We’ve become more ambitious about reaching Alpha Centauri – what changed?

The real innovation powering the idea of Starshot is not in terms of propulsion or even the lasers but of the miniaturisation of electronics.

Yuri Milner’s announcement last night that he’s investing $100 million into figuring out how thousands of chip-sized probes could be sent to the Alpha Centauri star system in 20 years must’ve felt like the future to many. The proposal, titled Starshot, imagines the probes to be fitted with small ‘sails’ a few hundred atoms thick that could be propelled by a powerful array of lasers fired from Earth to 60,000 km/s. And once they get to the Alpha Centauri stars A or B, they could take images with a 2 MP camera and transmit them to Earth through an optical communications channel. The radical R&D developed on the way to achieving these big goals could also be deployed to visiting planets within the Solar System in a matter of hours to days, as well as using the lasers and their optical systems to study asteroids and stars.

But strip away the radicalness and Starshot begins to resemble pieces of the previous century as well, pieces that make for a tradition in which Milner is only the latest, albeit most prominent, participant, and which provide an expanded frame of reference to examine what had to change for astronomers to dream of literally reaching for the stars. The three most prominent pieces are Orion, Daedalus and Daedalus’s derivative, Longshot. All three were reliant on technology that didn’t exist but soon would. Daedalus and Longshot in particular wanted to send unmanned probes to nearby stars within a 100 years. And even more specifically, Longshot is closer to Milner’s idea in its aspiring to:

  • Launch the probes from space, not from the ground
  • Envision and build a more efficient kind of propulsion, and
  • Send unmanned probes to Alpha Centauri

Commissioned by the British Interplanetary Society and led by an engineer named Alan Bond, Daedalus involved the designing of an unmanned probe that could be sent to Barnard’s Star, 5.9 lightyears away, in 50 years using contemporary technological ideas. At the time, in 1973-1978, the most efficient such idea was nuclear fusion – it was only two decades before that when another nuclear-fusion-propelled rocket, called Project Orion, had been under consideration by the physicists Theodore B. Taylor and Freeman Dyson. Because of the amount power and thrust produced by fusion was known to be very high, Bond’s Daedalus could be massive as well.

The size of the (unbuilt) Daedalus starship compared to the Empire State Building, which is 443 metres tall. Credit: Adrian Mann/bisbos.com
The size of the (unbuilt) Daedalus starship compared to the Empire State Building, which is 443 metres tall. Credit: Adrian Mann/bisbos.com

Conventional rockets that burn high-grade fuel in large quantities in a short span of time to get off the ground are limited by the pesky Tsiolkovsky rocket equation. At its simplest, the equation describes how a rocket that wants to carry more payloads must also carry more fuel to carry those payloads, in turn becoming even heavier, in turn having to carry even more fuel, in turn becoming even heavier, in turn having to carry even more fuel, and so forth… On the other hand, a small nuclear power plant carried onboard Daedalus’s rocket would seem to provide quick escape from the Tsiolkovsky problem – compressing small amounts of helium-3 (mined from the moon or the surface of Jupiter by hot-air balloons) using electron beams to yield 250 pellet-detonations/second sustained for 3.8 years. So, the review concluded with a suggestion that Project Daedalus’s rocket could weigh 54,000 tonnes (including fuel).

In 1986, interest in this idea was revived by a report of the US National Space Society’s National Commission on Space. It recommended focused research into human spaceflight, efficient and sustainable fuel options, astrometry and interstellar research unto developing a “pioneering” American mission in the early 21st century. Particularly, it suggested developing a “long-life, high-velocity spacecraft to be sent out of the Solar System on a trajectory to the nearest star”. These ideas were advanced by a team of engineering students and NASA scientists, working with the US Naval Academy, which published its own 74-page report in 1987 titled ‘Project Longshot: An Unmanned Probe to Alpha Centauri’. Like Daedalus, Longshot aspired to use inertial confinement fusion – using energetic beams of particles to confine pellets of helium-3 and deuterium to fusionable levels – but with four key differences.

