Bjarne Posted January 30, 2014 Share Posted January 30, 2014 How was the speed anomalies of the space probes NEAR, GALILEO, ROSETTA etc. measured I often hear that Doppler Effect was used. But how does that work ? Once I hear a atomic clock was ion board the Pioneer 10 and 11 space probes. A signal was send from earth and to the pioneer probes, - asking what time it is (on board) , the atomic clock on board replied, - and the signal was turn back to Earth with that information. Now it was easy to calculate the distance based on the time it took the signal to return. But this has (so far I understand) nothing with Doppler Effect measurement to do. What is this time calculation technic called ? So fare I understand Doppler it is to measure the change of wavelength of a certain frequency that is send from the space probe to the Earth - Correct ? And this doesn't involve time measurement of any kind ? Was different technique used for measuring the Space Probes anomalies ? ( I read somewhere that only Doppler was used when discovering the flyby anomalies ) Link to comment Share on other sites More sharing options...
swansont Posted January 30, 2014 Share Posted January 30, 2014 Once I hear a atomic clock was ion board the Pioneer 10 and 11 space probes. A signal was send from earth and to the pioneer probes, - asking what time it is (on board) , the atomic clock on board replied, … Perhaps you could investigate and find out if this is actually what they did. I can't find any mention of an atomic clock on board. Link to comment Share on other sites More sharing options...
Bjarne Posted January 30, 2014 Author Share Posted January 30, 2014 Perhaps you could investigate and find out if this is actually what they did. I can't find any mention of an atomic clock on board. I hear it many years ago in the a science hour in the radio. But I think this technic only was used in the space probes travellng to the edge of the solar system and longer New Question.. Some places at the internet I have read the flyby anomalies are of the of order 10e-4m/s^2 Other places that the order is the same as the order of the pioneer anomaly, - 10000 times smaller. So what is correct Link to comment Share on other sites More sharing options...
swansont Posted January 30, 2014 Share Posted January 30, 2014 I hear it many years ago in the a science hour in the radio. But I think this technic only was used in the space probes travellng to the edge of the solar system and longer New Question.. Some places at the internet I have read the flyby anomalies are of the of order 10e-4m/s^2 Other places that the order is the same as the order of the pioneer anomaly, - 10000 times smaller. So what is correct Saying you heard it, or read about it on the internet, is not a sufficient citation. It often doesn't provide enough information to answer a question. One possibility is you misread something or maybe a site is wrong, but there's no way to know this if I don't have access to the same information. For the original question: Doppler shift of a radio signal gives you a velocity, since you know what frequency was transmitted and what you receive. If you know the elapsed time, you can get a distance measurement. Link to comment Share on other sites More sharing options...
Ophiolite Posted January 30, 2014 Share Posted January 30, 2014 What you are speaking of in regard to atomic clocks sounds more like the experiment where atomic clocks were flown east-west and west-east around the world to to test resultant time dilation. As Swansont said, without more specifics there really isn't even a question to answer. Link to comment Share on other sites More sharing options...
Bjarne Posted January 30, 2014 Author Share Posted January 30, 2014 (edited) Saying you heard it, or read about it on the internet, is not a sufficient citation. It often doesn't provide enough information to answer a question. One possibility is you misread something or maybe a site is wrong, but there's no way to know this if I don't have access to the same information. For the original question: Doppler shift of a radio signal gives you a velocity, since you know what frequency was transmitted and what you receive. If you know the elapsed time, you can get a distance measurement. It was mentioned in an interview with John Leif Jørgensen from DTU (about 5 years ago) Because John had then invented a star camera navigation equipment today on board Juno. In this context the old Pioneer distance measurement eqipment was mentioned excactly e as I wrote it. So I am 100% sure you can count with this information I wrote (this man is not stupid, he know what he talks about) You can google translate more about the star camera navigation equipment invention here.. http://ing.dk/artikel/danske-stjernekameraer-rejser-til-jupiter-i-aften-120975 But this article is not mentioned anything about the equipment on board the Pioneer probes. I think it can be differcult to use Doppler on very large distances (?) so this is perhabs why a different system was used then...(?) Sorry I have no more information than that... New Question.. Some places at the internet I have read the flyby anomalies are of the of order 10e-4m/s^2 Other places that the order is the same as the order of the pioneer anomaly, - 10000 times smaller. So what is correct Edited January 30, 2014 by Bjarne Link to comment Share on other sites More sharing options...
