If two persons in the Expanse are communicating and don't know where the other person is, how can the communication find it's way to the target?

This goes double if people think the person is on another location than thought, as displayed in S05E07 around 11min 30sec when the Rocinante (Holden) receives the message from Razorback (Kamal). Kamal thought Holden was at Tycho station and would've send the message there. Holden, being close to Alex, receives the message nontheless and without the message passing through Tycho Station (which is mentioned by Holden saying 'Not much of a transmission delay').

With all the ships and the communication passing between them, the only logical explanation would be to use a wide beam and simply burst it out everywhere. That would be a lot of noise in the solar system but it would be an explanation. In aforementioned scene however, Kamal and Draper were hiding from the Free Navy and would've (IMO) avoided sending message that would reveal their position, it would therefore need to be a tight beam.

So, how does a message that needs to go from person A to B find its way if the sender does not know the receivers location?

  • 3
    How does the call find you on your mobile phone when you're not where you're supposed to be?
    – Valorum
    Dec 5, 2021 at 21:32
  • @Valorum There is a central provider that knows where I am as I am connected to a cell tower. If I am in a foreign country, the provider there probably notifies my provider that I am connected to their network and my provider can route the call there. That wouldn't explain how the Razorback could send the message so fast to the Rocinante. See DavidW comment to the answer. Furthermore, this works as with the speed of light, there is only a short delay in transmitting my position. In the star system, that delay is massive.
    – Shade
    Dec 6, 2021 at 8:32
  • With sufficiently good encryption, it would suffice to send the out-going message by tight beam to a secure repeater and then broadcast everywhere. Only the intended recipient can decrypt. The party at each end would have to know of one secure fixed-location relay but need not know where the message goes after that. More like TOR than like cell phones.
    – Ethan
    Dec 6, 2021 at 19:35
  • @Ethan And how to be sure the recipient gets the message? Lets say his communicator is broken or something...
    – Shade
    Dec 6, 2021 at 21:54
  • @Shade I may misunderstand the scenario, but how can a sender ever be sure in advance that the recipient will receive a message? If you get an answer back, then it arrived. If you get no answer back, you don't know - it might have arrived but the answer did not. Or it might have arrived but the recipient chose not to answer.
    – Ethan
    Dec 6, 2021 at 22:07

1 Answer 1


The same way cell phones work, when you call someone you don't know where they are, but each phone has an ID that's transmitted to the closest tower. So the tower knows where you are.

  • 1
    That would require every ship continuously beaming its location to one of a relatively small number of relays, which would maintain a catalog of all ship locations among them. There are more than a few operational security problems with this if you're trying to sneak around; even if the opposition can't commandeer or suborn a relay, they can just ghost one close enough to catch all traffic, tight beam or no.
    – DavidW
    Dec 6, 2021 at 1:02
  • @SteveDodds That would also require a central (or some central) providers and everything has to pass through them. With cell phones, that's no issue but it doesn't work (without huge delays) over astronomic distances. That also wouldn't explain how Kamal was able to send the message to Holden so fast.
    – Shade
    Dec 6, 2021 at 8:52

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