Astrometry

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Roger Stokes - 10 Dec 2003 17:00 GMT

I understand that the large and expensive Gaia astrometry satellite will
achieve very accurate stellar parallaxes from (I believe) the L2 point -
which still only gives a 2AU baseline. Why not put a cheaper, lighter, less
precise astrometry package on (say) Kuyper Express (or whatever it's called
now). It would presumably give good results once its 50-100 AU from the sun,
and it would give it something to do when it's not near the occasional KBO.

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Henry Spencer - 12 Dec 2003 22:01 GMT

>I understand that the large and expensive Gaia astrometry satellite will
>achieve very accurate stellar parallaxes from (I believe) the L2 point -
>which still only gives a 2AU baseline. Why not put a cheaper, lighter, less
>precise astrometry package on (say) Kuyper Express (or whatever it's called
>now)...

Several reasons. For one thing, you wait a decade to get a baseline
that's only a factor of ten longer, and Gaia's optics and electronics are
much more than ten times as good as a lightweight astrometry package
(bearing in mind that the Pluto mission really cannot spare much mass).

For another, you get *one* ten-times-longer baseline, which is good for
some parts of the sky and not others, while Gaia gets a set of baselines
as Earth goes around the Sun, giving you full-sky coverage.

For a third, you've got to live with the less-precise attitude control of
a spacecraft built for another purpose. And remember that Gaia wants to
spin and slowly rotate its spin axis, to scan the sky, while the Pluto
mission wants to keep its main antenna pointed at Earth.

There just isn't enough advantage to be had from the longer baseline to
be worth the extra trouble.

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MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. | henry@spsystems.net

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Space Forum / Space Flight / December 2003

Astrometry