The Engineering Side of Dust: Micrometeoroids and the Risk They Pose to Spacecraft

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The Engineering Side of Dust Micrometeoroids and
the Risk They Pose to Spacecraft

• W. J. Cooke
• Meteoroid Environment Office, EV13
• NASA Marshall Space Flight Center
• Huntsville, AL 35812 USA
• william.j.cooke_at_nasa.gov
• 256 544 9136

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History

• Established by NASA Headquarters Office of Safety
  and Mission Assurance (OSMA) at beginning of FY05
  as the NASA organization responsible for
  meteoroid environments pertaining to spacecraft
  engineering and operations.
• Result of recent Leonid meteor storms and
  Columbia Accident Investigations Board
  recommendations.
• First official NASA meteoroid program since 1970,
  when the meteoroid group at Johnson Space Center
  was disbanded.
• Located at Marshall Space Flight Center in
  Huntsville, Alabama.
• Part of the Natural Environments Branch, which is
  a component of the Spacecraft Vehicle Systems
  Department of the Engineering Directorate.

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Primary Functions

• Develop, maintain, and distribute a new, more
  accurate sporadic (background) meteoroid model
• Provide meteor shower forecasts to NASA
  spacecraft operators
• Conduct and manage research to improve sporadic
  and shower meteoroid models, including validation
  and uncertainty determination which are required
  inputs to Probabilistic Risk Assessments
• Coordinate the existing meteoroid expertise at
  NASA centers to help accomplish the above

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Current MEO Staff

• Dr. Bill Cooke Management and data analysis
• Ph.D. in Astronomy (Astrometry) University of
  Florida 1993
• Technical expert on meteoroid environment and
  effects, neutral thermosphere, solar activity,
  planetary defense, external contamination
  modeling
• Dr. Rob Suggs Data analysis and collection
• Ph.D. in Astronomy (Planetary Atmospheres), New
  Mexico State University 1984
• Space Environments Team Lead - 1999 to present
• JSC/Space Station Program Office 1994-1998
• Environments AIT Lead
• Attached Payloads Lead
• Heather McNamara - Modeling and software
  development
• Masters in Aerospace Engineering Auburn
  University 2005
• Software development including shuttle flight
  software (JSC) and ISS payload planning
• Danielle Moser
• UNITeS contractor supporting EV13
• Meteor stream modeling, radar analysis, and
  observation planning
• Wesley Swift
• Raytheon contractor supporting EV13
• Equipment design/construction and optical
  observation analysis

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What We Know
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Meteoroid Origins

• Kuiper Belt Objects

• Comets
• Short Period
• Long Period

• Planets or Moons

• Asteroids

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Flux Measurements
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How We Know

• Optical observations (infrared, visual,
  photographic, video)
• Rates (fluxes)
• Altitudes
• Brightnesses
• Velocities (combine with brightness to get mass)
• Structure (light curve modelling)
• Composition

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Visual

• IMO International Meteor Organization

• Pros
• Many experienced meteor observers.
• Good global coverage.
• Accessible data.

• Cons
• Visual observations hampered by
• Moon.
• Weather, poor seeing.
• Forecasts bias observers.

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NASA / MSFC / W. Cooke
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MSFC Meteor Camera
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Deep GenII Camera
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• Radar observations
• Rates (fluxes)
• Radar brightnesses
• Velocities
• Densities (through atmospheric deceleration)

• Crater Counts
• Returned surfaces (LDEF, HST solar arrays, etc)
• Moon (really big stuff)

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Radar Echoes
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CMOR
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Radiant Map
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Kwajalein
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Kwajalein KREMS Complex
ALTAIR
MMW
TRADEX
ALCOR
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Understanding of Biases

• Initial trail radius effect well known problem
  for patrol radars does it affect HPLAs?
• If not, then why do HPLAs only see fast meteors
  (i.e., apex source, but no helion or
  anti-helion)?
• How are observations affected by meteor
  fragmentation?
• Need more co-location of optical and radar
  systems simultaneous detections will enable
  consistency checks in velocity, mass, etc.

