The first satellite launched into space was the Soviet Sputnik-1. This was placed into low Earth orbit on 4 October 1957. |
As well as the 58 cm diameter sphere (mass 84 kg) which was Sputnik-1, the final stage of the launcher with a length of 30 m and a mass of 4000 kg also made it to orbit. Also in orbit was the protective shroud enclosing the satellite during the ascent through the atmosphere. And the mating adaptor from which the satellite was released. And probably smaller debris resulting from the pyrotechnic release of the shroud etc.
And so was born the first orbital artificial space debris.
PROJECT WEST FORD
An interesting space launch which resulted in a scientific uproar at the time was conducted by the US Army. The project
was devised by scientists of the Massachussetts Institute of
Technology in the time before global communication satellites.
Its purpose was to allow military X-band (8 GHz) communication
between the east and west coast of the USA.
It involved the launch, in May 1963, of 500 million copper dipoles (wires) into a 3600km circular orbit. Each dipole
was 25mm long and 2.5 microns in diameter.
There were worldwide complaints made about this experiment. Astronomers in particular were concerned that the dipoles would affect both optical and radio astronomy. Two
prominent British astronomers, Bernard Lovell and Martin
Ryle published a scientific paper about the possible effects in the prestigious journal "Monthly Notices of
the Royal Astronomical Society".
It turned out that none of predicted dire consequences
eventuated. It also was fairly much a failure in terms
of military communication. The particles dispersed
rapidly and no one could detect them after a few months.
Because of their large area to mass, it was assumed that
they would all reenter the Earth's atmosphere and burn up
within a few years.
It is thus was quite unexpected when a few years ago
a sensitive radar detected over 40,000 clumps of these
dipoles still in orbit.
CONTINUING ARTIFICIAL SPACE DEBRIS
The generation of artifical space debris has continued
throughout the space age. The graph below, from the NASA
Orbital Debris Program Office shows the number of space
objects tracked and catalogued by the US Space Surveillance
Network.
The categories of object are broken down into spacecraft,
orbiting rocket bodies, mission-related debris (eg payload
shrouds), and fragmentation debris. Although the graph indicates that approximately 3000 spacecraft are currently in
orbit, not all of these are operational. Those satellites
that have either failed or reached the end of their useful
life also contribute to the numbers of space debris.
In general all objects shown here will be 10cm or greater in
size, as that is limit below which current tracking is not
possible. Also not shown on the graph are several thousand
space objects that are being tracked but that have not been
catalogued.
Note that fragmentation debris is by far the largest contributor to the total number of objects on the graph.
These are objects that have been created from other objects
already in orbit. The three recent step increases in this
population are from 3 collisions, the first two deliberate,
and the third accidental.
We may summarise the current artificial space debris population in low Earth orbit as:
200,000 objects 2 million objects
NATURAL SPACE DEBRIS AND SPACE TRAVEL
As well as artificial space debris there is also a population
of natural space debris (meteoroids) that, while they don't
orbit the Earth, do pass through all orbital altitudes. In
fact prior to the space age, some scientists predicted that
the hazard from natural debris might be so great as to make
space travel very dangerous. In fact NASA spent considerable
effort in trying to evaluate this hazard. Ground visual and
radar observations were examined, and most of the early satellite carried meteoroid detectors.
The early satellite detectors were often microphones to
record the sound of a meteoroid impact. A large number
of impacts were recorded by these detectors and this
appeared to reinforce the idea of a large natural orbiting debris cloud. This was referred to as an anomalous debris
cloud because it indicated a population much larger than
ground observations (mainly radar) could account for.
Continued investigation found that microphone type detectors were registering impacts that were in fact expansion and contraction noises of satellite panels.
And thus it was found that the meteoroid collision hazard is usually low but not negligible.
WHAT IS ORBITAL SPACE DEBRIS?
We might define orbital space debris as essentially any object in Earth orbit that does not have a useful purpose. Below is one classification of Earth orbiting space objects. This has
been drawn from the volume 'Orbital Debris: A Technical Assessment' by the US National Research Council, and shows the wide range of sources that contribute and make up orbital space debris.
