Has anyone suggested measuring parallax of stars from a long distance
SPACE probe such as the NEW HORIZON PROBE or THE CASSINI PROBE ?

As  probes such as these will travel many times the diameter of the
Earths orbit, a telesope mounted on them should be able to obtain VERY
parallax measurements so it appears to me to be a reasonable idea.
  
Is there any reason why this idea is not feasible?

I would like a precise answer to this question. Links which mention the idea
I have suggested would be great. 
I AM NOT interested in hearing about other methods of Parallax measurement
regardless of how accurate they may be.  

Kind Regards

Mongolia

I don't know how well the two probes mentioned are equipped to make
such measurements.  But as for probes in general, obviously the bigger
the orbit, the farther out you could use the parallex to measure the
distance of stars.  But you would have to wait quite a while.  The
orbital period of Saturn, for example, is 29.46 years.  So you would
have to wait half of that length of time to get the two measurements
needed for the parallas method from the opposite sides of Saturn's
orbit.

ansel001-ga 

<<But you would have to wait quite a while.  The orbital period of
Saturn, for example, is 29.46 years.  So you would have to wait half
of that length of time to get the two measurements needed for the
parallas method from the opposite sides of Saturn's orbit.>>

Nope! not true. Think about how astronomers measure the parallax of stars 
at present. They take a photograph of a relatively nearby star (one
whose distance is been measured) with a very distant object in the
background
(such as a quasar) Then they wait 6 months as the earth will now be at
the other side of its orbit thereby using a natural baseline of 2
astronomical units. However it does not have to be the same telescope
which takes the second measurement. Similiarly when one measurement is
taken from Saturn
another can be taken from an earth based telescope (or the Hubble telescope
for that matter) . All that matters is that we have a baseline which
is considerably larger than 2 astronomical units. In this case we now
have a baseline of 30 astronomical units (an increase in accuracy of
15!)
        

Indeed as soon as a space probe is more than 2 astronomical units away
from the Earth we have already a longer baseline than the natural one
formed by the Earths orbit around the sun. For a more distant probe
such as 'New Horizon'
the accuracy will be far better and as the "New Horizon" will not be
stopping the farther away it gets the more accurate the Parallax
measurements will
become.

Which to get to your point about how well the Cassini and New Horizon
probes are equipped to make such measurements. The sad reality is that
neither is probably equipped at all to make such measurements.

Which is the point of my question. Why are astronomers and space
scientists missing this superb opportunity to obtain really accurate
parallax measurements?

The measurements of the distance of the more distant galaxies are
inaccurate to a degree of 25% to 50%. A lot of this derives from the
inaccurate measurement of our closer astronomical stellar neighbours.
A accurate measurement of our closer stars gives us a more accurate
distance measurement of the universe as a whole.

Kind Regards

Mongolia

I remember reading an article in the American 'Astronomy' magazine in
the 1990's about a proposal for the TAU (Thousand AU) mission. This
involved sending a probe out to 1000 AU to measure the extra solar
environment and interstellar environment (although 1000 AU is barely
interstellar, as the nearest star is some 265000 AU away!). I think
they discussed the massive improvement of distance measurement - being
able to get accurate measurements of stars up to 10,000 light years
away (one-third the distance to the centre of the Galaxy). It was
envisaged to take 50 years to reach that distance!
The mission was canned.
I thought they could send probes out in opposite directions and get
the same baseline in 25 years.
To do a survey in all directions of the Galactic plane would require
more than two probes however. At three or four probes would do - to
solve the problem of not being able to measure stars that are near the
baseline. You could of course use Earth based equipment as one part so
maybe sending a TAU type probe in the X, Y and Z directions would
surfice!

Dear x86_64x2-ga 

Interesting comment and only one which so far in any way address's my question.
If you every get hold of the article I would love to read it.

I am a little bit puzzled as to why you think two space probes are necessary?

(same as with anseI001 comment about taking measurments at extremes
end of saturn orbits)

A space probe 1000 au away would allow measurements to be taken from
the probe and the EARTH. The baseline would be 500 times that of the
diameter of the Earth's orbit. A considerable improvement in accuracy
of parallax measurement if we can get a probe out to that distance.

Mongolia

This was proposed some years ago in a mission tentatively named "TAU"
(Thousand Astronomical Unit). The idea was to send three Pioneer or
Voyager-type spacecraft deep outside the solar system on orthogonal
axes to measure parallax. The proposal died a quiet death when the
high-quality parallax data from ESA's Hipparchos pretty much filled
our needs.

you need multiple probes because the probe cannot measure parallax in
the direction it is moving.

keithpickering

Many thanks for your comments

"you need multiple probes because the probe cannot measure parallax in
the direction it is moving."

I don't understand this statement.

Lets take the normal way parallax is measured.
a telescope photographs a relatively close star which is located near
a Quasar. 6 months later another photograph is taken. When the
photographs are compared ther will be a shift in the position of the
nearby star relative to the quasar. This is caused by the relative
distance the earth has travelled in the intervening 6 months (two
astronomical units). THe actual movement of the earth at the time the
two  photographs are take should be irrelevent (unless it were close
to speed of light)

Perhaps I am missing something in your argeement but I would have 
thought the direction or speed of the speed of the  probe is largely
irrelvent.

Regards

Mongolia