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#21
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Some alien water mining, organic sucking reptiles are going to find the
Voyagers and follow them back to here and exploite us to oblivion. "Brian Tung" wrote in message ... Mike Williams wrote: If you made the repeater's receiving antenna a more reasonable size, say a tenth of the diameter of the biggest dish on Earth, then you have to place it at one tenth the distance from Voyager[1]. That's 81 AU from here. It took Voyager 28 years to get to a distance of 90 AU. If a repeater could go at the same speed it might take 25 years to get to 25 AU, by which time Voyager would be much further away. However, Voyager used gravitational slingshot effects that were available due to a particularly convenient alignment of the outer planets. Without this alignment, the repeater craft would not be able to achieve the same speed with similar technology, and certainly wouldn't be able to follow the same path now that the planets have moved. What's more, in a long chain, one bad link breaks the whole chain. Better to send another satellite whose dedicated purpose is to investigate deep solar system objects of interest. Brian Tung The Astronomy Corner at http://astro.isi.edu/ Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/ The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/ My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.690 / Virus Database: 451 - Release Date: 5/22/2004 |
#22
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Jonathan Silverlight wrote:
You're thinking of the Pioneers :-) (at least I hope you're joking !) AFAIK the Voyagers aren't behaving in the same way. If the Pioneer effect is real, then one would logically assume the Voyagers are "behaving in the same way." The reason no similar effect has been detected in the Voyager radio tracking data is due to the fact that the Voyagers, being 3-axis stabilized, have experienced many propulsive accelerations over their lifetimes, and have not been in spin-stable mode for long data tracking arcs, which overwhelms the signal. -- Alex R. Blackwell University of Hawaii |
#23
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In message , Alex R. Blackwell
writes Jonathan Silverlight wrote: You're thinking of the Pioneers :-) (at least I hope you're joking !) AFAIK the Voyagers aren't behaving in the same way. If the Pioneer effect is real, then one would logically assume the Voyagers are "behaving in the same way." The reason no similar effect has been detected in the Voyager radio tracking data is due to the fact that the Voyagers, being 3-axis stabilized, have experienced many propulsive accelerations over their lifetimes, and have not been in spin-stable mode for long data tracking arcs, which overwhelms the signal. My jokey post has drawn a more serious response than I expected, but will the Voyager Interstellar Mission provide the opportunity for the precision tracking that is required, or are small corrections still being made? |
#24
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Tim Auton tim.auton@uton.[groupSexWithoutTheY] writes:
(Abdul Ahad) wrote: when I noted the velocities of both probes (relative to the Sun) were edging lower by small amounts over the past 8 years: Any ideas as to what's causing this slow down anyone? Gravity. Well, as accurately as we can measure the deceleration is all due to gravity, but data from the Pioneer craft suggest there may be something else (too small to measure for the Voyager craft due to the way they are stabilised). Search for "pioneer anomaly". It's very interesting, mainly because nobody seems to know what's causing it. This is just wishful thinking by the theorists, who want something new to explain. A careful look at Pioneer shows there are a number of features that cause it to radiate a bit more of its heat in the anti-sunward direction. This is just right to account for the observed slowdown. Conventional Forces can Explain the Anomalous Acceleration of Pioneer 10, Phys.Rev. D67 (2003) 084021. http://arxiv.org/abs/gr-qc/0107092 I'm the author so my opinion may be somewhat biased, of course. Note that when they put Cassini into a gyro-only mode for the gravity wave searches, it experienced an anomalous acceleration about 3x that of Pioneer, due to non-isotropic waste heat radiation. This effect is difficult to model, and the pre-launch estimates were off by 50%. But the theorists then do a song and dance about how this can't apply to Pioneer, all engineering data to the contrary. Lou Scheffer |
#25
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Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s Any ideas as to what's causing this slow down anyone? The sun's gravity, of course. Paul Prove it! The probes are well in excess of escape velocity. You are implying that at the present rate, the influence will only increase and slow the probes down considerably. Why doesn't the sun slow planetary motion? |
