NASA figured out how to get data back from satellites orbiting the Moon — lots of data and fast. Michael Kassner looks at the technology that might eventually trickle down to earth.
NASA figured out how to get data back from satellites orbiting the Moon, lots of data and fast.
I don't recall the 1957 launch of Sputnik, but I do remember Explorer 1 being catapulted into orbit the next year. Being young, I didn't comprehend the significance. Today, I do. NASA manages to achieve what most people consider impossible.
The list of examples is long. NASA recently celebrated the anniversary of Apollo 11's lunar landing. Forty years later, that feat is still considered extraordinary: rocketing three astronauts in their spacecraft from Earth, landing on the Moon 384,403 kilometers away, and ultimately getting the trio back home.Two satellites
Once again, NASA is focusing on the Moon. On June 18, 2009, two satellites, Lunar Reconnaissance Orbiter (LRO) and Lunar CRater Observation and Sensing Satellite (LCROSS), began their journey to the Moon.
LCROSS is on a kamikaze mission. NASA plans on smashing the satellite into the Moon, creating a huge impact plume of Moon dust. Using spectrometers, scientists will analyze the plume in hopes of finding water.
LRO plans on being around longer. For the next year, the satellite will circle 50 kilometers above the moon, snapping pictures and creating high-resolution 3-D maps. Every day, LRO will send 461 gigabytes of data back to Earth-bound scientists.Math time That's a lot of data. An example may be the best way to fathom what NASA is trying to do. Let's use my Internet access. It has a download bandwidth of 6 megabits per second. First, we have to convert 461 gigabytes to megabits, which turns out to be 3,688,000 megabits. That number divided by 6 megabits per second will result in the download time. It comes to 614,666 seconds, approximately 170 hours, or seven days. Not quite good enough. One heck of a microwave
NASA needed to find a way to transmit data at a substantially higher bandwidth. NASA working with L-3 Communications Electron Technologies (L-3 ETI) came up with the solution. A traveling wave tube (TWT) amplifier with the following specifications:
"Provides 40 W of microwave power at 25.65 GHz needed to provide a 100-megabits-per-second (Mbps) Ka-band data link from lunar orbit to White Sands, New Mexico. The TWT has an RF efficiency of 50 percent, weighs 1.5 kg, and measures 370 by 90 by 90 mm."
By upping the bandwidth to 100 megabits per second, the time required to send 461 gigabytes back to Earth is reduced to a manageable 1o hours.
A rate of 100 megabits per second may not seem like much. Most 802.11n Wi-Fi radios are capable of that. Let's not forget the distance these signals are traveling. Radio signals travel at the speed of light (299,792 kilometers per second). At that speed, it still takes over a second for the signal to get back to Earth. Something Wi-Fi equipment developers aren't too worried about.Final thoughts
Like other NASA innovations, this technology will eventually trickle down to Earth-orbiting satellites and Earth-bound wireless networks. Imagine your smart phone having that kind of bandwidth anywhere in the world.