# Presentation: 336183

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

**Brent William Barbee, M.S.E.**
**Emergent Space Technologies, Inc.**
**July 11****th****, 2006**

## 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

## 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.

**Photograph of Comet Linear**
**C/2002 T7 [May 2004]**

**Galileo Photograph of Asteroid Gaspra**
**taken October 29****st****, 1991**

## 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.

## 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

## 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

## 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.**

## 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.

## 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)

## 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.

## 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.

## 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.

## 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

**Map Showing The Yucatan Location**

**Detailed Enhanced Image Showing**
**the K/T Crater Edge**

**Topographic Enhanced Image of the**
**180 km wide, 900 m Deep K/T Crater**

## 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*

## Background and Motivation

- 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.

*Rohde & Muller, Cycles in Fossil Diversity,  Letters to Nature, vol. 434, pgs. 208-210 *

## Background and Motivation

- 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.

| Size | 320 - 400 m | 1⁄4 mile |
| --- | --- | --- |
| Mass | 4.61010 kg | 130,000 Fully loaded 747
aircraft |
| Impact Velocity | 12.59 km/s | 28,000 mph |
| Impact Energy | 870 Mt | 43,500 Hiroshima Bombs
(20 Kt each) |
| Impact Probability | 1/38,000 | Comparable to death by snakebite or tornado. |

**2036 Apophis Collision Event Data**

**Asteroid 99942 Apophis (previously 2004 MN4)**

## 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.

## 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**

## 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.

## 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.

## 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."

## 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

## 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

## 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

## 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

## 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)

## 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

## 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/*

## 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.*

## 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.

## 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

## 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/*

## 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%.

## NEO Detection

*http://neo.jpl.nasa.gov/stats/*

## NEO Detection

*http://neo.jpl.nasa.gov/stats/*

## 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.

## NEO Threat Characterization

- Torino Scale

*http://impact.arc.nasa.gov/torino.cfm*

## 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

## 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.

## 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.

## 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*

## 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.

## 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.

## 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.

## 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.

## 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

## 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.

## 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.”

## 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

## 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

## NEO Deflection Methods

- Deflection is the preferred mode of mitigation.
- Most practical mitigation mode, given current and foreseeable technology.
- Energy requirements are tractable for a wide range of NEOs.
- Most controllable, generally.
- With practice we can develop proficiency and learn the pitfalls.
- This is absolutely critical if we are to be prepared.

## NEO Deflection Methods

- Deflection has its difficulties:
- Rubble piles or highly porous NEOs.
- Some proposed deflection systems are very challenging to implement due to:
- Anchoring to NEO surface.
- Complex proximity operations about NEO.
- NEO spin state.
- Long periods of operation on orbit in hostile space environment.
- Higher probabilities of failure.
- All proposed systems are currently untested.

## NEO Deflection Methods

- Some possible deflection systems:
- Gradual
- Solar concentrators
- Attached low-thrust thrusters
- Gravity tractor
- Impulsive
- Kinetic impactors
- Attached high-thrust thrusters
- Nuclear explosives
- Standoff blast
- Surface blast

*Gritzner, et al. “Mitigation technologies and*
*their requirements” Mitigation of Hazardous*
*Asteroids and Comets, Cambridge University*
*Press, 2004** *

**Conceptual Solar Collector Design**

## NEO Deflection Methods

- Nuclear explosives offer the following advantages:
- NEO spin state not a factor.
- No anchoring of equipment to NEO.
- No long operation on orbit.
- Highest available energy density.
- High capability for imparting momentum to a NEO.
- High energy density equates to easier launch from Earth.
- Multiple launches are more feasible.

## NEO Deflection Methods

- High momentum transfer performance:
- Can adequately deflect larger NEOs than other methods even with limited warning time.
- Technology is currently available.
- Puts former weapons of mass destruction to a use that benefits all humankind.
- Deflection is relatively controllable through proper positioning of the device prior to detonation.

## NEO Deflection Methods

- Nuclear explosive disadvantages:
- Untested.
- Required rendezvous and proximity operations are challenging in some cases.
- Requires special packaging inside launch vehicle to ensure containment in the event of launch vehicle failure.
- Danger of inadvertently fragmenting NEO in an undesirable fashion.