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• In-Situ spacecraft observations

• Several Explorer satellites
• Pegasus 1,2,3 (Apollo design)
• Helios 2
• LDEF
• Clementine, others

• Biggest problems with spacecraft (in-situ)
  observations
• Orbital debris contamination
• Small collecting area (1 m2)

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Flux Variability

• Sporadic flux not constant varies by about 40
  over course of year.
• Minimum March, April, May
• Maximum September, October

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Sporadic Directionality

• The meteoroid background is not isotropic, as
  assumed by many current models. 6 sources
  (radiants), as can be seen from diagram at right.
  Variants on this should hold true throughout
  inner Solar System.

Jones Brown (1999)
This has been known since 1957
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• In the following, coordinate system used is
  Sun-fixed - in the plane of the Earth's orbit
  (the ecliptic), with 0º longitude being located
  at the position of the Sun and 270º being the
  approximate direction of the Earth's motion.

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• From Earth, we see background meteors radiating
  from

• A source near the Sun (the Helion source,
  produced by short period comets)

• A source nearly opposite the Sun (the Anti-Helion
  source, produced by short period comets)

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Helion Sources
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• From Earth, we see background meteors radiating
  from

• A source near the Sun (the Helion source,
  produced by short period comets)

• A source nearly opposite the Sun (the Anti-Helion
  source, produced by short period comets)

• Two sources near the direction of Earth's
  velocity (the Apex sources, produced by long
  period comets)

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Apex Sources
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• From Earth, we see background meteors radiating
  from

• A source near the Sun (the Helion source,
  produced by short period comets)

• A source nearly opposite the Sun (the Anti-Helion
  source, produced by short period comets)

• Two sources near the direction of Earth's
  velocity (the Apex sources, produced by long
  period comets)

• Two sources located towards the Apex, but 60º
  above and below the plane of the ecliptic (the
  Toroidal sources, produced by Halley-family
  comets)

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Toroidal Sources
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• From Earth, we see background meteors radiating
  from

• A source near the Sun (the Helion source,
  produced by short period comets)

• A source nearly opposite the Sun (the Anti-Helion
  source, produced by short period comets)

• Two sources near the direction of Earth's
  velocity (the Apex sources, produced by long
  period comets)

• Two sources located towards the Apex, but 60º
  above and below the plane of the ecliptic (the
  Toroidal sources, produced by Halley-family
  comets)

• Sources located near the ecliptic poles (the
  asteroidal sources)

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Asteroidal Sources
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Velocity Distributions

• Observational biases (e.g.,echo ceiling effect
  and ionization dependence on v4 in the case of
  radar) make it difficult to derive velocity
  distributions.
• Canonical average speed of 17 km s-1 has been
  seriously questioned by investigators, some of
  which (Grün) have advocated speeds close to 40 km
  s-1.
• Work is underway to resolve at least some issues
  (biases).
• Could substantially alter penetration and risk
  analyses.

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Density

• ALTAIR radar determined ballistic coefficients
  (densities) from gt 1000 meteor decelerations in
  atmosphere.

• Would like equivalent in threat size regime (gt
  100mm).
• Need better models of meteoroid structure.

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Model Requirements

• Any accurate model of the meteoroid environment
  in near-Earth space must properly describe these
  aspects of the environment

• Flux

• Directionality

• Velocity distribution

• Density and composition

• At this time, there exists no model capable of
  providing all of these.

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Grün Model

• Model used most often for near-Earth space.
• Has no directionality, but spacecraft motion
  through meteoroids will induce a preferential
  direction towards vehicle RAM.
• Canonical reference is

Title Collisional balance of the meteoritic
complex Authors Grün, E. Zook, H. A.
Fechtig, H. Giese, R. H. Journal Icarus (ISSN
0019-1035), vol. 62, May 1985, p. 244-272.
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Mass Flux

• Surface area flux (m-2 yr-1) at 1 AU is given by

where
c0 3.156x107 c1 2200 c2 15 c3
1.3x10-9 c4 1011 c5 1027 c6 1.3x10-16 c7
106

• Meteoroid speed at 1 AU assumed to be 20 km s-1.

