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SPACE DEBRIS AND PRESENT ACTIVE DEBRIS
REMOVAL TECHNIQUES
Seminar Report

ABSTRACT
Space debris is a rapidly growing threat to space environment
and space activity. Recent statistical data shows that 70% of the catalogued objects in
Earth orbit, larger than 1 cm size, are in low earth orbit (LEO), which extends up to
2000 km. Collisions and explosions will further lead to catastrophic runaway debris
proliferation phenomenon known as “Kessler Syndrome’. As the LEO Debris is
steadily increasing, effective mitigation methods are quite essential to preserve the
space/near earth environment.
Various space debris mitigation techniques have been evolved over the
years such as predicting the collisions and accordingly maneuvering the satellites to
avoid collisions, protection of satellites from collisions and removal of space debris.
Predicting and maneuvering of satellites to avoid collision is not an effective solution
as it is limited to catalogued objects. Protection of satellites from collisions is also an
ineffective solution considering the mass, cost, etc. involved. Removal of space debris
can be divided into two broad categories namely (a) removal of existing space debris
by launching ‘Service satellite’ (b) planning ahead to de-orbit the satellites after useful
lifetime. Using service satellite, existing debris can be removed by numerous
techniques namely robotic arm based service satellite, electro-dynamic tether based
service satellite, net-based service satellites etc. To de-orbit satellites after useful
lifetime, many methods can be considered such as propulsion techniques, electro-dynamic
tether techniques, deployable sail etc.
i

CONTENTS
CHAPTER TITLE PAGE NO:
1. INTRODUCTION 1
2. SPACE DEBRIS 2
2.1 DEFINITION 2
2.2 THE NEED FOR ACTIVE DEBRIS REMOVAL 3
2.3 SPACE SURVEILLANCE NETWORK (SSN) 4
3. ACTIVE DEBRIS REMOVAL TECHNIQUES 6
3.1 ELECTRO-DYNAMIC TETHER 7
3.2 CAPTURE AND REMOVAL 9
3.2.1 CAPTURE USING NET DEVICE 9
3.2.2 ROBOTIC ARM BASED CAPTURE 10
3.3 LASER BASED TECHNIQUES 11
3.3.1 GROUND BASED LASER TECHNIQUE 12
3.3.2 SPACE BASED LASER TECHNIQUE 13
3.4 MOMENTUM EXCHANGE TETHERS 14
3.5 SOLAR SAILS 15
4. CHALLENGES IN INSTITUTING EFFECTIVE 17
SPACE DEBRIS REMOVAL
5. CONCLUSION 18
6. REFERENCES 19
ii

LIST OF FIGURES
FIGURE NO. TITLE PAGE NO:
2.1 THE DISTRIBUTION OF LOW EARTH 2
iii
ORBIT DEBRIS
2.2 POTENTIAL LONG TERM BENEFITS OF 4
LARGE DEBRIS MITIGATION
2.3 IRIDIUM 33 5
2.4 KOCMOC 2251 5
3.1 PRINCIPLE OF OPERATION OF
ELECTRO-DYNAMIC TETHER 7
3.2 ELECTRO-DYNAMIC TETHER FORCE BY
INTERACTION WITH PLASMA IN ATMOSPHERE 8
3.3 ORBITAL DEBRIS CAPTURE USING A NET 9
3.4 ROBOTIC ARM BASED SERVICE SATELLITE 10
3.5 CAPTURING USING ROBOTIC ARM 11
3.6 GROND BASED LASER 12
.
3.7 DEORBITIG BY LASER 13
3.8 SPACE BASED LASER 14
3.9 MOMENTUM EXCHANGE TETHER OPERARION 15
3.10 DEPLOYED SOLAR SAIL IN SPACE 16

