SPACECRAFT DESIGN TUTORIAL


HOW IT WORKS

Study of space travel begins with study of rockets and how they work. This card examines liquid and solid fuel rockets. Click on their respective buttons for a rocket tutorial before going to the following card which deals with the workings of spacecraft.

In order to understand how spacecraft work, it is helpful to examine an actual spacecraft system by system. The best known spacecraft of our time is the American Space Shuttle. It is a good example for study since it is a hybrid craft able to function both as a spacecraft and in some ways as an airplane. Since it must operate in space as well as the atmosphere, all systems must be present which allow the Shuttle to perform its mission within the laws of physics and science known to twentieth century man.

The means of studying spacecraft systems using the Shuttle is similar to that used to examine the comic book spacecraft in this program. Simply click on each Space Shuttle system pictured on the next card, and a description of how the system works appears for study. With each spacecraft system tutorial are questions based on the tutorial discussion using the comic book spacecraft shown in the program. After completing the tutorial on spacecraft and rockets, begin a review of each comic book artist's drawin, performing a study with knowledge gained in the tutorial.

This card and the card card are the heart of the program. Users of COMIC BOOK SPACE SCIENCE should examine all the hidden fields of this card before going to other cards in the stack. The purpose of this and the next card is explain rocket and spacecraft design.

Use of COMIC BOOK SPACE SCIENCE as an educational tool is aided by questions at the end of each discussion. Since the hidden fields overlap, each should be closed after using it. Each hidden field can serve as a lesson about a spacecraft or rocket system. The remaining cards are used as examples of the space technology discussed in each of the lessons. The lessons conclude with questions directing the student to the applicable comic book cover.

In order to understand the systems required by a spacecraft, a photo of the NASA Space Shuttle is shown on this card. Information about the Shuttle systems is opened by clicking on their location in the picture. The systems are: Propulsion, Orbital Maneuvering, Thermal Protection, Environmental Control, Guidance, Communications, Crew Provisions, Electrical Power (Generation and Distribution), Displays and Controls, Reaction Control, Aero-Control Surfaces, Main Propulsion (Boost), and Landing and Recovery.

Examine each system by clicking on its components, reading the discussion, and answering the related questions. Continue the study by reading the open and hidden fields on the remaining cards. Each card is a type of study of a design suggested by the comic book cover artist.


Space Shuttle Reference Instructions
(for the instructor or teacher)

This card and the next card are the heart of the program. Users of COMIC BOOK SPACE SCIENCE should examine all the hidden fields of this card before going to other cards in the stack. The purpose of this and the next card is to provide a brief tutorial course in rocket and spacecraft design.

In order to use COMIC BOOK SPACE SCIENCE as an educational tool, discussion of each spacecraft and rocket system includes questions. The questions are keyed to each system tutorial discussion and use the science fiction artwork on the remaining cards as resource material for answering the questions. The student not only acquires an appreciation of spacecraft engineering and the laws of science but also enjoys the interactive learning process of the program's "point and click" format.

A short word on the mechanics of using this card is needed. After a hidden field is opened and read, it should be closed before another is examined. Many of the hidden fields overlap and confusion could result.

The tutorial is comprised of a study of each of the main Space Shuttle systems. Each system represents system types found on most space boost systems or vehicles. These types are also depicted in science fiction artwork. The value of this study and program is the analysis of the various comic book space designs. NASA rocket designers often perform such "feasibility" studies on design concepts created by NASA and aerospace companies in fulfillment of studies for Mars missions, space stations, lunar habitats, new space transportation systems, and other programs. The author of this work spent more than a score of years performing such feasibility studies. Much of the narrative information regarding spacecraft systems is specific to the author's experience. Students in primary level science courses as well as those taking college spacecraft design courses will appreciate the tutorial and the questions following each narrative.

The narratives are written using simple sentence structure and vocabulary used by lay people. Where terms are not often used, a definition is provided.


Orbital Mechanics

The study of how bodies behave in space as a result of natural laws is called "Orbital Mechanics" or "Celestial Mechanics." The basis of orbital mechanics is Newton's and Kepler's laws:

Newton's laws of motion are simply stated:

1. A body at rest continues in a state of rest, and a body in uniform motion in a straight line continues such motion, unless acted upon by a force.

