The History of Space Radar - A Brief Survey of Radar Capabilities

By Maschenka Braganca

Airborne reconnaissance systems have been used since WWII to collect imagery, signals and measurement intelligence (IMINT, SIGINT, MASINT) and utilize photography, radar or . They are typically based on an airframe that is modified to carry a radar system that downlinks radar data directly to users in a theater of operations, i.e. to a communication and command station.

Radar is an object-detection system that uses electromagnetic waves (radio- or microwaves) to determine the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, maritime vessels, spacecraft, missiles and terrain. How this works is that the radar dish or antenna transmits short pulses of radio waves that bounce off any object in their path and the object returns a part of the wave's energy. On receiving its echoes, it then transmits another pulse and receives its echoes. This out-and-back cycle is repeated depending on the configuration of the radar. There are different types of radars, including those for weather, air traffic control and navigation. The type used for most intelligence, surveillance and reconnaissance (ISR) purposes is the early warning radar that can be ground-based, airborne or space-based. It is used primarily for the long-range detection of targets and allows for early alert of defenses, but serves many other purposes such as long-term surveillance or even treaty verification.

The most common technologies currently utilized for these capabilities are the synthetic aperture radar (SAR) and the ground moving target identification (GMTI). The SAR has been a technology used since the 1950s. It works in the same way as described above with the addition that pulses are transmitted from multiple spots while the SAR travelled on an aircraft or satellite and later get combined to create an image of larger coverage of certain terrain.

The moving target indication (MTI or GMTI) mode of operation of a radar allows to discriminate a target with respect to stationary clutter. For a sequence of radar pulses the moving target will be at different distance from the radar and the phase of the radar return from the target will be different for successive pulses, while the stationary clutter will always send back the same wave.

Airborne radar capabilities

A few examples of the most well-known airborne platforms that are involved in the collection of electronic intelligence (ELINT) in use right now are:

AWACS (Airborne Warning and Control System) for the air picture

AWACS or AEW&C (airborne early warning and control) are airborne radar systems designed to detect aircraft at long ranges, distinguish whether they are hostile and friendly and direct control and command for friendly aircraft. Its basic functions are situational awareness, surveillance and cooperation with command and control. Examples of these are the E-3 Sentry and the Hawkeye that have a Boeing 707/Northrop Grumman airframe that is modified to the AWACS configuration by carrying a rotating disk radar dome.

   The E-3 Sentry                                                             The E-2 Hawkeye

JSTARS (Joint Surveillance, Targeting, and Attack Radar System) for the ground situation

JSTARS is a joint development project of the US Air Force and Army for airborne surveillance and; it tracks ground vehicles and some aircraft, collects imagery, and relays tactical pictures to ground and air theater commanders. The airframe for the JSTARS is the Boeing 707-300 and has an attached radar antenna that can provide wide area surveillance, and utilizes SAR as well as GMTI. It can look from a long range, which the military refers to as a high standoff capability. It was first used in Operation Desert Storm 1991.

Rivet Joint aircraft for signals and communications intercept

The Rivet Joint reconnaissance aircraft supports theater commanders with near real time intelligence collection, analysis and dissemination capabilities. The Rivet Joint uses a modified Boeing RC-135 airframe with onboard sensors, which enables the mission crew to detect, identify and geo-locate electromagnetic signals and communications, snooping on enemy transmissions and radar emissions. The Rivet Joint was first used in Operation Desert Storm. There have been various types of RC-135s in service since 1961.

UAVs: Global Hawk

The RQ-4 Global Hawk is an unmanned air-vehicle (UAV) with an integrated sensor suite used by the US Navy and Air Force as a surveillance aircraft with various ISR capabilities. It can provide high resolution SAR that can penetrate cloud-cover and sandstorms and Electro-Optical/Infrared (EO/IR) imagery at long range with long loiter times over target areas. According to the Air Force, the capabilities of the aircraft allow more precise targeting of weapons and better protection of forces through superior surveillance capabilities. Its long endurance and long range are its main benefits that give it enormous flexibility.

Space-based Capabilities

The role of aerial reconnaissance is steadily being stretched out to include space capabilities which utilizes spacecraft and satellite imagery and allows for larger coverage of the earth. However, space reconnaissance is very expensive and it raises questions about the occupation of space and space law. The most recent project “Space Radar” would be a further development of this capability. It would be capable of producing large amount of data and would be downlinked to a command and control station just like its airborne counterparts. Space Radar is being designed to carry out four primary missions for the military and the intelligence community: 1) produce images of various locations utilizing the SAR technology, 2) provide moving target detection, 3) conduct high-resolution surveillance of terrain as well as 4) monitoring the open waters. This project was shelved because of high projected costs. The utility and viability of Space Radar is discussed in another blog post. But this post will review some of the existing capabilities and the recent developments.

The earliest program was the Discoverer or Corona in the late 1950s, which was a satellite whose mission was to take territorial photographs. Corona and other high-resolution reconnaissance satellites provided increasingly detailed information to U.S. intelligence analysts that served the purpose of intelligence collection, early warning of probable surprise attack from the USSR and later on arms control treaty verification. The mission of these satellites (“ferret satellites”) was to intercept the signals emitted by Soviet, Chinese, and other nations' air defenses or intercept communication and telemetry signals from missile tests (geosynchronous satellites).

Then there were a couple of other projects that were never fielded (Starlite).Currently the United States has a space radar capability, the so-called Lacrosse (Onyx) SAR satellites that were employed by NRO from the 1980s onwards. The last of the so-called Onyx satellites went into orbit in 2005. The need for a more advanced system was re-identified in 2001 with the “Space-Based Radar” (SBR) plan, which would be a constellation of satellites, the number of which has constantly been debated.

To address Congressional concerns and to arrive at a technically feasible solution, a scale-back effort was undertaken in January 2005 that restructured the SBR into a single joint space radar program, renamed “Space Radar” (SR). For this new effort, the Air Force was tasked with leading a multi-service, multi-agency effort to bring together requirements for both the DOD and Intelligence Community (IC) users in 2001.This approach  that should have made SR more affordable by merging IC and DOD requirements, however, turned out to be the one of the major stumbling blocks, as military and intelligence communities were unable to agree upon system requirements and control The dispute between the IC and DOD circled largely around the strength of aperture imagery and high revisit rates, as DOD requires more rigorous activity in tracking motion of moving objects than the Intel Community. This kind of high resolution, however is very expensive and the high projected costs (estimated $28 - $ 38 billion; c.f. $34 billion estimate by House Appropriations Committee) and some major technical issues ultimately doomed the program and led the NRO to terminate SR in 2008.

New Approaches in Space Radar

Following cancellation in March 2008, DOD has announced to move forward with its own space radar demonstration beginning in 2012. DOD is also trying to test the utility of data from international and commercial radar satellites already in orbit (such as Germany’s SAR-Lupe or Canada’s Radarset-2 and the Israeli TecSAR).

TecSAR (Northrop Grumman produced) achieved orbit in early 2008, is treated as one very credible option for DOD. It will be interesting to observe how this issue will be treated in the face of looming budget cuts, as commercial radar satellites might be able to sufficiently cater to defense and intelligence needs of radar.