Orbital Spacecrafts
Satellites, man-made objects launched into space, play a crucial role in our daily lives and scientific understanding. These celestial tools are designed for specific purposes, such as communication, Earth observation, weather monitoring, and navigation, and operate in various orbits tailored to different applications.
Types and Purposes of Satellites
Communication satellites, like Optus D1, provide services such as television, telephone, internet, and military communication. Ranging from tiny microsatellites (less than 1 kg) to large satellites (over 6,500 kg), they can offer a wide array of telecommunication services.
Remote sensing satellites capture imagery and data about Earth's surface and atmosphere for environmental monitoring, resource management, disaster response, and weather forecasting. Optical sensors detect sunlight reflected or emitted by Earth, while active sensors like radar provide detailed information even in cloudy or dark conditions. Examples of remote sensing satellites include Landsat and Sentinel-2, which offer high-resolution imaging with spectral bands covering visible, near-infrared, and thermal ranges.
Weather satellites monitor weather patterns and provide data for short- and mid-term forecasts and severe storm tracking. They employ visible, infrared, and water vapor channels for observations. The GOES series satellites, for instance, offer continuous coverage over the Americas and surrounding oceans.
Navigation satellites, like those in the GPS constellation, provide global positioning and timing services. They typically orbit at medium Earth altitudes.
Scientific and experimental satellites are used for space science research, Earth atmosphere studies, and space environment monitoring.
Common Satellite Orbits and Their Uses
Satellites primarily orbit the Earth in three common orbits: Low Earth orbit (LEO), Medium Earth orbit (MEO), and Geostationary orbit (GEO).
Low Earth orbit (LEO) extends from 160 to 2,000 km. LEO satellites are ideal for high-resolution Earth observation, remote sensing, and some communication satellites. However, due to their quick orbits, they provide smaller coverage but detailed images, requiring tracking antennas. Examples of LEO satellites include Landsat and Sentinel-2, which orbit at approximately 700–800 km.
Medium Earth orbit (MEO) extends from about 2,000 to 35,786 km. MEO satellites are mainly used for navigation (GPS, Galileo) and some weather satellites. They have longer orbital periods, and fewer satellites are needed for global coverage compared to LEO.
Geostationary orbit (GEO) is at 35,786 km above the Earth, with a time for one orbit being 24 hours to match the rotation of the Earth. Satellites in GEO orbit synchronously with Earth rotation, remaining fixed over one point, making them ideal for continuous communication and weather monitoring. Only three satellites are needed to cover the entire globe in GEO.
Polar orbits, such as those used by polar-orbiting weather satellites, circle the Earth's poles at approximately 833 km. They offer global coverage as Earth rotates beneath, making them useful for broader weather monitoring and environmental sensing.
Basic Components of Satellites
Satellites consist of two primary components: the payload and the bus or system. The payload is the instruments or devices performing the satellite's mission, such as cameras, sensors, or transponders for communication or remote sensing. The bus or system is the platform supporting payload operation, including power systems, thermal control, attitude control, propulsion, communication systems, data handling and processing units, and batteries for energy storage.
Satellites are essential tools for our modern world, providing invaluable services and expanding our understanding of space and Earth. Companies like Rocket Lab, founded by New Zealander Peter Beck, aim to make space more accessible by providing affordable rocket launch services, furthering the reach and potential of satellite technology.
