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Cassini helps calibrate NASA's communication network

Morgan Rehnberg, Correspondent
May 29, 2015, 23:49 UTC

Sen—The Cassini spacecraft might be one of the most accomplished and expensive robotic explorers ever to take to space, but even it cannot escape doing a chore every now and then. That was the situation earlier this week as the Saturn-studying mission paused its scientific observations to help perform tests on the Deep Space Network (DSN).

The DSN is the ultimate international texting plan. Three stations—spread around the Earth—handle communications between mission controllers and satellites out in the Solar System. Every week, Cassini transmits scientific and engineering data back home and receives its next batch of instructions at the blistering rate of 140 kilobits per second. That might not sound like much; it was only about a decade ago that mobile phones began to eclipse the speed with which NASA communicates to our farthest-flung explorers.

Other space agencies maintain similar networks, but none must communicate with spacecraft so numerous or distant as the DSN.

The vast nature of outer space makes this a remarkable feat. The intensity of a radio signal weakens as the square of the distance it travels. That means signals received at Saturn are about 100 times weaker than those received at Mars, even though the Red Planet is only ten times closer to Earth. To compensate, the DSN broadcasts with incredible power; this newest transmitter sent 80,000 watts Cassini’s way.

Cassini listened to ensure that the new transmitter was broadcasting with the expected signal strength. Once this was confirmed, the spacecraft returned to its observing plan—at least until its next chance to phone home from more than a billion km away.

The Cassini-Huygens mission is a collaborative effort between NASA, ESA, and the Italian Space Agency. Launched in 1997, it reached Saturn in 2004 and has since been studying the planet, its moons, and its rings. In 2005, the Huygens probe made the first landing on Titan, Saturn’s largest moon. After completing its second mission extension in 2017, Cassini will make a series of close passes to the planet and then end its time at Saturn by plunging into the planet’s atmosphere.