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Message: <blockquote data-quote="Ovinomancer" data-source="post: 8260198" data-attributes="member: 16814">Sigh.  We can see the Voyager probe because we know exactly where to look and exactly what to look for.  It's not because it's easy (or even very hard) to find, it's because it's impossible to find without the knowledge of precisely where to look.However, do not mind me, I'm only an electrical engineer specializing in communication systems.Wait, you claim that a great example of good science in the Expanse (you are correct here) should be discounted because it's just a TV show, and then put out a link to a site which is dedicated to and often cited novels, tv shows, and other fiction works as it's raison d'etre?   I mean, really?Now, I  happen to like that site, but it does some odd things, namely try to discuss different topics from different points of view or assumption sets without making it clear.  For example, it notes that active sensors degrade at 1/r^4, which is the perfect case if I can send my signal out in a single line (no spread) and the target reflects perfectly.  I, above, said 1/r^3, and that was for passive detection of a spherically radiating target, and this is because the energy density is being spread into that sphere, and so loses power accordingly.  With an active detector, you have more power loss than 1/r^2 in one direction because the signal has a spread.  We use the 1/r^2 and 1/r^4 terrestrially because it's a pretty good approximation for the very limited distances here, but, in space, distances are huge and this spreading factor quickly takes on importance.  Still, in the beginning of the article, they call this out as important, but then hide the issue in the later section under passive sensors by imagining a sufficiently powerful computer that will crunch the enormous data (we can't even scan much of the sky at once now, like a degree of arc or less at a time, and it takes weeks and we miss lots and lots of stuff!).  This pea, hidden under the mattress, is often overlooked -- it's a monumental problem that was swept under the rug in a single sentence!So, then, how do we detect Voyager?  Well, we know where to look, and Voyager is sending us a signal, using an antenna capable of a tight beam transmission, precisely aimed, so it's suffering as little spread loss as possible.  Even then, that beam is wider than the Earth when it arrives here, much wider.  But, it drags that loss down much closer to 1/r^2 rather than 1/r^3, and that makes a huge difference.  In other words, we can detect Voyager only because we know where to look, and then we only see it when it's shining it's very bright flashlight at us, the one with all the mirrors that focus all the light in one direction.</blockquote>

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