Go­ing On­line? Just Call Up the Near­est Laser Drone...

World­wide, four bil­lion peo­ple do not have In­ter­net ac­cess – yet. But from an al­ti­tude of 27 km, huge drones are to en­sure fast wire­less In­ter­net to the en­tire world with laser light that flashes up to one bil­lion times per sec­ond.

Science Illustrated - - TECHNOLOGY -

One sum­mer morn­ing in 2016, the peace of Ari­zona’s desert is in­ter­rupted by four ro­tat­ing pro­pel­lers that ac­cel­er­ate along a run­way, rest­ing on a metal sup­port on wheels. Shortly af­ter, a 42-m-wide air­craft lets go of the metal sup­port to take off, as­cend­ing up through the air lay­ers. The craft is a drone shaped like a huge, thin boomerang whose ends bend up­wards. In spite of its size, the drone is not to carry nei­ther goods, nor hu­mans. In­stead, it will use laser beams to sup­ply fast In­ter­net to the four bil­lion peo­ple in the world who do not have In­ter­net cov­er­age.

96 min­utes later, the plane lands again, and so, the first test flight of Face­book’s huge Aquila drone has been com­pleted. 112 years af­ter the Wright broth­ers' first flight be­came the be­gin­ning of a more con­nected world, Face­book has reached an im­por­tant mile­stone in its In­ter­net.org project, which is to form closer con­nec­tions be­tween the peo­ple of the world to­gether. Swarms of in­ter­con­nected drones with a hy­per-ef­fi­cient, aero­dy­namic struc­ture make up an im­por­tant el­e­ment of the am­bi­tious plans, whereas the de­vel­op­ment of his­tory’s first fly­ing In­ter­net net­work car­ried by fast-flash­ing laser trans­mit­ters makes up an­other one. In com­bi­na­tion, they could be the so­lu­tion to how to fill the In­ter­net "gaps" in Africa, South Amer­ica, Asia, etc., where in­suf­fi­cient in­fra­struc­ture and im­pass­able ter­rain make it un­prof­itable or im­pos­si­ble to lay down In­ter­net ca­bles.

Noth­ing is su­per­flu­ous

Prior to the test flight, Face­book has spent about two years de­vel­op­ing a drone, that, in its com­plete ver­sion, is meant to fly non­stop for 90 days – only pow­ered by so­lar en­ergy. The engi­neers aim to cre­ate a plane stripped of all un­nec­es­sary equip­ment such as a cabin and land­ing gear. The drone is pro­pelled by four mo­tors that con­sume 5,000 watts – cor­re­spond­ing to a mid-size heat pump. The en­ergy is gen­er­ated by so­lar cells cover­ing the en­tire un­der­side of the wing. The body is made of ul­tra-light car­bon fi­bre, so Aquila only weighs 450 kg.

Usu­ally, air­craft carry much more weight, re­quir­ing much more speed for the wings to pro­duce suf­fi­cient lift. Aquila’s low weight does not only ben­e­fit the lift, it also al­lows the drone to ma­noeu­vre at low speeds and very high al­ti­tudes. It can fly from 130 to 15 km/h up against the wind and at al­ti­tudes of up to 27 km. In com­par­i­son, a com­mer­cial air­liner typ­i­cally flies 700-1,000 km/h and never higher than 12 km.

Flash­ing laser light sends data

Dur­ing Aquila’s first land­ing on a gravel plain in the desert, the land­ing cal­cu­la­tions were in­ter­rupted by a wind gust, caus­ing con­sid­er­able bruises. So, engi­neers are still

op­ti­mis­ing the drone, as they are de­vel­op­ing the project’s sec­ond leg: com­bined laser trans­mit­ter and re­ceiver units, which are to carry the In­ter­net sig­nal from one drone to the next – and the next.

They are work­ing with a tech­nol­ogy known as Free-Space Op­ti­cal Com­mu­ni­ca­tion, FSO. Laser light im­i­tates ra­dio waves which are nor­mally used to trans­mit data be­tween routers, smart­phones, and more. In an or­di­nary WiFi net­work, data is con­verted into ra­dio waves by ad­just­ing the waves’ ac­cu­rate fre­quen­cies and when they start and stop. A unit such as a smart­phone de­codes the waves, and shows the de­sired con­tent in the dis­play. In an FSO net­work, ac­ti­vated and de­ac­ti­vated laser light pro­duces the 1s and 0s, which make up the bits, which com­bine into doc­u­ments, im­ages, and video on the In­ter­net.

The laser units work by a diode send­ing a sig­nal through the cen­tre of a lens. At the same time, the lens fo­cuses ex­ter­nal laser light onto a photo de­tec­tor be­hind the laser diode, which de­codes the fre­quency and in­ten­sity of the light flashes, con­vert­ing them into bits. The lasers of the Aquila drones flash bil­lions of times per sec­ond and can hence send huge quan­ti­ties of data very ac­cu­rately be­tween them across many kilo­me­tres. Ac­cord­ing to Face­book, they can hit an area the size of a coin from a dis­tance of 10 km.

