Systems Engineering Approach to the Mitigation of Hazardous Near-Earth Objects (NEOs)

1. Systems Engineering Approach to the Mitigation of Hazardous Near-Earth Objects (NEOs) Brent William Barbee, M.S.E. Emergent Space Technologies, Inc. July 11th, 2006

2. Overview • Background and Motivation • Systems Engineering Approach • Detection, Characterization, and Mitigation • Mitigation Modes • Deflection Methods • Optimal Impulsive NEO Deflection • Hazardous NEO Scenario Timeline • NEO Mitigation Mission Design Architecture • Conclusions

3. Background and Motivation • Near-Earth Objects (NEOs): • Asteroids and comets whose orbits are in close proximity to Earth’s orbit. • When the phasing is right, such NEOs will closely approach Earth. • Potentially Hazardous Asteroids (PHAs) have orbits that come to within 0.05 AU of Earth’s orbit. • If a NEO’s orbit intersects that of Earth, a collision is possible. • Depends on phasing (timing). • Annual meteor showers are caused by Earth passing through the paths of comets. Galileo Photograph of Asteroid Gaspra taken October 29st, 1991 Photograph of Comet Linear C/2002 T7 [May 2004]

4. Background and Motivation • Comets and asteroids: • Comets: • Have very eccentric, longer orbit periods. • Can be more difficult to detect. • Are much less numerous than Near-Earth Asteroids (NEAs). • Exhibit jets of volatiles due to heating when in proximity to the Sun. • Near-Earth Asteroids: • Orbits are within region of inner planets. • No volatiles. • Very numerous: • Thousands with mean diameter > 1 km. • Possibly millions with mean diameter of a few hundreds of meters or less.

5. Background and Motivation • Asteroid orbit classifications: • Earth-crossing: • Apollos • Semi-major axis > 1.0 AU • Perihelion distance < 1.107 AU • Atens • Semi-major axis < 1.0 AU • Perihelion distance > 0.983 AU • Mars-crossing: • Amors • 1.3 AU > perihelion distance > 1.017 AU

6. Background and Motivation • Asteroid composition classifications: • Wide variety of spectral classifications, but there are three main types: • S-type • Silicaceous, majority of inner asteroid belt • Iron mixed with iron- and magnesium-silicates • M-type • Metallic iron, most of middle asteroid belt • C-type • Carbonaceous, 75% of known asteroids

7. Background and Motivation • Some nomenclature: • Asteroid: • Small rocky body orbiting the Sun. • Meteoroid: • Small particle from a comet or asteroid orbiting the Sun. • Bolide: • Extraterrestrial body that collides with Earth, or • Exceptionally bright, “fireball” meteor. • Meteor: • The streak of light created in the sky when an asteroid enters Earth’s atmosphere. • Meteorite: • Solid remains of a meteoroid that survives atmospheric passage and lands on Earth’s surface intact. Photograph of a meteor entering Earth’s atmosphere.

8. Background and Motivation • NEO internal structure: • Monoliths or rubble piles? • A rubble pile is a non-cohesive (strengthless) asteroid held together only by gravity. • Ground observations of spin rates show that most asteroids are not required to be solid. • However, this is not conclusive evidence that such asteroids are in fact rubble piles. • Solid asteroids are more susceptible to mitigation techniques that rely on deflection, particularly impulsive deflection. • Porous asteroids may be more difficult to deflect.

9. Background and Motivation • Collisions with dangerous (large) NEOs are fortunately rare but do happen periodically. • Small NEOs collide with Earth on a regular basis, however. • Tunguska impact in 1908 destroyed 2000 km2 of forest in Siberia (and this is a “small” impact). • Devastated an area about the size of Rhode Island. • NEO thought to be ~ 60 m in mean diameter. • This sort of event is expected once per century, on average. • Annual meteor showers (e.g., Leonids, Geminids)

10. Background and Motivation • Upper atmosphere bolides (several per year): • It is believed that NEOs that are less than 50 m in mean diameter will burn up or explode in the upper atmosphere without reaching Earth’s surface. • Though some may reach lower altitudes before detonation. • Some reach the surface: meteorites. • There are numerous historical examples extending up to present day. • 1998: A small meteorite hit the ground 1 meter from a man playing golf. • June 6th, 2002: A ~ 10 m object exploded over the Mediterranean Sea, releasing about 26 kt of energy. • There were tensions between India and Pakistan at that time, so if this object had exploded over either country it could have sparked a war.

