Spaceflight Without Escape Velocity?
I will argue that it is unnecessary for an object to achieve 8km/hr to leave the Earth’s gravity, as long as it has a continued thrust which is greater than the pull of gravity. With such thrust a rocket could literally crawl from the Earth at one mile per hour. Obviously each rocket has this thrust or it would not leave the surface of the planet, where gravity is at its strongest. Escape velocity pertains only to objects without any additional thrust available. Reply Hello, J.D. Your argument is correct, but the conclusion you draw is not. Suppose you have a rocket of mass M accelerating from the pad with an acceleration a=g, which we will round off to 10 meter/second squared. That means its rocket must provide a thrust of 2Mg–Mg to support the weight of the rocket and Mg to accelerate it. To reach orbital velocity of 8000m/sec will take 800 seconds (8000/a = 8000/g). During that time the launch vehicle has to use half its thrust just to keep itself from falling–only half the thrust
