Swarming Proxima Centauri: Optical Communication Over Interstellar Distances

Abstract: Interstellar communications are achievable with gram-scale spacecraft using swarm techniques introduced herein if an adequate energy source, clocks and a suitable communications protocol exist. The essence of our approach to the Breakthrough Starshot challenge is to launch a long string of 100s of gram-scale interstellar probes at 0.2c in a firing campaign up to a year long, maintain continuous contact with them (directly amongst each other and via Earth utilizing the launch laser), and gradually, during the 20-year cruise, dynamically coalesce the long string into a lens-shaped mesh network $\sim$100,000 km across centered on the target planet Proxima b at the time of fly-by. In-flight formation would be accomplished using the "time on target" technique of grossly modulating the initial launch velocity between the head and the tail of the string, and combined with continual fine control or "velocity on target" by adjusting the attitude of selected probes, exploiting the drag imparted by the ISM. Such a swarm could tolerate significant attrition, e.g., by collisions enroute with interstellar dust grains, thus mitigating the risk that comes with "putting all your eggs in one basket". It would also enable the observation of Proxima b at close range from a multiplicity of viewpoints. Swarm synchronization with state-of-the-art space-rated clocks would enable operational coherence if not actual phase coherence in the swarm optical communications. Betavoltaic technology, which should be commercialized and space-rated in the next decade, can provide an adequate primary energy storage for these swarms. The combination would thus enable data return rates orders of magnitude greater than possible from a single probe.

• The paper demonstrates a novel swarming approach using hundreds of gram-scale probes that form a lens-shaped mesh network to transmit optical signals from Proxima Centauri.
• The methodology employs innovative Time-on-Target and Velocity-on-Target techniques to synchronize probe trajectories and counteract interstellar medium drag over four light-years.
• Key advancements include the use of state-of-the-art optical clocks and betavoltaic energy solutions, paving the way for efficient interstellar communications and future deep space missions.

Optical Communications Over Interstellar Distances with Swarming Probes

The paper, "Swarming Proxima Centauri: Optical Communications Over Interstellar Distances," explores the feasibility of interstellar communication using swarms of small-scale spacecraft. The focus is on achieving effective data transmission over four light-years to Proxima Centauri b, leveraging swarm technology and advanced energy solutions.

The authors propose a system where hundreds of gram-scale probes are dispatched over a year-long campaign at velocities of 0.2c, forming a lens-shaped mesh network. At flyby—20 years post-launch—the swarm would span approximately 100,000 km and utilize optical communication strategies to transmit data back to Earth.

Key Innovations and Techniques

1. Swarming Concept: The approach involves launching a sequence of probes that maintain continuous inter-probe and Earth communication via a launch laser. The sequence culminates in a mesh network upon reaching Proxima b, allowing for multi-angle observations and redundant data pathways.
2. Time and Velocity on Target Techniques: Gross "Time-on-Target" (ToT) methods involve launch velocity modulation, allowing the probe tail to catch the head. A finer "Velocity-on-Target" (VoT) leverages interstellar medium drag, attenuated by probe attitude adjustments, to maintain swarm coherence throughout travel.
3. Interstellar Communication Systems: Optical communication is core to the system, utilizing state-of-the-art optical clocks for precise timing and synchronization. The networked swarm enhances data rate by increasing photon transmission to Earth.
4. Energy Solutions: Betavoltaic technology using strontium-90, embedded in advanced metamaterials, offers a compact and space-rated energy source, sustaining the swarm's power needs throughout the mission lifespan, anticipated to last decades.
5. Trajectory and Control Challenges: Orbital predictions of target Proxima b require solving astrometric challenges, employing gravitational microlensing for precise orbital positioning well in advance of probe deployment.

Practical and Theoretical Implications

The use of synchronized swarms presents a viable path for deep space exploration beyond our solar system, tackling both energy and communication challenges posed by interstellar distances. The technology could significantly enhance our ability to conduct long-duration missions not only within our solar system but also to nearby stars. The study opens avenues for further development in swarm-based mission architectures and lays the groundwork for operational deployment in future space exploration missions.

Moreover, the choice of energy sources like betavoltaics indicates a shift from chemical to nuclear sources, emphasizing the necessity for continuous, reliable power in space applications. These advancements in power and communication technologies hint at broader applications, including planetary exploration and near-Earth astrobiological studies.

Future Directions

While the paper outlines a feasible strategy for interstellar communication with miniaturized spacecraft, ongoing technological developments are necessary. Future work may focus on refining trajectory calculations for planetary flybys and resolving long-term material durability challenges in space. There is also a need to further develop scalable manufacturing technologies for such highly specialized contraptions. Importantly, resolving unresolved challenges in probe synchronization and networked communication capabilities will further validate the approach for near-term missions.

This research emphasizes incremental yet ambitious steps toward unlocking the potential of interstellar travel and communication, an endeavor that could redefine humanity's reach in the universe.