees Minimal Risk of recovery if TXR were to Glitch (I/L shut off), as the transponder is always ‘sitting’ right at XA or BLF </li></ul></ul><ul><ul><li>Transfers (handovers between DSSs) could potentially occur without slewing above and below BLF, but in practice a sweep from above, through, and continuing past where BLF is, are used to guaranteed continuation of 2-way </li></ul></ul><ul><ul><li>Negative impacts to Radio Science [ Tuned XA(t) compared to fixed TSF frequency ] </li></ul></ul><ul><ul><ul><li>Uplink Tuning adds additional frequency instabilities and phase noise (compared to TSF) </li></ul></ul></ul><ul><ul><ul><li>Additional post-processing is needed to remove effect of ramped uplink </li></ul></ul></ul>Ramped vs. Non-Ramped
  3. 3. <ul><li>Analysis of Rhea encounter, if had used non-ramped Uplinking </li></ul><ul><ul><li>Uplinking starts using a single Doppler compensated XA, then ramps to TSF </li></ul></ul><ul><ul><li>The single TSF Frequency (ea. DSS), arrives at S/C at many different values (not at BLF) </li></ul></ul><ul><ul><li>Provides Increasing Stress on S/C transponder PLL, depending on Doppler Profile </li></ul></ul><ul><ul><li>Has increased Risk of 2-way recovery if TXR were to Glitch (I/L shut off), as the transponder has been pulled substantially away from BLF </li></ul></ul><ul><ul><li>Transfers still occur at BLF, but require a larger sweep from above, through, and continuing past where BLF is, as both DSSs start at their individual TSFs (to a “common” XA, BLF) </li></ul></ul><ul><ul><li>Reduced impacts to Radio Science [ fixed TSF frequency compared to Tuned XA(t) ] </li></ul></ul><ul><ul><ul><li>Fixed TSF uplink provides maximum frequency stabilities and reduced phase noise </li></ul></ul></ul><ul><ul><ul><li>Additional post-processing is not needed (there is no tuning nor effect of ramped uplinks) </li></ul></ul></ul>Ramped vs. Non-Ramped <ul><li>Closest approach (Gravity well  v/  t) forces causes XA-TSF to increase </li></ul><ul><ul><li>Larger differences between XA MAX and XA MIN , generate an “average” TSF further Doppler curve </li></ul></ul><ul><ul><li>Techniques can be used to reduce the differences between XA(t) and individual TSFs </li></ul></ul><ul><ul><ul><li>Restrict Predict duration to shorter periods, but still include enough for transfer between DSSs (min overlap) </li></ul></ul></ul><ul><ul><ul><li>Tune from TSF back to XA, Glitch uplink to load new PDX, which so loose 2-way (and Doppler) </li></ul></ul></ul>
  4. 4. <ul><li>Graphical Analysis if had used exactly same predicts, but had used non-ramped TSF technique (“BLF” at transfer between DSSs) </li></ul><ul><ul><li>See next page (5) </li></ul></ul><ul><ul><ul><li>TSF-BLF for DSS-34 is 49 kHz </li></ul></ul></ul><ul><ul><ul><li>TSF-BLF for DSS-63 is 106 kHz </li></ul></ul></ul><ul><li>Graphical Analysis if had Revised predict sets for minimal overlap </li></ul><ul><ul><li>See pages (6-7) </li></ul></ul><ul><ul><ul><li>TSF-BLF for DSS-34 is 25 kHz </li></ul></ul></ul><ul><ul><ul><li>TSF-BLF for DSS-63 is 53 kHz </li></ul></ul></ul>Ramped vs. Non-Ramped <ul><li>Drop Lock approach, enforcing a maximum deviation from BLF </li></ul><ul><ul><li>See pages (8-11) </li></ul></ul><ul><ul><li>Reduces stress on transponder PLL </li></ul></ul><ul><ul><li>Loss of Ranging data is severe for Cassini’s RTLT </li></ul></ul>
  5. 5. XFR at T 0 = 2245z TSF 34 = 7174.510 MHz TSF 63 = 7174.660 MHz TR MAX = (150 Hz/s) * (3600 s/hr) = 540 kHz/hr “ BLF” = 7174.559 MHz Nominal Non-Ramped Uplink Transfer at Closest Approach TSF – XA Difference = 49 kHz TSF – XA Difference = 106 kHz Uplink Transfer DSS-34 to DSS-63
  6. 6. TR MAX = (150 Hz/s) * (3600 s/hr) = 540 kHz/hr “ Improved” Non-Ramped Uplink Transfer at Closest Approach TSF 34 = 7174.535 MHz TSF 63 = 7174.611 MHz XFR at T 0 = 2245z “ BLF” = 7174.559 MHz By Shortening PDX Duration, We Reduce the XA MAX - XA MIN Difference, which brings TSFs closer to Doppler Curve TSF – XA Difference = 25 kHz TSF – XA Difference = 53 kHz Uplink Transfer DSS-34 to DSS-63
  7. 8. XFR at T 0 = 2245z TSF 34 = 7174.535 MHz TR MAX = (150 Hz/s) * (3600 s/hr) = 540 kHz/hr XFR at T 0 = 0550z TSF 63 = 7174.611 MHz “ BLF” = 7174.686 MHz 75 kHz 95 kHz TSF 14 = 7174.781 MHz
  8. 9. TSF 34 = 7174.535 MHz TR MAX = (150 Hz/s) * (3600 s/hr) = 540 kHz/hr 2 nd GDSCC PDX loaded to Restrict < 50 kHz “ BLF” = 7174.691 MHz 50 kHz 50 kHz TSF 14 = 7174.781 MHz “ BLF” = 7174.611 MHz TSF 14 = 7174.661 MHz LOSS OF UPINK, to LOAD PDX TSF 14 = 7174.611 MHz 1 st ORIGINAL 2 nd new PDX view period
  9. 10. Windowed Non-Ramped Uplinks T 0 331 / 0230 0430 0630 0830 1030 1230 1430 1630 T 0 + OWLT = T OWLT +2 +4 +6 +8 +10 +12 +14 DOWNLINK RNG OK U/L PDX Load Glitch, Loss of data in D/L “Pipeline” NEW RNG cycle U/L PDX Load Glitch, Loss of data in D/L “Pipeline” NEW RNG cycle UPLINK No RNG No RNG

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