On Fri, 27 Aug 2004 08:39:01 GMT, Painius wrote:
Never hesitate to be interesting, Jonathan... This is great stuff!

Where our spacecraft are concerned, let's see... we have found
gravitational anomalies associated with both the Pioneers, 10 and
11, also with the Ulysses and Galileo crafts, but i've found nothing
about any such anomalies associated with either Voyager, 1 or 2.

The Pioneers are probably not that mysterious. If we see our
young Sun beginning to spew out its solar wind at a million mph,
outcasting the smaller debris in its accretion disk to areas (still in
and near the ecliptic) beyond Neptune, then there is probably just
a lot of small masses out there pulling on them, helping the Sun
slow them down.

This has already been proposed and dismissed. If there were any large
concentration of mass outside Neptune, surely we would be able to detect
anomalies in Neptune's orbit? Also, this would imply incerasing
acceleration while the craft were inside of the bulk of these bodies and a
decrease once it traversed most of them on the way out.

And there may be some effect on them caused
by the abrubt and shocking slow down of the solar wind as well.
Maybe this "termination shock" has a small braking action on the
Pioneers? Then there's always the unknown effects of the Sun's
heliopause if it's been reached by the Pioneers.

I'm finding it hard to believe that solar wind has enough density at those
distances from the Sun to exert some drag on the spacecraft. If so, this
effect would have to be very noticeable here at Earth. We are talking about
a few particles per cubic centimeter here on Earth, hardly enough to do any
mechanical effect. Also, I don't believe the Pioneers arrived at the
termination shock since Voyager 1 overtook them and AFAIK, it hasn't
reached it either, yet.

Ulysses' orbit brings it near the ecliptic and near Jupiter, and i
wonder if the anomaly isn't more, or perhaps less, pronounced at
these times? I haven't been able to find anything on this. It's the
Galileo one which seems the most mysterious to me. Didn't it
always orbit closely to Jupiter? so wouldn't this close proximity
to a gas giant drown out any possible gravitational anomalies?

Perhaps Galileo measurements were made on route to Jupiter? In any case,
measuring this anomaly so close to the Sun is very difficult due to the
effects of solar radiation pressure which can be hard to model and take
into consideration. The anomaly with the Pioneers was observed once the
craft got far enough from the Sun for the light pressure to become
insignificant.

And the Voyagers? Well, Voyager 1 was shot out of the plane
of the ecliptic by Saturn, and Voyager 2 was shot out in about
the opposite direction, also away from the ecliptic, by its close
encounter with Neptune. Could this mean that, since no such
anomalies have been noted for these two, then there is a valid
association between these anomalies and the ecliptic?

The reason no anomalies were observed with the Voyagers is because none
*could* be measured. The two spacecraft are 3 axis stabilized, using
maneuvering thrusters to keep the antenna pointed at Earth. Constant firing
of these thrusters changes the spacecraft's momentum all the time (and in a
random fashion, too), thus drowning any anomaly out...

--
The butler did it.