Space Domain Awareness

Introducing ESSAR: The Equatorial Space Situational Awareness Radar

Just ONE widely-spaced reflector radar array can theoretically provide comprehensive, accurate cataloging of ALL Earth propagating objects in LEO and beyond!   It is not another traditional phased array for cataloging Space junk.  It doesn’t require multiple site locations to find and catalog all the objects.  It doesn’t require tracking each object to determine and catalog its orbit.


The first step in Space Situational Awareness (SSA) is detecting and characterizing what’s out there.  We’ve designed a radar system to do this, comprehensively.  That is, the system, by design, doesn’t just track and catalog what happens to go through its beam or what it’s tasked to ‘look’ at.  It is configured and located to find everything.  This is essential for superior battlespace preparation as well as everyday asset management.

Our notional Equatorial Space Situational Awareness Radar (ESSAR) uses widely-spaced large antenna radar arraying technology.  The radar system consists of large widely-spaced ground reflector antennas.  One group is used to form a transmit array and another, a receive array.

This patented, technology can theoretically outperform current state-of-the-art phased array systems with its super-high resolution and ability to catalog ALL Earth-propagating objects WITHOUT needing to track them.  Our AMOS 2018 paper can be found here.

Its patented optimal location and orientation, (on or near the Equator) and pointing towards the horizon, enables it to just stare out and wait for objects to come into view.  It operates on the principal that ALL propagating Earth-orbiting objects will frequently cross the Equator through the beam of our system.  

The very wide spacing of the ground reflectors determines angular resolution of the target.  Our antennas can be VERY widely spaced.  Cross range is as accurate as the range measurement enabling rapid, comprehensive, one-pass, un-cued detection.  Building a traditional phased array equivalent to the dimensions of this large reflector array is not feasible.

Of the 750k space objects > 1cm, traditional systems only detect a small percent of them.  ESSAR was designed for comprehensive, single-pass detection and accurate characterization of ALL Earth-propagating objects – without the need to track each object.  

ESSAR is not limited to objects >1cm.  It is expandable.  By adding array elements objects smaller or further away can be addressed.  It can operate 24/7 unlike optical systems that are limited to specific lighting conditions and clear skies. 


Traditional SSA phased arrays like the $1.6B Space Fence, as well as all optical systems require multiple instances of the same object.  They either track each detected object or detect the object from multiple antennas, putting this data together after detection (post-detection).  This is sub-optimal.

ESSAR uses multiple sensors that are coherently combined (before detection) so the data is put together as it is detected (pre-detection).  This has significant advantages.  For one, the detection sensitivity of ESSAR improves as number of sensors cubed (EIRP increases as N2 and G/T increases as N, for two-way coherent performance increasing as N3).  With this increase in sensitivity much smaller objects can be seen at much greater distances.  Traditional systems that track and systems that have multiple 1D traditional phased arrays are thus limited in the size of the objects that they can detect and the distance they can operate at.

Another benefit is the extent of the array.  The wider the spacing between the antennas, the narrower the beam and therefore, the higher the angular resolution.  Higher resolution means that very tiny objects can be characterized.  Using our arraying technology, the distance between the antennas is orders of magnitude greater than even the largest phased array, Space Fence. 

Generally, such a narrow beam is a problem since the object passes through it so quickly.  This is not a problem for ESSAR.  High accuracy, high precision, detection algorithms are able to use the data from the array of sensors to characterize the object’s orbit, immediately, as it passes through the beam (one-pass).

Although the array beam on the object is narrow, the beam of a single antenna is not.  It is the beamwidth of a single antenna that is used to detect an object.  This larger beamwidth drives the coverage area and thus the rate that all objects are cataloged.

The diameter of traditional phased arrays as well as single ground antennas is limited by a number of factors such as cost, power and voltage arcs.  The diameter of an array of widely-spaced antennas is not.  Therefore, ESSAR outperforms such systems when it comes to finding the smallest objects and going furthest into Space. 

Along with our advanced signal processing methods, whether the mission is orbital debris cataloging or GEO asset monitoring, an array of widely-spaced large ground antennas will provide the best results.


  • Rapid, comprehensive, un-cued detection of ALL Earth-propagating objects due to its location and orientation
  • Detects and characterizes objects in a SINGLE pass WITHOUT the need for multiple observations and/or tracking
  • A single SSA radar array system provides global coverage

All other SSA systems are not designed to comprehensively detect ALL propagating Earth-orbiting objects.   They only detect what happens to pass through their beam or what they are cued to go after.  By design, ESSAR is comprehensive.  Once the object’s orbit parameters are entered into a database, the object can be assigned to trackers, (e.g. traditional radar phased array and optical systems), for periodic updates. 

Importantly, only one ESSAR system is needed globally due to its patented location and orientation.   All Earth-propagating objects will pass through its beam.  Other technologies require numerous systems to be built and maintained – still lacking the comprehensive coverage of a single ESSAR system.


ALL propagating Earth-orbiting objects must frequently cross the equatorial plane.  A radar array of widely-spaced reflectors located on the Equator and staring toward the horizon ensures discovery of these objects.  They will pass through the beam (shown with a red oval in the second frame).   With an array of just four 12m antennas, comprehensive detection and one-pass orbit determination of objects, down to ‑40dBsm (marble sized) can be realized.  Results from High Fidelity modeling and simulation show that most can be found within just months.  Trackers (traditional phased arrays and optical systems) could be employed to keep the data updated once it is entered into the database.


  • Comprehensive cataloging of ALL Earth-propagating objects without tracking
  • Outperforms traditional phased array systems with respect to object size and distance
  • Low-cost system and expandable to MEO and GEO
  • Data can be used for Space asset collision avoidance or threat awareness
  • 24/7 availability due to the inherent redundancy of the array elements
  • Expandable for higher sensitivity or greater distances by adding antennas to the array
  • Robust, reliable, widely-spaced coherent transmit and calibrated receive arraying
  • Instantly available on power-up
  • Low risk: core technology has been successfully demonstrated (TRL-6)
  • Enables scheduled maintenance of individual antennas without system shut-down
  • Dispersed near-field radiation avoids personnel radiation hazard
  • Enables precision electronic beam control which reduces wear and tear on antennas
  • Larger field-of-view due to wider beam of smaller antennas
  • Higher angular resolution due the narrow beam width of the widely spaced array
  • Autonomous, continual self-calibration without the need for towers or satellites
  • Tolerance for COTS hardware and relaxed circuit stability requirements
  • Applicability to a wide range of antenna and array sizes
  • Immediate transition to ISAR imaging since the orbit is instantly known