Orbiting high over the lunar surface is LADEE, the Lunar Atmosphere and Dust Environment Explorer, with a mission to probe the moon’s exosphere and dust clouds. It will take readings using a number of spectrometers and specialized equipment, piling up stores of data as quickly as it can manage. In just 100 days of primary operation, it will compile enough information to change how we understand our only moon — but how to get that data back to us? File sizes have ballooned as sensing technology has advanced, but as of last year NASA could only download those files at about 10 kilobytes per second; even if we were so cruel as to ask the astronauts to go without streaming Game of Thrones premieres, the simple science demands a better, faster solution.
This week, NASA successfully tested just such an alternative, replacing traditional radio communications with specialized lasers and laser detection units. The Lunar Laser Communications Demonstration (LLCD) spent about 30 days sending information between lunar orbit and three receiving stations in the US and Spain. At an orbital distance of over 400,000 kilometers, this is a respectable distance over which to test communications — but Mars lies between 50 and 400 million kilometers from Earth, so don’t get cocky.
Last October, the LLCD was clocked at 622 megabits per second — or over 75 megabytes per second — but this 30-day test was a much more comprehensive check of its utility for all-purpose communication. This time, rather than simply downloading a pre-arranged file, NASA used the device for real communication with LADEE, and real collection of data. The lunar dust experiment was able to wake the LLCD in order to get its messages to Earth, an automated process that went off without a hitch, legitimizing its use for general-purpose missions. Check out a short video announcement from NASA’s Charles Bolden, the file of which was transmitted to the moon and back before posting to YouTube.
It took NASA just five minutes to transfer a gigabyte of information, and in fact the limiting factor in transfer speed turned out not to be the LLCD’s transmission from the moon to the Earth, but LADEE’s transmission to the LLCD just a few short miles away. This means that not only is the LLCD a workable solution today, but it already has a certain amount of future-proofing built in, ready to take advantage of speed upgrades in the components around it.
This latest test looked for more than just raw download speed, prioritizing things like signal reliability and accuracy, along with possible distance effects. There were quite a few problems that could have hurt this technology’s chances, but none seem to have materialized as a major issue. Even in broad daylight and through light clouds, the laser signal could be read without error. NASA was reportedly surprised to find so few impediments to their new laser ideas, finding that it worked well even at extremely oblique angles, when the satellite near the Earth’s horizon and its signals were forced to move through the thickest portions of the atmosphere. Thick clouds, or anything that blocks the majority of visible light obviously stops the lasers cold.
The LLCD is hardly the only method of space communication that suffers periods of black-out, and in general the LLCD represents not just an upgrade in bandwidth but also in versatility. The downside is, as mentioned, range; simply boosting power to the laser to make it cohere better over a longer distance is a losing game. A more reasonable solution, and one that NASA just so happens to be ramping up as their next experiment in this line, is the Lunar Communications Relay Demonstration (LCRD). This would see NASA pepper space with laser-routers to read and re-transmit laser signals from a new transmitter.
Even if NASA never significantly increases the range of these individual transmitters (unlikely), it will still only take a handful of them to allow total communication with Mars. Additionally, the more the agnecy launches, the easier it becomes to expand the system as a whole; the comms system is designed to be a general-purpose routing network, rather than a hardline from Mars to Earth.
These sorts of upgrades aren’t the sexiest, since they don’t directly reveal anything about the universe or allow us to explore some previously inaccessible portion of our solar system. On the other hand, they make our current efforts immensely faster and, more importantly, allow NASA to plan future missions without restrictions. Data is quickly becoming the most important commodity on Earth — which makes LLCD a gold mine in space.