#26
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Abdul Ahad wrote:
I was casually checking the weekly mission data archived he- http://voyager.jpl.nasa.gov/mission/...orts/index.htm when I noted the velocities of both probes (relative to the Sun) were edging lower by small amounts over the past 8 years: Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s [snip] Easy question with an easy answer, it's gravity. The Sun is pulling on the Voyager spacecraft and slowing it down. Almost too obvious eh? This is the way orbits work, if you have an exactly circular orbit then it just so happens that you balance out the falling / moving parts and the speed can stay constant. Otherwise speed will increase when falling into the Sun and decrease when heading away from the Sun, sans propulsive accelerations in the mix. |
#27
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Wasn't it Mike Hawk who wrote:
Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s Any ideas as to what's causing this slow down anyone? The sun's gravity, of course. Paul Prove it! The probes are well in excess of escape velocity. You are implying that at the present rate, the influence will only increase and slow the probes down considerably. Why doesn't the sun slow planetary motion? Without the Sun's gravity, the planets would travel in straight lines. It's gravity supplies the force that accelerates the planets inwards and causes them to move in ellipses. Voyager is moving away from the Sun, rather than around it, so the same force acts in a direction opposite to its motion, thus causing a deceleration. -- Mike Williams Gentleman of Leisure |
#28
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"Mike Hawk" wrote in message news:%ioCc.2364$933.1884@clgrps12... Jan 1996 Voyager 1: 17.4 km/s, Voyager 2: 16.1 km/s Jan 1999 Voayger 1: 17.3 km/s, Voayger 2: 15.9 km/s Jan 2002 Voyager 1: 17.2 km/s, Voyager 2: 15.7 km/s Jan 2004 Voayger 1: 17.2 km/s, Voyager 2: 15.7 km/s Any ideas as to what's causing this slow down anyone? The sun's gravity, of course. Paul Prove it! The probes are well in excess of escape velocity. You are implying that at the present rate, the influence will only increase and slow the probes down considerably. Why doesn't the sun slow planetary motion? How about you disprove it |
#29
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*Mike Hawk* wrote:
*Paul* wrote: *Abdul Ahad* wrote: Any ideas as to what's causing this slow down anyone? The sun's gravity, of course. Prove it! The probes are well in excess of escape velocity. ....which just means that 'when' they reach an infinite distance from the Sun that there would still be a greater than zero velocity. Are you suggesting that if you fire a projectile at (escape velocity + 1mm/s) that the projectile is no longer subject to gravity?, sounds like you're implying it to me ;-) You are implying that at the present rate, the influence will only increase and slow the probes down considerably. I don't think there's an implication of that in Pauls answer. Why doesn't the sun slow planetary motion? The centripetal force due to orbital motion balances the force due to the gravity of the Sun. So, the planet isn't climbing out of the Suns gravity well and doesn't exchange kinetic energy for gravitational potential energy; the planet orbits along a line of stable equipotential. For planets in elliptical orbits you do see a change in orbital velocity due to this exchange of kinetic and gravitional potential (it's why northern hemisphere summer here on Earth is technically slightly longer than southern hemisphere summer 6 months later), but Kepler and Newton largely sorted this out quite some time ago! -- Andrew Urquhart - My reply address is invalid, use: www.andrewu.co.uk/contact/ |
#30
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The centripetal force due to orbital motion balances the force due to the gravity of the Sun. So, the planet isn't climbing out of the Suns gravity well and doesn't exchange kinetic energy for gravitational potential energy; the planet orbits along a line of stable equipotential. For planets in elliptical orbits you do see a change in orbital velocity due to this exchange of kinetic and gravitional potential (it's why northern hemisphere summer here on Earth is technically slightly longer than southern hemisphere summer 6 months later), but Kepler and Newton largely sorted this out quite some time ago! -- It's funny. I recall reading an article in SA or some other legitimate magazine writen by REAL scientists pondering this question about the voyager slowdown. No where in the article did they even hint at the suns gravity. They just had no answer. Does this imply you all are smarter than them by offering up a simple explanation as "the suns gravity"? |
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