Section 1.7 - Engineering Specialties

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 other major engineering branches with some relevance to space projects. 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) OpenCourseWare website, which has an increasingly large collection of college level open source course material available (about 2250 so far). We list a number of their courses below, but they are not an exclusive source. Additional information can be found through the links below, the References Section at the end of this book, and the huge number of books written on engineering topics.

Aerospace Engineering

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:

Dynamics

In general physics and engineering, dynamics is the evolution of physical processes with time. General courses on this subject include:

• Dynamics (MIT)

• Aerospace Dynamics (MIT)

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:

• Aerodynamics (MIT)
• Aerodynamics of Viscous Fluids (MIT)
• Compressible Flow (MIT)

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:

• Astrodynamics (MIT)

Structures and Mechanisms

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:

• Structural Analysis and Design (MIT)

• Computational Methods in Aerospace Engineering (MIT)

• Plates and Shells (MIT)

• Computational Mechanics of Materials (MIT)

Power and Electrical Systems

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

Propulsion Systems in general include a source of power, and means of converting this power to propulsive force. The purpose of these systems is to move people or goods over some distance, usually as part of a Vehicle, an artificial carrier. Space Propulsion is 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. A variety of engineering specialties are therefore 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:

• Introduction to Propulsion Systems (MIT)

• Rocket Propulsion (MIT)

• Space Propulsion (MIT)

Thermal Systems

Thermal Systems have the function of keeping all parts of an space 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.

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 this varies according to distance. Secondary heat can come from reflection or thermal emission from nearby large objects. The main source of heat 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 effective temperature is about 3 K above absolute zero, or -273 C. This is much 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 heat or be very cold. For example propulsion systems can do both - generating large amounts of heat in a rocket engine, while having cryogenic temperatures in the propellant tanks.

Thermal control engineers analyze spacecraft environments and operations to determine what temperatures will occur. If hardware plus natural heat results in an unacceptable temperatures, then thermal control is required, and these engineers help design the solutions. Heat transfer in general is a topic of physics, and is addressed as a design task by mechanical engineers (see below), but specific problems and conditions in aerospace require specialized solutions. Some relevant online courses include:

• Thermal Energy (MIT)

• Radiative Transfer (MIT)

Control Systems

Control Systems Engineering is the specialty that applies Control Theory to design active systems with desired behaviors. Since most space systems have active components, they also need control elements. These include 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. The commands are implemented by actuators, such as a valve in a rocket engine that controls fuel flow. 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 manufactured parts of aerospace control systems 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 are used in everything from traffic lights to chemical plants, so the subject is taught to all kinds of engineers. Aerospace controls specialists deal with the particular problems of air and space operations, such as control of a rocket in flight, or a space system's robot arm. Some relevant online aerospace courses include:

• Principles of Automatic Control (MIT)

• Feedback Control Systems (MIT)

• Prototyping Avionics (MIT)

Space Environment

The Space Environment has a number of significantly different conditions than found on Earth. These must be accounted for in space systems design, and so specialists in environment effects on systems and people are needed. The space environment includes all external factors that can affect a system - such as free fall (zero gravity) or low gravity; vacuum, rarefied, or different atmospheres, which can cause drag, erosion, or electrostatic charging, and wide temperature fluctuations. Particular hazards to humans and space hardware are unique to space. They include:

• Meteoroids and Space Debris - Natural and artificial objects that, due to their high relative velocity, can cause damage on impact.

• Space 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 Solar System. Sources include Cosmic Rays, high energy particles and photons from the Sun, and trapped Radiation Belts around objects with magnetic fields. Artificial nuclear devices used in space can increase radiation levels, and thicknesses of mass or magnetic fields can shield from it.

Study of the space environment is part of the science of Astronomy, especially Astrophysics and Planetary Science. These fields have benefited greatly from space science missions, which have allowed measuring the environment directly. Environment effects engineers often come from the sciences first, then apply their knowledge to space projects. Alternately, they start from an engineering specialty, then add the relevant scientific knowledge, often at a graduate level.

