What is a reconnaissance satellite that uses photoelectric remote sensors to capture images of ground targets?

Photographic reconnaissance satellites are reconnaissance satellites that use photoelectric remote sensors to capture images of ground targets.

Photographic reconnaissance satellites are divided into two types: return type and transmission type according to the way in which reconnaissance information is sent back to the ground:

(1) Return type photoreconnaissance satellite: after taking pictures of the ground The film is stored in a recovery container on the satellite. After the earth photography mission is completed, the recovery container leaves the orbit and returns to the ground. Film can be recovered at sea, on land or in the air. Return-type satellites use the principle of film imaging to carry out reconnaissance photography. The images have high resolution, are intuitive, and are easy to analyze and identify.

(2) Transmission photographic reconnaissance satellite: Use the principle of photoelectric imaging to carry out reconnaissance photography. The image information is first recorded on the tape, and then the image information is sent to the ground when flying to the control area of ??the ground station.

Photographic reconnaissance satellites have the following characteristics:

(1) Orbit: They all adopt nearly circular low orbits, with altitudes generally below 300 kilometers. Some are used to obtain higher altitudes. Ground resolution, the altitude is reduced to 150 to 160 kilometers when taking pictures. Some satellites choose sun-synchronous orbits.

As long as the launch time is chosen appropriately, satellite Earth photography will have better lighting conditions, which is particularly beneficial to the interpretation of photos. Sometimes, in order to conduct repeated observations of strategic targets, the selected sun-synchronous orbit is also used as a return orbit.

(2) Control: Earth photography in orbit requires high-precision attitude control and stability control of the ground orientation in order to obtain relatively clear satellite reconnaissance photos. At the time of photography, the attitude control accuracy of the satellite is about 0.1 degrees, and the stability accuracy is about 0.001 degrees/second.

For long-term working photographic reconnaissance satellites, orbit control is required to maintain a certain orbital life. When necessary, a certain power compensation is given to the satellite to overcome the impact of atmospheric drag perturbation and the oblateness of the earth on the orbit.

(3) Ground resolution: The resolution of photos or TV images obtained by photographic reconnaissance satellites is relatively high. Long focal length optical systems are often used on satellites and the satellite's photographic height is lowered to improve ground resolution. The focal length of the "Big Bird" satellite camera is 2.44 meters, and the ground resolution is about 0.3 meters.