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NASA Additions/Changes to Grun Model

• Specd in NASA TM-4527 and SSP 30425.

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Earth Shielding

• Need to account for the fact that Earth blocks
  part of the meteoroid flux for vehicles in LEO

• Multiply the interplanetary flux at 1 AU by sf,
  the shielding factor.

(h is spacecraft altitude in km)
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Gravitational Focusing

• Earths gravity enhances (or focuses) the
  interplanetary flux by as much as a factor of 2.

• The flux corrected for Earth shielding must now
  be multiplied by the gravitational enhancement
  factor to get the flux in Earth orbit

(h is spacecraft altitude in km)
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Density

• Meteor densities represented by step function

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Velocity

• The normalized velocity distribution (with
  respect to Earth) is given in NASA TM-4527

• Average of this with respect to Earth is about 17
  km s-1 with respect to a spacecraft in LEO,
  about 19 km s-1.

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Are Things Better With Divine?

• JPL interplanetary model developed by Neil
  Divine canonical reference is

Title Five populations of interplanetary
meteoroids Authors Divine, Neil Journal
Journal of Geophysical Research, Volume 98, Issue
E9, September 25, 1993, pp.17029-17048

• Empirical fit to observations, has 5
  mathematical populations of meteoroids (core,
  halo, etc).

• JSC has b version with gravitational focusing
  can extract some directionality- does not match
  Earth observations.

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Divine vs. Earth Observations
Mark Matney, JSC
Jones Brown (1999)
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The Meteoroid Engineering Model (MEM)

• Physics-based approach observations used to
  calibrate model.
• Flux forced to match that of Grün at 1 A.U.

• Good directionality match.

• Velocity distribution matches the (very
  uncertain) observations.

• No densities yet.

• Model in beta stage

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• Starting with cometary and asteroidal orbit
  distributions, model particle delivery to
  spacecraft.
• Correct observed distributions for biases
• P-R drag, collisions taken into account
• Planetary perturbations not accounted for
• Calibrate source strengths by matching observed
  flux at Earth, elsewhere.
• Radar bias corrections extremely important
• Incorporate measured source strengths into
  engineering model gives penetrating fluxes on
  spacecraft surfaces.

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Sample Output
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Flux in Spacecraft System
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Average Speeds
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The Threat

• Why meteoroids are important to spacecraft
  operators

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The SOCIT Test

• Ground experiment design to investigate the
  effects of a hypervelocity impact upon a
  typical spacecraft.
• Satellite chosen was a Navy Transit/OSCAR
  (navigation/communications).
• A 160 g (4.8 cm) Al sphere was fired into the
  satellite at 6.1 km s-1.

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Before
After
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What Can Hurt
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Example Shuttle Impacts
STS-92 Window Impact 0.1mm Al particle 2 mm
diameter crater
STS-90 radiator penetration 0.3 mm paint
particle 1 mm diameter hole
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Perforation Aint the Whole Story

• M/OD strikes can cause failure though other
  mechanisms than perforation
• Electrical (v4.5) OLYMPUS
• Momentum Transfer Mariner IV, Pioneer 10
  (Concern to GP-B, microgravity)
• Failure of thermal protection systems or windows
  upon re-entry (STS, other manned vehicles)
• Contractors should perform probability of failure
  calculations for critical items.
• Requires cooperation between groups and more
  testing (hypervelocity, arcjet, etc.)

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The Plasma Factor

• Penetration potential of a meteoroid goes as
  speed2 current production potential goes as
  speed4.5.
• Meteoroid generates a charged plasma capable of
  producing a current pulse or spike for the
  Leonids this pulse can be several amperes.
• Olympus spacecraft disabled by such an event.
• This, not penetration, is considered to be
  greatest risk to spacecraft during showers with
  high speed meteoroids.

