Defense Support Program
Defense Support Program (DSP) satellites and associated ground facilities are an aging system of space-based infrared sensors that detect the intense heat of missile launches and nuclear explosions. They do not form images, but are electro-optical MASINT sensors that measure the intensity and wavelengths of radiation in a grid of locations on earth (i.e., spectroscopic MASINT), based on an idea first proposed in 1948 In the program, the first satellite was launched in 1970 and the last in 2007. They are due to be replaced by two variants of the Space-Based Infrared System (SBIRS), one in geosynchronous orbit as is DSP 
Their precessor was the prototype Missile Defense Alarm System (MIDAS). DSP has gone through a variety of names, as has the SBIRS system. Renamed called the Satellite Early Warning System (SEWS) in 1999, DSP remains the best-known name, as the descendant of several generations of spacecraft, which are operated by the Fourteenth Air Force. Originally, DSP was known by the classified name Program 949, and, after that became known, Program 647.
Originally intended to detect the intense heat of an ICBM launch, this system proved useful at a theater level in 1990-1991. It detected the launch of Iraqi SS-1 SCUD missiles in time to give early warning to potential targets.
- J.A. Curcio and J.A. Sanderson (26 July 1948), Further Investigations of the Radiation from Rocket Motor Flames, in Jeffrey Richelson, Space-Based Early Warning: From MIDAS to DSP to SBIR: Last DSP satellite to be launched tomorrow, National Security Archive, George Washington University, Naval Research Laboratory, NRL Report No. N-3327
- Jeffrey Richelson, ed. (9 November 2007), Space-Based Early Warning: From MIDAS to DSP to SBIR: Last DSP satellite to be launched tomorrow, National Security Archive, George Washington University, Electronic Briefing Book No. 235
- Steven Clark (10 December 2009), "First SBIRS early warning satellite delayed until 2011", Spaceflight Now
- Harold Brown (25 June 1962s), Memorandum for the Assistant Secretary of the Air Force (Research and Development), Subject: MIDAS System, in Jeffrey Richelson, Space-Based Early Warning: From MIDAS to DSP to SBIR: Last DSP satellite to be launched tomorrow, National Security Archive, George Washington University
- Jeffrey Richelson (1999), America's Space Sentinels: DSP Satellites and National Security, University of Kansas Press
- Interagency OPSEC Support Staff (May 1996), Operations Security Intelligence Threat Handbook, Section 3, Adversary Foreign Intelligence Operations