More Satellite Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

More Orbits 2 Importance of Orbits to Mission When should you start analyzing orbits to satisfy mission requirements? Can the orbit effect any of the following in the mission design? ― Revisit time of satellite to a point on earth? ― Amount of data that can be transferred between the satellite and ground? ― Space radiation environment? ― Power generation for the satellite? ― Thermal control on the satellite? ― Launch costs? Introduction to Space Systems and Spacecraft Design Space Systems Design

University of Idaho 3 Orbit References More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

4 Orbit Types LEO – Low Earth Orbit GEO – Geosynchronous Orbit HEO – Highly Elliptical Orbit N S N S Around Equator More Orbits Orbit References Introduction to Space Systems and Spacecraft Design Space Systems Design

5 Eclipse (max eclipse)Inclined (partial eclipse) Terminator Orbit (no eclipse) - Twilight Noon-Midnight Sun Orbit With Respect to Sun More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

6 More Orbits Orbit With Respect to Sun Introduction to Space Systems and Spacecraft Design Space Systems Design

7 Sun Winter Summer Equinox Earth's Axis More Orbits Orbit With Respect to Sun Introduction to Space Systems and Spacecraft Design Space Systems Design

8 Orbit Period Spacecraft Velocity Spacecraft Orbital Velocity and Orbit Period More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

9 km/s mi/hour convert X (km/s) x 60s/m x 60m/hour x (1/1.6) mi/km = X (km/s) x 2250 mi/hour V = (7.739 km/s) x 2250 mi/hour = 17,142 mi/hour What is ISS altitude? Spacecraft Orbital Velocity and Orbit Period -2 = 17,142 mi/hour h = (150) (1.852) = 278 km More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

10 Equations to Remember V cir = r -1/2 km/sec V esc = r -1/2 km/sec r - is from center of the earth More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

11 Changing Orbits LEO – Low Earth Orbit from a shuttle launch – 280 km N S 280 km V = km/s 35,786 km V = km/s LEO GEO Want to Change Orbit LEO to GEO How? More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

12 1.Change to a GTO (GEO transfer Orbit) For GTO Want: Vp = km/s Va = km/s 2.Circularize orbit Need V = km/s for GEO Change V = = km/s 3.Burn at Va to increase V to km/s for circular orbit at GEO How? LEO GEO Va Vp 35,786 km V = km/s More Orbits Changing Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

13 Other Ways to Change Orbits More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

14 Other Ways to Change Orbits More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

15 Now you have an orbit for your satellite. 1. Will it stay where you put it? 2. Is there anything that will change the orbit once you have it there? More Orbits Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

16 Special Effects on Orbits Sun WinterSummer Equinox What happens to the orbit plane as the earth rotates around the sun? More Orbits Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

17 What effects the orbit? J2 effect J22/J3 effect Lunar gravity Solar gravity Solar pressure Atmospheric drag Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

18 Solar Pressure/Radiation Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

19 Solar Pressure/Radiation Using solar radiation for propulsion. Solar Sails Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

20 Atmospheric Drag Drag Coefficient Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

21 Ballistic Coefficient How do they go through the atmosphere? Which stays in orbit longer – a bowling ball or a soccer ball of the same size? Bc = K (Mass/Cross Sectional Area) More Orbits Atmospheric Drag Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

22 More Orbits Atmospheric Drag Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

23 More Orbits Atmospheric Drag Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

24 Earth-moon tidal friction mechanism Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

25 Earth non-spherical effect Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design East-West drift occurs because the equator is not perfectly circular, so satellites drift slowly towards one of two longitudinal stable points.

26 Orbit References – GEO Station Keeping More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

27 Earth non-spherical effect Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design Due to luni-solar perturbations and the ellipticity of the Earth equator, an object placed in a GEO without any station- keeping would not stay there. It would start building up inclination at an initial rate of about 0.85 degrees per year. After 26.5 years the object would have an inclination of 15 degrees, decreasing back to zero after another 26.5 yearsEarthinclination

28 N S Inclination What is the effect of this? More Orbits Earth non-spherical effect Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

University of Idaho 29 N S < 90 o N S > 90 o < 90 0 Orbit Inclination > 90 0 Orbit Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

30 N Prograde Orbit I < 90 o Oblatness causes rotation clockwise More Orbits Earth non-spherical effect Orbits Perturbations N I > 90 o Oblatness causes rotation counter clockwise Introduction to Space Systems and Spacecraft Design Space Systems Design

31 Sun WinterSummer Equinox a aaa Orbit rotates to maintain same angle with sun Sun Synchronous Orbit More Orbits Earth non-spherical effect Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

32 Sun Synchronous Orbit More Orbits Earth non-spherical effect Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

33 More Orbits Earth non-spherical effect Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

34 Sun Synchronous Inclination More Orbits Orbits Perturbations Introduction to Space Systems and Spacecraft Design Space Systems Design

35 Special Molniya orbit has a stable orbit that is used by Russians to have high latitude communications – 2 satellites. Earth non-spherical effect Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

36 Earth non-spherical effect Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

37 Earth non-spherical effect Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

38 Effects are secular and accumulative Which are these? J2 effect J22/J3 effect Lunar gravity Solar pressure Atmospheric drag Earth non-spherical effect Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

39 GEO satellites have drift due to non-spherical earth 1.East-west drift 2.North-south drift Earth non-spherical effect Orbits Perturbations More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

40 Orbit References – GEO Station Keeping More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

Special Orbits 41 N S N S Zero Inclination GEO Orbits Satellite appears stationery to earth observer Inclination GEO Orbits Satellite appears go N-S & EW in a figure 8 to earth observer Geostationary OrbitGeosynchronous Orbit More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

42 GEO Orbits Characteristics More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

43 N S What is the maximum latitude that a GEO satellite can be viewed? GEO Orbits Characteristics More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

44 GEO Orbits Characteristics More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

45 GEO Orbits Characteristics More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

46 LEO Satellite Orbits More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

47 Footprint More Orbits LEO Orbits Characteristics Introduction to Space Systems and Spacecraft Design Space Systems Design

48 LEO Orbits Characteristics More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

49 LEO Orbits Characteristics More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

50 How do you find D i ? Use law of cosines. What is elevation angle on ground antenna? LEO Orbits Characteristics More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

51 Objects in Orbit Introduction to Space Systems and Spacecraft Design Space Systems Design

52 Objects in Orbit More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

53 Importance of Orbits to Mission When should you start analyzing orbits to satisfy mission requirements? Can the orbit effect any of the following in the mission design? ― Revisit time of satellite to a point on earth? ― Amount of data that can be transferred between the satellite and ground? ― Space radiation environment? ― Power generation for the satellite? ― Thermal control on the satellite? ― Launch costs? More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design

54 Questions? More Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design