Aside from air, water and fresh vegetables, what would need to survive on the moon? One thing that would likely of feature high on the list is a decent, reliable wireless internet. And thanks to a group of researches from MIT and Nasa this kind of connectivity could be within the realms of possibility.
Between them, the two organizations have demonstrated for the first time that data communication technology is capable of providing those in space with the same kind of connectivity we enjoy on Earth, and can even facilitate large data transfers and high-definition video streaming.
To do this it uses four separate telescopes based at a ground terminal in New Mexico to send the uplink signal to the moon. A laser transmitter that can send information as coded pulses of invisible infrared light feeds into each of the telescopes, which results in 40 watts of transmitter power.
Nasa and MIT will present their findings at the CLEO laser technology conference in California on 9 June, but the findings have also been detailed by the Optical Society. The team will explain how their laser-powered communication uplink between the moon and Earth breaks previous record transmission speeds—achieved by RF signals—by a factor of 4,800.
The team has transmitted data across the 384,633km distance between Earth and the moon at a rate of 19.44Mbps and has also managed to download data at a rate of 622Mbps. “Communicating at high data rates from Earth to the moon with laser beams is challenging because of the 400,000-kilometer distance spreading out the light beam,” says Mark Stevens of MIT Lincoln Laboratory. “It’s doubly difficult going through the atmosphere, because turbulence can bend light-causing rapid fading or dropouts of the signal at the receiver.”
Each of the four telescopes used to beam the connection to the moon transmits light through a different column of air, meaning that they all experience different bending effects from the atmosphere and increasing the chance that one of them will hit the receiver, which is hitched to a satellite currently orbiting the moon. The satellite is also equipped with a telescope, which collects the laser beam and focuses it into an optical fibre. A photodetector turns the pulses of light into electrical pulses, and from there they are converted into data.
It all sounds a bit hit and miss, and indeed less than a billionth of a watt from the 40-watt signal is actually received by the satellite. Fortunately, that is ten times the amount of signal needed for reliable communications, according to Stevens.
When they present their findings at CLEO, the researchers will comment on the importance of the lasers being able to operate through thin clouds in the Earth’s atmosphere. They will also explain how while the system has been designed for near-Earth missions, they have predicted it would also be able to be used on deep-space missions to Mars and other planets.