Space Debris and Its Effect on Satellites

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RAJA RAJESWRI ENGINEERING COLLEGE Adayalapattu, vanagaram post, Chennai – 600095. SPACE DEBRIS & ITS HAZARDS ON SATELLITE COMMUNICATIONS -A GPS based debris removal system (provided solutions to the problems discussed in the IEEE transaction by Prof. Elisabeth Paté-Cornell) IEEE Transactions on Aerospace and Electronic Systems, Vol. 37, No. 1, pp. 134-146, January 2001 By M.SUNDARAMOORTHY DEEPIKA VENUGOPAL email-id : [email protected] Contact Address: M.SUNDARAMOORTHY 101 G-BLOCK, MMDA COLONY, 1

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Transcript of Space Debris and Its Effect on Satellites

Page 1: Space Debris and Its Effect on Satellites

RAJA RAJESWRI ENGINEERING COLLEGE

Adayalapattu, vanagaram post, Chennai – 600095.

SPACE DEBRIS & ITS HAZARDS ON

SATELLITE COMMUNICATIONS

-A GPS based debris removal system

(provided solutions to the problems discussed in the IEEE transaction by Prof.

Elisabeth Paté-Cornell)

IEEE Transactions on Aerospace and Electronic Systems,

Vol. 37, No. 1, pp. 134-146, January 2001

By

M.SUNDARAMOORTHY

DEEPIKA VENUGOPAL

email-id : [email protected]

Contact Address: M.SUNDARAMOORTHY101 G-BLOCK, MMDA COLONY,ARUMBAKKAM,CHENNAI – 600106.

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ABSTRACT

The wireless communication and networking on a large scale is carried out

through satellites. Inter planetary communication is also made possible due to satellite

technology.

The various kinds of space debris or space junk that are revolving around our

earth in an orbit possess a threat to the satellite communications. Infact, these particles

whether tiny or big are on their way to destroy the whole system of satellites and

space stations orbiting around our globe in the near future. This deadly debris must be

eliminated in order to have a complete access to our earth orbiting satellites. The

concept of light pressure exerted by laser beams provides a valuable tool to eliminate

these particles. The following section gives an idea of reducing the space debris and

also eliminating them.

INTRODUCTION

In the modern era, communication plays a significant role in human life, a

country’s economy and further development in science and technology. The

communication system has developed to an extent that information exchange across

any part of the blue planet is very easy. This is possible due to the satellites revolving

around us. Every nook and corner of the earth can be accessed via satellites.

As Newton said, ”For every action there is an equal and opposite reaction”,

the development in the satellite technology heads in one direction launching many

satellites and the debris created due to these satellites possess a threat of destroying

the satellites and heads in the opposite direction. In the next 100 years, man’s thirst

for wider and better universal communication will lead in launching of many satellites

which in turn produces huge amount of debris. The space around the earth would get

so congested that it needs to be cleaned.

We have discussed about the various proposals that are made to clean the

space junk. We have also suggested methods, which use the radiation pressure exerted

by high intensity lasers and sunlight in removing space debris.

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SPACE JUNK

The unwanted materials that are revolving around the earth in different orbits are

called space junk. It can be classified into:

Natural junk- like meteorites, asteroids, comet tail etc

Man made junk-effluents from space missions, dead satellites, debris due to

collision, spent rocket stages, discarded equipment, and fragments from satellite

breakups etc.

Space junk can be created in several ways: When satellites separate from their

boosters, they shed shrouds and other bits and pieces. They can collide. Boosters can

malfunction and explode. Or spent booster segments with still-pressurized fuel tanks

can explode when hit by debris or after joints weaken from the constant freezing and

thawing. Solid-fuel motors can give off "slag" as part of their exhaust plumes.

A view of the space junk around earth

NASA estimates there are 4 million pounds of junk orbiting Earth. More than half the

impacting debris is manmade. It travels at about 10 kilometers per second (22,370

mph). Small asteroids and meteoroids, which is the natural debris typically, move at

twice that speed.

