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Antimatter-driven Deceleration at Proxima Centauri

Although I’ve often seen Arthur Conan Doyle’s Sherlock Holmes cited in various ways, I hadn’t chased down the source of this famous quote: “When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.” Gerald Jackson’s new paper identifies the story as Doyle’s “The Adventure of the Blanched Soldier,” which somehow escaped my attention when I read through the Sherlock Holmes corpus a couple of years back. I’m a great admirer of Doyle and love both Holmes and much of his other work, so it’s good to get this citation straight.

As I recall, Spock quotes Holmes to this effect in one of the Star Trek movies; this site’s resident movie buffs will know which one, but I’ve forgotten. In any case, a Star Trek reference comes into useful play here because what Jackson (Hbar Technologies, LLC) is writing about is antimatter, a futuristic thing indeed, but also in Jackson’s thinking a real candidate for a propulsion system that involves using small amounts of antimatter to initiate fission in depleted uranium. The latter is a by-product of the enrichment of natural uranium to make nuclear fuel.

Both thrust and electrical power emerge from this, and in Jackson’s hands, we are looking at a mission architecture that can not only travel to another star – the paper focuses on Proxima Centauri as well as Epsilon Eridani – but also decelerate. Jackson has been studying the matter for decades now, and has presented antimatter-based propulsion concepts for interstellar flight at, among other venues, symposia of the Tennessee Valley Interstellar Workshop (now the Interstellar Research Group). In the new paper, he looks at a 10-kilogram scale spacecraft with the capability of deceleration as well as a continuing source of internal power for the science mission.

Image: Depiction of the deceleration of interstellar spacecraft utilizing antimatter concept. Credit: Gerald Jackson.

On the matter of the impossible, the quote proves useful. Jackson applies it to the propulsion concepts we normally think of in terms of making an interstellar crossing. This is worth quoting:

Applying this Holmes Method to space propulsion concepts for exoplanet exploration, in this paper the term “impossible” is re-interpreted arbitrarily to mean any technology that requires: 1) new physics that has not been experimentally validated; 2) mission durations in excess of one thousand years; and 3) material properties that are not currently demonstrated or likely to be achievable during this century. For example, “warp drives” can currently be classified as impossible by criterion #1, and chemical rockets are impossible due to criterion #2. Breakthrough Starshot may very well be impossible according to criterion #3 simply because of the needed material properties of the accelerating sail that must survive a gigawatt laser beam for 30 minutes. Though traditional nuclear thermal rockets fail due to criterion #2, specific fusion-based propulsion systems might be feasible if breakeven nuclear fusion is ever achieved.

Can antimatter supply the lack? The kind of mission Jackson has been analyzing uses antimatter to initiate fission, so we could consider this a hybrid design, one with its roots in the ‘antimatter sail’ Jackson and Steve Howe have described in earlier technical papers. For the background on this earlier work, you can start by looking at Antimatter and the Sail, one of a number of articles here on Centauri Dreams that has explored the idea.

In this paper, we move the antimatter sail concept to a deceleration method, with the launch propulsion being handed off to other technologies. The sail’s antimatter-induced fission is not used only to decelerate, though. It also provides a crucial source of power for the decades-long science mission at target.

If we leave the launch and long cruise of the mission up to other technologies, we might see the kind of laser-beaming methods we’ve looked at in other contexts as part of this mission. But if Breakthrough Starshot can develop a model for a fast flyby of a nearby star (moving at a remarkable 20 percent of lightspeed) via a laser array, various problems emerge, especially in data acquisition and return. On the former, the issue is that a flyby mission at these velocities allows precious little time at target. Successful deceleration would allow in situ observations from a stable exoplanet orbit.

That’s a breathtaking idea, given how much energy we’re thinking about using to propel a beamed-sail flyby, but Jackson believes it’s a feasible mission objective. He gives a nod to other proposed deceleration methods, which have included using a ‘magnetic sail’ (magsail) to brake against a star’s stellar wind. The problem is that the interstellar medium is too tenuous to slow a craft moving at a substantial percentage of lightspeed for orbital insertion upon arrival – Jackson considers the notion in the ‘impossible’ camp, whereas antimatter may come in under the wire as merely ‘improbable.’ That difference in degree, he believes, is well worth exploring.

The antimatter concept described generates a high specific impulse thrust, with the author noting that approximately 98 percent of antiprotons that stop within uranium induce fission. It turns out that antiproton annihilation on the nucleus of any uranium isotope – and that includes non-fissile U238 – induces fission. In Jackson’s design, about ten percent of the annihilation energy released is channeled into thrust.