Enthalpy Posted January 30, 2014 Share Posted January 30, 2014 The founding paper (not its first edition though) is freely available there, thanks arXiv: http://arxiv.org/abs/gr-qc/0104064 it's long and in places difficult, so use its table of contents. A simpler introduction there, thanks Wiki http://en.wikipedia.org/wiki/Pioneer_anomaly http://en.wikipedia.org/wiki/Pioneer_10 I have not found a mention about an atomic clock aboard the Pionner. Rather, the board transmitter had a frequency locked to 240/221 the received frequency (already Doppler-shifted once at the uplink). All the Pioneer data is from Doppler shift, not from a propagation delay. As a result, it tells a speed mismatch rather than a range mismatch (or more exotic interpretations). Of course, acceleration, speed and position can be deduced from an other, but the uncertainties or noise differ according to the nature of the signal and its mathematical transformations. The "pioneer anomaly" was estimated to 8,74*10-8cm/s2 = 8,74*10-10m/s2. Notice the varied units! This is a small acceleration but noticeable in space. Over 10 years, it converts to 0.28m/s mismatch for a quarter-ton object, and to 44 thousand kilometers. In 2012, one of the authors of the founding paper published a study claiming that the recoil by infrared radiation explains the anomaly: http://arxiv.org/abs/1204.2507v1 despite this had been ruled out in the previous paper. My own negative opinion about radiation recoil and a few more is there: http://www.scienceforums.net/topic/79814-pioneer-anomaly-still/ where I also propose a mission (for deep space or for Earth flyby) that measures a range, not just a Doppler shift. The flyby anomaly was observed at other spacecraft, mainly at Earth flyby where observations are reliable and exotic effects less plausible. Taken as a speed mismatch, it's also a few mm/s over one flyby. Here everyone takes it as a speed, because other accelerations are strong but the speed magnitude versus Earth should remain widely untouched after/before the flyby. Whether both anomalies - if they exist - result from the same effect is very unclear. While the Pioneer anomaly can have many interpretations, including mundane, the flyby is considered more disturbing. A recent buzz paper alleged an anomaly in the GPS satellites orbits. Its figures don't add up, and I wouldn't give it importance. Link to comment Share on other sites More sharing options...
Strange Posted January 30, 2014 Share Posted January 30, 2014 New Question.. Some places at the internet I have read the flyby anomalies are of the of order 10e-4m/s^2 Other places that the order is the same as the order of the pioneer anomaly, - 10000 times smaller. So what is correct This paper seems to have some definitive information of the velocity / energy anomalies: http://arxiv.org/abs/astro-ph/0608087 It doesn't seem to represent it as acceleration, but I suppose you can work that out. I have not found a mention about an atomic clock aboard the Pionner. Rather, the board transmitter had a frequency locked to 240/221 the received frequency (already Doppler-shifted once at the uplink). All the Pioneer data is from Doppler shift, not from a propagation delay. As a result, it tells a speed mismatch rather than a range mismatch (or more exotic interpretations). Of course, acceleration, speed and position can be deduced from an other, but the uncertainties or noise differ according to the nature of the signal and its mathematical transformations. I thought they also got distance information from the transmission delay? Link to comment Share on other sites More sharing options...
Bjarne Posted January 30, 2014 Author Share Posted January 30, 2014 By googling pioneer + atomic clock, serveral speculation comes up, showing that the clocks on board maybe not was ticking as expected, and that this could cause the deceleration, wheby SR maybe was not correct etc... Also wikipedia Clock acceleration Clock acceleration is an alternate explanation to anomalous acceleration of the spacecraft towards the Sun. http://en.wikipedia.org/wiki/Pioneer_anomaly Link to comment Share on other sites More sharing options...
Strange Posted January 30, 2014 Share Posted January 30, 2014 Nowhere does that say anything about atomic clocks on Pioneer. There weren't any, as far as I know. Link to comment Share on other sites More sharing options...
Enthalpy Posted January 30, 2014 Share Posted January 30, 2014 No atomic clock onboard, and the downlink frequency was locked to the received uplink frequency, so any explanation by clock drift is nonsense. Some explanations were (are) more subtle (too subtle for me) and involve time running differently under Pioneer's conditions, in an amount not included in general relativity's computations, which were already included in Anderson's founding paper. Unfortunately, these explanations say "clock" as well, but are not of technological nature. Link to comment Share on other sites More sharing options...
