LLCD (Lunar Laser Communications Demonstration) space mission launched in September 2013 is NASA’s first step to try to revolutionize the current space communication world needy of a higher data rate. This fact led NASA to explore the Free Space Optics communications transmitting data throughout LASERs (Light Amplification by Stimulated Emission of Radiation). Related to the mission two main elements can be distinguished in LLCD when communicating: the spacecraft called LADEE which is orbiting and collecting information around the moon (images, video, dust particles, …) and the ground segments (three Earth stations responsible of sending and receiving data from the spacecraft).

LLCD Mission (Credits: NASA)

LLCD Mission (Credits: NASA)

“new form of communications in space”

This mission establishes the ability to encode data onto a beam of laser light and validating a new form of communications in space: “Laser communications.” This term refers to the use of the Laser light as the medium for data transmission. Actually, LLCD is operating in the near-infrared portion of the electromagnetic spectrum – in the realm of light photons – which are small packets of electromagnetic waves. The particularity of photons is that when they are transmitted together “in synch”, they form what is commonly known as a LASER beam.

“radio and microwave bands of the electromagnetic spectrum are getting close to capacity”

For many years, space communication networks have relied on the use of radiofrequency (RF) waves to transmit critical and space data from spacecraft to Earth. However, RF technology has struggled to meet the data rate demands of present and future space missions.  These constraints on NASA’s systems are expected to grow in an exponential way, over the coming decades. As a result, the radio and microwave bands of the electromagnetic spectrum are getting close to capacity. So, to work this issue out, NASA is exploring the use of laser-based communications technologies that will enable NASA to work within a less crowded bands.

“no absorption, no interferences, no chromatic aberration and neither any temperature troubles”

Dr. Julien Perchoux

Dr. Julien Perchoux

According to LASER professor J.Perchoux “One of the reasons why using LASERs in space communications is the enhance of data rate, because there is no absorption, no interferences, no chromatic aberration and neither any temperature troubles”. However, that’s not all, other important facts for exploring laser communications in space is the development of more efficient, cost-effective communications equipment.

In fact, because RF wavelengths are longer, the size of their transmission beam covers a wider area. Thus, receiving antennas for RF data transmissions must be extremely large. Nevertheless, LASER wavelengths are 10,000 times shorter, allowing data to be transmitted across tighter beams. The smaller wavelengths of laser-based communications are more secure, delivering the same amount of signal power to much smaller collecting antennas (point-to-point communication). This reduction in antenna’s size is applied for both ground and space receivers, which reduces also that from the satellite, along with cost and mass.

Therefore, Laser communication terminals can support higher data rates with lower mass, volume, power requirements, and cost savings for future missions. Actually, when using RF we would take 639 hours to download an average-size HD movie, however, with LLCD laser technology this will be done in only 8 minutes, which is approximately five thousand times quicker.

The first positive results have already been obtained, so maybe in a not so distant future, we will be able to watch a 3D HD video from the Moon or communicate in real-time with Mars or even beyond the Solar System. Besides, according to professor J.Perchoux “these kinds of communications also will need new communication protocols to be developed”. What is certain is that lot of expectation is surrounding this mission, but only the future will determine its true relevance.

Interviewee: Julien Perchoux, CNRS-LAAS researcher and Optoelectronic teacher at INP-ENSEEIHT


NASA LLCD Project Page

NASA Facts article about LLCD