Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jul 2, 2007 19:56:04 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? Also note that this tracking involved active radar techniques, not passive (I hope this is the right terminology). They didn't just bounce a radar signal off the vehicles. A signal was transmitted and detected by the target, and then the target transmitted a return signal. EDIT: Although my description of how the radar was used is correct, my use of terminology (active vs. passive) is apparantly inaccurate. Please see JayUtah's post #86 for a clarification.
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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 21:02:17 GMT -4
have just had a look at some of the capabilities of some nice mm and microwave radar, Acquisition and terminal stage radar, (both specialised systems) a lot of these seem to be able to pick up a vehicle at around 30 km, but only if it is moving, which would indicate they are using frame comparison (for want of a better word), in terminal radar guidance, a lot of systems work at very close range or have the systems themselves moving at speed and can use the same sort of reference systems for stationary objects, they also tend to have systems for preloading of radar return signatures into the discriminators increasing target locking. these differ completely in mapping, long range tracking, and geographic systems. (have a look at Fylingdales in Yorkshire, Ruddy Great Pyramid sat top'a'moor) It's fun trying to find Radar capabilities of SAMPSON or Fylingdales or Ground visualisation satellites are without running into small matters of MoD security
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Post by nomuse on Jul 2, 2007 21:14:15 GMT -4
Seems to me detecting doppler shift wouldn't be hard. So a moving object could reveal itself at close to the limits of resolution.
Doesn't help in imaging old lunar hardware, though. Particularly as tracking something needs only a point source...getting an image that looked like something more than a grey lump would require a heck of a lot more resolution.
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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 21:21:22 GMT -4
2 or 3 satellites setting up a good series of interfrometry sweeps.
or a couple of reference Laser beams, and a splitter on a second satellite and a giant orbital photographic plate to produce a hologram. I think I am starting to reach the expenditure point where we may as well wait for China to go there.
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Post by frenat on Jul 3, 2007 6:06:29 GMT -4
Seems to me detecting doppler shift wouldn't be hard. So a moving object could reveal itself at close to the limits of resolution. Doesn't help in imaging old lunar hardware, though. Particularly as tracking something needs only a point source...getting an image that looked like something more than a grey lump would require a heck of a lot more resolution. For tracking moving objects on the ground, yes they use a doppler shift to distinguish them from the stationary ground. Where the resolution comes into play then is in the concept of a resolution cell. If the resolution is say 10 meters and the resolution cell is 10 meters squared, then there could be multiple objects moving in that 10 meters squared area but they would all show up as one object on the radar return. There still is a resolution though as an object has to be of a certain size to reflect enough radar to be detectable.And of course as mentioned, for non moving objects they use a different concept and would not be able to see the objects on the moon. Even if we had some moving hardware up there now, the resolution is still not great enough to see anything with radar from the Earth. To try to make everything above clearer. An object can be picked up on radar if it is big enough to reflect enough radar back to be picked up, different enough from the surrounding area to be picked out, and it helps if it is moving as the doppler shift can be used to help pick it out as well.
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Post by Fnord Fred on Jul 3, 2007 7:31:02 GMT -4
Just as a matter of curiosity, would there be any value in sending a probe to the moon with the resolution to see the Apollo artifacts, besides seeing the Apollo artifacts? Would this be of use in planning future missions at all?
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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 3, 2007 8:21:43 GMT -4
outside of construction material longevity in Lunar conditions, I doubt it, I would expect that sending probes to other previously un probed sites would be the main effort. or if an anomoly was found at a site and further experimetation/data collection is required.
I doubt many places would be revisited unless a Serious reduction in costs/method could be found
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jul 3, 2007 8:32:41 GMT -4
Just as a matter of curiosity, would there be any value in sending a probe to the moon with the resolution to see the Apollo artifacts, besides seeing the Apollo artifacts? Would this be of use in planning future missions at all? This is exactly the purpose for Lunar Reconnaissance Orbiter. LRO is being sent to the Moon to perform landing site reconnaissance for future manned missions. The mission of LRO requires high resolution photography, it therefore offers the unique opportunity to put high resolution optics on a lunar satellite for a useful purpose other than just imaging the Apollo artifacts. The fortunate side affect of this it that it can image the artifacts. The mission of past lunar satellites was to perform mapping at larger scales, thus lower-resolution wider-field cameras were preferable. No space agency is silly enough to waste the money putting a camera on a satellite capable of imaging the Apollo artifacts unless that camera can also be used as part of the primary mission. LRO is the first opportunity to do both.