Bjarne Posted January 30, 2014 Author Share Posted January 30, 2014 (edited) No atomic clock onboard, and the downlink frequency was locked to the received uplink frequency, so any explanation by clock drift is nonsense. Possible We are all only humans I am, sure that I hear John say so, but he is maybe not an expert in these space probes equipment. Maybe John have misunderstood what was on board and what was proposed for the future, or what maybe he did not dig deeper into the Clock acceleration speculation... I Only found this NPL article... Quote.. Optical clocks have been proposed as a useful addition to future missions designed to resolvethe causes of the Pioneer anomaly with the scheme being to compare a stableclock on board the spacecraft with a reference clock located on earth. http://www.npl.co.uk/upload/pdf/atomic_clocks_space.pdf And as I wrote in this case it must be possible to send a signal, asking the space probe clock, - what time is it, - and get a reply..... something like this.. Dont Forget ..New Question.. Some places at the internet I have read the flyby anomalies are of the of order 10e-4m/s^2 Other places that the order is the same as the order of the pioneer anomaly, - 10000 times smaller. So what is correct Edited January 30, 2014 by Bjarne Link to comment Share on other sites More sharing options...
Strange Posted January 30, 2014 Share Posted January 30, 2014 Dont Forget ..New Question.. Some places at the internet I have read the flyby anomalies are of the of order 10e-4m/s^2 Other places that the order is the same as the order of the pioneer anomaly, - 10000 times smaller. So what is correct See post #8 Link to comment Share on other sites More sharing options...
Bjarne Posted January 30, 2014 Author Share Posted January 30, 2014 (edited) See post #8 The speed increment by perigee, and infinity (up to 13mm/s) is not a question. But there are a 2 very different opinions available at the internet, whether these fly by speed increments was a result of few minutes acceleration or whether it happens all the way from infinity (acceleration during a period of +/- 1 year) This is what confused me.. Edited January 30, 2014 by Bjarne Link to comment Share on other sites More sharing options...
Strange Posted January 30, 2014 Share Posted January 30, 2014 To work out the acceleration you would make some assumption about the period over which the anomalous speed change occurred. It seems to me that, as the cause of the change in speed is not known, any such calculation is likely to be completely arbitrary. Link to comment Share on other sites More sharing options...
Bjarne Posted January 31, 2014 Author Share Posted January 31, 2014 (edited) To work out the acceleration you would make some assumption about the period over which the anomalous speed change occurred. It seems to me that, as the cause of the change in speed is not known, any such calculation is likely to be completely arbitrary. I agree, all we can say is that by perigee and infinity we are able to discover that "something" is wrong, but we don't know what. So my guess is… The anomalies could be caused by a fast acceleration which seems to be the first direct impression. But it is also possible that we calculated some trajectories wrong, because something is different as we know, - whereby a slow acceleration can cause the same speed increment , but but first revealed, when the measured trajectory not follows the path we calculed and expected. So all we can say for certain is that we have an unexpected speed increment up to 13 mm/s Is this what you mean ? Edited January 31, 2014 by Bjarne Link to comment Share on other sites More sharing options...
Spyman Posted January 31, 2014 Share Posted January 31, 2014 As I understand it, the Flyby anomaly and the Pioneer anomaly are two completely different occurrences due to independent separate effects, where the Flyby anomaly is about spacecrafts passing close to Earth and the Pioneer anomaly is in regard to spacecrafts about twenty times the Earth-Sun distance out. The Pioneer anomaly is thought to have been resolved and was deemed to be caused by the heat radiation from the spacecraft's powersource, while the Flyby anomaly is still unresolved and is likely related to Earth's rotation and the spacecraft's trajectories. The Pioneer anomaly or Pioneer effect is the observed deviation from predicted accelerations of the Pioneer 10 and Pioneer 11 spacecraft after they passed about 20 astronomical units (3×109 km; 2×109 mi) on their trajectories out of the Solar System. ... By 2012 several papers by different groups, all reanalyzing the thermal radiation pressure forces inherent in the spacecraft, showed that a careful accounting of this could explain the entire anomaly, and thus the cause was mundane and did not point to any new phenomena or need for a different physical paradigm. The most detailed analysis to date, by some of the original investigators, explicitly looks at two methods of estimating thermal forces, then states "We find no statistically significant difference between the two estimates and conclude that once the thermal recoil force is properly accounted for, no anomalous acceleration remains."http://en.wikipedia.org/wiki/Pioneer_anomaly The flyby anomaly is an unexpected energy increase during Earth-flybys of spacecraft. This anomaly has been observed as shifts in the S-Band and X-Band Doppler and ranging telemetry. Taken together it causes a significant unaccounted velocity increase of over 13 mm/s during flybys. ... An analysis of the MESSENGER spacecraft (studying Mercury) did not reveal any significant unexpected velocity increase. This may be because MESSENGER both approached and departed Earth symmetrically about the equator (see data and proposed equation below). This suggests that the anomaly may be related to Earth's rotation.http://en.wikipedia.org/wiki/Flyby_anomaly 1 Link to comment Share on other sites More sharing options...
