The Neutral Atmosphere and Its Influence on Basic Orbital Dynamics at the Edge of Space Delores Knipp Department of Physics US Air Force Academy Colorado USA [email protected]Developed by members of the Department of Physics, USAFA Special credit to Dr Evelyn Patterson USAFA and Dr Esther Zirbel, Yale University Lt Omar Nava, Naval Post Graduate
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The Neutral Atmosphere and Its Influence on Basic Orbital Dynamics at the Edge of Space
The Neutral Atmosphere and Its Influence on Basic Orbital Dynamics at the Edge of Space. Delores Knipp Department of Physics US Air Force Academy Colorado USA [email protected]. Developed by members of the Department of Physics, USAFA - PowerPoint PPT Presentation
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The Neutral Atmosphere and Its Influence on Basic Orbital Dynamics at the Edge of Space
Delores KnippDepartment of PhysicsUS Air Force Academy
Introduction: Neutral Atmosphere & Orbital Dynamics
• Motivation
• Concepts
– Solar Cycle-Atmosphere Interaction
– Atmospheric Density and Temperature
– Mechanics/Dynamics of Drag
– Computational Concepts
• “What Ifs”
• Tomorrow
– Simulation
Objectives:
Understand sources of upper atmospheric heating
Appreciate the space weather regime- change from magnetized and non-collisional to gravitationally dominated and collisional interactions.
Determine the effects of neutral atmospheric drag on the motion of satellites that are in low enough orbits to be affected by the Earth’s atmosphere
Explore effects of time varying atmospheric temperature and density
Space Weather EffectsSpace Weather Effects
The effects of solar and magnetic storms—what scientists call space weather—extend from beyond Earth-orbit (BEO) to geostationary orbit (GEO) to the ground (Courtesy: L Lanzerotti)
MOTIVATION
•Track and identify active payloads and debris (DOD)•Collision avoidance and re-entry prediction (NASA) •Study the atmosphere’s density and temperature profile (Science)
Skylab, 1978
April 9, 1979
Impacts of the Variable Sun
As the Sun’s activity increases during the solar cycle the Earth’s upper atmosphere heats up and heaves up
Are Sunspots Related to Satellite Drag?
Sunspots Up Close
Courtesy La Palma Telescope
How can a Sun with more Spots be Hotter/Brighter?
Courtesy of Robert Cahalan, NASA
Where Does Energy Enter the Upper Atmosphere?
Dayside:
Solar EUV
and
Auroral particles
Nightside:
Joule Dissipation
and
Auroral Particles
After Killeen et al., 1988
The Solar Spectrum
(Courtesy S Solomon)
Courtesy of Judith Lean
Geomagnetic Activity Plays a Role in Upper Atmospheric Heating
Courtesy of US Air Force
Altitude-Time Profile for a Spherical Satellite
Observed and Simulated STARSHINE-1 Altitude Vs Time
Thin curve Simulated STARSHINE orbits Thick curve actual STARSHINE data
Vertical Forces on a Static Parcel of Air
• Weight = mgn(Vol)– m = average mass of air in amu– g = local gravitational acceleration– n = number density of gas molecules (#/Vol)– Vol = volume = dz * A
• dP – Change in pressure (decreases upwards)
• A– Area of horizontal surface
• P = nkT– T = temperature in °K– k = Boltzmann constant (=1.38x10-23 J/°K)
z
z+dz
Fup=PA
Fdown=(P+dP)A
Weight
Fnet = Fup-Fdown-Weight=0
PA-(P+dP)A = Weight
-dP A = Weight
A=area
z
More realistic Pressure-Height Variation
-dP A = Weight
-dP A = mgn dz A
dP =d(nkT)= -mgn dz
kT (dn) = - mgn dz
dn/n=-mgdz/kT
nz/n0=exp(-mgdz/kT)
mnz/mn0=exp(-mgdz/kT)
z/ 0=exp(-mgdz/kT)
Atmospheric Concepts• Need to know about the atmosphere in which satellites are orbiting. • The simple law of atmospheres states that, close to the earth's surface, the
atmospheric density decreases exponentially with elevation.
(z) = 0exp(-mgz/kT)
• This expression assumes that the acceleration due to gravity g, the temperature T, and the mean gas molecule mass, m, remain constant.
Altitude vs. Atmospheric Mass Density, Simple Law of Atmospheres
The figure on the right shows the altitude versus atmospheric mass density curves for three different temperatures. Which of the following is the correct ranking, from lowest temperature to highest temperature, for the three curves shown?
a) A, B, C b) C, B, A c) B, C, A d) A, C, B
Altitude vs. Atmospheric Mass Density, Comparing Different Models