## NEO Deflection Methods

- Sensitive to NEO physical properties.
- In the absence of good knowledge of NEO physical properties, the system must be over-designed.
- Requires amendment of the “Nuclear Test Ban Treaty” (1963).
- Public fear and misunderstanding.
- Political tensions.

## NEO Deflection Methods

- Standoff nuclear detonation:
- Nuclear device of proper yield is placed at the optimal detonation coordinates.
- Optimal distance from NEO surface.
- Optimal orientation of imparted impulse vector.
- Neutrons from the explosion penetrate 10-20 cm into NEO surface, superheating a thin shell of NEO material.
- Material blows off and imparts momentum to NEO.

*Artist’s Conception of a Standoff *
*Nuclear Detonation Applied to an*
*Asteroid*

*Ahrens, Thomas J. and Harris, Alan W., “Deflection and Fragmentation of*
*Near-Earth Asteroids,” Hazards Due to Comets & Asteroids: 909 – 913. 1994** *

*Wilkins, Peter A. Computer rendering of asteroid model using*
*Lightwave software (November 2005) *

## NEO Deflection Methods

- Standoff Nuclear Detonation Modeling For a 1 km Asteroid

**Imparted Momentum to 1 km NEO Test Cases**** **

*Holsapple, Keith A. “About deflecting asteroids and comets”*
*Mitigation of Hazardous Asteroids and Comets, Cambridge*
*University Press, 2004 *

## 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

## Optimal Deflection

- A deflection must applied in an optimal fashion.
- Imparted momentum is tiny compared to the NEO’s momentum.
- Application must be optimal in order to ensure effectiveness.
- There are impulse vector orientations that have little or no effect on the NEO’s subsequent motion.

## Impulsive deflection is applied at a particular point along the NEO’s orbit, at a particular time before Earth impact.
Impulse immediately alters the NEO’s heliocentric velocity.
Impulsive velocity change vector is parameterized.
It is always optimal to maximize the magnitude of the imparted velocity change, and this is a function of NEO properties and mitigation system technology.

- Impulsive deflection is applied at a particular point along the NEO’s orbit, at a particular time before Earth impact.
- Impulse immediately alters the NEO’s heliocentric velocity.
- Impulsive velocity change vector is parameterized.
- It is always optimal to maximize the magnitude of the imparted velocity change, and this is a function of NEO properties and mitigation system technology.

**Impulsive NEO Deflection**
**Problem Setup**

## Optimal Deflection

- Collision Condition:

- NEO-Earth Distance:

- Position Vector of NEO with respect to Earth:

- Deflection Condition:

- ~ small

- = original (**unmitigated**) time of collision

- = time of closest approach **after mitigation**

**A deflection may be interpreted as:**
*The forced transition of a collision event to*
*a close approach event.*

## Optimal Deflection

- There is a restriction on the range of
- times over which the performance
- index is evaluated.

- Performance index:

- *

- = time of original (**unmitigated**) close approach “event”

## Optimal Deflection

- Simulations
- of
- Dynamics

**OPTIMAL SOLUTION**

- Design Space:

## Two case studies were performed to assess the effectiveness of this methodology.
First case study examined azimuth and elevation angle effects.
Second case study examined time of deflection effects.
This case study also utilizes the NEO mitigation mission design architecture that will be presented later.

- Two case studies were performed to assess the effectiveness of this methodology.
- First case study examined azimuth and elevation angle effects.
- Second case study examined time of deflection effects.
- This case study also utilizes the NEO mitigation mission design architecture that will be presented later.

## Optimal Deflection

- First case study:
- Real asteroid: 1991 RB
- Asteroid closely approached Earth.
- Goal is to maximally increase close approach distance.
- Previous research used linearized dynamics and eigenspace analysis to optimize impulsive deflections.
- Linearization constrains time of deflection to be during NEO’s final solar orbit prior to impact or close approach.

## Optimal Deflection

- Comparison of methodologies:
- Different performance indices.
- Different dynamics models.
- Current work uses n-body simulation including the Sun, NEO, and Earth.
- Current methods do not employ linearizations.
- Both methods found that optimal impulse vectors lie in the NEO’s orbit plane.

