3 ms·

Larger than the power issue, it seems like latency would be a big challenge that would need to be solved to achieve Mars <=> Earth communication. There's alrea

Larger than the power issue, it seems like latency would be a big challenge that would need to be solved to achieve Mars <=> Earth communication. There's already a very high latency (about a day) with this proof-of-concept while waiting for the ISS to pass over the same station in California again. The latency would be significantly longer than a day for two single transceivers, one on Earth/ISS, and one on Mars, to align again once they've broken alignment—Earth-Mars oppositions happen about every two years. A solution to both problems would be more transceivers: the Earth to ISS station problem could be addressed by setting up more transceivers on earth underneath the ISS's ground tracks, enabling more frequent transmissions. The Mars solution would probably require a lot more cost/effort/creativity, but a mesh of transceivers, all in concentric orbit around the Sun between the Earth and Mars, should be able to relay data between the two points with a best-case 4- to 30-minute latency (bounded by speed of light, distance varies between Mars and Earth on a two-year period)

mnw21cam 12y ago
This is mentioned in the comments in the TCP implementation of the Linux kernel: 373 * ... Note that 120 sec is 374 * defined in the protocol as the maximum possible RTT. I guess 375 * we'll have to use something other than TCP to talk to the 376 * University of Mars. http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/net/ipv4/tcp_timer.c http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/n...
TheCraiggers 12y ago
Why would you need to wait for opposition? As long as you have direct line of sight to Mars, that is good enough. Granted, the latency is only going to increase when not in opposition, but they already have ways to deal with that, such as IPN. [1] Conjunction, of course, would be a much tougher feat without some sort of relay system. I'm sure that wouldn't be insurmountable though, and I think they built that into IPN as well, just like how the internet can route around problem areas. [1] http://en.wikipedia.org/wiki/Interplanetary_Internet http://en.wikipedia.org/wiki/Interplanetary_Internet

mnw21cam 12y ago

This is mentioned in the comments in the TCP implementation of the Linux kernel: 373 * ... Note that 120 sec is 374 * defined in the protocol as the maximum possible RTT. I guess 375 * we'll have to use something other than TCP to talk to the 376 * University of Mars. http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/net/ipv4/tcp_timer.c http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/n...

TheCraiggers 12y ago

Why would you need to wait for opposition? As long as you have direct line of sight to Mars, that is good enough. Granted, the latency is only going to increase when not in opposition, but they already have ways to deal with that, such as IPN. [1] Conjunction, of course, would be a much tougher feat without some sort of relay system. I'm sure that wouldn't be insurmountable though, and I think they built that into IPN as well, just like how the internet can route around problem areas. [1] http://en.wikipedia.org/wiki/Interplanetary_Internet http://en.wikipedia.org/wiki/Interplanetary_Internet