Swarming Proxima Centauri: Picospacecraft Swarms over Interstellar Distances

Scope and Mission Concept

• Swarm consists of gram-scale laser-sail probes traveling together to Proxima; physical swarm diameter ~100,000 km vs ~4×10¹³ km to the star.
• Some argue the phrase “swarm over interstellar distances” is misleading; others say it correctly describes a compact group traversing an interstellar gap, not spanning it.

Formation, Drag, and Station-Keeping

• Proposal: modulate initial boost so a long “string” of probes reconverges into a ~100,000 km “lens” near target; then use interstellar-medium drag plus attitude control to keep them together.
• Critics call this “literally impossible,” arguing you can’t both let trailing probes catch up and then maintain formation solely via drag.
• Supporters counter that at 0.2c the medium is effectively a constant headwind, and orientation can tune drag vector; details remain unclear.

Clock Sync, Coherence, and Communications

• Concept: precise onboard clocks plus known geometry let probes time-shift their transmissions so laser pulses add coherently at Earth, multiplying effective power.
• Skeptics note that optical coherence implies nm-scale spatial and extremely tight temporal control; likely requires inter-probe optical locking and more hardware than gram-scale allows.
• A referenced study suggests aiming for picosecond-level timing to boost SNR without full phase coherence; full phase-coherent operation is framed as longer-term.

Laser Propulsion, Beam Physics, and Materials

• High-power lasers (up to ~100 GW) accelerate ultralight sails. Discussion covers Rayleigh length, beam divergence, and Bessel beams; consensus that diffraction still limits far-field focusing.
• Major concern: even 0.001% absorption of 100 GW yields ~1 MW heating on a tiny sail, likely vaporizing it. Some cite Starshot-style work on ~10 m², ~100-atom-thick sails and radiative cooling as “barely plausible.”
• Back-of-envelope energy and acceleration estimates yield very long acceleration distances; critics doubt pointing accuracy and overall practicality.

Probe Design and Power

• Strong skepticism that gram-scale probes can integrate decades-long power, sensing, processing, comms, and station-keeping.
• Suggestions include using comms lasers for micro-impulse and local interactions within the swarm; concrete power-source designs remain unclear.

Broader Context, Alternatives, and Philosophy

• Comparisons to other visionary projects: solar gravity lens, Terrascope, and large distributed telescopes if coherence tech matures.
• Some view this as inspirational “dream engineering” akin to pitch-drop experiments and Voyager—valuable for spinoff science even if the main mission payoff is beyond current lifetimes.
• Others question why, if such swarms are feasible, we don’t already see alien equivalents; responses range from infrastructure requirements (en-route lasers) to “it just takes time.”