Satellite communications allows over-the-horizon communications with your balloon, and sometimes two-way communications. Satellite modems are radios that directly communicate with data communication satellites.

Several different networks of satellites exist, relevant ones are:

• Iridium
• Orbcomm
• Globalstar

• + Full global coverage, continuous service pole to pole
• + Inexpensive service
• + Inexpensive pre-assembled trackers available
• + Inexpensive components to build trackers
  • Bare Iridium 9602 Modem
  • RockBlock, Iridium 9602 Modem + Power and USB-Serial PCB - This is recommended over the bare modem

• - Significant length service dropouts regularly due to missing satellites
• + Two-way data
• + Inexpensive modem available: Digi m10 ~$150US ~115€
  • m10 has high power consumption - up to 12 milliwatt-hours per message session
• - Radio Frequency is VHF, requiring a VERY large heavy antenna
• - Very complex binary serial protocol
• - The primary messaging method uses live relay to ground station, requiring that the satellite passing overhead be able to see your modem AND the Orbcomm ground station at the same time
• - Difficult to obtain service for single modems

• - Coverage only near continents, not over much ocean
• - One-way data only - “modem –> internet”
• + Many cheap consumer devices available
  • FindMeSpot Position Tracker