DEBRIS MEASURMENTS AND MODELS
The debris population is measured with the use of both ground and space sensors. And models have been developed to interpolate in size regions where sensors do not cover and to extrapolate to objects not accessible to sensors. Models are
also used to propagate debris populations forward in time to examine the future consequences of various scenarios.
Natural space debris flux can be monitored through its interaction with the Earth's atmosphere:
Another view of the overall orbital space debris population,
both measured and extrapolated down to very small sizes, is
shown in the NASA graph below. This also indicates the different means used to monitor this population.
The smallest debris populations are estimated from microscopic
examination of spacecraft panels that have been exposed to
this flux in orbit. Much of this data has come from the NASA
Long Duration Exposure Facility (LDEF), shown below together
with a closeup of one panel that shows a multitude of small
impacts.
TRACKING SPACE DEBRIS
Both the USA and Russia (and/or the former Soviet Union) have
set up tracking networks to monitor the orbital space
object population. The European Union is now starting to
develop its own capability in this area.
Both the US Space Command and the Russian Space Agency maintain space object catalogs. The US Space Surveillance Network (SSN) employs about 30 global sensors to feed its catalog.
Details of the Russian space tracking network are not as
well known but include mobile maritime platforms, such as
the one shown below.
The primary SSN optical sensors are constituted in the
GEODSS (Ground-based Electro-Optical Deep Space Surveillance)
network. This consists of two one metre telescopes and
one 40 cm telescope. They observe objects out to geosynchronous orbit, and are stated to be able to see baseball size objects at the latter distance. There are
currently three operational GEODSS sites in New Mexico,
Hawaii and Diego Garcia. The Diego Garcia site is shown below. These sites are also being augmented by smaller
optical telescopes at various global locations.
The most data productive site in the Space Surveillance Network is a radar 'fence' that has been set up across the width of the North American continent. This sensor is called the SPASUR. It was intially operated by the US Navy under the name NAVSPASUR, but has recently been taken over by the US Air Force.
The main transmitter in this system is located near Lake Kickapoo (named after a local Indian tribe) in Northern Texas.
The transmitting complex comprises transmitter and antenna
elements spread over a north-south distance of more than 3 kilometres. The total effective radiated power is over
six billion watts. It is probably the most powerful transmitter in the world. And if ET is out there, this is
the terrestrial transmitter he is most likely to hear first.
This space fence is in essence a fan bean of radio energy
that is very narrow in the north-south direction, but that
spreads to cover the continental US in the east-west direction. Any orbital object that crosses this beam
(and most of them do) will reflect a portion of the radio
energy back to Earth where it will be detected by several
radio receivers completing the SPASUR system.
On the order of 10,000 observations each day are processed by this space sensor. It forms the backbone of the US Space
Surveillance Network because it can monitor such a large
area of space - it does have to be guided to track specific
objects as do most of the other sensors in the network.
Currently the SPASUR operates at a relatively low frequency (217 MHz). It is due to be upgraded to S-band (~ 2 GHz) for
higher accuracy.
Tracking radars are used to provide greater precision meausrements of range, velocity and direction. These are
of two sorts, those that track mechanically, and phased
array radars that can track electronically.
The SSN also has various collaborating sensors which are
used part time for operational tracking and part time
for special space debris research programs and campaigns.
DATA ANALYSIS AND AVAILABILITY
Data from all SSN sensors is sent to the Space Control Center underneath Cheyenne mountain near Colorado Springs.
Data is processed and produces the SATCAT or satellite catalog of orbital objects, either as a state vector or Keplerian orbital elements.
Data is made available to registered users via the NASA Orbital Information Group (OIG). Since 2002 only approved parties are issued registration. This includes most US entities and entities of friendly states. Data does not include orbital elements of US military satellites.
A subset of the SATCAT is freely available on the web via Celestrak. While this is very useful for tracking most active satellites, it is of no use for conjunction assessment (CONASS) and subsequent collision avoidance (COLA) purposes.
Many governments (particularly European) have expressed frustration with data delays and denials, and perceived
data degradation, and ESA has proposed a European tracking system for "space situational awareness". At present they use two radars and a dedicated optical telescope at Tenerife to observe high interest items and produce very limited local catalogs. Other telescopes are being enlisted to help in this task.
