Take a look at the image below. It’s a jet coming off the quasar 3C273. I call your attention to the length of this jet, some 100,000 light years, which is roughly the distance across the Milky Way. Jeff Greason pointed out at the Montreal symposium of the Interstellar Research Group that images like this suggest it may be possible for humans to produce ‘pinched’ relativistic electron jets over the much smaller distances needed to propel a spacecraft out of the Solar System. This is an intriguing image if you’re interested in high-energy beams pushing payloads to nearby stars.
Greason is a self-described ‘serial entrepreneur,’ the holder of some 29 patents and chief technologist of Electric Sky, which is all about beaming energy to craft much closer to home. But he moonlights as chairman of the Tau Zero Foundation and is a well known figure in interstellar studies. Placing beaming into context is a useful exercise, as it suggests alternative ways to generate and use a beam. In all of these, we want to carry little or no fuel aboard the craft, drawing our propulsion from the home system.
Image: Composite false-color image of the quasar jet 3C273, with emission from radio waves to X-rays extending over more than 100,000 light years. The black hole itself is to the left of the image. Colors indicate the wavelength region where energetic particles give off most of their energy: yellow contours show the radio emission, with denser contours for brighter emission (data from VLA); blue is for X-rays (Chandra); green for optical light (Hubble); and red is for infrared emission (Spitzer). Credit: Y. Uchiyama, M. Urry, H.-J. Röser, R. Perley, S. Jester.
Laser beaming to a starship comes first to mind, going back as it does to the days of Robert Forward and György Marx, who explored options in the infancy of the technology. Later work on laser ad well as microwave beaming has included such luminaries as Geoffrey Landis, Gregory Matloff and James Benford, not to mention today’s intense laser effort via Breakthrough Starshot and the ongoing work at UC-Santa Barbara under Philip Lubin. A separate track has followed beamed options using elementary particles or, indeed, larger particles; the name Clifford Singer comes first to mind here, though Landis has done key work. A major problem: Beam power is inversely proportional to effective range. If we’re after faster, bigger ships, we need to find a way to extend the range of whatever kind of beam we’re sending.
We’ve lost some of the scientists who have dug deeply into these matters. Dana Andrews died last January, and Jordin Kare left us some six years ago (I will have more to say about Dr. Andrews in a future post). Kare developed ‘sailbeam,’ which was a string of micro-sails sent as fuel fodder to a larger starship. Pushing neutral particles to the long ranges we need faces problems of beam divergence, and charged particle beams are even more tricky, because like charges cause the beam to diverge.
Greason outlined another possibility at Montreal, one he described as ‘no more than half of an idea,’ but one he’s hoping to provoke colleagues to explore. This beaming option uses the ‘pinch’ phenomenon, in which charged beams in a low-density plasma can confine themselves over long distances. The mechanism: A beam carrying a current creates a circular axial magnetic field which in turn confines the beam. ‘Pinching’ is a means of self-confinement of the beam that has been studied since the 1930s. A pinch forming a jet explains why solar proton events can strike the Earth despite the 1 AU distance, and why galaxy-spanning jets like that in the image above can form.
Image: Jeff Greason, chief technologist and co-founder of Electric Sky.
We normally hear about a ‘pinch’ in the context of fusion research, but here we’re more interested in the beam’s persistence than its ability to compress and heat a plasma. The beam persists until it loses energy by collisions, which causes the current sustaining it to weaken and lose confinement. Although Greason said that ion beams may prove feasible, he noted that we’re getting into territory where we simply lack data to know what will work. Issues of charge neutralization and return currents from the beam come into play, as do long-range oscillations that can affect the beam. But the idea of applying a magnetic field to a stream of electrons along a specific axis to create the z-pinch is well established. If we can create an electron beam using this method, we can resurrect the idea of using charged particle beams to push our starship.
How to use power beamed in this fashion once it arrives at the target craft is a significant question. Greason spoke of the beam striking a plasma-filled waveguide which can ‘couple to backwards plasma wave modes,’ in effect launching plasma in the opposite direction as reaction mass. This keys to existing work on plasma accelerators (so-called “wakefield” accelerators), which use similar physics. How much of the beamed energy can be returned in this way remains up for investigation.
The consequences of mastering pinched beaming technologies would be immense. If we can increase the range of a beam from 0.1 AU to 1000 AU, we open up the possibility of sending much larger spacecraft, up to 105 larger, at the same power levels. We go from a gram-sized spacecraft as contemplated by Breakthrough Starshot’s laser methods to one of 10 kilograms. In doing this we have also changed the acceleration time from minutes to months. That increased payload size is particularly useful when it allows a braking system aboard for long-term study of the target.
