2)Types of orbits
3) Sources of debris
4) Tracking and Measurement of debris
5) Clearance of space debris
WHAT ARE SPACE DEBRIS ?
Space debris , also known as orbital debris
, space junk and space waste
, is the collection of defunct objects in orbit
This includes everything from spent rocket
stages , old satellites , fragments from
disintegration , erosion and collision.
WHY ARE THEY A THREAT ?
Debris poses a growing threat to satellites and
could prevent the use of valuable orbits in the
Many pieces of debris are too small to monitor
but too large to shield satellites against.
1. Low Earth
2. Medium Earth
4. High Earth
Low Earth Orbit :
Situated at an altitude between 160km and 2000km from Earth’s surface.
It has a time period of about 127 minutes.
Objects below approx. 160km will experience very rapid orbital decay and
It is the simplest and most cost effective orbit for a satellite placement.
Currently , NASA tracks more than 8,500 objects larger than 10 cm in LEO.
Situated from 2000 km to
36,000 km above Earth’s
The most common use for
satellites in this region is for
navigation , communication
and space environment
Has an orbital period of 12
Earth Orbit :
It is a circular orbit at 35,786 km
above Earth’s surface and following the
Earth’s rotation .
An object in such an orbit has an
orbital period equal to the Earth’s
rotational period .
This makes them useful for
communications , as receiver on Earth
can always point in the same direction.
Situated at above 36,000 km.
Little used by satellites .
Orbital periods of such orbits are greater than 24 hours.
Hence , satellites have an apparent retrograde motion .
Debris in LEO :
Satellites in LEO are in many different orbital planes
providing global coverage and the 15 orbits per day
typical of LEO satellites result in frequent approaches
between object pairs.
After space debris is created , the orbital plane’s
direction will change over time , and thus collisions
can occur from virtually any direction . This leads to a
Debris at higher altitudes :
At higher altitudes , where atmospheric drag is less significant , orbital
decay takes much longer .
This issue is especially problematic in the valuable GEO orbits where
satellites are often clustered to share the same orbital paths .
It has been estimated that at least one close approach ( within 50 metres )
takes place every year .
On a positive note , relative velocities in GEO are low , compared to LEO
(about 1.5 kmps ).
This means that the debris field from such a collision will not have the
drastic effects as that of LEO , atleast over a short term .
SOURCES OF DEBRIS :
Tracking of debris :
Radar and optical detectors such as LIDAR are the main
tools used for tracking space debris.
Radio waves have been recently used. These waves are
transmitted into space and they bounce off of space junk
back to the origin that will detect and track the object.
Ground based radar facilities and space telescopes are
also used to track the debris.
Measurement of debris :
Returned hardware of space debris is a valuable source of
information of the environment .
Close examination of its surfaces allows an analysis of the
directional distribution and composition of the debris flux .
Some of the modules used were :
LDEF (Long duration exposure facility ) satellite
EURECA ( European Retrievable carrier )
Some methods are :
Electro dynamic tethers
Space nets and collectors
Tug-like satellites :
The tug like satellites drag the debris to a safe altitude
in order for it to burn up in the atmosphere .
It creates an electron emission to create a difference in
potential between the debris as negative and itself as
The satellite then uses its own thrusters to propel itself
along with the debris to a safer orbit .
Electro-dynamic tethers :
An electro-dynamic tether
provides a simple and reliable
alternative to the conventional
rocket thrusters .
It works on the basic principle of
Lorentz force and Fleming’s Left
hand rule .
Magnetic force is exerted on a
current carrying wire in a direction
perpendicular to both the flow of
current and the magnetic field .
Laser brooms :
The laser broom uses a powerful ground based laser to ablate the
front surface off of debris and thereby produce a rocket like thrust
that slows the object .
With continued application the debris will eventually decrease their
altitude enough to become subject to atmospheric drag .
Additionally , the momentum of photons in the laser beam could be
used to impart thrust on the debris directly.
The current technology used is the Hydrogen fluoride chemical
energy powered laser.
Although this thrust would be tiny , it may be enough to
move small debris into new orbits that do not intersect those
of working satellites.
Solar sails :
The Solar sails uses the pressure
from sunlight to navigate an object,
just like a naval sail uses wind.
This way debris can be navigated
out of orbit and burn into the
The only problem with the solar
sail is that its very hard to navigate
the junk into the ocean and hence
might be pretty dangerous.
Space nets :
Space nets or
eject a huge net
that ‘fishes’ or
collects the debris
and is later
disposed off into a
graveyard orbit .
is the Sling Sat .
It has two
which collect the
debris as it is in
Donald Kessler (Kessler 1981), "Sources of Orbital Debris
and the Projected Environment for Future Spacecraft“