A group of dedicated amateur satellite observers track and produce orbital elements for most US military satellites - these
can be accessed via SEESAT.
PROBLEMS OF ORBITAL SPACE DEBRIS
Orbital space debris can give rise to a range of problems in four main areas:
Reentry Hazard
Most reentering space debris ablates totally as it passes
through increasingly dense atmosphere in a fiery conflagration. Only the largest objects (usually > 10 tons initial mass) partially survive the reentry process.
Fragments normally fall to ground at their terminal velocity which may range from almost zero to ~ 200 m/s.
Abrasion of optical surfaces of satellite sensors by prolific micron sized particles. Reduces sensor life.
Early particle collection experiments (eg Skylab) found titanium in space - assigned a solar origin.
NASA now routinely conducts a survivability analysis on all large satellites.
Radiation Problems
In the early 1970's US gamma ray detectors on some scientific satellites detected strange events. The US military classified some of this data in 1973.
It turned out that Soviet RORSAT (Radar Ocean Reconnaisance) satellites were carrying nuclear reactors to provide enough energy to run the high power radars.
One of these satellites (Cosmos 954) survived reentry over Canada on Jan 24, 1978 and scattered radioactive material. The Canadian government presented the Soviets with a $6M cleanup bill.
To avoid similar problems, further satellites ejected the reactor cores to higher altitudes at the end of the satellite useful like. However, this process has resulted in the release of highly radioactive NaK (sodium-potassium) coolant particles. These droplets represent a unique space debris class.
Space Science and Debris
Abrasion of optical surfaces on satellite sensors by prolific micron sized debris particles can reduce sensor life.
Mistaken identity: early space particle collection experiments (eg by Skylab) found titanium in space. It was initially thought that this must have come from the Sun. Later on it was found be from paint that had flaked off various orbital rocket bodies and some satellites.
On 23 May 1985 a Greek astronomer captures on film a flash
from the part of the Moon's surface not illuminated by the
Sun. Such transient lunar phenomenon or TLP have always
been a much debated topic, but this appears to settle the
matter once and for all. Could it be a meteoroid impact,
a volcanic eruption/outgassing or maybe some kind of
ionisation phenomenon. It turned out to be none of these.
Several years later satellite investigators showed that it
was in fact a glint off a derelict US military weather satellite. Several other claimed new astronomical
phenomenon have later been revealed to be due to space debris.
Astronomy - Image Debris Trails
When photographing near the celestial equator the problem
becomes a lot worse because of the number of large satellites
and debris objects that are in or near geosynchronous orbit.
The following image shows almost 20 trails from these objects over a total of one hour exposure. Imaging was interrupted
every 10 seconds for 10 seconds to allow underlying fainter
objects to be seen. The bright short trail in the center of the image is the asteroid Vesta.
Astronomy - Skyglow
Radio Astronomy - Transient Events
DEBRIS VISUAL MAGNITUDE
It is not easy to predict the visibility, from the ground,
of a space object. Many factors influence the actual
brightness, but we can make a rough estimate by considering
a spherical object that is half illuminated by the Sun when
directly overhead an observer. The albedo (reflection
coefficient) of the object is assumed to be around 0.1,
a value not atypical for an object in low Earth orbit.
The graph below is a guide to the brightness of such an
object as a function of object altitude and size. The
brightness is given in astronomical magnitudes, where the
brightest star Sirius has a magnitude of -1 and 6 is the
faintest magnituide visible to the unaided eye.
HYPERVELOCITY COLLISIONS
A hypervelocity collision is defined as one wherein the kinetic energy of the impactor is greater than the explosive energy released by the same mass of high explosive (eg TNT).
Thus 1/2 v2 = 4.2 x 106 giving
vh ~ 3 km/s
A hypervelocity collision displays more properties of an explosion than a typical low velocity collision.
The average relative collisional velocity in low Earth orbit is around 10 km/s (compared to the typical orbital velocity of 7 to 8 km/s), and thus practically all space debris collisions in LEO will be hypervelocity collisions. The impactor is usually totally destroyed.
