I love this statement (from the Preventing Busy Signals page): "The Deep Space Network (DSN) communicates with nearly all spacecraft flying throughout our solar system."
Mars to Earth at an average of 29 kbits/s
41–50 of 88 posts
Re: Mars to Earth at an average of 29 kbits/s
#42So, it's basically like dial-up back in the day.
Re: Mars to Earth at an average of 29 kbits/s
#43I'm wondering how do they prevent non-NASA entities from sending commands to the rover - are they using some sort of cryptographic signatures when sending the commands?
I'm not sure about Curiosity in particular, but I work in the space industry and can say that commands are normally timestamped and encrypted. The encryption stops someone from commanding the spacecraft, the timestamp stops someone from recording a transmission and resending it later.
So there’s basically a real Goldeneye key. And you could really use a Goldeneye key duplicator before leaving Severneya!
Re: Mars to Earth at an average of 29 kbits/s
#44It's awesome that they've been involving the public so much in the details of how the rover mission really works. I'd actually been wondering about this exact question, since it seems to be one of the limiting factors for the quality of images and such. From a physics standpoint, sending data is clearly a lot more complicated than I'd previously assumed.
Yes, the clue is in the comparison to 'home modems'. The technology was finalised 2004, which means design around 2000 or so? I'm impressed with the reception technology that allows 'direct to home' communication at all given the power levels available.
Absolutely, this seems like one of the most amazing in a long string of incredible things. There’s only enough energy to power two 60w light bulbs, and yet it can transmit all the way to earth while also powering the computer running the thing.
Re: Mars to Earth at an average of 29 kbits/s
#45What's the latency of that data connection?
It varies. As others have said, it's currently just under 14 minutes.
But it can be as low as 3 minutes or as high as 21 minutes, depending on the distance from Earth to Mars. Which of course varies as they orbit the sun.
Re: Mars to Earth at an average of 29 kbits/s
#46So one wonders at what point you uplink to a satellite with ejectable flash drives which, when full, detach, make a gravity sling shot pass to leave orbit and then burn for a rendezvous with earth 9 months later. If I did the math right a 1TB drive returned from Mars in 9 months would be an effective bandwidth of 470K bits per second (or 47K bytes per second)
I see one huge issue: if you lose the flash drive, you lose ALL of the data you collected. At least you a assured to get part of the data when it is broadcast.
Re: Mars to Earth at an average of 29 kbits/s
#47So one wonders at what point you uplink to a satellite with ejectable flash drives which, when full, detach, make a gravity sling shot pass to leave orbit and then burn for a rendezvous with earth 9 months later. If I did the math right a 1TB drive returned from Mars in 9 months would be an effective bandwidth of 470K bits per second (or 47K bytes per second)
470K bits == 58.75K bytes (assuming 8-bit bytes)
Typically bytes are coded 8N1 (or 1 start bit, one stop bit, and 8 data bits) so 10 baud gets you 1 byte. Hence the nominal divide by 10 (this is 8b/10b encoding)
But in a pedantic sort of way, the computation should add extra bits for ECC since the drive has ECC bits already embedded in it, so a 1TB drive probably has more than 10 Tbits it is probably closer to 15 - 20 terabits.
Re: Mars to Earth at an average of 29 kbits/s
#48This may be a silly question, but I don't understand why the bandwidth is so low. I understand the latency will be high, since you're limited by the speed of light; but wouldn't you be able to get more bandwidth just by increasing the spectrum of light used, as well as the baud of the transmitter/receiver?
Re: Mars to Earth at an average of 29 kbits/s
#49So one wonders at what point you uplink to a satellite with ejectable flash drives which, when full, detach, make a gravity sling shot pass to leave orbit and then burn for a rendezvous with earth 9 months later. If I did the math right a 1TB drive returned from Mars in 9 months would be an effective bandwidth of 470K bits per second (or 47K bytes per second)
While we are dreaming, it would be better to have said flash drive picked up by a spacestation, refueled in orbit, and shot back to Mars. Hmm. If storage continues to improve as fast as it has been, once the space infrastructure is there, this might be cost effective. We have a lot of data to send. In particular, we are going to need to have a local cache of the internet on Mars. At best, the average minimum latency…
We need to find some hive-mind aliens and dissect them in order to develop philotic protocols for instant transmission.
0 latency on funny cat videos from Uranus.
Re: Mars to Earth at an average of 29 kbits/s
#50Does anyone know more about the architecture of this space radio network? For example does it use tcp/ip on top over radio or is it packet switched as with amateur packet radio?
Here's the protocol stacks http://public.ccsds.org/publications/default.aspx , here's source code for some higher layers https://ion.ocp.ohiou.edu/