swansont Posted January 31, 2014 Share Posted January 31, 2014 To work out the acceleration you would make some assumption about the period over which the anomalous speed change occurred. It seems to me that, as the cause of the change in speed is not known, any such calculation is likely to be completely arbitrary. OTOH, the two values under scrutiny are different by a factor of 10,000, so even a rough approximation is likely to rule out one of the answers. Link to comment Share on other sites More sharing options...
Enthalpy Posted January 31, 2014 Share Posted January 31, 2014 The Pioneer anomaly is thought to have been resolved and was deemed to be caused by the heat radiation from the spacecraft's powersource [...] By 2012 several papers by different groups, all reanalyzing the thermal radiation pressure forces inherent in the spacecraft, showed that a careful accounting of this could explain the entire anomaly [...] I am not impressed that little bit by said several papers by different groups. I've put my arguments in the thread linked above. The numbers in the paper by Turyshev don't fit. Their computer simulation I suppose does, but other bounds or observations put different constraints. The other group even states "we did not have the thermal caracteristics of the spacecraft, but nevertheless we modelled it". Figure that out. Between a paper that states "out computer tells that, believe us" and three multiplications and divisions that say "no", I choose the second one. [...] by perigee and infinity we are able to discover that "something" is wrong, but we don't know what. [...] The anomalies could be caused by a fast acceleration which seems to be the first direct impression. [...] whereby a slow acceleration can cause the same speed increment , but but first revealed, when the measured trajectory not follows the path we calculed and expected. So all we can say for certain is that we have an unexpected speed increment up to 13 mm/s Measuring speed to 3mm/s accuracy (=2*10-11) takes time. At, say, 3GHz with a decent signal-to-noise, it would need only 5s, but the atmosphere brings much uncertainty, other causes probably too. I doubt (should I?) that the perigee speed is measured so accurately. More probably, this accuracy is attained over hours, which implies: long before and long after the flyby. So no sensible information must exist about when the speed changes - provided it does - and we ignore if the hypothetical acceleration is short (1000s * 10-5m/s2) or long (100,000s * 10-7m/s2, still 100 times the Pioneer anomaly). That's why only the flyby speed mismatch is published. By the way, varied space probes have given varied speed mismatch, from increment to decrement, including none. Also: a geosynchronous transfer orbit resembles a flyby, and we have a wealth of data for them - even with a higher perigee that brakes less in the upper atmosphere. Some failed circularizations have leaved the satellites on such orbits, which accumulate thousands of perigee passes. Very strong checks can be made with these existing items (or, as I propose in the pdf, simple purpose craft can stay on such an orbit and carry hardware for more accurate measures). Link to comment Share on other sites More sharing options...
Bjarne Posted January 31, 2014 Author Share Posted January 31, 2014 (edited) I am not impressed that little bit by said several papers by different groups. I've put my arguments in the thread linked above. The numbers in the paper by Turyshev don't fit. Their computer simulation I suppose does, but other bounds or observations put different constraints. The other group even states "we did not have the thermal caracteristics of the spacecraft, but nevertheless we modelled it". Figure that out. Between a paper that states "out computer tells that, believe us" and three multiplications and divisions that say "no", I choose the second one. Measuring speed to 3mm/s accuracy (=2*10-11) takes time. At, say, 3GHz with a decent signal-to-noise, it would need only 5s, but the atmosphere brings much uncertainty, other causes probably too. I doubt (should I?) that the perigee speed is measured so accurately. More probably, this accuracy is attained over hours, which implies: long before and long after the flyby. So no sensible information must exist about when the speed changes - provided it does - and we ignore if the hypothetical acceleration is short (1000s * 10-5m/s2) or long (100,000s * 10-7m/s2, still 100 times the Pioneer anomaly). That's why only the flyby speed mismatch is published. By the way, varied space probes have given varied speed mismatch, from increment to decrement, including none. Also: a geosynchronous transfer orbit resembles a flyby, and we have a wealth of data for them - even with a higher perigee that brakes less in the upper atmosphere. Some failed circularizations have leaved the satellites on such orbits, which accumulate thousands of perigee passes. Very strong checks can be made with these existing items (or, as I propose in the pdf, simple purpose craft can stay on such an orbit and carry hardware for more accurate measures). It look obvious to me that the flyby anomaly is increasing more or less proportional to the trajectories are asymmetric relative to the equator. If the anomaly is due to an acceleration of order 10e-4m/s^2 it is really strange. Which kind of possible force is possible to blame ? - nothing, - even not theoretical. When possibilities to the Space probes anomalies are discusses, SR has often been mentioned, we still can’t be sure whether this is an option. In 2016 ISS will be able to do some serious SR /GR testing http://www.esa.int/Our_Activities/Human_Spaceflight/Human_Spaceflight_Research/Atomic_Clock_Ensemble_in_Space_ACES I wonder what would for example happen if SR only can be fully understood in an absolute anisotropic reference frame (asymmetric to equator). Are there any reason that this should not should be an option ? If not I think the anomaly could develop during a half of the “orbit” (trajectory) period (I mean during +/- 1 year period as such period normally take) and the acceleration therefore only of order 10e-9m/s^2. Then would calculated trajectories simple not fit to these we are measuring. Is that an option Edited January 31, 2014 by Bjarne Link to comment Share on other sites More sharing options...