DEBRIS DAMAGE
Minor Collisions
Even paint flakes can cause problems.
Over 100 space shuttle windows have had to have been replaced due to debris cratering (at $100k a window).
At right is a paint flake that has been captured by a remarkable substance known as aerogel. Analysis shows the
presence of titanium, part of the white pigment in paint.
Micrometeoroid Window Impact
Just to show that natural space debris has a non-negligible
impact hazard, a window of the space shuttle STS-126 was
cratered by a micrometeorite. That it was natural and not artificial space debris is shown in the chemical analysis
of the cratering residue, which contained not titanium but
minerals found in meteorites.
More Serious Impacts
Space Debris Penetration
Any impactor over 10mm in size is bad news for any spacecraft.
The graph below gives a rough guide to penetration depth as a function of impactor size and speed. The ordinate is an aluminium equivalent thickness in millimetres.
ISS Debris Damage
The NASA image below shows the location of a small debris
impact crater on the handrail of an airlock on the international space station.
At first thought one might tend to disregard such a minor
event. But imagine if you were an astronaut running your
hand around this handrail. And it just happened to tear
your glove, allowing your spacesuit to slowly depressurise
....!
Space Shuttle Debris Damage Sizes
The figure below, from the NASA Orbital Debris Program Office shows well the damage that impactors of various sizes might
cause to a space shuttle.
SPACE DEBRIS DYNAMICS
The orbital space debris population is a function of debris
source and debris sinks.
We shall now examine various sinks and source in more detail.
Space Debris from Rocket Fuel
Fragmentations - Explosions
This source currently accounts for the majority of artificial orbital space debris. These may be deliberate or accidental. The Soviets used to routinely destroy satellites at end of life to preserve secrecy.
Accidental fragmentation typically occurs due to the release of stored energy, either from unspent fuel or batteries. Hypergolic fuels are notorious. In Delta rockets the separation wall between fuel (hydrazine) and oxidiser (nitrogen tetroxide) would erode and spontaneous reaction would take place, fragmenting the upper stage motor and casing into a major debris source.
From 1961 to present there have been approximately 250 known fragmentations.
Accidental Collisions
Only four accidental collisions have been recorded to date. The current low probability of collision makes this a minor source of space debris - at the present time.
Deliberate Collisions - ASAT Tests
The Soviets used in-orbit satellites to close on the target satellite. The antisatellite satellite would then be exploded, showering the target with debris.
Approximately 20 ASAT tests of this nature were believed to have been conducted in the Soviet era.
No Russian ASAT test has been conducted over the last two decades, although a senior Russian military general has recently indicated that tests may soon resume due to the recent Chinese and US tests.
On 12 Jan 2007 China launched a ground based missile and destroyed an old meteorological satellite, creating the worst debris cloud in the history of space flight.
The object population in low Earth orbit before and after
this collision is shown in the NASA plot below.
ANALYSING COLLISIONS
One of
the most useful aids to analyse collisions is known as
the Gabbard diagram, after John Gabbard of NASA.
A Gabbard diagram is a plot of the perigee and apogee altitudes
of each object in the collision versus its orbital period.
The intersection of the two 'arms' is the collisional height.
COLLISIONAL CASCADE
In 1978 two NASA employees wrote a paper that was published
in the Journal of Geophysical Research. Its title was
"Collision Frequency of Artificial Satellites: The Creation
of a Debris Belt" and the authors were Donald Kessler and
Burt Cours-Palais. This was written before any accidental
had happened. It pointed out that when the debris numbers
in low Earth orbit become great enough, a chain reaction
could occur that would rapidly increase the debris
population to a point where normal satellite operations would
no longer be possible.
Today this scenario is termed the "Kessler Syndrome".
The reality
ORBITAL DECAY - A DEBRIS SINK
A small but important amount of the Earth's atmosphere
extends to an altitude of 1000 km or more. This will cause
aerodynamic drag on all satellites with the following very
approximate decay times.
The above table assumes an average mass to area ratio of
around 100 kg per square metre(the range encountered in larger space objects is usually between 50 and 200), and a drag
coefficient CD ~ 2.
