TheNaval Ocean Surveillance System (NOSS) is a series ofsignals-intelligencesatellites that have conductedelectronic signals intelligence for theU.S. Navy since the early 1970s.^[1] The first series of satellites were codenamed "White Cloud" or "PARCAE", while second- and third-generation satellites have used the codenames "Ranger" and "Intruder".

The system is operated by the United States Navy, and its main purpose wastacticalgeolocation ofSoviet Navy assets during theCold War. NOSS involvessatellite clusters operating inlow Earth orbit to detect radar and other electronic transmissions from ships at sea and locate them using thetime difference of arrival technique.^[2]

The first generation of NOSS satellites was developed by theNaval Research Laboratory (NRL) based on the previous generations of electronic listening satellites:Grab (1960–1962) andPoppy (1962–1971). Eight clusters of 3 satellites were launched between 1976 and 1987.^[3]

Each launch carried out by anAtlas F,E orH) with a dispenser placed three sub-satellites into orbit. The dispenser is responsible, thanks to itssolid propellant engine, for placing the three sub-satellites into their operational orbit of 1,050 × 1,150km with an inclination of 63°. To be able to track ships, the three satellites maintain a triangular formation with a distance between 30 and 240 km .

Each satellite has on one of its faces a series of antennas intended to collect the signals emitted by ships which are kept constantly turned towards the Earth. The satellite's orientation is maintained bygravity gradient pointed towards the Earth thanks to a boom 10 to 15 meters long.

The second generation of NOSS satellites, first launched in 1990, adopted the same configuration as the previous generation. The satellites were launched in clusters of three with aTitan Launch Dispenser (TLD) responsible for positioning them in their operational orbit (1,100 × 1,100  km with an inclination of 63.4°) and adopted a triangular configuration.

Four NOSS-2 cluster launches took place between 1990 and 1996 (one failure in 1993).[4]^[5] The satellites were much heavier and had to be launched by aTitan IV rocket.

The dispenser played a secondary role: after ejecting the NOSS satellites, it placed itself in an elliptical orbit (1,100 × 9,000  km) where a dedicated telecommunications module (Satellite Launch Dispenser Communications System orSLDCOM) was used for tactical military telecommunications.

The third generation was deployed after 2001. Unlike previous generations, the satellites are launched and operate in pairs and don't require a dispenser. The combined mass of a satellites pair is 6,500  kg. The orbit is identical to previous generations: 1,100 × 1,100km with an inclination of 64°.

Eight pairs of satellites were launched between 2001 and 2017.[6] The launchers used wereAtlas II,Atlas III andAtlas V.

Note: * One satellite from each third generation pair is officially catalogued as debris.[1][2]

The costs of the NOSS satellites (excluding costs for the launch vehicle), which were destroyed in a Titan IV launch failure in 1993, were US$800 million (inflation adjusted US$ 1.7 billion in 2024).^[8]

• Poppy (satellite)
• Yaogan
• CERES (satellite)

• NOSS @ astronautix.com
• BBC – h2g2 – Naval Ocean Surveillance Satellites – a 'UFO'

• Reconnaissance satellites of the United States
• Signals intelligence satellites
• Military space program of the United States
• Satellite series
• Military equipment introduced in the 1970s
• Derelict satellites orbiting Earth

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