Signals intelligence (SIGINT) satellites in the US are developed and launched jointly by the USAF and the National Reconnaissance Office, with the support of the National Security Agency (NSA). The current family is believed to focus on two large satellites based on the Lockheed Martin Milstar bus, supported by smaller Mercury satellites which also exist in data relay versions.
The first US SIGINT satellites were launched in the late 1960s and were based on the same Lockheed Agena bus as the early Keyhole photo-reconnaissance satellites. The USAF sponsored the Canyon series, which had the primary objective of establishing an Electronic Order of Battle (EOB) for the Soviet Union.
The slightly later Hughes Jumpseat, first launched in 1971, was based on the same bus as the Intelsat 4 commercial GTO communications satellite. However, Jumpseat was placed in a highly elliptical orbit (HEO) in order to provide maximum observation time over the northern Soviet Union.
The success of Jumpseat led to the development of Rhyolite, also known as Program 720 and Program 472, which was developed by TRW for the CIA's Science & Technology Directorate and focused on TELINT (telemetry intelligence). The CIA's main goal was to determine the performance parameters of Soviet ICBM and space launch boosters. The first Rhyolite launch took place from Cape Canaveral on 19 June 1970, using an Atlas Agena, but it was reportedly stranded in a transfer orbit. Successful launches followed in March 1973, December 1977, and April 1978. They reportedly carried an antenna with a diameter of approximately 21 m. The dish was kept rigid by a framework grid. Several additional, smaller antennas picked up microwave, radio, radar and telephone signals. The primary downlink station, named Pine Gap, was located near Alice Springs, Australia, to prevent enemy interception of the signals. The signal streams were encrypted, then beamed via another geosynchronous satellite to Fort Meade for code breaking and signal and traffic analysis.
In 1975, TRW's ambitious 3-axis-stabilised Argus (or Advanced Rhyolite) TELINT satellite programme, to be fitted with a 40 m antenna, was cancelled. and its role was absorbed by Rhyolite. Development of an updated version of Argus, code named Aquacade, began in 1979. With a launch mass of 2,270 kg, it was 8 times heavier than Rhyolite. It apparently carried two large dish antennas, one for signals monitoring across the entire radio spectrum and the other for downlink to Alice Springs. It was initially developed with launch by the Shuttle - still to make its maiden flight - in mind. This would have the advantage of allowing a much larger satellite to be launched into low Earth orbit (LEO), and checkout by the astronauts before deployment. However, slips in the Shuttle development schedule led Congress to direct Aquacade to be redesigned for launch on a Titan 34-D/IUS. Nevertheless, the first Aquacade (designated USA 8) lifted off on the Shuttle Discovery on 24 January 1985. An Inertial Upper Stage (IUS) was used to boost it into GEO over a period of five hours. The second Aquacade (USA 48) was launched by the Shuttle on 23 November 1989.
Meanwhile, the US began to design a new SIGINT satellite known as Chalet. Three of these, each with a mass of about 1.2 tonnes, were launched between 1978-1981 by Titan III-C boosters. Their primary mission was to intercept conversations carried on UHF radio links which used antennas oriented in the direction of the stationary orbit, or antennas with wide main lobes. Three upgraded versions, known as Vortex, were launched between 1984-1989. They could apparently intercept radio frequencies in the centimetric band. With a mass of 1.4-1.6 tonnes, they were launched by Titan 34D boosters. The second of these did not reach its operational orbit due to a failure of the transfer stage.
The pinnacle of US SIGINT satellite development was the adaptation of Lockheed's Milstar bus to the SIGINT role, creating a 5,200 kg intelligence collection platform capable of surviving a full- scale nuclear war. It existed in two versions. The HEO version, with Boeing as prime integrator, was called Trumpet. Launched from Cape Canaveral by Titan IV on 3 May 1994 (USA 103), 10 July 1995 (USA-112) and 8 November 1997 (USA 136), their payload was probably developed in parallel with Milstar in 1983-91. In addition to its SIGINT role, Trumpet also served as the polar component of the Milstar communications system. The satellites flew in a 1,100 × 39,059 km (Molniya-like) orbit, inclination 63.6°. They apparently carry a large (100 m diameter?) deployable mesh antenna designed and built by Harris Corporation.
The GEO satellite was called Mercury, also known as Advanced Vortex. Three Mercurys were built. The first two were launched on 27 August 1994 (USA 105), and 24 April 1996 (USA 118). The third, on 12 August 1998, was a failure.
The latest GEO version is generally reported to be called Orion, often known as Advanced Orion. The name Mentor has also been used. The first launch of this series (USA 110) took place on a Titan IV-Centaur from Cape Canaveral on 14 May 1995. Others followed on 9 May 1998 (USA 139) and 9 September 2003 (USA 171). The most recent launch (USA 202 / NROL-26) took place on 18 January 2009 (GMT). Since the Titan IV was no longer in production, it was launched to GEO by a Delta IV Heavy fitted with a 5 m diameter fairing. The combined cost of the NROL-26 spacecraft and booster was said to be more than USD2 billion. Both USA-171 and USA-202 were launched well beyond their original planned dates, largely due to launcher problems. Launches of Trumpets and Advanced Orions were distinguished by the 26 m Titan IV payload shroud versus the 23 m shroud for Mercury. Spacecraft launch mass is 5 to 6 tonnes and design life is eight to 12 years.
In 1998 the NRO announced plans to combine the three separate classes of Sigint satellites into an Integrated Overhead SIGINT Architecture (IOSA) in order to "improve SIGINT performance and avoid costs by consolidating systems, utilising.new satellite and data processing technologies." IOSA was designed specifically to integrate the large Trumpet and Advanced Orion satellites to create the Intruder. The follow-on IOSA-2 architecture would have added LEO SIGINT satellites using Time Difference of Arrival (TDOA) geolocation techniques. However, the IOSA-2 programme was cancelled in September 2000 due to projected cost.
The NROL-15 launch of 29 June 2012 is suspected to be the eighth satellite in the Orion (Advanced Orion) series since May 1995, but the use of an upgraded Delta IV Heavy with higher thrust suggested that a modified version of the satellites may have been delivered to GEO.
Launches of a new series of SIGINT satellites to Molniya orbits began in 2006. USA 184 (NROL- 22) was launched by a Delta IV-M+(4,2) on 28 June 2006, and USA 200 was launched by an Atlas V 411 on 13 March 2008. The name of the new programme is not known, but it is generally known by observers as Advanced Trumpet, Improved Trumpet, or Trumpet Follow-On since they appear to be replacements for the Trumpet series. In addition to the SIGINT payloads, these spacecraft were equipped with NASA's TWINS magnetospheric research instruments and SBIRS-HEO missile detection sensors.
The most recent addition to the series in Molniya orbits was NROL-35 (USA 237), which was launched from Vandenberg Air Force Base on 13 December 2014. The Atlas V 541 Centaur upper stage was fitted with an RL10C engine for the first time. NROL-35 is thought to carry the third SBIRS-HEO instrument, but it did not carry a TWINS payload.
The Intruder (NOSS-3), the third generation of the NOSS satellites carry equipment to track ships and aircraft via their radio transmissions. Positions of the origin of the transmissions are determined by triangulation. Each launch consists of two satellites of similar size in the same orbit, and both satellites manoeuvre to keep station relative to one another. The most recent launch was NROL-55 (USA 264) on 8 October 2015.
Jane's Space Systems and Industry