Low Energy Neutral Atom Imager for VESPER

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Low Energy Neutral Atom Imager for VESPER
LENA images will be among the first of the direct
solar wind interaction with an unmagnetized
planetary atmosphere

• Science Focus Questions
• How intensely do the solar wind and Venus' upper
  atmosphere exchange matter and energy?
• What is the nature and extent of the hot
  atmospheric corona produced around Venus?
• What is the rate of escaping atmospheric atoms
  driven by the solar wind interaction?
• Charge exchange, collisions, electrodynamics
• How does the upper atmosphere of Venus respond to
  solar wind and solar EUV changes?
• Stream interaction regions, flares and coronal
  mass ejections?

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Low Energy Neutral Atom Imager for VESPER
LENA images will be among the first of the direct
solar wind interaction with an unmagnetized
planetary atmosphere

• The LENA Instrument Team
• GSFC science Moore , Chornay, Collier, Fok,
  Keller
• GSFC engineering Lobell, Johnson, Rozmarynowski,
  
• LMATC Fuselier, Hertzberg Charged particle
  optics
• UMD Hamilton TOF electronics? HVPSs?
• U. Bern P. Wurz Conversion surface physics
• U. Denver T. Stephen Surface physics and
  neutral beam
• New for VESPER
• GSFC J A Slavin, Solar wind interaction
• APL S Livi TOF electronics
• UM A F Nagy Venus Aeronomy
• UKans T Cravens Solar wind interaction

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Why Study the Solar Wind Interaction?
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Divergent Evolution of Terrestrial "Twins"

• Venus ended up without a magnetic dynamo or
  intrinsic magnetic field, probably owing to it's
  slow rotation.
• Venus' atmosphere subjected to direct impact of
  solar wind energy, instead of local auroral zone
  electrodynamics.
• Earth undergoes quasi-periodic geomagnetic
  reversals, with Venus-like conditions limited to
  brief null periods.
• Venus is parched and possibly lost an ocean of
  water.
• It may have lost substantial amounts of heavy
  gases also.

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LENA Imaging for VESPER

• Science Issues
• Solar wind coupling of mass, momentum, heat
• Atmospheric response
• Observables
• Solar wind interaction
• Solar wind neutral atoms
• Atmospheric escape
• Thermal and hot light atoms
• Hot heavy atoms
• Analysis Tools
• Tanaka MHD simulation
• Winglee multifluid MHD
• Fok image code

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Orbital Deployment
Cross-track observation path
Locus of tangency
Target Locations
Mode 1
Cross-Track Right or Left
Mode 2
In-Track Forward or Aft
Mode 3
Note Replace with rendered picture
Nadir
4000 x 500 Km Altitude Orbit
Orbit ground track and In-track observation path
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Solar Wind Interaction with Venus
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Plasma Atmosphere Models
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Simulated LENA Imager View
Note view from upstream, different color scales
apply 10 eV emission 1000 eV
emission H O H O
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Simulated LENA Imager View

• Note view from downstream, different color
  scales apply 10 eV emission
  1000 eV emission
• H O H O

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Simulated LENA Imager View
Note view from over N pole, sun to right,
different color scales apply 10 eV
emission 1000 eV emission H
O H O
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Simulated LENA Imager View
Note view from slightly above equator, sun to
right 10 eV emission 1000 eV
emission H O H O
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Ionospheric Outflow vs Solar Wind Pressure
-Moore, et al., GRL, p.1143, 2001. -Fuselier,
et al., GRL, p.1163, 2001, JGR, in press 2002.
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Solar Wind Interaction with Earths Geocorona
-Collier, et al., JGR, p,24,893, 2001.
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LENA Exterior and Interior
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LENA Lessons Learned and Changes

• Conversion surface technology
• Polished polycrystaline W
• Difficult-to-remove water vapor coating is active
• Testing since LENA
• U Bern, U Denver group shows LENA surface not
  bad!
• Eventual erosion in space
• CVD (chemically vapor deposited) diamond
  comparable or better
• Unlikely to erode

Efficiency detected/incident
Energy eV
Next Generation Surface?
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LENA Block Diagram
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M/?M
?E/E
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360 bytes/image12pix x 3E x 5M x 2byte/pix
576 bps, avg (_at_ 5s/image)
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nonoperational
Lossless Compression
8 x 100
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LENA Imager Accomodation
View into Apertures
LENA FOV 8x100
LENA
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Conclusion
LENA images will be among the first of the direct
solar wind interaction with an unmagnetized
planetary atmosphere

• Spaceflight-proven technique with high technical
  readiness level.
• Effective method for measuring the interaction of
  the solar wind with planetary environments.
• First to explore global loss of Venus' atmosphere
  in response to solar wind.

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Why study Venus Aeronomy?
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The Pioneer-Venus View
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Solar Wind Charge Exchange in the Magnetosheath
Simulations of SWLENA Spinograms Flux computed
along line of sight from s/c to 50 RE to create
image every 2 minutes. Images collapsed to orbit
plane, laid up as strips. Upper Panel sun in
FOV Lower Panel sun beyond FOV
Observations of SWLENAs as Spinograms Flux
measured by IMAGE LENA imager, at 2 minute time
spacing. Images are collapsed to orbit plane,
laid up as strips vs. time. Upper panel sun in
FOV Lower panel sun beyond FOV
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Solar Wind-Geocoronal Charge Exchange