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If you can receive and re-transmit a data packet over the airwaves quickly enough, you can store data by tossing data packets at a reflective object (say, the Moon). The packet will take a couple of seconds to make the round trip, in which time many more packets could have been sent. The reflected
packets are re-transmitted as soon as they're received.
You can keep many more packets in the air than you need to store locally, in much the same way that a juggler can keep more balls (bowling pins, chainsaws) in the air than he has hands. Each packet can be accessed once on each round trip. Reads are fast. Access time is slow, but hey, it's free.
Satellite Internet providers
http://www.satsig.net/
This isn't quite Earth-to-Moon - but gives us ideas on bandwidth. [Jinbish, May 08 2006, last modified May 09 2006]
[link]
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I’m sorry, but we lost all your data in the clouds. |
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Make sure you stick a post-it note on the plug asking the night-watchman not to use the socket for his portable tv. |
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Only problem is that radio bandwidth is finite and generally already used for applications... Assuming we can find some available bandwidth for uplink and downlink (symmetrical bands, obvioulsy), we then have to consider the time the signal will take to travel to the moon and back (2 x 400000km approx./3 x 10^8 = 8/3 seconds) then the storage is equal to the effective bit-rate (Mbps) x 8/3... |
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Halfbaked to the max. (+) |
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------------------\
+<---------------/ |
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//juggler can keep more ... chainsaws in the air than he has hands.//
... Or audience members/assistants in the vicinity. |
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Byte per metre, by my back-of-envelope, would be the overall bit-rate used over the bandwidth - say 15Mbps for a DVB signal times 8/3 then divided by 8*10^8.... so that's about 5*10^-2 or half a bit per kilometre, or 1 byte every 16km. |
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[zen tom] Periscopes as a storage
medium? |
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[miasere] - I don't think so -
//You can keep many more packets in the air than you need to store locally//
That's the untruth right there, at least with radio waves... but what if we used carrier pigeons! We could small, handwritten notes or maybe microfilm to the legs of an army of carrier pigeons and send them to their desitination. Once at the destination a new team could carry the information back. |
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That's not in the spirit of the idea, but it would have a greater storage capacity at approximately the same as, er... a load of microfilm. |
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DVB - Digital Video Broadcast, uses MPEG 2 transport and associated coding (OFDM modulation scheme - highest bit rate we got, I think, but requires tight synchronisation). Bit rates can be as high as 32Mbps, but the signal isn't as robust. It's used for terrestrial and satellite TV. It only made sense to suggest when talking about the Earth-to-Moon idea. We can use some other modulation scheme & EM bandwidth. I just don't have any numebrs, or idea, to hand. Besides, my link shows that renatable Internet style bandwidth via satellite ain't cheap! |
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We'll have to go further into halfbaked-ness to come up with a transmission medium/scheme... If we are bouncing off stuff from Earth then we need to use at least one device in geostationary orbits. |
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Well, you could use masses of forward error correction and immediately delete what you've just sent; or perhaps use fountain codes... but you'd no doubt get the message back before you completely sent the original message... So it still doesn't make any more sense - but that's why I like it! |
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cute in description, but you are basically describing any large networked system. The routers and firewalls on the net already perform this juggling act |
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[zen]: You've got it. Fountain codes basically represent the sent message spread over a whole load of transmitted packets. There isn't a need for re-transmissions or acknowledgement packets. You just keep sending the packets out and sooner or later you'll get a packet with the info you missed.... like someone standing with a cup next to a fountain. If you miss one drop you can just wait for the next 5. |
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However, the problem with fountain codes is that the sender needs to estimate when to stop sending out packets! So the point of reliability that [phlish] raises is still valid. The idea is flawed and won't work - but I like it's halfbakedness so much I'll try and argue to the contrary. |
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Would it be possible to do something like this with a superconducting data cable formed into a loop? |
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I've got jotted notes for the same idea from a few years ago. I never got a chance to post it here :-/ |
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Anyway, to compat the obvious dangers (and low storage capacity), effectively a RAID would be needed. Multiple reflectors, some duplicating data and others adding storage. Relay around a series of satalites in synchronous orbit to increase the capacity. |
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Problem is, it just isn't worth it. How much does it cost to launch the reflectors into place, and how much does it cost to continually clean and re-transmit the reflected signals, compared to the ammount of practicle storage space? Take into account the inherent instability, and you got a thoroughly half-baked idea. |
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I like this idea. [zen_tom]'s spin reminds me of an older idea posted here in which by looking very close to a black hole, one can look at Earth because the outbound light from earth wraps clear around the hole. |
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There must be something smooth and reflective in space. Maybe some ice planet? It is just a matter of finding it. The farther away the better. |
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If nothing reflective can be found, another option would be to use high velocity charged particles as the medium. I am not confiednt they reflect very well, so they would have to impact something which then emitted em that we could detect. |
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A better idea would be having the light orbit a tiny black hole in a slightly unstable orbit that would decay on certain intervals, and immediatley be reflected back into its orbit after being read. *smiles |
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