1. Retired NASA Senior Scientist for Orbital Debris Research
An Introduction to the Kessler Syndrome: Collisional Cascade of Orbital Debris National Climatic Data Center May 23, 2012
by Don Kessler
Retired NASA Senior Scientist for Orbital Debris Research
Asheville NC

2. Common Program Issues: Climate Change and Orbital debris
Require international agreements
Program elements include modeling, measurements, mitigation
Models predict a “tipping point”
Thermosphere
Shield spacecraft to ensure planned life

3. Major Planets of the Solar System: Circular Orbits confined to a plane A stable system
Stability in any orbiting system is only achieved if all objects are in circular obits around the Equatorial plane of the central object, and separated by sufficient distance so that other forces to do cause their paths to cross….with rare exceptions (e.g. Neptune and Pluto; Trojan asteroids).

4. Meteoroids come from Comets and Asteroids (contribute to a slightly unstable system)

5. Orbital Debris (larger than a softball): Mostly circular orbits with high inclinations
An unstable system such as this will slowly move towards stability as results of a large number of catastrophic collisions…where the new orbits of the early fragments are dispersed into new orbits dominated by the forces of the energy exchanges. Each catastrophic collision will produce about 100 fragments large enough to breakup another satellite (i.e, the “collision potential” of the satellite is multiplied by 2 orders of magnitude), plus thousands to millions of smaller fragments that represent a hazard to other spacecraft. After many collisions…. when mostly dust remains in in orbit…. momentum exchanges become important, until the momentum vector of the remaining dust particles share the same direction orbital plane, finally approaching a stable distribution of orbits where the dust can form a ring of debris (like Saturn’s ring), or coalesce into a larger object.
A very unstable system

6. Iridium 33/Cosmos 2251 Collision Iridium Constellation of 66 communication satellites

7. Iridium/Cosmos Collision
One year after the Iridium/Cosmos collision, about 2000 fragments cataloged, as longitudes of nodes randomize
Cosmos 2251 Debris
Right ascension of ascending node randomize. Slower for near polar orbits.
Iridium 33 Debris

8. Number of Cataloged Objects in Earth Orbit
Anti-satellite Test plus the Iridium/Cosmos Collision doubled fragment count
Iridium/Cosmos
China Anti-satellite
2 events doubled fragment count. Had remained nearly constant for 20 years following Ariane explosion in 1986
Year
1981: Upper stage explosion mitigation
1996: Began 25-yr Rule

9. Predicted Collisions in LEO Compared to observed collisions
Historical
Business as Usual
Post-Mission Disposal
No Future Launches
Data (excludes Cerise)
Past collisions: 1991-Cosmos 1934/Cosmos 926 debris; : Cerise-Ariane Debris; Thor-Burner rocket-China fragment; Iridium 33-Cosmos 2251.
Iridium 33 & Cosmos 2251
Thor-Burner upper stage
Cosmos 1934

10. Single collision between satellites produces:
Damage to 8” x 8” x 4” Aluminum Block hit at orbital speeds with ¾ inch plastic cylinder
Single collision between satellites produces:
10,000 fragments size of ¾” cylinder in this test
100,000 smaller fragments but large enough to significantly damage most spacecraft

11. Every returned spacecraft surface has craters from orbital debris impacts
Examples of impact craters found on the Shuttle. The window pit cause the window to be replaced to ensure that the window would not fracture under the pressures cause by the next launch. Had the impact shown on the right, which hit the radiator surface, actually hit a radiator tube which circulates the radiator fluid, the mission would have had to be terminated.
STS-118 Radiator panel Puncture
2 mm titanium-rich debris
Entry hole 7 mm
Exit hole 14 mm
Orbital debris impacts on returned spacecraft surfaces exceed the number of meteoroid impacts. Materials melted into the craters include aluminum, titanium, paint, copper, silicone, circuit board, sodium-potassium

12. Intact Rocket Bodies and Payloads: Regions of Instability in 1999
10-7
10-8
10-9
10-10
Unstable
Runaway
Runaway
1999 Catalogue
of intact objects
Spatial Density, Number/km3
Such a determination was made in 2000 using the 1999 catalogue. Two regions were concluded to be in a Runaway condition, and most of LEO was concluded to be Unstable. The Runaway condition between 700 km and 1000 km is what we are beginning to observe today, with collisions between catalogued objects becoming more frequent. However the Runaway just below 1500 km is very slow since most of the satellites at this altitude are smaller and less massive…and therefore not of immediate concern. However, without adherence to current mitigation guidelines, these region will expand, and the rate of collision will increase.
Altitude, Km
Altitude, Km

13. Geosynchronous Orbit: Less of an immediate problem Beginning of a long-term problem

14. Program Elements Modeling: Debris sources and sinks
Measurements: Ground and in-situ
Spacecraft shielding: Design and testing
Mitigation1: Minimize creation of debris
Collision avoidance: Against tracked objects
Reentry ground hazard: Largest tracked objects
Remediation2: Remove debris from orbit
1 Supported in 1988 National Space Policy
2 Added in 2010 National Space Policy