Enthalpy Posted February 1, 2014 Share Posted February 1, 2014 Uuuh? Where do you pick one year? The speed varies between arrival and departure of the probe. The effect is small, did you realize that? Maybe there is something, maybe not - and checking for such effects on well-known satellites orbiting for decades, instead of probes passing by, would tell a lot. For instance the Navsat (the GPS satellites) have very well observed orbits. Until there are better observations, I wouldn't risk a claim like "anomaly" and "which force - none". If you have a GR explanation to propose, just formulate it, some forum members here are used to GR. Link to comment Share on other sites More sharing options...
Bjarne Posted February 2, 2014 Author Share Posted February 2, 2014 Deep Space Atomic Clock Ticks Toward Success Link to comment Share on other sites More sharing options...
swansont Posted February 2, 2014 Share Posted February 2, 2014 The video confirms that the atomic clocks are currently on the ground, and that Doppler and time-of-flight are used for ranging. Which is what I said. Link to comment Share on other sites More sharing options...
Bjarne Posted February 2, 2014 Author Share Posted February 2, 2014 (edited) The video confirms that the atomic clocks are currently on the ground, and that Doppler and time-of-flight are used for ranging. Which is what I said. Agree, but it will be different in the future Edit...PS Nobody knows what causes these strange hiccups in spacecraft speed but there is no shortage of theories, some of which we’ve discussed here and here. If scientists are ever to get to the root of this phenomenon, they need to have a way of measuring it repeatedly, unambiguously and in detail. But flyby’s are few and far between. And even when they do occur, NASA’s Deep Space Network which monitors spacecraft from the ground is not designed to study the effect in detail. The most serious problem is that the network cannot follow spacecraft when they are very close to Earth. This results in a gap in communications during a flyby lasting a few hours, just when the most interesting effect is happening. As a result, the fly-by anomaly has never been caught in flagrante. Instead, it arises as the difference between the observed and expected velocity after a flyby Sourece http://www.technologyreview.com/view/425472/gps-satellites-could-solve-flyby-anomaly/ More about this future option here http://www.spacesafetymagazine.com/2012/11/26/esa-ste-quest-mission-unravel-origin-flyby-anomaly/ Edited February 2, 2014 by Bjarne Link to comment Share on other sites More sharing options...
Spyman Posted February 4, 2014 Share Posted February 4, 2014 I am not impressed that little bit by said several papers by different groups. I've put my arguments in the thread linked above. The numbers in the paper by Turyshev don't fit. Their computer simulation I suppose does, but other bounds or observations put different constraints. The other group even states "we did not have the thermal caracteristics of the spacecraft, but nevertheless we modelled it". Figure that out. Between a paper that states "out computer tells that, believe us" and three multiplications and divisions that say "no", I choose the second one. Turyshev and his team are professionals working at the NASA Jet Propulsion Laboratory, they have access to detailed design documentation and extensive mission data from which they constructed a comprehensive thermal model and history of the spacecraft's journey. Their papers have been thoroughly examined with critical eyes by experts in this field, any flaws or "numbers that don't fit" would have been found and pointed out by now. So I don't think you can brush off their papers with a back of the envelope estimation that came up a little short. Link to comment Share on other sites More sharing options...
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