I k m1.02 v4.48 L-1
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Affected Spacecraft

• Run-ins with meteoroids

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Olympus

• What ESA communication satellite.
• Event Struck by a Perseid near the time of the
  shower peak in August 1993.
• Consequences Impact-generated plasma cloud
  produced current that disabled the attitude
  control system spacecraft sent tumbling.
• Outcome By the time attitude was restored the
  onboard fuel had been exhausted, ending the
  mission.

ESA
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Chandra X-Ray Observatory

• What NASA observatory.
• Event Struck by a Leonid or sporadic(?) near
  the time of Leonid shower peak in November 2003.
• Consequences
• Pointing stability discrepancy indicated strike,
  as no evidence of spurious thruster firings or an
  indication of an internal cause.
• Change in momentum caused a wobble.
• Outcome All systems continued to operate
  normally following the event.

Chandra
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Damage to Other Satellites

• Three recent satellite anomalies
• November 2002 ? Leonid strike on ComSat
• April 2004 ? North Apex Sporadic ?
• November 2004 ? Leonid or Sporadic ?

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Mariner IV

• What NASA planetary exploration spacecraft.
• Event Encountered meteoroid stream between the
  orbits of Earth and Mars in September 1967.

• Consequences
• Cosmic dust detector registered 17 hits within 15
  minutes 2-3 orders of magnitude more hits
  estimated over entire craft.
• Bombardment caused temporary change in attitude
  but no loss of power torqued about the
  roll-axis.
• One-degree temperature drop indicative of thermal
  shield damage.
• Outcome Resumed normal operation within 1 week.

JPL
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More Detail

• Giotto registered 12000 impacts in 171 minutes
  (589000 km) passing within 596 km of Comet Halley
  (detector size ?)
• 70/minute
• During the earlier mission, a total of 235 hits
  were recorded in 225 days.
• 7 x 10-4 /minute
• Number of hits during shower was 1500x higher
  than average, and only 60x lower than Giottos
  hit rate at closest approach to Halley
• (again hit rate not flux as Giotto had a suite of
  detectors of various sizes)

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Comet Encke?
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Taking a closer look

• Checking current comet and meteor shower orbit
  databases, P. Weigert and J. Vaubaillon located
  the known possible meteor streams M4 might have
  encountered.

A sample of the closer orbits
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The top candidates

• Three comet orbits were within 0.1 AU as well as
  2 weak meteor shower orbits (Corvids and Southern
  Piscids)

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The top suspect

• The comet orbit passing closest to M4s position
  at the time of the storm was comet D/Swift 1895
  Q1.
• Additionally, the nominal position of this lost
  comet itself was only 20 milliion km from M4 at
  this time.

Swift a3.73 AU, q1.3 AU, e0.65, i 3
deg
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Questions can we convict D/Swift?

• How close was the Comet Swift and/or its
  meteoroid stream to M4 really?
• D/Swift was observed for only 6 months in 1895.
  Though many observations were made, no proper
  error calculations were made.
• The observations are published and available, and
  codes to compute the errors (eg. CODES) are on
  hand.
• Work is needed to collect the observations,
  correct them to the proper reference epoch,
  compute the error ellipse, etc.

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Current status

• Mariner IV may have been the first spacecraft to
  visit the vicinity of a comet, 19 years before
  the flotilla of craft met Halley in 1986 (and
  before ISEE/3-ICE met Giacobini-Zinner in 1985).
• We may be able to determine that the impacts
  suffered by M4 (probably) resulted from a passage
  through a cometary meteoroid stream or the debris
  of or perhaps even the coma of an undetected
  dead or nearly-dead comet
• Mariner 4 may have hit a hot spot that should
  be avoided by future Mars missions.
• We may be able to characterize the only(?)
  measured high-threat interplanetary meteoroid
  stream

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Meteor Shower Forecasting
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Meteor Streams

• A meteor stream consists of particles ejected
  from the parent comet during a single passage
  around the Sun.
• Produce meteor showers and storms here on Earth.

• Over time, the slight differences between the
  comets and particles velocities, combined with
  the perturbations caused by planetary gravity and
  solar radiation pressure, change the orbit of the
  stream so that it no longer follows the exact
  path of the comet.

