Plenary: Mr. Jeff Greason

Sunbeam: Near-Sun Statites as Beam Platforms for Beam-Driven Rockets

Photon, particle, or macroscopic pellet beamriders have long been recognized as one of the key approaches to interstellar flight.  The constraints of previous solutions limit their application to either very small (gram scale) payloads or such large power levels as to constitute prohibitive capital costs to construct the required beam infrastructure.  

We sought solutions with very long beam ranges and with very high specific power (power per unit mass) of the beam platform to produce beam solutions for macroscopic spacecraft to interstellar-relevant velocities.

The approach chosen was long-range particle beams, pinched either by space-charge neutralization of a current carrying beam (Bennett pinch), or use of highly relativistic electron beams (relativistic pinch).   We surveyed various methods of extracting solar energy to drive the beam to find one with high specific power.

Heavy particle beams cannot scale to very high power without exceeding current limits for pinch confinement unless driven to higher velocities than is energetically efficient.   Relativistic electron beams appear to have potential for extreme range in the space environment (potentially up to 100AU).   Thermionic conversion state of the art is well below theoretical limits; theoretically achievable performance of high-temperature thermionic converters placed close to the Sun (0.05-0.1 AU), can produce gigawatts of power from a credibly launchable piece of infrastructure (100 tonnes).   A plasma magnet sail appears able to transport the resulting beam platform from a cislunar departure point to a solar statite station such that the target star system is in opposition continuously, allowing for the beam to be on for arbitrary periods.  

The challenge to make use of this technology, either as direct power for larger craft or as a means of driving pellets to interact with pellet-pushed spacecraft, is efficient and lightweight conversion of the electron beam to thrust.   Several avenues of approach are laid out but as yet this is not a solved problem.

The use of relativistic electron beams as carriers of energy, rather than momentum, opens up new avenues of development for interplanetary and interstellar propulsion.  Much more work is needed on how to make use of that energy for propulsion.