Earth Orbiting Debris: A threat to our infrastructure Why is limiting the amount of debris a difficult problem? What is the damage to spacecraft? How do we measure the debris environment? What is being done to limit debris growth? What is the predicted amount of future debris? Have we passed a tipping point and how do we reverse it? Minnesota IMAX Lecture October 3, 2013 By Don Kessler Retired NASA Chief Scientist for Orbital Debris Research

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).

Comets, Asteroids and Meteoroids*: Contribute to an unstable system *Meteoroids: Small fragments of comets and asteroids

Were the events related? February 15, 2013 Asteroid fragment 150 ft diameter Central Russia -- Stone asteroid fragment 60 ft diameter 16 hours later Were the events related?

Iron fragment at 13 km/sec 50,000 Years Ago Iron fragment at 13 km/sec Earth covered with fossil craters Early comet impacts believed to be responsible for water on Earth Some believe comets contributed to formation of life Comet or asteroid impacts as large as 10 miles across expected every 100 million years -Crater several hundred miles across -Dust ejected into stratosphere -Caused disappearance of many species Meteor Crater, Arizona Nearly 1-mile across Caused by an iron asteroid fragment, 160 ft. across Expect similar events every 100,000 years.

Orbital Debris (larger than a softball): Mostly circular orbits with high inclinations An unstable system such as this will slowly move towards stability as result 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

Iridium approaching Cosmos Will they collide?

Iridium Approaching Cosmos …and other objects with uncertain positions Size of green disk represents uncertainty in position An object passed within 2 miles of Iridium33 every day

Iridium 33-Cosmos 2251 Collision Iridium Constellation of 66 communication satellites Perfect example of what should now be expected about every 10 years Red= fragments from collision; Green is rest of catalog...size represents uncertainty in position

Collisions with Earth & Collisions with Spacecraft Aluminum ball at 6 km/sec Iron fragment at 13 km/sec ½ inch Earth covered with fossil craters Early comet impacts believed to be responsible for water on Earth Some believe comets contributed to formation of life Comet or asteroid impacts as large as 10 miles across expected every 100 million years -Crater several hundred miles across -Dust ejected into stratosphere -Caused disappearance of many species Meteor crater on Earth Aluminum target in lab Most debris collisions with spacecraft are at 10 km/sec

Sampling debris as small as a BB Measurements: Objects smaller than a marble: Cause significant damage breakup modles predict large number Show impact sample Space Station shielding Telescopes X-Band Radar (Better) (Best)

X-Band Radar Detection Rate Compared to Rate Expected from Catalog 20 times as many marbles as softballs 200 times as many BBs as softballs The discovery of orbiting liquid metal spheres Unexpected peak: From USSR Dumping of Reactor Coolant Haystack Radar Rate Catalog Rate 20 times as many marble sized objects as catalogued! 20 times as many marble-size debris as softball-size

Number of orbital debris impacts exceed meteoroid impacts Returned Spacecraft Surfaces: Craters from Orbital Debris Impacts 100’s of millions of objects smaller than a BB STS-92 window pit 0.1 mm aluminum debris 2 mm diameter crater STS-118 radiator panel 2 mm titanium-rich debris Entry hole 7 mm, exit hole 14 mm In LEO, conclusive data quickly became available, by examining returned spacecraft surfaces, such as these. In LEO, the orbital debris hazard exceeds the hazards from natural meteoroids...which pass though Earth orbit line the recent close approach of Asteroid 2012 DA14. 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. Materials melted into the craters include aluminum, titanium, paint, copper, silicon, circuit board material, sodium-potassium Number of orbital debris impacts exceed meteoroid impacts

Limiting Debris Population Growth 1982 NASA Mitigation Policy: Prevent explosions in orbit 1987 US Policy: Establish International Forum 1996 NASA Mitigation Policy: Require disposal or reentry within 25 years Mitigation Policies now accepted by the IADC and UN Mitigation: Early Policy

Number of Cataloged Objects in Earth Orbit 15000 10000 5000 Anti-satellite test plus the Iridium/Cosmos collision doubled fragment count Total Fragments Spacecraft Mission-related Rocket bodies Worked between 1980s and 2007 What is colliding? Catalogued objects larger than 10 cm....limited by the 70 cm wave length used to maintain the cataloge. In terms of number, most are fragments, with about half being massive enough to catastrophically breakup another spacecraft. In terms of mass and area, most are rocket bodies and non-operational spacecraft. 2 events doubled fragment count. Had remained nearly constant for 20 years following Ariane explosion in 1986 Collisions produce more small particles than explosions. Sample measurement with shorter wavelength radar count about 10 times more fragments larger than 1 cm. 1960 1970 1980 1990 2000 2010 Year

Future Catalog Growth Assuming today’s launch rate None follow 25 year disposal rule 95% follow rule We have passed a tipping point!!

Mitigation vs. Remediation “An ounce of prevention is worth a pound of cure” 30 year policy of mitigation only Much cheaper than remediation All studies have concluded policy is insufficient Could have prevented remediation, if begun earlier 2010 US President’s National Space Policy: Pursue research and development of technologies and techniques …. to mitigate and remove on-orbit debris… Debris removal is likely the only option to stabilize LEO Natural law offers some solutions Technology can be applied to make them work Remediation and Policy: What do we do about it? For 30 years we’ve had a mitigation only policy; cheap and hopefully effective Energy to maneuver in orbit is the major cost driver in remediation

Debris Removal Issues: Maneuvering in orbit & capturing debris Many ideas, none fully tested Tether Laser Net

Good Goal, Bad Concept The Institute of Scrap Iron and Steel 1983 magazine cover:

Debris Removal or Collection? Depends on planned use of space Growth? Which regions? Technology developments Propulsion Collision warning Value of raw material in orbit for industrial use? Satellite servicing? Industrialization of space? Unique opportunities for removal and collection In LEO: Remove or collect? But given the cost of placing what we now call debris in orbit, removal or collect? Removal: increases hazard on ground, permanently eliminates what could be a future raw material Inclination distribution of most mass is confined to 4 or 5 bands provides a unique opportunity for either.

Other Regions of Earth Orbit as seen over South Pole Mostly rocket bodies used to place objects in GEO GEO

Other Regions of Earth Orbit as seen over equator GEO Debris GPS Constellation USSR / Russian Military

Other Regions of Earth Orbit So far, only talking about LEO. What about other regions? Good news: Collision decreases with altitude Bad news: Natural sink disappears above LEO, and consequences of current policies are forever. If there are easy changes in current polices that can reduce the responsibly of future generations to manage the debris environment, we have a responsibility to try to do them. Collision rate decreases with altitude. The natural atmospheric “sink” disappears above LEO

Long-term Management Strategy Required Mitigation alone is insufficient Strategy could include combinations of: Active removal from orbit Satellite servicing Recycling of satellite materials Advanced collision warning and avoidance Redefinition of an acceptable geosynch orbit International consensus-building planned over next 5 years: best removal concepts Large, diverse group to: Establish maximum acceptable hazard. Adding increasing amounts of shielding is not an option...it only increases the amount of mass (fuel) in orbit and speeds up the process Evaluate options considering the economic impact of those options and then make recommendations Establish a test program

Conclusions Satellites in Earth orbital space are an integral part of our infrastructure Without significant changes in our use of space, the Earth orbital environment will continue to degrade Now is the time to reevaluate how we use Earth orbit and determine the necessary steps to maintain it for future use In Conclusion: Earth orbital space is part of out infrastructure Without changes the environment for that infrastructure will become unacceptable....it is only a question of when. There are sensible steps that can begin now in how to manage the long-term environment.