## Optimal Deflection

- State transition matrix (Battin 1987):

- Change in position due to a change in velocity:

- Performance index:

- Performance index in the current
- notation:

- Relationship to the current notation:

- Point at which
- deflection is applied

- NEO on perturbed trajectory

- NEO on unperturbed trajectory

- Perturbed trajectory

- Unperturbed trajectory

**Previous Research Performance Index**

*P*

## Optimal Deflection

**Orientations of Optimal Deflection Impulse Vectors**

**Magnitudes of Optimal Deflections**

- _Asteroid Physical Parameters:_
- Mean diameter ............................. 500 – 1100 m
- Avg. mean diameter ...................... 800 m
- Assumed mean density .................. 2.7 g/cm3
- Computed mass (spherical model) .... 7.241011 kg

- Epoch: 8/18/2005, 00:00:00 UT

- JPL Orbital Elements for Asteroid 1991 RB

- m/s

- Optimal deflections are computed  such that the asteroid deflection is maximized on September 19th, 1998.

*B.A. Conway “Optimal interception and deflection of Earth-approaching asteroids using*
*low-thrust electric propulsion” Mitigation of Hazardous Asteroids and Comets,*
*Cambridge University Press, 2004 *

## Optimal Deflection

- Optimal Solution

- Near-Optimal Solution

- Case (a): Using Previous Research
- Performance Index

*** Solution space appears to show two nearly identical optimal solutions.**
*** Solution space also shows two nearly identical worst solutions, and both**
**   ****appear to still successfully move the asteroid further away from Earth.**

## Optimal Deflection

- * Achieved deflection is 16% less than that found by previous study.
- * Optimal orientation of the deflection impulse vector differs by 10%.

- Optimal Solution

*** Solution space shows one distinct optimal solution.**
*** Solution space shows one distinct anti-optimal solution that actually pushes the**
**   ****asteroid closer to Earth.**
*** Solution space shows two solutions that have zero effect.**

- Case (b): Using Current Performance Index

**Structure of Solution Space Using**
**Current Performance Index**

**Optimal Solution**

**Zero-Effect Solutions**

**Anti-Optimal Solution**

## Optimal Deflection

-  Optimal elevation angle is zero.
-  There is a spread of about ±20-30° about the optimal elevation angle
-    for which most (~ 90%) of the maximal deflection is still achieved.

- Elevation Angle Effects

## Optimal Deflection

- There is a spread of azimuth angles, approximately ±15-20°, about the optimal for which most (~90%) of the maximal deflection is still achieved.

- Azimuth Angle Effects

## Optimal Deflection

- Conclusions:
- Optimal deflections performed shortly before impact may have significant radial components.
- Optimal deflection impulse vectors lie in the NEO’s orbital plane.
- There is a moderate range of angles about the optimal for which most of the deflection is still achieved.

## 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

## NEO Scenario Timeline

- A general hazardous NEO scenario has a timeline associated with it.
- Events ranging from initial detection to Earth collision, if threat goes unmitigated.
- Analysis indicates steps that will maximize our chances of successful mitigation.
- Lays foundation for requirements derivation and mitigation mission planning.

## NEO Scenario Timeline

- Forward Time

**NEO Detected**

**- NEO determined**
**  ****to be a threat**
**- Mitigation mission**
**  ****planning begins**

**- Mission planning**
**  ****reaches critical mass**
**- Construction of **
**   ****spacecraft and **
**   ****preparation of launch**
**   ****vehicle begin**

**Spacecraft carrying**
**the chosen mitigation**
**system launches**

**Spacecraft**
**performs**
**rendezvous**
**with NEO**

**Mitigation system**
**is positioned and**
**prepared for**
**activation**

**Time of Unmitigated**
**Earth Impact**

**Continuum of available**
**deflection times **

**NEO Collision Mitigation Timeline**

** These two events may be collapsed into *_*one*_* event, which is ****Interception****, depending on the Mitigation system requirements*

## NEO Scenario Timeline

- Goal is to _maximize_ the *Continuum of Available Deflection Times:*
- Generally, the earlier a deflection can be applied, the more effective it will be.
- Steps:
- Detect all NEOs as early as possible.
- Minimize time to determine if a given NEO is a threat.
- Minimize Mission Planning Time.
- Minimize Spacecraft / Launch Vehicle construction and preparation time.
- Optimize rendezvous or interception trajectory according to:
- Minimum Flight Time
- Optimal Deflection Principles
- Fuel / Technology Constraints* *