This method demands a space-based platform – these ideas are inapplicable when applied to a ground installation and a beam through the atmosphere. Beaming from a location near the Sun offers obvious access to power and could be made possible through a near-Solar statite; i.e., an installation that ‘hovers’ over the Sun at Parker Solar Probe distances. Greason adds that to add maximum stability to the beam, the statite would have to transmit from a location between the Sun and the target star; i.e, the flow should be with the current of the solar wind as opposed to across the stream.
Image: Can we operate a statite at 0.05 AU from the Sun? This NASA visualization of the Parker Solar Probe highlights the kind of conditions the craft would be operating in.
The operative statite technology is thermionics, where electrons ‘boil’ out of a hot cathode and collect on a cold anode. Greason’s statite winds up with approximately 50 kilowatts per square meter of useful power; factoring in the thickness of the foils used in the installation, he calculates 150 kilowatts per square kilogram. A 1 gigawatt electron beam results. So operating at about 11 solar radii, we can produce the beam we need while also being forced to tackle the issues involved in maintaining a statite in position. One possibility is a plasma magnet sail to make use of the supersonic solar wind, a notion Greason has been exploring for years. See Alex Tolley’s The Plasma Magnet Drive: A Simple, Cheap Drive for the Solar System and Beyond for more.
Greason’s tightly reasoned, no-nonsense approach makes him a hugely appealing speaker. He’s offering a concept that opens out into all kinds of research questions, and spurring interested parties to advance the construct. A symposium of like-minded scientists and engineers like that in Montreal provides the kind of venue to gin up that support. The implication of being able to reach 20 percent of lightspeed with a multi-kilogram spacecraft is driver enough. A craft like that could begin exploration of nearby stars in stellar orbit there, rather than blowing through the destination system within a matter of minutes. What smaller beam installations near Earth could do for interplanetary exploration is left to the imagination of the reader.
This will require incredible accuracy in aiming the beam over a light year or so, especially given that we can see where they were a year ago at best and riding out a solar storm while remaining utterly still seems awfully challenging.
Actually, Jeff assumes using the beam over no more than 1000 AU, so the problem becomes a bit easier. I do recall Bob Forward’s beamed lightsail deceleration strategy, which called for laser beaming across light years, but this proposal doesn’t push that far.
Rewatching the presentation, I wonder if the slide that has both the effective distance changing from 0.1A U to 1000 AU (10,000x) and his figure for increased mass of the spacecraft vs the BS 1 gm version (100,000x) was why Greason stumbled a bit on the size of the craft “10 kg..100kg…10kg”. I think the slide needs to be corrected in the next version to indicate the size increase to 10,000x.
Regarding the use of plasma to be ejected to provide thrust. No details were given, but I wonder if this is where the plasma magnet/wave rider concept helps, as this magsail effectively entrains the local ions into a current to sustain the magnetic field. The ion density is low, but if the craft receives an electron beam that would make it negatively charged, this would attract the positive ions so that they could be concentrated into a denser plasma that would be both the propellant and the positive attractor for the electron beam. Using the plasma in the ISM is the requirement to eliminate the limitations of the rocket equation to reach the fractional c velocity. Or is the plasma purely a means to create an effective drag like a sail to propel the craft? I am not clear on what is proposed.
Regarding the impact of magnetic fields and beam bending. Idk the orientation of the beam in the image that spans 100,000 ly. Is it interacting with the galaxy’s magnetic field? If so, there is some bending, but it is fairly straight over its length. Is this a clue for the dynamics of relativistic beams?
The plasma magnet (Rotating Magnetic Field) entrains local “electrons” (not ions) into a (rotating) current disc that creates a steady dipole magnetic field according to Slough 2006 NIAC final report – see Figure 2 of
https://www.niac.usra.edu/files/studies/final_report/917Slough.pdf
The resulting “large scale magnetospheric object” from that figure caption has a bow shock and magnetopause whose outer layers are negatively charged (inner layers are positively charged) so the overall area is quasi-neutral and I believe would deflect an electron beam – that is how a magnetic sail works. See https://en.wikipedia.org/wiki/Magnetic_sail
As I recall from your analysis of Greason’s reaction drive it is not the plasma in the ISM that eliminates the limitation of the rocket equation, but your analysis that the spacecraft ejecting propellant at (half) the velocity of the apparent plasma wind that creates a polynomial versus exponential mass ratio equation.
See Figure 2 of associated text https://centauri-dreams.org/2020/03/27/introducing-the-q-drive-a-concept-that-offers-the-possibility-of-interstellar-flight/
Your result in that post was a significant insight for me – I couldn’t follow Greason’s derivation in the reaction drive paper.