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Major Annual Showers


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Forecasting TechniquesDistance Vs. Time
(pre-1990s)

• Comet nodal crossings plotted versus time since
  comet perihelion indicator of relative shower
  strength.
• Simple.
• Reasonably good indicator of shower strength.
• Shower maximum at comet nodal crossing.
• No durations or multiple peaks.

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Rao, Sky and Telescope
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Forecasting TechniquesStream Modeling

• Particles ejected from comet and dynamically
  evolved. Ensemble of particles near target at
  chosen time determines shower characteristics.
• Numerically intensive many thousands (millions)
  of particles.
• Multiple peaks times and intensities of shower
  maxima can be obtained.
• Shower durations difficult to derive.

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Annual Forecast (ISS Shuttle)

• Due end of January of each year.
• Showers with potential to outburst/storm are
  evaluated using stream model technique.
• Re-evaluations likely as new information becomes
  available.
• Maximum ZHRs, peak times, and durations are added
  to existing database of normal showers.
• Penetrating fluxes are generated at 1 hour
  intervals for entire year.

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FRR Forecast Generation

• Mission launch and end time received from JSC-KX
• Computer code generates penetrating fluxes at 1
  minute intervals for mission.
• Flux factors computed relative to the sporadic
  meteoroid background.
• Calculations sent to JSC-KX for inclusion in
  mission meteoroid/orbital debris risk assessment
  (Shuttle version of BUMPER code).
• 6-hour fluences also calculated for EVA risk.

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Accuracy

• Forecast peak timings good forecast fluxes are
  generally on the high side (factors of a few).

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MEO Activities
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Sporadic Environment Monitoring

• Instituted in late March of 2005 to monitor
  environment while Shuttle is aloft.
• Makes use of the University of Western Ontarios
  CMOR radar to provide daily sporadic and shower
  fluxes down to sub-millimeter sizes.
• Necessary to establish uncertainties in
  environment.
• Current average deviation from model 0.3
• Maximum deviation from model - 25
• Seasonal variability indicated.

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Simultaneous Radar/Optical

• Began joint effort with University of Western
  Ontario in simultaneously measuring meteors in
  optical and radar wavelengths. Task involves
  automated meteor station co-located with radar.
• Software (Meteor44) developed by EV13.
• All-weather meteor camera housings also
  developed.
• Necessary step in separating observational biases
  from environmental variations.

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Data Mining

• LDEF Interplanetary Dust Experiment data
  revisited in search for shower signatures none
  found.
• Pegasus 1, 2, and 3 meteoroid data sets acquired
  for re-determination of sporadic and shower
  fluxes utilizing modern techniques.

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Apollo Passive Seismic Experiment Measurements of
the Lunar Meteoroid Environment

• Earths atmosphere protects inhabitants from
  meteors smaller than 30 meters Moon has no
  atmosphere and so its surface is continuously
  bombarded by meteoroids.
• Apollo Passive Seismic Experiments recorded data
  from deployment until 1977 (4 seismic stations)
  Over 11,000 events recorded, with greater than
  1700 being positively identified as caused by
  meteoroid impacts.
• Modern computing and techniques enable a
  superior reanalysis of this data, which can
  establish estimates for the lunar meteoroid flux
  at various sizes. Correlations with meteor shower
  activity can also be made.

• Establishes high mass end of the meteoroid flux
  in near-Earth space obvious implications for
  lunar exploration/habitation. Also pertinent to
  planetary defense in helping establish the
  frequency of small asteroid impactors.
• Provides validation points for new sporadic
  meteoroid models currently in work. These models
  will be used in design of CEV and other vehicles
  bound for the Moon.
• Provides validation points for lunar meteor
  shower forecasting models.
• Can be combined with data from future returned
  lunar surfaces to construct complete picture of
  lunar meteoroid environment

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Mars Meteor Observations

• Drs. Cooke and Suggs were collaborators on the
  MER team.
• Assisted in developing observation plans for
  meteor observations using the Spirit rover.
• Suggs has analyzed several nights of PanCam
  imagery no meteors detected as of this date.
• Lots of cosmic ray hits, though

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R2
L1
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Lunar Secondary Environment

• Cratering caused by impacts produce ejecta of all
  sizes.
• Ejecta can travel far from impact site on
  ballistic trajectories or even escape lunar
  gravity.
• These can consitute a hazard to operations on or
  near the lunar surface (suits can be penetrated
  by particles less than 0.5 mm in diameter).
• Environment not well known requires knowledge
  of flux of primary impactors (meteoroids, small
  asteroids) and their speeds and compositions,
  plus a good understanding of cratering dynamics.

