Wednesday, August 19, 2009

The Ultimate Long Distance Communication

Anyone who's vacationed in the mountains or lived on a farm knows that it's hard to get good internet access or a strong cell phone signal in a remote area. Communicating across great distances has always been a challenge. So when NASA engineers designed the Lunar Reconnaissance Orbiter (LRO), they knew it would need an extraordinary communications system.

Over the next year, the LRO, NASA's diligent robotic scout, will collect more information about the moon's surface and environment than any previous mission. It takes a powerful system to send all of this information more than 238,800 miles back to Earth.

A 13-inch-long tube, called a Traveling Wave Tube Amplifier, is making it possible for scientists to receive massive amounts of images and data from the orbiter at an unusually fast rate. It is the first high data rate K-band transmitter to fly on a NASA spacecraft.

With this new amplifier, LRO can transmit 461 gigabytes of data per day. That's more information than you can find in a four-story library. And it transmits this information at a rate of up to 100 megabytes per second. By comparison, typical high-speed internet service provides about 1 to 3 megabytes per second.

As the orbiter collects information about the moon's geography, climate and environment, the communication system transmits this information to a receiver at a Ka band antenna network at White Sands Test Facility in New Mexico. Scientists are using the data to compile high-resolution, 3D maps of the lunar surface.

"We're sending back more data than ever, faster and it's nearly real time," said Glenn project manager Todd Peterson. Traveling Wave Tube Amplifiers have been used for other planetary missions, such as Kepler and Cassini, but previous designs were less powerful. According to Rainee Simons, chief of Glenn's Electron and Optoelectronic Device Branch, engineers had to redesign the internal circuitry of the amplifier.

"In order to provide the power and frequency needed to send communications from the vicinity of the moon, it had to be custom designed and handmade," he said.

The orbiter's Traveling Wave Tube Amplifier is also more efficient than previous amplifiers. When it comes to launching satellites, weight means money. The heavier the spacecraft, the more fuel it needs to reach orbit. Because the new amplifier packs more power into a lighter design than previous microwave amplifiers, it's cheaper to fly.

The amplifier underwent vigorous spaceflight testing -- including vibration, thermal vacuum, radiation and electromagnetic interference tests -- to ensure that it could withstand the intense conditions of launch and lunar orbit.

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