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Kepler Spacecraft Relays Star Data to Earth


NASA's Kepler spacecraft is currently located 32 million kilometers from Earth. Its mission is to discover Earth-size planets in or new the habitable zone and determine how many of the billions of stars in our galaxy have such planets. The Kepler spacecraft uses two different systems to communicate with Earth.

While it is in its "science attitude," it uses a lower data rate (10 bps to 16 Kbps) X-band system with a low-gain antenna. A Ka-band system with a data rate of up to 4.33125 Mbps using a high-gain antenna is available, but it is not pointed at the Earth while the satellite is collecting in its science attitude.

On Tuesday, April 26, NASA reoriented the Kepler spacecraft to allow use of the high-gain antenna and successfully download all data collected since March 20. The download required 45 minutes for engineering data, and 5.25 hours for 37 days of science data. In all, 93 gigabits of data were downloaded before the spacecraft was reoriented to science attitude. The project team must now wait for the spacecraft to return to the thermal condition it was in before the break. When the sun shines on a different part of the structure, it warps slightly, changing the angle between the star trackers and the telescope line of sight. The total break, including collection of calibration data, was about 17 hours, less than the 20 hours allowed per month.

The data is downlinked using NASA's Deep Space Network and sent to the Mission Operations Center in Boulder, Colo. and on to the Data Management Center in Baltimore where the raw pixel data is archived. The data is then transmitted to the Kepler Science Operations Center at NASA's Ames Research Center at Moffett Field, Calif.