2. Change of motion is proportional to the force causing the change, and the change is in the direction of the application of the force.

3. For every action there is an equal and opposite reaction, or the actions of two bodies affecting each other are always opposite and equal.

A fourth law of Newton's was derived from the above three laws after Newton examined the movement of the planets. This law is called Newton's Law of Universal Gravitation:

Every two bodies of matter in the entire universe attract one another with a force acting along the imaginary line which would join them, and the strength of the attracting force becomes weaker as they are farther apart.

Orbital Mechanics is the name given the study of bodies in space because in some way all things are moving in an orbit. The orbital movement may be around the Earth, around the Sun, around a galaxy, or around the nucleus of an atom. Though an object appears stationary on Earth, its frame of reference is moving with the rotating Earth. It is not stationary but orbiting in a circle about the center of the Earth 4,000 miles away.

The first person to explain the nature of orbits was a German astronomer named Johannes Kepler (1571-1630). Kepler died twelve years before Newton's (1642-1727) birth. Because he was a mathematician, Kepler was able to find equations explaining the orbits of planets after studying them. He authored his discoveries as Kepler's Laws of Planetary Motion. Before looking at Kepler's laws, it is important to understand the mathematical figure Kepler used to describe orbits.

In the early years of the study of astronomy, scientists guessed that the planets moved around the sun in circular orbits. In mathematics, a circle is described as a curved line on which every point is at an equal distance from a fixed point. If the sun were the fixed point, and if each of the planets traveled on a unique curved path on which every point was at an equal distance from the Sun, the orbit would be a perfect circle. The surface on which the planet's orbit or circle could be drawn is called the plane of the orbit.

After studying the motion of the planets, Kepler decided each planet's orbit was not a perfect circle. Instead, the shape of the path seemed to be oblong. Using his knowledge of mathematics, Kepler described the paths as ellipses. A circle is a special type of a more general curve called an ellipse. To visualize how mathematics explains an ellipse, drawn a 6 inch line in the center of a one foot square piece of cardboard. Thumbtack each end of a 12 inch string to the ends of the line. The string is twice the length of the drawn line. With a pencil tip, pull the string taunt away from the line drawn on the cardboard. Keeping the string taunt with the pencil tip, move the pencil tip onto the cardboard. Maintaining the same tautness, move the pencil on the cardboard to draw a curve determined by keeping the string taunt.

The length of the string and the location of the end points of the string determine the curve drawn. The curve is called an ellipse. Each of the fixed end points of the string are called foci. As the line drawn on the paper is shorter and shorter with respect to the string, the ellipse becomes more circular until the line's end points are at the same point on the cardboard making a perfect circle. This demonstrates that a circle is a special case of an ellipse.

The body around which a planet, spacecraft, moon, or manmade satellite orbits is always at one focus of the ellipse. So for Earth, one focus of the ellipse of its orbit is the Sun. For a communication satellite orbiting Earth, one focus of its orbit is at the center of the Earth.

Before continuing, it is important to understand why satellites and planets orbit about the Earth and Sun. Newton's first three laws and the law of gravitation explain the phenomenon of one body orbiting about a much larger body. The simplest definition of an orbit is simply the closed curved path of one body about another body. To understand the forces which shape the orbit, we look to Newton's laws. The first law of Newton states that a body in motion remains in motion in a straight line unless a force acts on it in another direction. We know that orbits are not straight lines. They are curved lines. What forces act to continually maintain the closed curved path of an object in orbit? As an example, consider the Earth and a NASA spacecraft such as the Space Shuttle. We know the force of gravity acts on the Shuttle when it is in orbit, but what force keeps gravity from pulling the Shuttle down to Earth?

A yo-yo feat known as "around the world" provides a useful object lesson to explain the force which keeps gravity from pulling the Shuttle back to Earth. In performing the yo-yo trick called around the world, the force of throwing the yo-yo away from the hand is large compared to the usual yo-yo force for an up and down path. This force is similar to the boost thrust of a rocket's engines. The rocket thrust first fires toward the Earth in order to propel the rocket directly away from the Earth to reach the orbital altitude. The idea is to travel through the atmosphere quickly minimizing the time the rocket is in the atmosphere. This reduces frictional losses due to air molecules, but the rocket must also firealong the path of the orbit to attain the correct orbital velocity.