Life Support Systems

The space environment is generally hostile to humans, and life in general. For space projects that involve living things, a Life Support System is then needed to provide suitable conditions. Basic structure contains an atmosphere, and thermal control keeps temperatures in a habitable range. These were covered previously. Beyond this, humans need the right atmosphere mix, water, and food. Because of the closed environment, liquid, solid, and gaseous wastes (including especially CO₂) must be removed, both from people and other system operations, and microbes controlled. In free fall conditions air does not circulate by convection, so circulation fans are needed to prevent "dead zones" where harmful concentrations of gases can accumulate. Biological systems can be used to recycle wastes and supply food, like they do on Earth, but this is still in early research. Most life support systems to date have single-use supplies of food, and limited recycling of other materials.

Engineering of life support systems is cross-disciplinary, involving both biology and mechanical systems. Specialists therefore come from areas like Bioengineering and Mechanical Engineering (see below). They typically learn about the specific design of life support on the job, because there are so few examples of life support for space that it has not developed an educational path yet. Related work is done for airplanes, high altitude climbing, and working underwater. Life support systems can be large enough for a number of people, or small enough for a single person, as in a space suit.

Human Factors

Human Factors, also is the aspect of design that takes account of the interaction of a system and the people who use it. People can't be designed the way a piece of hardware can, so the system design has to accommodate their capabilities and limitations. The people may be passive, as in airplane passengers, or active, as in the flight crew. Subject areas in this field include physical, cognitive, and organizational interactions. Because of the unique conditions in space, like having to do repairs while in zero gravity and a bulky space suit, or working with a large support team on the ground, the various subject areas have assumed importance in aerospace. Human factors also includes topics like how to design control inputs and information displays for zero gravity or high acceleration, and how to maintain crew training on a long mission.

The roots of human factors design extend as far back as people have made tools, since the tools must fit our hands, and the strength we have to wield them. The modern development draws from disciplines like psychology, engineering, biomechanics, industrial design, physiology, and anthropometry. A relevant online course is:

• Human Factors Engineering (MIT)

• Human Control of Automated Systems (MIT)

Simulation and Test

Aerospace systems are often complex, and therefore expensive. The environment and operating conditions in which they operate are different and more severe than those normally found on the Earth's surface, and failures can be catastrophic. So to ensure basic functionality, safety, reliability, and meeting design requirements, the Simulation and System Test specialties have developed.

Simulation includes early mathematical and computational modeling, and physical scale models or functional simulators. They reproduce important aspects of a system, but do not use the actual hardware and software products. Testing uses actual materials, components, subsystems, up to completed products. Test can be in simulated environments, like a Vacuum Chamber, or in the actual operating environment. For complete aerospace vehicles, the latter is called Flight Test. For very large and complex systems, such as the International Space Station, there was no way to test it as a whole. Instead its parts were tested on the ground, extensive analysis was performed, and the ability to repair and update parts as needed had to suffice.

The Hardware and Software test planning should ideally start early in a project. Specialists in these areas are often drawn from the respective design fields, and from Systems Engineering experience.

Other Engineering Specialties

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 experience that spans across multiple specialties or is concentrated in a narrow area within only one. Where we listed individual courses for specialties within aerospace engineering above, the larger engineering fields tend to have whole academic departments or even entire institutions devoted to them.

Bioengineering

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. The MIT Department of Biological Engineering lists a number of open courses on this subject.

Agriculture

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. Growing plants in space is at an early experimental stage. This is expected to increase greatly in coming decades, since growing food and other products, and production of oxygen as a by-product, would greatly reduce supplies needed from Earth.

Biomedical Engineering

Biomedical Engineering applies engineering principles and design concepts to medicine and biology for healthcare purposes. It is a relatively new field with a heavy emphasis on research and development. For space projects, it is applied to keep crew and research animals in good condition, and also a subject of research on the effects of space conditions.

Chemical Engineering

Chemical Engineering is the application of physical and life sciences, and applied mathematics and economics, to produce, transform, transport, and properly use chemicals, materials, energy, and useful products. It is a broad field with many specialized branches, and typically has a full set of courses at schools such as MIT's Department of Chemical Engineering. Historically, the relevance to space projects has been supplying propellants for rockets, and the alloys and other materials to build them and their payloads. In the future, extracting fuel and other products from space locations will require modified versions of chemical plants.

