The multi-disciplinary character at Onera
Romulus
Multi-satellite orbital radars for surveillance
Context, positioning and objectives
Earth observation from space for civil or defense purposes, involves the use of varied payloads including radars, which are interesting due to their all weather capability.
Studies of concepts have been conducted to enlarge and enrich the observation capabilities of these radars currently based on Synthetic Aperture Radar (SAR) imaging.
Detecting and locating moving objects and mapping of speed fields are two such paths for development.
However, to detect and locate moving objects on land from space, antennas made of sub-arrays (often juxtaposed) and very large in size (several tens or even hundreds of meters) are required. At present, the technology is not mature enough to allow such space antennas to be manufactured and it is impossible to deploy such structures all in one piece on the same satellite, hence the idea of distributing these radar sensors on several platforms grouped in formation, in a coordinated manner, and recombining the signals.
Artist's view of the Romulus concept [see large size]
The main advantage of such a concept results from the global size (from hundreds of meters to a few kilometers) of the network thus formed. The multiplicity of available radar channels offers increased possibilities of space-time type processing, in the larger sense of the term, and thus enables us to consider operating methods and performances not accessible with a single platform radar.
In this context, the Romulus project (Multi-satellite orbital radars for surveillance) aims to explore new detection, location and reconnaissance concepts based on the use of space radars distributed on platforms flying in formation. The main objectives are:
- Study of distributed space radars by establishing optimal performances associated with different configurations and operating methods, identification and characterization of hard points.
- Satellite design based on the development of mission analysis tools and the analysis of their control as a single virtual vehicle.
- Study of solutions for motorizing satellites.
Contribution of work
The work done as part of this project quantified the attainable performances for the following themes and highlighted the contribution of distribution in relation to monolithic architectures:
- Detection of moving objects using a STAP*/MTI* technique
-> Improvement of minimum detectable speeds and improvement in the azimuth location linked to the overall size of the distributed antenna.
- Implementation of a technique that combines views from different observation angles
-> Improvement in distance resolution of SAR images
- Mapping of speed fields (currents, wake, etc.) using ATI* technique
-> Speed precision is linked to the size of the longitudinal interferometric base.
* STAP: Space Time Adaptive Processing
* MTI: Moving Target Indicator
* ATI: Along Track Interferometry
Prospects
The possible extensions could be:
- acquisition of experimental data in ATI configuration using ONERA's Ramses airborne radar system and its exploitation for estimating performances in a real environment.
- study of the concept's interest in other themes such as:
- high resolution 3D imaging (mono-pass, multiples bases)
- change detection in observed zone (differential interferometry, etc.)
- high resolution imaging of moving objects (vehicles, ships…)
- techniques for restoring differential trajectography to get precise data on position to the order of a millimeter on the three axes.
- a methodological extension developed in this context to other configurations, especially drones.
Some results
Following figures illustrate the distribution's contribution to the theme of detection of moving targets using a STAP/MTI technique. First figure shows the gains on improving minimum detectable speeds and the second quantifies the gains with regards the precision of azimuth location.
Improvement in minimum detectable speed [see details]
Improvement in precision of azimuth location [see details]
Key words
Distributed radar – Flight in formation – STAP – GMTI – SAR