## NEO Scenario Timeline

- System requirements
- Detection Systems
- Long range, high-resolution, view as much of the sky as possible.
- Space-based systems achieve these requirements better than ground-based systems.
- Characterization Systems
- High accuracy
- Ground- or Space-based system improvements (radar & optical).
- Development of rapid deployment, low mass x-band transponder beacon placement missions.
- On NEO body
- On NEO orbit

## NEO Scenario Timeline

- Mitigation Mission Planning
- Develop comprehensive means of devising efficient and effective (tend towards optimized) mitigation missions.
- Spacecraft / Mitigation System Construction Systems
- Develop proficiency with the operation of various mitigation systems.
- Field tests during non-emergency times.
- Spacecraft and mitigation equipment components should be modular and able to be assembled reliably in rapid fashion.
- Mitigation Spacecraft Launch System
- Able to be constructed and prepared for launch rapidly so as to be able to take advantage of earliest launch window.

## NEO Scenario Timeline

- We don’t necessarily want to have pre-built mitigation systems on standby.
- Collision of dangerous NEOs is a low-frequency event.
- Maintenance costs.
- Uniqueness of NEO scenarios requires custom designs.
- We can still improve our rapid deployment skills and develop modular systems that have both mitigation and other applications.
- NEO Science
- NEO Resource Utilization

## 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

## Mission Design Architecture

- NEO Mitigation Mission Planning Architecture:
- Three phases:
- Detection and Reconnaissance
- Design Cycle (Iterative)
- Execution

**Detection**
**And**
**Reconnaissance**

**Design Cycle**

**Execution**

**ITERATE UNTIL**
**WORKING DESIGN**
**IS REACHED**
**ITERATE FURTHER**
**FOR OPTIMIZATION**

## Mission Design Architecture

- Design Cycle

- Detection & Reconnaissance

**Estimate NEO Physical**
**Properties From Ground**
**Observations And Computer**
**Models**

**Accurate Physical**
**Properties Obtained**

**NEO Orbit Is**
**Accurately Known**

**Use Estimate of NEO**
**Orbit From Ground**
**Observations**

**Simulate NEO Orbit**
**As Accurately As**
**Possible**

**Will NEO Indeed**
**Collide With**
**Earth?**

**NEO is Discovered**
**with Non-Zero Probability**
**of Earth Collision**

**Estimate Earth**
**Collision Time**

- START

**Send Science****Mission To NEO**

**Create The Most**
**Accurate Physical**
**Model Of NEO Possible**

**STOP**

**Is There Enough**
**Time For A**
**Preliminary**
**Science Mission?**

**Is There Enough**
**Time To Deliver A**
**Transponder Beacon**
**To The NEO?**

**Send Beacon**
**Mission To NEO**

- YES

- NO

- NO

- NO

- NO

- YES

- YES

## Mission Design Architecture

- Design Cycle

**Select NEO**
**Mitigation System**

- Execution

**Does Mass Budget**
**Allow For Science/**
**Beacon Equipment**
**To Gather Pre-**
**And Post-**
**Mitigation Data?**

**Does Payload Mass**
**Require On-Orbit**
**Assembly?**

**Maximum Mitigation**
**Potential Is Fixed**

**Determine Optimal**
**Mitigation Operations**

**Determine Launch**
**Windows For NEO**
**Rendezvous Or**
**Interception**

**Determine NEO**
**Rendezvous Or**
**Interception Trajectory**
**And Maneuvers**

**Determine Thruster**
**And Fuel**
**Requirements**

**Design Spacecraft To**
**Deliver And Operate**
**Mitigation System**

**Determine Total**
**Launch Payload Mass**

**Determine Requirements**
**For Launch Vehicle(s)**

**Design Spacecraft**
**And Equipment For**
**Science To Be **
**Included With**
**Mitigation Mission**

**Design On-Orbit**
**Assembly Mission**
**Phases and Spacecraft**

- Knowledge Of NEO Physical Properties

- Knowledge of NEO Orbit

- YES

- YES

- TOP LEVEL OF DESIGN CYCLE

## Mission Design Architecture

**Re-Enter Design Cycle**
**At TOP LEVEL**

- Execution

- Requirements for Launch Vehicle(s)

**Is Mission**
**Feasible?**

**EXECUTE**
**MISSION**

**Finalize Mission Phases And**
**Mission Objectives And**
**Develop Contingency Plans**

**Make Final Selection(s) Of **
**Launch Vehicle(s)**

- YES

- NO

- To TOP LEVEL Of Design Cycle

## Mission Design Architecture

- Following this mission design process will produce effective missions.
- However, we must accept that scenarios theoretically exist for which there is no mitigation solution due to technological and/or timing constraints.
- In this case we must follow other contingency procedures, such as evacuation and/or sheltering, depending on the level of threat.

