Transcript Slide 1
More Satellite Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design More Orbits 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 2 More Orbits Orbit References Introduction to Space Systems and Spacecraft Design University Space Systems of Idaho Design 3 More Orbits N Orbit References Orbit Types GEO – Geosynchronous Orbit LEO – Low Earth Orbit S Around Equator HEO – Highly Elliptical Orbit S Introduction to Space Systems and Spacecraft Design Space Systems Design 4 More Orbits Orbit With Respect to Sun Noon-Midnight (max eclipse) Inclined (partial eclipse) Sun Eclipse Terminator Orbit - Twilight (no eclipse) Introduction to Space Systems and Spacecraft Design Space Systems Design 5 More Orbits Orbit With Respect to Sun Introduction to Space Systems and Spacecraft Design Space Systems Design 6 More Orbits Orbit With Respect to Sun Equinox Earth's Axis Summer Winter Sun Equinox Introduction to Space Systems and Spacecraft Design Space Systems Design 7 More Orbits Spacecraft Orbital Velocity and Orbit Period Spacecraft Velocity Orbit Period Introduction to Space Systems and Spacecraft Design Space Systems Design 8 More Orbits Spacecraft Orbital Velocity and Orbit Period -2 What is ISS altitude? h = (150) (1.852) = 278 km = 17,142 mi/hour convert km/s mi/hour 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 Introduction to Space Systems and Spacecraft Design Space Systems Design 9 More Orbits Equations to Remember Vcir = 631.3481 r-1/2 km/sec Vesc = 892.8611 r-1/2 km/sec r Introduction to Space Systems and Spacecraft Design Space Systems Design - is from center of the earth 10 Changing Orbits More Orbits LEO – Low Earth Orbit from a shuttle launch – 280 km 35,786 km V = 3.0727 km/s GEO N 280 km V = 7.738 km/s LEO S How? Want to Change Orbit LEO to GEO Introduction to Space Systems and Spacecraft Design Space Systems Design 11 Changing Orbits More Orbits How? 35,786 km V = 3.0727 km/s GEO 1. Change to a GTO (GEO transfer Orbit) For GTO Va Want: Vp = 10.169 km/s Va = 1.606 km/s 2. Circularize orbit Need Vp LEO V = 3.0727 km/s for GEO Change V = 3.0727-1.606 = 1.4667 km/s 3. Burn at Va to increase V to 3.0727 km/s for circular orbit at GEO Introduction to Space Systems and Spacecraft Design Space Systems Design 12 More Orbits Other Ways to Change Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design 13 More Orbits Other Ways to Change Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design 14 More Orbits Orbits Perturbations 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? Introduction to Space Systems and Spacecraft Design Space Systems Design 15 More Orbits Orbits Perturbations Special Effects on Orbits Equinox Winter Summer Sun Equinox What happens to the orbit plane as the earth rotates around the sun? Introduction to Space Systems and Spacecraft Design Space Systems Design 16 More Orbits Orbits Perturbations What effects the orbit? J2 effect J22/J3 effect Lunar gravity Solar gravity Solar pressure Atmospheric drag Introduction to Space Systems and Spacecraft Design Space Systems Design 17 More Orbits Orbits Perturbations Solar Pressure/Radiation Introduction to Space Systems and Spacecraft Design Space Systems Design 18 More Orbits Orbits Perturbations Solar Pressure/Radiation Using solar radiation for propulsion. Solar Sails Introduction to Space Systems and Spacecraft Design Space Systems Design 19 More Orbits Orbits Perturbations Atmospheric Drag Drag Coefficient Introduction to Space Systems and Spacecraft Design Space Systems Design 20 More Orbits Orbits Perturbations Atmospheric Drag Ballistic Coefficient Bc = K (Mass/Cross Sectional Area) How do they go through the atmosphere? Which stays in orbit longer – a bowling ball or a soccer ball of the same size? Introduction to Space Systems and Spacecraft Design Space Systems Design 21 More Orbits Orbits Perturbations Atmospheric Drag Introduction to Space Systems and Spacecraft Design Space Systems Design 22 More Orbits Orbits Perturbations Atmospheric Drag Introduction to Space Systems and Spacecraft Design Space Systems Design 23 More Orbits Orbits Perturbations Earth-moon tidal friction mechanism Introduction to Space Systems and Spacecraft Design Space Systems Design 24 More Orbits Orbits Perturbations Earth non-spherical effect East-West drift occurs because the equator is not perfectly circular, so satellites drift slowly towards one of two longitudinal stable points. Introduction to Space Systems and Spacecraft Design Space Systems Design 25 More Orbits Orbit References – GEO Station Keeping Introduction to Space Systems and Spacecraft Design Space Systems