NROL-129 - Naval Ocean Surveillance System (NOSS) 2020
A Northrop Grumman Minotaur 4 solid propellant rocket launched the NROL-129 mission for the National Reconnaissance Office on 15 July 2020 at 9:46 a.m. Eastern from NASA’s Wallops Flight Facility in Virginia. The NROL designations refer to the launch, not to the payload. The flight aimed southeast toward a likely 43 deg inclination low Earth orbit. The classified NROL-129 mission carried four remote sensing payloads 2020-046A through 2020-046D. The NROL-129 mission is represented by two launch patches featuring two warrior figures working together to defend our nation’s interests and deny enemies sanctuary. The patches include the phrase “Our Time has Come,” which symbolizes that these payloads will enable the NRO’s continued support to both defense and intelligence operations in support of national security.
NROL-129 was the first Minotaur mission from Wallops since 2013 and the second orbital launch from the Mid-Atlantic Regional Spaceport (MARS) launch pads in 2020. Minotaur rockets have been launched from Wallops for nearly 14 years. The launch was awarded in late 2017 and was planned for fall 2019, but was delayed to July 2020. The Minotaur 4 debuted in 2010. It can launch payloads of up to 1,730 kilograms to low Earth orbit. NRO booked two more Minotaur launches scheduled for 2021, NROL-111 and NROL-174.
The National Reconnaissance Office (NRO) is an Intelligence Community element and Department of Defense organization responsible for developing, acquiring, launching and operating America’s reconnaissance satellites, as well as operating associated data processing facilities in support of national security. Using NRO data, the National Security Agency, National Geospatial-Intelligence Agency, and other NRO mission partners produce intelligence products for the President, Congress, national policymakers, warfighters, and civil users. The NRO uses a variety of satellites to meet these mission needs.
Signals Intelligence (SIGINT) is intelligence gathering by interception of signals, whether it be communication between people (Communications Intelligence, abbreviated to COMINT) or electronic signals not directly used in communication. It provides wide-area situational awareness and intelligence gathering by means of collection, identification, categorisation and geo-location of complex emitters. Airborne COMINT significantly improves the efficiency of monitoring and intelligence missions.
Surveillance from space has long been a concern of naval commanders at sea. Not only can it identify a naval task force as a possible military target, but it may also lead to an unwanted confrontation with possibly far greater military and political consequences. Ships at sea are potentially subject to many kinds of surveillance. Traditionally, the important components of a surveillance system have been aircraft, shipping, submarines, land-based radar, and communications sensors. In recent years, however, surveillance systems have added land-based acoustic sensors and earth-orbiting satellites with varied sensing capabilities.
The presence of satellites with surveillance capabilities greatly diminishes the effectiveness of a track plan which is intended to circumnavigate areas of the ocean where surveillance is likely. Since surveillance satellites can cover all areas of the ocean, a track plan by itself would be an ineffective countermeasure for satellite surveillance. The task force commander can, however, predict a satellite's motion and use that information to his advantage. The ephemeris data for an adversary satellite is either known or can be calculated from observation data. The ground track, which is traced out by movement of the satellite's sub-orbital point across the earth's surface, can then be predicted with precision. The satellite's ground track will usually intersect the commander's track plan at regular, predictable intervals.
A typical non-synchronous satellite with surveillance capabilities normally has an orbital period of about ninety minutes. The time interval between successive detection zones is roughly equal to one orbital period, depending on the angle of inclination between the ships' track plan and the satellite's ground track. Furthermore, from the vantage point of the task force commander, each detection zone lasts for only a few minutes because the satellite moves so quickly; for a satellite having a ninety-minute orbital period and an effective swath diameter of 1,000 nautical miles, the ships' exposure time to surveillance would be less than four minutes.
Radio interferometers known in the art obtain the angular position of a radio source by measuring the difference in radio path lengths from a source to each of a group of antennas. Radio interferometer systems generally comprise antennas spaced apart by a distance called base and equal to a few wavelengths of the incoming signal. The antennas are respectively coupled to phase measurement devices for determining the relative phase shift between the signals received by each antenna. The knowledge of this phase shift enables to determine the direction of a source, which is, for example, a warship.
Generally, the source concerned is extremely remote and the signal-to-noise ratio is small, thus setting a limit to the system sensitivity. To increase sensitivity, phase correlation is generally used which necessitates the use of a third antenna. The latter is inter-posed halfway between the two antennas, to give a third signal whose phase is taken as a reference. However, under certain conditions, it is not possible to use a third antenna, for example for technological reasons.
A radio interferometer comprising: a first and a second aerial for collecting the signal from a remote source for measuring the phase shift between said signal as respectively collected by said first and said second aerial; a first and a second chain, identical to each other, respectively connected to said first and second aerials, said first and second chains comprising respectively in series a plurality of mixers and amplifier stages and a first and second output, respectively; frequency translating means connected to said mixers of said first and said second chains for deriving from said signal, as respectively picked up by said aerials, a first and a second wave of the same low frequency having respective phase shifts with respect to a reference phase.
The addition of another baseline, normal to the first, provides a second angle to the radio source. All of the angle measurements are made as direction cosines. Accordingly, two such measurements allow the third direction cosine to be calculated, to determine the angular position of the radio source. Obviously, it is desirable and necessary to obtain radio wave phase data which is more accurate to calculate the exact position of the radio source.
It is known to use a pair of antennas to detect the location of an electromagnetic signal. The pair of antennas is arranged such that the spacing between the two antennas is such that the phase difference of the signals arriving at the antennas can be calculated using Bragg's law. The phase difference of the incident electromagnetic signal at the two antennas can be measured and the location of the electromagnetic signal can then be determined from the angle at which the signals approach the two antennas using Bragg's law.
