Aerospace Design

ABSTRACT: Aerospace design is crucial to the development and manufacturing of aircraft and spacecraft. Since the introduction of aircraft in the nineteenth century, aerospace design has led to the production of countless flight vehicles, including spacecraft used for space exploration. Aerospace design involves a design process, which may take several years to complete. The phases of this process typically are system/mission requirements, conceptual design, preliminary design, and critical design. With spacecraft, the design generally includes major components such as the mission payload and the platform. The design of the Space Shuttle is one good example.

FIELDS OF STUDY: Aerospace Engineering, Astronautics; Space Technology

Learning to Fly

The term "aerospace" refers to Earth’s atmosphere and the space beyond. Aerospace design or aerospace engineering is the branch of science and technology that focuses on creating and manufacturing effective aircraft and spacecraft. Aerospace design is divided into two subfields: aeronautic design and astronautical design. Aeronautic design refers to the creation of machines that fly in Earth’s atmosphere. Astronautical design deals with designing and developing spacecraft and their launch vehicles, generally powered by highly powerful rockets. The aerospace industry caters to military, industrial, and commercial consumers.

The history of aerospace design begins with the history of aviation. The first powered lighter-than-air craft existed as early as the 1850s. Jules Henri Giffard (1825–82) invented a steam-powered airship in 1852. Ferdinand von Zeppelin (1838–1917) introduced rigid airships in 1900; they came to be known as "zeppelins" and later as "blimps." Brothers Orville (1871–1948) and Wilbur Wright (1867–1912) designed a heavier-than-air, piloted airplane that is generally credited as the first of its kind to execute a successful powered flight, in 1903. Air flight designs continued to progress throughout the twentieth century, paving the way for the development of rotary winged aircraft such as helicopters, which use revolving wings or blades to lift into the air. Powerful air flight engines that fuel modern aircrafts did not emerge until the mid-twentieth century.

At the same time that engine design was advancing, aerospace engineers also began developing machinery that would take humans to the upper atmosphere and into space. Konstantin Tsiolkovsky (1857–1935), known as the Russian father of rocketry, was a pioneer of astronautics with his insightful studies in space travel and rocket science. American engineer Robert Goddard launched the first liquid-fueled rocket in 1926. Goddard continually improved his rocket design over the years. His calculations contributed to the development of other rocket-powered devices, such as ballistic missiles. Tsiolkovsky and German scientist Hermann Oberth (1894–1989) independently made similar breakthroughs in the same time period.

During World War I and World War II, aerospace design saw rampant progress as military engineers pursued higher performance aircraft design. In particular, advances in rocket research during World War II laid the foundation for astronautics. Continued advances in aerospace design were spurred by the Cold War and the space race between the United States and the Soviet Union. The competition to reach outer space led to the launch of the first spacecraft, Sputnik I, by the Soviet Union in 1957. The United States established the National Aeronautics and Space Association (NASA) in 1958. Aerospace engineers designed a wide range of spacecraft to explore space, incorporating new technologies and capabilities as they became available. For example, in 1969, an American-made spacecraft successfully sent astronauts to the moon, which marked the first time humans landed on the moon. Many other spacecraft have been used to carry out missions elsewhere in the solar system. Artificial satellites have proven critical to twenty-first-century communications systems and become widespread with a variety of designs and functions.

Design Process

The design process of a spacecraft generally occurs in the following phases: system/mission requirements, conceptual design, preliminary design, and critical design. Some of these phases can take years to complete. In the system/mission requirements phase, the requirements of the spacecraft are addressed. The type of mission the spacecraft will be used for helps determine these requirements, as specific tasks may dictate certain design elements. For example, a deep space probe would require a significantly different design than a weather monitoring satellite.

The conceptual design phase deals with several possible system concepts that could fulfill the requirements of the mission. These concepts are first conceived and then analyzed. After the most suitable concept is chosen, costs and risks are examined and schedules are made.

The preliminary design phase involves several tasks. Variations of the selected concept are identified, examined, and improved. Specifications for each subsystem and component level are identified. The projected performance of the systems and subsystems is analyzed. Documents are composed, and an initial parts list is put together. This phase may run for several years, depending on the novelty and complexity of the mission.

Lastly, the critical design phase, or detailed design phase, takes place. During this phase, the detailed characteristics of the structural design of the spacecraft are established. Equipment, payload, the crew, and provisions are all taken into account. Plumbing, wiring, and other secondary structures are reviewed. Various tests involving design verification are performed, including tests of electronic circuit models and software models. Design and performance margin estimates are improved. Test and evaluation plans are settled. Like the preliminary design phase, the critical design phase may take several years to complete.

Once the design process has been completed, the spacecraft can finally be built. It is then tested before being delivered for use.

