Getting the Picture

Getting the picture is the task of the Deep Space Network. The digital data bitstream can be transmitted from a spacecraft in various frequencies and at different bitrates. The bitstream is received by huge antenna receivers at any one of the three Deep Space Network sites around the globe - Goldstone, California; Canberra, Australia; and Madrid, Spain. The data are relayed using microwave links, communications satellites, land lines, and submarine cables to the Jet Propulsion Laboratory (JPL), in Pasadena, California.

	Cassini image data are compressed by factors between 1:1 and 8:1 and use image data rates between about 40 kilobits (kbs) to 165 kbs per second. For Cassini images compressed at 2:1 and transmitted at X-band at approximately 165 kbs, here is the formula — CCD image size = 1,024 × 1,024 = 1,048,576 pixels × 12 bits per pixel × 3 filters ÷ 2 (compression ratio) ÷ 165,000 bits ÷ 60 seconds (data rate) = approximately 2 minutes to transmit the red, green, and blue images required to construct a color image.

Sending the Data to Earth
How fast do images get to Earth? Each spacecraft is different, but factors such as distance from Earth, data amount and sending rate, and type of antenna all play a part. Onboard data encoding reduces the amount of data and speeds up the transmission rate, and data compression allows retention of the most scientifically valuable information while minimizing or eliminating redundant or less valuable data.

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Images from Space | Taking the Picture | Getting the Picture
Making the Picture | Deep Space Network