Laser-based communications has the ability to beam enormous amounts of data at high speed, but the use of this technology in space is still in its infancy. To help push things along, ESA’s proposed Asteroid Impact Mission (AIM) will carry out a record-setting demonstration of space laser communications across a distance of 75 million kilometers (46 million mi) while orbiting a binary asteroid.
One of the major bottlenecks in deep space exploration is the primitive nature of the communications systems. Presently, all deep space missions use radio systems developed in 1960s that are incapable of handling the huge distances and massive amounts of data that current spacecraft must contend with. The result is that missions like New Horizons, which is now speeding beyond the orbit of Pluto, will take 16 months to transmit back data collected during its very brief flyby of the dwarf planet.
One of the most promising ways of solving this problem is to replace or augment radio links with lasers. These have inherent advantages over radio, not the least of which is that they have a much greater bandwidth capacity and their ability to produce a narrow, coherent beam means that they use less power over longer distances – a prime concern for spacecraft that often have to make do with power levels usually associated with incandescent bulbs.
So far, such technology has been tested from lunar orbit by NASA's LADEE mission, from near-Earth orbit from the International Space Station, and will be further tested next year on a CubeSat mission. Now, ESA want to take the technology to the next level by transmitting laser-borne data from deep space across millions of miles.
Still awaiting approval from ESA’s Ministerial Council by December 2016, AIM is one of two spacecraft that make up the Asteroid Impact & Deflection Assessment (AIDA) mission, which is a joint project by ESA, the German Aerospace Center, Observatoire de la Côte d'Azur, NASA, and the Johns Hopkins University Applied Physics Laboratory.
AIDA consists of the NASA-developed Double Asteroid Redirection Test (DART) and AIM. This deep-space technology demonstration mission is designed to not only be the first to explore a double asteroid, but also to test the feasibility of deflecting an asteroid should it prove a menace to Earth or a general hazard to space navigation.
The idea is that the DART spacecraft will impact the smaller of the two asteroids that make up (65803) Didymos. Meanwhile, AIM, which will orbit the larger body, will record the event and calculate the degree of deflection caused by the strike. In addition, AIM will also study the asteroids and carry out technology experiments, such as long-range laser communications.
The laser communications system weighs in at 39.3 kg (86.6 lb) and is built around a 13.5 cm (5.3 in)-diameter laser telescope transmitter. This helps focus the high-frequency laser into a tight beam that spreads out to a width of only 1,100 km (683 mi) after traveling 75 million km (46 million mi) to Earth. ESA says that a radio beam would spread out to a diameter larger than the entire Earth.
Meanwhile, the 1-m (39 in) receiver telescope back on Earth will use a sophisticated photon counter to assess the signal reliability, so engineers can determine ways to improve the quantity and speed of data returned. To aid in this, ESA has already issued technology pre-development contracts to address key areas such as telescope design, detector electronics, and coarse and fine-pointing systems needed to align the transmitter and receiver on a spot in the sky equivalent of the width of the planet Mars as seen from Earth.
In the spirit of waste not, want not, the agency says it will also be use the AIM laser as an altimeter to help map the topography of Didymos.
"Optical communications in general is not yet a well-established technology for space and ESA’s European Data Relay System (EDRS) will be the first commercial application," says ESA optics engineer Zoran Sodnik. "In principle it works something like Morse code, with encoded rapid flashes on and off. ERDS with satellites in high orbits will use laser links to return environmental data from Europe’s low-orbiting Sentinel satellites on a real-time basis, a technique previously demonstrated using ESA’s Alphasat and Artemis telecom missions.
"In 2013 ESA’s Optical Ground Station in Tenerife participated in a two-way contact with NASA’s LADEE lunar orbiter, across 400,000 km (250,000 mi). But AIM will need to operate much further: we are benchmarking a maximum span of 75 million km, or half the distance between Earth and the Sun. That might sound like a lot, but operating around Mars one day will involve much further distances still."
Source: ESA