A similar result was published in 1959 and 1990 and is straightforward to derive as described here:
https://forum.nasaspaceflight.com/index.php?topic=37511.0
Imagining those interplanetary uses… I picture piggybacking an alternating current onto the plasma plume, akin to the electromechanical vibrations we hear around Saturn. A probe at the far end might recharge its batteries with the AC vibrational energy using impedance effects, like one of those single-lead testers you use to identify the hot wire in an electrical outlet. An asteroid miner could do the same but more so, using its rock as a “ground” like any household customer on Earth. The presentation says power transmission might be possible using “wave modes”, but is there an upper limit to the frequency of the AC you could transmit? I’d think any mildly concentrated plasma could act like a power wire through space, with the AC providing the same advantages that made it catch on on Earth.
Of interest
https://arxiv.org/pdf/2310.17578.pdf
A 9 trillion amplification using two lens is quite impressive !
I suppose if we had a large current carrying disc in a lagrange point we could funnel the solar wind into the centre, because it is already ionised we simply accelerate it using solar power from the sun. The probe to be accelerated is put at the centre which gets hit by the accelerated solar wind either directly or interactions with an onboard magnetic field. Or using an electric field design.
https://electric-sailing.fi/
It’s a shame the electric design never went far when it surely could have.
I don’t think we need worry about the consequences of new technologies making earlier probes obsolete. A civilization’s first interstellar missions will no doubt be launched towards nearby targets, or at any rate, nearby interesting or high priority destinations.
If new, higher velocity drives become available before the first wave of probes arrive, it makes more sense that other more distant targets will be assigned to the newer, faster probes. Either that, or the new swift probes will be sent to targets that the first wave of exploration visited and reported especially unexpected and important discoveries.
It can be safely assumed that the launching and management of interstellar vehicles will be an expensive proposition for any civilization, especially during their initial explorations of their immediate neighborhoods. I doubt it would make sense to launch multiple expeditions to the same place simply because they had a faster propulsion system available. I suspect any improvements in propulsion technology would be aimed at more distant destinations.
There is one characteristic of interstellar exploration that has not been studied and which I believe merits our consideration. If a string of stars can be identified which can be visited by one probe, that is, a collection of destinations that extends radially from the the original point of departure, it might make sense to visit them all with one mission, making fly-bys of each star in turn. The probe would use most of its potential delta-v in accelerating towards the nearest destination. and then less energetic maneuvers, and gravity assists for subsequent targets further out. The mission trajectory would describe an arc, with inflection points at each encounter. Low-thrust but high efficiency propulsion could be used between encounters because the intervals between stars would be so long. This would increase the utility of each mission by having it visit several destinations, even if only one was considered high priority, or otherwise of great interest.
I don’t visualize one fly-by probe or impact to a close neighbor, but a long term program of multiple probes, with follow-ups, perhaps even orbiters and landers to targets that merit closer inspection. Orbiters and landers require so much energy that those maneuvers would be reserved only for the most important targets.
We’re talking about a Thousand Year Plan. Not a million, just a thousand. It would require long-term planning and a long term infrastructure to manage it and collect the data. I suspect after visiting, at most, several hundred nearby stars and finding pretty much the same snowballs and slag heaps around all of them, most civilizations capable of interstellar travel will just give it up and devote themselves to tending their own garden instead. Cultures that arise inside crowded open clusters, or develop FTL, may find it worthwhile to continue their explorations, but I doubt most will bother.
I doubt we will. Our own exploration of our solar system has been occasionally brilliant, it has challenged our technology and our bureaucracies, but there has been little in the way of long term planning, of building each step carefully on past ones, with a view to preparing for future ones.
My apologies. I posted these remarks here incorrectly, I meant to comment on the previous subject for discussion; “The Order of Interstellar Arrival”. Please forgive my error.
Jeff Greason‘’s ‘no more than half of an idea’ may be even less. Even with optimal background plasma conditions, generating just the right self-fields, the beam suffers erosion at the front of the beam, both inductive erosion and magnetic.
We’re not ‘getting into territory where we simply lack data to know what will work’. During the 1970s, and especially the 1980s, an enormous amount of work occured on the question of how to propagate particle beams in several environments, including the atmosphere and space. In the work I did 40 to 50 years ago (23 papers in 8 years!) on beam propagation effects, I struggled in a host of experiments to try to propagate electron beams efficiently.
If you inject into a vacuum the beam explodes by charge repulsion. If you inject into ionized plasma, the beam explodes because there are no fields to contain the transverse velocity component, and the more intense the beam is, the larger that component is. The only propagation regimes that work, even over short distances, depends on precisely the right background medium and fields. Issues of charge neutralization and return currents from the beam come into play, as do growing oscillations (instabilities, actually) that can affect, in fact, destroy, the beam. The only propagation regimes that work are either:
1) strong guiding magnetic fields, either axial or azimuthal, in a background plasma,
2) a partially ionized low-density medium wherein charge neutralization occurs but current neutralization is only partial. This is called the ion-focused regime.
My conclusion: using charged particle beams to push a starship would be impossible.