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• Latest model (1969) considered overly-conservative
  .
• Necessary to establish flux of large meteoroids
  in near-Earth space. Use flux and meteoroid
  compositions in hydrocodes capable of tracking
  ejecta until escape or impact with lunar surface.
• Calibrate hydrocodes by hypervelocity tests using
  appropriate lunar simulants.
• Meteoroid Environment Office and EV13 already
  working on establishing flux of large meteoroids
  striking lunar surface.

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Equipment

• Telescopes
• 2 Meade RCX400 14 Ritchey-Chrétien
• Recording Devices
• Astrovid Stellacam EX
• Sony Digital 8 recorder

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Observing the Moon

• Dark side only
• Earthshine illuminates lunar features
• Crescent and quarter phases 0.1 to 0.5 solar
  illumination
• 5 nights waxing (evening)
• 5 nights waning (morning)
• 4-6 nights of data a month, weather dependent
• Observing procedure
• Aim scope at Moon
• Record video with WinDV
• CCD camera ? Digital 8 recorder ? hard drive
• Wait and reposition

Camera Field of View
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Searching for Flashes

• LunaCon was written in IDL by Wesley Swift
• Program searches video for flashes, frame by
  frame
• Search parameters defined by user
• Compiles list of impact suspects
• 10 100 suspects per video

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Lunar Impact of November 7, 2005

• EV13 observers, in the process of prototyping a
  system for monitoring lunar impacts, recorded a
  probable impact flash in the 1st 2 hours of video
  taken with the system.
• Meteor was probably a member of the Taurid shower
  responsible for numerous fireballs observed on
  Earth in late October/early November.

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• Determination of the light curve (intensity as a
  function of time) enabled the meteoroid mass to
  be calculated at 4 kg.
• The above mass, combined with the speed of the
  Taurid meteors, gives a striking power of about
  650 lbs of TNT (produced a crater about 8 m in
  diameter).

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Simple Hydrocode Simulation of the Impact

• Meteoroid 5 inch diameter, solid granite
• Regolith 2 x 4 inch granite gravel
• Ejecta masses not computed fragments not tracked
• At end of simulation, crater is 6 m wide, 3 m
  deep and still growing.

SPH calculations by Steve Evans, EM50
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May 2 Impact
1/7th actual speed
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May 2 Impact
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May 2 Impact Statistics
Duration of flash Estimated peak magnitude Peak
power flux reaching detector Total energy flux
reaching detector Detected energy generated by
impact Estimated kinetic energy of
impactor Estimated mass of impactor Estimated
diameter of impactor Estimated crater diameter
500 ms 6.86 4.94 10-11 W/m2 4.58 10-12
J/m2 3.394 107 J 1.6974 1010 J (4.06 tons of
TNT) 17.5 kg 32 cm (r 1 g/cm3) 13.5 m
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June 3 Impact
June 21 Impact


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What Weve Seen So Far
Results in 30 hours of observations
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7
1
4
6
3


2
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Park Forest

• Just before midnight (0550 UT) on March 27 of
  2003, a meteor with a diameter of about 1 m and a
  mass of approximately 11,000 kg disintegrated
  less than 18 km above the Chicago suburb of Park
  Forest.

• Debris scattered over a fairly large area minor
  damage to property reported.

• Had the meteor hit intact, there would have been
  a 0.4 0.6 kiloton explosion in this suburban
  area.

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Police Footage
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Photos
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Kiloton Events 1998-2002