What's slowing down the two Voyagers?

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

Any ideas as to what's causing this slow down anyone? I was expecting
no decelerations until we reach the first signs of the theoretical
'Oort Cloud' or some other medium that would equally lead to an
extinction of Voyagers' onboard radio telemetry relay by a
proportional measure. Is the craft's speed reduction connected in some
way with the expected slow down in the speed of the solar wind as it
nears the 'termination shock' I wonder... Or is there some hitherto
unknown relativistic effect of some kind at play here?

Abdul Ahad

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

Any ideas as to what's causing this slow down anyone?

The sun's gravity, of course.

Paul

"Paul F. Dietz" wrote ...
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

Any ideas as to what's causing this slow down anyone?

The sun's gravity, of course.

I had a look round on Google and came across the following dissertion
on gravitational interaction with Voyager.

http://makeashorterlink.com/?D2D5231A8

*Paul F. Dietz* wrote:
Abdul Ahad wrote:
[snip]
I noted the velocities of both probes (relative to the Sun) were
edging lower by small amounts over the past 8 years:
[snip]
Any ideas as to what's causing this slow down anyone?

The sun's gravity, of course.

More verbosely put as: kinetic energy is being exchanged for gravitional
potential energy as each probe climbs out of the Suns gravity well.
--
Andrew Urquhart
- My reply address is invalid, use: www.andrewu.co.uk/contact/

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?

"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

*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/

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"?

Mike Hawk wrote:

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"?


IIRC that article didn't dispute that Voyagers and Pioneers weren't
slowing down due to gravity, but that their rate of deceleration was
greater than expected.
Here's part of the article http://tinyurl.com/2jpnz

Shawn

P.S. Tinyurl.com said the original url had 239 characters!

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