Beamed Energy Propulsion

Propulsion of craft using beamed energy, or by the use of mass particle streams

Image from Steve Bowers
The Starwisp class interstellar probe is a lightweight mesh propelled by a microwave laser beam, based on a concept by Robert Forward

The greatest drawback of the reaction driven rocket, whether it derives its energy from chemical reactions or antimatter, is the need to carry its own fuel and propellant on board. To avoid this, various kinds of passive propulsion have been developed, from the basic solar (stellar) sail which uses the light pressure of the local star for propulsion, to more advanced laser-driven concepts, which use powerful stationary lasers or masers for propulsion. Laser-propelled craft can be simple sails, or the laser beam can be used to heat propellant which is expelled to provide thrust. Other concepts such as the magsail use a magnetically constrained cloud of particles as a sail surface.

Beamrider 2
Image from Steve Bowers
The particle beam, or Beamrider, concept
Modern laser-driven craft use a large or megascale laser or microwave transmitter to propel space-craft at high velocities. Such craft use a huge sail, which can be many thousands or millions of kilometers in area. However light particles can only transfer a very small amount of momentum to a ship, so particle beams, which can transfer much greater amounts of momentum, are often used.

The particle beam concept, often known as the Beamrider, uses a collimated beam of particles with mass to transfer momentum to the craft. This is the basis of the interstellar Beamrider Network, established by the Deeper Covenant long ago.

The massive particles used by a particle beam momentum transfer system may be relatively simple, such as magnetic particles propelled by a mass-driver towards the target, or small metallic light sails propelled by laser over long distances. But to maximise the transferred thrust the particles can be given rudimentary steering systems of their own, which are controlled bu automated systems to home in on the vessel to be accelerated. Such so-called smart particles can improve the efficiency of particle beam propulsion systems considerably.

Cycler and Beamstation
Image from Steve Bowers
The G. David Nordley, an interstellar cycler ship propelled by a beam of smart particles (collected by a magnetic sail created by a superconducting loop at the rear)
Beamed power projectors, known as Boostbeams, are usually located near a star, where energy is cheap, or sometimes extract power from the magnetic field of a gas giant or brown dwarf. The energy required for beamed power propulsion can be considerable, but the energy available in such locations is generally more than adequate. In some cases entire Dyson power swarms dedicate their collected energy to the propulsion of beamed power vessels in the local neighborhood.
Image from Steve Bowers
A boostbeam powered by a solar collection array. Boostbeams use local sources of power such as solar energy or planetary magnetic fields to produce propulsive beams carrying momentum.
Many Conversion Drive ships (and other reaction-drive craft) in the modern Era use a reconfigurable Magnetic Drive Sail to accelerate and decelerate, a system which relies on boostbeams where available.

Some classes of fuelless Thermal Rocket and of Electric Drive rocket use beamed power to supply energy to the drive systems. Wherever there is not enough solar energy for a solar-powered thermal or electric rocket to work, a laser or maser may be used instead.
beamrider station
Image from Steve Bowers
A beamrider boostbeam in orbit around a gas giant. This example extracts energy from the planet's magnetic field to power the smart particle beam.

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Development Notes
Text by M. Alan Kazlev, Mauk Mcamuk, Chris Shaeffer and Steve Bowers
Initially published on 08 October 2001.