11. Background and Motivation • Earth’s geologic record (surface and strata) shows evidence of many impacts, ranging in size from small to extinction-level events. • Most craters on Earth’s surface are masked by weathering and foliage. • Shocked quartz is a telltale sign of an impact site. • Examples: • Barringer crater in Arizona • Chicxulub in the Yucatan peninsula • Newly discovered Wilkes Land crater in Antarctica.

12. Background and Motivation • Barringer crater in Arizona: • ~ 50,000 years ago. • 55 km east of Flagstaff, near Winslow. • 1200 m wide, 170 m deep. • Caused by a nickel-iron meteorite ~ 50 m in size. • 2.5 Mt explosion: • All life within 4 km killed instantly. • Everything within 22 km leveled. • Hurricance-force winds out to 40 km.

13. Background and Motivation • Chicxulub crater: • Cretacious/Tertiary (K/T) boundary extinction event. • ~ 65 million years ago • More than 70% of species made extinct, including the dinosaurs • Caused by the impact of a 9 – 19 km diameter NEO in the Yucatan Peninsula near Chicxulub Topographic Enhanced Image of the 180 km wide, 900 m Deep K/T Crater Detailed Enhanced Image Showing the K/T Crater Edge Map Showing The Yucatan Location

14. Background and Motivation • Newly discovered Wilkes Land crater in Antarctica. • ~ 480 km wide • Believed to have been caused by a NEO up to 48 km in mean diameter. • Likely cause of the Permian-Triassic extinction 250 million years ago. • Confirmation pending. • If so, the impact killed off most life on Earth at the time. • Eventually allowed dinosaurs to flourish. Ohio State University

15. Researchers have found patterns of periodic extinction in the fossil record. 62  3 million years 140  15 million years Cause for some periodic extinctions may be NEO impacts. NEO impact did cause the K/T boundary extinction ~65 million years ago. Background and Motivation Rohde & Muller, Cycles in Fossil Diversity, Letters to Nature, vol. 434, pgs. 208-210

16. Apophis is the Greek name for the Egyptian God Apep, who is the God of death, destruction, and darkness. This asteroid will pass within ~ 30,000 km of Earth’s surface on April 13th, 2029. If it passes through a “keyhole” location in space, it will return to impact in Earth in 2036. Probability fluctuates as observations are made. Background and Motivation Asteroid 99942 Apophis (previously 2004 MN4) 2036 Apophis Collision Event Data

17. Background and Motivation • Motivation for studying and learning how to mitigate NEO collisions with Earth: • Small but dangerous NEOs collide regularly. • Large and catastrophic NEOs have collided in the past and will do so again. • The ability as a species to save ourselves from this celestial threat is a true milestone.

18. Background and Motivation • Early detection, accurate threat assessment, and scientific characterization are all essential to mitigation, so these are motivated also. • We already want to study NEOs to advance solar system science and have deployed spacecraft missions to do so. • NEAR • Deep Impact • Hayabusa (MUSES-C) Asteroid Eros Seen During NEAR Mission Comet Tempel 1 Stuck During Deep Impact Mission Asteroid Itokawa Seen During Hayabusa Mission

19. Background and Motivation • Congressional mandate to NASA on December 22, 2005: • "The U.S. Congress has declared that the general welfare and security of the United States require that the unique competence of NASA be directed to detecting, tracking, cataloguing, and characterizing near-Earth asteroids and comets in order to provide warning and mitigation of the potential hazard of such near-Earth objects to the Earth.

20. Background and Motivation • The NASA Administrator shall plan, develop, and implement a Near-Earth Object Survey program to detect, track, catalogue, and characterize the physical characteristics of near- Earth objects equal to or greater than 140 meters in diameter in order to assess the threat of such near-Earth objects to the Earth. It shall be the goal of the Survey program to achieve 90% completion of its near-Earth object catalogue (based on statistically predicted populations of near-Earth objects) within 15 years after the date of enactment of this Act.

21. Background and Motivation • The NASA Administrator shall transmit to Congress not later than 1 year after the date of enactment of this Act an initial report that provides the following: • (A) An analysis of possible alternatives that NASA may employ to carry out the Survey program, including ground-based and space-based alternatives with technical descriptions. • (B) A recommended option and proposed budget to carry out the Survey program pursuant to the recommended option. • (C) Analysis of possible alternatives that NASA could employ to divert an object on a likely collision course with Earth."

