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Radio Occultation: Unraveling Saturn's Rings
This image was produced by sending radio signals through the rings.

If you were to shout at the top of your lungs, how far away could people hear you? How much softer would your voice be if you where behind a curtain, a thick door or a brick wall?

Cassini's Radio Science Subsystem (RSS) is designed to take measurements using radio waves beamed to Earth that explore similar concepts at a distance of more than a billion kilometers (more than 621 million miles).

"Our instrument can measure exactly how well you could hear somebody talking, and the quality of the sound traveling through whatever is between you and the speaker," explains Sami Asmar, RSS task leader. "By studying the changes in your voice as it goes through various materials, we'd learn information on the composition and characteristics of the door or the curtain behind which you'd be talking. For us, the materials are the rings of Saturn or the planet's atmosphere."

The largest instrument on the mission, RSS is split in two parts: one resides on the spacecraft, the other at stations equipped to receive very stable radio signals at each of the three Deep Space Network complexes.

Radio Science Subsystem (RSS)
The Radio Science Subsystem will perform a series of radio occultations of Saturn's rings.

The instrument's split personality allows it to measure the forces acting on the spacecraft by detecting slight changes in the frequency of radio signals sent from the spacecraft to Earth. It also measures how radio signals are affected by whatever material comes between the spacecraft and Earth -- allowing scientists to study the composition and properties of Saturn's rings and atmosphere.

The Radio Science instrument can measure changes in velocity less than a micron per second at enormous distances allowing scientists to gain information on the interior structure of the planet and its many natural satellites.

At a Glance

Cassini is the only deep space mission to transmit to Earth at three radio wavelengths (approximately 14 cm wavelength, designated S-band; 4 cm, designated X-band; and 1 cm, designated Ka-band) simultaneously. Click here for data acquisition.
    • Mass (current best estimate) = 14.38 kg
    • Peak Operating Power (current best estimate) = 80.70 W
    • Peak Data Rate (current best estimate) = not applicable: carrier only (the RSS sensing devices are on Earth at the Deep Space Stations in California, Spain and Australia)