Seminar report on GPS based Space Debris Removal System

Gps based Space Debris Removal System 2014-2015

Dept of ECE, VIT Page 1

CHAPTER 1

INTRODUCTION

Space debris, also known as orbital debris, space junk, and space waste, is the

collection of defunct objects in orbit around Earth. This includes everything from

spent rocket stages, old satellites, fragments from disintegration, erosion, and

collisions. Since orbits overlap with new spacecraft, debris may collide with

operational spacecraft.

Since the number of satellites in Earth orbit is steadily increasing, space

debris, if left unchecked, will eventually pose a serious hazard to near-Earth space

activities, and so effective measures to mitigate it are becoming urgent. Equipping

new satellites with an end- of-life de-orbit and orbital lifetime reduction capabil-

ity could be an effective future means of reducing the amount of debris by

reducing the probability of collisions between objects, while using spacecraft to

actively remove debris objects and to retrieve failed satellites are possible

measures to address existing space debris.

Most space debris is less than 1cm (0.39in) including dust from solid rocket

motors, surface degradation products such as paint flakes, and coolant released by

nuclear power satellites. Impacts of these particles cause erosive damage similar

to sand blasting.

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.

Currently about 19,000 pieces of debris larger than 5 cm are tracked, with

another 300,000 pieces smaller than 1 cm below 2000 km altitude. For

comparison, ISS orbits in the 300–400 km range and both the 2009 collision and

2007 antisat test event occurred at between 800–900 km.



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.

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.



Fig. 2.1 Tracked orbital debris population catalogued by U.S. Air Force as of 2010.

2.2 SPACE DEBRIS EVENTS AND ITS ENVIRONMENT

There has been a steady growth of space debris since the launch of Sputnik in

1957, with jumps following two of the largest debris creating events in history: the

2007 Chinese anti-satellite (ASAT) test and the 2009 Iridium-Cosmos collision.

The first of these events occurred on January 11, 2007, when China

intentionally destroyed its Fengyun-1C satellite while testing its newly developed

ground-based ASAT system. It was the largest debris-creating event in history,

producing at least 150,000 pieces of debris larger than one centimeter (NASA

2008, 3). The resulting debris has spread into nearpolar orbits ranging in altitude

from 200 to 4,000 kilometers. Roughly 80 percent of this debris is expected to

stay in orbit for at least the next one hundred years and threatens to impact

operating satellites (CelesTrak 2009). The test illustrates how a single unilateral



action in space can create long-term implications for all space-faring nations and

users of satellite services.

The second major space-debris creating event was the accidental collision

between an active Iridium satellite and a defunct Russian military satellite on

February 10, 2009. The collision created two debris clouds holding more than

200,000 pieces of debris larger than one centimeter at similar altitudes to those of

the 2007 Chinese ASAT test (Johnson 2009b). It was the first time two intact

satellites accidentally crashed in orbit, challenging the ―Big Sky Theory‖.

Currently, the highest spatial densities of space debris are in near-polar orbits

with altitudes of 800 to 1,000 kilometers. These are known as ―critical orbits‖

because they are most likely to reach the point where the production rate of new

debris owing to collisions exceeds that of natural removal resulting from

atmospheric drag. They exist because several large fragmentation events have

occurred in these regions, such as the two described above, and because debris

lifetimes can last up to decades at these altitudes.

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:

1. Predict when and where a decaying space object will re-enter the Earth's

atmosphere;

2. 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;

3. Chart the present position of space objects and plot their anticipated orbital

paths;



4. Detect new man-made objects in space;

5. Correctly map objects travelling in the earth's orbit;

6. Produce a running catalog of man-made space objects;

7. Determine which country owns a re-entering space object;

8. Inform NASA whether or not objects may interfere with satellites and

International Space Station orbits.

The following table shows the estimated amount of debris objects by their

size:

Table. 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.



