Natural Environment Near L2

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Natural Environment Near L2

• Steve Evans
• MSFC-ED44 / Environments Group

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Contributors

• Gravity Perturbations Dr. Steve Evans, MSFC
• Plasmas Mr. Bill Blackwell, Sverdrup
  Dr. Joe Minow,
  Sverdrup
• Ionizing Radiation Mr. Richard Altstatt,
  Sverdrup
• Electromagnetic Dr. Jeff Anderson, MSFC
  Thermal Dr. Jere Justus, CSC
• Meteoroids Dr. Bill Cooke, CSC

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Natural Environment Near L2

• Dynamical system and perturbations
• Plasmas Solar wind and Geotail
• Ionizing Radiation Solar and Galactic
• Electromagnetic / Thermal
• Micrometeoroids Sporadic background
  and Streams

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Dynamical System
Circular Restricted Three-Body Problem
L2 is at 1.5x106 km or 236 RE outside the
Earths orbit.
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Perturbations at L2
Perturber Maximum Accelerations, nano-g
X Y Z Earth-Moon about 56 60 7
Barycenter Aligned Planets 42 36
2 Radiation Pressure 93 41
41 (0o) (35o) (35o) Spacecraft mass
2800 kg, area 300 m2, RAU 1.01, and
reflectivity 90. Tilt angle
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Plasma Environment
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Geotail Plasma Regimes
Lobe radius is determined from Tsyganenko
geomagnetic field model. Tsyganenko, N. A., A
Magnetospheric Magnetic Field Model With a Warped
Tail Current Sheet, Planet. Space Sci., 37, 5 -
20, 1989. Tsyganenko, N. A., Modeling the
Earths Magnetospheric Magnetic Field Confined
Within a Realistic Magnetopause, J. Geophys.
Res., 100, 5599 - 5612, 1995.
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L2 Plasma Characteristics
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Magnetotail Orientation
Orientation depends on solar wind flow
velocity. At Earth, average direction is 4 deg
east of the Sun-Earth line. In-plane
aberration tan b (VE VSW,Y) /
VSW,X Out-of-plane aberration tan g VSW,Z
/(VSW,X)2 (VSW,Y)21/2
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3-Body Dynamics Plasma Model LRAD
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3-Body Dynamics Plasma Model LRAD
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Plasma Regime Immersion
LRAD calculates flux and fluence at points along
the orbit. Results of a 1000-run Monte Carlo
fluence statistics calculation over a 180-day
span, for a halo orbit with Z-amplitude 125,000
km Inside Magnetosheath 78.11 of time Solar
Wind 12.77 Plasma Mantle 5.91 Plasma
Sheet 3.22 N/S Lobe 0.00
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Ionizing Radiation
This section of the definition document
considers extreme or worst case conditions.
Designs meeting these conditions will withstand
more benign ones.
Two components Galactic - omnidirectional
flux - 85 protons, 14 alphas, 1 heavier -
energies up to 109 eV (GeV) - 1012 eV
(TeV) Solar - during eruptive events, may exceed
GCR flux by factors of 103 - 104 - solar
proton flux will be most important
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Ionizing Radiation
Solar ionizing flux correlates with solar
activity cycle. Increased solar wind turbulence
during the active phase leads to increased
scattering of GCR and reduction of GCR flux, by
up to a factor of 103 in some cases. This strong
influence of the solar cycle on the nature of the
ionizing radiation flux should be considered in
the mission and vehicle design activities.
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Ionizing Radiaton Damage
Electronics Immediate damage from Single Event
Effects - from bit flipping to burn-out due
to parasitic currents - usually due to
energetic heavy ions Long-term damage from Total
Ionizing Dose - accumulated lattice defects
- charge trapping in amorphous regions -
degrading performance / sensor sensitivity
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Ionizing Radiation Damage
Other Materials Electrons - surface
damage Protons and heavy ions - deeper
penetration damage Increased surface hardness,
loss of ultimate tensile strength, embrittlement,
degraded optical electrical properties Differen
t materials have different responses
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Ionizing Radiation Damage
For polymers, breaking and relinking of
energetic bonds results in embrittlement, loss of
strength, and possible degradation of electrical
and optical properties. For NGST sunshield this
damage will be compounded by intense solar UV on
the sunward side, intense cold on the shaded
layers, and penetrations by micro- meteoroids.
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Electromagnetic / Thermal
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Solar Irradiance
Solar irradiance at 1 AU 1367 W/m2
Earth Position Irradiance at L2 Perihelion
1389 W/m2 1 AU 1340 Aphelion
1296
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Possible Eclipse Zones
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Natural Radio Noise
Galactic Radio Noise - numerous sources
throughout Galaxy - ranges from 15 MHz to 100
GHz - declines about 10 dBW/Hz - could be
important for communication between 40 and 250
MHz
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Solar Radio Noise
Quiet Sun - during times of low sunspot activity,
the minimum or basic component of solar radio
emission
Disturbed Sun - during times of high sunspot and
eruptive activity - slowly varying
component, 10 - 21 cm - rapidly varying
component, assoc. w. flares, w. max. flux
in meter to millimeter range
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Solar Radio Noise
