Star Journey and Exponential Tendencies

Reminiscing about a few of Robert Ahead’s mind-boggling ideas, as I did in my final publish, jogs my memory that it was each Ahead in addition to the Daedalus challenge that satisfied many individuals to look deeper into the prospect of interstellar flight. Not that there weren’t predecessors – Les Shepherd comes instantly to thoughts (see The Worldship of 1953) – however Ahead was capable of advance a key level: Interstellar flight is feasible inside recognized physics. He argued that the issue was one in every of engineering.

Daedalus made the identical level. When the British Interplanetary Society got here up with a starship design that grew out of freelance scientists and engineers engaged on their very own dime in a pleasant pub, the notion was to not really construct a starship that will bankrupt a complete planet for a easy flyby mission. Somewhat, it was to reveal that even with applied sciences that may very well be extrapolated within the Nineteen Seventies, there have been methods to succeed in the celebrities inside the realm of recognized physics. Starflight was extremely onerous and costly, but when it have been potential, we may strive to determine tips on how to make it possible.

And if figuring it out takes centuries fairly than a long time, what of it? The celebrities are a aim for humanity, not for people. Reaching them is a multi-generational effort that builds one mission at a time. At any level within the course of, we do what we are able to.

What steps can we take alongside the best way to start out transferring up the type of technological ladder that Phil Lubin and Alexander Cohen study of their current paper? As a result of you possibly can’t simply bounce to Ahead’s 1000-kilometer sails pushed by a beam from an influence station in photo voltaic orbit that feeds a huge Fresnel lens constructed within the outer Photo voltaic System between the orbits of Saturn and Uranus. The laser energy demand for a few of Ahead’s missions is roughly 1000 instances our present energy consumption. That’s to say, 1000 instances the ability consumption of our total civilization.

Clearly, we’ve to discover a strategy to begin on the different finish, simply how beamed power applied sciences can produce early advantages via far smaller-scale missions proper right here within the Photo voltaic System. Lubin and Cohen hope to construct on these by leveraging the exponential development we see in some sectors of the electronics and photonics industries, which supplies us that tough transferring goal we checked out final time. How precisely are you able to estimate the place we’ll be in ten years? How steady is the time period ‘exponential’?

These are tough questions, however we do see tendencies right here which are sharply totally different from what we’ve noticed in chemical rocketry, the place we’re nonetheless utilizing launch automobiles that anybody watching a Mercury astronaut blast off in 1961 would perceive. Client demand doesn’t drive chemical propulsion, however by way of energy beaming, we clearly do have electronics and photonics industries by which the function of the patron performs a key function. We additionally see the exponential development in functionality paralleled by exponential decreases in value in areas that may profit beamed applied sciences.

Lubin and Cohen see such development as the important thing to a sustainable program that builds functionality in a collection of steps, transferring ever outward by way of mission complexity and pace. Take a look at tendencies in photonics, as proven in Determine 5 of their paper.

Picture (click on to enlarge): That is Determine 5 from the paper. Caption: (a) Image of present 1-3 kW class Yb laser amplifier which kinds the baseline strategy for our design. Fiber output is proven at decrease left. Mass is approx 5 kg and measurement is roughly that of this web page. This may evolve quickly, however is already adequate to start. Courtesy Nufern. (b) CW fiber laser energy vs 12 months over 25 years exhibiting a “Moore’s Legislation” like development with a doubling time of about 20 months. (c) CW fiber lasers and Yb fiber laser amplifiers (baselined on this paper) value/watt with an inflation index correction to convey it to 2016 {dollars}. Notice the superb match to an exponential with a price “halving” time of 18 months.

Such development makes growing a cost-optimized mannequin for beamed propulsion a tough proposition. We’ve talked in these pages earlier than concerning the want for such a mannequin, significantly in Jim Benford’s Beamer Know-how for Reaching the Photo voltaic Gravity Focus Line, the place he introduced his evaluation of value optimized methods working at totally different wavelengths. That article grew out of his paper “Intermediate Beamers for Starshot: Probes to the Solar’s Inside Gravity Focus” (JBIS 72, pg. 51), written with Greg Matloff in 2019. I must also point out Benford’s “Starship Sails Propelled by Price-Optimized Directed Vitality” (JBIS 66, pg. 85 – summary), and word that Kevin Parkin authored “The Breakthrough Starshot System Mannequin” (Acta Astronautica 152, 370–384) in 2018 (full textual content). So sources are there for comparative evaluation on the matter.