LIST OF TABLES
TABLE NO. TITLE PAGE NO:
1 ESTIMATED AMOUNT OF ORBITAL DEBRIS 5
iv

SPACE DEBRIS AND PRESENT ACTIVE DEBRIS REMOVAL TECHNIQUES
CHAPTER 1
INTRODUCTION
Past design practices and deliberate and inadvertent explosions in space
have created a significant debris population in operationally important orbits. The
debris consists of spent spacecraft and rocket stages, separation devices, and products
of explosion. Much of this debris is resident at altitudes of considerable operational
interest. Two types of space debris are of concern: 1) large objects whose population is
large relative to the population of similar masses in the natural flux; and 2) A large
number of smaller objects whose size distribution approximates natural meteoroids.
The interaction of these two classes of objects, combined with their long residual times
in orbit, leads to the further concern that inevitable there will be collisions producing
additional fragments and causing the total population to grow rapidly.
Some efforts to provide a definitive assessment of the orbiting debris
problem have been and are being made by various government agencies and
international organizations. Principal areas of concern are the hazards related to
tracked, untracked, and future debris populations. Studies are being conducted in the
areas of technology, space vehicle design, and operational procedures. Among these
are ground-and- space-based detection techniques, comprehensive models of earth-space
environment, spacecraft designs to limit accidental explosions, and different
collision-hazard assessment methods. Occasional collision avoidance and orbit-transfer
maneuvers are being implemented for selected satellites in geosynchronous orbits. The
results and experience gained from the activities will, in time, create a better
understanding of the problem and all its implications so that appropriate actions can be
taken to maintain a relatively low- risk environment for future satellite systems.
Dept. of ECE, LMCST 1

CHAPTER 2
SPACE DEBRIS
2.1 DEFINITION
Satellites have become an integral part of the human society but they
unfortunately leave behind an undesirable by-product called space debris. Orbital space
debris is any man-made object orbiting around earth which no longer serves a useful
function. Non-functional spacecrafts, abandoned launch vehicle stages, mission related
objects and fragments from breakups are all considered orbital space debris. Since the
last decade there are growing concerns that artificial orbital debris generated by space
activities is degrading the near earth space environment. Recent statistical data shows
that 70% of the catalogued objects in Earth orbit, larger than 1 cm size, are in low earth
orbit (LEO). Figure 1 shows the distribution of LEO debris. The increasing threat
posed by space debris to active satellite demands high attention. Collisions and
explosions will proliferate the debris population drastically thereby degrading the space
environment further.
Fig 2.1 The distribution of low earth orbit (LEO) debris as a function of altitude and declination.
The lifetime of all orbital debris depends on their size and altitude. In
LEO, an object below 400 km will deorbit within a few months because of atmospheric
drag and gravitational force, whereas, objects above 600 km may stay in the orbit for

tens of years. As the LEO is a limited resource, it is very important to explore the
various space debris mitigation techniques and suitable measures are to be taken to
solve the space debris problem.
Three categories of space debris, depending on their size:
1. Category I (<1cm) - They can make significant damage to vulnerable parts of a
satellite.
2. Category II (1-10cm) - They tend to seriously damage or destroy a satellite in a
collision.
3. Category III (>10cm) – They may completely destroy a satellite in a collision
and can be tracked easily.
2.2 THE NEED FOR ACTIVE DEBRIS REMOVAL
Long term forecasting predicts approximately 20 catastrophic collisions
during the next 200 years. The need for a service vehicle having adequate
maneuverability, rendezvous and docking capability, and the ability to make a secure
attachment to an arbitrarily rotating object was realized. Projections for the future state
of orbital debris show that if all launch activity was stopped now, the debris field
would continue to grow, with cascading failures making the space environment
essentially unusable by 2100.
Projections showing the use of ADR technology demonstrate that if
three to five pieces of the most concerning debris objects were removed per year,
this environment could be stabilized, and that the removal of ten or more per
year would begin the process of mitigating the problem. Figure 2 shows the
predicted effect of actively removing objects to mitigate the growth of the debris
population.

