pioneer 10 acceleration

Craig Markwardt wrote in message ...
(Nodem Info. Sys.) writes:
I've had time to study the Cassini measurements and yes, there is no
anomaly. However, the reason for this is the way the measurement
methos differs from the other probes. The Cassini time-delay
measurement should show no real change in the velocity, which is
expected and fully consistent with my result.

You are in fact incorrect. The recent Cassini results published in
Nature are based on radiometric Doppler tracking, just as the Anderson
et al results for Pioneer 10, 11, and other spacecraft results were.

The difference is that the Cassini spacecraft is able to transpond at
dual frequencies, so analysts are able to correct for the solar plasma
more precisely than for previous spacecraft. Thus, the Cassini data
are even more sensitive to velocity changes than the previous data
were.

CM

I guess I should have been a bit more specific. The Doppler tracking
data includes a 'modeled' acceleration, which is partly determined by
the time-delay measurement. In gr-qc/0308010, this is given as -26.7
* 10^-8 cm/s^2, and it would appear that the 'Pioneer anomaly' has
been inadvertently rolled into this number, but still makes up less
than a third of it.

The Cassini spacecraft doesn't make the best platform to test the
Pioneer anomaly, but it has shown that this anomaly is not a real
change in velocity (ruling out alternative gravity theories).

My prediction implies an 'apparent' deceleration of 8.14 * 10^-8
cm/s^2 in radial velocity. So far no observations have disagreed with
this.

(Nodem Info. Sys.) writes:

The Cassini spacecraft doesn't make the best platform to test the
Pioneer anomaly, but it has shown that this anomaly is not a real
change in velocity (ruling out alternative gravity theories).

How has the Cassini spacecraft shown that the Pioneer anomaly is not a
real change in velocity?

CM

Craig Markwardt wrote in message ...
(Nodem Info. Sys.) writes:

The Cassini spacecraft doesn't make the best platform to test the
Pioneer anomaly, but it has shown that this anomaly is not a real
change in velocity (ruling out alternative gravity theories).

How has the Cassini spacecraft shown that the Pioneer anomaly is not a
real change in velocity?

CM

I believe that there is a discrepancy between the time-delay and
Doppler ranging measurements. The modeled acceleration can be
measured from the time-delay, however, the Pioneer anomaly will only
show up on the Doppler ranging (in addition to the modeled
acceleration). If the anomaly was due to a real change in velocity,
then both measurement methods would give the same result.

I thought there was something about this in the paper I referenced,
but it looks like it was withdrawn from the archives. I've contacted
John Anderson to see if he can shed any light on this matter.

I'll keep you posted.

Alastair

(Nodem Info. Sys.) writes:
Craig Markwardt wrote in message ...
(Nodem Info. Sys.) writes:

The Cassini spacecraft doesn't make the best platform to test the
Pioneer anomaly, but it has shown that this anomaly is not a real
change in velocity (ruling out alternative gravity theories).

How has the Cassini spacecraft shown that the Pioneer anomaly is not a
real change in velocity?

CM

I believe that there is a discrepancy between the time-delay and
Doppler ranging measurements. The modeled acceleration can be
measured from the time-delay, however, the Pioneer anomaly will only
show up on the Doppler ranging (in addition to the modeled
acceleration). If the anomaly was due to a real change in velocity,
then both measurement methods would give the same result.

You are incorrect. All the measurement methods are the same, i.e.,
Cassini and the other spacecraft mentioned in this thread *all* use
Doppler tracking. The published paper in Nature does *not* use
"time-delay" (ranging). There is no such thing as "Doppler ranging,"
since Doppler tracking and ranging are quite independent techniques.

It is likely that any conclusions drawn from your incorrect premises
are thus irrelevant.

CM

Craig Markwardt wrote in message ...
(Nodem Info. Sys.) writes:

I believe that there is a discrepancy between the time-delay and
Doppler ranging measurements. The modeled acceleration can be
measured from the time-delay, however, the Pioneer anomaly will only
show up on the Doppler ranging (in addition to the modeled
acceleration). If the anomaly was due to a real change in velocity,
then both measurement methods would give the same result.

You are incorrect. All the measurement methods are the same, i.e.,
Cassini and the other spacecraft mentioned in this thread *all* use
Doppler tracking. The published paper in Nature does *not* use
"time-delay" (ranging). There is no such thing as "Doppler ranging,"
since Doppler tracking and ranging are quite independent techniques.

It is likely that any conclusions drawn from your incorrect premises
are thus irrelevant.

CM

Sorry about using the wrong terminology, I guess I confused you a bit
there.

Let me clarify things he

According to the Nature article you mention, there is a 'modeled'
acceleration considered to be due entirely to the non-isotropic
radiation from the RTGs. The article states this as around 30 x 10^-8
cm/s^2, which is almost 4 times the Pioneer anomaly (the sign is the
same for both). According to the article, "Deriving this acceleration
from a model of the spacecraft is a difficult task". Therefore it
must be measured, and then the measurement is *assumed* to relate to
*known* parameters such as the radiation from RTGs.