## Mission Design Architecture

- Second case study:
- Applies mitigation mission design architecture.
- Proceeds through one iteration of the design cycle.
- Each component of the design cycle is treated to first order.
- A working solution is achieved after one iteration, and further optimization is possible.
- Examines time of deflection effects.

## Mission Design Architecture

- A complete mission plan to deflect a fictitious NEO is devised.
- The fictitious NEO parameters are taken from a document entitled “Athos, Porthos, Aramis & D’Artagnan: Four Planning Scenarios for Planetary Protection” by David K. Lynch, Ph.D. and Glenn E. Peterson, Ph.D. of The Aerospace Corporation.
- The purpose of the document is to present four characteristic NEO impact scenarios so that mission planners can devise solutions.

- _Given Scenario Parameters:_

- Asteroid name ..................... D’Artagnan
- Date of Discovery ................. February 22nd, 2004, 00:00:00 UT
- Date of Earth Impact ............. September 14th, 2009, 11:04:26.117 UT
- Shape ................................ Ellipsoidal
- Dimensions ......................... 110120 130 m
- Density .............................. 4.0 g/cm3
- Computed Asteroid Mass ....... 3.594109 kg
- Compositional Type ...............S (silicaceous)
- Orbit Type ........................... Aten

## Mission Design Architecture

- Impact Location ..................... Lyon, France
- Population at Impact Location....415,000 (city proper) / 1.26 million (urban area)
- Impact Velocity ...................... 14 km/s
- Impact Energy ....................... 84 Mt

*** For reference, the largest nuclear bomb ever tested on Earth had a yield of 50 Mt.**

**Idealized Structural Diagram of Asteroid D’Artagnan**** **

**Computer-generated Model of Asteroid D’Artagnan**** **

*Wilkins, Peter A. Computer rendering of asteroid model using*
*Lightwave software (November 2005) *

## Mission Design Architecture

**D’Artagnan’s Orbital Elements at the Time of Detection**

**D’Artagnan and Earth Orbits in The Ecliptic Plane**

**NEO Orbit**

## Mission Design Architecture

**Perceived Impact Probability and Corresponding Threat **
**Rating as a Function of Observed Data Arc**** **

-  A case study performed by Chesley, *et al*
-   found that it took approximately a year of
-   continuous observation to determine that a
-   simulated impacting asteroid had a high
-   probability of Earth impact (~ > 50%).
-  Their simulated impactor was 17 years out and
-   D’Artagnan is only 5 years out so orbit
-   propagation errors would be less.
-  It will be assumed that D’Artagnan is perceived
-   to have an alarming probability of impact
-   (> 50%) by 6 months after initial discovery.
-   **Mitigation mission planning begins at this**
**  ****point.**

- Time Until D’Artagnan is Determined to be a Threat

*Chesley, et al. “Earth impactors: orbital characteristics and warning times”*
*Mitigation of Hazardous Asteroids and Comets, Cambridge University Press, 2004 *

## Mission Design Architecture

- It is assumed that a mitigation mission can be designed and a spacecraft readied for launch by one year after initial threat determination.
- The NEAR Shoemaker mission went from concept to launch in three years.
- Mitigating D’Artagnan is an emergency situation so it is assumed that work will proceed much faster.
- Since the impact is only about 4 years away by the time a spacecraft can be prepared, there is no time for a preliminary science mission.
- Mission planners are forced to use estimates of D’Artagnan’s physical parameters based on ground observations.
- Mission planners choose to use a standoff nuclear detonation to deflect D’Artagnan.
- Technology is readily available and mission complexity is minimized.

## Mission Design Architecture

**Temporal Maximized Deflection Map with Perihelion Passages Marked by Red Arrows**

**Deflection as a Function of Azimuth for Various Deflection Times**

**Deflection Optimization Results for a Velocity Change Magnitude of 5.0 cm/s**

-  It is hoped that the spacecraft can deliver the nuclear device to the asteroid within 1 year of launch.
-  Deflection times are scanned at a resolution of 5 months, beginning at 2.5 years from the time of
-    initial detection.
-  Times for which D’Artagnan is at perihelion are included.
-  The elevation angle is set to zero and azimuth angles are scanned at a 1 resolution.

