Contents
Spacecraft subsystems
A
spacecraft system comprises various subsystems, dependent upon mission
profile. Spacecraft subsystems may include: attitude determination and
control (variously called ADAC, ADC or ACS), guidance, navigation and
control (GNC or GN&C), communications (COMS), command and data
handling (CDH or C&DH), power (EPS), thermal control (TCS),
propulsion, structures, and payload.
- Life support
- Spacecraft intended for human spaceflight must also include a life support system for the crew.
- Attitude control
- Spacecraft need an attitude control subsystem to be correctly oriented in space and respond to external torques and forces properly. The attitude control subsystem consists of sensors and actuators,
together with controlling algorithms. The attitude control subsystem
permits proper pointing for the science objective, sun pointing for
power to the solar arrays and earth-pointing for communications.
- GNC
- Guidance refers to the calculation of the commands (usually done by
the CDH subsystem) needed to steer the spacecraft where it is desired to
be. Navigation means determining a spacecraft's orbital elements
or position. Control means adjusting the path of the spacecraft to meet
mission requirements. On some missions, GNC and Attitude Control are
combined into one subsystem of the spacecraft.
- Command and data handling
- The CDH subsystem receives commands from the communications
subsystem, performs validation and decoding of the commands, and
distributes the commands to the appropriate spacecraft subsystems and
components. The CDH also receives housekeeping data and science data
from the other spacecraft subsystems and components, and packages the
data for storage on a solid state recorder
or transmission to the ground via the communications subsystem. Other
functions of the CDH include maintaining the spacecraft clock and
state-of-health monitoring.
- Power
- Spacecraft need an electrical power generation and distribution
subsystem for powering the various spacecraft subsystems. For spacecraft
near the Sun, solar panels are frequently used to generate electrical power. Spacecraft designed to operate in more distant locations, for example Jupiter, might employ a Radioisotope Thermoelectric Generator
(RTG) to generate electrical power. Electrical power is sent through
power conditioning equipment before it passes through a power
distribution unit over an electrical bus to other spacecraft components.
Batteries are typically connected to the bus via a battery charge
regulator, and the batteries are used to provide electrical power during
periods when primary power is not available, for example when a Low Earth Orbit (LEO) spacecraft is eclipsed by the Earth.
- Thermal control
- Spacecraft must be engineered to withstand transit through the Earth's atmosphere and the space environment. They must operate in a vacuum with temperatures potentially ranging across hundreds of degrees Celsius
as well as (if subject to reentry) in the presence of plasmas. Material
requirements are such that either high melting temperature, low density
materials such as Be and C-C or (possibly due to the lower thickness
requirements despite its high density) W or ablative C-C composites are
used. Depending on mission profile, spacecraft may also need to operate
on the surface of another planetary body. The thermal control subsystem
can be passive, dependent on the selection of materials with specific
radiative properties. Active thermal control makes use of electrical
heaters and certain actuators such as louvers to control temperature ranges of equipments within specific ranges.
- Propulsion
- Spacecraft may or may not have a propulsion subsystem, depending upon whether or not the mission profile calls for propulsion. The Swift
spacecraft is an example of a spacecraft that does not have a
propulsion subsystem. Typically though, LEO spacecraft (for example Terra (EOS AM-1) include a propulsion subsystem for altitude adjustments (called drag make-up maneuvers) and inclination
adjustment maneuvers. A propulsion system is also needed for spacecraft
that perform momentum management maneuvers. Components of a
conventional propulsion subsystem include fuel, tankage, valves, pipes,
and thrusters.
The TCS interfaces with the propulsion subsystem by monitoring the
temperature of those components, and by preheating tanks and thrusters
in preparation for a spacecraft maneuver.
- Structures
- Spacecraft must be engineered to withstand launch loads imparted by
the launch vehicle, and must have a point of attachment for all the
other subsystems. Depending upon mission profile, the structural
subsystem might need to withstand loads imparted by entry into the atmosphere of another planetary body, and landing on the surface of another planetary body.
- Payload
- The payload is dependent upon the mission of the spacecraft, and is
typically regarded as the part of the spacecraft "that pays the bills".
Typical payloads could include scientific instruments (cameras, telescopes, or particle detectors, for example), cargo, or a human crew.
- Ground segment
- The ground segment, though not technically part of the spacecraft,
is vital to the operation of the spacecraft. Typical components of a
ground segment in use during normal operations include a mission
operations facility where the flight operations team conducts the
operations of the spacecraft, a data processing and storage facility,
ground stations to radiate signals to and receive signals from the
spacecraft, and a voice and data communications network to connect all
mission elements.
- Launch vehicle
- The launch vehicle is used to propel the spacecraft from the Earth's surface, through the atmosphere, and into an orbit, the exact orbit being dependent upon mission configuration. The launch vehicle may be expendable or reusable.
Sumber:
1. Wikipedia
2. http://astrophysicsblogs.blogspot.com/2008/09/25.html
