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  • This episode of Real Engineering is brought to you by Brilliant, a problem solving website

  • that teaches you to think like an engineer.

  • On the 24th of May, SpaceX launched a Falcon 9 rocket filled with 60 satellites into space.

  • This marked the beginning of their ambitious new project calledStarlinkwhich aims

  • to provide high quality broadband internet to the most isolated parts of the planet,

  • while also providing low latency connectivity to already well connected cities.

  • [1] SpaceX aim to make their broadband as accessible as possible, claiming that anyone

  • will be able to connect to their network if they buy the pizza box-sized antenna which

  • SpaceX is developing themselves.

  • This launch of 60 satellites, was just the first of many.

  • Spacex has 12,000 satellites [12] planned for launch over the next decade, dramatically

  • increasing the total amount of spacecraft around Earth's orbit.

  • This will cost SpaceX billions of dollars, so they must have a good reason for doing

  • so.

  • Let's see how this network will work, and how it will compete with existing internet

  • providers.

  • Back in 2015, Elon announced that SpaceX had began working on a communication satellite

  • network, stating that there is a significant unmet demand for low-cost global broadband

  • capabilities.

  • Around that time, SpaceX opened a new facility in Redmond, Washington to develop and manufacture

  • these new communication satellites.

  • The initial plan was to launch two prototype satellites into orbit by 2016 and have the

  • initial satellite consetllation up and running by 2020.

  • But the company struggled to develop a receiver that could be easily installed by the user

  • for a low cost, this delayed the program and the initial prototype satellites weren't

  • launched until 2018.

  • After a successful launch of the two prototypes, Tintin-A and B, which allowed SpaceX to test

  • and refine their satellite design, SpaceX kept pretty quiet about what was next for

  • the Starlink project, until November 2018 when SpaceX received the approval from the

  • FCC to deploy 7,500 satellites into orbit, on top of the 4,400 that were already approved.

  • On May 24th, the first batch of production satellites were launched into orbit and people

  • around the world quickly started to spot the train of satellites moving across the night

  • sky.

  • This launch is a sign of things to come, while this initial group of satellites are not fully

  • functional [8], they will be used to test things like the earth communications systems

  • and the krypton thrusters which will be used to autonomously avoid debris and de-orbit

  • the spacecraft once it has reached the end of its lifecycle.

  • Let's look at these functionalities first.

  • We have explored how ion thrusters work in the past, which you can watch for more detail,

  • but essentially they use electric potential to fire ions out of the spacecraft to provide

  • propulsion.

  • Xenon is ideally used, because it has a high atomic mass allowing it to provide more kick

  • per atom, while being inert and having a high storage density lending itself to long term

  • storage on a spacecraft.

  • However SpaceX opted for krypton, as xenon's rarity makes it a far more expensive propellant.

  • [2] This ion thruster will initially be used to raise the starlink satellites from their

  • release orbits at 440 km to their final orbital height of 550 km[1].

  • They will also be used in conjunction with on board control momentum gyroscopes located

  • here, and the US Governments' space debris collision prediction system to allow the satellites

  • to adjust their orbits to dodge collisions, which we have also spoken about in more detail

  • in a previous video.

  • When the satellites have reached the end of their service life they can then use the same

  • attitude controls and thrusters to de-orbit the satellite.

  • Space X have included all the necessary hardware to minimise space debris risk.

  • In their Federal Communications Commission approval application [3], they claim that

  • 95% of the satellite will burn up on re-entry.

  • With only the ion thruster internal structure and silicon carbide components, standing a

  • chance of survival.

  • Those silicon carbide components are likely to survive, as they are essential materials

  • for the operation of lasers and thus have an extremely high melting point of 2,750°C.

  • [9]

  • Which brings us to our communications abilities, the primary function of the satellite.

  • Spacex have been tight lipped on many of the details of the satellite, but thanks to that

  • FCC filing [3] we know that the satellites will contain 5 1.5 kilogram silicon carbide

  • components, which indicates that each satellite will contain 5 individual lasers.

  • These lasers, like our fibre optic cables here on earth, will use light pulses to transmit

  • information between satellites.

  • Transmitting with light in space offers one massive advantage over transmitting with light

  • here on earth however.

  • The speed of light is not constant in every material, in fact, light travels 47% slower

  • in glass than in a vacuum.

