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Ranging and Pioneer
The position of Pioneer was calculated from Doppler information. Ranging
was not available. Can anyone explain why ranging could not be used? Is this just a limit on available technology, or is there a more fundamental reason? Regards -- Charles Francis substitute charles for NotI to email |
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Ranging and Pioneer
Oh No wrote: The position of Pioneer was calculated from Doppler information. Ranging was not available. Can anyone explain why ranging could not be used? Is this just a limit on available technology, or is there a more fundamental reason? gr-qc/0104064 Spud |
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Ranging and Pioneer
Thus spake Spud
Oh No wrote: The position of Pioneer was calculated from Doppler information. Ranging was not available. Can anyone explain why ranging could not be used? Is this just a limit on available technology, or is there a more fundamental reason? gr-qc/0104064 Many thanks. If I understand Anderson correctly it is merely an engineering constraint. With a (perhaps greatly) amplified signal it should be possible to reduce integration times to achieve correlation so that the signal can be returned without a substantial range delay. Anyway that is the basis on which I am working at the moment. But I am not an engineer, and I was hoping this might be confirmed. My arguments would take quite a different form if this was a fundamental constraint. Regards -- Charles Francis substitute charles for NotI to email |
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Ranging and Pioneer
Oh No wrote:
Thus spake Spud Oh No wrote: The position of Pioneer was calculated from Doppler information. Ranging was not available. Can anyone explain why ranging could not be used? Is this just a limit on available technology, or is there a more fundamental reason? gr-qc/0104064 Many thanks. If I understand Anderson correctly it is merely an engineering constraint. With a (perhaps greatly) amplified signal it should be possible to reduce integration times to achieve correlation so that the signal can be returned without a substantial range delay. Anyway that is the basis on which I am working at the moment. But I am not an engineer, and I was hoping this might be confirmed. My arguments would take quite a different form if this was a fundamental constraint. http://arxiv.org/abs/gr-qc/0205059 Pioneer anomaly http://arXiv.org/abs/gr-qc/0307042 Rationalized Pioneer anomaly http://arXiv.org/abs/gr-qc/9810085 Believable rationalized Pioneer anomaly http://arXiv.org/abs/gr-qc/gr-qc/0310088 Believable Pioneer anomaly updated http://www.arxiv.org/abs/gr-qc/0411020 Pioneer anomaly http://arXiv.org/abs/physics/0502123 Commentary on Pioneer anomaly minutia http://arXiv.org/abs/gr-qc/0506139 http://math.ucr.edu/home/baez/open.questions.html -- Uncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/qz3.pdf |
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Ranging and Pioneer
"Oh No" wrote in message ... Thus spake Spud ... gr-qc/0104064 Many thanks. If I understand Anderson correctly it is merely an engineering constraint. With a (perhaps greatly) amplified signal it should be possible to reduce integration times to achieve correlation so that the signal can be returned without a substantial range delay. The problem was more fundamental. Reading between the lines, and from some personal correspondence, the rate of change of the carrier frequency was I believe limited in choice by the design of the exciter or correlator equipment. The narrow bandwidth required to get an acceptable SNR at the craft meant the minimum sweep rate was too fast and the craft lost lock on the uplink. Increased gain at the craft wouldn't help, only more transmit power, but that was in the 100's of kW already and being routed through their largest (70m) dishes. Anyway that is the basis on which I am working at the moment. But I am not an engineer, and I was hoping this might be confirmed. My arguments would take quite a different form if this was a fundamental constraint. It was purely an equipment limitation, possibly exacerbated by radiation damage during the Jupiter flyby though that is my speculation. BTW, I am a digital and systems engineer in a company working significantly in HF comms. George |
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Ranging and Pioneer
Thus spake George Dishman
"Oh No" wrote in message k... Thus spake Spud ... gr-qc/0104064 Many thanks. If I understand Anderson correctly it is merely an engineering constraint. With a (perhaps greatly) amplified signal it should be possible to reduce integration times to achieve correlation so that the signal can be returned without a substantial range delay. The problem was more fundamental. Reading between the lines, and from some personal correspondence, the rate of change of the carrier frequency was I believe limited in choice by the design of the exciter or correlator equipment. The narrow bandwidth required to get an acceptable SNR at the craft meant the minimum sweep rate was too fast and the craft lost lock on the uplink. Increased gain at the craft wouldn't help, only more transmit power, but that was in the 100's of kW already and being routed through their largest (70m) dishes. Considering that on Earth we pick up a signal of 8kW from Pioneer, it doesn't sound to me as though the amplitude of the signal sent to Pioneer was really too low. Loss of lock on frequency modulation sounds interesting. I might be helpful to understand this more precisely. Can you give more detail on how the signal is encoded. Anyway that is the basis on which I am working at the moment. But I am not an engineer, and I was hoping this might be confirmed. My arguments would take quite a different form if this was a fundamental constraint. It was purely an equipment limitation, possibly exacerbated by radiation damage during the Jupiter flyby though that is my speculation. I am slightly