Turn up your STEREO

Contributed by
Oct 26, 2006

Last night as I write this, NASA successfully launched the STEREO satellite (Solar TErrestrial RElations Observatory), a mission to observe the Sun literally in 3D. STEREO is actually two satellites: one will orbit the Sun ahead of the Earth, and the other behind. Since the angles to the Sun will be different for the two spacecraft, they can make observations that can be assembled into a three-dimensional view of our nearest star. Each probe packs a suite of instruments to look at how the Sun's magnetic field is able to lift off and launch vast amounts of solar plasma out into space. These coronal mass ejections can travel as fast as a million miles per hour, and can damage satellites in Earth orbit. This "space weather" makes long term space travel difficult, and NASA is pretty serious about understanding how all this works. STEREO is a big step toward that.

I'm fascinated by STEREO's orbit, too. Both spacecraft will use the Moon to swing them out into solar orbit, what's called a "walkaway" orbit. Instead of being at a constant distance from Earth, they will, over time, drift away from the Earth, moving out about 22 degrees per year:

So, as time goes on, the angle between the two probes will increase. Eventually they'll both be on the other side of the Sun as seen from Earth! That won't happen for about 8 years, looks like, and the nominal mission profile is for two years. Usually, if a mission does well, it gets extended. But this one has a built in terminal stage! This is all pretty cool, and I'm very interested in seeing the images once they come down... but it'll be a few months. First the probes need to be swung by the Moon, and that won't happen for two months, and even then it'll be a little while before the scientists and engineers can shake down the spacecraft and make sure everything is working up to snuff.

My congratulations to the STEREO team!

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