Download
1 / 64
650 likes | 748 Vues
Launch Vehicles and Orbits. How Rockets Work. Newton's Laws of Motion are: An object at rest tends to remain at rest An object in motion tends to remain in motion For every action there is an equal and opposite reaction. Conservation of Momentum.
E N D
How Rockets Work • Newton's Laws of Motion are: • An object at rest tends to remain at rest • An object in motion tends to remain in motion • For every action there is an equal and opposite reaction
Conservation of Momentum • Newton's Laws are all contained in a more general principle called conservation of momentum. • Momentum is mass times velocity • In a system that is not disturbed from outside, the total momentum stays constant.
Conservation of Momentum Means: • If velocity is zero, momentum is zero (Newton's First Law) • If velocity is not zero, and mass doesn't change, then velocity doesn't change (Newton's Second Law)
Conservation of Momentum and Newton’s Third Law • If mass changes somehow, then so does velocity. • If an object is stationary, and flings off mass, the rest of the mass moves in the opposite direction. • The flung off mass has positive momentum, the rest has negative momentum, and the total momentum remains zero (Newton's Third Law).
Rockets and Jets • Rockets and jets work according to Newton's Third Law. • They fire mass out at high speed and acquire velocity in the opposite direction. • They do not need something to push against. They move because they are expelling exhaust gases at high speeds. • Tthe rocket or jet is pushing mass away, and the mass is pushing back (equal and opposite reaction.)
How Rockets and Jets Differ • Rockets and jets expel mass by burning fuel. • A jet gets the oxygen for combustion from the atmosphere • A rocket carries oxygen in some form with it. • Thus rockets can function outside the Earth's atmosphere; jets can't.
Rockets are Mostly Fuel (and Oxygen) • A rocket or jet has to carry all its remaining fuel with it. (And oxygen, if it’s a rocket). • Most of the mass of the Space Shuttle is fuel, and most of that is used to get the remaining fuel off the ground. • The miles-per-gallon fuel economy of the Space Shuttle in its first foot off the ground is pretty terrible!
About Orbits and Satellites • Satellites travel elliptical paths with the center of the Earth at one focus (Kepler's First Law) • Inertia causes object to continue moving in a straight line • Gravity pulls object to Earth • Balance between the two = orbit
Important Orbits • Low vs. High Inclination • Almost all are Prograde • Polar Orbits for global coverage • Circular Orbits strongly preferred • Constant altitude • Constant speed • Sun-Synchronous • Geosynchronous • 12-Hour (GPS)
About Orbits • You do not need to expend fuel to stay in orbit • Satellites need attitude control fuel to correct for atmospheric drag, lunar and solar gravity, etc. • May want thrusters to help maintain orbits • Spin stabilization helps • Once below 200 km, atmospheric braking leads to re-entry
About Orbits • The focus of a satellite orbit is the center of the earth • The plane of a satellite orbit always passes through the center of the earth • There is no such thing as an orbit over the poles, over a small region, etc. • It is possible to have an orbit over the equator
Precession • Put sideways force on anything moving in a circle, it will precess • Precession affects planetary rotation • Precession also affects orbits • We can control precession of satellites by selecting orbital inclination • Fixed with respect to stars • Fixed with respect to sun
Three Pioneers of Rocketry • Konstantin Tsiolkovsky (1857-1935) • Worked out theoretical problems of spaceflight • Robert Goddard (1882-1945) • First Liquid Fuel Rocket • Hermann Oberth (1894-1989) • Helped create operational rockets
From Sapwood to Sputnik • An existing rocket, the SS-6, was used. • The warhead section was removed • A cluster of four more SS-6 engines was bolted around a central engine • Very Dependable
Sputnik I • October 4, 1957 • S- (with) + put’ (path) +-nik (one who) =Sputnik • Literally, one who follows the same path
Sensor Technology • Passive (senses only ambient signals) • Active (emits signals) • Imaging • Non-Imaging • Scanning (mechanical or electronic) • Non-scanning
A Noble Myth “In my life, I've seen the images from space of a blue-white-green world — there are no political lines drawn on this planet. • Luis J. Rodriguez “The border between the United States and Mexico is an imaginary line. It cannot be seen from space” • The Border Zone: A History of Trade between the United States and Mexico, Julia Albright; Age of Irony, Winter 2004