Fig 2.2 Potential Long Term Benefits of Large Debris Mitigation
2.3 SPACE SURVEILLANCE NETWORK (SSN)
The United States Space Surveillance Network detects, tracks, catalogs
and identifies artificial objects orbiting Earth, i.e. active/inactive satellites,
spent rocket bodies, or fragmentation debris. The system is the responsibility of
the Joint Functional Component Command for Space, part of the United States
Strategic Command (USSTRATCOM). Space surveillance accomplishes the
following:
 Predict when and where a decaying space object will re-enter the Earth's
atmosphere;
 Prevent a returning space object, which to radar looks like a missile, from triggering
a false alarm in missile-attack warning sensors of the U.S. and other countries;
 Chart the present position of space objects and plot their anticipated orbital paths;
 Detect new man-made objects in space;
 Correctly map objects travelling in the earth's orbit;
 Produce a running catalog of man-made space objects;
 Determine which country owns a re-entering space object;

 Inform NASA whether or not objects may interfere with satellites and International
Space Station orbits.
There is currently more than 15,000 objects, which are tracked and kept
in a catalog by SSN but the actual space debris number is much more than the
cataloged. The following table shows the estimated amount of debris objects by their
size:
Debris Size 0.1-1cm 1-10cm >10cm
Total Number at all
altitudes
150million 780,000 23,000
Debris in Low-Earth
Orbit
20 million 400,000 15,000
Table 2.1 Estimated amount of orbital debris
The 2009 satellite collision was the first accidental hypervelocity
collision between two intact artificial satellites in low Earth orbit. It occurred on
February 10, 2009.In that unprecedented space collision, a commercial communication
satellite (IRIDIUM33) and a dysfunctional Russian satellite (COSMOS 2251)
impacted each other above Northern Siberia, creating a cloud of new debris objects.
Till now, over 1719 large fragments have been observed from this collision.
Fig 2.3 Iridium 33 Fig 2.4 Космос 2251

CHAPTER 3
ACTIVE DEBRIS REMOVAL TECHNIQUES
To solve the issue of current debris in orbit, several solutions have been
proposed. Other than removing objects near the end of their life using onboard
propulsion systems (which only applies to operational objects with propulsion
systems), a proposal has been made to reduce the risks associated with current objects
in orbit: active space debris removal (ADR).Protection of spacecrafts and collision
avoidance are the measures in which space debris multiplication is avoided thereby
mitigating the space debris. Removal of space debris is one more measure that can be
used to clean up the space environment.
Studies have shown that the active removal of at least ten objects from
LEO region is the most effective way to prevent debris collision from cascading.
Removal of existing space debris consists of recovering the debris or make them return
to earth. For this purpose, a dedicated space mission is required.
The space mission called ‘Service satellite’ has to identify the ‘target
satellite’, capture it and should either recover it or deorbit it. For deorbiting the
dysfunctional satellites, the ‘Service satellite’ carrying a number of deorbiting devices
performs rendezvous with identified targets and mates with it by means of robotic arm.
A deorbiting device is attached to the target by means of second robotic arm after which
the service satellite detaches itself from the target and activates the deorbiting device
to perform the required operation.
A very large number of possibilities have been identified to perform the
deorbiting of the spacecraft itself. Following methods can be envisaged for removal
of existing space debris using a service satellite or to perform the deorbiting of the
spacecraft:

3.1 ELECTRO-DYNAMIC TETHER
In general, a tether is a long cable (up to 100 km or longer) that connects
two or more spacecraft or scientific packages. Tethers in space can be used for a variety
of applications such as power generation, propulsion, remote atmosphere sensing, and
momentum transfer for orbital maneuvers, microgravity experimentation, and artificial
gravity generation. Electro-dynamic tethers are conducting wires that can be either
insulated or bare, and that makes use of an ambient field to induce a voltage drop across
its length.
Electro-dynamic tether moves in the Earth’s magnetic field and is
surrounded by ionospheric plasma. The solar arrays generate an electric current that is
driven through the long conductor. The magnetic field induces a Lorentz force on the
conductor that is proportional to length, current, and local strength and direction of the
magnetic field. Electrons are collected from the plasma near one end of the bare
conductor, and are ejected by an electron emitter at the other end.
Fig 3.1 Principle of operation of an electro-dynamic tether
The use of Electro-Dynamic Tethers (EDTs) takes advantage of the
effect of placing a conductive element in the Earth’s magnetic field. The object to be

