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Further refinements in the use of Iridium for polar applications

Further refinements in the use of Iridium for polar applications. David Meldrum and Duncan Mercer Scottish Association for Marine Science www.sams.ac.uk. Satcom systems available to buoy operators. Features of Iridium. 66+ satellites in low earth orbit Designed for voice communications

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Further refinements in the use of Iridium for polar applications

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  1. Further refinements in the use of Iridium for polar applications David Meldrum and Duncan Mercer Scottish Association for Marine Science www.sams.ac.uk DBCP Workshop, Chennai October 2004

  2. Satcom systems available to buoy operators DBCP Workshop, Chennai October 2004

  3. Features of Iridium • 66+ satellites in low earth orbit • Designed for voice communications • Real-time: inter-satellite comms • 2-way • True global • Compact antenna • Future more or less assured • Detested by Argos DBCP Workshop, Chennai October 2004

  4. Iridium constellation DBCP Workshop, Chennai October 2004

  5. DBCP Workshop, Chennai October 2004

  6. Iridium in the GreenIce project • Climate change – is the Arctic ice thinning? • Average ice thickness difficult to measure • Nagurny theory: spectrum of swell waves penetrating ice is a function of area averaged thickness • Small waves (λ = 1500m , 4mm pk-to-pk) • Need to resolve 1 radian tilt (strain 4x10-8) • 75kbyte/day of spectral and other data • Latest deployments spring/summer 2004 • Met data on GTS via Metocean SVP-Bs and Argos DBCP Workshop, Chennai October 2004

  7. Iridium – modes of access • Dial-up over voice circuit • Modem to modem • ~300bytes/s • ~$1/min connect time • A bit flaky – unexplained call drops • Short Burst Data (SBD) • E-mail service • Mobile originated packet transfer • ~2 kbyte max packet size • ~$1/kbyte • More or less bomb-proof • Short Message Service • Can be used to wake mobile up for SBD xfer • Direct Internet • Various flavours…. DBCP Workshop, Chennai October 2004

  8. Short Burst Data Pathways MODEM IRIDIUM NETWORK +SBDWB TX Buffer SENSOR +SBDI RX Buffer +SBDRB INTERNET Data@SBD.Iridium.com USER Iridium@sams.ac.uk • Simple AT commands DBCP Workshop, Chennai October 2004

  9. Example e-mail received by user (MO message) From: <Iridium SBD Service (Tempe, AZ)> Sent: Tue, 23 Sep 2003 22:02:24 Subject: SBD Msg From Unit: 300090807080903 MOMSN:152 MTMSN:0 Session Status: TRANSFER OK Message Size (bytes): 1960 Unit Location: Lat = 56.457321 Long = -5.458788 CEPradius = 2 Message is attached. DBCP Workshop, Chennai October 2004

  10. SBD Delivery Latency seconds DBCP Workshop, Chennai October 2004

  11. DBCP Workshop, Chennai October 2004

  12. DBCP Workshop, Chennai October 2004

  13. SBD vs Dial Up • SBD easy to implement…. • Cost penalty? DBCP Workshop, Chennai October 2004

  14. SBD vs Dial Up • SBD easy to implement…. • Cost penalty? • $115k for 6 months! DBCP Workshop, Chennai October 2004

  15. Revisit dial-up! • Charged at 1$/min, 10¢/kbyte or better • Identify cause of call drops • Modify ZMODEM protocol • Create outbound file queue to deal with remaining call drops • Establish dedicated modem and server • Array of 5 platforms has run without problem since May DBCP Workshop, Chennai October 2004

  16. DBCP Workshop, Chennai October 2004

  17. DBCP Workshop, Chennai October 2004

  18. DBCP Workshop, Chennai October 2004

  19. Impulse event – tilt record DBCP Workshop, Chennai October 2004

  20. DBCP Workshop, Chennai October 2004

  21. DBCP Workshop, Chennai October 2004

  22. DBCP Workshop, Chennai October 2004

  23. History repeats itself… • Early problems for the Argos user • Why buy Argos? • Argos promises to meet user need • The system works! • How does it work? • Will it do a new task? • Suck it and see • The system doesn’t work… • God Only Knows (GOK) • Satellite Operator Only Knows (SOOK) • Whom do you contact? • The system costs more than you can afford… • Tariff and invoices incomprehensible DBCP Workshop, Chennai October 2004

  24. One solution – maybe for Iridium too? • DBCP Technical Co-ordinator (1987) • Based at Argos Toulouse • Access to all elements of chain, incl GTS • Access to Argos technical team • JTA negotiations • Discounted price for global bulk purchase • Tariff and invoices still incomprehensible • System still costs more than you can afford • At least the mess is partly of our own making…. DBCP Workshop, Chennai October 2004

  25. DBCP Workshop, Chennai October 2004

  26. IRIDIUM DBCP Workshop, Chennai October 2004

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