CHAPTER 3

TYPES OF ORBITS

Since the launch of the first satellite in 1957 humans have been placing an

increasing number of objects in orbit around the Earth. This trend has accelerated

in recent years thanks to the increase in number of states which have the capability

to launch satellites and the recognition of the many socioeconomic and national

security benefits that can be derived from space. There are currently close to 1000

active satellites on orbit, operated by dozens of state and international

organizations. More importantly, each satellite that is placed into orbit is

accompanied by one or more pieces of non-functional objects, known as space

debris. More than 20,000 pieces of space debris larger than 10 cm are regularly

tracked in Earth orbit, and scientific research shows that there are roughly 500,000

additional pieces between 1 and 10 cm in size that are not regularly tracked.

Although the average amount of space debris per cubic kilometer is small, it is

concentrated in the regions of Earth orbit that are most heavily utilized…and thus

poses a significant hazard to operational spacecraft.

The artificial satellites are classified for the size (large >1000 kg, medium size

500 –1000kg, small (minisatellites 100-500 kg, microsatellites 10-100 kg,

nanosatellites 1-10 kg, picosatellites 0,1-1 kg and femtosatellites <100 g)); for the

applications (exploration, communications, navigation and observation); for the

character (military, civil and dual); and for the orbital height (LEO, MEO, HEO,

GEO).

3.1 LOW EARTH ORBIT ( LEO )

LEO (Low Earth Orbit, which means low orbits). Orbiting the Earth at a

distance between 500 and 2000 km of and its speed allows them to fly around the

world in 2 hours approximately, with a velocity between 20000 and 25000 km/h.

They are used to provide geological data on the movement of Earth's plates,

remote sensing, spatial investigation, metereology, vigilance and the phone



industry satellite. Allow the determination of space debris and the utilization of

the electromagnetic spectrum.

Fig. 3.1 LEO

Most satellites, the International Space Station, the Space Shuttle, and the

Hubble Space Telescope are all in Low Earth Orbit (commonly called "LEO").

This orbit is almost identical to our previous baseball orbiting example, except

that it is high enough to miss all the mountains and also high enough that

atmospheric drag won't bring it right back home again.

Every satellite, space probe and manned mission has the potential to create

space debris. Any impact between two objects of sizeable mass can spall off

shrapnel debris from the force of collision. Each piece of shrapnel has the

potential to cause further damage, creating even more space debris. With a large

enough collision (such as one between a space station and a defunct satellite), the

amount of cascading debris could be enough to render Low Earth Orbit essentially

unusable.

3.1.1 Advantages of LEO:

Low Earth Orbit is used for things that we want to visit often with the Space

Shuttle, like the Hubble Space Telescope and the International Space Station. This

is convenient for installing new instruments, fixing things that are broken, and

inspecting damage. It is also about the only way we can have people go up, do

experiments, and return in a relatively short time.



3.1.2 Disadvantage of LEO:

The first is that there is still some atmospheric drag. Even though the amount

of atmosphere is far too little to breath, there is enough to place a small amount of

drag on the satellite or other object. As a result, over time these objects slow down

and their orbits slowly decay. Simply put, the satellite or spacecraft slows down

and this allows the influence of gravity to pull the object towards the Earth.

3.2 MEDIUM EARTH ORBIT ( MEO):

MEO (Medium Earth Orbit, stockings orbits). Are satellites moving on orbits

close moderately of about 20000 km. Its use is intended for mobiles

communications, navigation (GPS), measurements of space experiments and

effective use of the electromagnetic spectrum.

A medium earth orbit (MEO) satellite is one with an orbit within the range

from a few hundred miles to a few thousand miles above the earth's surface.

Satellites of this type orbit higher than low earth orbit (LEO) satellites, but lower

than geostationary satellites.

The orbital periods of MEO satellites range from about two to 12 hours. Some

MEO satellites orbit in near perfect circles, and therefore have constant altitude

and travel at a constant speed. Other MEO satellites revolve in elongated orbits.

