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How does China do it for global navigation?

Release date:2021-12-29Author source:KinghelmViews:596

June 23, 2020

Xichang Satellite Launch Center

The long march rocket carriesmostafteroneBeidou networking satellite

Cut through the sky

(at 9:43, the last global networking satellite of Beidou 3 was launched, photographer @ Nan Yong

 
 
 


subsequently

The satellite will reach an orbit about 36000 kilometers from the earth's surface

Its stable operation

Mark

ChinaBeidou satellite navigation systemUnifiedFully completed


This isOnehugeEngineering

In space46 navigation satellites

Around the earth day and night

More than 2700 reference stations on the ground

It is distributed in the north and south of the river

A "dragnet" spread out

 
(Beidou "complete body", including 16 beidou-2 satellites and 30 beidou-3 satellites, cartography @ Zheng Borong / Institute of planetary Research)        
   
 
   
       
 


This is also adifficultEngineering

More than 80000 staff

More than 300 R & D units

Fought for more than 20 years

Finally the dream came true

(in the past 20 years, the long march rocket, as the only carrier of the Beidou satellite, has been launched 44 times. The following figure shows the scene of the long march 3B rocket carrying the 39th and 40th Beidou satellites waiting to be launched, photographer @ Shi Yue)



This is aessentialEngineering

Now Beidou has been widely used in

Power, finance, communication and transportation

Agriculture, surveying and mapping, disaster reduction and relief, etc

All aspects of production and life

China will get rid of

Global positioning system (GPS)Dependence of

(the Beijing Zhangjiakou high-speed railway running at the speed of 350 km / h can realize the parking accuracy error from driving once braking to parking, which is less than 10 cm. The following figure shows the Beijing Zhangjiakou high-speed railway crossing the river, photographer @ Zhao Bin)


And with the help of Beidou

Chinese missiles haveUltra high precision guidance capability

The sharp weapon of national defense is becoming sharper and sharper

(on October 1, 2019, julang-2 missile team in the military parade of the General Assembly celebrating the 70th anniversary of the founding of the people's Republic of China, photo source @ People's vision)


nowadays

Beidou System (BDS)It has covered the whole world

Global positioning system with the United States(GPS

GLONASS system in Russia

OhAllianceGalileo

It is also known as the world's four major satellite navigation systems (GNSS)


Grinding a sword in 20 years

How did China do it?

 


 01 

NavigationsatelliteSecret of


To get our location

Need to be deployed in space

At least 3 navigation satellites


They constantly emit electromagnetic signals

We use navigation equipment to receive signals

The signal is generated between sending and receivingtime difference

Multiplied by the propagation rate of the electromagnetic wave (speed of light)

We can calculate our distance from the satellite

 

When there is only one navigation satellite

Satellite centric

WeThe distance from the satellite is the radius

You get onesphere

Any point on the sphere

Could be our location

The speed of light is about 3 & times;teneightm/s. Position determined by a navigation satellite -- sphere, cartography @ Zheng Borong / Institute of planetary Research)

 
 
       
 


If there are 2 navigation satellites

Two spheres intersect to get onecircumference

Any point on the circumference

Could be our location

(two navigation satellites)Fixed position - circumference, cartography @ Zheng Borong / Institute of planetary Research)



If there are 3 navigation satellites

Three spheres intersect to get a and BTwo points

Any of two points

It could also be our location

(location determined by three navigation satellites - two points), cartography @ Zheng Borong / Institute of planetary Research)



And between the two points

have onlyPoint B is near the surface

So we locked our only position

(there is only one intersection with the earth's surface, cartography @ Zheng Borong / Institute of planetary Research)



That's itIt's the secret of navigation satellites

NamelyThree ball intersection positioningprinciple


actually

stayWhen measuring time

There will be various errors

To eliminate errors

Often also needThe fourthSatellite assistance


meanwhileIn order to ensure that we can

Can receive more than four navigation satellite signals

The total number of satellites orbiting the earth is often much higher than four

For example, GPS in the United States and GLONASS in Russia

The number of navigation satellites is more than 24

(GPS system positioning diagram. There are more than 4 satellites above the same point. The original image is from @ Wikipedia, reproduced @ Zheng Borong / Institute of planetary Research)



however

In the 1990s

Want a short timeLaunch the same number of navigation satellites

For China, which is relatively backward in aerospace and navigation technology

It's almost an impossible dream

Can I use itleastSatellite

Achieve the goal of positioning?