DEBRIS MODELS AND SIMULATIONS
US and European researchers have developed computer models
to describe the current orbital object population and allow
this to be propagated into the future under various
assumptions.
A simple model developed by Farinella and Cordelli at the
Universtry of Pisa (Italy) serves to illustrate to basic
evolution of an orbital population. It can be coded easily
and quickly and serves as a good student exercise which is
not clouded by too many details. One output from this model
is shown below.
The inferences we draw from these models is that low Earth
orbit, in the absence of delibrate debris reduction
measures, will
probably become unusable in a few hundred years. Exactly how
many years will depend greatly on the number of continuing fragmentations and deliberate collisions we see in the near future. A war in which space assets are targeted would be
catastrophic. And we must remember that it is not only
space activities that will. Astronomy and other ground based activities will be affected as well.
Several decades ago, the intrepid explorer Thor Heyrdahl
told us that the Earth's oceans were a finite resource,
and that we couldn't continue to dump waste cargo into them
without experiencing problems in the future. It is sobering
to realise that low Earth orbit, with its staggering volume
of one trillion cubic kilometres, is likewise a finite
resource that we must use wisely.
SPACECRAFT SHIELDING
In the early 1950's Fred Whipple suggested the 'bumper
shield' as a mass effective way to protect satellites
from meteoroid damage.
DEBRIS MITIGATION
Following Kessler's 1978 paper, NASA started to develop
guidelines to keep down the amount of debris generated
by space launches and to minimise the possibility of later
fragmentations. Other countries soon followed suit, and in
2007, after ten years of intense debate and negotiation,
the United Nations General Assembly approved a set of
guidelines for orbital space debris mitigation. These can be summed up under seven points:
Now these guidelines are fine and if adopted should minimise the generation of debris from continuiung space activities.
However, the only thing that will really solve the problem
is the active removal of debris from low Earth orbit.
Many different ideas have been proposed, and the first
conference on this problem was held in early 2010. However,
no consensus was reached. All active solutions so far are
very expensive and engineering nightmares.
One such published scheme would deploy a 5 MW peak power
(30 kW average power) laser to deorbit the 1 to 20 cm sized
debris population over a 2 year period at a total cost of
$200 million.
Although this appears reasonable, there are many scientific
and engineering problems to be solved. But overiding all
these are the political hurdles that would need to be overcome to deploy such a system, and in the end this is
probably the biggest problem we face.
CONASS and COLA - Protecting Current Assets
Conjunction assessment (CONASS) leading to possible collision avoidance (COLA) action are affirmative actions that not only
look toward protecting current space assets, but also look
toward the possible prevention of further accidental collisions that generate even more space debris.
The Iridium-Cosmos collision should not have happened. It did so only because of insufficient computer resources in CONASS.
Prior to this collision CONASS was applied only to high value resources (eg Space Shuttle and ISS). To remedy this
deficiency the US Air Force has set up and staffed a new
conjunction assessment office. This office has been
given a mandate to liase with space industry to try
and prevent the repetition of the Iridium collision,
and to improve space situational awareness in general.
The space shuttle has had to perform a COLA maneuvre about every 10 flights. A recent short notice to the ISS resulted in astronauts sheltering in a Soyuz return capsule.
A commercial firm now offers a CONASS service for the space industry.
AUSTRALIA'S ROLE
The notion of space debris may seem remote to most Australians. Australia has only a few active satellites
in orbit and has generated only a small amount of space
debris itself. Unfortunately, everyone is going to be
affected by the problem of continuing space debris generation (and the large Australian astronomical community will be in the forefront of secondary effects). It is
thus appropriate that Australia should be involved in this
international issue.
Below are listed some points in which Australia has taken a role in space debris as well as suggestions for further
action:
Approximately
20,000 objects
>10cm diameter
>1cm
>1mm
Explorer 1 satellite
Meteoroid enters Earth's
atmosphere creating a meteor
1995 was the year in which artificial space debris numbers exceeded the natural space debris flux in low Earth orbit for all particle sizes above 1mm.
Artificial space debris requires considerably more resources
to monitor because of the constantly changing environment, and the need to assign specific space objects to specific space events (eg producing an object catalog). Both optical and radar ground based sensors are used.