James, it also depends on the charge to mass ratio of particles used, for instance if we had bucky balls filled with elements the divergence would be a lot less and the recombination with electrons again would have a much lower effect on the trajectory of the particles.
I suppose if we had these bucky balls filled with heavy elements we could fire alternate ones of different charge. One has a positive charge and then the next one a negative charge then the stream of charged particles would tend to want to pull together along the line of them and not fly off in different directions.
Wasn’t the argument for using electrons that it was easy to accelerate them to relativistic velocities? Using buckyballs, or indeed any more massive particle is a move in the direction of sensing small masses to accelerate the sail.
I suppose it does make it easier to intersperse positive and negative changed buckyballs, with each charged ball given a different energy to ensure that the velocities are the same for all charged balls. I imagine the electric field to accelerate the particles is reversed rapidly to create a neutral stream.
One problem with this approach is that any perturbing magnetic or electric field will split the beam. Another is that the means to attract the beams – an electric charge in Greason’s idea, would not work unless one was prepared to lose half the beam energy. OTOH, maybe a magnetic scoop would work for both charged particles.
I am still intrigued as to what is holding the quasar jet together. This paper On pair content of quasar jets suggests that they are dominated by protons with electron-positron pairs.
If so, then the the use of the quasar jet to support the pinched electron beam is not exactly relevant, as there are opposite changes at least holding the electrons and positrons together, even if they annihilate each other eventually.
Can someone with knowledge of this weigh in on this issue?
It is easier to accelerate electrons but do we really need fraction of c velocities when the spacecraft only needs to go a hundred or a thousand kilometres per second for now. As each alternate Bucky ball will be given a charge positive or negative it could be arranged that they are attached to each other along the line eventually combining near the spacecraft for direct push or still charged to be repelled by a strong magnetic field. And yes charge switching would have to be high speed to allow acceleration of the different charged particles. And yes electric and magnetic fields would affect the path but at high enough velocity divergence would be lower, also allowing early recombination would cause them to be neutral.
We could use nano particles of PTFE as the negative charge carrier with Buckyballs as the positive ones, just need to match their masses up closely. The neat thing is they can be used in a normal particle accelerator.
3C 273. Had to mull this one over for a while. And my perspective of this phenomenon over the years is from a bit different perspective. But maybe there
is a handoff somewhere.
Some might remember this object (3C 273) nostalgically. But perhaps for those who either weren’t around or have simply moved on, this was the 3rd Cambridge Catalog of Radio sources object that coined the term “quasar” and launched a million color TV sets. Back in the 1960s it was initially known as a varying light source with large red shift, suggesting a very bright ( absolute magnitude) compact object as well as a radio emitter. Subsequently identified as an “active” black hole in the center of a galaxy about 2.5 billion light years removed. An accretion disk surrounding it and …
About the internals of black holes we know total mass, the orientation and intensity of the magnetic field, and the rotation … Well, I should be careful.
We know which way the magnetic field rotates and I presume we know the rotational orientation of the momentum associated with its mass. The distinction here is that the magnetic field and rotational axis associated with momentum could be different and likely is. Otherwise no light house. For Newtonian mechanics, rotating fluid spheres become oblate. Polar diameter becomes lower than equatorial and masses in orbit with inclinations experience precession in their orbital planes. Leads one to suspect that you get an enormous fan and compressor effect.
This operation is associated with an estimated 800 million solar mass black hole.
Does the effect that is observed in smaller size objects. Example? What’s the difference between a neutron star and a pulsar?
Or how about this one: SS 433?
SS 433 is a binary system comprising a main sequence A star somewhat modified by “exposure” and a stellar mass black hole exhibiting similar behavior to the 3C 272. Despite precise period measurements, sources are cagey about mass. Shall we say about 3 solar masses for the A and about 15 for the black hole? The jet velocites north and south are about .26 of c.
So the mechanism is scaled down somewhat from the 800 million solar mass illustrative example. Not sure what the measured exhaust velocities imply. But if the object is to obtain higher v/c values, one might need to look at the equivalent to near nozzle exit velocities for this natural system and ones that technology can possibly devise.
In early phases of stellar system formation, accretion disks around stars result in similar E-M nozzle effects for similar reasons. But I believe that the velocities to which these blobs obtain ( Herbig-Haro objects) are on in the hundreds of kilometers per second. The same sort of interaction with the surrounding accretion disk and the primary ( a forming star perhaps not yet even on the main sequence of sustained hydrogen fusion) but with a strong magnetic field.
So there are a couple of patterns and trends here. As the astrophysical phenomena occur on less massive or compact scales, the particle acceleration becomes lower. Though there are mysteries associated with these jets, they are not all necessarily relativistic processes. Likely some fluid dynamics details to tie down too.
There are masers and lasers. Can there be a thing such as a matter “laser”? Using such things , for example, as Bose-Einstein condensates?
Robert Clark