 02 

Stagger start


A bold plan

Born in the sky


Chen Fangyun

"Two bombs and one satellite" meritorious service, famous electronics scientist

Proposed for the first timeConsisting of two satellites

Double star positioning system

 

The subtlety is

A "brain" is set on the ground

Ground control center

 

Using ground control center

People can be around the earth"Virtual" a sphere

And through the interaction between control center, satellite and user

Calculate the user's location

(the ground control center can provide the user's elevation and other known data, and has strong solution ability. Schematic diagram of double star positioning principle and mapping@Zheng Borong / Institute of planetary research


meanwhile

Both satellites are in geostationary orbit

Its orbital height is 35786 km

The operation cycle is consistent with the earth's rotation cycle

Can always face the same side of the earth

It ensures the signal coverage in the whole period

Geostationary orbit diagram,drafting@Zheng Borong / Institute of planetary research

 

Since 1994squareThe project was officially approved

By 2000Two Beidou satellitesSuccessful orbit

More than 6 years of research and development

The idea of the Big Dipper

Finally became a reality

This isBeidou 1

 

Its signal

It can basically cover the whole territory of China

(Beidou-1 covers 70 & deg; - 145 & deg;, north latitude5°- 55°, Drawing @ Wang Chaoyang & Zheng BoRong / Planetary Institute

 

Users can not only receive location information

Still like“send message”Actively send text messages as well

This is particularly critical when seeking help and assistance

And for like“radio”General

GPS and other systems receiving data in one direction

This is impossible

(the advantage of "texting" is that it can not only know its own location, but also tell others, which is of great significance in some dangerous situations such as earthquake and ocean going. The following figure shows the rescue scene in the Wenchuan earthquake in 2008, photographer @ Jia junyang)


This feature is an international initiative

The father of American GPSParkinsonprofessor

Later, he praised this function

I can know where you are and where I am

What a wonderful experience

 

however

Defects of Beidou-1

It's also obvious

 

Its positioning accuracy is 20-100 meters

The time accuracy is 20-100 nanoseconds

It is significantly different from the 10 meters and 20 nanoseconds of GPS in the same period

And only 150 users can be online at the same time

It is also far from the goal of global coverage

 

also

"Texting" interactive mode

The process is cumbersome and the signal is easy to be intercepted

It not only leads to a delay of about 1 second in positioning

It is also easy to expose its position

For high-speed aircraft and missiles

Every second is life and death

Confidentiality is even more important in military operations

(comparison of positioning operation between Beidou-1 and GPS system,Drawing@Zheng Borong / Institute of planetary research


Beidou 1

Although the performance is a little simple

But it basically solved the problem of our navigation system from scratch

Beidou's dream has begun to falter

Will it be all right next?



 03 

Overcome difficulties


Since 2010

Xichang Satellite Launch Center has become very busy

In less than three years

14 navigation satellites will be launched from here

Five satellites were launched in 2010

Three satellites were launched in 2011

Six satellites were launched in 2012

(in 2007 and 2009, one beidou-2 experimental satellite has been launched respectively. The following figure shows the same frame of the two launch towers of Xichang Satellite Launch Center and the rocket transport locomotive, photographer @ Yu Ming)


 

meanwhile

Ground supporting systems such as operation and control are also spread out

Satellite and ground adjustment tests are also being carried out simultaneously

End of 2012

Successful networking of the new system

This is it.Beidou 2

(operation diagram of beidou-2 system,Drawing@Zheng Borong / Institute of planetary research


Compared with Beidou-1

Its coverage has expanded significantly

Expand to most regions of the Asia Pacific Region

The positioning accuracy has also been improved from 20m to 10m

The time accuracy is up to 10 nanoseconds

(beidou-2 covers 70 & deg; - 150 & deg;, 55 & deg; - 55 & deg;, mapping @ Wang Chaoyang&Zheng Borong / Institute of planetary research



Beidou-1's unique communication function

It has also been completely inherited

It can help more people in emergency communication

(on April 25, 2015, a magnitude 8.1 earthquake occurred in Nepal, and rescue workers carried out search and rescue with the help of Beidou. The following figure shows the post earthquake scene in new tubalchak area, Nepal,Picture source @ People's vision)



However, such an upgrade

It's not plain sailing

In front of scientists

numerous crises

 

One of the difficulties is



How are satellites laid out



Optimal orbit for navigation satellite

It's about 20000 kilometers high

Mid circular orbit

It is the best choice to achieve global coverage

Satellites of GPS and other systems are distributed here

(schematic diagram of different orbit types and satellites,drafting@Chen Siqi & Chen Sui / Institute of planetary Research)



however

Medium circular orbit satellite

Flying over the target areaShort time

That means

Want to achieve stable coverage of this area

Enough satellites must be launched


But then

Technology for launching such satellites

It is not yet mature in China

If all medium circular tracks are used

It is undoubtedly full of risks


In order to achieve the goal in the short term

Chinese scientists find another way

For the first time“Mix and match”Satellite layout

By arranging troops

14 satellites in three orbits

 

except4 medium circular orbit satellitesOutside

also5 tilt synchronous orbit satellites

Ensure the long-term coverage of the signal to the Asia Pacific region

5 geostationary satellites

Realize the stable coverage of this area all the time

Tilt synchronizationOrbital satelliteOperating cycle and track heightSame as geostationary satellite.Tilt synchronous orbit satelliteIt is used for positioning and is the first in China. The following figure shows the beidou-2 systemSchematic drawing of three tracks@Zheng Borong / Institute of planetary Research)




