In the context of aviation and aerospace, the "Aerial Common Sensor" (ACS) refers to a proposed unmanned aerial vehicle (UAV) or manned aircraft system designed to perform various Intelligence, Surveillance, and Reconnaissance (ISR) missions for the United States military.

The Aerial Common Sensor program was initiated in the early 2000s by the US Army and the US Air Force to develop a common, multi-mission aircraft that could be used for a variety of tasks, including:

1. Intelligence, Surveillance, and Reconnaissance (ISR)
2. Communications Relay
3. Electronic Warfare (EW)
4. Battle Management

The ACS was intended to be a modular, open-architecture system that could be easily configured to meet specific mission requirements. It would have been equipped with advanced sensors, such as radar, electro-optical, and infrared sensors, as well as communication systems to transmit data in real-time.

The ACS program was envisioned to provide a common platform for various military branches, reducing development and operational costs, and enhancing interoperability between different services. However, the program faced significant technical and financial challenges, and it was ultimately canceled in 2006 due to cost overruns, technical issues, and changing military priorities.

Although the Aerial Common Sensor program was not successful, the concept of a multi-mission, modular aircraft system has continued to evolve, and similar initiatives have been pursued in various forms, such as the US Army's Enhanced Medium Altitude Reconnaissance and Surveillance System (EMARSS) and the US Air Force's MQ-9 Reaper UAV program.