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What's slowing down the two Voyagers?



 
 
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  #21  
Old June 23rd 04, 10:01 PM
Rodney Kelp
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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



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  #22  
Old June 23rd 04, 10:50 PM
Alex R. Blackwell
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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  
Old June 23rd 04, 11:19 PM
Jonathan Silverlight
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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  
Old June 23rd 04, 11:43 PM
Louis Scheffer
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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  
Old June 24th 04, 12:24 AM
Mike Hawk
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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  
Old June 24th 04, 12:32 AM
Christopher M. Jones
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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  
Old June 24th 04, 01:00 AM
Mike Williams
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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  
Old June 24th 04, 01:00 AM
Insane Ranter
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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  
Old June 24th 04, 01:03 AM
Andrew Urquhart
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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  
Old June 24th 04, 01:41 AM
Mike Hawk
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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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