Further refinements in the use of Iridium for

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

Satcom systems available to buoy operators Inmarsat D+ Pager GEO < 1 kbyte/day GOES, Meteosat Messaging GEO < 5 kbyte/day Argos Messaging LEO < 5 kbyte/day Aprize. Sat Messaging LEO ? ? Inmarsat C Messaging GEO < 10 kbyte/day Orbcomm Messaging LEO < 50 kbyte/day Iridium Voice Big LEO 1 Mbyte/hr DBCP Workshop, Chennai October 2004

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

Iridium constellation DBCP Workshop, Chennai October 2004

DBCP Workshop, Chennai October 2004

Iridium in the Green. Ice 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 = 1500 m , 4 mm pk-to-pk) • Need to resolve 1 radian tilt (strain 4 x 10 -8) • 75 kbyte/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

Iridium – modes of access • Dial-up over voice circuit • • Modem to modem ~300 bytes/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

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

Example e-mail received by user (MO message) From: 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

SBD Delivery Latency seconds DBCP Workshop, Chennai October 2004

DBCP Workshop, Chennai October 2004

DBCP Workshop, Chennai October 2004

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

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

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

DBCP Workshop, Chennai October 2004

DBCP Workshop, Chennai October 2004

DBCP Workshop, Chennai October 2004

Impulse event – tilt record DBCP Workshop, Chennai October 2004

DBCP Workshop, Chennai October 2004

DBCP Workshop, Chennai October 2004

DBCP Workshop, Chennai October 2004

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

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

DBCP Workshop, Chennai October 2004

DBCP Workshop, Chennai October 2004 IRIDIUM