Name: Why SpaceX is Making Starlink
Uploaded: 2021-06-09T09:59:11.000Z
Duration: 16 min 1 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

基礎受動態

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 called “Starlink” which 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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

[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.

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