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SHIELD SHIELD A Comprehensive Earth Protection System Robert

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SHIELD SHIELD A Comprehensive Earth Protection System Robert Powered By Docstoc
					     SHIELD
   A Comprehensive
Earth-Protection System
             Robert E. Gold
             Johns Hopkins University
             Applied Physics Laboratory

             robert.gold@jhuapl.edu

             Washington 240-228-5412
             Baltimore 443-778-5412
                           SHIELD
                    Earth Impact Fatalities
                                                   Historical Fatalities
                                                   from Worst Disasters
                                                   by Type
                                                   Epidemic        75 million
                                                   Famine           9-13 million
                                                   Flood            900,000
                                                   Earthquake       830,000
                                                   Cyclone         >300,000
                                                   Conflagration    140,000
                                                   Landslide       >100,000
                                                   Tsunami           36,000
                                                   Volcano           30,000
                                                   Avalanche         20,000




Average mortality from impacts as a function of
 energy for the current population of the Earth.
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                   SHIELD
       How Big, How Often, How Bad
                                        s   Impact speed = 20 km/s
                                        s   ρ== 3 g/cm3
                                        s   From Shoemaker (1983)




Cumulative energy-frequency curve for
        impacts on the Earth.
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        SHIELD
Tunguska Blast, Siberia 1908




                        Tunguska in perspective


    Annual probability is 1 in 300.
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  SHIELD
Size of the Threat
                s   Distribution of
                    Earth-crossing
                    asteroids from the
                    Spaceguard survey
                    (Morrison 1992)
                s    ~10% of 1-km
                     asteroids have been
                     discovered




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            SHIELD
Inadequate Earth-Based Discovery Rate
                       s   Worldwide search effort has
                           fewer than 100 people.
                       s   Nearly 1/3 of all NEOs
                           are discovered at their
                           closest approach to Earth.




                           Discovery completeness of Earth-
                           crossing asteroids resulting from
                           whole-sky surveys.
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                        SHIELD
       Bimodal Threat: Comets vs. Asteroids
Parameter        Long Period Comets              Asteroids

Impact velocity ~58 km/sec                       ~20 km/sec
Warning time Typically 2 months to 2 years       Decades after survey
                                                 complete. Days to
                                                 decades before.
Orbit            Often high inclination or       Typically low
inclinations     retrograde orbits which are     inclination,prograde
                 difficult to reach.             orbits.
Mitigation       Rendezvous difficult due to      Rendezvous, flyby, or
techniques       high velocity. Limited to flyby impact methods.
                 or impact methods. Require
                 very accurate terminal guidance.

Note: LPCs constitute 5 to 10% of the Earth impactors and 25 to 50% of
the craters larger than 20 km in diameter.
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                       SHIELD
               A Few Points to Remember

s   KE ==½ mv2
s   Mass of 1 km diameter asteroid is ~ 1.7 ✕ 109 tons.
s   Energy of an asteroid impacting at 3 km/sec is equivalent
    to the energy of the same mass of TNT.
s   Typical asteroid impact velocity is 20 km/sec. Energy equals
    44 times the mass of TNT.
s   Typical comet impact velocity is 58 km/sec. Energy equals
    374 times the mass of TNT.


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     SHIELD
Shield Acknowledgements

                  s   Excellent work exists on
                      individual aspects of
                      Earth protection.

                  s   SHIELD extends it to an
                      overall Earth protection
                      system.
                      •   Detection
                      •   Command and control
                      •   Multi-tiered defensive
                          system




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   SHIELD
Total System Concept




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                               SHIELD
                  Need For Space-Based Detection

s   Advantages
    •   Optimal location
    •   Observing time
    •   Sensitivity
s   Results
    •   Detection of Aten asteroids not observable from Earth
    •   Increased warning time for long period comets
         x   From days or months to years
         x   Ability to view comets approaching from the opposite side of the Sun
    •   Increased observing time by ≥ 4
    •   Greater areal coverage
    •   Better limiting magnitude
    •   Reduced time to complete catalog
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                        SHIELD
                      Sentry Instruments
s   1-2 meter diameter telescope
s   10,000 x 10,000 pixel charge coupled device (CCD)
s   Computing power
     • 1 PC-equivalent processor for image processing
     • 1/2 of a PC-equivalent processor for orbit calculations
     • < 10 MB (RAM)
     • 100 GB digital storage
        x 90 GB storage for images

        x <10 GB storage for catalog, star charts, etc

s   Communications
     • RF or newer technology at 1024 bps to ground
     • Optical cross link for sentry-to-sentry communications at
       1024 bps
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                                                SHIELD
     Detection Distance from Venus, Earth and
  Jupiter Orbits (1-km object, Vm = 22, 20, and 18)




                                                             Asteroid
                                                              Main

                                                               Belt
         Mercury




                                                                                                     Jupiter
                   Venus

                           Earth



                                     Mars
  Sun




                           1.0              2.0                   3.0         4.0              5.0             Distance from Sun
                                                                                                                      (AU)
                                                    Main
                       Earth orbit                asteroid
                                                    belt                                                 Jupiter orbit
Venus orbit




