Merged document 14

SPACE DEBRIS AND PRESENT ACTIVE DEBRIS

REMOVAL TECHNIQUES

Seminar Report

i

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.

ii

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

iii

LIST OF FIGURES

FIGURE NO. TITLE PAGE NO:

2.1 THE DISTRIBUTION OF LOW EARTH 2

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

iv

LIST OF TABLES

TABLE NO. TITLE PAGE NO:

1 ESTIMATED AMOUNT OF ORBITAL DEBRIS 5

SPACE DEBRIS AND PRESENT ACTIVE DEBRIS REMOVAL TECHNIQUES

Dept. of ECE, LMCST 1

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.



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;

http://en.wikipedia.org/wiki/Geocentric_orbit

http://en.wikipedia.org/wiki/Satellite

http://en.wikipedia.org/wiki/Rocket

http://en.wikipedia.org/wiki/Space_debris

http://en.wikipedia.org/wiki/Joint_Functional_Component_Command_for_Space

http://en.wikipedia.org/wiki/United_States_Strategic_Command

http://en.wikipedia.org/wiki/United_States_Strategic_Command

http://en.wikipedia.org/wiki/Orbital_decay

http://en.wikipedia.org/wiki/Atmospheric_entry

http://en.wikipedia.org/wiki/Earth%27s_atmosphere

http://en.wikipedia.org/wiki/Earth%27s_atmosphere

http://en.wikipedia.org/wiki/Radar

http://en.wikipedia.org/wiki/False_alarm



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

http://en.wikipedia.org/wiki/NASA

http://en.wikipedia.org/wiki/Satellite

http://en.wikipedia.org/wiki/International_Space_Station

http://en.wikipedia.org/wiki/International_Space_Station



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

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[8] Jonathan W Campbell, Using Lasers in Space: Laser Orbital debris removal and

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[9] “Position paper on orbital debris,” International Academy of Astronautics, 8 March

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[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.