CSEM

"CSEM" usually stands for "Co-Spacecraft Electric Field Measurements." Co-spacecraft electric field measurements (CSEM) are measurements of the electric field that are made between two spacecraft that are in close proximity to each other. CSEM is a technique that is used to study the plasma environment in space and to measure the interactions between spacecraft and the plasma.

Plasma is a state of matter in which atoms are ionized and free electrons are present. It is a common form of matter in space, and it can be found in the Earth's magnetosphere, the solar wind, and other regions of the solar system. The electric field of a plasma is an important factor that affects the behavior of spacecraft and other objects in space, and CSEM is used to measure and study this electric field.

CSEM measurements are typically made using specialized instruments and sensors that are installed on the spacecraft. These instruments can include electric field detectors, current sensors, and other sensors that are designed to measure the electric field and its effects on the spacecraft. CSEM measurements are used to improve our understanding of the plasma environment in space and to design spacecraft and other systems that are better able to operate in this environment.

Here are a few examples of spacecraft that have been used for co-spacecraft electric field measurements:

• Cluster: The Cluster mission was a European Space Agency (ESA) mission that involved a constellation of four spacecraft that were used to study the Earth's magnetosphere. The spacecraft were equipped with a variety of instruments, including electric field detectors and current sensors, that were used to make CSEM measurements. The mission was launched in 2000 and operated until 2010.

• MMS: The MMS (Magnetospheric Multiscale) mission is a NASA mission that involves four spacecraft that are used to study the Earth's magnetosphere and the plasma environment in space. The spacecraft are equipped with a variety of instruments, including electric field detectors and current sensors, that are used to make CSEM measurements. The MMS mission was launched in 2015 and is still ongoing.

• Double Star: The Double Star mission was a joint mission between the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS) that involved two spacecraft that were used to study the Earth's magnetosphere. The spacecraft were equipped with a variety of instruments, including electric field detectors and current sensors, that were used to make CSEM measurements. The mission was launched in 2003 and operated until 2010.

• THEMIS: The THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission is a NASA mission that involves a constellation of five spacecraft that are used to study the Earth's magnetosphere. The spacecraft are equipped with a variety of instruments, including electric field detectors and current sensors, that are used to make CSEM measurements. The THEMIS mission was launched in 2007 and is still ongoing.

Overall, these are just a few examples of spacecraft that have been used for co-spacecraft electric field measurements. There have been many other spacecraft missions that have included CSEM as a key component of their scientific objectives.