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Fundamentals of Rocket Propulsion: Achieving Orbits and Beyond

Learn the basics of rocket propulsion, understanding the generation of thrust, forces acting on a rocket, momentum balance, effective exhaust velocity, and requirements to reach orbit. Dive into concepts like effective exhaust velocity and geostationary orbits.

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Fundamentals of Rocket Propulsion: Achieving Orbits and Beyond

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  1. Basics of Rocket Propulsion P M V Subbarao Professor Mechanical Engineering Department Continuously accelerating Control Volume…. Travel with continuously varying Drag & Gravity…. No Source of Oxygen or working Fluid….

  2. Basics of Rocket : generation of Thrust Rocket takes mass stored inside combustion chamber and throws it backwards, to use the reaction force to propel the vehicle. This is known as Rocket Propulsion Rocket ejects mass at a given momentum rate from the nozzle and receives a thrust in the opposite direction. Momentum rate of ejects:

  3. Thrust generated by Rocket Ejects

  4. Basic Forces Acting on A Rocket • T = Rocket thrust • D = Rocket Dynamic Drag • Vr = Velocity of rocket • mejects = Mass flow rate of ejects • mr= Mass of the rocket

  5. Force Balance on A Rocket Conservation of mass:

  6. MOMENTUM BALANCE FOR A ROCKET Rocket mass X Acceleration = Thrust – Drag -gravity effect

  7. EFFECTIVE EXHAUST VELOCITY The total mechanical impulse (total change of omentum) generated by an applied force, T, is: The total propellant mass expended is The instantaneous change of momentum per unit expenditure of propellant mass defines the effective exhaust velocity.

  8. Finite Duration of Flying A rocket is designed for a finite duration of flying, known as time of burnout, tb.

  9. Requirements to REACH An ORBIT • For a typical launch vehicle headed to an orbit, aerodynamic drag losses are in the order of 100 to 500 m/sec. • Gravitational losses are larger, generally ranging from 700 to 1200 m/sec depending on the shape of the trajectory to orbit. • By far the largest term is the equation for the space velocity increment. • The lowest altitude where a stable orbit can be maintained, is at an altitude of 185 km. • This requires an Orbital velocity approximately 7777 m/sec.

  10. Launching Time Requirements to REACH An ORBIT • To reach this velocity from a Space Center, a rocket requires an ideal velocity increment of 9050 m/sec. • The velocity due to the rotation of the Earth is approximately 427 m/sec, assuming gravitational plus drag losses of 1700 m/sec. • A Hydrogen-Oxygen system with an effective average exhaust velocity (from sea-level to vacuum) of 4000 m/sec would require mri/ mrf = 9.7.

  11. Geostationary orbit • A circular geosynchronous orbit in the plane of the Earth's equator has a radius of approximately 42,164 km from the center of the Earth. • A satellite in such an orbit is at an altitude of approximately 35,786 km above mean sea level. • It maintains the same position relative to the Earth's surface. • If one could see a satellite in geostationary orbit, it would appear to hover at the same point in the sky. • Orbital velocity is 11,066 km/hr= 3.07 km/sec.

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