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Other Natural Sources
Magnetospheric and Solar Wind Plasmas - emit
with frequencies from 1 to 10 MHz down to dc -
electron plasma frequency given by fp 0.90
MHz ne / (104/cm3) 1/2 (External emissions
with frequencies below the plasma frequency will
be severely damped, and will not reach the
spacecraft. There may be locally generated
electrostatic noise at the local plasma
frequency.)
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Other Natural Sources
Discrete objects, plus the cosmic background
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Artificial Radio Noise
Narrow band signals in the range 1 MHz to 300 GHz
can penetrate the ionosphere, and may be
detectable. Electric field, E, at a distance r
from a radio frequency transmitter is given
by E (30 ERP)1/2 / r where ERP is the
effective radiated power in watts (product
of transmitter power and antenna gain), r is in
km, and E is given in mV/m. A 10 kW radar with
antenna gain of 40 dB would produce a field of
only 37 mV/m at L2.
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Meteoroid Environment
Sporadic Background - always present - 6
primary radiant directions
Streams - most have identified comet sources -
highly directional - limited to specific times
of year
Particle densities 0.2 to 8.0 g/cm3, depending
on size Particle speeds from 20 to 72 km/s,
depending on source
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Sporadic Meteoroid Flux
Grun model FGrun c0(c1m0.306 c2)-4.38
c3(m c4m2 c5m4)-0.36 c6(m
c7m2)-0.85 where c0 3.156x107 c1 2200 c2
15 c3 1.3x10-9 c4 1011 c5 1027 c6
1.3x10-16 c7 106
This expression considers particle mass. To
convert to size, which is used in penetration
equations, we need a density, but the little data
available shows density is size dependent.
Recommended mean values are 2 g/cm3 for particles
below 10-6 g 1 g/cm3 for those between 10-6 and
0.01 g and 0.5 g/cm3 for masses above 0.01 g.
Grun et al., Collisional Balance of the
Meteoric Complex, Icarus, 62, 244-272, 1985.
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Sporadic Meteoroid Directionality
90
5 , 35 km/s
15 , 55 km/s
60
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Ecliptic Latitude
30 , 29 km/s
30 , 29 km/s
0
-30
15 , 55 km/s
-60
5 , 35 km/s
-90
0 90
180 270
360
Heliocentric Longitude
Brown Jones, A Determination of the Strengths
of the Sporadic Radio-Meteor Sources, Internation
al Conference on Meteoroids, August, 1994.
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Modeling Meteoroid Flux on an Oriented Surface
Estimate of flux, fn, seen by a spacecraft
surface with normal vector n
where G(q,f,i) is that part of a gaussian flux
distribution peaking at radiant i visible from
surface with normal n f is angle between n and
the line of sight and q is azimuthal angle about
the normal. Integrating G(q,f,i) over all angles
gives the fraction of the Grun flux due to
radiant i seen in the above table. Summing over
all six radiants gives the total flux seen by the
surface.
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Meteoroid Streams
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Example Meteor Stream Density Variations
Location of enhancements in Perseid meteor stream
column density during a span of fifty years
centered on 1990. Based on dynamical calculations
by Peter Brown, University of Western Ontario.
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Backups
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Earth Motion About Barycenter
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Perturbation Sources
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Perturbation Sources
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Plasma Environment
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L2 Plasma Characteristics
Plasma data sources Geotail Comprehensive
Plasma Instrument EPIC Science Team -
University of Iowa. Nishida, in
Sun-Earth Plasma Connections, AGU, Washington,
D.C., 1999. IMP-8 - MIT Instrument - National
Space Science Data Center. HEOS-2 Rosenbauer
et al., J. Geophys. Res., 80, 2723, 1975. ISEE-3
Gloeckler et al., Geophys. Res. Let., 11, 603,
1984. IMP-6, IMP-7, IMP-8 Feldman et al., in
The Solar Output and Its Variation, Assoc. Univ.
Press, Boulder, 1977.
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L2 Plasma Characteristics
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L2 Plasma Characteristics
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LRAD Plasma Flux Statistics
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Magnetosheath Flux Spectra
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Plasma Mantle Flux Spectra
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Plasma Sheet Flux Spectra
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Plasma Fluence Calculations
Dynamical model based on equations and
parameter values of Richardson and Farquhar is
included in LRAD to provide orbital ephemeris for
fluence calculations. To obtain statistical
fluences
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Example of Fluence Statistics
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Energetic Ionospheric Ions from Substorms
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Ionizing Radiation
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Ionizing Radiation
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Solar Irradiance
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Solar Irradiance
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Solar Irradiance
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Solar Irradiance