Al­ti­tude en­sures free pas­sage

As the name im­plies, Free-Space Op­ti­cal Com­mu­ni­ca­tion re­quires that noth­ing in­ter­feres with the light pass­ing be­tween trans­mit­ter and re­ceiver. So, FSO data trans­fer has par­tic­u­larly been used for com­mu­ni­ca­tion be­tween satel­lites and in space. Close to Earth, the tech­nol­ogy has been lim­ited, be­cause it is dif­fi­cult to achieve high data speeds across long dis­tances due to dis­turb­ing air par­ti­cles such as fog and rain.

In this case, laser light is markedly dif­fer­ent from ra­dio waves, which can func­tion through the walls of a house. This is be­cause of the waves’ dif­fer­ent lengths and fre­quen­cies. An or­di­nary WiFi router's ra­dio waves are usu­ally rel­a­tively long – such as 12.5 cm for the most or­di­nary fre­quency of 2.4 GHz. FSO data trans­fer uses in­frared light, whose wave­lengths are only 700-1000 nanome­tres and fre­quen­cies of 300 GHz-430 THz, near to vis­i­ble light. Waves with such mi­nor lengths face a greater risk of in­ter­act­ing with air par­ti­cles and so weak­en­ing the sig­nal. The par­ti­cles block out the light, mean­ing that bits of the data pack­ets fail, and the dig­i­tal con­tent such as an im­age will not reach the user in per­fect shape. The prob­lem dis­ap­pears at Aquila’s work­ing al­ti­tude of 18-27 km above Earth, where the con­cen­tra­tion of par­ti­cles only makes up 5 % of the con­cen­tra­tion at sea level. So, FSO is very ef­fi­cient. The drones can trans­fer data at up to 30 gi­ga­bits per sec­ond

be­tween them – that is about 30 times faster than or­di­nary In­ter­net con­nec­tions on Earth, which rarely ex­ceed 100 megabits/sec­ond.

High fre­quency, no bot­tle­necks

When the drones have taken flight, they are hooked up with the phys­i­cal In­ter­net via ca­bles and an­ten­nas on the ground, and Face­book is also in­no­va­tive in this re­spect. The com­pany aims to send the sig­nal to the drones from an­ten­nas by means of mil­lime­tre waves. They cover fre­quen­cies of 30-300 GHz and are a cross­breed be­tween ra­dio waves and in­frared light. More specif­i­cally, they will make use of the E band, which uses fre­quen­cies of 60-90 GHz – un­like the WiFi net­work of about 2.4-5 GHz. The broad spec­trum of fre­quen­cies en­sures that the net­work will not be over­loaded – such as the WiFi net­work of a café will eas­ily be in case of many users at the same time. The E band has ex­isted since the 1970s, but be­fore Face­book’s engi­neers re­fined it, it was both en­ergy and space-in­ten­sive: a tech­nol­ogy that was not at all suited for a drone.

In the most re­cent tests with mil­lime­tre waves, Face­book has sent data to a plane at an al­ti­tude of 6000m at speeds enough to stream 4,000 HD films at the same time. It is also mil­lime­tre waves that are to send the In­ter­net sig­nal from the drones to the re­ceiver units and on to the users’ smart­phones or com­put­ers on the ground.

Tech giants con­nect the world

Face­book sees a ma­jor de­vel­op­ment po­ten­tial in sup­ply­ing In­ter­net to all peo­ple in the world, get­ting four bil­lion new po­ten­tial cus­tomers. But the com­pany is not alone. Other tech com­pa­nies such as Google and SpaceX are de­vel­op­ing bal­loons or satel­lites with the same aim. Aquila’s cur­rent cli­max was reached on 22 May 2017, when it flew in a clear, sunny sky for 106 min­utes, be­fore land­ing as it was sup­posed to on a plain al­most un­harmed. If Face­book reaches its goal of build­ing drones that can fly for 90 days and com­mu­ni­cate via FSO, it will be two ma­jor mile­stones for drone and com­mu­ni­ca­tion tech­nol­ogy, re­spec­tively. More­over, Aquila can be used for sci­en­tific re­search, etc., which re­quires the mon­i­tor­ing and study­ing of large re­gions at the same time and over long pe­ri­ods of time.

How­ever, the im­me­di­ate in­ten­tion of the global In­ter­net so­lu­tions is to make sure that farm­ers in South Su­dan have ac­cess to weather fore­casts and girls in Pak­istan have ac­cess to an en­cy­clo­pe­dia – and to con­nect any desert, moun­tain peak, and jun­gle – in short, bring­ing the world closer to­gether. So, Face­book or one of its ma­jor com­peti­tors will close the ring that the Wright broth­ers ini­ti­ated in 1903.

The drone flew for 96 min­utes. The aim is 90 days of non-stop flight.

Aquilla’s first test flight took place from a metal sup­port on wheels pulled by a large ve­hi­cle.

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