Civil Engineering

Civil Engineering deals with the design, construction, and maintenance of the built environment, including roads, bridges, canals, dams, and buildings. As an empirical practice it is as old as Civilization (both words derive from the Latin civitas, or city). As a scientific and technical field it began around 1800. For space projects to date it is mostly related to factory locations and launch sites on Earth. In the future it will be applied to construction at locations beyond Earth. As one of the older engineering fields, it typically has a full set of courses, such as at MIT's Department of Civil and Environmental Engineering. Branches of civil engineering include Environmental, Geotechnical, Structural, Transport, and Water Resources Engineering. Since all the materials used to build with must be obtained from the natural environment, it is closely related to Mining Engineering (see below).

Electrical Engineering

Electrical Engineering deals with the applications of electricity, electromagnetism, and electronics. It became an identifiable field after about 1850. Most space systems have electrical components, and the specialized aspects are noted above under aerospace engineering. More general electrical engineering is used today in supplying power to offices, factories, and launch sites for space projects. It is also used in computer hardware, software, and communications networks for development and operation of space systems. Future uses include electric launch and space propulsion methods, and solar power delivery from orbit. As one of the larger fields, it has a range of courses, such as at MIT's Department of Electrical Engineering and Computer Science

Industrial Engineering

Industrial Engineering deals with the optimization of complex processes or systems, and improvement of productivity, quality, efficiency, and profitability of businesses. Traditionally it encompassed planning of industrial production systems (factories), but has broadened in scope to a wide range of complex operations. Industrial is distinguished by being concerned with the whole business and supply chain, where manufacturing engineering (part of mechanical below) is concerned with individual production machines and tasks.

Mechanical Engineering

Mechanical Engineering applies the principles of physics and materials science for the design, analysis, manufacturing, and maintenance of mechanical systems. Specialized mechanical systems for space are listed above under aerospace engineering. Other specialties include acoustical, manufacturing, thermal, sports, vehicle, power, and energy engineering. Mechanical systems such as turbopumps and valves are core elements of rocket engines. Wheels, suspensions, drive motors, and robot arms enable rovers to perform complex tasks on planet surfaces. As a modern technical field, mechanical engineering has grown since about 1800, with the development of Machine Tools and engines to drive them. As one of the largest engineering fields today, it has a very large range of courses, such as at MIT's Department of Mechanical Engineering

Mining Engineering

Mining Engineering is concerned with extracting and processing minerals from the natural environment. Modern civilization uses vast quantities of materials. So this field of engineering, and closely related sciences, have developed to support those uses. At present, mining on Earth is not directly related to space projects, as raw materials are normally processed by intermediate factories and plants before being used to build hardware. This may change with the development of integrated and automated production systems. In space itself, extracting materials is of great interest to avoid the high energy and financial cost of launch from Earth, and making available new sources of materials and energy. Mining in space is still in the research and early development stage.

Nuclear Engineering

Nuclear Engineering is concerned with applications of nuclear processes like fission and fusion. These processes can release very large amounts of energy. On Earth the primary use is for power generation in Nuclear Reactors. Some space missions today carry sources based on radioactive decay. In the future fission and possibly fusion reactors can supply power when solar is insufficient. Nuclear engineering deals with high energy radiation, which also is part of the natural space environment. Although a fairly new field, dating to the 1940's, it has developed extensive specialized knowledge, such as courses from MIT's Department of Nuclear Science and Engineering.

Software Engineering

Software Engineering is the systematic application of engineering methods to the design, development, and maintenance of Software - the changeable instructions and data that computers use. This field is young, only developing from about 1950, but has rapidly grown due to the rapid advance of computer hardware and electronics in general. Software is an integral part of modern space projects, from initial concept formulation using Productivity Software, to collection and analysis of mission data and control of remote spacecraft. Essentially all engineers use software, and many develop software as part of their work in other specialties. However creating complex and reliable software, where the consequences of errors mean loss of life or expensive systems, requires teams of specialists dedicated to the task. Software engineering is closely related to Computer Science, and their teaching is often combined in one set of courses, like at MIT's Department of Electrical Engineering and Computer Science.