Laser communications

DID YOU KNOW?

Alexander Graham Bell believed the photophone – a device that transmits speech via light – was his best invention

Laser communications

Find out how the LADEE probe is experimenting with a new-and-improved way to keep in touch with astronomers on Earth as it studies the Moon

During its time in the Moon’s orbit, NASA’s LADEE (Lunar Atmosphere and Dust Environment Explorer) spacecraft is carrying a Lunar Laser Communication Demonstration (LLCD) as part of its payload. This space terminal is designed to perform much better than traditional radio communications systems, beaming signals fi ve times faster from the Moon to Earth.

On the spacecraft end, there’s a 0.5-watt laser that fi res through a ten-centimetre (3.9-inch) telescope, sending a laser beam encoded with data the 384,400 kilometres (238,855 miles) back to Earth. This works in much the same way as data is transmitted via infrared lasers in fi bre-optic cables on the ground. The main station, or Lunar Lasercom Ground Terminal, is located in White Sands, New Mexico, and houses eight telescopes: four 15-centimetre (six-inch) refracting telescopes to send data and four 40-centimetre (16-inch) refl ecting telescopes to collect and focus the beam.

LADEE launched on 6 September 2013 from NASA’s Wallops Flight Facility, Virginia, and a series of LLCD experiments are scheduled to begin in late-2013 and continue into early-2014. If the LLCD is successful, laser communications could become the new standard, leading to faster, more cost-effective and more effi cient communication throughout space.

LADEE’s payload

LADEE has three scientifi c instruments along with the LLCD, which will interact with a terrestrial terminal

UVS

The UV-Vis Spectrometer (UVS) looks to pin down the composition of the lunar atmosphere by studying light signatures.

No one-trick pony

In addition to the LLCD, LADEE carries three scientifi c instruments. The LDEX, or Lunar Dust EXperiment, will measure dust on the Moon. The Neutral Mass Spectrometer (NMS) will study the composition, density and time variability of the exosphere, and the Ultraviolet and Visible Light Spectrometer (UVS) will look at the composition of the lunar atmosphere.

LADEE’s mission goals include documenting the dust environment in order to help design future missions and also attempt to solve the mystery of whether the Apollo astronaut sightings of diffuse emissions above the surface were lunar dust, or an electrically charged sodium glow. The spacecraft will orbit around the Moon’s equator for 100 days.

LDEX

The Lunar Dust EXperiment (LDEX) directly collects and analyses dust from the Moon’s outer atmosphere.

LLCD

The LLCD experiment sends and receives data using pulsed beams of light, much faster than radio signals.

Transmitting telescopes

Smaller telescopes on the ground refract the laser beam to transmit data back to the LLCD.

NMS

The Neutral Mass Spectrometer (NMS) measures fl uctuations in the exosphere of the Moon across different orbits.

LADEE launched on a Minotaur rocket on 6 September 2013

Receiving telescopes

The larger telescopes at the ground station refl ect and refi ne the laser beam from the LLCD.