Space debris


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This presentation gives a basic idea of the increasing space debris and some important methods to clear them .

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Space debris

  2. 2. CONTENTS 1) Introduction 2)Types of orbits 3) Sources of debris 4) Tracking and Measurement of debris 5) Clearance of space debris 6) References
  3. 3. WHAT ARE SPACE DEBRIS ?  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 collision.
  4. 4. WHY ARE THEY A THREAT ?  Debris poses a growing threat to satellites and could prevent the use of valuable orbits in the future. Many pieces of debris are too small to monitor but too large to shield satellites against.
  5. 5. TYPES OF ORBITS : 1. Low Earth Orbit 2. Medium Earth Orbit 3. Geostationary Orbit 4. High Earth Orbit
  6. 6. 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 altitude loss.  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.
  7. 7. Medium Earth Orbit : Situated from 2000 km to 36,000 km above Earth’s surface. The most common use for satellites in this region is for navigation , communication and space environment science. Has an orbital period of 12 hours .
  8. 8. Geostationary 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.
  9. 9. High Earth Orbit :  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 .
  10. 10. 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 cascading effect.
  11. 11. 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 .
  12. 12. SOURCES OF DEBRIS :  Dead spacecrafts Boosters Lost equipment
  13. 13. 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.
  14. 14. 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 )  STS-61 Endeavour  STS-109 Columbia
  16. 16. Some methods are :  Tug-like satellites  Electro dynamic tethers  Laser brooms  Solar sails  Space nets and collectors
  17. 17. 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 positive . The satellite then uses its own thrusters to propel itself along with the debris to a safer orbit .
  18. 18. 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 .
  19. 19. 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. …contd
  20. 20.  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.
  21. 21. 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 atmosphere. 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.
  22. 22. Space nets : Space nets or umbrellas are satellites which eject a huge net that ‘fishes’ or collects the debris and is later disposed off into a graveyard orbit .
  23. 23. Collector satellites : The most commonly used collector satellite is the Sling Sat . It has two extended arms which collect the debris as it is in motion .
  24. 24. REFERENCE :  Donald Kessler (Kessler 1981), "Sources of Orbital Debris and the Projected Environment for Future Spacecraft“    
  25. 25. QUESTIONS????? Thank you…