de-orbited is connected via a tether to a de-orbiting element, and both ends have a
means of providing electrical contact to the ambient ionospheric plasma. The
interaction of the conducting tether moving at orbital speeds induces current flow along
the tether, causing a Lorentz force due to the interaction between the tether and the
Earth’s magnetic field; this causes an acceleration on the object to which the tether is
attached. Figure 4 shows a notional EDT system and the resulting force on the
spacecraft to which it is attached.
A tether made of conductive aluminum and massing only 2 to 2.5% of
the mass of the object to be de-orbited is sufficient to provide significant deceleration
and speed up the de-orbit process. Studies have shown that for high-inclination, low-altitude
LEO satellites (e.g., Iridium constellation), the time required for de-orbit from
a 780 km altitude orbit can be reduced from 100 years to 1 year. The technology
constraints involve potential difficulty in attaching the tether, but this could be done via
a harpoon, a hooked net, or an adhesive suction cup. The cross-sectional area and
possibility of conjunction collisions with other objects is also increased with the use of
the tethers, but less so than with other proposed methods. This approach is the preferred
method that our analysis adopts for removal of debris objects from low-Earth orbit.
Fig 3.2 Electro-Dynamic Tethers Create a Force by Interacting with Plasma in the Earth’s Atmosphere

3.2 CAPTURE AND REMOVAL
Capture and removal to a parking/disposal orbit is another promising
technique, and various initiatives have been under way to study these scenarios.
Essentially, the techniques involve the capture of an arbitrarily rotating object via
robotic arms or other means. The captured object is then moved via a velocity impulse
from the ADR vehicle to a new disposal orbit. This technique is not particularly useful
in LEO, but is the preferred disposal method in GEO, by which satellites, rocket stages,
etc. would be hauled to a higher parking/graveyard orbit, generally referred to as super
synchronous orbit. In these orbits, the periapses of the disposed satellite cannot enter
the geostationary orbit altitude, even with solar radiation pressure and lunar
gravitational perturbations. However, given that this practice is a relatively recent
requirement, there continues to be a need to remove older satellites, malfunctioning
satellites, and space debris from geostationary orbit.
3.2.1 CAPTURE USING NET DEVICE
The capture by means of a net device is based on its deployment around
the debris being targeted as shown in Figure 3.2. Once the debris is surrounded, the net
is closed and the debris is captured. The net is considered as a one shot device that
cannot be ground-tested before operation. Capturing objects with the net is still
considered to be a relatively new form of ADR, which requires further assessment. Net
technology is inherently complex, and best suited for targeting debris with no breakable
parts in medium and high orbits.
Fig 3.3 Orbital debris capture using a net

3.2.1 ROBOTIC ARM BASED CAPTURE
The robotic arm based capture and removal techniques uses a service
satellite which captures the target satellite using a robotic arm. Here the limitations are
that these techniques are extremely complex, costly, requires complex maneuvering of
the service satellite. Figure 3.3 illustrates the concept of robotic arm based service
satellite used to deorbit the spacecraft.
Fig. 3.4 robotic arm based service satellite concepts
Robotic systems are capturing devices classified according to the
number of actuator arms. The single arm robotic capturing devices are equipped with
a single tool, usually a claw at the end of the arm, which is used to interface with the
debris. The multi-arm robotic capturing devices have several arms or tentacles
equipped with claws or other grabbing mechanisms at the extremities to grapple the
debris with several contact points. These capturing devices are attached to a servicing
vehicle or satellite, enabling active controlled re- entry or on-orbit servicing for passive
re-entry. Graveyard deorbiting is also possible, as robotic systems can be operational
at any altitude. They allow reuse in several missions, and aborting and re-starting
operations within a single mission. Single arm robotic devices capture and manipulate
debris using a mechatronic tool at the extremity of the arm. The mechatronics elements,
which perform the berthing and docking maneuvers, are one of the main challenges in
robotic systems.

