5 ms·

I'm nervous asking, but a little curious what kind of equipment someone would need to give it different instructions. Does it use 1970s encryption? How big woul

by treve 3y ago

I'm nervous asking, but a little curious what kind of equipment someone would need to give it different instructions. Does it use 1970s encryption? How big would your radio need to be?

mvkel 3y ago
No encryption; security through expensivity. A major developed nation would be the only candidate with enough resources to build something to communicate with Voyager. But to what end? Voyagers are sent commands using the DSN, which is in high demand: https://arstechnica.com/space/2023/08/nasas-artemis-i-mission-nearly-broke-the-deep-space-network/ https://arstechnica.com/space/2023/08/nasas-artemis-i-missio... They need big radios (the biggest!) because the signal strength coming back from the probes these days are very weak, only one-tenth of a billion-trillionth of a watt.
- eth0ws 3y ago
  I thought you were being handwave-y about the signal being returned because that's an obscenely small amount of power, but you're right. Hardware that is probably 50 years old at this stage, in the cold of (interstellar)space, and we're still able to talk to it despite the signal after its long journey back being ~0.000000000000000001w.
  - toomuchtodo 3y ago
    Applied radio astronomy with a transmit component.
  - brcmthrowaway 3y ago
    I still havent figured out how people decide signals under the noise floor
    - Vecr 3y ago
      A lot of the signal processioning/decoding gear is cryogenic. Maybe everything to the ADC?
    - tails4e 3y ago
      Essentially averaging. To put it simply, noise is random while the signal is not. So if you average 2x the noise reduces but sqrt(2) but the signal remains. Keep doing that and you have the signal appear out of the noise. GPS operates at a negative SNR. That also uses code division multiple access to allow multiple transmitters to operate on the same frequency and the signals do not interfere.
      - op00to 3y ago
        Look up viterbi algorithm. Imagine you're watching a trail of animal footprints in the snow, but the snow has covered parts of the trail (noise), so some prints are unclear. You're trying to figure out exactly which path the animal took. The Viterbi algorithm is like a detective method for doing just that, but instead of animal tracks, it's used for decoding messages or signals that got partially scrambled during transmission.
        mvkel 3y ago
        This is fascinating. It sounds like viterbi builds probabilities from known data, is that right? Is it essentially looking at the faint signal now and comparing it to data from when the signal was stronger and extrapolating?
        op00to 3y ago
        That’s how I understand it. I think it uses knowledge of the state changes, what they should be like, and selects the most likely one from a table of options. Based on what it knows about the signal, it guessed whether it’s more likely to be a or b. I use it with ham radio, where the software I use sends signals well under the noise floor (-23db) that can still get across call signs, signal reports, and maybe a thank you. The naked ear would not hear a thing at the low end of received signal.
      - brcmthrowaway 3y ago
        I need a Jupyter notebook example!
eru 3y ago
> Does it use 1970s encryption? That would actually be fine, because you can do encryption in software. So you wouldn't need to keep any physical artifacts from the 1970s around.
- tempay 3y ago
  I think OP's concern was more around that it's likely easy to break any encryption that was used in the 1970s so someone could send the spacecraft malicious commands. That said, only America, China, Europe, India, Japan and Russia have deep space networks and none of them have anything to gain from investing the resources into trying to harm Voyager. Even with weak encryption it's likely difficult to collect enough samples to be able to break it and even once it's broken you still need to figure out a valid set of commands to send to achive your goal.
  - wolverine876 3y ago
    > it's likely easy to break any encryption that was used in the 1970s I wouldn't jump to that conclusion. Some things encrypted now are intended to be secure for 50 years.
    - Dylan16807 3y ago
      We have much better chances of designing a cryptography system today that can survive 50 years of math, and with computers a billion times faster we can make the encryption O((1.something)^billion) times harder to brute force. Nothing in the 70s was capable of resisting today's attacks. You mention a one-time pad in another comment. In theory they could have sacrificed a bunch of tape space to store a pad for commands.
      - pxx 3y ago
        Encryption in the 70s resists today's attacks just fine. DES was weakened on purpose (short key length, but the idea for 3DES dates from 1978). In the asymmetric realm you still can't break a full length RSA key. Maybe it's not fully contemporaneous with Voyager but the claim that 70s encryption is insufficient doesn't stand up to scrutiny

by treve 3y ago

I'm nervous asking, but a little curious what kind of equipment someone would need to give it different instructions. Does it use 1970s encryption? How big would your radio need to be?

