Space Science: An Introduction (1964)

[Music] for centuries men have looked into the sky and wonder Ed such things as how the Sun affects the Earth's atmosphere and how the planets were formed today we are finding answers to such questions for the exploration of space has begun and with it the new and exciting field of Space Science has developed we can think of space as beginning where our atmosphere is too thin to have much effect on objects moving through this is at an altitude of about 60 M regions of space have been given different names for example cislunar space is between the Earth and the moon a distance of about 240,000 miles about 40,000 mil from the surface of the Moon lunar space begins here the moon begins to be the most important gravitational influence in space interplanetary space is all the space through which the planets move it is also called solar space because the sun is the principal gravitational influence here Interstellar space lies between the stars of our galaxy and Intergalactic space lies between the galaxies the first step in exploring space is overcoming the gravity of the earth we overcome gravity every time we throw a ball into the air gravity and air resistance slow the ball until it stops Rising then gravity pulls it back to Earth again the ball can be made to rise Higher by throwing it with more Force the more Force you use the higher an object will go an arrow will travel far higher than a ball can be thrown a bullet can be shot higher than an arrow a jet will go even higher than a bullet because the great force that moves it is continuous a jet engine depends on air but Rockets can operate beyond the atmosphere rocket engines Supply the large continuous force needed to overcome gravity for travel into space what happens to these space Vehicles can be demonstrated with this saucer representing space and this metal ball representing a space vehicle some space Vehicles rise into space and then fall back to Earth again some stay in space following a path or orbit around the Earth and some escape the Earth let's see first why some space Vehicles fall back to Earth here is a rocket on its pad ready for launching the countdown which is the fueling and checking of all the important parts of the rocket is nearly completed nearby are the people who direct the countdown the final minutes and seconds are called off on a loud speaker 7 6 5 4 3 2 1 now the fuel begins burning in the rocket engine hot gases rush out the end of the rocket and the rocket begins to rise let's see why the gas is rushing downward Force the rocket upward in a rocket this upward force is called thrust if the thrust is great enough the rocket will rise into space as the rocket Rises its velocity rapidly increases its motion is said to be accelerating for an object to accelerate certain forces must act on it we can see these same forces at work in an elevator this man in the space suit standing on the scale will help us see what happens when an object accelerates with the elevator at rest the man and his suit weigh 157 lb the weight is caused by the force of gravity the man's weight will seem to increase as the elevator goes up and accelerates from zero to its maximum speed now now the elevator begins accelerating upward let's stop the action here the man's weight seems to have increased from 157 lb to 259 lb this is because the force that causes the acceleration upward is accompanied by an opposite force that pushes downward on the man because this downward Force acts like the force of gravity it is called a G force or Gravity Force if the man's weight had doubled we would say that he was undergoing a force of two G's a man riding a rocket that is being launched undergoes forces of many G's as the rocket speed increases to thousands of milph the rocket continues coasting upward into space after its fuel is used up if the rocket is traveling less than about 18,000 mph the pull of gravity gra it will gradually slow the rocket until its Rising stops then gravity pulls the rocket back toward Earth again as the rocket re-enters the dense part of the atmosphere its speed decreases and friction with the air causes it to get very hot re-entering the atmosphere is called re-entry the heat of re-entry can destroy an object as it returns from space unless it is built to withstand high temperatures an object will stay in orbit around the Earth if it has the proper speed and direction this rocket that will place a satellite in orbit is actually composed of several sections or stages each stage may be powered by one or more rockets at the top a nose cone protects the satellite many satellites like this one are now in space orbiting the Earth they are called artificial Earth satellites because they are meant to travel around the earth as the moon does the moon is the Earth's natural satellite to see why a satellite goes into orbit let's look at the metal ball in the saucer again we saw that with a little push the ball goes up a short distance and falls back to Earth the harder the ball is pushed the farther it travels before it falls to Earth this time it went nearly halfway around the world we can make the ball travel all the way around the world several times by giving the ball a sideways motion and a high enough velocity now the ball is in Orbit the velocity required for an object to St in orbit is called orbital velocity for an object within a few hundred miles of the earth orbital velocity is about 18,000 mph a rocket that places a satellite into orbit at first Rises directly upward but the direction must change for the satellite to go into orbit there are several ways of changing the direction of a rocket in Flight sometimes small Rockets are attached to the main rocket firing one of the small Rockets will change the direction of the main rocket another way to change a Rocket's direction is by having a movable rocket motor the motor is pivoted tilting the engine in One Direction moves the rocket in the opposite direction as the rocket Rises all the fuel in the first stage is used up then the first stage Falls away and the next stage begins operating each stage increases the satellite speed until the satellite in its protective nose cone is traveling at orbital velocity and moving nearly parallel to the surface of the Earth then the nose cone separates from the last stage and splits apart then the satellite is released now let's stop the ball in the saucer here if it weren't for the Earth's gravity a satellite's motion would carry it in a straight line away from the earth but because gravity pulls the satellite toward the center of the earth the satellite instead follows a curved path around the earth as long as the satellite has the proper velocity the force of gravity will hold it in orbit but will not be great enough to pull the satellite back to Earth the orbit is a closed curve called an ellipse at this point along the elliptical orbit the ball has reached its farthest point from Earth this point is called a satellite's apoy the point at which a satellite is closest to Earth is called its Pary as a satellite travels in orbit it appears to have no weight to see why let's look at the man in the elevator again now at the top floor of the building his weight is again about 157 lb but let's go down now as the elevator accelerates downward the man's weight will seem to grow less let's stop the action when the man's weight seems to decrease from 157 lb to 60 lb if we could increase the speed of the elevator until it was accelerating at the same rate as an object falling to Earth then the scale would indicate that the man's weight had dropped to zero he would have entered a condition of what is called weightlessness or zero g this is exactly the condition that a satellite is in as a it falls around the earth both the satellite and people or objects it carries are said to be weightless as these men are in an airplane that is flying along a special curve through the atmosphere a satellite will continue orbiting the Earth until friction between the satellite and air slows it below orbital velocity and the satellite fall to Earth to send an object into space so that it doesn't return to Earth a rocket must be used that will give it enough thrust to reach what is called escape velocity about 25,000 mph at this velocity an object will not go into orbit around the Earth instead it will travel so far into space that other bodies begin to exert a stronger gravit ational influence than Earth does by achieving escape velocity Rockets have already traveled as far as the moon and the planets today we are steadily perfecting our skills in overcoming the Earth's gravity and adding to our knowledge of the growing field of Space Science oh