## Mission Design Architecture

-  Deflections applied at perihelion passages clearly yield the best deflections.
-  The best overall deflection occurs at the perihelion passage about 2.75 years
-   after initial detection.
- Thus the chosen time of deflection is about 2.75 years after initial detection,
-   which is 15 months after mitigation spacecraft launch.

- Optimal Impulse Vector Azimuth .... 182 (178.06 apart from asteroid velocity vector)
- Optimal Time of Deflection ............11/28/2006, 14:24:00 UT (2.767 years after detection)
- Deflection Magnitude ................... 10487 km (~ 1.64 Earth radii)

**Deflection Optimization Results for a Velocity Change Magnitude of 5.0 cm/s**

**Deflection Optimization Summary**

## Mission Design Architecture

-  Time from detection to threat determination ............... 0.5 years
-  Time from detection to mitigation spacecraft launch .... 1.5 years
-  Time from detection to deflection ............................ 2.767 years
-  Deflection velocity change magnitude ..................... 5 cm/s
-  Nuclear device and yield .......................................68 Kt (W-85)
-  Optimal deflection azimuth angle ............................ 182 (178.06 from velocity vector)
-  Optimal time of deflection ...................................... 11/28/2006, 14:24:00 UT
-  Optimized deflection distance ................................. 10487 km
-  Launch vehicle .................................................... Boeing Delta IV Heavy
-  Rendezvous Thruster ........................................... Pratt & Whitney RL 10
-  Proximity Operations Thrusters .............................. DASA CHT Monopropellant
-  Launch Date ....................................................... 8/25/2005
-  Arrival Date ........................................................ 10/8/2006
-  Time of Flight ...................................................... 13.733 months
-  Spacecraft Launch Mass ....................................... 7960 kg
-  Spacecraft Arrival Mass ......................................... 820 kg
-  Optimal Standoff Detonation Distance ...................... 2.76 m
-  Time available to Position Nuclear Device ................. 51.6 days

- Mitigation Mission Design Results

## Mission Design Architecture

- The principle is that optimized missions may be developed by:
- Optimizing each component in the process to the extent possible.
- Iteration of the Design Cycle.
- Sampling the design space is required, so making some a priori assumptions makes the process more efficient.
- Establish general principles.

## Mission Design Architecture

- Generally, the best time to deflect is the first logistically available perihelion passage of the NEO.
- Optimal deflecting impulse vector characteristics:
- Lies in the NEO’s orbit plane.
- Is close to opposite the NEO’s velocity vector for deflections applied with at least a few years of lead time.
- Has more radial component when deflection is applied with little lead time.
- There is an appreciable spread of orientations about the optimal for which most of the maximum deflection is still achieved.
- Robust.
- Is best determined by formulating the problem using the performance index presented herein and using detailed dynamics models.

## 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

## Conclusions

- Ongoing work:
- Deflection system research and design.
- Develop and _**TEST**_ viable mitigation technologies.
- Optimization of overall mitigation system.
- Hybrid Optimal Control Theory
- Categorical variables.
- No a priori assumptions.
- Cost modeling for various example mitigation missions.

## Conclusions

- Ongoing work:
- Cost modeling for actual missions that will test mitigation systems and simultaneously gather NEO science data as per usual.
- Selection of target asteroids for mitigation system testing.
- Safety.
- Scientific interest.
- Define perceived impact probability thresholds for taking action.

## Conclusions

- Detection and Characterization systems must be maintained, enhanced, and expanded:
- Space-based observatories
- More NEO science missions
- Combine these with mitigation missions for synergy.
- Might even combine with resource utilization technology test missions for additional synergy.
- Rapid-deployment beacon mission development.

## Conclusions

- Continue and enhance NEO science missions.
- _Incorporate mitigation system tests._
- Build proficiency.
- Learn the pitfalls.
- Demonstrate that we as a species have the ability to mitigate the hazard posed by an incoming NEO.
- True species milestone.

## Questions?

*http://www2.jpl.nasa.gov/sl9/image81.html*