To get into space, a satellite would use rocket motors. Once in the correct position, the satellite would use thrusters to stay in that position. Otherwise, solar wind, gravitational effects of the Earth and Moon, as well as Earth’s magnetic field could cause the satellite to drift off-course. Because there is nothing in space to stop a satellite from moving, if it got knocked off course it would continue in that direction forever, or until it fell into Earth’s orbit in another place. For the rocket motors and thrusters, a satellite would also need a source of fuel. One piece of equipment not included in this cart is the fuel tank that would be required if these propulsion elements used chemical fuel.
To face in the correct direction, the satellite would need what is called an attitude control system. This system is necessary because again, even the slightest external force could send the satellite spinning, and nothing would cause it to stop. One way to stabilize the satellite is to force it to spin. The rotation builds up angular momentum, which makes it more resistant to being knocked out of alignment by a tiny external force. These satellites are usually cyclindrical in shape and are known as spin-stabilized satellites, or spinners. A disadvantage of spinners is that there must be equipment to “despin” instruments such as cameras, so that they are not constantly whirling around when taking pictures.
Another way to stabilize the satellite is three-axis stabilization, which uses special gyroscopes known as reaction wheels or momentum wheels. These are small wheels inside the satellite that can spin in either direction. One way this works is to have three small wheels responsible for the three axes of space, each of which can spin in either direction when the satellite’s attitude equipment detects misalignment.
The mechanisms for attitude control are not included in this cart. Although they are an important part of the satellite, we had to limit the equipment available so as not to overwhelm visitors with too many props and concepts that are not central to the understanding of the general concepts of remote sensing.
Parts of a Satellite | Maneuvering | Power Supply | Thermal Controls | Communications Devices | OCO-2 and ASCENDS | NASA Missions