100 megabytes per second from the moon

Sept. 14, 2009

by Mark Ollig

I found a new Facebook friend last week called LRO.

LRO is literally out-of-this-world.

NASA’s Lunar Reconnaissance Orbiter, or LRO, was launched June 18 and has been orbiting the moon since June 23.

The primary purpose of LRO is to perform investigations to prepare for future lunar exploration missions.

March 7, the LRO started a Facebook page and since then, 804 Facebook users have become fans of it (including yours truly).

The LRO is responsible for those recent photographs of the Apollo landing sites that NASA released.

For me, to see the landing stage of the Apollo 11 Lunar Excursion Module in 2009, 40 years from when it was last seen on the moon was incredible. ,

Over the years I had often wondered why we could not point some high-powered telescope from earth to look at those old Apollo landing sites. I found out land-based telescopes just could not get a clear enough image. And focusing the Hubble Telescope towards the moon in order to see the landing sites would have been like trying to read a newspaper with a pair of high-powered binoculars; the image would just be a blur, as the moon is simply too close to the orbiting Hubble.

Traveling along with the LRO is a 13-inch-long tube device, called a Traveling Wave Tube Amplifier, which makes it possible for scientists on earth to receive large amounts of images and data from the LRO at an extraordinarily high-speed data rate.

This device uses electrodes in a vacuum tube to amplify microwave signals. It’s ideal for sending large amounts of data over a lengthy distance because it provides more power and more efficiency than its alternative, the transistor amplifier.

With this new amplifier, the LRO can transmit 461 gigabytes of data per day. That’s more information than you can find in some libraries. And it transmits this information at a data rate of up to 100 megabytes per second.

A company called L-3 Communications Electron Technologies, built the amplifier under the supervision of NASA’s Glenn Research Center in Cleveland, OH.

I found out Traveling Wave Tube Amplifiers have been used for other space missions, such as Kepler and Cassini, but those earlier designs weren’t as powerful as this one.

Rainee Simons, who is chief of Glenn’s Electron and Optoelectronic Device Branch, said their 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.

When I was reading about the LRO, NASA kept referring to it as a “traveling wave tube amplifier in a vacuum” which gave me some pause to think back to when I was in school learning about electrical vacuum tubes with a glass envelope, and names like triodes and pentodes, which are now mostly seen in museums, I suppose.

There is no way NASA is sending old-style vacuum tube technology to the moon in 2009, I thought – but could they be?

So, what did this ever-questioning writer do? The same thing I did back in eighth grade when I was working on my science fair project about the moon while attending Holy Trinity School.

I wrote to NASA.

The person I contacted was Katherine Martin, who is with NASA’s media relations office.

She was kind enough to answer the following question I asked of her.

B&B: I would like to know if the Traveling Wave Tube Amplifier is completely “solid-state” and if the word “tube” represents the tube case the electronics are contained in, or if it has any reference to the old vacuum tube technology.

KM: “The Lunar Reconnaissance Orbiter (LRO) traveling-wave tube amplifier is a microwave vacuum electronics- based device, which operates at a center frequency of 25.65 GHz and delivers 40 watts RF power. It is not a transistor or any other solid-state device. It is not an old vacuum tube technology with a glass envelope, like the triodes and pentodes. Modern traveling-wave tube amplifiers are metal ceramic structures.”

I appreciate Kim’s help in clearing up my concerns and clarifying that NASA is definitely not using old vacuum tube technology in outer space.

For more information about the LRO moon mission, visit: http://www.nasa.gov/lro.

To become a fan of LRO on Facebook, just enter “LRO” in the search on the top right corner of the Facebook homepage and request to be a fan.

On this week’s Web Site of The Week forum, the Bits_blogger has uploaded some of the detailed pictures from the LRO mission and video of the launch, as well. Be sure to stop by and check it out.