# Presentation: 385507

## Natural Environment Near L2

- Steve Evans
- MSFC-ED44 / Environments Group

## 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

## 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

## Dynamical System

- Circular Restricted Three-Body Problem

- L2 is at 1.5x106 km or ~236 RE  outside the Earth’s orbit.

## 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

## Plasma Environment

## 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 Earth’s Magnetospheric Magnetic Field Confined Within
- a Realistic Magnetopause,” _J. Geophys. Res_., **100**, 5599 - 5612, 1995.

## L2 Plasma Characteristics

## 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  = (VE + VSW,Y) / VSW,X
- Out-of-plane aberration:
- 	tan  = VSW,Z /[(VSW,X)2 + (VSW,Y)2]1/2

## 3-Body Dynamics & Plasma Model: LRAD

## 3-Body Dynamics & Plasma Model: LRAD

## 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

## 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

## 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.

## 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

## 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
- Different materials have different responses

## 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.

## Electromagnetic / Thermal

## Solar Irradiance

- _Earth Position_		_Irradiance at L2_
-    Perihelion		   1389 W/m2
-       1 AU		   1340
-     Aphelion		   1296

- Solar irradiance at 1 AU = 1367 W/m2

## Possible Eclipse Zones

## 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

## 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

## Solar Radio Noise

## 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.)

## Other Natural Sources

- Discrete objects, plus the cosmic background

## 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 ***V*/m at L2.

## 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

## 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.

## Sporadic Meteoroid Directionality

- 30% , 29 km/s

- 30% , 29 km/s

- 15% , 55 km/s

- 15% , 55 km/s

- 5% , 35 km/s

- 5% , 35 km/s

- Heliocentric Longitude

- Ecliptic
- Latitude

- 0                             90                            180                          270                         360

- +30

- +60

- +90

- 0

- -30

- -60

- -90

- Brown & Jones, “A Determination of the Strengths of the Sporadic Radio-Meteor Sources,”
*International Conference on Meteoroids*, August, 1994.

## Modeling Meteoroid Flux on an Oriented Surface

- Estimate of flux, fn, seen by a spacecraft surface with normal vector ***n*** :

- where G(,,*i*) is that part of a gaussian flux distribution peaking at radiant *i* visible from
- surface with normal ***n*** ;  is angle between ***n*** and the line of sight; and  is azimuthal angle
- about the normal.  Integrating G(,,*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.

## Meteoroid Streams

## 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.

## Backups

## Earth Motion About Barycenter

## Perturbation Sources

## Perturbation Sources

## Slide 37

## Plasma Environment

## 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.

## L2 Plasma Characteristics

## L2 Plasma Characteristics

## LRAD Plasma Flux Statistics

## Magnetosheath Flux Spectra

## Plasma Mantle Flux Spectra

## Plasma Sheet Flux Spectra

## 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:

## Example of Fluence Statistics

## Energetic Ionospheric Ions from Substorms

## Ionizing Radiation

## Ionizing Radiation

## Solar Irradiance

## Solar Irradiance

## Solar Irradiance

## Solar Irradiance