Space based sensors are also starting to be used for space object surveillance. Special spacecraft with collection
panels and other passive monitors have been left in low
Earth orbit and then retrieved. Examination of the impacts
on these satellites give very useful information about the
smaller sizes of debris objects - those which are much too
small to be detected by other sensors.
US Navy photo
US Navy photo
FPS-85
EglinAFB, Florida - Dedicated
Cobra Dane, Aleutians - Partial
FPQ-14
Kaena Pt, Hawaii - Partial
Haystack and Haystack Auxilliary radars
Operated by MIT, Massachusets
Mauii Space Surveillance and Supercomputing
Operated by the US Air Force Research Laboratory
These problems are now discussed in more detail.
NASA reentry and breakup plot
The probability is extremely low, but this woman was 'hit' by a piece of thermal blanket from the US MSX satellite.
Space object trails showing up on astronomical images
is becoming an increasing problem. A recent astronomical
imagery book by a famous astrophotography containing about 200
spectaculat astronomical images had satellite/debris trails across a dozen of them. A trail through a beautiful galactic
image that has taken several hours to expose can be very
frustrating, but in photometric research where many hundreds
of images are often processed manually without human
oversight, a trail through the target object could result
in false data.
LEO satellite/debris trail image by
Alan Brockman - Ningaloo Skies
GEO satellite/debris trails image by
Alan Brockman - Ningaloo Skies
Skyglow is the sky brightness between the stars.
This comes from a number of sources: scattering from aerosols and chemical reactions in the lowest ionosphere (~80 km).
When the concentration of 100 micron sized debris particles becomes very large, this may be the predominant skyglow source.
Skyglow limits ground imaging magnitudes.
Large pieces of space debris, as well as operational spacecraft, will reflect radio signals from ground transmitters back to the ground.
Meteors do the same thing, but usually at frequencies <200 MHz. Metallic debris will echo microwave frequencies.
Even radio quiet zones cannot legislate against this type of transient interference.
For TNT this energy is 4.2 x 106 Joule/kg
At right is an impact crater discovered on a Hubble Space Telescope solar panel.
STS-118 radiator impact damage. The ingress hole is almost 10mm diameter. The exit hole is much larger and very irregular. This is typical of all penetrating
impacts.
At right is a hole found in the Hubble downlink antenna,
the result of a space debris impact.
At right is a ground based hypervelocity impact of a 2mm Al sphere into an Al target 18mm in thickness. Note crater and incipient spall opposite impact. Note that the sphere shown
in the bottom of the crater is indicative only - the actual
impactor, identical in size, was totally destroyed in the
impact.
Solid rocket fuel is a profligate producer of space debris. Slag particles from the exhaust may range from microns to centimetres.
Cosmos 2421 recently underwent a severe fragmentation producing over 250 trackable fragments.
The first 4 US ASAT tests were conducted by firing a missile from an F-15 fighter in a steep climb. The P-78 solwind satellite was destroyed on 3 Sep 1985. The last of these tests was conducted in October 1986. The program was terminated by Congress.
The last and most recent test was conducted by an SM-3 missile launched from a USN Aegis class destroyer. The satellite destroyed was the failed intelligence USA-193 craft. The reason given was reentry debris mitigation, but may have also been secrecy related.
Analysing collision requires a laborious collection of
data, making sure that all object orbits collected do
indeed belong to the specified event, and that all
possible tracked objects have been collected.
The realisation
In a Science paper published Jan 2006, Kessler's successor states that the debris population is now sufficient, that without any further launches to LEO, collisional cascading will exponentially increase the space debris population, it becoming the dominant production mechanism in 50 yrs.
Initial Altitude(km)
Satellite Lifetime
300 1 month
400 1 year
500 10 years
700 decades
900 centuries
1200 millenia
This has been refined over the years, and applied to
the largest and most expensive space assets such as the
International Space Station, to provide protection mainly against orbital space debris.
NASA space debris report images
The last item applies only to geosynchronous orbit.
The most plausible scheme is arguably that of laser deorbit.
This involves a ground based laser beam used to cause surface
ablation of debris less than one kg in mass to produce a reaction force which lowers the perigee of the object for a rapid atmospheric decay.