The length of the yo-yo string compares to the Shuttle's orbital altitude above the center of the Earth, and the hand is comparable to the center of the Earth. The yo-yo travels away from the hand until the tension in the string restricts its path (Newton's first law). The way the yo-yo is thrown is very significant in performing the around the world (orbit) trick.

Like a rocket, the throw must not only accelerate the yo-yo in a straight line away from the body of the thrower but also provide a looping or whirling type of force or motion along the orbit of the yo-yo. The resulting velocity along the yo-yo's orbit creates a force away from the thrower's hand known as CENTRIFUGAL (outpulling) force. The tension on the string balances the pull of the centrifugal force and the yo-yo orbits the hand in a circular loop with a radius of the yo-yo string's extended length. The string tension is a CENTRIPETAL (inpulling) force.

Science fiction authors often are in error in discussing travel between the planets and stars. They treat rockets as though they are airplanes trying to fly across the country. Airplanes do not need to use orbital mechanics. Luke Skywalker points his interplanetary rocket fighter at a planet such as Mars and simply rockets there in the same fashion a jet fighter pilot would fly a combat mission. The process of reaching Mars from Earth is quite dependent on orbital mechanics discussed above. Let's examine the approaches used by NASA to reach planets such as Mercury, Venus, and Mars with unmanned planetary spacecraft. When astronauts make the same journey, perhaps 20 years from now, the same approaches will apply.

When a body is boosted by rockets into space, it must achieve a minimum orbital velocity to create centrifugal force equal to the pull of gravity. This is known as orbital velocity. For low Earth orbit, it is approximately 17,000 miles per hour. As a rocket's thrust adds velocity along the orbit, the altitude of the orbit grows. The far point of the elliptic orbit increases in distance from Earth as thrust accelerates the rocket. With increasing distance of the APOGEE, the influence of Earth's gravity lessens. Finally, an orbital velocity and distant APOGEE is reached where Earth's gravity has become so weak that the body has actually escaped its influence. This is known as Earth's ESCAPE VELOCITY. At this velocity, the Earth can no longer pull the vehicle back again. The value of ESCAPE VELOCITY for each planet, the moon, and the Sun is different because each has a different mass. Different orbital velocities (centrifugal force) are required to balance the various gravities resulting from the masses of attracting bodies. Earth's ESCAPE VELOCITY is about 7 miles a second or 26,000 miles per hour.

Questions:

1. Click on the table of contents button at the lower right. Click on DENNIS THE MENACE IN SPACE on the contents card. Click on the trail of the rocket to learn about steering a spaceship. Why does the rocket's route violate Newton's laws?

2. Click on MIGHTY MOUSE IN SPACE. How does Mighty Mouse violate Newton's laws?


Solid Rocket : How It Works.

Solid rocket technology is among the most ancient. It is several thousand years old. Among the most famous solid rockets are the two large solid rockets used by the NASA Space Shuttle. These are known as the "SRBs" or Solid Rocket Boosters. Each is 149 feet tall and 12.2 feet in diameter. Unlike liquid rockets which can be shut off if they fail, a very significant disadvantage of solid rockets is that once started, they cannot be stopped. If a number of them are clustered in a rocket system, failure of a single solid rocket in the cluster can result in loss of the booster due to inability to steer the remaining rockets. A memorable example is the tragic mission of the Space Shuttle Challenger.

Accounts of history tell of ancient Chinese civilizations using solid rockets. Every time we sing America's national anthem, the Star Spangled Banner, we sing the words..."and the rockets red glare" which Francis Scott Key wrote as he watched rockets used in the War of 1812.

The solid rocket first evolved as a result of its simple design consisting of a case, a solid fuel like gun powder, an igniter, a place for the fuel to burn called the combustion chamber, and a nozzle. The solid rocket's reliability results from its simplicity. It has few parts which can fail. A shortcoming of solid rockets is the relative low energy of solid fuels compared to others which rockets use. Also, once started, they can not be stopped.

The fuel of a solid rocket requires oxygen to burn. Both the fuel and oxidizer are combined in a solid rocket into one substance called the solid propellant. The amount of energy in a propellant or rocket system is known as its Isp (specific impulse). Isp is the amount of force in pounds created by one pound of propellant burning for one second. If a pound of solid propellant burned for one second and imparted a force of 230 pounds, the Isp or specific impulse of the propellant would be 230.

