Spacecraft are vehicles designed to explore outer space. Piloted or unpiloted, spacecraft are deployed into orbit for collecting data or carrying out other functions that must withstand its harsh environment.
Reentry requires spacecraft to withstand intense frictional forces that create intense heat; to protect itself against this risk, spacecraft must feature a thick body.
Definition
Spacecraft is a general term referring to piloted and unpiloted vehicles designed for travel through Earth’s outer atmosphere and space, usually piloted by pilots but sometimes unpiloted vehicles as well. Sometimes more specific names may apply depending on their function or mission profile.
Crewed spacecraft may be known as spaceships and their passengers astronauts (American) or cosmonauts (Russian). Additionally, there is also an uncrewed class known as space telescopes which observe celestial objects from orbit rather than using Earth-bound telescopes where light pollution obfuscates their observations.
Spacecraft require considerable propulsion capabilities in order to escape Earth’s gravity and reach space. Once in space, however, their propulsion force needs no medium against which to generate propellant force; so they utilize three small rockets distributed along their three planes for maneuverability.
Functions
Spacecraft have various subsystems that comprise its operation. These include attitude determination and control (ADC or ACS); guidance, navigation and control (GNC or GN&C); communications; power; command and data handling (CDH).
CDH subsystem serves various functions on board spacecraft. These include transmitting science and housekeeping data back to Earth via radio frequencies as well as receiving instructions for on-board systems from ground stations using high gain antennas called communications.
Figure 8.6 provides an energy-time spectrogram of plasma particle data collected by NASA Van Allen Probe A spacecraft. The HOPE H+ differential number flux can be clearly observed as a silver line in this spectrogram with an energy channel width of 400eV; both instruments were aware of this event.
Design
Engineers designing spacecraft must keep four key factors in mind when developing spacecraft: cost, time, performance and reliability. These four criteria help define the scope and scale of each project while making their iteration possible.
Spacecraft must be capable of maneuvering effectively in space to function. To this end, their navigation and control subsystems must calculate necessary commands that allow a spacecraft to meet its goals – using sensors and actuators as necessary.
Bus is the term used for the structure of a spacecraft that serves as the platform to attach other subsystems, like instrument modules and avionics, as well as appendages like booms and antennas. Furthermore, this bus defines its geometry while housing delicate modules requiring mechanical and thermal stability as well as providing power support for subsystems and appendages.
Materials
Spacecraft components must be designed to withstand the extreme environment of space, from temperature fluctuations that may reach hundreds of degrees Celsius to radiation that could damage parts and pose health risks to astronauts.
Most spacecraft utilize graphite-epoxy composites for structural elements. These composites come in various orientations and fiber concentrations to offer various properties like strength, rigidity and low thermal expansion.
Many spacecraft feature solar wings to position onboard instruments so they face towards the Sun; some also carry drogue parachutes for slowing and stabilizing descent, and ion drives or nuclear engines can alter trajectory as needed. All require power sources that may include solar panels or storage batteries for onboard power management.
Technology
Space technology encompasses all the techniques necessary for the construction, operation and control of satellites and other space vehicles as well as human spaceflight missions, planetary exploration activities and scientific studies.
Spacecraft require propulsion in the form of conventional chemical rockets, ion drives or nuclear generators in order to alter their trajectory, while power is needed for operating equipment and communications systems such as the drum-shaped Meteosat or nonspining box satellites that may be painted white to reflect sunlight.
Spacecraft require heat shields to withstand the high temperatures encountered upon entry to Earth’s atmosphere and radiation exposure, as well as extreme cold temperatures. They must also be designed specifically for specific tasks with their components tailored for that environment; national and international regulations also must be abided by when using this technology.