Perfect approach of communication in Space …
In space communication is very difficult for obvious reasons but most importantly required the most proven medium is Laser-based data transmission. The use of lasers for telecommunications in space is an application of laser communications and visible light communication. In outer space, the communication range of free-space optical communication is currently of the order of several thousand kilometers, but has the potential to bridge interplanetary distances of millions of kilometers, using optical telescopes as beam expanders and laser beams transmits data perfectly & precisely.
For years, laser light has been merely a system for piping light around corners and into the inaccessible places to allow the hidden to be lighted. But now, laser light has evolved into a system of significantly greater importance and use. Throughout the world, it is now being used to transmit voice, television and data signals as light waves. Its advantages as compared with conventional coaxial cable or twisted wire pairs are manifold. As a result, millions of dollars are being spent to put these light wave communication systems into operation. Interest in fiber as a medium began in 1966 when C. Kao and G.A. Hock ham at Standard Telecommunications Laboratory predicated that by removing the impurities in the glass, 20 dB/km attenuations would be achievable. One of the most interesting developments in recent years in the field of telecommunication is the use of laser light to carry information over large distances. It has been proved in the past decade that light wave transmission through laser light is superior to transmission through other lights. Typically, laser light has a much lower transmission loss per unit length (0.15-5db/km) and is not susceptible to electromagnetic interference. Economically also, it serves our purpose. The ever increasing cost and the lack of space available in the congested metropolitan cities asks for advent of a less costly laser system.
Benefits of Laser Communication
- Higher Availability – Wireless bridges often provide high availability over leased lines offering five nines availability and rapid response to fault finding a down link.
- High Bandwidths – Wireless laser bridges can offer up to 10 gbps bandwidth which is often greater than leased lines with a lower total cost of ownership
- License Free Operation – Unlike radio wireless bridges, free space optic links do not require a license from OFCOM. This is because they do not operate within radio frequencies.
- Compact & Discreet – The hardware is small and compact and suitable for discrete application street-level deployments in challenging high density environments.
- Rapid Deployment – Leased lines can have a 3-4 month lead time to install. Laser links can be designed and installed within minimal time scales.
- Immune from RF Interference – Ideal for areas where the use of leased lines is expensive and where high noise levels can interfere with radio transmitted data.
Laser communication in space
The first gigabit laser-based communication was achieved by the European Space Agency and called the European Data Relay System (EDRS) on November 28, 2014. The initial images have just been demonstrated, and a working system is expected to be in place in the 2015-2016 timeframe. NASA’s OPALS announced a breakthrough in space-to-ground communication December 9, 2014, uploading 175 megabytes in 3.5 seconds. Their system is also able to re-acquire tracking after the signal was lost due to cloud cover. In January 2013, NASA used lasers to beam an image of the Mona Lisa to the Lunar Reconnaissance Orbiter roughly 390,000 km (240,000 mi) away. To compensate for atmospheric interference, an error correction code algorithm similar to that used in CDs was implemented. The distance records for optical communications involved detection and emission of laser light by space probes. A two-way distance record for communication was set by the Mercury laser altimeter instrument aboard the MESSENGER spacecraft. This infrared diode neodymium laser, designed as a laser altimeter for a Mercury orbit mission, was able to communicate across a distance of 24 million km (15 million miles), as the craft neared Earth on a fly-by in May, 2005. The previous record had been set with a one-way detection of laser light from Earth, by the Galileo probe, as two ground-based lasers were seen from 6 million km by the out-bound probe, in 1992.
Secure Communications Using Laser
Secure communications have been proposed using a laser N-slit interferometer where the laser signal takes the form of an interferometric pattern. Any attempt to intercept the signal causes the collapse of the interferometric pattern. This technique has been demonstrated to work over propagation distances of practical interest and, in principle, it could be applied over large distances in space. Assuming available laser technology, and considering the divergence of the interferometric signals, the range for satellite-to-satellite communications has been estimated to be approximately 2000 km. For space vehicles or space stations, the range of communications is estimated to increase up to 10000 km.
Laser Revolution in Space Communications
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 Laser. 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 and the ground segments. 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. 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 less crowded bands.
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.
NASA installs space laser on the ISS
NASA has successfully completed the first test of the International Space Station’s new OPALS laser communications system. OPALS link the ISS to an observatory here on Earth at very high speeds, allowing for the real-time transmission of high-resolution video among other things. This is orders of magnitude faster than existing radio-based links, and is a significant step forward for future space exploration. If we ever want a real-time video feed from the surface of Mars — or if you ever want to have an intergalactic Skype call with your loved ones after humanity colonizes the Milky Way — then lasers, and other advanced communications technologies, will be required. OPALS are essentially a self-contained laser turret, with a two-axis gimbals that’s used for very accurate targeting. As ISS comes over the horizon, Table Mountain Observatory turns on an optical beacon that OPALS locks onto. Because the ISS orbits at such a low altitude it’s only in contact with the observatory for approximately 100 seconds. The most complex part of OPALS is keeping the laser on-target for the full duration. During that 100-second window, OPALS modulates a 2.5-watt infrared (1550nm) laser with digital data — in this case, a repeating loop of a 30-second. During the first test, the laser link was maintained for 148 seconds, transferring a total of around 1 gigabyte of data — a transfer rate of around 6MB/sec, or a link speed of around 50 Mbps. NASA says it would’ve taken more than 10 minutes to transfer the same amount of data via traditional S-band and Ku-band radio links. NASA is rather excited at the prospect of using lasers instead of radio links. An OPAL follows on from the success of LADEE last year, which beamed data back from the Moon at 600Mbps. Both OPALS and LADEE are important steps towards future probes and rovers that will travel deep into the cosmos and use lasers to beam high-resolution scientific data back to Earth. So you have some idea, the Mars Reconnaissance Orbiter — which relays data from Curiosity — has one of the fastest deep-space radio links, and it maxes out at just 6Mbps. If it was capable of 50Mbps or 600Mbps we’d be able to learn a lot more about the red planet. Likewise, if humanity ever colonizes some other planets, we’re going to need something a lot better than radio waves if we want to build a high-bandwidth galnet.
Conclusion
Laser communication for Space will definitely sees a bright future for its advantages and un-explored possibilities. May be in 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.