More than 200 objects, most of them rubbish bags, were released by the Mir space

station during its first 10 years of operation.

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HOW DOES IT AFFECT?

Thousands of nuts, bolts, gloves and other debris from space missions form an

orbiting garbage dump around Earth, presenting a hazard to spacecraft. Some of the

bits and pieces scream along at 17,500 mph.

Small junk, some of it created by rocket explosions, can rip holes in a spacecraft or

disable a satellite by causing electrical shorts that result from clouds of superheated

gas, called plasma, that are sometimes generated in an impact.

The risk of satellites being hit by debris is increasing at an alarming rate. The solar

panels present in the satellites are very delicate. So even very small size debris could

be a cause for the malfunctioning of the panel, which in turn may interrupt the

efficiency of the data transfer.

In communication systems the satellites usually are grouped into networks. If a

satellite is being hit by big debris then there is every possibility of it losing its ability

to function properly. This may break the communication network leading to large

amount of financial and material loss for a certain amount of time until a replacement

is made.

The most space debris created by a spacecraft's destruction was due to the upper stage

of a Pegasus rocket launched in 1994. Its explosion in 1996 generated a cloud of some

300,000 fragments bigger than 4 mm and 700 among them were big enough to be

catalogued. This explosion alone doubled the Hubble Space Telescope collision risk.

To prove this we have found a ¾ inch hole in the Hubble. Even a speck of paint from

a satellite dug a pit in a space shuttle window nearly a quarter inch wide. The

replacement was made at the cost of $50,000.

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This graph shows the alarming trend of the growth of the space debris field

POSSIBLE STEPS TO REMOVE SPACE JUNK

There are quite a lot of prototypes to avoid the space junk issue. As engineers we

must have the responsibility in keeping our environment clean, which includes space

also. Some of the proposed techniques to reduce or eliminate the manmade debris are

given below:

Attaching rocket motors to debris

Preventing the satellites by maneuvering and shielding techniques

Electrodynamic tether.

We propose our ideas to eliminate the debris using radiation pressure by the following

methods.

Deceleration of debris using the radiation pressure of laser beams.

Focussing of sunlight (lensing) on the debris and decelerating it.

ATTACHING ROCKET MOTORS TO THE DEBRIS

Huge debris like the dead satellites, spent rocket stages, bigger fragments of the

satellite breakups are decelerated using rocket motors attached to them. A rocket

motor is attached to the debris using a space shuttle mission from the earth; the motor

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is triggered at a direction opposite to the movement of the debris. Thus the velocity of

the junk reduces and its altitude decreases. The debris is brought down to the earth’s

atmosphere where it is burned up due to friction.

As this method needs a separate space mission to send the required components to

perform the operation, it is very costly. Rocket motors can be stored in the

International Space Station and can be used to bring dead satellites down. This would

be cheaper and more efficient.

SATELLITE MANEUVERING AND SHIELDING

The modern satellites and space probes that are to be launched in the future must have

various type of manoeuvring options so that it escapes from being hit by a junk that is

unable to be detected by the ground based radars. It must be designed in such a way

that it can withstand hypervelocity impacts of small pieces of debris. The whole

satellite cannot be maneuvered as the communication signals might get interrupted.

So the functional part of the satellite should be shielded in order to protect it from the

impact of small debris. While the delicate parts like the solar cell panels should be

maneuverable.

ELECTRODYNAMIC TETHER

One of the latest developments in the space junk removal program is that of the

introduction of the electrodynamic tether. The tether is a conducting wire that is

several tens of kilometers in length and is controlled by a spacecraft. A tether is

essentially just something used to tie one object to another. On Earth, tethers are

generally used to keep something in place. In space, however, tethers could serve

several useful purposes.

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A tether deployed from a rocket stage

According to faraday's law when a current carrying conductor cuts a magnetic field,

forces are developed in the conductor, which is in the direction to oppose the cause of

its movement.

