Origin

Spacecraft design was born as a discipline in the 50s and 60s with the advent of American and Russian space exploration

Space exploration

Space exploration is the use of space technology to explore outer space. Physical exploration of space is conducted both by human spaceflights and by robotic spacecraft....

 programs. Since then it has progressed, although typically less than comparable terrestrial technologies. This is for a large part due to the challenging space environment, but also to the lack of basic R&D, and to other cultural factors within the design community. On the other hand, another reason for slow space travel application design is the high energy cost, and low efficiency, for achieving orbit. This cost might be seen as too high a "start-up-cost."

Indeed the shallow view is that we have been to the Moon, we have space stations, we have workable planetary orbital space craft, and we can get to Mars if someone put up the funding. What seems to be needed next is an efficient way to achieve orbit.

Areas of Engineering Covered

The design of spacecraft

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

 covers a broad area, including the design of both robotic spacecraft

Robotic spacecraft

A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...

 (satellite

Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

s and planetary probes), and spacecraft for human spaceflight

Human spaceflight

Human spaceflight is spaceflight with humans on the spacecraft. When a spacecraft is manned, it can be piloted directly, as opposed to machine or robotic space probes and remotely-controlled satellites....

 (spaceship

Spacecraft

A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

s and space station

Space station

A space station is a spacecraft capable of supporting a crew which is designed to remain in space for an extended period of time, and to which other spacecraft can dock. A space station is distinguished from other spacecraft used for human spaceflight by its lack of major propulsion or landing...

s). The design of spacecraft is somewhat related to the design of rocket

Rocket

A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...

s and missile

Missile

Though a missile may be any thrown or launched object, it colloquially almost always refers to a self-propelled guided weapon system.-Etymology:The word missile comes from the Latin verb mittere, meaning "to send"...

s.

Spacecraft design brings together aspects of various disciplines, namely:

• Astronautics
  Astronautics
  Astronautics, and related astronautical engineering, is the theory and practice of navigation beyond the Earth's atmosphere. In other words, it is the science and technology of space flight....
  
  for mission design and derivation of the design requirements,
• Systems engineering
  Systems engineering
  Systems engineering is an interdisciplinary field of engineering that focuses on how complex engineering projects should be designed and managed over the life cycle of the project. Issues such as logistics, the coordination of different teams, and automatic control of machinery become more...
  
  for maintaining the design baseline and derivation of subsystem requirements, said subsystems listed below:
• Communications engineering for the design of the Telemetry
  Telemetry
  Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...
  
  , Tracking, and Command (TTC) subsystem, which uses technologies and techniques of terrestrial radio
  Radio
  Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
  
   and digital communications to communicate with the ground, and to perform Ranging
  Ranging
  Ranging is a process or method to determine the distance from one location or position to another location or position. Another term for this method is lateration, see unilateration...
  
  .
• Computer engineering
  Computer engineering
  Computer engineering, also called computer systems engineering, is a discipline that integrates several fields of electrical engineering and computer science required to develop computer systems. Computer engineers usually have training in electronic engineering, software design, and...
  
  for the design of the On-Board Data Handling
  On-Board Data Handling
  The On-Board Data Handling subsystem of a spacecraft is the subsystem which carries and stores data between the various electronics units and the ground segment, via the Telemetry, Tracking and Command subsystem....
  
   (OBDH) subsystem, which includes on-board computers and computer bus
  Computer bus
  In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
  
  es. This subsystem is mainly based on terrestrial technologies, but unlike most of them, it must: cope with space environment, be highly autonomous and provide higher fault-tolerance.
  • It may incorporate space qualified radiation-hardened
    Radiation hardening
    Radiation hardening is a method of designing and testing electronic components and systems to make them resistant to damage or malfunctions caused by ionizing radiation , such as would be encountered in outer space, high-altitude flight, around nuclear reactors, particle accelerators, or during...
    
     components.
  • It may use techniques to further improve fault-tolerance, such as use of watchdog timers
    Watchdog timer
    A watchdog timer is a computer hardware or software timer that triggers a system reset or other corrective action if the main program, due to some fault condition, such as a hang, neglects to regularly service the watchdog A watchdog timer (or computer operating properly (COP) timer) is a computer...
    
