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Post by PhantomWolf on Jul 2, 2007 19:06:32 GMT -4
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furi
Mars
The Secret is to keep banging those rocks together.
Posts: 260
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Post by furi on Jul 2, 2007 19:12:46 GMT -4
just thinking on radar, don't a lot of the really long range land based Radars rely on magnetic propagation or secondary reflections rather than direct traditional Radar technique, and the really accurate Tracking Mapping and Targeting systems tend to be a bit larger and heavier than your average lunar satellite
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Post by inconceivable on Jul 2, 2007 19:14:39 GMT -4
I am having a hard time with this one. Please walk me through this. RADAR can detect fixed objects. Space based RADARs can even track cars, along with boats and planes. Radar is a radio signal so the return can be amplified. So the RADAR would bounce off the LMs, rovers, etc. and would be received and amplifed but nothing would show.
Bob B. - Radar has far lower resolution than optical instruments. If you can't see it optically, you sure as heck won't see it with radar.
So, if I can see a plane then It won't show up on RADAR?
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Post by Data Cable on Jul 2, 2007 19:23:03 GMT -4
Space based RADARs can even track cars, along with boats and planes. Uhhh, could you provide a source for this? Amplified by what? You seem to be missing a basic concept here. RADAR doesn't only reflect off of metallic objects, it will also be reflected off of the moon. This is what is meant above by "resolution." RADAR simply cannot pick out a relatively tiny detail such as an LM descent stage or an LRV against the background of the lunar surface itself.
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Post by JayUtah on Jul 2, 2007 19:36:44 GMT -4
So the RADAR would bounce off the LMs, rovers, etc. and would be received and amplifed but nothing would show.
Radar would also bounce off the lunar surface immediately surrounding those objects and it would be impossible to distinguish those returns from those of the Apollo hardware.
Apollo spacecraft indeed carried radar to help them rendezvous with each other. That radar can see the spacecraft in space, but not on the ground because it can't distinguish the radar "picture" of the landed spacecraft from the ground around it.
So, if I can see a plane then It won't show up on RADAR?
That's not the idea of resultion. If your eyes can distinguish a P-51 from an F-16 because it can see and recognize the detailed features, radar may still not be able to although it can tell there is a plane there in each case. Radar can't see, for example, the difference in detailed features between many different models of airplane even when the eye could.
The problem of resolution is acute because spotting an airplane or space junk against the return-less void of space doesn't require much resolution. As I said, it's like a piece of confetti against a black background -- you don't have to see very well to recognize it's there. But confetti against a tin-foil background requires very sharp vision. Radar's "vision" -- pound for pound -- isn't as good as optical vision in terms of sharpness.
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Post by PhantomWolf on Jul 2, 2007 19:37:46 GMT -4
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Post by JayUtah on Jul 2, 2007 19:38:41 GMT -4
Amplifying a signal doesn't make it cleaner. It just amplifies the noise along with it. Turning up the brightness on your monitor doesn't correct a fuzzy image.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jul 2, 2007 19:45:35 GMT -4
Bob B. - Radar has far lower resolution than optical instruments. If you can't see it optically, you sure as heck won't see it with radar. So, if I can see a plane then It won't show up on RADAR? Bouncing a radio signal of an isolated object and detecting the return is not the same as resolving an object resting on a surface. To "see" the object on the surface requires a resolution finer than the dimensions of the object. Radio resolution is thousands of times worse than optical resolution (resolution is proportional to the wavelength of the light).
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Post by inconceivable on Jul 2, 2007 19:49:54 GMT -4
Also, the CSM had RADAR to track the LM and the LM had RADAR to track the CSM. Also, they were tracked by the Manned Space Flight Network. While the LM was on the surface of the moon it was tracked by the CSM rendesvous RADAR. So why wouldn't a satellite equipped with RADAR not have the same capabilities today?
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Post by PhantomWolf on Jul 2, 2007 19:50:23 GMT -4
Just to give the scale to Bob's argument here. Visible light has a wavelength in nanometres (10-9). Imaging Radar has a wavelength in millimetres (10-3).
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furi
Mars
The Secret is to keep banging those rocks together.
Posts: 260
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Post by furi on Jul 2, 2007 19:51:11 GMT -4
spotting an Aircraft in the sky is relatively easy with discriminator circuits, as the sky doesn't offer much of a return, clouds smoke rain however can muck it up a bit, which led to the to the production of Chaff (or Window as us Tommies called it) for specifically that reason.
and also why radar systems are a lot more prone to ECM systems than Laser or Optical systems (although a damn good smoke screen is good for doing that too)
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Post by JayUtah on Jul 2, 2007 19:51:24 GMT -4
Space based RADARs can even track cars, along with boats and planes.
No. You may be thinking of synthetic-aperture radar systems. They do not currently track objects, nor can they because of how the synthetic aperture arrangement works. They take a series of correlated radar pictures of stationary targets and then use supercomputers to try to extract additional resolution using signal-processing algorithms. The radar to do this is about the size of a car, and the computer to do the processing is currently about the size of a tennis court and requires as much electricity as a city block.
Obviously the computer wouldn't need to be sent to the Moon, but the radar transceiver would, and that's a huge thing to put in lunar orbit just yet. It would be possible to use SAR to achieve radar resolution needed to see the Apollo landers, but it wouldn't be any easier than trying to achieve the optical resolution necessary. In fact, probably harder.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jul 2, 2007 19:51:35 GMT -4
While the LM was on the surface of the moon it was tracked by the CSM rendesvous RADAR. No it wasn't.
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Post by PhantomWolf on Jul 2, 2007 19:52:27 GMT -4
Also, the CSM had RADAR to track the LM and the LM had RADAR to track the CSM. Also, they were tracked by the Manned Space Flight Network. While the LM was on the surface of the moon it was tracked by the CSM rendesvous RADAR. So why wouldn't a satellite equipped with RADAR not have the same capabilities today? You're still missing the point. Tracking != Resolving. The CSM radar could tell there was a big object there, but that was it. It couldn't have painted a picture of it. In the same way you could detect the LM descent stage on Imaging Radar, but it'd be a dot, you couldn't tell the difference between it and a big rock.
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Post by JayUtah on Jul 2, 2007 19:53:17 GMT -4
While the LM was on the surface of the moon it was tracked by the CSM rendesvous RADAR.
No. Only in flight, and only because there was an active transmission.
So why wouldn't a satellite equipped with RADAR not have the same capabilities today?
Because tracking and imaging are two different things. The LM would be lost in the ground clutter of any radar that we can currently send.
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