First, instead of obtaining helium-3 from the moon or the clouds of Jupiter, the team suggested using particle accelerators. Second, the nuclear reactions would be executed at small scales within a “pulsed fusion microexplosion drive”. A magnetic casing surrounding the drive chamber would then channel out a stream of charged particles produced in the reaction to create thrust. Third, while Daedalus would fly by the Alpha Centauri system’s stars (and release smaller probes), Longshot was designed to be able to get into orbit around the star Alpha Centauri B. Fourth, and most important, the fusion reactor was not to be used to launch Longshot from the ground nor away from Earth but only to propel it through space over 100 years. This was because of the risk of the fusion reactor going out of control in or close to Earth’s atmosphere. The team recommended sending each of the spacecraft’s modules to a space station (the ISS would be built a decade later), then assembling and launching it from there.

Illustrations showing how the inertial fusion reactions inside Longshot’s reactors would power the rocket. Credit: stanford.edu
Illustrations showing how the inertial fusion reactions inside Longshot’s reactors would power the rocket. Credit: stanford.edu

The report was published only three years after the sci-fi writer Robert L. Forward described his idea of the Starwisp, a satellite fit with a sail that would be pushed on by beams of microwave radiation shot from Earth – much like Starshot. However, the Longshot report devotes three pages to discussing why a “laser-pumped light sail” might not be a good idea. The authors write: “The single impulse required to reach the designated system in 100 years was determined to be 13,500 km/sec. The size of a laser with continuous output, to accelerate the payload to 13,500 km/sec in a year, is 3.75 Terra Watts.” The payload mass was considered to be 30,000 kg. The specific impulse (Isp, evaluated in the table below) is measured in seconds – it’s the duration over which a rocket engine must be fired in order to achieve a proportional amount of thrust given the fuel is flowing into the engine at a fixed rate.

Table considering trade-offs between various propulsion options and their feasibilities. Credit: stanford.edu
Table considering trade-offs between various propulsion options and their feasibilities. Credit: stanford.edu

The Starshot team works around this problem by shrinking the size of the spacecraft (StarChip) to a little bigger than a postage stamp – allowing a 100-gigawatt laser to propel it to very large velocities in a few dozen minutes. (A back-of-the-envelope calculation discounting effects of the atmosphere shows a 50-MW laser working at 100% efficiency will suffice to push a 10-gram StarChip + sail to 60,000 km/s in 30 minutes.) Another boon of the small size is that the power required to operate such instruments is very low, whereas Longshot required a 300-kW fission reactor to power its payload. So, the real innovation on this front is not in terms of propulsion or even the lasers but of the miniaturisation of electronics.

One of the scientists involved in the StarChip team is Zachary R. Manchester, who launched a project called KickSat in 2011 and which was selected for the NASA CubeSat Launch Initiative in 2015. A press statement accompanying the selection reads: “the Sprite [a single “ChipSat”] is a tiny spacecraft that includes power, sensor and communication systems on a printed circuit board measuring 3.5 by 3.5 centimetres with a thickness of a few millimetres and a mass of a few grams”. Each StarChip is likely to turn out to be something similar.

A batch of KickSat Sprites lying on a table. Credit: @zacinaction on Twitter
A batch of KickSat Sprites lying on a table. Credit: @zacinaction on Twitter
A preview of KickSat-2 showing its component circuits. Credit: @spacecraftlab on Twitter
A preview of KickSat-2 showing its component circuits. Credit: @spacecraftlab on Twitter

However, the miniaturisation of electronics doesn’t solve the other problems the Longshot team anticipated, and which Milner’s team has chosen to overlook in favour of compensatory correcting techniques. The biggest among them is deceleration. Even the Longshot’s 100-year transit from a space station in Earth-orbit to a star 4.37 lightyears away consists of accelerating for about 71 years followed by 29 years of deceleration. In contrast, the StarChip fleet won’t decelerate but pretty much sneeze past Alpha Centauri, making rapid well-timed measurements.