However let’s discuss some extra concerning the laser driver that may produce the beam wanted to energy house missions like these within the Lubin and Cohen paper, remembering that whereas interstellar flight is a long-term aim, a lot smaller methods can develop via such analysis as we take a look at and refine missions of scientific worth to close by targets. The authors see the photon driver as a phased laser array, the concept being to switch a single large laser with quite a few laser amplifiers in what known as a “MOPA (Grasp Oscillator Energy Amplifier) configuration with a baseline of Yb [ytterbium] amplifiers working at 1064 nm.”

Lubin has been engaged on this idea via his Starlight program at UC-Santa Barbara, which has acquired Part I and II funding via NASA’s Revolutionary Superior Ideas program underneath the headings DEEP-IN (Directed Vitality Propulsion for Interstellar Exploration) and DEIS (Directed Vitality Interstellar Research). You’ll additionally acknowledge the laser-driven sail idea as a key a part of the Breakthrough Starshot effort, for which Lubin continues to function a advisor.

Essential to the laser array idea in financial phrases is that the array replaces typical optics with quite a few low-cost optical parts. The thought scales in fascinating methods, because the paper notes:

The fundamental system topology is scalable to any degree of energy and array measurement the place the tradeoff is between the spacecraft mass and pace and therefore the “steps on the ladder.” One of many benefits of this strategy is that when a laser driver is constructed it may be used on all kinds of missions, from massive mass interplanetary to low mass interstellar probes, and might be amortized over a really massive vary of missions.

So instantly we’re speaking about constructing not a one-off interstellar mission (one other Daedalus, although utilizing beamed power fairly than fusion and at a a lot totally different scale), however fairly a system that may start producing scientific returns early within the course of as we resolve such points as part locking to keep up the integrity of the beam. The authors liken this strategy to constructing a supercomputer from numerous modest processors. Because it scales up, such a system may produce:

  • Beamed energy for ion engine methods (as mentioned within the earlier publish);
  • Energy to distant spacecraft, probably eliminating onboard radioisotope thermoelectric turbines (RTG);
  • Planetary protection methods towards asteroids and comets;
  • Laser scanning (LIDAR) to establish close by objects and analyze them.

Take this to a full-scale 50 to 100 GW system and you may push a tiny payload (like Starshot’s ‘spacecraft on a chip’) to maybe 25 p.c of lightspeed utilizing a meter-class reflective sail illuminated for a matter of not more than minutes. Whether or not you might get information again from it’s one other matter, and a extreme constraint upon the Starshot program, although one which continues to be analyzed by its scientists.

However let me dwell on nearer prospects: A system like this might additionally push a 100 kg payload to 0.01 c and – the one that actually catches my eye – a ten,000 kg payload to greater than 1,000 kilometers per second. At this scale of mass, the authors assume we’d be higher off going to IDM strategies, with the beam supplying energy to onboard propulsion, however the level is we might have startlingly swift choices for reaching the outer Photo voltaic System and past with payloads permitting complicated operations there.

If we are able to construct it, a laser array like this may be modular, drawing on mass manufacturing for its key parts and thus reaching economies of scale. It’s an enabler for interstellar missions but additionally a software for constructing infrastructure within the Photo voltaic System:

There are very massive economies of scale in such a system along with the exponential development. The system has no expendables, is totally stable state, and might run repeatedly for years on finish. Industrial fiber lasers have MTBF in extra of fifty,000 hours. The revolution in stable state lighting together with upcoming laser lighting will solely additional improve the efficiency and decrease prices. The “wall plug” effectivity is great at 42% as of this 12 months. The identical fundamental system will also be used as a phased array telescope for the obtain aspect within the laser communications in addition to for future kilometer-scale telescopes for specialised functions comparable to spectroscopy of exoplanet atmospheres and excessive redshift cosmology research…

Such capabilities need to be matched towards the problems inevitable in such a design. These concepts are reliant on the prospect of business capability catching up, a course of that’s mitigated by discovering applied sciences pushed by different sectors or produced in mass portions in order to succeed in the wanted value level. A serious problem: Can laser amplifiers parallel what is going on within the present LED lighting market, the place prices proceed to plummet? A parallel motion in laser amplifiers would, over the following 20 years, cut back their value sufficient that it could not dominate the general system value.

