SVN23PRN23 INTEGRITY FAILURE OF 01 JANUARY 2004 - PowerPoint PPT Presentation
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SVN23PRN23 INTEGRITY FAILURE OF 01 JANUARY 2004
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Users can independently see the SV's PRN codes. Also where SV shows up in the almanac data ... PRN-23 Anomaly Timeline. SVN-23 Suffered an Integrity Failure on ... – PowerPoint PPT presentation
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Title: SVN23PRN23 INTEGRITY FAILURE OF 01 JANUARY 2004
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SVN-23/PRN-23INTEGRITY FAILUREOF01 JANUARY 2004
- Capt Heather Eastlack
- 2nd Space Operations Squadron
- Written by K. Kovach
- 9 Mar 04
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OUTLINE
- Note on Nomenclature
- Message to Remember
- The SVN-23/PRN-23 Integrity Failure
- The Range of User Impacts
- Recommended Preventative
- Summary
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A NOTE ON NOMENCLATURE
- SVN-23 is the "Space Vehicle Number"
- The production line number
- Permanently "painted on the satellite's inside"
- Users have no independent way to see the SVN
- PRN-23 is the "PseudoRandom Noise code" (PRN)
Number - Identifies P(Y)-code C/A-code broadcast by SV
- Users can independently see the SV's PRN codes
- Also where SV shows up in the almanac data
- Known as the "SV ID" number in ICD-GPS-200
- SVN-23 was Broadcasting as PRN-23 on 01 Jan 04
- A GPS SV's PRN number is ground selectable
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PRN-23 Anomaly Timeline
- SVN-23 Suffered an Integrity Failure on 01 Jan 04
- Operating on a Rubidium clock
- Clock failed at about 1830Z (Holiday Afternoon)
- Clock failure caused a substantial frequency
error - Varied over time, max sustained error was 371 Hz
at L1 - 371 Hz at L1 gives an 70.6 m/sec pseudorange rate
error - An integrity failure because no timely warning
issued - The Operational Control Segment (OCS) Set SVN-23
Unhealthy at - about 2118Z
- Accumulated pseudorange error was about 285,000 m
- No SATZAP procedure performed
- SATZAP changes identity of the SV's PRN code
- SVN-23 remained trackable as PRN-23
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23
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International GPS Service (IGS) 5-MINUTE DATA
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IGS 5-MINUTE DATA
Failure at 1830. Loss of tracking.
Set Unhealthy at 2118.
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Master Control Station (MCS) IGS DATA
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FAA DATA -- FIRST 10 MINUTES
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SVN-23 RECOVERY
- SVN-23 Clock Switched Off at 2305Z on 1 Jan 04
- One Cesium clock remained on-board (marginal)
- SVN-23 Service Restored
- Set HEALTHY at 2253Z on 20 Jan 04
- SVN-23 End-of-Life (PRN23 available for IIR-12)
- Set DEAD at 2030Z on 5 Feb 04
- Decommissioned (unavailable to users) at 2200Z on
13 Feb 04
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CONTEXT
- This is the First Major Integrity Failure Since
2001 - Integrity failures are rare (!)
- For Aviation, Integrity Requirement is 1-10-7/hr
- Or 1 integrity failure per 1,142 years
- Obviously, SVs will Never meet the Aviation
- Integrity Requirement Alone
- Would need a 1,000-fold improvement
- Integrity Failure Rate for GPS SVs is ?3 per year
- Specified in SPS Performance Standard
- Specified in PPS Performance Standard
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GOOD NEWS
- IIR/IIR-M Satellites Don't Have This Failure Mode
- It has been fixed (!)
- Run two clocks concurrently
- Atomic (Rubidium)
- VCXO (Quartz)
- Monitor short-term difference between the clocks
- If difference greater than a threshold (5 m)
- Immediately switch to non-standard code
- IIR/IIR-M Satellites thus Provide Integrity
- 1,000-fold improvement for large errors
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