Jackson analyzes an architecture in which the uranium “propagates as a singly-charged atomic ion beam confined to an electrostatic trap.” The trap can be likened in its effects to what magnetic storage rings do when they confine particle beams, providing a stable confinement for charged particles. Antiprotons are sent in the same direction as the uranium ions, reaching the same velocity in the central region, where the matter/antimatter annihilation occurs. Because the uranium is in the form of a sparse cloud, the energetic fission ‘daughters’ escape with little energy loss.

Here is Jackson’s depiction of an electrostatic annihilation trap. In this design, both the positively charged uranium ions and the negatively charged antiprotons are confined.

Image: This is Figure 1 from the paper. Caption: Axial and radial confinement electrodes (top) and two-species electrostatic potential well (bottom) of a lightweight charged-particle trap that mixes U238 with antiprotons.

A workable design? The author argues that it is, saying:

Longitudinal confinement is created by forming an axial electrostatic potential well with a set of end electrodes indicated in figure 1. To accomplish the goal of having oppositely charged antiprotons and uranium ions traveling together for the majority of their motion back and forth (left/right in the figure) across the trap, this electrostatic potential has a double-well architecture. This type of two-species axial confinement has been experimentally demonstrated [53].

The movement of antiprotons and uranium ions within the trap is complex:

The antiprotons oscillate along the trap axis across a smaller distance, reflected by a negative potential “hill”. In this reflection region the positively charged uranium ions are accelerated to a higher kinetic energy. Beyond the antiproton reflection region a larger positive potential hill is established that subsequently reflects the uranium ions. Because the two particle species must have equal velocity in the central region of the trap, and the fact that the antiprotons have a charge density of -1/nucleon and the uranium ions have a charge density of +1/(238 nucleons), the voltage gradient required to reflect the uranium ions is roughly 238 times greater than that required to reflect the antiprotons.

The design must reckon with the fact that the fission daughters escape the trap in all directions, which is compensated for through a focusing system in the form of an electrostatic nozzle that produces a collimated exhaust beam. The author is working with a prototype electrostatic trap coupled to an electrostatic nozzle to explore the effects of lower-energy electrons produced by the uranium-antiproton annihilation events as well as the electrostatic charge distribution within the fission daughters.

Decelerating at Proxima Centauri in this scheme involves a propulsive burn lasting ten years as the craft sheds kinetic energy on the long arc into the planetary system. Under these calculations, a 200 year mission to Proxima requires 35 grams of total antiproton mass. Upping this to a 56-year mission moving at 0.1 c demands 590 grams.

Addendum: I wrote ’35 kilograms’ in the above paragraph before I caught the error. Thanks, Alex Tolley, for pointing this out!

Current antimatter production remains in the nanogram range. What to do? In work for NASA’s Innovative Advanced Concepts office, Jackson has argued that despite minuscule current production, antimatter can be vastly ramped up. He believes that production of 20 grams of antimatter per year is a feasible goal. More on this issue, to which Jackson has been devoting his life for many years now, in the next post.

The paper is Jackson, “Deceleration of Exoplanet Missions Utilizing Scarce Antimatter,” in press at Acta Astronautica (2022). Abstract.

{ 27 comments… add one }
  • Michael Fidler March 22, 2022, 10:45

    Has anybody keeped antimatter around for 56 years?

    But lets combine it with this, I’m sure it will work :-}

    NASA Inertial Drive With a Helical Engine Using a Particle Accelerator.


    An Antimatter Helical Engine Using a Particle Accelerator…

    • Alex Tolley March 22, 2022, 13:11

      Hmm. It looks like another reactionless drive that swaps unbalanced flywheels by changing the ion mass by varying their speed. I am not buying it, even if it has a NASA imprimatur. Let a real physics expert analyze this, but it looks like it cannot work as advertised to me.

      • Brett Bellmore March 23, 2022, 8:03

        The helical engine, like several ‘space drives’, relies on failing to account for the momentum involved in moving the energy around. It’s actually kind of embarrassing that anyone who passed even introductory physics would take it seriously.

        I’ve had to conclude that a fair number of people nominally educated in physics have never internalized Einstein’s work, and are still doing Newtonian physics with an inconsistent relativistic “patch”.