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Post by inconceivable on Jul 3, 2007 18:12:17 GMT -4
If you go to www.friends-partners.org/oldfriends/mwade/craft/lmdlsion.htm scroll down to Consequences of eliminating the Apollo CSM rendezvous radar it clearly states the CSM radar would be tracking the LEM while on the surface of the moon in order to update the launch conditions. So it is not just a clear "No" for an answer.
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Post by JayUtah on Jul 3, 2007 18:27:53 GMT -4
As was already said, those were transponsive operations. In the original design the LM was to emit transponder signals received by the CSM rendezvous radar. In the final design, a rendezvous radar on the LM received transponder signals from the CSM. Active radar was not used in this way; the target was an emitter, not merely a reflector.
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Post by LunarOrbit on Jul 3, 2007 22:34:40 GMT -4
As was already said, those were transponsive operations. In the original design the LM was to emit transponder signals received by the CSM rendezvous radar. In the final design, a rendezvous radar on the LM received transponder signals from the CSM. Active radar was not used in this way; the target was an emitter, not merely a reflector. So active radar is like playing "Marco Polo". The CSM yells "Marco!" and the LM responds "Polo!". Passive radar would be like if you yelled "Marco!" and had to listen for the echo bouncing off the person in the swimming pool in order to find them... which would make the game much more difficult (unless you're a dolphin).
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Post by JayUtah on Jul 3, 2007 23:13:58 GMT -4
Radar technology can operate in several modes.
Trasponsive radar sends out signals that are received and recognized by equipment on prospective targets that in turn transmits a formatted signal back to the transceiver. This was the mode in which Apollo rendezvous radar nominally operated. Early Apollo missions tested the mechanism with ground based equipment and later with LM flight equipment.
Active radar sends out signals that reflect off the target body and are received and interpreted by the transceiver. Radar altimetry works this way, as does air defense search and fire-control radar. Stealth technology is based on scattering or absorbing incident radar energy rather than reflecting it back in the direction of the transceiver. During the later stages of rendezvous, Apollo radar could operate in this mode. The radar reflectivity of the Apollo spacecraft was measured and calibrated during early Apollo missions.
It is this mode that would have to be used to image Apollo landing sites in the radar wavelengths, and extracting a usable image at higher resolution than naturally occurs requires computationally combining elements of some form of synthetic aperture, either from precisely-timed radar images from the same transceiver or coordinated images from two precisely-spaced transceivers. Currently the equipment to do this is not being contemplated for any lunar mission as such resolution is not needed at present and the equipment is bulky. This mode was not contemplated for or used to track landed Apollo spacecraft.
Two passive modes exist. The first presumes the target is an emitter; the receiver applies signal-processing procedures to localize and range the received emission. Instrument landing systems, radio navigation, and anti-radiation pre-emption munitions all use these principles in different ways. This is the general method used by MSFN tracking stations to assist Apollo navigation. Ground stations successfully correlated their measurements derived from passive signal processing to commanded RCS maneuvers aboard the spacecraft.
The second uses ambient radio-frequency illumination (e.g., broadcast television signals). Targets reflect ambient radio signals and can, in some cases, be visible against relative quiescent backgrounds. This mode is not especially effective and was not used for Apollo. Its primary use is covert radar detection.
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Post by Ginnie on Jul 3, 2007 23:50:08 GMT -4
Nomuse, I think if you spent 20 minutes a day practicing, you would develop callouses in about a month, from my experience.
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Post by gwiz on Jul 4, 2007 5:10:06 GMT -4
If you're familar with air traffic control techniques, it's the difference between primary and secondary radar. Primary radar bounces an echo off the target aircraft, secondary radar gets a response from the target's transponder. Apart from giving a stronger return, the latter has the advantage that the transponder can add data to the returned signal, for example identifying the aircraft and giving the onboard altimeter reading.
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Post by 3onthetree on Jul 5, 2007 23:57:42 GMT -4
I see a lot of reasons here as to why it's so difficult to provide conclusive proof of the Apollo landing sites. It all reminds me of that Kennedy thing, not because it's easy but because it's something or rather. I reckon if they can land safely multiple times, get out and hop around, get back in and choof off forty years ago without so much as a bad bag of Tang. Surely they can take some pictures now.
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