The Neutral Atmosphere and Its Influence on Basic Orbital Dynamics at the Edge of Space

1. 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 delores.knipp@usafa.af.mil 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 School

2. 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 Introduction: Neutral Atmosphere & Orbital Dynamics

3. Space Weather Effects Space 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)

4. MOTIVATION Skylab, 1978 April 9, 1979 • Track and identify active payloads and debris (DOD) • Collision avoidance and re-entry prediction (NASA) • Study the atmosphere’s density and temperature profile (Science)

5. 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

6. Are Sunspots Related to Satellite Drag?

7. Sunspots Up Close Courtesy La Palma Telescope

8. How can a Sun with more Spots be Hotter/Brighter? Courtesy of Robert Cahalan, NASA

9. Where Does Energy Enter the Upper Atmosphere? Nightside: Joule Dissipation and Auroral Particles Dayside: Solar EUV and Auroral particles After Killeen et al., 1988

11. The Solar Spectrum (Courtesy S Solomon)

12. Courtesy of Judith Lean

13. Geomagnetic Activity Plays a Role in Upper Atmospheric Heating Courtesy of US Air Force

14. Altitude-Time Profile for a Spherical Satellite Thin curve Simulated STARSHINE orbits Thick curve actual STARSHINE data

15. Vertical Forces on a Static Parcel of Air Fdown=(P+dP)A z+dz • 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 A=area Weight Fup=PA Fnet = Fup-Fdown-Weight=0 PA-(P+dP)A = Weight -dP A = Weight

16. 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)

17. 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.

18. Correcting for variations in “g”

19. Concept: What if “g” Varies? MSIS Atmosphere

20. Concept: What if the Temperature Varies? MSIS Atmosphere

21. Concept Check 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

23. TIEGCM Density Profile

24. MSIS Hot

25. MSIS Cool

26. Mechanics Concepts Kinetic Energy • Satellites in orbit experience a centripetal acceleration • Solve for speed • Associated kinetic energy

27. Mechanics Concepts Potential and Total Energy • Potential Energy Significance of “-” sign? • Total Mechanical Energy • Solve for Altitude • Total Mechanical Energy is constant unless non-conservative forces act

28. Mechanics Concepts Drag Force and Work • Drag Force • Work Done by Drag

29. Assumptions • Circular orbit • No change in orbital parameters during the satellite period • Satellite does not tumble (A and Cd constant) • Atmosphere • Law of Atmospheres • MSIS Atmosphere—temperature and density • No seasonal, day/night or spatial variations in the atmospheric density

30. Iterative Techniques and Formulation and Graphics Concepts Newton’s Second Law Energy Conservation Newton’s Second Law Energy Conservation…Etc

31. Iterative Technique

32. Iterative Technique

35. Concept Check In a subsequent orbit, after work has been done by the drag force, the satellite would have a) less kinetic energy and less potential energy b) more kinetic energy and less potential energy c) less kinetic energy and more potential energy

38. Concept Check A satellite orbiting in a dense atmosphere will (at next orbit) be a) at lower altitude and ahead of schedule b) at higher altitude and ahead of schedule c) at lower altitude and behind schedule d) at higher altitude and behind schedule

39. Atmospheric Drag EXPECTED POSITION ACTUAL POSITION Radar Receiver

40. Time-Varying Activity

43. The Atmosphere can have Significant Temporal and Spatial Variability in Temperature and Density Location of heating associated with low energy particles bombarding the nightside auroral zone

44. Solar EUV and Particle Power

45. Joule Power –Two Hemispheres

46. 10 Most Powerful Events of Last 30 Years(Knipp et al., 2005) 15 Apr 7 Jul 3 Mar 10 Oct 6 Jun 5 May 15&16 Jul 6 Nov 30 Oct 79 82 89 89 91 92 00 01 03

47. Altitude Profile nominal Level 3 disturbance at hr 100 for 10 hr Return to nominal Level 2 Disturbance All Hours

48. Altitude Speed Mechanical Energy Drag Force

49. Orbital Drag Lab: Boundary Values for Space Shuttle Orbit

50. Ideal and model atmospheres