15. Summary
Collisions in orbit between spacecraft are the visible symptom of deeper problems
Runaway increase in hazardous fragments
Increasing cost of space related activities
Loss of critical satellites
Mitigation has proven insufficient
Remediation required
Interdisciplinary fields of study
Scientist and Engineers
Operations
Legal
Political
Coordination required between fields of study
Large objects can and do make a lot of small objects. Colliding at 10 km/sec in LEO, they cause a lot of damage by these small objects.
One must either get rid of the large objects, or make sure the large objects stay intact; however it is nearly impossible to keep spacecraft intact with the high inclination orbits that are necessary for certain operations. Without an effective strategy to manage the environment, the cost of space activities will increase….either from adding extra shielding to all spacecraft, or from removing massive objects from orbit.

16. End
No plan to use remaining slides

17. Pre-Space Age Knowledge of Meteoroids
Potential Hazard to Spacecraft
Earth-based observations
-Comets
-Asteroids
-Meteors
-Meteorites
-Zodiacal Light
Potential hazard for spacecraft
-Measured Flux
-Uncertainty in size
-Flight experiments required
-Hazard proved to be manageable
Pre-space observations of comets, etc. lead to most NASA centers in the early 60’s to have a meteoroid research group in order to protect man in space. Initially, there was a large uncertain in the size distribution and velocity of meteoroids. Spacecraft and ground measurements resolved that uncertain, much more accurately defining the environment. However, this environment resulted in very little design changes to spacecraft (some extra shielding on the Apollo LEM, and lunar space suite…a meteoroid shield on Skylab, which fell off during launch), so nearly all that research ended around 1970.
1966 Leonid meteor shower

18. Major Accomplishments over the last 30 years
Measured the environment very small sizes
Established international organization (IADC)
UN acceptance of Debris Mitigation Guidelines
Minimize possibility of explosions in orbit
Require reentry within 25 years after operations
Concluded current debris environment has exceeded a “critical density”
Current National Space Policy expands debris activities
Over the last 30 years, the NASA program has matured significantly, with measurements of the space environment for debris sizes from microns to centimeters. Their models include new debris sources (NaK, aluminum oxide, paint), they provide operation support for NASA’s manned missions as well as some DoD operations. The program test various spacecraft shielding designs with hypervelocity test facilities. NASA was key in establishing the IADC (Inter Agency Space Debris Coordination Committee), and international organization. Through the IADC, the UN has accepted debris mitigation guidelines that were developed by NASA. IADC members have concluded we have likely reached a threshold where some debris must returned from orbit in prevent future debris growth. As a result, the current Nation Space Policy directs NASA and DoD to come up with techniques to remove on-orbit debris.

19. Necessary Remedial Action to Stabilize LEO
The only way to reduce or eliminate the instability is to reduce the number of intact objects
NASA study concludes removing between 5 and 10 massive objects per year is sufficient
Could be accomplished with fewer than 5 to 10 additional launches per year over the current average of 75.
2010 President’s Space Policy:
Pursue research and development of technologies and techniques …. to mitigate and remove on-orbit debris…
The only way to reduce or eliminate these regions of instability is to reduce the number of intact objects in orbit. NASA studies have concluded that if between 5 and 10 selective objects are removed per year (depending on the amount of adherence to mitigation guideline)….for the next 100 years… then the LEO would become stabilized. Since the current world launch rate is about 75 launcher per year and if only 5 or 10 additional launches per year are required to remove the 5 or 10 objects, then the cost to perform this remedial action would only increase the cost to space programs by about 15%. The current Space Policy asks NASA and DoD to develop techniques to remove debris, so as a result of new technologies, there may be techniques to that could remove debris more cheaply.

20. Techniques to Remove Debris
Debris Sweeper: Debris comes to Remover
-Eliminates debris that happens to pass within 20 km
-40 km diameter natural Earth moon
-Very large “catcher” that can quickly maneuver 20 km
-Space or Ground based laser
Debris Grabber: Remover goes to debris
-Small spacecraft retrieves one intact object per launch
-Large spacecraft retrieves several intact objects with similar inclinations per launch
-Tethers
Fundamentally, there are two techniques to remove debris. The “sweeper” concept is based on the way nature would remove smaller objects from orbit. If the Earth had a natural moon that was about 40 km in diameter, in an orbit that passed through all of LEO, and has sufficient gravity to capture all the ejecta after each collision, then it could clear LEO in a few years of all debris. A large foam ball has been proposed to do the same thing, but that would require placing too much mass into orbit….plus it would also remove operational satellites. A single massive “debris catcher” that can quickly maneuver 20 km after sensing an approaching object, or using lasers to ‘slow down’ debris that passes within 20 km might become an option that is selective about which objects it captures.
A ‘debris grabber’ matches the orbit of debris it expects to remove. It may be possible for a single grabber to retrieve several objects before it reenters….especially if the grabber is a tether. However, tethers have their own debris problems in that they can easily be severed by small debris.