So what we have is something that contains the Pioneer anomaly, but
because it is labeled as 'modeled'... poof!.. the 'unmodeled' Pioneer
anomaly is not there. Now that's a great bit of science!

The time-delay *ranging* measurements (assume we will make a series of
them over a period of time) can be used to measure the velocity of the
probe, and the change in velocity of the probe (acceleration). This
acceleration can be used to gain a true measurement of what is
considered as the 'modeled' acceleration (this would come out around
19 x 10^-8 cm/s^2).

The Doppler *tracking* measurements will contain an additional effect
caused by the curvature of space time, resulting in an additional
apparent acceleration of 8.143 x 10^-8 cm/s^2 towards the observer.
The combined 'modeled' and 'Pioneer anomaly' acceleration would add up
to around the 27 x 10^-8 cm/s^2 figure quoted in the article.

So how did that article show there was no Pioneer anomaly?

Dark energy could be causing the anomalous acceleration of pioneer 10.
The solar system is surrounded by the spherical Oort cloud.If dark
energy consists of particles that flow into the galaxy, the Oort cloud
would shield
the solar system from those particles.However a gap in the Oort cloud
would allow some dark energy particles to flow into the solar system.
Dark energy accounts for up to 70 per cent of the mass of the universe
and the universe has an approximate average mass density of 10 ^ -27
kg/ m^3.So, as an approximation, dark energy has a mass density of
about
10 ^ -27 kg/ m^ 3 too.If dark energy particles move at close to the
speed of light then 10 ^ -27 kg of them will move through one metre in
10 ^ -8 seconds. The particles will have a total momentum of 10 ^ -27
x 10 ^ 8 = 10 ^ -19.
The maximum force the particles can exert in 10 ^ -8 seconds on one
square metre of pioneer 10 is given by Force = rate of change of
momentum / time
Force = (10 ^ -19 minus 0 ) / 10 ^ - 8 = 10 ^ -11 Newtons.
Now assuming pioneer 10 has an area facing the direction of travel of
the dark energy particles through the Oort cloud and that area is at
most 100 square metres (perhaps someone on sci.physics.research knows
the exact area!)
then the total force on pioneer 10 due to dark energy is 10 ^ -11 x
100 Newtons = 10 ^ - 9 Newtons.Since acceleration = force / mass and
assuming pioneer 10 has a mass of about 1000 kg ( again, perhaps
someone on sci.physics.research can put an exact figure to this), then
the acceleration of pioneer 10 towards the sun caused by dark energy
particles would be about
10 ^ - 9 / 1000 = 10 ^ -12 m / s ^2.The figure Nasa gives is 10 ^ -10
m / s ^2.
If the exact mass and area of pioneer 10 are used, the answer given
for the acceleration of pioneer 10 due to dark energy flowing through
a gap in the Oort cloud could well be a lot closer to the value Nasa
gives.

In message , alistair
writes
Dark energy could be causing the anomalous acceleration of pioneer
10.
The solar system is surrounded by the spherical Oort cloud.If dark
energy consists of particles that flow into the galaxy, the Oort
cloud
would shield
the solar system from those particles.However a gap in the Oort cloud
would allow some dark energy particles to flow into the solar system.


ANDRE?MICHAUD wrote:

There are a few problems with this idea :-)

The paper by Anderson et al. which everyone cites is available online
at
http://xxx.lanl.gov/abs/http://www....gr-qc/0104064. It has figures
for the mass of
the Pioneers (223 kg dry mass) and their surface area (or at least
that
of the dish antenna, which accounts for nearly all of it. It's a 2.74
meter dish giving an area of 5.9 square meters.
Also, the two Pioneers are going in nearly opposite directions.


ALISTAIR writes:

The mass and surface area you quote for Pioneer 10 would give an
acceleration for Pioneer 10 that is roughly only one third smaller
than the figure I calculated of 10^ -12 m/s^2.The correct figure NASA
gives is 10^-10 m /s^2.
However, if dark energy consists of particles with rest mass and these
particles in our part of the Milky Way move at 99.9999 per cent the
speed of light then there would be a relativistic mass increase by a
factor of 10000 compared to the average expectation for dark energy
mass which would have to be moving at a speed of around 1/3 that of
light.Whether or not dark energy actually has a different mass density
in galaxies compared to intergalactic space,I couldn't say.There is
also the possibility that dark energy coming through a gap in the Oort
cloud could pick up speed and mass if it has fluid like properties (
though I think such a Bernouilli flow is unlikely given how large the
mass increase would be).Both these factors could give the acceleration
NASA quotes.The fact that the Pioneers are moving in opposite
directions is irrelevant because the Oort cloud could have other gaps
in it which allow dark energy particles into the solar sytem.