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A satellite of that age would have used a very simple analog repeater or linear transponder, meaning that there is no communications logic occurring on the sate

A satellite of that age would have used a very simple analog repeater or linear transponder, meaning that there is no communications logic occurring on the satellite. Any digital modulation, and more so encryption, would be the responsibility of the ground stations. This is still a common design pattern for satellites, referred to as the "bent pipe" model since the space segment is merely a "bend" with no logic, but it is subject to abuse by unauthorized operators so there's usually some degree of at least authentication today. Military satellites launched into the '80s continued to use analogue transponders and, to some extent to this day, see unauthorized use. The only real deterrent was the difficulty of obtaining inexpensive equipment for satellite bands but the widespread use of DVB and VSATs changed that during the '90s and '00s. That said, all related documents may very well have been classified at the time (owing especially to the lack of any authentication!) and even when declassify-on dates pass there is often institutional resistance to going through the motions of releasing this material, especially since Lincoln Labs (a contractor) would not be authorized to do so and would have to forward the request on to someone else. A more formal FOIA request, followed by appeals if necessary, can often unstick these wheels since it creates a legal obligation that a more casual media request does not.

tlrobinson 7y ago
> A satellite of that age would have used a very simple analog repeater or linear transponder, meaning that there is no communications logic occurring on the satellite. It's broadcasting telemetry, isn't there a chance it also accepts commands? > Military satellites launched into the '80s continued to use analogue transponders and, to some extent to this day, see unauthorized use. The only real deterrent was the difficulty of obtaining inexpensive equipment for satellite bands but the widespread use of DVB and VSATs changed that during the '90s and '00s. WIRED had an article about this awhile back: https://www.wired.com/2009/04/fleetcom/ https://www.wired.com/2009/04/fleetcom/
- jplayer01 7y ago
  Oh, this is fascinating. Just a bit disappointing that the article doesn't mention at all why it's possible for random people in Brazil to access these satellites.
  - oyebenny 7y ago
    > Oh, this is fascinating. Just a bit disappointing that the article doesn't mention at all why it's possible for random people in Brazil to access these satellites. This is my question as well.
    - tonyarkles 7y ago
      The Fleetcom satellites are, if I recall, just “bent pipe” satellites. There receive on one frequency and retransmit on another with zero logic onboard. Analog, digital, whatever. If you wanted them to encrypt their broadcasts, you’d just encrypt the signal before transmitting on the ground and it would happily rebroadcast your encrypted signal back to earth.
    - ColanR 7y ago
      From the article, to answer the hardware side of your question, which was mine as well. > To use the satellite, pirates typically take an ordinary ham radio transmitter, which operates in the 144- to 148-MHZ range, and add a frequency doubler cobbled from coils and a varactor diode. That lets the radio stretch into the lower end of FLTSATCOM's 292- to 317-MHz uplink range. All the gear can be bought near any truck stop for less than $500. Ads on specialized websites offer to perform the conversion for less than $100. Taught the ropes, even rough electricians can make Bolinha-ware.
  - matheusmoreira 7y ago
    These specific satellites have no security. They just retransmit any signal that comes at them. Makes me wonder who else is using them...
    - jplayer01 7y ago
      Seems weird to me. They made these things when they were at war with Eurasia. Seems like it'd be a good idea to ensure only you could use them.
      - matheusmoreira 7y ago
jandrese 7y ago
I'd assume "sending commands to the satellite" would involve some sort of digital encoding. If you just want to bounce signals off of it then you probably just need to figure out the frequency and polarization (trial and error?), but if you wanted to issue a command I'd assume you need some sort of protocol.
unixhero 7y ago
Dude out of curiosity who are you and how can I learn all the things you know.
- dylan604 7y ago
  I knew a guy that was part of the beginnings of the cable frontier running numerous cable headends. Any time he needs to align a new dish, he does it by hand. He knows where a specific satellite is, and a particular signal coming from it. Once he finds it, he pans the dish across the line of satellites until he gets to the one needed. As you pan across the sky, you can use a scope to see each of the birds come in and out of alignment. The constellations are known, so you map out which ones are which. Some of the signals are scrambled, but there's a lot to be learned, and if it is TV broadcast, decoders are available. A lot of this gear is available second/third/fourth hand now. With the right gear, it is possible to learn a lot of this stuff on your own with some google searches. Learning to decode what's already coming down is just a step on the way to learning about what goes up. Useless satellite trivia: from time to time, it becomes necessary to adjust the orbit of the satellites (like a wandering disabled satellite). They do not fire boosters to raise/lower the orbit directly as that requires too much fuel. Instead, they speed up/slow down the horizontal speed to increase/decrease altitude. With enough notice, they can do this very incrementally and fuel efficiently.
  - JshWright 7y ago
    The necessary equipment is also crazy cheap at this point. You could easily start listening to satellites with a $20 USB SDR dongle and a DIY antenna. If someone wants a cheap way to learn orbital mechanics (like why you accelerate/decelerate to raise/lower your orbit), pick up a copy of Kerbal Space Program.
- panzagl 7y ago
  Space Force is accepting enlistments and commissions.
- JshWright 7y ago
  I'm not the person you're replying to, but my answer would be "stay curious, and don't be afraid to follow that curiosity down a lot of rabbit holes".
wrigby 7y ago
Yeah, most geostationary communications birds use analog transponders, even to this day. There's a lot of fancy command and control, but the actual payload is just analog RF circuitry, even using tube-based power amplifiers. I have no idea about these older satellites, but on modern stuff there's a separate Telemetry, Command, and Control (TT&C) link. Maybe this bird is only transmitting telemetry though?
moftz 7y ago
It's an experimental satellite, it's downlinking data rather than just being a bent-pipe relay. This is right before SGLS and the mass adoption of S-band (USB) so it's going to likely be a basic VHF BPSK kind of signal. This is also before encryption was easy so it's likely going to be in the clear.
sandworm101 7y ago
>> This is still a common design pattern for satellites, referred to as the "bent pipe" model since If it is a communications satellite. It is also a common design pattern for military satellites to be mislabeled as "communications" when they actually do other things. So too is it common for "communications" to also cover intercept of enemy communications. Old secrets can still be embarrassing.