22. Overview • Background and Motivation • Systems Engineering Approach • Detection, Characterization, and Mitigation • Mitigation Modes • Deflection Methods • Optimal Impulsive NEO Deflection • Hazardous NEO Scenario Timeline • NEO Mitigation Mission Design Architecture • Conclusions

23. Systems Engineering • There is no “silver bullet” solution to the NEO mitigation problem. • Each scenario is unique. • At our current level of knowledge and experience, we can derive generalized requirements and principles. • Actual experience gained in practicing on test NEOs will greatly improve our proficiencies: • NEO Mitigation • NEO Science • NEO Resource Utilization

24. Systems Engineering • The holistic NEO mitigation problem consists of several key phases: • Initial Detection • Threat Assessment • Probability of impact • Threat Characterization • NEO orbit • NEO physical properties • Threat mitigation

25. Systems Engineering • Mitigation requires: • Initial discovery of the threatening NEO. • Assessment of the threat. • Scientific characterization of the NEO. • Thus all systems must work cooperatively. • Detection and tracking • Threat characterization • NEO physical characterization • NEO mitigation mission planning and design

26. Systems Engineering • This complex problem is best treated with a Systems Engineering approach • Interdisciplinary: • Optics and radar (detection, tracking, threat assessment) • Orbital mechanics and Statistical Estimation Theory (NEO orbit characterization) • Planetary science (NEO physical characterization techniques) • Spacecraft Mission Design (physical characterization missions, mitigation missions)

27. Systems Engineering • Systems: • Detection and tracking • Optical and radar • Ground- and space-based • Orbit modeling and impact probability assessment • Post-processing of observational data • Spacecraft transponder beacon mission deployed to NEO • Physical characterization • Ground or space observatory data processing • Spacecraft science mission deployed to NEO • Mitigation system • Spacecraft mitigation mission deployed to NEO

28. Systems Engineering • Spacecraft systems: • Launch vehicles • Thrusters • Spacecraft bus • Spacecraft avionics (GNC) • Spacecraft science instrumentation • Spacecraft communications and data handling • NEO mitigation system • And more … http://near.jhuapl.edu/spacecraft/

29. Systems Engineering • We will focus on mitigation systems and spacecraft missions for mitigation. • Requirements follow from analysis of the general hazardous NEO scenario. • Scenario is expressed as a timeline comprised of events. • Each event has an associated system. • Generalized mitigation mission architecture has been devised and will be presented. • Requirements drive this architecture. • The most important requirement is simply this: If a NEO is on a collision course with Earth, we must prevent the collision.

30. Systems Engineering • Fault tolerance and redundancy take on critical importance in the case of a civilization-threatening NEO ( 1 km). • Robust design practices. • Multiple mitigation spacecraft and launch systems. • In the case of a deflection, if all craft remain operational the opportunity exists to apply multiple deflections to enhance effectiveness.

31. Overview • Background and Motivation • Systems Engineering Approach • Detection, Characterization, and Mitigation • Mitigation Modes • Deflection Methods • Optimal Impulsive NEO Deflection • Hazardous NEO Scenario Timeline • NEO Mitigation Mission Design Architecture • Conclusions

32. NEO Detection • NEO discovery and cataloguing: • Detection and observations: • LINEAR • NEAT • LONEOS • Catalina Sky Survey • Spacewatch • Tracking and threat characterization: • Near-Earth Asteroid Tracking (NEAT) program at JPL • Near-Earth Objects Dynamic Site (NEODyS) in Pisa, Italy http://www.ll.mit.edu/LINEAR/

33. NEO Detection • Current statistics (June 30th, 2006): • 4131 NEOs discovered thus far. • 838 NEOs 1 km in size or greater. • 784 PHAs (orbits come within 0.05 AU of Earth’s orbit) • Spaceguard Goal: • Established in May 1998. • Discover 90% of NEAs  1 km by 2008. • As of 2005 we believe we’re at 73%.

34. NEO Detection http://neo.jpl.nasa.gov/stats/

35. NEO Detection http://neo.jpl.nasa.gov/stats/

36. NEO Orbit Characterization • Orbit propagation and collision detection: • Knowledge and classification of NEO orbits • Identification of PHAs • Determination of collision probabilities • Ground or space observatories • Space observatories offer more coverage and better observations. • Allows detection and characterization goals to be met much more swiftly but at higher cost. • Transponder missions • X-band transponder: • Position accuracies on the order of 100 m and velocity accuracies on the order of 0.1 mm/s within a geocentric distance of 2 AU, assuming a 35 m receiving dish on Earth. • Requires 5 W of power.

