You can use any of the LEO/MEO Satcomm services that support simplex and/or duplex data transmission, which currently are Globalstar or Iridium. These are far e

You can use any of the LEO/MEO Satcomm services that support simplex and/or duplex data transmission, which currently are Globalstar or Iridium. These are far easier to target since you don't need as much transmitter power resp. precise pointing like you need when talking to GSO satellites. Though, bandwidth is a trade-off, but I suppose the amount of data acquired by ADS-B receivers is less than the available bandwidth, especially in (relatively) low-traffic regions like the oceans. Edit: To be clear, that only covers the data transmission part from the vessel and not picking up ADS-B signals. For the latter, the Iridium NEXT satellites will be equipped with ADS-B receivers directly.