Fig 3.5 Capturing using robotic arm
Due to the large number of the small to medium debris (< 10cm),
capture of individually targeted debris is inefficient. Orbital maneuvering energies are
far too excessive, as is the cost. To overcome this problem, “debris sweepers” are used
to cover large cross sectional areas in orbital zones where operational satellites are most
affected by potential collisions in an attempt to catch small and medium debris that are
difficult to track individually. The number of debris that these devices could capture is
determined by the statistics of the debris density, distribution, and the area swept by
the sweeper.
3.3 LASER BASED TECHNIQUES
A high power pulsed laser is used to ablate the layers of the
dysfunctional satellite thereby producing enough cumulative thrust to deorbit the
spacecraft. This laser can be either ground based laser or space based laser. In this
technique, the surface material of the debris becomes the propellant i.e. the intensity of
the laser must be sufficiently high to cause the material on the surface of the debris to
form vapour and this expansion of the vapour imparts a thrust to the object. The
limitation of this technique is that it requires precise orbital parameters of the target

spacecraft and laser should have high illumination power. Mainly the laser based
techniques are two types:
1. Ground based laser technique
2. Space based laser technique
3.3.1 GROUND BASED LASER TECHNIQUE
Lasers are designed to target debris between one and ten centimeters in
diameter. Collisions with such debris are commonly of such high velocity that
considerable damage and numerous secondary fragments are the result. The laser
broom is intended to be used at high enough power to penetrate through the atmosphere
with enough remaining power to ablate material from the target. The ablating material
imparts a small thrust that lowers its orbital perigee into the upper atmosphere, thereby
increasing drag so that its remaining orbital life is short. The laser would operate in
pulsed mode to avoid self-shielding of the target by the ablated plasma. The power
levels of lasers in this concept are well below the power levels in concepts for more
rapidly effective anti-satellite weapons.
Fig 3.6 Ground based laser

NASA research in 2011 indicated that firing a laser beam at a piece of
space junk could alter velocity by 0.04 inches (1.0 mm) per second. Persisting with
these small velocity changes for a few hours per day could alter its course by 650 feet
(200 m) per day. While not causing the junk to reenter, this could maneuver it to avoid
a collision
Fig 3.7 Deorbiting by laser
Some of the major advantages of ground based laser are that they
provide very high power and technology is much mature. But the Energy lose is
significantly much higher due to atmospheric absorption and they cannot be moved
freely in a huge range.
3.3.2 SPACE BASED LASER TECHNIQUE
This technique is similar to the ground based laser technique. The only
difference is that the laser beam is produced by a service satellite. This avoides the
limitations seen from the ground based laser technique. The major advantages are that
that
1. There is no negative atmospheric effects
2. be able to track and target debris with a much larger field of view
3. focus on targets for longer periods of time

Fig 3.8 Space based laser
But the main disadvantages of the space based laser techniques are the
cost is much larger to build, lunch and operate and it can be used as a space-based
antisatellite weapon system.
3.4 MOMENTUM EXCHANGE TETHERS
Momentum exchange tethers are part of another potential solution and
involve the tethering of two spacecraft. Generally, a vehicle in a higher orbit will attach
a tether to a lower vehicle. The difference in velocity and perturbing accelerations will
cause both vehicles to swing along an arc defined by the joining tether. If the lower
object is released at the point of greatest retrograde velocity, this will lower its perigee
while the apogee will be raised for the higher object. Figure 3.8 shows the operation of
the momentum exchange tether.

Fig 3.9 Momentum Exchange Tether Operation
The Momentum-Exchange Tether is a long, thin cable that attaches two
masses together in space and is capable of imparting momentum to objects that come
within its grasp. This cable has a large mass on one end and is intended to be deployed
into orbit around Earth.
3.5 SOLAR SAILS
Solar sails have gained some attention as a possible debris removal
technique. Basically, the concept is simple: a reflecting material, which may be very
thin, is deployed from an orbiting body and solar photons that strike the material are
reflected, imparting acceleration to the orbiting body. Solar sails are more useful for
orbit modifications in which there is no net exchange of energy and are therefore
particularly suitable for altering orbital eccentricity. The largest contribution to altitude
lowering or de-orbiting actually comes from an increased atmospheric drag rather than
the solar/photon effect.