Solid rocket propellant burns only where its surface is exposed. The sketch at left shows that propellant can only burn in the central burning port of the solid rocket. The burning occurs from the inside out along the entire length of the port. Small particles of oxidizer are mixed throughout the solid fuel. Of the two materials in the propellant, the fuel is known as the binder because it gives the propellant mechanical strength while the oxidizer does not have mechanical strength. The oxidizer is usually a crystalline substance called ammonium perchlorate. It makes up about 75 % of the weight of the solid propellant.

Companies that make solid propellants cast them in blocks shaped to fit snugly in the round rocket case. Each block of propellant is called a grain. The space shuttle solid rocket has very large grains which are stacked to make up the solid rocket propellant load. Grains can now be made over 20 feet in diameter.

Questions:

1. Shuttle designers chose to cluster two solid rockets about the Shuttle liquid rocket fuel tank. One of the first men to attempt to cluster solid rockets to increase the total thrust force was a Chinese man named Wan Ho. About 300 years ago, Wan Ho strapped himself into a chair with 47 solid war rockets clustered behind him. At Wan's command, his assistants lit 47 fuses. What do you think was the result?

A. Wan disappeared.
B. Wan rocketed into the air.
C. Wan became the man in the moon.

Discuss your answer with regard to how a solid rocket works speculating on the following: Wan's igniting system, Wan's steering capability, Wan's method of determining the number of solid war rockets needed.

2. When the Challenger solid rocket booster failed, the hot gas from the central burning port escaped through a joint between two of the large sections of solid propellant grain. Those, who analyzed the accident, examined carefully what would happen to the vehicle if one of the two SRBs failed. Even before the STS-51L mission resulted in the loss of the Challenger astronauts, analysis showed loss of an SRB during ascent would be fatal. Wan's rocket used 47 SRBs instead of two. What would happen if Wan's solid rockets did not have sufficient thrust to move Wan?

Hint: The Shuttle solid rockets become very hot while firing. This requires a special thermal design to cool the SRB case and nozzle mechanisms. Movement of the rocket through the atmosphere away from the hot gases ejected from its nozzle helps in cooling. A stationary rocket does not enjoy this benefit. If Wan had not used enough rockets, his chair and rockets would fail to move through the air. If this were the case, what might result from the heat of 47 stationary rockets?

3. What else might Wan's design have overlooked which might have caused an unfortunate explosion like the Challenger disaster?

Hint: How would you have ignited the rockets at the same time? What would be the result of trying to light 47 fuses at once?

The above questions show how very dangerous rocketry can be. It is a hobby that requires much study, safe practices, and proven materials. It, like learning to fly an airplane, requires training and direction by experts experienced in the field.

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Liquid Rocket : How It Works.

The name "liquid rocket" explains the basic difference from a solid rocket. Rocket propellant is in a liquid rather than solid state. The basic parts of a liquid fuel rocket are shown at the left. Among these are the tanks for fuel and oxidizer, a pressurization system (P*) which pushes both fuel and oxidizer into the thrust chamber for combustion, and the engine nozzle which optimizes the flow of hot gases from the rocket.

Additional supporting parts are the regulators (R*) which optimize the pressure applied to each tank for propellant transfer and the valves which control the flow of oxidizer and fuel to the thrust chamber. These parts help start, stop, and throttle liquid rockets.

The list of essential liquid rocket parts includes:
1. Propellants Tanks
2. A Propellant Feed System
3. A Thrust Chamber
4. Controls (regulators, valves, sensors, and igniters)

Liquid rockets are of two fuel types: monopropellant and bipropellant. Monopropellant type rockets are simplest of the two with the liquid fuel and oxidizer contained in a single tank. No fuel and oxidizer must be mixed. The liquid bipropellant rocket engine is more complex. It requires two tanks, two injectors to mix the fuel in the combustion chamber, and two feed systems. Some liquid rocket engines use gravity to force the flow of propellant from their tanks while others use pumps to accelerate the flow of propellants to the combustion chamber.

Question:

1. Browse through the stack and note where rocket engines are shown. Based on the discussions of solid and liquid rockets, explain which type of engine (solid or liquid) would be best for the application displayed by the comic book artist.


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