Re: @ Zmodem
> heliostationary polar orbit above the sun.
Such an orbit does not exist and the only one to go "Sun poles" was Ulysses and that took a lot of slingshotting and was over fast.
At The Mission, we read:
STEREO (Solar TErrestrial RElations Observatory) is the third mission in NASA's Solar Terrestrial Probes program (STP). The mission, launched in October 2006, has provided a unique and revolutionary view of the Sun-Earth System. The two nearly identical observatories - one ahead of Earth in its orbit, the other trailing behind - have traced the flow of energy and matter from the Sun to Earth. STEREO has revealed the 3D structure of coronal mass ejections; violent eruptions of matter from the sun that can disrupt satellites and power grids, and help us understand why they happen. STEREO is a key addition to the fleet of space weather detection satellites by providing more accurate alerts for the arrival time of Earth-directed solar ejections with its unique side-viewing perspective.
So we have two sats, at 1 AU (i.e. Earth) orbit, and I would bet at the Lagrange Points.
The Jimbo's Horde page has a nice explanation, which leads to this picture of the STEREO's pair current location. So not at the Lagrange points.
To think that the budget for this probably had to be horse-traded over.