The second difficulty is

 


How to improve the accuracy

 


Electromagnetic waves travel at the speed of light

Even if there is a time error of 1 nanosecond

The resulting distance error will also be 0.3m

 

So the accuracy of satellite navigation and positioning

It mainly depends on the satelliteAtomic clock accuracy

And between satellites, ground stations and users

time synchronization

 

International universal spaceborne atomic clock

Accuracy needs to reachten-13

It is equivalent to an error of 1 second every 100000 years

And the countries with this technology at that time

Only the United States, Russia and Switzerland

(the following figure is the artistic imagination of the US GPS satellite, photo source @ NASA)



The atomic clock used by Beidou 1

It is imported from Switzerland

But by Beidou two

Cooperation in the introduction of atomic clocks was interrupted

 

therefore

If Beidou 2 wants to complete successfully

The Chinese must race against time

Realize the independent development of atomic clock

(the satellites and launch vehicles of the Beidou satellite navigation system are developed and produced by the China Academy of space technology and the China Academy of launch vehicle technology affiliated to China Aerospace Science and Technology Corporation, respectively, as shown in the figure belowThe staff of China Academy of space technology are debugging the equipment, photographer @ Gou Bingchen)



The urgency of time goes far beyond that

Difficulty 3

It's a satellite



How to launch on time



According to the rules of the International Telecommunication Union

Orbit and signal frequency of satellite operation

Application must be made in advance before use

And must be within 7 years after the application is approved

Complete satellite launch, orbit entry and signal reception

Otherwise, the relevant resources will be recycled


April 18, 2000

China's application was approved

This means that in the next seven years

Satellites and rockets must be foolproof

(the fairing after the docking of satellite and rocket is stretched and deformed at the edge of the picture due to wide-angle shootingShadow master @ Nan Yong)

Scientists work day and night

Repeated experiments and tests

Master relevant satellite technology within 7 years

Overcome the difficulties of atomic clock in 2 years

even to the extent thatUse onlyMore than 10 days

Complete satellite removal, testing, and then reinstallation

A series of complex operations

FixedSudden failure before launch

(the engine of the satellite has failed. Experts are carefully checking the equipment. The second person from the right is academician sun Jiadong, chief designer of Beidou 1 and 2 systems. Photo)Shadow master @ Nan Yong)



April 17, 20078 p.m

When people successfully receive the signal

Deadline from track failure

There are only four hours left



thus

Experience and break through the technical blockade

A satellite navigation system covering the Asia Pacific region has been completed

Distance enables global navigation

Only the last step



 04 

nets above and snares below


Last step

Will be acomprehensiveUpgrade of


Beidou-3 satellite

service lifeFrom 8 years to more than 10 years

Its components

Full implementationMade in China

Atomic clockContinuous performance upgrade

The accuracy has reached 10 million years, with a difference of 1 second


hereRocket technology

It is no longer a constraint

The launch of one arrow and two stars has been "perfect"


End of 2017

launchoneArrow 2Star


2018

launch9 arrows 17 stars


2019

launch6 arrows and 8 stars


2020

launch3 arrows and 3 stars


Less than 3 years

30satellite

At an unprecedented rate

Launch and complete networking

(on June 23, 2020, the last global networking satellite of Beidou 3 was launched, photographer @ Shi Yue)



therefore



In space

 


threeGrainsGeostationary orbit satellite

It is distributed directly over the equator


3 tilt synchronous orbit satellites

Stable coverage of the Asia Pacific Region


24 medium circular orbit satellites

Running around the earth day and night


Together they form

A hugeSatellite network

Hanging in space

It can be called a huge pictureSkynet


from then on

Day or night

Anywhere on earth

People can see 5-6 Beidou satellites when they look up

Global coverageGoal of

Finally realized

(operation diagram of beidou-3 system, cartography @ Zheng Borong / Institute of planetary Research)

 

That's not enough

When the satellite flies over China

In the absence of ground control commands

satelliteNormal track operation cannot be guaranteed


to this end

People build bridges between satellites

Communication and ranging can be carried out between each other

Mutual supervision and automatic formation maintenance

Intricate composition

Inter satellite link

 

