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Comment by xyst | Hacker News Reader

How do they issue updates to the system on mars?

Very slowly, given the bandwidth is about 3Kbps (https://mars.nasa.gov/mars2020/spacecraft/rover/communicatio...)

I torrented GTA Vice City at a similar speed when I was young. I'm sure NASA has that level of patience.

Is Limewire running on the rover? I hope they don't download an update and it turns out it's a dragon ball amv with a linkin park soundtrack.

They're running Kazaa so there's a risk an update involves horses (yes, LimeWire and Kazaa were both Gnutella consumers)

Where'd you get that?

> The mass- and power-constrained rover can achieve high data rates of up to 2 megabits per second on the relatively short-distance relay link to the orbiters overhead. The orbiters then use their much larger antennas and transmitters to relay that data on the long-distance link back to Earth.

> Transmission Rates Up to 2 megabits per second on the rover-to-orbiter relay link.

And using DSN Now, we can also see that the speed from Earth to those orbiters is also 2Mbps.

The Rover-to-Orbiter is 2Mbps, whereas the X-Band High-Gain Antenna link is 3Kbps:

> 160/500 bits per second or faster to/from the Deep Space Network's 112-foot-diameter (34-meter-diameter) antennas or at 800/3000 bits per second or faster to/from the Deep Space Network's 230-foot-diameter (70 meter-diameter)

I'm a bit surprised the Rover talks directly to Earth for the high speed data transfer. I would have expected a large dish in Martian orbit being used to relay the signal down to the rover's relatively tiny high gain antenna. Even when you account for the fact that the satellite will only be overhead part of the time the link budget calculation would be enormously different.

They do, from the link in the comment you replied to:

> Most often, Mars 2020 uses its ultra-high frequency (UHF) antenna (about 400 megahertz) to communicate with Earth through NASA's orbiters around Mars. Because the rover and orbiter antennas are within close range of each other, they act a little like walky-talkies compared to the long-range telecommunications with Earth provided by the low-gain and high-gain antennas.

Wow! it's a flashback to the dial up days. Still impressive. Look forward to when we are able to advance this technology.

Latency must be crazy too.

1374311 millisecond ping time right now

so roughly Wellington to Reykjavik

sudo apt upgrade --high-gain

May be they can first upload something to an orbiter, and then use it as a secondary source for updates for the computers on the planet?

From what I understand they use the Mars Reconnaissance Orbiter to do exactly that when the rover loses direct line of sight to Earth.

Interesting. It makes sense to do something like that.

Orbital Content Delivery Network

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

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.

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.

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.

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.

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/techn...

Edit: Corrected hours to minutes. Brainfart on my part.

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