Space debris poses a hazard to satellites and spacecraft. Thousands of small pieces of debris orbit Earth at high speeds and can damage satellites through collision. The risk of impact is increasing as the amount of debris grows. Proposed solutions to reduce debris include attaching rocket motors to slow objects, preventing collision through satellite maneuvering and shielding, and using electrodynamic tethers to deorbit junk. Other ideas are to use radiation pressure from lasers or sunlight to slow debris for atmospheric reentry and removal. With the growing number of satellites launched, space debris will increasingly threaten continued space exploration and use unless addressed.

1. SPACE DEBRIS & ITS HAZARDS ON
SATELLITE COMMUNICATIONS
-A GPS based debris removal system
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
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2. 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.
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.
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3. • 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
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
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4. generally used to keep something in place. In space, however, tethers could serve
several useful purposes.
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
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5. flow in a direction such that the tether is brought down into sub orbital levels along
with the debris. Thus the debris is deorbited.
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.
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6. By Einstein’s equation,
E = m c^2
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
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7. dt = time required to reduce the velocity from v1 to v2
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/Apower=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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8. 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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9. 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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10. 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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