DARPA eyes reconfigurable optical communications to connect current and future satellite constellations

Sept. 15, 2021
Space-BACN seeks to develop an intersatellite optical communications terminal that is low size, weight, power, and cost (SWaP-C).

ARLINGTON, Va. – U.S. military researchers are approaching industry to develop a reconfigurable multi-protocol intersatellite optical communications terminal to connect satellite constellations that otherwise would not be able to communicate.

Officials of the U.S. Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., issued a solicitation on Monday (DARPA-PS-21-01) for two technical areas of the Space-Based Adaptive Communications Node (Space-BACN) project.

Space-BACN seeks to develop an intersatellite optical communications terminal that is low size, weight, power, and cost (SWaP-C); easy to integrate; and operate on platforms in low Earth orbit (LEO). The project involves space-based communications, optical intersatellite links, reconfigurable modems, modular components, and space command and control.

Space-BACN aims to overcome today's lack of on-orbit interoperability among current and future space communications. There is yet no standardization of communications or optical intersatellite links in this domain, researchers point out.

Related: DARPA Blackjack technology demonstration to pave the way to military satellite communications mesh network

New satellite constellations in different stages of acquisition are procuring single-waveform crosslink communication systems that only interconnect their own constellation, but not with other constellations. These single-waveform systems consist almost exclusively of custom-made components, and have little to no reconfigurability.

While most waveforms operate within the same wavelength band, they differ in wavelengths, polarization, clock rate, spatial acquisition sequence, modulation format, framing, and error correction coding. As each constellation acquires its own proprietary communications links, satellite communications (SATCOM) becomes severely fragmented with only isolated islands of connectivity.

Instead, the Space-BACN program seeks to create a reconfigurable space-to-space optical communications terminal that can connect heterogeneous constellations that operate on different optical intersatellite link specifications that otherwise would not be able to communicate with one another.

The Space-BACN terminal should support most current and future single wavelength waveforms in space to speeds of 100 gigabits per second; use less than 100 Watts of power; and cost less than $100,000; and integrates easily into most satellites.

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The Space-BACN program consists of three technical areas -- two of which are part of this solicitation: A modular, low SWaP-C optical aperture to separate the front end of the optical intersatellite link from the signal processing via single-mode fiber; and a reconfigurable modem able to support several optical waveforms as fast as 100 gigabits per second on one wavelength.

The optical aperture will include an overall terminal controller, responsible for pointing, acquisition, and tracking (pointing, acquisition, and tracking) functions; terminal command and telemetry; and transmit optical amplification and optional receive low-noise optical amplification.

The aperture will couple light into an single-mode fiber to achieve the coherent processing necessary for flexible high-rate optical communications.

Key challenges include focusing and stabilizing light over variable thermal, shock, and vibration environments; operating on any pair of transmit and receive wavelengths within the specified optical bandwidth; and accommodating any of several pointing, acquisition, and tracking sequences.

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Traditional diffraction-limited optical apertures for space typically are incredibly expensive and only producible in small quantities because they are engineered, tuned, and hardened. Instead, Space-BACN aims to simplify the design and automate assembly and tuning of the optical components.

The reconfigurable modem will capitalize on advanced integrated technologies like A/D and D/A converters that sample at rates faster than 50 gigabits per second; narrow-linewidth tunable lasers; optical in-phase and quadrature (IQ) modulators; and equalizers.

To date, reconfigurable communications systems have been demonstrated only in RF, not in optical. Recent advances in optical communications and digital signal processing technologies, however, have made a 100-gigabit-per-second reconfigurable space terminal within reach. Commercial data communications applications have led to volume-manufacturable integrated photonic circuits for ubiquitous, low SWaP-C, high-rate data transceivers.

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The reconfigurable modem will support several waveforms within the limits of sampling rate, where a specific single-wavelength waveform includes the details of symbol amplitude and phase, modulation, framing, and forward error correction.

Companies interested should email three-page abstracts no later than 4 Oct. 2021 to DARPA at [email protected]. Those submitting promising abstracts will be invited to make oral presentations and submit formal proposals.

Email questions or concerns to DARPA at [email protected] by 28 Sept. 2021. More information is online at http://www.fbodaily.com/archive/2021/09-September/15-Sep-2021/FBO-06130406.htm.

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