37. NEO Threat Characterization • Torino Scale http://impact.arc.nasa.gov/torino.cfm

38. NEO Threat Characterization • Palermo Scale - Palermo Scale Value - Probability of Impact - Annual Background Probability of Impact for a NEO with Same Kinetic Energy - Time in Years Before Impact

39. NEO Threat Characterization • The Torino scale is intended for communicating impact risk to the general public. • The Palermo scale is intended for impact risk communication within the scientific and engineering communities. • Both scales rate threat by cross-referencing: • Impact energy. • Probability of impact.

40. NEO Threat Characterization • Perceived probability of impact is what matters. • We will take action based on our best estimate of the impact probability. • We currently have not defined a probability threshold for taking action. • Probability x Cost vs. Mission and Operations Cost? • It is crucial to have high quality observations and prediction methods. • Many lives or our entire civilization are at stake. • NEO mitigation missions are highly-resource intensive.

41. NEO Characterization • NEO physical characterization: • Physical properties • Mass • Density • Porosity • Internal structure and composition • Surface chemical composition • Spin state Near-Infrared Spectrograph Used in NEAR Mission John Hopkins University/Applied Physis Laboratory, (1998). NEAR Near-Infrared Spectrometer. Near Earth Asteroid Rendezvous. http://near.jhuapl.edu/fact_sheets/NIS.pdf

42. NEO Characterization • NEO characterization • Ground or space observatory systems • The observational data from these systems can provide estimates for a NEO’s bulk properties. • These need to be created. • Spacecraft science missions • On-orbit NEO science is the only way to gather accurate and detailed physical data on the NEO. • Such information is crucial for effective mitigation system design.

43. NEO Mitigation • The primary requirement is that the incoming NEO does not collide with Earth. • If we can mitigate once and it remains a future threat, we can mitigate it again. • The secondary requirement is that all possible future collisions of that NEO with Earth are also eliminated. • Gravitational keyholes must be considered. • There are three modes of mitigation: annihilation, fragmentation, and deflection.

44. NEO Mitigation • Gravitational keyholes • Small regions in space near Earth defined by the dynamics between the NEO and Earth such that: • If the NEO passes through a given keyhole, it will be placed onto a “resonant” orbit by Earth’s gravity, causing the NEO to return to collide with Earth some number of orbits later. • Example: 7:6 resonance – NEO orbits the sun 6 more times while the Earth orbits 7 more times and at the end of the 7th Earth orbit, the NEO collides with Earth.

45. NEO Mitigation • If it is known in advance that a NEO will pass through a keyhole, it is sufficient to deflect the NEO just enough to nudge its trajectory outside of the keyhole. • Generally requires less v than a maximal deflection. • Care should be taken to avoid other keyholes. • It is still better to move the NEO’s path such that is passes by Earth at a great distance if possible. • Asteroid orbits that pass near keyholes are dangerous.

46. Overview • Background and Motivation • Systems Engineering Approach • Detection, Characterization, and Mitigation • Mitigation Modes • Deflection Methods • Optimal Impulsive NEO Deflection • Hazardous NEO Scenario Timeline • NEO Mitigation Mission Design Architecture • Conclusions

47. NEO Mitigation Modes • Annihilation • Reduction of NEO to vapor or fine-grain dust cloud by energy application or pulverization. • Provides the highest assurance that the threat is permanently eliminated. • Requires the most energy out of the three modes. • Energy requirements are generally prohibitive. • Required technologies are generally unavailable. • Ultra high-power laser beams. • Sets of many high-yield explosives. • Antimatter torpedoes. • Series of ultra-high energy kinetic impactors.

48. NEO Mitigation Modes • Fragmentation • Reduction of NEO to (hopefully) small but not necessarily negligible pieces. • Provides assurance that the threat is permanently eliminated only if the largest fragment is smaller than the threshold for burning up in Earth’s atmosphere (~ 20 – 50 m). • Least controllable mitigation mode. • Medium to high energy requirements. • Examples: • Properly placed explosives (conventional or nuclear). • Sufficiently energetic kinetic impactor(s). • Tungsten bullet “cutters.”

49. NEO Mitigation Modes • Deflection • Modification of NEO’s orbit such that it misses Earth rather than collides. • Potentially provides the least assurance that the threat is permanently eliminated. • Gravitational keyholes. • NEO still exists. • Most controllable mitigation mode. • Low to medium energy requirements. • Examples: • Nuclear detonations (surface or standoff). • Attached thrusters (low or high thrust) • Solar concentrators • Gravity tractors

50. Overview • Background and Motivation • Systems Engineering Approach • Detection, Characterization, and Mitigation • Mitigation Modes • Deflection Methods • Optimal Impulsive NEO Deflection • Hazardous NEO Scenario Timeline • NEO Mitigation Mission Design Architecture • Conclusions