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NASA Laser Communication System Sets Record with Transmissions to and from Moon

nasa.gov

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Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#51

Post by trentmb »

pilom wrote: post #46
peeters wrote: post #12

The article cites 622 Mbps down, 20 Mbps error-free up. Is the implication that the 622 Mbps down is before error correction? Either way, it's pretty incredible. Even if the 622 Mbps down isn't completely error free, but maybe 99%, you just need to use a video compression algorithm that is error tolerant.

Why is it easier to transmit from the moon to earth? Here we have more power and larger/better/faster/more tuned lasers than the space vehicle does. Seems like getting earth's transmit rate way up would be relatively easy while getting the vehicle's transmit rate up would be really really hard.

More, fancier equipment on Earth to receive and perform signal analysis?

It's easier to get a new sensor online on Earth than on the moon.

Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#52

Post by toomuchtodo »

sslayer wrote: post #27
toomuchtodo wrote: post #14

Earlier quoted context omitted.

Or we figure out how to use quantum entanglement or gravity as information transfer mechanisms.

Spooky TCP

Someone get Vint Cerf on the line; this will make a fine RFC.

Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#53

Post by aggie »

dghughes wrote: post #44

I remember reading on reddit or maybe it was here on HN that a laser is not a thing it's a method i.e. LASER, we use LASER not a laser.

Language evolves. Unless you're writing a technical document it's usually best to go with what is commonly used and understood.

Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#54

Post by tobylane »

pilom wrote: post #46
peeters wrote: post #12

The article cites 622 Mbps down, 20 Mbps error-free up. Is the implication that the 622 Mbps down is before error correction? Either way, it's pretty incredible. Even if the 622 Mbps down isn't completely error free, but maybe 99%, you just need to use a video compression algorithm that is error tolerant.

Why is it easier to transmit from the moon to earth? Here we have more power and larger/better/faster/more tuned lasers than the space vehicle does. Seems like getting earth's transmit rate way up would be relatively easy while getting the vehicle's transmit rate up would be really really hard.

Possibly it is due to the much wider dishes here. You can speak quietly to someone using a gramophone-like hearing aid.

Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#55

Post by jewel »

knowaveragejoe wrote: post #45
VLM wrote: post #43

Earlier quoted context omitted.

I'm annoyed that gaming is defined solely as multi-player FPS twitch games. Astronauts / colonists into chess, go, poker, real role playing games, pretty much anything that happens in a casino, single player of any sort, wouldn't really notice.

Besides, the speeds mentioned here would be more than enough for multi-player twitch FPS too.

A game like an FPS doesn't need much speed (they can work with modem-level bitrate). They instead depend on having low latency, or ping time. Since the moon is so far away, it takes a signal 1.3 seconds to travel to or from it.

Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#56

Post by jpmattia »

s800 wrote: post #42

622mbps is interesting. Same as OC-12c... Something COTS?

> Something COTS?

Probably outside of the transmission/receiver. Choosing a conventional speed allows them to use plenty of off-the-shelf electronics (FEC chips, etc) and then focus on the transmission.

Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#57

Post by rel »

paulgerr wrote: post #5
erid wrote: post #4

The latency must be huge though.

2.6 second round trip for light, so pretty huge ping times.

I worked at NASA (AMES) on a project to put small mobile robots on the moon. Our biggest goal was to create a tele-operated mode where from earth we could actively roam around the moon. The hardest part was that factoring in a 4 second delay from our commands to the network stacks to the rover on the moon, and then that video from the moon back to our computers and then creating good judgement. A 4 second delay seems insignificant but is in fact detrimental to intuitive controlling.

Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#58

Post by chrischen »

swamp40 wrote: post #38
danbruc wrote: post #24

Earlier quoted context omitted.

Gravity propagates at the speed of light, too.

I think that's a debatable topic. Some say it is just a pure geometric effect of curved space (and thus instantaneous), not a force of nature that propagates.

Then we can tug on gravity to send signals instantaneously!

Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#59

Post by stonemetal »

rodh wrote: post #15
erid wrote: post #4

The latency must be huge though.

I'd imagine TCP, as a protocol starts to fall over with moon-to-earth latencies. Or would it? Perhaps simply increasing the retransmission timer would give us interplanetary internet. I wonder.

TCP uses RTT time to try to guess network congestion. Having worked on software that almost always had satellite hops, it sucks on long links. Primarily what you notice is that you get limited bandwidth because the TCP stack is throttling to prevent congestion. Not sure what RTT is to the moon and back but you would want to use something like TCP Hybla that does network congestion control a different way.

http://en.wikipedia.org/wiki/TCP_congestion-avoidance_algori...

Re: NASA Laser Communication System Sets Record with Transmissions to and from Moon

#60

Post by [deleted] »

pilom wrote: post #46
peeters wrote: post #12

The article cites 622 Mbps down, 20 Mbps error-free up. Is the implication that the 622 Mbps down is before error correction? Either way, it's pretty incredible. Even if the 622 Mbps down isn't completely error free, but maybe 99%, you just need to use a video compression algorithm that is error tolerant.

Why is it easier to transmit from the moon to earth? Here we have more power and larger/better/faster/more tuned lasers than the space vehicle does. Seems like getting earth's transmit rate way up would be relatively easy while getting the vehicle's transmit rate up would be really really hard.

[deleted]
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