Ground segment

A ground segment consists of all the parts on Earth that help control and support spacecraft. It is different from the spacecraft itself, called the space segment, and the tools people use to get information, called the user segment. The ground segment is very important because it lets people manage spacecraft and share important information, like data from experiments and messages from the spacecraft.

The main parts of a ground segment include special stations on Earth that talk to spacecraft using radio waves, places where teams watch over and guide the spacecraft, and computers used by people who help with the mission. There are also places where spacecraft are put together and tested, areas where they are launched into space, and networks that help all these parts talk to each other.

These ground segment parts are used in almost every space mission, whether it is for business, the military, or science. The parts can be in the same place or far apart, and sometimes different groups run them. Some parts can even help more than one spacecraft at the same time.

Elements

Ground stations

Main article: Ground station

Ground stations help connect spacecraft in space with people on Earth. They send and receive important information using radio waves. Networks like NASA’s Near Earth Network and Space Network can talk to many spacecraft at once by sharing time.

These stations can often be controlled from far away, and they usually have backup stations ready if something goes wrong.

Transmission and reception

Before sending messages to a spacecraft, the information is changed into radio waves. These waves travel through the air to the spacecraft. When messages come back, they are changed back into useful data and checked for mistakes.

One spacecraft might use different radio frequencies for different kinds of information.

Passes

The times when a ground station can talk to a spacecraft depend on where the station is and the path the spacecraft takes in space. Some networks use special satellites to talk to spacecraft even when they are far away.

Tracking and ranging

Ground stations need to know where a spacecraft is to aim their antennas properly. They also check how far away the spacecraft is and make sure everything is working well.

Mission control centers

See also: List of mission control centers

Mission control centers are where people watch over spacecraft and send them important commands. They check the spacecraft’s health, talk to crews if there are people on board, and keep records of everything that happens. Like ground stations, there are often backup control centers in case something goes wrong.

Telemetry processing

Control centers look at the information sent back from spacecraft to see how everything is doing. They sort the information, check for mistakes, and turn numbers into useful data. They also watch for any problems and show the data in easy-to-understand ways.

Commanding

Commands to spacecraft are carefully prepared and checked before being sent. They can be sent right away or as part of a planned set of instructions. The spacecraft usually send back a message saying they got the command.

Analysis and support

Mission control centers also plan where the spacecraft will go, check for possible problems, and keep track of how everything is doing over time.

Staffing

People work at mission control centers all the time or during important moments, like when the spacecraft is starting its journey. Sometimes, computers can handle a lot of the work, but people are ready to step in if needed.

Remote terminals

Remote terminals are special places on the ground where different teams, like scientists and engineers, can look at spacecraft data or send messages. These are separate from the main mission control center.

Terminals used by everyday people, like for TV or phones, are called the “user segment.” These either talk directly to spacecraft or use the ground segment to send and receive data.

Integration and test facilities

Before a spacecraft is sent to space, it is put together and tested at special facilities. This makes sure that the spacecraft and the ground systems can talk to each other and work well before the launch.

Launch facilities

Launch facilities are where rockets take off. They connect to the ground network to send important information during the launch. The rocket itself is sometimes called a “transfer segment” because it moves things between Earth and space.

Ground networks

Ground networks are like roads for information, letting different parts of the ground system talk to each other. They use many ways to connect, like special lines or secure online paths. It’s very important that these networks are reliable and safe, so they often have backup parts and strong security to keep data protected.

Costs

The cost of setting up and running a ground segment can change a lot. One study found it makes up about 5% of the total cost of a space system. Another report showed that operating costs alone are about 8% of the total cost of a space mission. Other costs include integration and testing (3.2%), ground facilities (2.6%), and ground systems engineering (1.1%).

Costs for the ground segment depend on the need for buildings, equipment, software, networks, security, and staff. The cost of ground stations depends on how strong the signal needs to be, which radio frequencies are used, and whether existing buildings can be used. Some control centers use automation to save on staff costs.

Images

• Antenna belonging to the Deep Space Network

Space Telescope Operations Control Center at [Goddard Space Flight Center](/wiki/Goddard_Space_Flight_Center), during servicing of the [Hubble Space Telescope](/wiki/Hubble_Space_Telescope)

Integration of flight hardware at a [JAXA](/wiki/JAXA) facility in [Tsukuba](/wiki/Tsukuba,_Ibaraki), Japan

Decommissioned launch site at the [Guiana Space Centre](/wiki/Guiana_Space_Centre)