[GlentoranMark (OP)]

I've been thinking this for some time but could we use the instruments on all 4 spacecraft to measure parralex? I know the instruments are obsolete but the baseline to the Earth is massively increased.

Would it be practical?

[SeanB]

The major problem is that these spacecraft no longer have the power to drive the cameras, as the nuclear power source they use is slowly dropping in power. As well the cameras are not really designed to operate as telescopes, they are not very sensitive, and do not have a high enough resolution to be able to get meaningful data out of them if they could be powered. They are basically a 40 year old TV camera, built very well, but still limited by the technology available at the time.

[JMLCarter]

Maybe we should send a new telescope off into deep space, something using an ion drive. Would it be able to measure parallax (err, in 20 years) - and could that be any use?

and should that be a new thread (hijacker?)?

[Soul Surfer]

The Hipparcos satellite operating between 1989 and 1993 measured the parallax and proper motions of more than 100,000 stars to better than .001 arc sec.  for full details see  http://en.wikipedia.org/wiki/Hipparcos.  These provided a precision yardstick upon which all our knowledge of distances in the rest of the universe is based.

[yor_on]

That was a incredible feat of imaginative engineering Soul Surfer. It got me curious to if it still was working but sadly it seems to have 'died' out there 1993. Hipparcos: mission accomplished