    .
• Software engineering
  Software engineering
  Software Engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software, and the study of these approaches; that is, the application of engineering to software...
  
  for the on-board software which runs all the on-board applications, as well as low-level control software. This subsystem is very similar to terrestrial real-time and embedded software designs,
• Electrical engineering
  Electrical engineering
  Electrical engineering is a field of engineering that generally deals with the study and application of electricity, electronics and electromagnetism. The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical...
  
  for the design of the power subsystem, which generates, stores and distributes the electrical power
  Electric power
  Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt.-Circuits:Electric power, like mechanical power, is represented by the letter P in electrical equations...
  
   to all the on-board equipments,
• Control theory
  Control theory
  Control theory is an interdisciplinary branch of engineering and mathematics that deals with the behavior of dynamical systems. The desired output of a system is called the reference...
  
  for the design of the Attitude and Orbit
  Orbit
  In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
  
   Control (AOCS) subsystem, which points the spacecraft correctly, and maintains or changes the orbit according to the mission profile; Although the techniques in AOCS design are common with terrestrial methods, the hardware used for actuation and sensing in space is usually very specific to spacecraft,
• Thermal engineering for the design of the thermal control subsystem, which maintains environmental conditions compatible with operations of the spacecraft equipments; This subsystem has very space-specific technologies, since in space, radiation
  Radiation
  In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
  
   and conduction
  Heat conduction
  In heat transfer, conduction is a mode of transfer of energy within and between bodies of matter, due to a temperature gradient. Conduction means collisional and diffusive transfer of kinetic energy of particles of ponderable matter . Conduction takes place in all forms of ponderable matter, viz....
  
   usually dominate as thermal effects, by opposition with Earth where convection
  Convection
  Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
  
   is typically the main one,
• Propulsion
  Spacecraft propulsion
  Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...
  
   engineering for the design of the propulsion subsystem, which provides means of transporting the spacecraft from one orbit to another. This is the only technology which is really specific to spacecraft design. Popular culture has made a cliché
  Cliché
  A cliché or cliche is an expression, idea, or element of an artistic work which has been overused to the point of losing its original meaning or effect, especially when at some earlier time it was considered meaningful or novel. In phraseology, the term has taken on a more technical meaning,...
  
   of spacecraft propulsion engineers, as embodied by the term rocket science
  Aerospace engineering
  Aerospace engineering is the primary branch of engineering concerned with the design, construction and science of aircraft and spacecraft. It is divided into two major and overlapping branches: aeronautical engineering and astronautical engineering...
  
  ,
• Mechanical engineering
  Mechanical engineering
  Mechanical engineering is a discipline of engineering that applies the principles of physics and materials science for analysis, design, manufacturing, and maintenance of mechanical systems. It is the branch of engineering that involves the production and usage of heat and mechanical power for the...
  
  for the design of the spacecraft structures and mechanisms. These include beams, panels, and deployable appendages or separation devices (to separate from the launch vehicle
  Launch vehicle
  In spaceflight, a launch vehicle or carrier rocket is a rocket used to carry a payload from the Earth's surface into outer space. A launch system includes the launch vehicle, the launch pad and other infrastructure....
  
  ).
• Thermal engineering
  Thermal engineering
  Heating or cooling of processes, equipment, or enclosed environments are within the purview of thermal engineering.One or more of the following disciplines may be involved in solving a particular thermal engineering problem:*Thermodynamics*Fluid mechanics...
  
  for the design of the spacecraft thermal control
  Spacecraft thermal control
  In spacecraft design, the Thermal Control System has the function to keep all the spacecraft parts within acceptable temperature ranges during all mission phases, withstanding the external environment, which can vary in a wide range as the spacecraft is exposed to deep space or to solar or...
  
  , which includes radiators, multi-layer insulation
  Multi-layer insulation
  Multi-layer insulation, or MLI, is thermal insulation composed of multiple layers of thin sheets often used on spacecraft. It one of the main items of the spacecraft thermal design, mainly intended to reduce heat loss by thermal radiation. In its basic form, it does not appreciably insulate...
  
   and electrical heaters to keep all the spacecraft equipment within acceptable temperatures.

Structure

The spacecraft bus carries the payload. Its subsystems support the payload and helps in pointing the payload correctly. It puts the payload in the right orbit and keeps it there. It provides housekeeping functions. It also provides orbit and attitude maintainance, electric power, command, telemetry and data handling, structure and rigidity, temperature control, data storage and communication, if required. The payload and spacecraft bus may be different units or it may be a combined one. The booster adapter provides the load-carrying interface with the vehicle (payload and spacecraft bus together).

The spacecraft may also have a propellant load, which is used to drive or push the vehicle upwards, and a propulsion kick stage. The propellant commonly used is a compressed gas like nitrogen, liquid such as monopropellant hydrazine or solid fuel, which is used for velocity corrections and attitude control. In a kick stage (also called apogee boost motor, propulsion module, or integral propulsion stage) a separate rocket motor is used to send the spacecraft into its mission orbit.
While designing a spacecraft, the orbit which is going to be used should be considered into the point as it affects attitude control, thermal design, and the electric power subsystem. But these effects are secondary as compared to the effect caused on the payload due to the orbit. Thus while designing the mission; the designer selects such an orbit which increases the payload performance. The designer even calculates the required spacecraft performance characteristics such as pointing, thermal control, power quantity, and duty cycle. The spacecraft is then made, which satisfies all the requirements.

