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Hi, folks, I'm Joe Gurman, the STEREO project scientist
at NASA's Goddard Space Flight in Greenbelt, MD.
STEREO, or the Solar Terrestrial Relations Observatory,
is a NASA mission consisting of 2 spacecraft, orbiting the sun in orbits just
inside and outside the Earth, with the objective of learning more
about solar activity and how it propagates through the heliosphere.
Today, we are talking about what is going with the STEREO mission.
over the next year and a half or so, that includes both a period of superior
conjunction, when the spacecraft on the other side of the sun from the Earth,
and also a longer period on the other side of that, when the Earth
the high gain antennae will have to off-pointed for once
opting toward the Earth because of a thermal problem.
During those weeks of superior conjunction for each spacecraft, the noise level
of getting their signals back will be too high, simply because
the antennae here on Earth will be looking at the sun as well as the spacecraft.
During that period, we won't be able to communicate with the spacecraft,
and after about 3 days, there's a timer on the spacecraft that will go off
and put it in safe mode. It will also turn off the power
to the instruments. And that's a period of about 15 weeks on the ahead spacecraft
and 9 weeks on the behind spacecraft. Fortunately,
those periods don't overlap. In August 2014,
we will reach a situation where the high gain antennae on the STEREO spacecraft
will be pointing back toward Earth, but seeing too much of the sun.
That means that the feed of the focus of that antennae will be getting too
hot, and we will have to start off-pointing the antennae, and using the weaker
so-called side lobes to communicate with the Earth. That means we can't
get back as much data in the given amount of time as we could before.
We are going to be carefully cherry-picking the which data we send back
during that period. That's a period of about 16 months on the ahead spacecraft
and 14 months on the behind spacecraft, and it will take us
to approximately the beginning of 2016 when we can resume
normal operations on the main lobe of the antennae. During those periods of
time, we will be down to about 7.4 kilobits a second
and 1.7 kilobits a second science telemetry.
It's worth noting that even the smaller of the 2 numbers is a
factor of 10 greater than the rate we currently get back from Voyager 2,
which is at the outer limits of the solar system. Those data are certainly
worth taking, and we believe the data from STEREO are worth taking too
as STEREO gives us the only view of what's going at the far side of the sun
and in the heliosphere on that side as well.
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