Another problem is whether the StarChip sails will be able to withstand the effects of being hit by a 100-GW laser. Recent sail-based experiments like IKAROS and LightSail-1 have demonstrated their feasibility, at least when it comes to being propelled by photons streaming out from the Sun, as well as engineering limitations. Borrowing on lessons from these missions, the Starshot collaboration has proposed that a suitable metamaterial (composed of various materials) be built to be extremely reflective and absorb as few of the laser’s photons as possible. According to a calculation on the website, absorbing even 1-10,000th of the laser’s energy will mean the sail becoming quickly overheated, and that this has to be reduced to a billionth. In fact, as is often overlooked, having endless possibilities also means having endless engineering challenges, and there are enough for Breakthrough Starshot to warrant the $100-million from Milner.

What makes the project truly exciting is its implicit synecdoche – that none of its challenges are real deal-breakers even as surmounting all of them together would give birth to a wild new idea in interstellar research. Unlike Orion, Daedalus or Longshot, Starshot stays clear of the controversies and technical limitations attendant to nuclear power, and is largely divorced from political considerations apropos research-funding. Most importantly, in hindsight, Starshot isn’t proposing a bigger-therefore-better idea, rather taking a break from the past to better leverage our advanced abilities to manipulate materials as well as showing a way out of Tsiolkovsky’s tyranny (even with a nuclear engine, Daedalus’s conceivers suggested the rocket carry 50,000 tonnes of fuel – and it represented a more serious design effort than what went into Longshot). As with all human enterprises, Starshot is worth celebrating if only for the drastic leap in efficiency it represents.

The Wire
April 13, 2016

Winterwolf VII

At that moment, the semi-AI beeped completion, and 34 jumped out of the chair in one fluid motion and lunged at 32, pinning him to the floor as the gun spilled from his hand and clattered a few feet away. Did you upgrade yourself?! 32 simply smiled. I REPEAT, DID YOU UPGRADE YOURSELF?! “No!” Why not? “Because I want to stop this war. I want to go home.” No, you don’t. “I don’t?” The grip loosened and 32 was able to turn his head to face 34’s. You must be upgraded. “No!” He screamed without regard, and incessantly, struggling all the while, kicking and grabbing at 34’s crystal frame; however, neither relented in their individual efforts. Eventually, just as the final pellet was about to be fired, 32 was strapped in and the semi-AI had been mounted to the binary-encryption projector. There is no time. They are coming. I will not let you receive all the memories. Know simply what is to be known, for your future is short.

32’s scream was abruptly silenced, casting upon his person a ghostly sheen, because wherefrom the alarm had issued there was only an faint-blue darkness, the face contorted with terror and the jaw held open by the lack of electric impulse.

Twelve minutes later, the door banged open and six members of the crew tumbled in, clumsily wielding guns and looking around frantically. When they spotted the two cyborgs standing next to the viewing port, they held their guns up and advanced.

“You! What’re you doing here? What happened to Commander Fanderay?!” The two part-machines turned around to face the advancing belligerents, a strange expression on their faces: their eyebrows were flicking, cheeks flushing and unflushing over and over. The Earthborn couldn’t understand any of it, and in response, they brought their guns closer and closer. “Which of you killed Commander Fanderay?” one of them yelled. One of the cyborgs answered in the negative, and the men immediately trained their guns on the other one, and saw a quick transition in his facial features. The gel in 32’s eyes was diluted by an array of microfluid valves set behind his “eyes”, quickly expanding and pushing the iris films out. His eyebrows adjusted and consequently widened across the structure of his square face, but only by a few millimeters. The hydraulic pistons underneath his jaw went slack and muscle control across most of his limbs was lost, rendering them momentarily slackened. All this 34 observed with indifference: 32 was finally human.

