4 ms·

With data uplink? Same way as your mobile phone gets system updates (OTA).

xyst 6y ago
Wonder what the speeds and delay/latency is like? Did they achieve near theoretical limits of light between earth and mars, or was it a different transport layer? Would love to one day communicate with a person on another planet. Maybe this is something 3 or 4 generations from now will be able to do.
- jandrese 6y ago
  It's radio waves. I'm not sure what other transport layers you are expecting to use between Earth and Mars. The latency is measured in minutes. Obviously something like TCP won't work. Typically they would use something like DTN. https://www.nasa.gov/directorates/heo/scan/engineering/technology/disruption_tolerant_networking https://www.nasa.gov/directorates/heo/scan/engineering/techn... Edit: Corrected hours to minutes. Brainfart on my part.
  - deleted 6y ago
    [deleted]
- vesinisa 6y ago
  The bandwidth is pretty good, considering those super high res photos they send back. There's space in between, and Mars has a very thin atmosphere, so you can communicate with radio quite well I'd bet. Latency is indeed a major issue, it's about 11.5 minutes per direction. The newest rover actually has some A.I. for that reason to let it drive autonomously and not always have to wait for next commands from Earth.
  - bluGill 6y ago
    Latency might be 11.5 minutes now (I didn't check, but I'll believe it), but it ranges between about 2 minutes and about 20 minutes depending on how the earth/mars orbits line up.
- giantrobot 6y ago
  The latency is anywhere from ~5 to ~20 minutes depending on the distance between Earth and Mars at the time. As for bandwidth, there's a couple different answers. Perseverance has two X-band transceivers, one with a high-gain antenna and one with a lower gain omni-directional antenna. It's also got a UHF transceiver it can use to relay communications through the MRO and MAVEN orbiters. The direct X-band transceivers are pretty low bandwidth and are mainly used for rover telemetry. They're low bandwidth because the the antennas are relatively small and the radios aren't super high powered. It takes the 35 and 70 meter dishes of the Deep Space Network just to receiver and send signals to them. The high gain X-band radio (~8GHz) can downlink to Earth at between 160 and 800 bps (yes bits per second) and uplink between 500 to 3000 bps. The low gain radio is mostly receive only and can uplink between 10 and 30 bps. That's enough for densely packed telemetry data and administration commands. The UHF (~400MHz) transceiver talks to either the MRO and MAVEN orbiters. Because that link is pretty short range (200-300km) it's much higher bandwidth. The rover can uplink to the orbiters at about 2Mbps. MRO (I'm not sure about MAVEN) is able to downlink to Earth between 500Kbps and 6Mbps depending on the distance between Earth and Mars. Typically the rover will send its mission data (images, sensor data, etc) to an orbiter while its overhead which will buffer it and then relay it to Earth when its view of Earth is the clearest. MRO and MAVEN complete multiple orbits per sol (Martian day) so there's several opportunities for the rover to upload its mission data and get it back to Earth. All the radio signals travel at the speed of light but the distance is what affects the latency. Mars and Earth are many tens of millions of kilometers apart so it just takes a while, even at the speed of light, to cross that distance. Communicating with another person on Mars would be more like sending each other voicemail messages than anywhere close to a real-time conversation.

xyst 6y ago

Wonder what the speeds and delay/latency is like? Did they achieve near theoretical limits of light between earth and mars, or was it a different transport layer? Would love to one day communicate with a person on another planet. Maybe this is something 3 or 4 generations from now will be able to do.

jandrese 6y ago
It's radio waves. I'm not sure what other transport layers you are expecting to use between Earth and Mars. The latency is measured in minutes. Obviously something like TCP won't work. Typically they would use something like DTN. https://www.nasa.gov/directorates/heo/scan/engineering/technology/disruption_tolerant_networking https://www.nasa.gov/directorates/heo/scan/engineering/techn... Edit: Corrected hours to minutes. Brainfart on my part.
- deleted 6y ago
  [deleted]
vesinisa 6y ago
The bandwidth is pretty good, considering those super high res photos they send back. There's space in between, and Mars has a very thin atmosphere, so you can communicate with radio quite well I'd bet. Latency is indeed a major issue, it's about 11.5 minutes per direction. The newest rover actually has some A.I. for that reason to let it drive autonomously and not always have to wait for next commands from Earth.
- bluGill 6y ago
  Latency might be 11.5 minutes now (I didn't check, but I'll believe it), but it ranges between about 2 minutes and about 20 minutes depending on how the earth/mars orbits line up.
giantrobot 6y ago
The latency is anywhere from ~5 to ~20 minutes depending on the distance between Earth and Mars at the time. As for bandwidth, there's a couple different answers. Perseverance has two X-band transceivers, one with a high-gain antenna and one with a lower gain omni-directional antenna. It's also got a UHF transceiver it can use to relay communications through the MRO and MAVEN orbiters. The direct X-band transceivers are pretty low bandwidth and are mainly used for rover telemetry. They're low bandwidth because the the antennas are relatively small and the radios aren't super high powered. It takes the 35 and 70 meter dishes of the Deep Space Network just to receiver and send signals to them. The high gain X-band radio (~8GHz) can downlink to Earth at between 160 and 800 bps (yes bits per second) and uplink between 500 to 3000 bps. The low gain radio is mostly receive only and can uplink between 10 and 30 bps. That's enough for densely packed telemetry data and administration commands. The UHF (~400MHz) transceiver talks to either the MRO and MAVEN orbiters. Because that link is pretty short range (200-300km) it's much higher bandwidth. The rover can uplink to the orbiters at about 2Mbps. MRO (I'm not sure about MAVEN) is able to downlink to Earth between 500Kbps and 6Mbps depending on the distance between Earth and Mars. Typically the rover will send its mission data (images, sensor data, etc) to an orbiter while its overhead which will buffer it and then relay it to Earth when its view of Earth is the clearest. MRO and MAVEN complete multiple orbits per sol (Martian day) so there's several opportunities for the rover to upload its mission data and get it back to Earth. All the radio signals travel at the speed of light but the distance is what affects the latency. Mars and Earth are many tens of millions of kilometers apart so it just takes a while, even at the speed of light, to cross that distance. Communicating with another person on Mars would be more like sending each other voicemail messages than anywhere close to a real-time conversation.