This is greatly reduced

System dependence on ground station

even ifAll ground stations failed

The Beidou system can still pass the inter satellite link

Maintain autonomous operation for up to 60 days

(schematic diagram of inter satellite link, cartography @ Zheng Borong / Institute of planetary Research)



meanwhile

In China



Above the ground



More than 2700 ground reference stations

And several data processing centers

Also spread out on the land of China

Form a ground data processing network

Even if the satellite signal is affected

Various terrain, building occlusion and reflection

It can also provide additional ground information supplement

personFoundation reinforcement system

(Beidou foundation enhancement system consists of frame network and regional enhanced density network, including 155 frame network reference stations and more than 2700 regional enhanced density network reference stations. The following figure shows the distribution of frame website points, cartography @ Wang Chaoyang & Zheng Borong / Institute of planetary Research)



After this correction and treatment

The error of the whole system is reduced again and again

Accuracy continues to increase

It can be meter level or decimeter level

Even centimeter or millimeter

 

Can be accurate to

Establishment of electronic fence

Ensure that the shared bicycle stops within the specified range

(a temporary storage place for shared bicycles in Xiangyang City, Hubei Province, photo source @ VCG)



Can be accurate to

In the parade square

The squadron of various types of equipment marched at a constant speed

Each flight echelon is not bad in meters and seconds

The distance error is within plus or minus 10 cm

(on September 23, 2019, the flight echelon during the rehearsal of the National Day military parade, photographer @ Shicheng Tian Weitao)



Can be accurate to

Monitoring dams, bridges, etc

Appearance deformation of the project

(please watch the horizontal screen. At the bottom right of the screen is Xiluodu Hydropower Station, the second largest hydropower station in China.At present, more than 150 monitoring points have been installed on the slopes on both sides of the hydropower station, and continuously provide millimeter precision data to find potential safety hazards in time, photographer @ Chai Junfeng)



in addition

Beidou chip

It can be implanted into a mobile phone

As of the third quarter of 2019

Among the more than 400 mobile phones applied for network access in the Chinese market

Nearly 300 models support Beidou navigation

(the driver is using mobile navigation,Photographer @ Ren bingxu



It can be equipped with transportation tools

As of December 2019

More than 6.5 million operating vehicles

40000 postal and express vehicles

More than 3200 inland river navigation facilities

More than 2900 marine navigation facilities

All have been equipped with Beidou system

Become the world's largest dynamic supervision system for operating vehicles

(outside the Niujiaotuo light rail station in Chongqing, a bus runs on the viaduct,Photographer @ Shi Cheng Cui Li



thus

It is composed of Tianluo and geonet

This is the ultimate form of Beidou system evolution

Beidou 3



 05 

Beidou 20 years


2000-2020

Launched from the first star of Beidou-1

To the last satellite of Beidou 3

It's been 20 years


20 years

Face many difficulties

Scientists never retreat

They camped step by step

The first step is for China

The second step is Asia Pacific

The third step, for the world


today

ChinafinallyYes

Own satellite navigation system

future

It will be open to the world

It will also become a part of the lives of more than 7 billion people

(Beidou line fault indicator shall be installed in the power line to accurately find the accident location, eliminate the fault in time and reduce the power failure time.The following picture shows the power transmission towers rising one after another in the valley, photographer @ Qiu Huining)



In the air

Fugitive pollutants

Incorporated into the environmental monitoring information system

From now on, we will not escape the "eye" of Beidou

(Beidou system can be used to obtain the real-time position of relevant monitoring points of air pollutants, and the communication function of Beidou can be used to send the information to the monitoring center.The following figure shows the factory chimney being discharged as a schematic, photographer @ Qiu Huining


 

Between fields

Through the cooperation between Beidou system and agricultural equipment

It can grasp the information of cultivation depth and row spacing in real time

Increase operation efficiency by 50%

Output increased by 5% - 8%

(the following figure shows the working scene of the planter equipped with Beidou navigation system, located in Jilin Province,Photographer @ Qiu Huining



And the border

The harsh environment with high mountains, dense forests and deep valleys

As a result, the communication facilities cannot be fully covered

And the border guards rely on the Beidou system

It can still deliver information in a timely and stable manner

(in areas that cannot be covered by mobile phone base stations, Beidou's positioning and communication functions become very important,The picture below shows border officers and soldiers patrolling the border, photographer@Han Jun Li


however

theseIt's not enough

Like the father of Chinese satellites

Chief designer of Beidou 1 and 2 systems

Sun JiadongSaid


The key to building Beidou is still to use it. Only when it is used more widely and deeply, will it be the winner.

 


yes

Scientists have been arrayed for 20 years

finallyWeave a "dragnet"

China's own satellite navigation system

And finally from imagination to reality


And this

Just the beginning of the story

Every day in the future

Is China's Beidou satellite navigation system

The true place of responsibility and mission


This article is reproduced from“Planetary Institute”, support the protection of intellectual property rights. Please indicate the original source and author for reprint. If there is infringement, please contact us to delete      


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