3 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
David Smith
Duke University
The increasing population of spacefaring vehicles and satellites motivates increasingly powerful technologies for space situational awareness (SSA). While the US space surveillance network (SSN) is able to monitor objects down to about four inches in size using, for example, the latest upgrade to the space fence, the associated requirements limit implementation to ground-based tracking of low earth orbit (LEO) objects using kilometer-scale radar arrays. Beyond LEO, the prospect of cislunar traffic and the extreme distances involved render ground-based arrays impractical. This limitation is fundamental to coherent radar systems: for a given detection performance, the required array size grows in direct proportion to the target distance. As a result, it can in fact become simpler to decrease the sensing distance rather than extend array sizes, and this can only be achieved by shifting to a space-based SSA platform.
Although space-deployed radar systems offer distinct advantages in terms of sensing capabilities, the large distances associated with cislunar surveillance still require extremely large apertures for adequate performance. This poses significant practical challenges based on limitations to modern deployable structures which, to date, cannot consistently achieve dimensions greater than 100 meters. This limitation arises because state-of-the-art deployable antennas, including membrane, mesh, and inflatable architectures, require the entire structure to be housed inside a single launch fairing. In contrast, the prospect of in-space assembly suggests the potential for scalable structures that are not limited by launch constraints and so can meet the challenging requirements of long-range SSA.
We propose a spaceborne radar system that pairs the demonstrated performance of robotically assembled mechanically stable structures with reconfigurable, volumetric electromagnetic metamaterials. The former technology enables modular and precise construction of arbitrary volumetric structures, while the latter offers a sophisticated and readily compatible design platform for achieving the challenging requirements of long-range SSA. Both approaches exploit a unit cell-driven, modular design procedure that enables nearly arbitrary scaling for mechanically and electromagnetically robust antenna platforms. The ability to reliably assemble and control volumetric antenna structures in this way provides access to new and powerful capabilities including steering over wide fields of view (FOV) without the need for slow, mechanical slewing of the antenna.
The proposed work will demonstrate the feasibility and scalability of a reconfigurable, volumetric S-band metamaterial for achieving various beam steering capabilities. This effort will include advancement of metamaterial design strategies for omnidirectional electromagnetic beam forming and initial assessment/design of a reconfigurable unit cell compatible with robotic assembly. The development of the metamaterial design procedure will exploit a numerically efficient dipole model that has been previously validated at smaller scales, while the metamaterial element design will proceed by established full-wave numerical methods. System design concepts will incorporate practical constraints according to successful demonstrations of robot assembly by the Automated Reconfigurable Mission Adaptive Digital Assembly Systems (ARMADAS) project.
While the project will target SSA applications, the design considerations involved are equally applicable to missions requiring large physical apertures such as low-frequency radiometry for earth observation and deep-space communications. Since the performance (resolution, sensitivity) of all beam steering, radar, and observation missions improves with increased aperture sizes, the realization of alternative electromagnetic strategies that offer reduced CSWaP can provide advantages across a wide range of NASA programs.
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