Section 1.7 - Engineering Specialties< Space Transport and Engineering Methods
In Section 1.5 - Systems Engineering we discussed methods to coordinate the work across a large project. Complex space projects require more knowledge and experience than any single individual can have. Such projects need teams of people not only because there is a lot of work to do, but also because each person supplies a different set of skills. For the design portion of a project, the field of engineering is divided into a number of Branches of knowledge, with specialists who concentrate on wider or narrower portions of it. The specialists address different areas of design, and different areas of application to a given project.
Much of the actual work for current space projects happens on Earth, in places like offices, factories, launch sites, and control centers. Building and operating those locations uses much of the same engineering knowledge as any other large project on Earth. For the in-space segment of projects, many of the specialties are still relevant. For example, nearly all space hardware has structural parts, and their design is the province of mechanical engineers. In the future, more production and construction will happen in space. This is in contrast to today, where mostly finished hardware is launched from Earth. So the importance of additional fields like mining and industrial engineering will increase, with suitable modifications for operation in space. In the farther future, extremely large projects described as Astrophysical or Planetary Engineering are possible. Examples are Terraforming, making a body more Earth-like, or changing the orbit of a large asteroid. Such very large projects are mostly speculative, except for the human-caused 43% increase in CO2 in the Earth's atmosphere. This is anti-terraforming our planet - making it less Earth-like than its original state. Large-scale space projects are one way to correct this problem if it becomes too severe. Very large projects like these are not yet organized as a distinct specialty, but would include knowledge from many areas of science and engineering.
One branch in particular, Aerospace Engineering, is concerned with the design and construction of vehicles and hardware that travel to and operate in air or space. We discuss it first, because it is nearly always involved to some degree in space projects. It should be remembered that aerospace engineers are part of a team, and not the only skill required. Although engineering has many branches, they all rest on a common foundation of the sciences and mathematics, so there is some overlap between them. For example, aerospace and mechanical engineers analyze loads on space vehicle structures the same way civil engineers analyze them for ground structures. Where they differ is in what materials are used, where the loads come from, and their operating environment.
The remainder of this section lists the other major engineering branches. We will not go into great detail about them, but a space systems designer, whether generalist or specialist, should at least know what other areas exist besides their own. They can then find detailed information on a topic, or find specialists as needed, when it is beyond their own area of knowledge. For those who want to learn more about a particular area, one place to start is the Massachusetts Institute of Technology (MIT) OpenCoursewWare website, which has an increasingly large collection of college level open source course material available (about 2250 so far). Additional information can be found through the links below or in the References Section at the end of this book.
This is the primary field concerned with the design of systems which operate in the atmosphere and space. It is further divided into Aeronautics, having to do with flight and operation in an atmosphere, and Astronautics, having to do with travel and operation in the space environment. The latter is the primary subject of this book. An introductory course on this subject is Introduction to Aerospace Engineering and Design (MIT). Aerospace engineering work is also divided into specialties according to how travel is accomplished, the environment that systems travel through and operate in, and the internal subsystems which make up vehicles and other space hardware. These specialties include:
In general physics and engineering, dynamics is the evolution of physical processes with time. General courses on this subject include:
Within aerospace engineering these particular areas of dynamics are important:
- Aerodynamics - uses knowledge of fluid and gas dynamics as applied to the interactions of atmospheres with primarily solid objects such as vehicles. Vehicles going to space, or returning from it, must traverse the Earth's atmosphere. Some transport methods also actively use the atmosphere, and some destinations in space have their own atmospheres to be navigated. A combination of high velocity and atmospheric density can create large forces and high temperatures. These must be accounted for in design. Natural movements of atmospheres, such as wind and Gravity Waves, fall under the operating environment for aerospace systems. Relevant online courses include:
- Astrodynamics - which is also known as Orbital Mechanics, is the application of ballistics and Celestial Mechanics to practical problems. Celestial mechanics is the branch of astronomy that deals with the motions of natural objects in space. Space systems that are not using propulsion, nor interacting with atmospheres or magnetic fields, follow the same motions as natural objects. The path a system follows, called a Trajectory or Flight Path, can be set up with periods of natural motion under gravity, and periods of active propulsion. The natural motion can include coasting between objects, and Gravity Assists, which are close passes of a larger object to affect velocity and direction. Relevant online courses are:
Structures and MechanismsEdit
Structures and mechanisms are the load bearing and mechanical parts of an aerospace system. The primary structure carries the main loads from gravity, acceleration, aerodynamic forces, etc. Secondary structure holds equipment items in position, which are lesser loads. Mechanisms are the moving parts of the system, such as joints and actuators. Typical mechanisms do steering for a rocket engine, or unfolding and pointing of solar arrays. Aerospace engineers can specialize in this design area, but they have significant overlap with Structural and Mechanical Engineers, who also deal with load-bearing structures. The specific knowledge for aerospace systems involves operating conditions like high accelerations, vibrations, large temperature ranges, and exposure to vacuum. It also involves specialty materials to save weight. These are used for performance and program cost reasons. Underlying knowledge for this system includes Materials Science, which covers the relationship between the structure of materials at atomic scale and their larger scale properties, and the selection of materials for particular applications. It also includes Solid Mechanics, which is the behavior of continuous solid matter under external actions, such as forces, temperature changes, or applied movements. Modern design of structures and mechanisms is usually performed with computer-aided software, and increasingly is integrated in process. This goes from defining the shape of parts, to analysis and simulation, optimization, and then submitting design files to computer-controlled factory equipment to produce them. Once designed, a structural Test Article is often built to prove the physical version can withstand all the design conditions. Relevant online courses for this subject include:
Power and Electrical SystemsEdit
This system is concerned with the supply of power, and electrical systems such as heaters and motors, with respect to aerospace systems in particular. It overlaps with Electrical Engineering, which is the more general subject (see below). Some space equipment needs high levels of power for a short time, like during launch of a chemical rocket. This can be produced by an Auxiliary Power Unit which uses a turbine and chemical fuel. For longer-term needs, solar arrays and sometimes nuclear sources are currently used. Selection of power sources for space projects requires understanding their operating environment, need for long-term operation without maintenance, and other special conditions. Once generated, the power may be stored temporarily in devices like Batteries, and in all cases is distributed through cabling, with fault protection, switching, regulation, and control.
