Ultrahigh Acceleration Neutral Particle Beam Driven Sails

James Benford presents his Ultrahigh Acceleration Neutral Particle Beam-Driven Sails at Space Access 2019.

The Neutral Particle Beam-Driven Sails could enable an interstellar probe to alpha centauri that would be 1000 times larger and 60% of the speed of the current Starshot laser-driven proposal.

Centauri Dreams had an article on the neutral beam driven sails.

A second Centauri Dreams article reviews costs estimates for the Beam Driven system.

James goes over the engineering for a 1 kg probe that can be sent to a nearby star in about seventy years using neutral beam propulsion and a magnetic sail. The concept has been challenged because the beam diameter was too large, due to inherent divergence, so that most of the beam would miss the sail. Increasing the acceleration from 1000 g’s to 100,000 g’s along with reducing the final speed from 10% of lightspeed to 6% of lightspeed solves the issue of accelerating before the beam spreads too much.

They would start with lower speed systems, lower mass Magsails for faster missions in the inner solar system. As the system grows, the neutral beam System grows and technology improves. Economies of scale lead to faster missions with larger payloads. As interplanetary commerce begins to develop, making commerce operate efficiently, outcompeting the long transit times of rockets between the planets and asteroids, the System evolves.

MagSail is a huge ring of superconducting wire attached to a space vehicle.

Benford is using a neutral particle beam to propel the magsail.

Drift Tube Linac drift rube regions separated by acceleration regions. There are many linac accelerators.

Rocket launched BEAR (Beam Experiment aboard a rocket) was launched 30 years ago. A neutral particle beam generator was actually deployed and operated in space and its performance was measured. On July 13, 1989 the Beam Experiment Aboard Rocket (BEAR) linear accelerator was successfully launched and operated in space by Los Alamos National Laboratory.

The neutral particle beam approach is conceptually similar to photon beams such as the laser-driven Starshot project. A disadvantage of reflecting photons from the sail will be that they carry away much of the energy because they exchange only momentum with the sail. Neutral particle beams transfer energy, which is much more efficient. The reflecting particles may in principle be left unmoving in space after reflection and thus the efficient energy efficiency can approach 100%.

The thrust per watt beam power is maximized when the particle velocity is twice the spacecraft velocity. The Magsail, with a hoop force from the magnetic field, is an ideal structure because it is under tension. High-strength low-density fibers make this lightweight system capable of handling large forces from high accelerations. The rapidly moving magnetic field of the Magsail, seen in the frame of the beam as an electric field, ionizes the incoming neutral beam particles.

Since beam divergence is fundamentally limited, high accelerations can be used to insure the sail will stay within the beam until it reaches the desired final velocity, even with microradian divergence. This leads to ultrahigh, 100,000 g’s, 1 million m/s2 to accelerate to 0.06 c. The Starshot system, a laser beam-driven 1 gram sail with the goal of reaching 0.2c, has been quantified in a detailed system model by Kevin Parkin. It too uses 100000-1 million g’s. Magsail-beam interaction remains an aspect of this concept that needs further study, probably by simulations.

7 thoughts on “Ultrahigh Acceleration Neutral Particle Beam Driven Sails”

  1. Small correction – the plan calls for a magsail, which is a superconducting loop of wire, so area of sail doesn’t matter so much. The loop would be around 0.22gram per meter, about 0.15mm in diameter, if my math is right.

  2. A nanobot driven beam sail? Interesting.

    The nanobots would need mostly energy, and a laser beam can provide them that. The guidance can be optical (using micro-mirrors/light pressure) and would be mostly slight correction to stay around the laser beam.

    Interestingly, science fiction writers have come up with similar ideas.

    Stephen Baxter’s “Proxima” novel depicts an interstellar probe made of trillions of AI nanomachines, shedding layers upon layers of (sentient) parts of itself into a collimated laser, to make an ablative matter beam sail.

    The probe arrives to Proxima and its sentient AI is a bit upset with humans, because they didn’t reveal to it what would be the cost of the trip (killing huge amounts of its ‘sisters’).

  3. In principle, if you reduce the acceleration, and enlarge the “particles” enough, you can have particles with their own guidance systems, and beam divergence becomes a non-issue.

    What’s the smallest particle capable of having its own guidance and propulsion system? Probably bacterial size.

  4. Well, perhaps the neutral particle beam would be useful for astroid deflection. The beam – as outlined above – would accelerate 1 kg with 100 000g, i.e. the particles exert 100 000 N force on their object, or about 100 tons (guys, I know ton is not a unit of force…). This may be sufficient to deflect an astroid.

    But at what cost? A nuclear power plant – for comparison – typically costs some dollar per Watt. So lets say 5 USD per Watt, which would then give a particle beamer price of 90 000 billion dollars. That’s quite some bill to pay, I would say. Would it be possible to make an astroid deflection system for less money than 90 000 billion dollars, using some other means..? Well, considering that the world GDP is somewhere around 75 000 billion dollars, and considering that the whole space industry is worth 350 billion dollars per year, I would think the answer is yes…

  5. Yes – much lower acceleration over longer time is clearly needed.
    Shouldn’t be impossible to stage the accelerators and have many of them along the route. If the plan is to first use the system for interplanetary transport, there will have to be accelerators at end-points of the routes for both acceleration and deceleration. Accelerators should be possible to move around because they can propell themselves to some degree.

    A practical problem with having more than one accelerator is alignment and where to put them. They have to be aligned with the vessel and the target destination. Anything orbiting the sun or a planet will not be very aligned very often. I also think it will be practically impossible to hit a remote star without being able to do course corrections along the way. There will be unforeseen perturbations just like we have already within the solar system.

    I think we may need anti-matter to make space travel feasible between nearest star systems. Maybe particle beams of anti matter? Maybe that would allow for maneuverability and even breaking. If we can’t solve breaking, there is not much point visiting places at relativistic speed. Better to spend the resources on telescopes to gather information.

    The suggested neutral particle beam system should be useful for asteroid deflection if designed properly. That should make it easier to fund.

  6. First off, the cost estimates are ridiculous. Is he seriously proposing to build a neutral particle beam of 18 TW (!) for a measly 1.45 billion USD !?! Come on. That would be something like 10 kW of power per dollar. Again, come on..!

    Second thing, if the sail accelerates with 100 000g, what instruments can you have on it? A a camera? A computer? An if the enormous sail (1.46 km diameter) is accelerated, how will you “anchor” a camera? The areal density of the sail would be 60 ug per m2 (~1 nm thickness?). That “dot” would tear through that thin fabric like a bullet. A single gram would “pull” at a single point with the force of 100 N, which basically would tear the nm thin sheet to shreds.


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