  • This offers starlink one huge advantage that will likely be it's primary money maker.

  • It provides the potential of lower latency information over long distance, in simpler

  • terms let's imagine this as a race between data packets.

  • A user in London wants the new adjusted price of a stock on the NASDAQ from the New York

  • stock exchange.

  • If this information were use a typical route, let's say through the AC-2 cable [RI-3],

  • which has a return journey of about 12,800 kilometres to make through our glass fibre

  • optic cable.

  • In a vacuum light travels at a speed of 299,792,458 meters per second [5].

  • The speed of travel in glass depends on the refractive index and the refractive index

  • depends on wavelength, but we will take the reduction as 1.47 times slower than the speed

  • of light in a vacuum [203940448 m/s].

  • [6] This means the data packet will take roughly 0.063 seconds to make the round trip, and

  • thus has a latency of 0.063 seconds, or 62.7 milliseconds.

  • With the additional steps that add to this latency like the conversion of light signals

  • to electrical signals on either end of the optical cable, traffic queues, and the transfer

  • to our final computer terminal, this total time comes out at about 76 milliseconds.

  • Figuring out the latency for Starlink is a lot more difficult, as we have no real world

  • measurements to go by, but we can make some educated guesses with the help of Mark Handley,

  • a communications professor in University College London.

  • [10]

  • The first source of latency for Starlink will be during the up and down link process, where

  • we need to transfer our information to and from earth.

  • We know this will be done with phase array antenna, which are radio antenna that can

  • control the direction of their transmission without moving parts, instead they use destructive

  • and constructive interference [7] to control the direction of the radio wave.

  • Each satellite has a cone beam with a 81 degree range of view.

  • With an orbit of 550 kilometres each satellite can cover a circular area with a radius of

  • 500 kilometre.

  • At SpaceX's originally planned orbit this coverage had a radius of 1060 kilometres.

  • Lowering the altitude of a satellite decreases the area it can cover, but also decreases

  • the latency.

  • This is particularly noticeable for typical communications satellites operating in geostationary

  • orbit at an altitude of about 36,000 kilometres.

  • The time it takes data to travel up to the satellite and back down travelling at the

  • speed of light is around 240 milliseconds [13] 369% slower than our subsea cable.

  • However, since Starlink is intending to operate at a much lower altitude, the up and down

  • link theoretical latency could be as low as 3.6 ms.

  • This is why SpaceX needs so many satellites in their constellation in order to provide

  • worldwide coverage.

  • Each individual starlink satellite has four phased array antenna located here, here, here

  • and here.

  • This directional beam was an essential part of SpaceX's FCC approval application [3],

  • as thousands of satellites broadcasting undirected radio waves would cause significant amounts

  • of interference with other communication methods.

  • Once that data is received by one starlink satellite, it can begin to transmit that information

  • between satellites using lasers.

  • Each time we hop from satellites there will be a small delay as the laser light is converted

  • to an electric signal and back again, but it is too miniscule to consider.

  • Things get tricky here with using lasers, as we need to accurately hit the receiver

  • on neighbouring satellites to transmit that data.

  • Let's look at SpaceX's proposed constellation to see how this will work.

  • Space X's first phase of 1584 satellites will occupy 24 orbital planes, with 66 satellites

  • in each plane inclined at 53 degrees.

  • That will look something like this.

  • Communication between neighbouring satellites in the same orbital plane is relatively simple,

  • as these satellites will remain in relatively stable positions in relation to each other.

  • This gives us a solid line of communication along a single orbital plane, but in many

  • cases a single orbital plane will not connect two locations, so we need to be able transfer

  • information between these planes too.

  • This requires precise tracking, as the satellites travelling in neighbouring orbital planes

  • are travelling incredibly quickly and will come in and out of view.

  • This means the starlink satellite will need to switch to a new satellite in the network.

  • This can take time, the best figure I could find is about a minute [9] for the European

  • Space Agency's Data Relay Satellite System, which is a currently operating geostationary

  • internet constellation designed to serve european imaging satellites, and other time critical

  • applications.

  • Such as serving emergency forces in remote areas, like those fighting forest fires.

  • Starlink may be faster, but it won't be instantaneous, and thus it has 5 optical communication

  • systems on board to maintain a steady connection to 4 satellites at all times.