Propulsion Systems in general include a source of power, and means over converting this power to propulsive force. The purpose of these systems is moving people or goods over some distance, usually as part of a Vehicle, an artificial carrier. Space Propulsion are the methods of propulsion useful for space projects. Some of them only work in space. Others work in an atmosphere or on the surface of an object, and are then similar to methods used on Earth. A wide variety of space transport methods are listed in Part 2 of this book. Not all of them involve vehicles with propulsion systems. For the ones that do, chemical, electrical, nuclear, and other power sources are used. So a variety of engineering specialties are involved in their design. Aerospace propulsion engineers have specific experience in one or more of the space transport methods, as opposed to transport methods used on Earth. Relevant online courses include:
Thermal Control SystemsEdit
The air and space environment, and the operation of internal systems, can generate wide variations of temperature. The main natural source of heat is the Sun, which is nominally 36% more intense in space due to lack of atmosphere, but varies according to distance. Secondary heat can come from reflection or thermal emission from nearby large objects. The main source of loss is the Cosmic Background, which is in all directions in the sky behind individual foreground objects. It consists mainly of the Cosmic Microwave and Cosmic Infrared Backgrounds. Their combined emission is about 3 K above absolute zero, or -273 C. This is colder than most space hardware, so more heat is lost to the background than gained from it. Besides the natural environment, operating hardware that makes up a space system can generate waste heat. In the case of propulsion systems this can be extremely large amounts.
Thermal Control Systems have the function of keeping all parts of an operating system within acceptable temperature ranges. This includes passive methods that work because of their inherent properties, such as insulation, coatings, thermal couplers and isolators, reflectors, and radioisotope heaters. Active methods use devices like electric heaters, heat transfer fluids and radiator panels, mechanical louvers, and thermoelectric coolers.
Heat transfer in general is a topic of physics, and addressed by mechanical engineering (see below), but specific problems and conditions in aerospace require specialized solutions. Some relevant online courses include:
When an air or space system is operating, these are the parts which make it behave in desired ways. It includes sensors and instruments to detect the current status, devices to transmit, store, and process the data thus generated, methods to generate the appropriate response, and to transmit commands to other parts of the system to change their operation. Typically control systems operate in a Closed Loop fashion. This is where a cycle of detecting status, processing data, issuing commands, and then detecting the new status repeats multiple times. The parts of the control system that are manufactured are are often called Avionics, short for "aviation electronics", even if used in space systems. Human-in-the-Loop control systems include humans as part of their operation. For example, airplane pilots use their eyes, brains, and hands as part of the control loop. Control systems can include the following elements:
- Ground Software
- Data and Communications Hardware
- Flight Software
- Sensors and Instruments
- Artificial Intelligence and Autonomous Operation
- Trained Operators
Relevant online course is:
With respect to space systems in particular, the environment has significantly different conditions than found on Earth. The space environment includes all external factors that can affect a system - such as lack of atmosphere, gravity, and wide temperature fluctuations, among others. The following are particular hazards to humans and space hardware:
- Meteoroid and Debris - Natural and artificial objects that, due to their high relative velocity, can cause damage on impact.
- Radiation - Particles of high enough energy to damage people and equipment. On the Earth's surface we are sheltered by the magnetic field and atmosphere from the naturally high radiation levels that exist most other places in the Universe.
Life Support SystemsEdit
This is the area involving meeting the needs of humans and other living things when they are present in an aerospace system.
Life support keeps humans alive. Human factors considers people as a functioning element of a system. That includes how to design control inputs and information displays, maintaining crew training on a long mission. Relevant online course is:
Simulation and TestEdit
Aerospace systems are often complex, and the conditions in which they operate are different than those normally found on the Earth's surface. Thus one distinct area has developed to simulate the conditions, and how the system will function within them, electronically before building hardware. Another distinct area is to test physical components, models, and materials in the proper conditions, and Flight Test, which is testing the entire system to see if it operates properly. For very large and complex systems, such as the International Space Station, there was no way to test it as a whole. Therefore testing it's parts on the ground, extensive analysis, and the ability to repair or update ones that needed improvement has to suffice.
Other Engineering SpecialtiesEdit
The following are major conventional divisions of the engineering field into specialties, listed alphabetically. Knowledge in general does not have such divisions, they are made by humans for historical and teaching purposes. A given engineer may have knowledge and work that spans across multiple specialties or is concentrated in a narrow area within only one.
Biological Engineering, or "Bioengineering" applies knowledge from the biological sciences towards satisfying human needs. This includes producing food, materials, energy, maintaining human health, and the natural environment. As an engineering field it has developed rapidly since about 1960, because of the increased understanding of genetics, and development of tools to manipulate it.
Agricultural Engineering is the subset of Bioengineering concerned primarily with food, wood, fibers, biofuel, medicinal, and other material products produced on land. As a human activity, Agriculture extends back to the origin of civilization. As one based on scientific knowledge it has greatly improved in the last 200 years, and as an engineering field extends back to about 1900.