As the long wire of an electrodynamic tether passes through Earth's magnetic field, it

sets up a voltage along the tether. This voltage makes electrons flow down the tether,

like water flowing down a pipe. If the tether has the right systems to allow it to collect

and emit electrons, then an electrical current (the flow of electrons) will move through

the tether. Any time an electrical current flows in a magnetic field, there is a force

developed and this force is used to maneuver the tether. The energy required by the

tether is collected from the sun through the solar panels.

A small vehicle called the space sheepdog accompanies the tether. This space

sheepdog is released near a piece of debris, flying around it looking for a suitable

point to latch onto. Once the debris is attached to the space sheepdog it brings it to the

tether and gets connected with it. At that moment the current in the tether is made to

flow in a direction such that the tether is brought down into sub orbital levels along

with the debris. Thus the debris is deorbited.

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The tether is once again raised to higher altitudes by changing the current direction.

Thus the tether can be reused for many times to clear the debris.

MOMENTUM TRANSFER MECHANISM USING TETHER

As the altitude of the space satellites increases the risk of collision with debris

decreases. The tether apart from decelerating the debris particles can also perform

other functions like increasing the satellites altitude by using the momentum of the

junk.

The tether is attached to the spacecraft at one end and junk at the other. By carefully

controlling the forces produced on the tether the two masses are set to rotating about

each other. Releasing the spacecraft at the appropriate moment would send it to a

higher orbit while the junk ends up in a lower orbit.

Various views of a momentum exchange tether

DECELERATION OF DEBRIS USING RADIATION PRESSURE

RADIATION PRESSURE:

The pressure exerted by light on an object is called radiation pressure. By using

radiation pressure we can introduce a force in a direction opposite to that of the debris

thereby slowing it down.

Radiation pressure=Force exerted on debris/area of debris.

By Einstein’s equation,

E = m c^2

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Momentum, p = mc

Therefore E = cp. ---- (1)

W.K.T Radiation pressure (R.P) = Rate of change of momentum per unit area.

From eqn (1), p = E/c

dp/dt=dE/dt*1/c

W.K.T. power = rate of change of Energy = dE/dt

dp/dt = power/c.

Therefore, R.P = power / (area*c)

W.K.T. Intensity(I) = power/area

Radiation pressure (R.P)=intensity of light/velocity of light =I/c

(For total Absorption)

R.P=2 I/c (for total reflection of light).

For an object to remain in orbit at altitudes below 620 miles (1,000 km), it must travel

at speeds of nearly 18,000 miles per hour. It's within this region of space that critical

satellites and craft, including the International Space Station and the shuttle, operate.

So in order to deorbit the debris its velocity should be brought below 18000 mph.

The intensity of radiation required to deorbit the debris can be derived as follows:

According to the law of conservation of momentum,

If two objects collide,

The momentum lost by one object = momentum gained by the other.

Loss of momentum of incident radiation= gain of momentum of debris

But, radiation pressure=rate of change of momentum/Area

I/c = dp/dt*1/A (For total Absorption)

= m*dv/dt *1/A where dv = v1-v2

V1=velocity of debris

v2=velocity at which debris deorbits (i.e. less than 18000 mph)

Therefore intensity of radiation required, I=mc/A*(v1-v2)/dt

dt = time required to reduce the velocity from v1 to v2

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As all the quantities are constant,

Intensity of radiation 1/time required.

So if the intensity of radiation is more, then the time taken to deorbit the debris will be

less.

DECELERATION OF DEBRIS USING LASER BEAM:

The word LASER stands for Light Amplification by Stimulated Emission of

radiation. The laser beam is monochromatic, coherent, and highly intense and does

not diverge at all.

By using highly intense laser beam it is possible to slow down the debris thereby

making it to reenter earth’s atmosphere. The intensity of laser beam required is

directly proportional to the mass and inversely proportional to the surface area of the

debris. Radars and other detecting devices cannot spot the debris that is smaller in size

and so it cannot be deorbited easily.

Example to show the possibility of using laser beam to de orbit debris:

Consider debris of mass 10g present in an area A orbiting with a velocity of 10 Km/s.

In order to de orbit the debris it should orbit at velocity less than 8Km/s.