mvkel 3y ago

No encryption; security through expensivity. A major developed nation would be the only candidate with enough resources to build something to communicate with Voyager. But to what end? Voyagers are sent commands using the DSN, which is in high demand: https://arstechnica.com/space/2023/08/nasas-artemis-i-mission-nearly-broke-the-deep-space-network/ https://arstechnica.com/space/2023/08/nasas-artemis-i-missio... They need big radios (the biggest!) because the signal strength coming back from the probes these days are very weak, only one-tenth of a billion-trillionth of a watt.

eth0ws 3y ago
I thought you were being handwave-y about the signal being returned because that's an obscenely small amount of power, but you're right. Hardware that is probably 50 years old at this stage, in the cold of (interstellar)space, and we're still able to talk to it despite the signal after its long journey back being ~0.000000000000000001w.
- toomuchtodo 3y ago
  Applied radio astronomy with a transmit component.
- brcmthrowaway 3y ago
  I still havent figured out how people decide signals under the noise floor
  - Vecr 3y ago
    A lot of the signal processioning/decoding gear is cryogenic. Maybe everything to the ADC?
  - tails4e 3y ago
    Essentially averaging. To put it simply, noise is random while the signal is not. So if you average 2x the noise reduces but sqrt(2) but the signal remains. Keep doing that and you have the signal appear out of the noise. GPS operates at a negative SNR. That also uses code division multiple access to allow multiple transmitters to operate on the same frequency and the signals do not interfere.
    - op00to 3y ago
      Look up viterbi algorithm. Imagine you're watching a trail of animal footprints in the snow, but the snow has covered parts of the trail (noise), so some prints are unclear. You're trying to figure out exactly which path the animal took. The Viterbi algorithm is like a detective method for doing just that, but instead of animal tracks, it's used for decoding messages or signals that got partially scrambled during transmission.
      - mvkel 3y ago
        This is fascinating. It sounds like viterbi builds probabilities from known data, is that right? Is it essentially looking at the faint signal now and comparing it to data from when the signal was stronger and extrapolating?
        op00to 3y ago
        That’s how I understand it. I think it uses knowledge of the state changes, what they should be like, and selects the most likely one from a table of options. Based on what it knows about the signal, it guessed whether it’s more likely to be a or b. I use it with ham radio, where the software I use sends signals well under the noise floor (-23db) that can still get across call signs, signal reports, and maybe a thank you. The naked ear would not hear a thing at the low end of received signal.
    - brcmthrowaway 3y ago
      I need a Jupyter notebook example!

eru 3y ago

> Does it use 1970s encryption? That would actually be fine, because you can do encryption in software. So you wouldn't need to keep any physical artifacts from the 1970s around.

tempay 3y ago
I think OP's concern was more around that it's likely easy to break any encryption that was used in the 1970s so someone could send the spacecraft malicious commands. That said, only America, China, Europe, India, Japan and Russia have deep space networks and none of them have anything to gain from investing the resources into trying to harm Voyager. Even with weak encryption it's likely difficult to collect enough samples to be able to break it and even once it's broken you still need to figure out a valid set of commands to send to achive your goal.
- wolverine876 3y ago
  > it's likely easy to break any encryption that was used in the 1970s I wouldn't jump to that conclusion. Some things encrypted now are intended to be secure for 50 years.
  - Dylan16807 3y ago
    We have much better chances of designing a cryptography system today that can survive 50 years of math, and with computers a billion times faster we can make the encryption O((1.something)^billion) times harder to brute force. Nothing in the 70s was capable of resisting today's attacks. You mention a one-time pad in another comment. In theory they could have sacrificed a bunch of tape space to store a pad for commands.
    - pxx 3y ago
      Encryption in the 70s resists today's attacks just fine. DES was weakened on purpose (short key length, but the idea for 3DES dates from 1978). In the asymmetric realm you still can't break a full length RSA key. Maybe it's not fully contemporaneous with Voyager but the claim that 70s encryption is insufficient doesn't stand up to scrutiny