sceptical about the equipment failure theory, because it would mean the equipment from both pioneers failed in the same way at much the same place. I would also be a little surprised if radiation from Jupiter is energetic enough to cause such damage. After all other space craft have flown close to the sun and survived. Equipment limitation seems probable. It would be more satisfying if one could identify a cause for the limitation, since clearly it was not expected from the design parameters. Your response has caused me to wonder if there is an unmodeled effect in the uplink which might contribute to loss of lock. Clearly there is a Doppler variation in the signal received by Pioneer due to orbital motion of the Earth of 30,000m/s which must have been taken into account. But how narrow is the bandwidth, and how accurately does this need to be predicted? Could an unmodelled effect as small as _+-2m/s (varying annually) contribute to loss of lock? BTW, I am a digital and systems engineer in a company working significantly in HF comms. It's clear you know a lot about this kind of thing, and your input is much appreciated. Regards -- Charles Francis substitute charles for NotI to email |
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Ranging and Pioneer
In article .com, Spud writes:
Oh No wrote: The position of Pioneer was calculated from Doppler information. Ranging was not available. Can anyone explain why ranging could not be used? Is this just a limit on available technology, or is there a more fundamental reason? gr-qc/0104064 Spud Just wanted to ask something about this. In order to measure Doppler shift, you need to measure frequency accurately right? And in order to measure frequency accurately you have to have an accurate clock. I founded an IRC network (Newnet Internet Relay Chat). We had a problem with servers being out of sync, clocks didn't agree. Part of our network was using national institute of standards and technologies NIST time server, others were using a time server at Nasa. The root of the problem turned out that NASA's time server was about five seconds off of NIST's. Now I thought NIST was supposed to be THE gold standard, which would mean that NASA's clock is off. And if NASA's clock isn't accurate, then by extension neither is the precise measure of frequency and thus Doppler shift. So I can't help but wonder while we're re-writing the laws of cosmology on the basis of the unexpected Doppler shift of Pioneer I and II, if we might be really doing so on the basis of an incorrectly calibrated clock at NASA. -- -_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_- Eskimo North Linux Friendly Internet Access, Shell Accounts, and Hosting. Knowledgable human assistance, not telephone trees or script readers. See our web site: http://www.eskimo.com/ (206) 812-0051 or (800) 246-6874. |
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Ranging and Pioneer
In article , Nanook wrote:
Part of our network was using national institute of standards and technologies NIST time server, others were using a time server at Nasa. The root of the problem turned out that NASA's time server was about five seconds off of NIST's. Now I thought NIST was supposed to be THE gold standard, which would mean that NASA's clock is off. And if NASA's clock isn't accurate, then by extension neither is the precise measure of frequency and thus Doppler shift. I was under the impression that the "gold standard" for time is a collaborative thing between a number of national and international time services, not tied to any one machine or even site. A five *second* difference between clocks that are meant to be accurate to microseconds per year/ millennium (I can't remember which) I don't think is credible. More credible would be that your network topology either had some sort of horrible delay-inducing asymmetric loop in it to one of the time sources, or that you were asking the wrong questions of one of the machines. E.g., getting time according to UTC from one machine, but something corrected to local noon from the other (that would give time differences of up to several minutes a day, if I remember my horology correctly, but variable at different times of the year). -- Aidan Karley, FGS Aberdeen, Scotland Written at Tue, 11 Jul 2006 03:13 +0100, but posted later. |
#9
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Ranging and Pioneer
In article , Nanook
wrote: The root of the problem turned out that NASA's time server was about five seconds off of NIST's. Now I thought NIST was supposed to be THE gold standard, which would mean that NASA's clock is off. And if NASA's clock isn't accurate, then by extension neither is the precise measure of frequency and thus Doppler shift. NASA is a big organization. They don't have 'a clock'. Are the timeservers you were using supposed to be public timeservers? What stratum are they? If you are setting up a large IRC network, you shouldn't be hitting high level time servers. Get one of your machines to be the only one to contact a good server (or some other source like a cheap GPS clock) and have others contact that machine. Anyway, when I got to my current job, I pointed my NTP client at time.where.I.work , which worked as an NTP server. When I noticed that the time on my computer was way off, I tracked down the owner of that machine. He didn't know his computer's NTP server port was active, he just had a desktop computer named 'time' and a laptop named 'space'. So anyway, it is unlikely that the Pioneer anomaly is due to an inaccurate NTP server. -- David M. Palmer (formerly @clark.net, @ematic.com) |
#10
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Ranging and Pioneer
In article , David M. Palmer
wrote: So anyway, it is unlikely that the Pioneer anomaly is due to an inaccurate NTP server. Doesn't the Pioneer anomaly predate the development of NTP anyway? -- Aidan Karley, FGS Aberdeen, Scotland Written at Wed, 12 Jul 2006 09:30 +0100, but posted later. |
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