  • If we now use this system, transmitting from New York to London and back, with the shortest

  • path possible, using the speed of light in a vacuum as our transfer speed, we can achieve

  • a latency as low as 43 milliseconds.

  • Even if we took the shortest route possible with an optic fibre, which does not exist,

  • this would take about 55 milliseconds, a 28% decrease in speed.

  • The actual current return trip time for your average Joe is about 76 milliseconds, as we

  • saw earlier.

  • A 77% decrease in speed.

  • This is a huge deal for the two financial markets working out of these cities, with

  • millions of dollars being moved in fractions of a second, having a lower latency would

  • provide a massive advantage in capitalizing on price swings.

  • In fact, it wouldn't be the first time a communications company has made a massive

  • investment to specifically serve these groups.

  • The Hibernian Express cable is a privately owned optic cable that is currently the lowest

  • latency connection between the NY4 data centre in Secaucus, New Jersey and the LD4 data centre

  • in Slough, England at just 59.95 milliseconds, 39.4% slower than our best time with Starlink.

  • [11] The previous best time was held by the AC-1 cable at 65 milliseconds.

  • At a cost of 300 million dollars this 5 millisecond increase in speed was justified to just connect

  • across the Atlantic.

  • Imagine how much these time sensitive industries will be willing to pay for a 17 millisecond

  • increase in speed.

  • It becomes even more valuable when you realise this time differential increases with increased

  • transmission distance.

  • New York to London is a relatively short distance.

  • The improvements would be even more pronounced for a London to Singapore transmission, for

  • every additional kilometre we travel the potential gains in speed increase rapidly [5].

  • [RI-2] But SpaceX aren't just planning on serving this super fast internet to some customers,

  • they primarily advertise this system as a way to connect every human on this planet

  • to the internet, and they should have plenty of bandwidth left over to serve these people.

  • Although the internet has been one of the fastest growing technologies in human history,

  • by the end of 2019 more than half of the world's population will still be offline (4 billion).

  • Users will connect to this internet using a Starlink terminal which will cost around

  • $200 each, this will still be far outside the purchasing power of many third world citizens,

  • but it's a start and vastly cheaper then similar currently available receivers like

  • the Kymeta version at a price of $30,000[15].

  • Elon Musk says that these will be flat enough to fit onto the roof of a car and other vehicles

  • like ships and airplanes.

  • This will allow Starlink to compete with traditional internet providers.

  • It's estimated that moving the US from a 4G to a 5G wireless connection will cost around

  • $150 billion in fiber optic cabling alone over the next 7 years, [16] SpaceX plan to

  • complete their entire Stralink project for as little as $10 billion.

  • Each Starlink satellite cost around $300,000 which is already a massive cut in cost for

  • communication satellites.

  • SpaceX are also saving on launch costs, as they are launching on their own Falcon 9 rocket,

  • something that no other satellite manufacturer has.

  • If everything goes to plan, Starlink is estimated to generate $30 billion to $50 billion in

  • revenue each year on the back of premium stock exchange memberships [14], demolishing their

  • current annual revenue of around $3 billion.

  • And this is a vital part of Elon Musk's long term goals.

  • The money generated from Starlink will mean SpaceX will have vastly more funding than

  • NASA.

  • Which could go on to fund research and development of new rockets and the technology needed to

  • monetise lunar and martian colonies.

  • For now the project is simply connecting the world even more and potentially opening avenues

  • Widely available internet will help solve this problem, and platforms like Brilliant

  • have taken great steps to remedy this through their high quality interactive math and science

  • learning.

  • Brilliant has helped thousands of users realize their potential in math and science, and it's

  • stories like this why I am proud to promote Brilliant every month.

  • They have a huge number of courses that will allow you to educate yourself.

  • From foundational maths courses to courses taylored for you to ace the American Mathematics

  • Competition, with others geared for computer science and physics.

  • Brilliant recently introduced a new feature, calledDaily Challenges”, which will

  • present with you with interesting scientific and mathematical problems to test your brain

  • every day.

  • If I have inspired you and you want to educate yourself, then go to brilliant.org/RealEngineering

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为什么 SpaceX 正在制作 Starlink(Why SpaceX is Making Starlink)

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    joey joey 發佈於 2021 年 06 月 09 日
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