Typical Components

Most spacecraft share two key components: the mission payload and the platform, or the bus. The mission payload includes all of the equipment that is specific to the mission, such as scientific instruments and probes, rather than general operation. The platform comprises all other parts of the spacecraft, used to deliver the payload. It consists of several subsystems, including the structures subsystem, thermal control subsystem, electrical power subsystem, attitude control subsystem, and telemetry, tracking, and commanding (TT&C) subsystem.

The structures subsystem serves various functions such as enclosing, supporting, and protecting the other subsystems, as well as sustaining stresses and loads. It also provides a connection to the launch vehicle. Two main types of structure subsystems exist: open truss and body mounted. The open-truss type typically has the shape of a box or cylinder, while the body-mounted type does not have a definite shape. The choice of structural materials is an important consideration in aerospace design. Light, durable, and heat-resistant materials, such as aluminum, titanium, and some plastics, are typically used.

The thermal control subsystem regulates the temperature of the spacecraft’s components. This helps guarantee that the components function properly throughout the mission. Different components require different temperatures. Thermal control systems may be active or passive. Active thermal control involves the use of electrical heaters, cooling systems, and louvers. Passive thermal control includes the use of heat sinks, thermal coatings and insulations, and phase-change materials (PCM). With passive thermal control, electrical power is not needed and there are no moving parts or fluids.

The electrical power subsystem provides the power the spacecraft needs for the duration of the mission, which can last for years. In most cases, the subsystem includes the following components: a source of energy; a device that converts the energy into electricity; a device that stores the electrical energy; and a system that conditions, charges, discharges, distributes, and regulates the electrical energy. The source of energy is generally solar radiation, nuclear power, or chemical reactions.

The attitude control subsystem deals with the process and hardware necessary for obtaining and sustaining the proper orientation in space, or attitude. It has several functions, including maintaining an orbit (station keeping), adjusting an orbit, and stabilization. That subsystem typically includes navigation sensors, a guidance section, and a control section. As with thermal control, the attitude control may be either active or passive. Active attitude control uses continuous decision making and hardware that are closed loop. This includes the use of thrusters, electromagnets, and reaction wheels. Passive attitude control uses open-loop environmental torques to sustain attitude, such as gravity gradient and solar sails.

The telemetry, tracking, and commanding (TT&C) subsystem involves communication with operators on the ground. Telemetry uses a radio link to transmit measurement data to those operators. It is typically used for improving spacecraft performance and for monitoring the health of the spacecraft, including the payload. Tracking and commanding deals with the spacecraft’s position. Tracking is used to report the spacecraft’s position to the ground station, while commanding is used to change the spacecraft’s position. Some common tracking methods are the use of a beacon or a transponder, Doppler tracking, optical tracking, interferometer tracking, and radar tracking and ranging. Commanding is achieved through coded instructions that the ground station sends to the aircraft.

Practical Example

A good example of aerospace design is that of the Space Shuttle, officially called the Space Transportation System (STS). In 1969, US president Richard Nixon established the Space Task Group to study the United States’ future in space exploration. Among other things, the group envisioned a reusable spaceflight vehicle. It was not long before NASA, along with industry contractors, began the design process of such a vehicle. The process involved numerous studies, including design, engineering, cost, and risk studies. Some of the studies focused on the concepts of an orbiter, dual solid-propellant rocket motors, a reusable piloted booster, and a disposable liquid-propellant tank.

In 1972, the design of the Space Shuttle was moved forward. It would feature an orbiter, three main engines, two solid rocket boosters (SRBs), and an external tank (ET). The orbiter would house the crew, the SRBs would provide the shuttle’s lift at the beginning of its flight, and the ET would hold fuel for the main engines. All of the components would be reusable, except for the ET, which would be jettisoned after launch. Refinements continued to be made as the project continued and systems were tested.

The first orbiter spacecraft, named Enterprise, was completed in 1976 and underwent several flight tests. However, Enterprise was merely a test vehicle and was not used for any actual space missions. In 1981, the first Space Shuttle mission took place. Columbia lifted off from the Kennedy Space Center and became the first orbiter in space. Over the next several decades, several shuttles successfully performed many space missions.

PRINCIPAL TERMS

• attitude control: the process of obtaining and sustaining the proper orientation in space.
• mission payload: the extra equipment carried by a craft for a specific mission. For a launch vehicle, payload usually refers to scientific instruments, satellites, probes, and spacecraft attached to the launcher.
• platform: all parts of a spacecraft that are not part of the payload; also known as the bus.
• telemetry: the process of transmitting measurement data via radio to operators on the ground. Telemetry is used to improve spaceflight performance and accuracy. It provides important information about standard operational health and status of a craft as well as mission-specific payload data.
• thermal control: the system aboard a spacecraft that controls the temperature of various components to ensure safety and accuracy during a mission.
• tracking and commanding: tracking takes account of a craft’s position in relation to the ground base with transponders, radar, or other systems. Commanding refers to the ground station sending signals to a craft to change settings such as ascent and orbit paths.

Bibliography

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