Attitude Determination and Control

The attitude determination and control subsystem

Attitude control system

In spaceflight, the attitude control system or attitude determination and control system of a spacecraft consists of equipment to measure, report and change the orientation of the vehicle.- Components :...

 (ADCS) is used to change direction and altitude of the spacecraft. There are some external torque

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

s acting on the spacecraft along the axis passing through its centre of gravity which can reorient the ship in any direction or can give it a spin. The ADCS nullifies these torques by applying equal and opposite torques using the propulsion and navigation subsystems. Moment of inertia of the body is to be calculated to determine the external torques which also requires determination of vehicle's absolute altitude using sensors. The property called 'gyroscopic stiffness' is used to reduce the spinning effect.
The simplest spacecraft achieve control by spinning or interacting with the Earth's magnetic or gravity fields. Sometimes they are uncontrolled. Spacecraft may have several bodies or they are attached to important parts, such as solar arrays or communication antennas which need individual attitude pointing. For controlling the appendage's attitude, actuators are been used, with separate sensors and controllers.
The various types of control techniques used are :

• Passive Control Techniques.
• Spin Control Techniques.
• Three-axis Control Techniques.

Telemetry, Tracking, and Command

Telemetry, tracking, and command (TT&C) is used for communication between spacecraft and the ground systems. The subsystem functions are:

• Controlling of spacecraft by the operator on earth
• Receive the uplink commands, process and send them to other subsystems for implication.
• Receive the downlink commands from subsystems, process and transmit them to earth.
• Inform constantly about the spacecraft position.

Communication

The process of sending information towards the spacecraft is called uplink or forward link and the opposite process is called downlink or return link. Uplink consists of commands and ranging tones where as downlink consists of status telemetry, ranging tones and even may include payload data. Receiver, transmitter and a wide-angle (hemispheric or omnidirectional) antenna are the main components of a basic communication subsystem. Systems with high data rates may even use a directional antenna, if required. The subsystem can provide us with the coherence between uplink and downlink signals, with the help of which we can measure range-rate Doppler shifts. The communication subsystem is sized by data rate, allowable error rate, communication path length, and RF frequency.

Power

The electrical power subsystem (EPS) consists of 4 subunits :

• Power Source (Battery, solar cell, fuelcells, thermoelectric couple)
• Storage unit (No. of batteries in series)
• Power Distribution (Cabling, switching, shock protection)
• Power Regulation and Control (To prevent battery overcharging and overheating)

Thermal

Thermal control subsystem (TCS) is used to maintain the temperature of all spacecraft components within certain limits. Both upper and lower limits are defined for each component. There are two limits, namely, operational (in working conditions) and survival (in non-working conditions). Temperature is controlled by using insulators, radiators, heaters, louvers and by giving proper surface finish to components.

Propulsion

The main function of the propulsion subsystem is to provide thrust so as to change the spacecraft's translational velocity or to apply torques to change its angular momentum. There is no requirement of thrust and hence even no requirement of propulsion equipment in a simplest spacecraft. But many of them need a controlled thrust in their system, so their design includes some form of metered propulsion (a propulsion system that can be turned on and off in small increments).
Thrusting is used for the following purposes: for changing the orbital parameters, to control attitude during thrusting, correct velocity errors, maneuver, counter disturbance forces (e.g., drag), and control and correct angular momentum. The propulsion subsystem includes a propellant, tankage, distribution system, pressurant, and propellant controls. It also includes thrusters or engines.

Spacecraft designing history

Since the last forty years, Spacecraft Design has grown from nowhere to well-defined techniques along with analysis tools, manufacturing technology, and space-qualified hardware.

For designing a spacecraft, we need to understand the mission, Payload's size and characteristics, in addition with the things to which the system is restricted, such as orbit, lifetime, and operations. A spacecraft operated without a crew consists of at least three elements: a Payload, a Spacecraft-bus, and a Booster Adapter.
The payload is somewhat odd kind of equipment used in the mission. It is the combination of hardware and software that interacts with the portion of the outside world that the spacecraft is looking for to succeed in the mission objectives. For each mission, unique payloads are used. The spacecraft bus helps to keep the payload healthy and pointed in the right direction. The spacecraft is connected to its launch vehicle through the Booster Adapter.