        • Andrei March 23, 2022, 22:32

          Indeed, I checked on the link before reading the comments and arrived at the same conclusion. That there has to be a catch to that idea of this ‘helical engine’. While the first sentence mention the Mach thruster, it seem to be a quite different system and if the MET actually work then it require MW of power to achieve trust in the mN range. This proposal have the same problem, and if a flight ready 165 MW powersource actually were available, there might be a few alternative propulsion methods that could provide even better acceleration by using miniscule amounts of fuel efficiently by accelerating it to tremendous speed – or perhaps even use some component of the interstellar medium it encounter enroute for propulsion.
          Another red flag is that the proposal have been removed from that NASA repository for technical documents.

  • Alex Tolley March 22, 2022, 12:06

    Looking at the available information on this long-gestating and evolving concept, while not “impossible”, there are 2 main weaknesses that seem to be hurridly passed over:

    1. The acceleration to the various fractions of lightspeed needs another vehicle, whether a different propulsion mode or a concomitantly larger version of the deceleration vehicle.
    The table shown in the video around 4 minutes from the talk at the IRG Interstellar Symposium in 2021 implies that the acceleration and deceleration periods total around 10 years, despite an earlier slide stating a 10-year acceleration phase is required. The concept is vague as to whether a 2 stage vehicle is still needed, or just the single stage to do both stages at each end of the journey.

    2. The energy cost, the production rate of antimatter, and its conversion to storable material are very light on details. If there is skepticism with building phased laser arrays for even 1gm interstellar sails, manufacturing anti-matter in up to fractions of a kilogram is orders of magnitude more difficult and expensive.

    The impression I get is that the concept is pushed on the science mission, rather than on the feasibility of the thrust generating mechanism. These should be separate issues, with any presentation focussing on the technology to achieve the mission. It may be poor presentation skills, but to me, it looks like the technology issues are skipped over.

    Lastly, Jackson was rather flippant over the mission time. The baseline 200 years was answered with “what’s the hurry?” and some dissembling over cathedral building. As the travel time is reduced, the antimatter requirement and energy produced rise exponentially:

    Doubling the velocity from 0.1c to 0.2c (the Breakthrough Starshot velocity), I calculate the amount of antimatter increases to 18 kilograms (from 590 g), and the power to 1200MW (from 40MW) (rather like the rocket equation).

    So what we have is a concept that marries parts of the fission fragment rocket with the Dyson medusa design for capturing atomic explosions, but uses the difficult issue of manufacturing antimatter to generate the fission fragments from depleted uranium. Is the benefit to reduce the scale of the craft?
    My sense is that the focus is on deceleration as this is the hard part of the interstellar journey to solve. Laser arrays are not going to be effective light-years distant, and as stated, various drag schemes may not be sufficient (although the plasma magnet approach is mentioned in passing as a way to increase the drag area in the ISM). Whether this particular approach really makes sense I leave to the experts.

    • Brett Bellmore March 23, 2022, 15:07

      “The baseline 200 years was answered with “what’s the hurry?” ”

      Easily answered, btw: It today you spend a billion dollars sending a probe on a 200 year trip, and 50 years from today someone launches a probe on a 100 year trip to the same destination? Congrats: You just wasted a billion dollars.

  • Ronald P. Marriott March 22, 2022, 13:45

    Antihydrogen fusion is a natural occurring source of energy that creates atmospheric sprites. In the fusion process (the same as regular fusion) helium is produced, in this case antihelium which can be found in the outside ring of the Van Allen belt protecting us from the sun. The terrestrial gamma rays produced are the signature of Antihydrogen fusion being released. Everyone’s idea of using annihilation for producing energy to propel a vehicle is actually a waste of energy as when the components are together Antihydrogen fusion is converting anti helium to light or electromagnetic radiation that is more effective. Antihydrogen fusion is a twelve foot ringed disc consisting of Antihydrogen fusion in three energy levels wrapped in antihelium and liquid oxygen. If you google atmospheric sprites at high speed you will see the energy discharging from our plasma tubes surrounding the planet creating atmospheric sprites.

    • Alex Tolley March 23, 2022, 6:53

      AFAICS, this seems to be your personal belief that is not supported by any verified experiments.

      If this is not the case, please post a journal paper reference.

    • Deanna Shaw March 23, 2022, 8:37

      Is the quantity and density of anti-helium in our outer Van Allen belts enough to justify launching a vehicle to try and collect it?

      • Adam J Crowl March 23, 2022, 17:58

        Deanna Shaw,
        There was a NIAC grant to study that question a few years back. Apparently Saturn’s Van Allen Belts could store vastly more antimatter than Earth’s. The suggested concept for scooping the antimatter needs a Plasma Magnet to produce big enough fields for a viable capture rate.

