Directory of U.S. Military Rockets and Missiles
Appendix 3: Space Vehicles
Copyright © 2003-2008 Jos Heyman
(HTML formatting by Andreas Parsch)


The Integrated Missile Early Warning System (IMEWS) or Defense Satellite Program (DSP), was an operational system of military early warning satellites. Built by TRW, the satellites were equipped with television cameras and infrared sensors operating through a Schmidt telescope which was offset from the main axis of the telescope by 7.5° so that, with the satellite spinning at 6 rpm, a conical scanning pattern was achieved. Over several scans this allowed observers to distinguish between a stationary heat source, such as a forest fire, and a moving heat source, such as a missile.

Also known as Code 647 and LS-3A, the first generation of satellites is believed to have carried an array of 2000 infrared sensors whereas the second generation carried 6000 such sensors. The satellites are believed to have had a length of 7.01 m, a diameter of 2.78 m and a mass of 1100 kg. The operational system consisted of five satellites of which three were operational and two in-orbit spares. The locations which have been mentioned in subsequent reference sources included 36°W, 70°W, 85°W, 105°W, 134°W, 72°E and 75°E and it is suggested that satellites were periodically shifted to other locations.

Photo: Author's collection
IMEWS-4 (1973-040A)

IMEWS-10, IMEWS-11 and IMEWS-12 incorporated significant modifications to improve their performance and were designated as LS-3B.

Photo: Author's collection
IMEWS-21 (2001-033A)

The third generation, commencing with IMEWS-14 comprised nine satellites. They had a length of 10 m, a diameter of 4.15 m and a mass of 2500 kg. The operational system consisted of three satellites in geostationary orbit over the Atlantic, Pacific and Indian Oceans. The satellites were equipped with an improved telescope and 6000 infrared sensors with future versions having a capacity of 24,000 sensors. Some or all of the satellites in the series also carried a magnetospheric plasma analyser to measure low-energy ions and plasma, as well as a particle analyser, to measure energetic particles.

Image: USAF

Name Intl. Designation Launch Notes
IMEWS-11970-093A 6-Nov-1970Also known as Ops-5960; failed to achieve correct orbit
IMEWS-21971-039A 5-May-1971Also known as Ops-3811
IMEWS-31972-010A 1-Mar-1972Also known as Ops-1570
IMEWS-41973-040A12-Jun-1973Also known as Ops-6157
IMEWS-51975-118A14-Dec-1975Also known as Ops-3165
IMEWS-61976-059A26-Jun-1976Also known as Ops-2112
IMEWS-71977-007A 6-Feb-1977Also known as Ops-3151
IMEWS-81979-053A10-Jun-1979Also known as Ops-7484
IMEWS-91981-025A16-Mar-1981Also known as Ops-7350
IMEWS-101982-019A6-Mar-1982Also known as Ops-8701
IMEWS-111984-037A14-Apr-1984Also known as Ops-7641
IMEWS-121984-129A22-Dec-1984Also known as USA-7
IMEWS-131987-097A29-Nov-1987Also known as USA-28
IMEWS-141989-046A14-Jun-1989Also known as USA-39
IMEWS-151990-095A13-Nov-1990Also known as USA-65
IMEWS-161991-080B25-Nov-1991Also known as USA-74
IMEWS-171994-084A22-Dec-1994Also known as USA-107
IMEWS-181997-008A24-Feb-1997Also known as USA-130
IMEWS-191999-017A 9-Apr-1999Also known as USA-142; failed to achieve correct orbit
IMEWS-202000-024A 8-May-2000Also known as USA-149
IMEWS-212001-033A 6-Aug-2001Also known as USA-159
IMEWS-222004-004A14-Feb-2004Also known as USA-176
IMEWS-232007-054A11-Nov-2007Also known as USA-197

Launch dates of the IMEWS series

The launches of the last two IMEWS satellites, IMEWS-24 and -25, were cancelled.


The primary objective of the early warning satellite development was to fill the gaps in the coverage provided by the land based Ballistic Missile Early Warning System utilised by the United States to provide an early detection of a missile attack. The system initially consisted of a chain of three large radar stations which observed the USSR.


The Missile Detection And Surveillance (Midas) series of experimental military early warning satellites tested the feasibility of complementing the land based Ballistic Missile Early Warning System. The spacecraft were built by Lockheed and were based on the Agena upper stage. The satellites were equipped with infrared sensors developed by IT&T, which could detect missiles as soon as they would be launched. These sensors had only a limited capability and were not successful.

The first two satellites in the series were placed in relatively low orbits, which was all that could be achieved for the 2000 kg satellite in combination with the Atlas Agena A launch vehicle. Subsequent satellites were lighter (1600 kg) due to the use of solar cells instead of batteries, and did use the Atlas Agena B combination, allowing them to be placed in a higher orbit of about 3500 km, commencing with Midas-3. Midas-2 also carried a magnetometer, a micrometeorite detector and an ion and electron detector as ancillary instruments.

It is believed that the programme was only partially successful due to the limited capability of the sensors that were carried. The Midas series of satellites were also used to place ancillary satellites of a technology nature in orbit, whilst Midas-4 and Midas-7 conducted the Project Westford experiments in communications.

Name Intl. Designation Launch Re-entry Notes
Midas-1---26-Feb-1960--- Failed to orbit
Midas-21960 ζ124-May-19607-Feb-1974  
Midas-31961 σ112-Jul-1961   
Midas-41961 αδ121-Oct-1961  Used in Project Westford
Midas-51962 κ19-Apr-1962   
Midas-6---17-Dec-1962--- Also known as Ops-5201; failed to orbit
Midas-71963-014A9-May-1963  Used in Project Westford
Midas-8---12-Jun-1963--- Also known as Ops-1240; failed to orbit
Midas-91963-030A19-Jul-1963  Failed to separate from ERS-10

Launch dates of the Midas series

Improved Midas

The sensor development undertaken as part of the Midas programme led briefly to a satellite proposal identified as Code 461. This programme was cancelled in favour of the Code 266 programme which the author has labelled as Improved Midas. The three satellites in this series are believed to have tested the use of television cameras in conjunction with the infra-red detectors but may have been unsuccessful.

Photo: Author's collection
Improved Midas-2 (1966-077A)

Name Intl. Designation Launch Re-entry Notes
I. Midas-11966-051A9-Jun-19663-Dec-1966 Also known as Ops-1960 and FTV-1351
I. Midas-21966-077A19-Aug-1966  Also known as Ops-0856 and FTV-1352
I. Midas-31966-089A5-Oct-1966  Also known as Ops-1920 and FTV-1353

Launch dates of the Improved Midas series


For some years it was thought that a series of six satellites launched between 1968 and 1975 were the Ballistic Missile Early Warning System (BMEWS) series to replace the earlier Midas system of military early warning satellites. Also referred to as Code 949, the satellites were thought to have been built by TRW and were reported to be equipped with infrared sensors developed by Aerojet and a television system developed by RCA. Information gathered since then have identified the satellites as part of the Canyon and Rhyolite series of intelligence gathering satellites.

Back to Directory of U.S. Military Rockets and Missiles, Appendix 3

Last Updated: 18 January 2008