Technological Advances to Evolve Satellite Communications at a Faster Pace

Michael Simon, Ph.D., MBA, VP CAES Advanced Technology & Engineering

History has shown that companies and defence communities that are committed to investing in and accelerating new technology development will ultimately dominate the market and the battlespace respectively. This truth is especially relevant today in the satellite communications (SATCOM) domain, where a revolution is occurring. Gone are the days when communication links were limited to Geosynchronous Earth Orbit (GEO) satellites with per-user data rates and latencies of 10 megabits per second and one second respectively. Now, the user demand for ever-increasing bandwidth has become insatiable, necessitation rapid adoption of technological change. Technologies fielded today run the risk of becoming stale in several years. Because they require the fewest terrestrial assets, offer the lowest latency, have global reach, and can be refreshed on multi-year cycles much faster than terrestrial communication infrastructure assets and GEO spacecraft, Low Earth Orbit (LEO) satellite constellations are the best means to rapidly develop and insert new global reach communications technologies.

SATCOM technologies are now progressing so fast that one small satellite supporting thousands of beams with many thousands of user terminals and latency lower than terrestrial fiber is possible. Where traditionally, the space industry has adopted little risk tolerance, what is now required to achieve this ubiquitous communication vision on the part of the companies funding LEO constellations, is the acceptance of reasonable risk to leapfrog next-generation capabilities and achieve next-next generation capabilities. Companies that can accept this reasonable risk will be first to market with next-next generation capabilities and capture the largest market share. Likewise, defense communities that can accept this reasonable risk will be first-to-field, providing marked strategic and tactical advantages. This assurance of multi-year technology insertion provides a business and investment case for payload providers to perform payload technology incremental research and development (R&D) to raise the Technology Readiness Level (TRL) for promising technologies as quickly as possible from low TRLs of 1 to 3 up to TRL 6 and test flight readiness.

Next-generation technologies that are already on the cusp of incorporation are advanced node Application Specific Integrated Circuits (ASICs) constructed from 5 nanometer (nm) and 7nm processes to support extremely high throughput of terabits per second and ultra-low power beamformers. Also being fielded are laser-based Optical Intersatellite Links (OISLs), and Optical interconnects from Field Programmable Gate Arrays and ASICs to OISLs each with terabits per second throughput.

One can therefore envision a next-next generation end state where SATCOM payloads include even more technological advances, which are continuously developed, inserted, and deployed on multi-year refresh cycles. Many of these technologies can be applied to user terminals as well.

In one possible next-next generation technological advance, payloads would utilize Microwave Photonic Frequency up / down Conversion (MPFC), where size, weight, and power, cost (SWaPC), are greatly minimized. This type of conversion is standard terrestrially but has yet to take root in space applications. MPFC uses Radio Frequency (RF) to drive optical carrier modulation through fiber using the Kerr effect (and other means). Then, by utilizing multiple laser sources and frequency mixing, up / down conversion can be achieved without dedicated RF Integrated Circuits (ICs). Because laser sources support multiple antenna elements, SWaPC is greatly reduced. Broad band conversion from L up to Q / V-Bands is also possible, which reduces the Analog to Digital Converter and Digital to Analog Converter sample rate requirements, further reducing SWaPC. Contrary to electrical up / down conversion, apertures using MPFC can be located at a multi-meter distance from processing hardware, enabling preferable spacecraft bus configurations.

In another new technological advance, additively manufactured antenna elements and phased array and Active Electronically Scanned Array apertures at Ku-band and higher frequencies can be employed to greatly lower SWaPC and system complexity and offer higher gain using advanced surface plating treatments above 110 gigahertz operation. This approach enables smaller self-contained sub-array unit cells to be separately tested in extremely low cost and small near-field testers for dramatic yield improvement and then assembled piecewise for maximum scalability.

All photonic payloads incorporating MPFC, photonic beamforming, and OSILs can also be envisioned.

On the more exotic technologies, one can consider metamaterial-based or enhanced antennas that implement transformation optics. Transformation optics relies on the concept of physical space and electromagnetic space being distinct. Physical space is the space within which the physical antenna resides. Electromagnetic space is the space with which electromagnetic energy interacts. In 2006, researchers were able to demonstrate a two-dimensional cloak of an object from an incident microwave plane wave using an annular series of metamaterial structures surrounding the object to be cloaked. The plane wave passed through the metamaterial structures and the object such that it emerged (some minor disturbances not withstanding) disturbance free. The metamaterial structures implement transformations between the physical and electromagnetic space, which have different curvatures. This is accomplished by tailoring the local permittivity and permeability of the physical space using metamaterials. Transformations can be defined that minimize antenna physical dimensions while maintaining or improving classical antenna performance, greatly improving SWaPC.

One can also consider extremely wide band tunable (direct current to terahertz), over many orders of magnitude, electrically small quantum systems like phased arrays made from Rydberg cells (artificial atoms), where atomic vapor (typically rubidium or cesium), are increased in energy level using Vertical Cavity Surface Emitting Laser probe and control lasers to excited Rydberg atomic states. The probe laser excites the atom to a low excited state and the control laser to a higher excited state inducing what is termed Electromagnetically Induced Transparency (EIT) across an optical frequency range. EIT opens a window of high probe laser transmission. Incident RF and microwave energy that is resonant or close to resonant with a Rydberg state, alter the Rydberg atom interaction with the laser light so that the EIT window splits (becomes modulated), and the modulation can be read out using photodetectors. The readout constitutes RF and microwave sensing. Rydberg cells currently operate in receive mode only, but consider the possibilities if Rydberg cells could be designed to operate in transmit mode too? Disruptively broad-band SATCOM would result.

Adopting new technologies will also address several LEO constellation criticisms. Through new technology insertion, the number of satellites required for existing and planned LEO constellations can be reduced from the tens of thousands to the hundreds. Reducing constellation size is important to keep LEO space debris and possible LEO space collisions at bay, and solar panel-induced light pollution, which impacts terrestrial astronomy, to a minimum.

If companies and defense communities can commit to adopting a more risk-tolerant stance toward R&D and fielding SATCOM technologies to be incorporated into next-next generation space segment LEO constellations on multi-year cycles, the SATCOM can not only evolve faster to meet the ever-increasing demand for user bandwidth but individual spacecraft and overall constellation size can simultaneously be reduced.

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