                                                                          Ellipses represent
                                                                        Sentry sensitivity VM=22


                                                             VM=22                                                       VM=22
                                                VM=20                                                               VM=20
                                        VM=18                                                                    VM=18


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        SHIELD
Location and Number of Sentries
                    s   Orbits entirely within Earth’s
                        are necessary to find all Atens
                    s   Venus swingby is most cost-
                        effective to achieve such orbits
                    s   All asteroids that cross Earth’s
                        orbit can be found
                    s   Need 4 to 6 Sentries for
                        complete sky coverage (for
                        faster asteroid survey and long-
                        period comets)
                    s   Orbital period about 240 days
                        for faster sky coverage than is
                        possible from Earth
                    s   Can launch every 19 months
                    s   5-month transfer to Venus
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                              SHIELD
                Deflection Simplifies With Lead Time




s   Only small velocity change required   s   Deflection much easier decades ahead

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                          SHIELD
                     Deflection Techniques

s   Kinetic Energy
     •Impact the asteroid at high speeds

s   Propulsive (chemical, electrical, nuclear, solar sails, mass drivers)
     •Dock a thrusting device to asteroid

s   Directed Energy (laser, solar collector)
     •Vaporize asteroid material to form a jet

s   Nuclear Detonation (standoff, surface, buried)
     •Deflect from blast impulse or ejected matter, or fragment
      asteroid



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   SHIELD
Technique Efficiencies




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 SHIELD
How Big, How Soon




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                          SHIELD
         Deflection Technologies and Efficiencies

s Efficiency
   •Nuclear surface detonation
   •Solar sail
   •Kinetic energy

s Near-Term Technologies
   •Chemical thrusters
   •Nuclear detonations
   •Kinetic energy

s Future Technologies
   •Solar sails, directed energy, and mass drivers have enormous potential
   •State-of-the-art electric thrusters are too weak

s Nuclear systems face political and social problems

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                          SHIELD
                       Soldier Summary I
s   Soldier functions
     • Survey target
         x Characterize physical properties, rotation, composition,
           strength
     • Modify asteroid orbit; prevent Earth intercept
         x Dock, grapple, intercept

         x Impart ∆V to asteroid

s   Scenarios: Rendezvous vs Intercept
     • Rendezvous: All-in-one soldier (chemical rocket, electric
       propulsion)
         x Scouts asteroid from orbit

         x Docks and diverts

     • Intercept: Scout / Soldier pair (impactor, nuclear deflection)
         x Dedicated Scout precedes Soldier

         x Soldier carries guidance control for targeting

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                       SHIELD
                     Soldier Summary II
s   Scouting Instrument Complement
     • Imager/spectrometer (composition/regolith)
     • Ground-penetrating radar (structure/regolith)
     • Seismic network (structure/composition)
     • Data processing and communications packages
s   Pushing Equipment (Rendezvous)
     • Anchors - couple soldier to surface
     • Gimbals - alter orientation to provide thrust in proper
       direction
     • Electronics/communications; sector firing, thruster control
     • Power systems
s   Pushing Equipment (Intercept)
     • Inert mass (kinetic)/warhead (nuclear)
     • Guidance and control and targeting computers and thrusters
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            SHIELD
Location and Number of Soldiers
  Contour Trajectory
      Ecliptic-Plane   s   Should have 6 or more soldiers
          Projection
   Rotating System,    s   4 or more in Venus-return
          with Fixed       orbits for good coverage
     Sun-Earth Line
                       s   High-energy Venus-return
                           orbits, like Contour’s Earth-
                           return orbits, shown at left
                       s   2 or more launch-on-demand
                           from Earth for quick response,
                           flexibility
                       s   Some comets reached from
                           Mars, Jupiter, but periods long
                       s   Rendezvous usually requires
                           large low-thrust system, Jupiter
                           gravity assist

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 SHIELD
Soldier Description




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                                   SHIELD
                Flowchart of SHIELD Detection
               and Mitigation of an Earth Impactor
              Search for near-Earth
                    objects
                                                           Mobilize soldiers
             Sentry locates object and
                propagates orbit


Update all            Impact                                Rendezvous
                                                       R          or           I
 catalogs             Earth?
                                                              intercept

   No                    Yes             Yes
                  Sentry informs
                      Earth                        Soldier                  Scout
                                               rendezvous and            rendezvous
          Earth performs detailed                 examine               and examine
        observations and calculations
                                                Soldier docks          Soldier flyby/
                                                 with object           impact object
                     Confirm
                     impact?
                                               Soldier deflects           Deflect/
                                                   object             fragment object
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            SHIELD
          We Can Start Today

                           s   Sentry can be MIDEX
                           s 1-m telescopes exist

                           s Mid-size Explorers
                               have been proposed
                               with pointing, etc.
                           s Electronics and
                               computing exist



It is time to extend the asteroid catalog.

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SHIELD
 Summary




           “All I’m saying is now
           is the time to develop
           the technology to
           deflect the asteroid.”


           (The New Yorker, 1998)
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