That is problematic. Lubin and Cohen level out that LED prices are pushed by the massive quantity wanted. There isn’t a such demand in laser amplifiers. Can we anticipate the exponential development to proceed on this space? I requested Dr. Lubin about this in an e-mail. Given the significance of the difficulty, I need to quote his response at some size:

There are a variety of the way we’re wanting on the economics of laser amplifiers. At present we’re utilizing fiber primarily based amplifiers pumped by diode lasers. There are different forms of amplification that embrace direct semiconductor amplifiers often known as SOA (Semiconductor Optical Amplifier). That is an rising expertise that could be a path ahead sooner or later. That is an instance of attempting to foretell the long run primarily based on present expertise. Usually the long run is not only “extra of the identical” however fairly the long run usually is disrupted by new applied sciences. That is a part of a future we seek advice from as “built-in photonics” the place the part shifting and amplification are achieved “on wafer” very like computation is completed “on wafer” with the CPU, reminiscence, GPU and auxiliary electronics all built-in in a single parts (chip/ wafer).

Lubin makes use of the analogy of a contemporary private laptop as in comparison with an ENIAC machine from 1943, as we went from room-sized computer systems that drew 100 kW to one thing that, right this moment, we are able to maintain in our fingers and carry in our pockets. We get pleasure from a contemporary model that’s about 1 billion instances quicker and encompasses a billion instances the reminiscence. And he continues:

Within the case of our present strategy of utilizing fiber primarily based amplifiers the “intrinsic uncooked supplies value” of the fiber laser amplifier may be very low and in the event you have a look at each a part of the complete system, the intrinsic prices are fairly low per sub component. This works to our benefit as we are able to take a look at the essential system efficiency incrementally and as we enlarge the dimensions to extend its functionality, we will cut back the ultimate prices because of the persevering with exponential development in expertise. To some extent that is much like deploying photo voltaic PV [photovoltaics]. The extra we deploy the cheaper it will get per watt deployed, and what was not way back conceivable by way of scale is now readily achieved.

Therefore the necessity to learn the way to optimize the price of the laser array that’s important to a beamed power propulsion infrastructure. The paper is obtainable as an try to supply such a price operate, to soak up the big selection of system parameters and their complicated connections. Evaluating their outcomes to previous NASA applications, Lubin and Cohen level out that exponential applied sciences essentially change the sport, with the price of the analysis and improvement part being amortised over a long time. Furthermore, directed power methods are pushed by market components in areas as various as telecommunications and industrial electronics in a long-term improvement part.

An efficient value mannequin generates the most effective value given the parameters essential to supply a product. A price operate that takes into consideration the complicated interconnections right here is, to say the least, difficult, and I go away the reader to discover the equations the authors develop within the seek for value minimums, relating system parameters to the physics. Thus pace and mass are associated to energy, array measurement, wavelength, and so forth. The mannequin additionally examines staged system objectives – in different phrases, it considers the assorted milestones that may be achieved because the system grows.

Keep in mind that it is a value mannequin, not a price estimate, which the authors argue wouldn’t be not credible given the long-term nature of the proposed program. However it’s a mannequin primarily based on value expectations drawn from current applied sciences. We are able to see that the worldwide photonics market is anticipated to exceed $1 trillion by this 12 months (rising from $180 billion in 2016), with annual development charges of 20 p.c.

These are numbers that dwarf the present chemical launch business; Lubin and Cohen contemplate them to disclose the “engine upon which a DE program could be propelled” via the combination of photonics and mass manufacturing. Whereas basic physics drives the analytical value mannequin, it’s the long run rising tendencies that set the fee parameters within the mannequin.

Right now’s paper is Lubin & Cohen, “The Economics of Interstellar Flight,” to be revealed in a particular problem of Acta Astronautica (preprint).


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