The perigee (lowest altitude) of an elliptical-orbit satellite is much less than

apogee (greatest altitude). The orbital speed is much greater near perigee than near

apogee. As seen from a point on the surface, a satellite in an elongated orbit

crosses the sky in just a few minutes when it is near perigee, as compared to

several hours when it is near apogee. Elliptical-orbit satellites are easiest to access

near apogee, because the earth-based antenna orientation does not have to be

changed often, and the satellite is above the horizon for a fairly long time.

A fleet of several MEO satellites, with orbits properly coordinated, can

provide global wireless communication coverage. Because MEO satellites are

closer to the earth than geostationary satellites, earth-based transmitters with

relatively low power and modest-sized antennas can access the system. Because



MEO satellites orbit at higher altitudes than LEO satellites, the useful footprint

(coverage area on the earth's surface) is greater for each satellite. Thus a global-

coverage fleet of MEO satellites can have fewer members than a global-coverage

fleet of LEO satellites.

3.3 GEOSTATIONARY ORBITS:

As the height of a satellite increases, so the time for the satellite to orbit

increases. At a height of 35790 km, it takes 24 hours for the satellite to orbit. This

type of orbit is known as a geosynchronous orbit, i.e. it is synchronized with the

Earth.

One particular form of geosynchronous orbit is known as a geostationary

orbit. In this type of orbit the satellite rotates in the same direction as the rotation

of the Earth and has an approximate 24 hour period. This means that it revolves at

the same angular velocity as the Earth and in the same direction and therefore

remains in the same position relative to the Earth.

GEO satellites provide the kind of continuous monitoring necessary for

intensive data analysis. By orbiting the equatorial plane of the Earth at a speed

matching the Earth's rotation, these satellites can continuously stay above one

position on the Earth's surface. Because they stay above a fixed spot on the

surface, they provide a constant vigil for the atmospheric "triggers" for severe

weather conditions such as tornadoes, flash floods, hail storms, and hurricanes.

When these conditions develop these GEO satellites are able to monitor storm

development and track their movements.

3.3.1 Applications of Geostationary Satellites:

Geostationary satellites have modernized and transformed worldwide

communications, television broadcasting, and meteorological and weather

forecasting. They also have a number of significant defense and intelligence

applications.



3.4 HIGHLY ELLIPTICAL ORBIT (HEO):

HEO (Highly Elliptical Orbit, highly elliptical orbits). These satellites do

not follow a circular orbit, but its orbit is elliptical. This implies that much greater

distances reached at the point furthest from the orbit. They are often used to map

the surface of the Earth, as they can detect a wide angle of Earth's surface. The

perigee about 500 km and apogee of 50000 km, your orbit is tilted, the period

varies from 8 to 24 hours, used in communications and space surveillance and

very sensitive to the asymmetry of the Earth (the orbit is stabilized if i=63.435°).

Remember Kepler's second law: an object in orbit about Earth moves

much faster when it is close to Earth than when it is farther away. Perigee is the

closest point and apogee is the farthest (for Earth - for the Sun we say aphelion

and perihelion). If the orbit is very elliptical, the satellite will spend most of its

time near apogee (the furthest point in its orbit) where it moves very slowly. Thus

it can be above home base most of the time, taking a break once each orbit to

speed around the other side.

Fig. 3.2

With the highly elliptical orbit described above, the satellite has long dwell time

over one area, but at certain times when the satellite is on the high speed portion

of the orbit, there is no coverage over the desired area. To solve this problem we

could have two satellites on similar orbits, but timed to be on opposite sides of the



orbit at any given time. In this way, there will always be one satellite over the

desired coverage area at all times.

Fig. 3.3

If we want continuous coverage over the entire planet at all times, such as the

Department of Defense's Global Positioning System (GPS), then we must have a

constellation of satellites with orbits that are both different in location and time.

Fig. 3.4



In this way, there is a satellite over every part of the Earth at any given time. In

the case of the GPS system, there are three or more satellites covering any

location on the planet.

