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Monday, March 9, 2015

Solar Dynamics Observatory

Magnetic Flux on the surface of the Sun. NASA photo.
Solar material traces out magnetic fields emanating from the surface of the sun. They show up as white lines in this image that was made by combined data from two sensors.

The SDO (Solar Dynamics Observatory) is in a geosynchronous orbit, but it is not stationary relative to the Earth's surface like the communications satellites. The plane of its orbit is inclined relative to the Earth so that it almost always has the sun in view. However, in three months things will have changed 90 degrees and the satellite will now be passing through the Earth's shadow once a day.

One of two antennas dedicated to round-the-clock reception of data from the Solar Dynamics Observatory. Each antennae is almost 60 feet in diameter. Photo by Tim C. Gregor.
The SDO is dumping a terabyte of data through a dedicated downlink, using a pair of antennaes at the White Sands Missile Range in New Mexico. While the satellite is not perfectly still relative to the Earth, it doesn't move very fast. Since it is geosynchronous, the longitude doesn't change, but since the orbit is inclined, the elevation is going to slowly oscillate with a period of a year. You could probably get by with going out and adjusting the antennae with a wrench once a day.

A terabyte of data used to be large. Now you can buy 3 terabyte disk drives for $100. Still, SDO is going to be filling them up quickly, dumping a boat load of data down the link every day, day after day, year after year. And this is just one satellite. NASA must have a really big server farm.

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