Design 26 More Orbits Orbits Perturbations Earth non-spherical effect Due to luni-solar perturbations and the ellipticity of the Earth equator, an object placed in a GEO without any stationkeeping 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 years Introduction to Space Systems and Spacecraft Design Space Systems Design 27 Orbits Perturbations More Orbits Earth non-spherical effect N Inclination S What is the effect of this? Introduction to Space Systems and Spacecraft Design Space Systems Design 28 Orbits Perturbations More Orbits Inclination > 900 Orbit < 900 Orbit N N > 90o < 90o S Introduction to Space Systems and Spacecraft Design University Space Systems of Idaho Design S 29 Orbits Perturbations More Orbits Earth non-spherical effect Oblatness causes rotation counter clockwise N I > 90o Introduction to Space Systems and Spacecraft Design Space Systems Design Oblatness causes rotation clockwise N Prograde Orbit I < 90o 30 Orbits Perturbations More Orbits Earth non-spherical effect Orbit rotates to maintain same angle with sun Sun Synchronous Orbit a Equinox Summer a Winter a Sun Equinox a Introduction to Space Systems and Spacecraft Design Space Systems Design 31 More Orbits Orbits Perturbations Earth non-spherical effect Sun Synchronous Orbit Introduction to Space Systems and Spacecraft Design Space Systems Design 32 More Orbits Orbits Perturbations Earth non-spherical effect Introduction to Space Systems and Spacecraft Design Space Systems Design 33 More Orbits Orbits Perturbations Sun Synchronous Inclination Introduction to Space Systems and Spacecraft Design Space Systems Design 34 More Orbits Orbits Perturbations Earth non-spherical effect Special Molniya orbit has a stable orbit that is used by Russians to have high latitude communications – 2 satellites. Introduction to Space Systems and Spacecraft Design Space Systems Design 35 More Orbits Orbits Perturbations Earth non-spherical effect Introduction to Space Systems and Spacecraft Design Space Systems Design 36 More Orbits Orbits Perturbations Earth non-spherical effect Introduction to Space Systems and Spacecraft Design Space Systems Design 37 More Orbits Orbits Perturbations Earth non-spherical effect Effects are secular and accumulative Which are these? J2 effect J22/J3 effect Lunar gravity Solar pressure Atmospheric drag Introduction to Space Systems and Spacecraft Design Space Systems Design 38 More Orbits Orbits Perturbations Earth non-spherical effect GEO satellites have drift due to non-spherical earth 1. East-west drift 2. North-south drift Introduction to Space Systems and Spacecraft Design Space Systems Design 39 More Orbits Orbit References – GEO Station Keeping Introduction to Space Systems and Spacecraft Design Space Systems Design 40 Special Orbits More Orbits Geostationary Orbit N S Geosynchronous Orbit N S Zero Inclination GEO Orbits Inclination GEO Orbits Satellite appears stationery to earth observer Satellite appears go N-S & EW in a figure 8 to earth observer Introduction to Space Systems and Spacecraft Design Space Systems Design 41 More Orbits GEO Orbits Characteristics Introduction to Space Systems and Spacecraft Design Space Systems Design 42 More Orbits GEO Orbits Characteristics N S What is the maximum latitude that a GEO satellite can be viewed? Introduction to Space Systems and Spacecraft Design Space Systems Design 43 More Orbits GEO Orbits Characteristics Introduction to Space Systems and Spacecraft Design Space Systems Design 44 More Orbits GEO Orbits Characteristics Introduction to Space Systems and Spacecraft Design Space Systems Design 45 More Orbits LEO Satellite Orbits Introduction to Space Systems and Spacecraft Design Space Systems Design 46 More Orbits LEO Orbits Characteristics Footprint Introduction to Space Systems and Spacecraft Design Space Systems Design 47 More Orbits LEO Orbits Characteristics Introduction to Space Systems and Spacecraft Design Space Systems Design 48 48 More Orbits LEO Orbits Characteristics Introduction to Space Systems and Spacecraft Design Space Systems Design 49 More Orbits LEO Orbits Characteristics What is elevation angle on ground antenna? How do you find Di? Use law of cosines. Introduction to Space Systems and Spacecraft Design Space Systems Design 50 Objects in Orbit Introduction to Space Systems and Spacecraft Design Space Systems Design 51 51 More Orbits Objects in Orbit Introduction to Space Systems and Spacecraft Design Space Systems Design 52 More Orbits 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 53 More Orbits Questions? Introduction to Space Systems and Spacecraft Design Space Systems Design 54