Eqn (2) gives I=mc/A*(v1-v2)/dt

Also W.K.T. I=power/Apower=I*A

Therefore Power = mc(v1-v2)/dt

Time required to de orbit debris = dt = mc(v1-v2)/power of laser beam

Consider the use of a laser beam of 20MW power.

Therefore time = 0.01*3*10^8*(10000-7800)/(20 *10^6)----(since velocity of debris

should be less than 8000m/s, we take it as 7800m/s.)

Amount of time for which the laser beam should be focussed on the debris = 330

seconds

This is possible if we can do it from the ISS it would not cost much either.

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A view of debris reentering earth’s atmosphere

Artificial debris installed with GPS (Global Positioning System) can be set to orbit in

a region where the debris population is more. Thus we can detect the movement of the

debris using GPS. Then by using a laser broom, which is nothing but a highly intense

laser beam in the order of megawatts of power, we can deorbit the debris of various

sizes present in that region.

After laser brooms sweep the debris, they slow down and come to sub-orbital levels

finally reentering into the earth’s atmosphere thus getting destroyed. As the artificial

debris is also among those being swept it would be possible to observe the path taken

by the debris during their reentry phase, which could be of great use for future

analysis.

FOCUSSING OF SUNLIGHT

As seen earlier laser beam can be used to slow down the debris and deorbit them.

Radiation pressure exerted by sunlight can also be used effectively.

The lensing of light on any object increases the intensity of radiation. For e.g. when

suns rays are focussed on a piece of paper by a convex lens, the paper burns due to the

increase in intensity.

The sun's effect on a comet tail is a good example of the effect of radiation pressure.

As the comet approaches the sun, due to the radiation pressure the dust and gaseous

particles of it gets pushed back forming its tail. Thus by using the radiation pressure

of the sun we can clean the space in a natural way.

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THE FUTURE IS DARK !!!!!!!!!

In the next 100 years due to man’s thirst of exploring the final frontier more and more

satellites will be launched.

Ever since Sputnik, humans have lobbed more than 20,000 metric tons of hardware

into orbit. In addition, the number of operating satellites is expected to grow from 700

today to as many as 3,000 in 2020.

The number of satellites that are sent every year is increasing at an alarming rate. Due

to this in the near future the space around us will get so polluted that it forms a layer

of debris preventing the satellites from going past it.

Even the communication signals from the earth to the space missions being carried

out on other planets and vice versa might be attenuated or even blocked.

Thus ultimately mans aim of conquering the solar system and other galaxies will fade

away.

This graph shows the trend of increasing numbers of catastrophic debris collisions

in space due to space

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As it can be seen from the graph, the number of collisions increases tremendously

which in turn increases the number of debris.

So it is our responsibility to keep the environment around the earth clean thereby by

increasing our chance to find a new home (some other planet to live). Thus we

increase the possibility of finding new friends with the help of the advanced

communication technology.

Thus it is in our hands to decide whether the future is going to be either dark and

gloomy or clean and spacious.

CONCLUSION

There are various methods in which the space debris issue can be handled. Methods

like attaching rocket motors in debris, using of electrodynamic tether, radiation

pressure, providing better shielding, manoeuvring and automatic de orbiting systems

in the future space missions will help in solving the problem. The implementation of

these techniques would lead to a bright future.

Satellite communication would develop faster as there will be no hindrance to it.

Every point in the earth, even the poles could be linked via satellites. Communication

will be faster, better and cheaper. Exploring the outer space would be easier and inter

planetary communication will flourish.

Even though this problem might look unimportant and is being neglected by people, it

is of great concern for the developments in space and technology. A part of the

International Space Station should be allocated for space debris removal and control

called as Debris removal station. This monitors the motion, size, and mass of the

debris and removes them using an appropriate method suitable for that particular

debris.

The hazards caused by the space debris will be immense. It requires a lot of financial,

materialistic and manpower to restore the damage done.

Prevention is better than cure. Its high time we start thinking about space junk and act

cautiously.

“The beginning is always today” should be our approach, otherwise the future will be

a ?.

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