tl;dr - Does distance affect bandwidth?
Read this article: http://gizmodo.com/why-itll-take-new-horizons-16-months-to-send-us-this-we-1717769317
... which reads as if the literal distance is part of why it'll take so long to get New Horizon's data. That doesn't seem right.
I get there's latency -- but, in this case, that should just mean it takes forever for New Horizons to get started. Once the stream is started, the distance shouldn't matter. That is, I don't see how the distance affects the bandwidth.
Am i missing something? Does distance affect bandwidth?
http://gizmodo.com/why-itll-take-new-horizons-16-months-to-send-us-this-we-1717769317
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If you are sending acknowledgements, frequently, and the sender needs to receive that ack before continuing, then yes.
ReplyDeleteAlso, the lower the frequency, the less prone to noise and interference, and the farther it can travel. The lower the frequency, the slower the data.
Arnold Cassell That first is more latency, which, yeah. It takes a looong time to get a response and change instructions. Yeah.
ReplyDeleteA better researcher than I -- Dianne Harris -- found this:
https://books.google.com/books?id=oZfpYIUKDrUC&lpg=PA38&ots=xu4Xze8I6y&dq=new%20horizons%20twta&pg=PA38#v=onepage&q=new%20horizons%20twta&f=false
... which in section 6.3 shows a graph of distance from earth and effective bandwidth. Short answer: Yes, ridiculous distance does affect bandwidth. I don't quite understand why -- a result of not studying enough physics, I imagine.
Arnold Cassell It probably has to do with frequency? Can you make anything more of that than I can?
ReplyDeleteSpace is weird!
ReplyDeleteFrequency, a little bit, also HUGE data packets with a LOT of redundancy and error checking, also probably Doppler and relativistic effects.
Again, space is weird.
p.s. 900 bits/s is SUPER SLOW
Its amazing: I managed to pass abstract linear algebra and number theory and have published papers in cog sci. But, i cannot wrap my brain around relativistic effects for more than ... some amount of subjective time? An amount of time that differs based upon your frame of reference?
ReplyDeleteThose things i have the words for, but not the math. So i don't really understand them!
Ad yet, without relativistic corrections, GPS doesn't work.
ReplyDeleteReads to me like it's just a lot of data. Bandwidth is probably narrow for hi res imagery.
ReplyDeleteTodd Sprang No. As New Horizons gets further away, the bandwidth goes down.
ReplyDeleteSignal attenuation?
ReplyDeleteyeah i'm gonna go with signal attenuation https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=deep%20space%20signal%20attenuation
ReplyDeleteIt's all signal. Your transmitted energy spreads as it travels, and your receiving antenna only gets the energy that hits it. Hence less signal more noise. Hence less bits.
ReplyDeleteA simple antenna might transmit a sphere of energy, and the further you get your antenna's percentage of the sphere's surface. I'm sure they use a highly directional antenna, but that just means the energy is a cone.
Sean Leventhal , Todd Sprang and Arnold Cassell What would happen if we had a relay station halfway? I'm thinking a cone expands with the square of distance, so if you half the distance, then you've quartered the loss. And maybe doubled the speed. Yes?
ReplyDeleteProbably better than doubled the speed. There is a square law dropoff in power with distance. It would be expensive of course, and would not help latency.
ReplyDeleteGlad we're both figuring on square of distance. So, this is why star trek you need comm relays everywhere for a message to work.
ReplyDeleteNew Horizons is basically T A L K I N G _ S L O W L Y _ A N D _ C L E A R L Y to make sure what it's sending can be heard back on Earth.
ReplyDeleteCan't remember the formula, but there is a correlation between power, distance and signal capacity in radio transmission (or any transmission for that matter). The biggest factor in this is the inverse square law for distance. New Horizons can't increase its power output, so to ensure the signal is still readable back at Earth it reduces the bandwidth.
yes a repeater should mitigate the problem (it's really no different than networking, just at a much huger scale). only issue is setting that up at jupiter and uranus. :)
ReplyDelete... and none of these distances are in straight lines, and other celestial objects can get in the way (like our own moon, and the Sun for half of the year...) , and the New Horizons has to know when to pause (because of something in the way) and a repeater would have to have the power and navigational capabilities to keep (roughly) between the two endpoints, and...
ReplyDelete... space is hard.
Arnold Cassell So, we tossed New Horizons that way ::points:::
ReplyDeleteWhat if, every few years, we launched comms probes that way ::points::
If we one could listen to the ones in front of tit, then turn around and talk to us, could we keep in contact and have higher bandwidth for a long time?
Or, is this foolish?
Again, space is weird. We don't launch things in straight lines... we have to expend a LOT of energy to break orbit, and then spend a lot of time and energy slingshotting things around heavier objects, like moons and planets.
ReplyDeleteI am completely confident that NASA did the budget analysis and decided this was the cheapest way to get what they wanted.
If money were not an issue, sure, I could see a network of repeating stations in solar orbit, much like the satellites we use around Earth currently.
But following New Horizons as it leaves? EEsh. I mean, maybe, but I don't want to be the lead on the that team. There's no persistent "road" that NH is taking. Best we could do is send some on calculated periodic intercept courses... the math for which is PhD level.
Arnold Cassell Right, NASA is filled with really smart people. I'm spitballing and thinking, not criticizing.
ReplyDeletewhat would be a good position to capture incoming voices? Would we want to get out of the plane of the planets altogether, and head towards solar north?
That I don't know. But I'll wager that trying to sit up there would cost fuel to maintain, and I do know that fuel is heavy and an absolute last resort.
ReplyDeleteThere's also the distance from the solar plane to calculate; the farther "North" you are, the less interference, but the greater the total distance the messages would have to travel.
Plus the solar system itself is constantly in motion... would you be trying to lead the motion of the sun or follow it?
Depends: Does the sun have lagrange points?
ReplyDeleteTo the googles!
ReplyDelete