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Given existing low-orbit and geo-synchronous satellites, would it be possible to build a device that could send a signal to a satellite and then have that signal received on another device? Essentially I'm wondering whether it would be possible to reverse-engineer satellite phones (without just dismantling an existing one) to send/receive signals, and if so, what would be the steps involved? Both in terms of hardware as well as any additional steps needed (e.g. figuring out the frequency that existing satellites are listening on, any encryption/decryption that would have to happen, etc).

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    $\begingroup$ Relevant: security.stackexchange.com/questions/6424/… $\endgroup$ – Paul Oct 13 '18 at 22:18
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    $\begingroup$ Welcome to Space! This is really a question about the electronics inside satellite phones. However I think it is too broad to ask in Electronics SE in its current form, and there's no prior research cited. In other words, no information about what you've read or studied about satellite phones. So I wouldn't ask this there either. $\endgroup$ – uhoh Oct 14 '18 at 0:16
  • $\begingroup$ About reverse-engineering of the encryption, you could have a look at existing questions in Security SE to see if it's already been addressed. $\endgroup$ – uhoh Oct 14 '18 at 1:20
  • $\begingroup$ Becca, you can very easily insert the prior research: google a little bit, and insert what you found. $\endgroup$ – peterh Oct 14 '18 at 4:56
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    $\begingroup$ This would be considered off topic on Electronics SE since no specific satellite standard is identified and what remains to be asked about is a protocol security question, not an electronics one. $\endgroup$ – Chris Stratton Oct 15 '18 at 14:38
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As a radio matter, yes. Amateur radio operators have built and contacted their own satellites, had conversations with Astronauts and Cosmonauts who were licensed Amateurs orbiting on the Shuttle, MIR, and ISS, and bounced signals off the moon, which is not only far beyond even geosynchronous orbit, but a fairly lossy reflector compared to an active satellite transponder. And done all of these with home built equipment as well as commercially purchased gear.

As an access code matter, probably not, at least in the intent of the satellite owners. Commercial satellites, especially those with end user terminals sold to the public are generally going to be somewhat locked down. Someone might be able to figure out how to emulate an approved terminal like a satellite phone (especially an aging scheme where flaws might have since been discovered), but it's certainly not the design intent to support DIY efforts.

As a legal matter, almost certainly not. Most commercial radio services are limited to type accepted equipment (or else that signed off on by a licensed professional technician) which excludes that home built by an individual. Home building amateur radio gear is permitted, but as with all operations under the Amateur Radio Service, that can only be used on frequencies where amateur radio operations are permitted, which is not where commercial satellites would be. And even if there is a case where a commercial satellite allocation and an amateur radio band share the same frequency range, such cross-service operation would not be permitted. These rules will be fairly consistent from jurisdiction to jurisdiction, differing slightly in allowed frequencies but not in general intent.

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  • $\begingroup$ Thanks, that is helpful. My use case is a hypothetical time when government/legal restrictions have collapsed, so I am more interested in the technical ability than legality. However, this post and others have made me think that trying to come up with some kind of communication scheme would be better served by ham radio (possibly using APRS) bounced off some kind of satellite like the ISS that's set to digipeater mode, than trying to rebuild a satellite phone. $\endgroup$ – Becca Oct 15 '18 at 13:45
  • $\begingroup$ Great answer! Is type accepted a legal term? If you can add a link, that would be great. Welcome to Space! $\endgroup$ – uhoh Oct 15 '18 at 20:49

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