Fig. 3.5 Highly elliptical satellite orbit, HEO

3.4.1Highly elliptical orbit, HEO, applications:

The highly elliptical satellite orbit can be used to provide coverage over any

point on the globe. The HEO is not limited to equatorial orbits like the

geostationary orbit and the resulting lack of high latitude and polar coverage.

As a result it ability to provide high latitude and polar coverage, countries such

as Russia which need coverage over polar and near polar areas make significant

use of highly elliptical orbits, HEO.

With two satellites in any orbit, they are able to provide continuous coverage.

The main disadvantage is that the satellite position from a point on the Earth does

not remain the same.



CHAPTER 4

APPROACHES TO ACTIVE DEBRIS

REMOVAL

Various approaches to remove debris from space have been proposed, and

some seem more technologically feasible than others. Techniques range from

attaching tethers, solar sails, or solid rocket motors to debris objects, to active

capture via nets followed by removal to other orbits. Of these techniques, one

seems particularly feasible and is selected for use in the study presented herein.

4.1 ELECTRO-DYNAMIC TETHERS:

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 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.

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 shows a notional EDT system and the resulting force

on the spacecraft to which it is attached.

Fig.4.1 Electro-Dynamic Tethers Create a Force by Interacting with Plasma in the

Earth’s Atmosphere

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.8 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.

The EDT captures as pace junk in a net the size of a house. The lifespan of

EDT is not limited by the size of its fuel tank. That’s because this junk capturer is

powered not by liquid fuel, but by a long conducting wire that generates electricity

through as it moves through the earths magnetic field. So an EDT vehicle could

operate indefinitely. It could target a piece of debris capture it in a net, deliver it



into the earths atmosphere and then turn around and start over again. On average it

takes 10 days to remove an object, so each EDT vehicle could remove 36 objects

per year.

4.2 LASER BROOMS:

Lasers in space raise romantic notions of efficiently vaporizing debris material

that could pose a risk to other objects in orbit. The use of lasers for ADR activities

is questionable at best, partially due to a requirement to keep a very focused beam

pointed at a rapidly and arbitrarily moving target for a long period of time, such

that the surface can be ablated enough to induce an acceleration. Moreover,

generating adequate levels of power for a space-based laser is beyond our current

space power generation capabilities. Additionally, the use of such lasers in space

could be problematic with respect to existing international weapons treaties and

UN regulations. Also, many of the objects that could be removed may contain

unspent propellant that could explode if heated by a laser, thus causing more

debris. While lasers may be of some use in removing smaller debris objects, they

are not relevant to the study presented herein.

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.



4.2.1 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.

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.4.2 Ground based 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.

Fig.4.3Deorbiting by laser

4.2.2 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

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

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.



Fig.4.4 Space based laser

4.3 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.

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



Fig.4.5 Deployed solar sail in space

4.4 SPACE NETS:

The capture by means of a net device is based on its deployment around the

debris being targeted as shown in Fig. 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.4.6 Orbital debris capture using a space net



4.5 COLLECTOR SATELLITES:

TAMU Space Sweeper with Sling-Sat(4S) :

This technique is also about capturing of space debris but with a very less

amount of fuel usage. A university in Texas proposed this idea. The sling sat will

work on swinging capturing an object, then swinging it towards Earth’s

atmosphere to destroy it and then using the momentum to go towards the next

piece of debris for same process. By this technique, the fuel consumption will be

very less as the sling sat will use the momentum gained by throwing the debris.

To remove the space debris, many ideas have come up from different parts of

the world. But an idea that sounds most technical is to clean the debris object by

object. Obviously to travel for each object (and sometimes very widely spaced

objects) the spacecraft will require loads of fuel making it a much inefficient

project. The 4S system points to correct this flaw. It will trap the debris at the ends

of a spinning satellite, and then throw the object down while rotating in Earth's

atmosphere in order to destroy it. Then it will make use of the momentum

exchanged during the two actions to move towards the next piece to be captured.

This will minimize the fuel usage and extend the operational lifetime.

Fig.4.7 TAMU Sweeper with Sling-Sat



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.



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