SPACE DEBRIS Roger Thompson Sr. Engineering Specialist Abstract: Space debris is a growing concern among satellite operators because the number of objects that have the potential to destroy a satellite now number in the hundreds of thousands. The history of space debris generation, tracking, modeling, and prediction is presented. Examples of debris generating events are used to illustrate the complexity of the problem and the risk to satellite operations. Deficiencies in our ability to quantify and mitigate the risk are noted. Animations of space debris orbits over the last 40 years visually illustrate the rapidly increasing density of the space debris environment. Roger Thompson Sr. Engineering Specialist

WHAT IS SPACE DEBRIS? Obsolete spacecraft, parts of satellites or rockets AND Fragments of spacecraft that have broken up or collided

how many breakups and COLLISIONS? Prior to 1 August 2007, there have been 194 fragmentations and 51 anomalous events1 Most of the debris comes from propellant explosions and deliberate action 56 were deliberate 99 were accidental: 88 propulsion, 8 battery, 3 collisions 39 have unknown causes The have been only 4 known collisions between tracked objects 1991 Cosmos 1275 debris and Cosmos 1934 (inactive) (not discovered until 2005) 1996 Cerise active satellite and Ariane 1 Debris 2005 Thor Burner 2A debris and CZ-4 Debris 2009 Iridium 33 active satellite and Cosmos 2251 (inactive) [1] History of On-Orbit Satellite Fragmentations 14th ed., NASA Orbital Debris Program Office, June 2008)

HOW DO WE KNOW ABOUT SPACE DEBRIS? JSpOC gets approx 400,000 observations and 85,000 tracks PER DAY. 12,000 observations and 2500 tracks are uncorrelated (can’t be identified) Graphic from USSTRATCOM Space Control and Space Surveillance Fact Sheet

SPACE DEBRIS COMES IN ALL SIZES From microscopic particles To obsolete spacecraft and rocket bodies tens of feet in length Photographs Courtesy of NASA

But we can only track “large” objects 10 cm 5 cm 1 cm 3 mm 1 mm

How Much space debris is there? Size Class Quantity Collision Risk ~10 cm or larger Over 19,000 Catastrophic damage Tracked and cataloged We can try to avoid these 1 cm to ~10 cm Over 500,000 (estimated) Most can’t be tracked Major to catastrophic damage Constant daily risk to satellites 1 mm to 1 cm Over 10,000,000 Can’t be tracked Localized damage 3 mm = upper limit of shielding Constant but lower risk

IS SMALL DEBRIS REALLY A PROBLEM? It may be small, but it is moving at 17,000 mph! That kind of energy can damage anything it hits

IS SMALL DEBRIS REALLY A PROBLEM? Hubble Space Telescope antenna damage Photograph Courtesy of NASA

IS SMALL DEBRIS REALLY A PROBLEM? This panel, returned from the Hubble Space Telescope after 7 years in space , has 69 space debris impacts Photograph Courtesy of NASA 1994: Shuttle window had a ½ inch crater that penetrated all but one of the layers of the window NASA determined the cause was a 1/8 inch diameter paint chip

HOW CAN WE PROTECT SPACECRAFT? For very small debris, an outer shield can protect critical components Photograph Courtesy of NASA

Mass (g) aluminum sphere HOW CAN WE PROTECT SPACECRAFT? For very small debris, an outer shield can protect critical components For large debris, maneuvering out of the path is the only option At 10 km/sec typical LEO impact speed Debris size Mass (g) aluminum sphere Kinetic Energy (J) Equiv TNT (kg) Energy similar to 1 mm 0.0014 71 0.0003 Baseball 3 mm 0.038 1,910 0.008 Bullets 1 cm 1.41 70,700 0.3 Falling anvil 5 cm 176.7 8,840,000 37 Hit by bus 10 cm 1,413.7 70,700,000 300 Large bomb

PREDICTING COLLISIONS Not a yes/no result, we have to work with probabilities Exact orbits and positions are never known Copyright Aerospace Corporation

Remember those four known collisions? 1991 Cosmos 1275 debris and Cosmos 1934 Predicted miss distance 512 meters Probability of collision 1.7E-5 (~1 : 50,000) 1996 Cerise active satellite and Ariane 1 Debris Predicted miss distance 882 meters Probability of collision 5.6E-7 (~1 : 2,000,000) 2005 Thor Burner 2A debris and CZ-4 Debris Predicted miss distance 877 meters Probability of collision 1.8E-6 (~1 : 500,000) 2009 Iridium 33 active satellite and Cosmos 2251 Predicted miss distance 584 meters Probability of collision 1.3E-5 (~1 : 100,000)

WHAT HAPPENS WHEN OBJECTS COLLIDE? First animation includes only 10 cm and greater fragments Model predicts 1,184 fragments Only 245 (20%) are shown in animation Second animation includes 1 cm and greater fragments Collision with these objects will probably destroy a satellite Model predicts 148,062 fragments Only 11,364 (less than 8%) are shown in animation

WHAT HAPPENS TO SPACE DEBRIS? Debris in very low orbits slowly loses altitude and re-enters the atmosphere Most of time it burns up during re-entry Sometimes, it survives and lands back on Earth Debris in higher orbits can remain for hundreds or thousands of years Photograph Courtesy of NASA

UNCONTROLLED DEBRIS RE-ENTRY Objects pose a risk to life and property if they survive re-entry This tank landed 150 ft from a house Photograph Courtesy of NASA

UNCONTROLLED DEBRIS RE-ENTRY It is impossible to predict exactly where objects will land Copyright Aerospace Corporation

UNCONTROLLED DEBRIS RE-ENTRY We can calculate a probable impact zone But it may cover thousands of square miles (28,000 for Columbia) Initial Breakup Catastrophic Breakup Secondary Breakup Main Debris field Low Mass Debris Jan. 1978: Soviet satellite reenters, breaks up, and lands in Canada. spreads radioactive debris over 124,000 sq. miles

CONTROLLED DEBRIS RE-ENTRY Spacecraft that are no longer needed are sometimes programmed to re-enter and impact in the ocean Photograph Courtesy of NASA

IT ALL BEGAN WITH THE FIRST SATELLITE Since the October 1957 launch of the world’s first satellite, Sputnik 1 More than 4,500 space missions have been conducted, producing over 19,000 tracked pieces of debris still in orbit. America’s Vanguard 1 is the oldest piece of space debris Photograph Courtesy of NASA #5 Vanguard I #16 Vanguard I R/B 3/17/1958 # 426 Oldest Agena upper stage 9/29/1962 Aug 2010 added 6 debris objects from 1965 launch of a Titan 3C Aug 2011 added a debris object from a 1970 launch Still finding/cataloging FY-1C debris from 2007, now over 8 years after the event (20 more added Nov 2015)