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Voyager still actually gets up to a whopping 1.4 kbps downlink! (but only 16 bps uplink) https://voyager.jpl.nasa.gov/mission/spacecraft/ https://voyager.jpl.n

Voyager still actually gets up to a whopping 1.4 kbps downlink! (but only 16 bps uplink) https://voyager.jpl.nasa.gov/mission/spacecraft/ https://voyager.jpl.nasa.gov/mission/spacecraft/

perihelions 5y ago
That's a bit confusing; shouldn't it be the other way around? Because they're using the same antennas in both directions, but the power budget on the Earth-transmitting side is much higher. (Asked in the spirit of curiosity; I'm ignorant of radio physics).
- NikolaNovak 5y ago
  I'm assuming that our ability to computationally aid / resolve signal is far higher than voyager's.
  - jamiek88 5y ago
    Plus receiver size.
    - johnwalkr 5y ago
      It’s mainly this and it’s normal for spacecraft (especially in deep space) to have orders of magnitude more datarate on downlink.
  - phire 5y ago
    That's a factor, but I think it's more that there was never a need for large data uplinks to Voyager, while they needed to downlink large amounts of science data. The uplink and downlink are in different frequency bands, S-band (2-4ghz) for uplink and X-band (8-12ghz) for downlink and have different amounts of radio frequency bandwidth allocated. Additionally, Voyager's High-gain antenna has a much narrower beamwidth in X-band at 0.5°, compared to 2.3° for S-band, though I have no idea if that's a factor.
- dr_orpheus 5y ago
  There are a couple of factors at play here. The first is that the downlink is at a higher frequency (X-band, 8.4 GHz) so there is more available bandwidth and the beamwidth of the antenna is tighter at a higher frequency (i.e. the power is more focused). The uplink is at 2.3 GHz, but part of the advantage of the larger beamwidth is that you are able to command the spacecraft if there is an anomaly and it is the high gain antenna is more offpointed. There is also a low gain omnidirectional S-band antenna in case it is really offpointed. Although the signals both come through the high gain antenna there are two different feeds for the X-band and S-band. If you take a look at the picture of the antenna on Wikipedia [0] you can see the X-band feed is the prime focus behind the subreflector. The S-band feed is mounted on the subreflector so its not seeing the optimally focused signal (which the lower frequencies are less sensitive to this overall loss of focus for the reasons above). Generally a lot of spacecraft are designed with a much higher downlink to get science data down, but you only need a pretty small link to get commands up to the spacecraft. [0] https://en.wikipedia.org/wiki/Voyager_1#Communication_system https://en.wikipedia.org/wiki/Voyager_1#Communication_system

Voyager still actually gets up to a whopping 1.4 kbps downlink! (but only 16 bps uplink) https://voyager.jpl.nasa.gov/mission/spacecraft/ https://voyager.jpl.nasa.gov/mission/spacecraft/

perihelions 5y ago

That's a bit confusing; shouldn't it be the other way around? Because they're using the same antennas in both directions, but the power budget on the Earth-transmitting side is much higher. (Asked in the spirit of curiosity; I'm ignorant of radio physics).

NikolaNovak 5y ago
I'm assuming that our ability to computationally aid / resolve signal is far higher than voyager's.
- jamiek88 5y ago
  Plus receiver size.
  - johnwalkr 5y ago
    It’s mainly this and it’s normal for spacecraft (especially in deep space) to have orders of magnitude more datarate on downlink.
- phire 5y ago
  That's a factor, but I think it's more that there was never a need for large data uplinks to Voyager, while they needed to downlink large amounts of science data. The uplink and downlink are in different frequency bands, S-band (2-4ghz) for uplink and X-band (8-12ghz) for downlink and have different amounts of radio frequency bandwidth allocated. Additionally, Voyager's High-gain antenna has a much narrower beamwidth in X-band at 0.5°, compared to 2.3° for S-band, though I have no idea if that's a factor.
dr_orpheus 5y ago
There are a couple of factors at play here. The first is that the downlink is at a higher frequency (X-band, 8.4 GHz) so there is more available bandwidth and the beamwidth of the antenna is tighter at a higher frequency (i.e. the power is more focused). The uplink is at 2.3 GHz, but part of the advantage of the larger beamwidth is that you are able to command the spacecraft if there is an anomaly and it is the high gain antenna is more offpointed. There is also a low gain omnidirectional S-band antenna in case it is really offpointed. Although the signals both come through the high gain antenna there are two different feeds for the X-band and S-band. If you take a look at the picture of the antenna on Wikipedia [0] you can see the X-band feed is the prime focus behind the subreflector. The S-band feed is mounted on the subreflector so its not seeing the optimally focused signal (which the lower frequencies are less sensitive to this overall loss of focus for the reasons above). Generally a lot of spacecraft are designed with a much higher downlink to get science data down, but you only need a pretty small link to get commands up to the spacecraft. [0] https://en.wikipedia.org/wiki/Voyager_1#Communication_system https://en.wikipedia.org/wiki/Voyager_1#Communication_system