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HindustanTimes Thu,24 Apr 2014

World

NASA beams Mona Lisa to Moon with laser
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Washington, January 18, 2013
First Published: 16:38 IST(18/1/2013)
Last Updated: 16:38 IST(18/1/2013)

In a major advance in laser communication, NASA scientists have beamed a picture of Leonardo da Vinci's masterpiece, Mona Lisa, to a powerful spacecraft orbiting the Moon.

The first laser signal carrying the iconic image, fired from an installation in Maryland, beamed the Mona Lisa to the Moon to be received 384,400 km away by NASA's Lunar Reconnaissance Orbiter (LRO), which has been orbiting the Moon since 2009.

The Mona Lisa transmission is a major advance in laser communication for interplanetary spacecraft, NASA scientists said.

By transmitting the image piggyback on laser pulses, the team achieved simultaneous laser communication and tracking.

The success of the laser transmission was verified by returning the image to Earth using the spacecraft's radio telemetry system.

"This is the first time anyone has achieved one-way laser communication at planetary distances," said Lunar Orbiter Laser Altimeter, LOLA's principal investigator, David Smith of the Massachusetts Institute of Technology.

"In the near future, this type of simple laser communication might serve as a backup for the radio communication that satellites use. In the more distant future, it may allow communication at higher data rates than present radio links can provide," he said in a statement.

Typically, satellites that go beyond Earth orbit use radio waves for tracking and communication. LRO is the only satellite in orbit around a body other than Earth to be tracked by laser as well.

"Because LRO is already set up to receive laser signals through the LOLA instrument, we had a unique opportunity to demonstrate one-way laser communication with a distant satellite," says Xiaoli Sun, a LOLA scientist at NASA Goddard.

Precise timing was the key to transmitting the image. Sun and colleagues divided the Mona Lisa image into an array of 152 pixels by 200 pixels. Every pixel was converted into a shade of gray, represented by a number between zero and 4,095.

Each pixel was transmitted by a laser pulse, with the pulse being fired in one of 4,096 possible time slots during a brief time window allotted for laser tracking. The complete image was transmitted at a data rate of about 300 bits per second.

The laser pulses were received by LRO's LOLA instrument, which reconstructed the image based on the arrival times of the laser pulses from Earth.

This was accomplished without interfering with LOLA's primary task of mapping the Moon's elevation and terrain.


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