The CONASS warning area is 5km radial and 25km in-orbit. The COLA maneuvre area is 2 km radial and 5km in-orbit.
Joseph Loftus (31/08/1930 - 04/09/2005) Joseph Loftus was one of the earliest proponents of the importance of space debris. He gained an international reputation in this field, and was known as the godfather of the NASA Orbital Debris Program Office. His efforts led to the funding and establishment of that office in 1979. |
Donald Kessler Donald Kessler was the first Chief Scientist and Program Manager of the NASA Orbital Debris Program Office. He is widely remembered for the 1978 paper on the possibility of collisional cascading leading to a severe orbital debris crisis. This is now referred to as the Kessler syndrome. He was the first to predict the presence of large amounts of small uncataloged space debris. He retired from NASA in 1996 and is now an independent space debris consultant. |
Nicholas Johnson Nicholas Johnson is the current Chief Scientist and Program Manager for the NASA Orbital Debris Program Office. Prior to this appointment he worked in private industry on space debris problems and as an expert on the Soviet space program. He was the co-author of the first book solely devoted to orbital space debris. |
John Africano (27/07/2006 - 08/02/1951) John Africano was an astronomer with diverse interests. In the latter part of his life he concentrated on measurements of space debris, working in both the civilian and military communities. He was an avid communicator and educator, and co-organised the annual AMOS Technical Conference on Mauii. |
Walter Flury Walter Flury, now retired, was a leading European scientist on space debris issues, bringing these to the attention of a wide audience in the 1980's. He was the first coordinator of space activities within ESA and launched the first European Conference on Space Debris in 1993. |
Heiner Klinkrad Heiner Klinkrad is the current head of the European Space Agency Space Debris Office. He assumed this position in 2006. He leads the ESA delegation to the Inter-Agency Space Debris Coordination Committee. |
SPACE DEBRIS PLACES AND ORGANISATIONS
OTHER ISSUES
Fragmentation Debris Responsibility
Geosynchronous Orbital Debris
This guide has concentrated mostly on space debris in low Earth orbit. It is in this regime that the problem of
space debris is most acute. However, geosynchronous
orbit has problems of its own, and some of these have
largely gone unnoticed, because the increased distance
to GEO makes detection of smaller objects very difficult
with ground based sensors.
One of the main differences about geosynchronous orbit is the
absence of atmospheric drag and decay as a sink for the
debris population. The four main perturbating forces
on an object in or near geosynchronous orbit are gravitational
forces due to the Earth's oblateness, the Moon and the Sun,
and solar radiation pressure.
The standard procedure to dispose of a geosat at the end of
its life is to boost it into a supersynchronous orbit - that
is an orbit above geosynchronous orbit. It is now agreed
that these graveyard orbits should be at least 300 km above
the active geosynchronous belt.
To solve the sensing problem, the US Air Force has
recently launched a satellite into
GEO that can maneuvre around the orbital belt, allowing
both observation of the overall environment, and
observation of individual satellites that may experience
problems.
A NASA simulation of the GEO space object population is
shown below.
Aerogel
MORE INFORMATION
BOOKS
JOURNALS
Australian Space Academy - 2010
NASA Orbital Debris Program Office (ODPO)
ESA - ESTEC Space Debris Office
Inter-Agency Space Debris Coordination Committee
United Nations Office for Outer Space Affairs
International Academy of Astronautics
Center for Orbital and Reentry Studies (CORDS)
Part of The Aerospace Corporation
International Institute of Space Law
Center for Space Standards and Innovation (CSSI)
CSSI is a research arm of Analytical Graphics Inc
(AGI).
University of Pisa
The Space Mechanics Group is located in the
Department of Mathematics and is very active in space
debris population modelling,
NASA Orbital Debris Program Office
Aerogel is a remarkable manmade material that has a
density between on tenth and one hundredth that of water.
It is the only known substance that can stop a hypervelocity
object without destroying it in the process, and it has
allowed us to examine and determine the nature of various
particles of space debris.
Density 8 to 120 kg/m3
WEB
Unfortunately only two volumes of
this journal were ever published.