tlrobinson 7y ago

> A satellite of that age would have used a very simple analog repeater or linear transponder, meaning that there is no communications logic occurring on the satellite. It's broadcasting telemetry, isn't there a chance it also accepts commands? > Military satellites launched into the '80s continued to use analogue transponders and, to some extent to this day, see unauthorized use. The only real deterrent was the difficulty of obtaining inexpensive equipment for satellite bands but the widespread use of DVB and VSATs changed that during the '90s and '00s. WIRED had an article about this awhile back: https://www.wired.com/2009/04/fleetcom/ https://www.wired.com/2009/04/fleetcom/

jplayer01 7y ago
Oh, this is fascinating. Just a bit disappointing that the article doesn't mention at all why it's possible for random people in Brazil to access these satellites.
- oyebenny 7y ago
  > Oh, this is fascinating. Just a bit disappointing that the article doesn't mention at all why it's possible for random people in Brazil to access these satellites. This is my question as well.
  - tonyarkles 7y ago
    The Fleetcom satellites are, if I recall, just “bent pipe” satellites. There receive on one frequency and retransmit on another with zero logic onboard. Analog, digital, whatever. If you wanted them to encrypt their broadcasts, you’d just encrypt the signal before transmitting on the ground and it would happily rebroadcast your encrypted signal back to earth.
  - ColanR 7y ago
    From the article, to answer the hardware side of your question, which was mine as well. > To use the satellite, pirates typically take an ordinary ham radio transmitter, which operates in the 144- to 148-MHZ range, and add a frequency doubler cobbled from coils and a varactor diode. That lets the radio stretch into the lower end of FLTSATCOM's 292- to 317-MHz uplink range. All the gear can be bought near any truck stop for less than $500. Ads on specialized websites offer to perform the conversion for less than $100. Taught the ropes, even rough electricians can make Bolinha-ware.
- matheusmoreira 7y ago
  These specific satellites have no security. They just retransmit any signal that comes at them. Makes me wonder who else is using them...
  - jplayer01 7y ago
    Seems weird to me. They made these things when they were at war with Eurasia. Seems like it'd be a good idea to ensure only you could use them.
    - matheusmoreira 7y ago

jandrese 7y ago

I'd assume "sending commands to the satellite" would involve some sort of digital encoding. If you just want to bounce signals off of it then you probably just need to figure out the frequency and polarization (trial and error?), but if you wanted to issue a command I'd assume you need some sort of protocol.

unixhero 7y ago

Dude out of curiosity who are you and how can I learn all the things you know.

dylan604 7y ago
I knew a guy that was part of the beginnings of the cable frontier running numerous cable headends. Any time he needs to align a new dish, he does it by hand. He knows where a specific satellite is, and a particular signal coming from it. Once he finds it, he pans the dish across the line of satellites until he gets to the one needed. As you pan across the sky, you can use a scope to see each of the birds come in and out of alignment. The constellations are known, so you map out which ones are which. Some of the signals are scrambled, but there's a lot to be learned, and if it is TV broadcast, decoders are available. A lot of this gear is available second/third/fourth hand now. With the right gear, it is possible to learn a lot of this stuff on your own with some google searches. Learning to decode what's already coming down is just a step on the way to learning about what goes up. Useless satellite trivia: from time to time, it becomes necessary to adjust the orbit of the satellites (like a wandering disabled satellite). They do not fire boosters to raise/lower the orbit directly as that requires too much fuel. Instead, they speed up/slow down the horizontal speed to increase/decrease altitude. With enough notice, they can do this very incrementally and fuel efficiently.
- JshWright 7y ago
  The necessary equipment is also crazy cheap at this point. You could easily start listening to satellites with a $20 USB SDR dongle and a DIY antenna. If someone wants a cheap way to learn orbital mechanics (like why you accelerate/decelerate to raise/lower your orbit), pick up a copy of Kerbal Space Program.
panzagl 7y ago
Space Force is accepting enlistments and commissions.
JshWright 7y ago
I'm not the person you're replying to, but my answer would be "stay curious, and don't be afraid to follow that curiosity down a lot of rabbit holes".

wrigby 7y ago

Yeah, most geostationary communications birds use analog transponders, even to this day. There's a lot of fancy command and control, but the actual payload is just analog RF circuitry, even using tube-based power amplifiers. I have no idea about these older satellites, but on modern stuff there's a separate Telemetry, Command, and Control (TT&C) link. Maybe this bird is only transmitting telemetry though?

moftz 7y ago

It's an experimental satellite, it's downlinking data rather than just being a bent-pipe relay. This is right before SGLS and the mass adoption of S-band (USB) so it's going to likely be a basic VHF BPSK kind of signal. This is also before encryption was easy so it's likely going to be in the clear.

sandworm101 7y ago

>> This is still a common design pattern for satellites, referred to as the "bent pipe" model since If it is a communications satellite. It is also a common design pattern for military satellites to be mislabeled as "communications" when they actually do other things. So too is it common for "communications" to also cover intercept of enemy communications. Old secrets can still be embarrassing.