Is Voyager Accelerating?

"Dat's Me" wrote in message
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On Tue, 23 Mar 2004 10:21:27 -0800, Starlord wrote:

I would guess they'd pick up a tiny bit of speed as the pull of the sun
became less on them. Not talking great amounts, maybe a few feet per
min.

Add to that: As the Sun's gravitational pull drops off, the gravitational
pull of other objects (Kuiper Belt, Oort Cloud & other Stars) would have
slightly more effect/pull on the probes. Btw, are the probes heading
toward, or away from, the Galactic Centre? Could make a difference.

Probably not much of one. The whole solar system is in
free-fall in the galaxy, which is a mighty big system.

The gravitational gradient due to the galactic field across
the whole width of the solar system and quite a bit beyond
is probably quite flat. The solar system and the probes
would partake of virtually the same accelerations.

On Wed, 24 Mar 2004 07:42:13 +0000, Jonathan Silverlight wrote:

In message , Ugo
writes
On Tue, 23 Mar 2004 20:36:24 +0000, Jonathan Silverlight wrote:

In message , Ugo
writes
Maybe BenignVanilla actually meant about the "anomalous" acceleration of
the Pioneer probes. AFAIK, it's currently unknown why it exists, though
there are several theories. Measuring the Voyagers' acceleration is useless
beacause they are 3 axis stabilized spacecraft and their attitude thruster
firings always change the craft speed, even by the smallest bit. This tends
to mask the very small anomalous acceleration, if it indeed exists.

And don't forget that the anomalous acceleration is toward the Sun -
it's a deceleration, in everyday language. AFAICS the acceleration has
not been seen for Cassini, although its original discoverers say Cassini
is not a suitable platform to measure it.

Right, because Cassini is also 3-axis stabilized and not spin stabilized
like the Pioneers.

It isn't that simple. Cassini is doing experiments to detect
gravitational waves, and a paper was published in Nature last year on a
test of relativity.

Now that you mention it, Cassini also has reaction wheels which provide
attitude adjustments in addition to thrusters. This would allow these sort
of measurements, but IIRC not on a long scale because the wheels' momentum
needs to be periodically "unloaded".

It's carrying a K-band transponder designed by the
Italians for just such an experiment, and the Italians seem to have
accurately modelled the thermal emission which is the most likely cause
of the Pioneer effect.

Are you referring to the RTG heat emissions?


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In message , Ugo
writes
On Wed, 24 Mar 2004 07:42:13 +0000, Jonathan Silverlight wrote:

It isn't that simple. Cassini is doing experiments to detect
gravitational waves, and a paper was published in Nature last year on a
test of relativity.

Now that you mention it, Cassini also has reaction wheels which provide
attitude adjustments in addition to thrusters. This would allow these sort
of measurements, but IIRC not on a long scale because the wheels' momentum
needs to be periodically "unloaded".

It's carrying a K-band transponder designed by the
Italians for just such an experiment, and the Italians seem to have
accurately modelled the thermal emission which is the most likely cause
of the Pioneer effect.

Are you referring to the RTG heat emissions?

Yes.
I found the papers I referred to earlier in this thread.
The Nature paper is "A test of general relativity using radio links with
the Cassini spacecraft" B Bertotti, L Iess and P Tortora, Nature vol
425. No. 6956 p. 374, doi:10.1038/nature01997 and the Anderson one is
http://arxiv.org/abs/gr-qc/0308010v1. Their paper was withdrawn, but
the original was still on the Arxiv server last time I looked.
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On Wed, 24 Mar 2004 08:37:03 -0500, G=EMC^2 Glazier wrote:

Dat's Me It takes more energy for the Voyager to leave Earth and be made
to fall into the sun,than going towards the Oort belt. Bert

I know that Bert.

But as someone pointed out, after getting past a certain point, the
Pioneer probes appeared/were accelerating. Something had to be causing
it and we were hypothesizing.

Dat's Me Let me apologize I should know you were away of that fact.
I'll bring in my own thought why the Voyager is picking up speed in the
direction it is going. It is going in the direction of the Milky Way
core. It has billions of stars and BH in the direction it is going and
very few in comparison in back of it. It is showing us that Mach theory
is right. It shows that the inverse square law is being obeyed. It shows
the Voyager had the escape velocity to move completely away from the
solar system and the sun is 99% of the gravity field of the solar
system. The Voyager will never slow down unless it passes the core of
the Milky Way,and it will keep decelerating come to a stop,and
accelerate back in the opposite direction. Bert

In message , Dat's Me
writes
On Wed, 24 Mar 2004 08:37:03 -0500, G=EMC^2 Glazier wrote:

Dat's Me It takes more energy for the Voyager to leave Earth and be made
to fall into the sun,than going towards the Oort belt. Bert

I know that Bert.

But as someone pointed out, after getting past a certain point, the
Pioneer probes appeared/were accelerating. Something had to be causing
it and we were hypothesizing.

Careful :-) The "acceleration" on the Pioneers is actually what most
people would call a deceleration - an unexplained slowing down. And
no-one can tell if it starts at a certain point. It was only detectable
when solar radiation pressure dropped enough to allow its detection, and
it seems to have been constant since then, but it might have been
present from the moment the Pioneers left Earth - or Jupiter.
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On Thu, 25 Mar 2004 18:43:05 +0000, Jonathan Silverlight wrote:

Careful :-) The "acceleration" on the Pioneers is actually what most
people would call a deceleration - an unexplained slowing down. And no-one
can tell if it starts at a certain point. It was only detectable when
solar radiation pressure dropped enough to allow its detection, and it
seems to have been constant since then, but it might have been present
from the moment the Pioneers left Earth - or Jupiter.

Thanks for that - I didn't see (or perhaps correctly interpret) that point.

Dat's Me Voyager once leaving the solar system and accelerating towards
a greater gravity fields(stars in front) has lots going for it. It
has the inverse gravity for getting greater in the direction it is going
and getting weaker in its back side. As it accelerates faster and faster
its inertia keeps going up(gets heavier) that means greater gravity
attraction. As it nears light speed the space in the direction it is
going shrinks(foreshortens) To make this thought clearer lets say the
Voyager reaches "C" and the star it is heading for is 20 light years
away. It will get there in 15 years. Bert PS This does not
violate SR because I made the space shorter,and did not make the object
go faster. Kind of tricky thinking but its reality PPS Don't jump on me
for the Voyager reaching"c" I know it can never go that fast,and I was
just making a profound point