Fig 3.10 Deployed solar sail in space
Some of the major advantages of solar sails are
1. It is an effective option for disposal of objects in very high orbits
2. require no propellant or engines
But the only disadvantage is that it is hard to deployment and control

CHAPTER 4
CHALLENGES IN INSTITUTING EFFECTIVE SPACE DEBRIS
REMOVAL
There are so many challenges in instituting an effective space debris removal.
 Here the Active space Debris Removal (ADR) techniques require substantial
time and money to develop and deploy. It costs around $10,000 per kilogram to
lunch anything into a medium level orbit.
 Also the technical challenges for the making of space debris remover satellites
or spacecrafts are very difficult.
 Another problem with ADR technique is that there is a higher possibility of
changing space debris removal systems into another space debris.
 Another main problem with the space debris removal is the lack of clear policies
on the international level. Currently the ownership of a satellite or upper stage
of a rocket remains with the country that launched it even after the satellite or
rocket upper stage is no longer used. This means that one country cannot
remove the debris launched from a second country without that second
country’s permission.

CHAPTER 5
CONCLUSION
There are many methods for active debris removal and some of the
important methods have been listed here. These methods can effectively help in
removing the active debris in space and thus improve operations of satellites by not
interfering in their operation. This will also help in reducing dangers of satellites
collision with space debris. The removal of existing space debris have been explored
to minimize the space debris threat. However, the realistic and effective method to
solve space debris problem is to avoid any new debris generation.
Studies indicate that usage of propulsion systems by decelerating
spacecrafts is not an effective solution as it increases complexity, mass and cost.
Electro-dynamic tether systems can be considered for removing the spacecrafts after
useful lifetime to greatly increase the orbital decay of the spacecraft. Numerical
analysis indicate that EDT systems massing just 2 to 5% of the total spacecraft mass
can deorbit the spacecraft within few months thus providing significant mass/cost
savings compared to propulsion systems. Electro-dynamic tether technique has been
proposed as an innovative solution to deorbit the spacecrafts after useful lifetime.
So our space exploration agencies like ISRO and NASA should explore the possibilities
to prevent orbital space debris by using efficient and economic techniques like EDT to
keep our space environment safe for the future scientific space explorations.

CHAPTER 6
REFERENCES
[1] Jesse R Quinlan, A preliminary systems-level analysis of candidate active space
debris removal architectures, AAS 11-253.
[2] Robert Osiander and Paul Ostdiek, Handbook of Space Engineering, Archaeology.
[3] Marco M. Castronuovo, Active space debris removal-A preliminary mission
analysis and design, Acta Astronautica 69 (2011) 848-859.
[4] Carmen Pardini, Toshiya Hanada and Paula H Krisko, Benefits and risks of using
electrodynamic tethers to de-orbit spacecrafts, Acta Astronautica 64 (2009) 571-588.
[5] Robert P Hoyt and Robert L Forward, The Terminator Tether: Autonomous deorbit
of LEO spacecraft for space debris mitigation, AIAA-00—0329.
[6] Holger Burkhardt, Martin Sippel, et, Evaluation of propulsion systems for satellite
end-of-life deorbiting, Germany, AIAA-2002—4208.
[7] Shin Ichiro Nishida, Satomi Kawamoto, etc. , Space debris removal system using a
small satellite, Acta Astronautica 65(2009) 95-102.
[8] Jonathan W Campbell, Using Lasers in Space: Laser Orbital debris removal and
asteroid deflection
[9] “Position paper on orbital debris,” International Academy of Astronautics, 8 March
1993.
[10] David S. F. Portree and Joseph P. Loftus, Jr., Orbital Debris and Near-Earth
Environmental Management: A Chronology, NASA reference publication 1320, 1993.
[11] Patera, R. P., and Ailor, W. H., The realities of re-entry disposal, AAS Paper 98-
174, Feb. 1998.
[12] Vladimir A. Chobotov, Orbital Mechanics, 3rd ed., AIAA education series, 2002.

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