        • Jeff Wright March 27, 2022, 2:39

          CT PROFAC as it were.

  • ljk March 22, 2022, 14:38

    Since when did the Cassini probe to Saturn become an interstellar vessel? WOULD it make a good interstellar probe?

  • chirlu March 22, 2022, 17:58
    • Alex Tolley March 23, 2022, 7:01

      That MF article was almost like the description of a game at the center of Hesse’s “The Glass Bead Game”.

  • Jeff Wright March 22, 2022, 18:05

    Johndale Solem’s Medusa scaled down?

  • charlie March 23, 2022, 0:49

    collecting of antimatter from outer space !

    MARS in 3 days

  • Brett Bellmore March 23, 2022, 8:44

    Current particle accelerators are optimized for converting funding into physics papers. It seems quite likely that an accelerator optimized for producing anti-protons could do so with a much higher efficiency. Though likely not impressively high…

    So, a fission fragment rocket, (A favorite of mine!) supercharged with antimatter. Could it operate in a dusty plasma mode instead of a particle trap mode? Are there better isotopes to use in place of the U238?

    I like that it gets you away from having to use gamma rays as an exhaust, and solves the criticality problem in storing nuclear fuel. So it seems scaleable, assuming a source of anti-protons.

    It solves the problem of a craft requiring expensive remote support, always a problem in using beamed propulsion at the far end of a trip. Want to bet the farm on the beam being turned back on in 200 years?

    Is it suitable for in system propulsion in our solar system?

    • Jeff Wright March 24, 2022, 2:43

      I wonder if antimatter might be coupled with Rubbia’ Americiam concept and ablative nozzles for a NSWR set up. Could ablative nozzles hold useful elements-and perhaps jacketed thrust streams with hotter inner cores have colder thrust streams between it and the nozzle. Layered approaches.

  • Geoffrey Hillend March 25, 2022, 19:01

    I am not sure I get the propulsion concept here, but it still looks to me like it uses a reaction mass. Anything with a specific impulse must always have a reaction mass. “The specific impulse is defined as the rocket thrust divided by the rate of the propellant mass flowing through the engine. P. 36, Frontiers of Propulsion Science.

    The problem with this concept paper is that it does not say where we get the anti matter protons which I assume is from a particle collider. How about getting anti matter from another source like radioactive decay and trapping the anti protons in a magnetic field until there is a lot of them and then fire them at a Uranium 235? This gives me an idea of making anti matter faster than particle colliders. Anti protons are not the only type of antimatter, there are positrons. Can radioactive positron decay be trapped in a magnetic field and be made faster than in a particle collider? Another idea is to design an positron factory using the gamma rays of a powerful, free electron gamma ray laser which uses an undulator. This has not been invented yet, but it not outside than range of possibility. X ray lasers use undulators and magnetic fields so making there more powerful is plausible. The idea is to make positrons quickly and store them in a magnetic field in a vacuum. A fast acceleration requires a large anti matter explosion. The only problem I have with an anti matter relativistic rocket is that there has to be many fail safes and redundancies with the magnetic field storage, so there wont be an explosion.

  • Geoffrey Hillend March 25, 2022, 19:42

    My idea was to combine many beams of gamma rays together to make many positrons quickly and trap them in a magnetic field for storage and of course recombine them with matter later to make anti matter propulsion. This might require many of undulators or even a powerful, superconducting magnetic.

  • Michael March 26, 2022, 3:02

    If we collected atoms along the way to the star system there could be enough fuel to brake with when combined with anti matter. If we could collect say around a 10 to 100 sq m swath of space to the target star by use of a magnetic field or deflector there should be enough energy from the mass to energy reation to stop.

  • Juan G. C. March 26, 2022, 6:10

    As far as I know, Sherlock Holmes’ quote comes from The Hound of the Baskervilles, where he eliminates the possibility of the Hound being of supernatural origin.

    • Paul Gilster March 26, 2022, 12:26

      I don’t know which is right, “The Hound of the Baskervilles” or the Holmes short story that Gerry cited in his paper. Anyone else know for sure?

      • Alex Tolley March 26, 2022, 19:00

        According to Wikiquotes, the story where this phrase is used is in “The Adventure of the Blanched Soldier”

        The Adventure of the Blanched Soldier

        • Paul Gilster March 27, 2022, 6:14

          Yes, that’s what Jackson aays as well.

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