Winterwolf VI

“Right. Caution. Good. Anyway, where was I? Yes! Evolution! This race of new humans was enabled to evolve at an accelerated pace, to mutate and reform within a decade without having to wait for a million years, with a genetically implanted trigger that would terminate mutatory control once human intelligence was reached.” The New Chance. “Fantastic! Yes! And do you know who they really are?” Humans? “They are us, you idiot! We are the New Chance!” Silence. “Hmm. The people of the New Chance quickly attained human intelligence, in a little less than two centuries, in fact, but the trigger never went off. Why? Can you tell me why, 34?” Because the New Chance lived through an alternate history, the quick development of intelligence was used by the bodies developing in the local environment to acquire complementary adaptation systems. The trigger did go off, but it had as consequence… nothing. “Yes! We were as babies born with super-human intelligence!”

“And then, 2051 arrived when the Earthborn discovered that we had colonized almost seven arcseconds of the Milky Way. And, I suppose, this is where our ‘histories’ start to differ?” I suppose so, too. “As for the logical consistency–” There were no logical inconsistencies. “So you agree with me?!” 32 was elated. I don’t. “Why not?!” Deflation. Because I can tell you five stories, ten stories… no, I can tell you a thousand stories that comprise the facts in your knowledge and yet amount to disparate conclusions. “Are you telling me my facts weren’t unique?” I’m telling you that no fact is unique. “Oh…” You seem confused. “How do you affirm your disbelief, then?” Because, now, I am equipped only to serve Master Fanderay, whom you have slain. “What?!” Because, now, even though your facts may be just as unique as mine are, we are part of a reality that is antecedent to our actions. I understand you. You wish to terminate this mission because you believe the Winterwolf is a warship conceived to join war with the New Chance IV, the last outpost of the New Chance. , however, believe that and your… adopted kind squandered your intelligence, corrupted your purpose, and abused the world around. Now, you are faced with nuclear war.

Winterwolf IV

CE34 came to life. He felt great innocence, although that could have meant nothing in particular to CE34 because he wouldn’t have known the corruption of innocence. The room he was in was empty. Nothing odd about that. His memories, his knowledge signaled nothing disturbing or being as cause for concern. He looked down. His body seemed complete: part human, part metal, part plastic. He removed himself from the chair he was on and stood up, erect, and even as he did, the wires connected to him automatically disconnected and dropped to the floor. At that moment, he could feel a vibration beneath his feet, even as with a terribly loud clunk that seemed to quake the room he was in, CE34 observed through the viewing port with awe as a giant metal bird crawled into view, just simply floating there. A few seconds later, as he gaped agog, his elbows resting on the rails and him craning his neck to see as much as of the apparition as possible, the bird jerked downward and then blasted off. Its journey took it slowly out of sight of CE34, the spiral path it followed dragging it to the location of a Tesla coil.

“What are you doing?” I am looking out the window. Who are you? “My name is Doriant Fanderay.” Master Fanderay. I remember your name from… from, uh… somewhere. “Don’t push yourself. Here, come, sit down.” Yes, Master Fanderay. “You can call me Doriant.” Yes, Master Fanderay. “Fine. What’s your name?” My name is Thirty Four, Master Fanderay. “What class are you?” I’m a computational engine, Master Fanderay. “Hmm. Where are you from?” I am from the planet called Earth, Master Fanderay. “Who created you?” I was manufactured by Starlight Systems in the year 2051, Master Fanderay. “Good, good. Can you tell me where we are?” Yes, Master Fanderay. We are on a mission to rescue the stricken inhabitants of NC4 from a self-precipitated nuclear winter. “Yes, and how will be of help to us?” I have knowl –… I seem to have knowledge… of the planet’s geography, topology and weather, Master Fanderay.

Doriant stood up suddenly. “Where’s your mate?” Who, Master– “Where’s CE32?!” The huge man ran frantically to the door, and as soon as he was on command deck on his portion of the bay area, he picked up a communicator and yelled quick words to his captain at the other end of the line. Just as he set down the transmitter, a bustling commotion could be discerned from the lower levels, and the sights and sounds of strobes and alarms catapulted back to life. Even so, he still heard the click behind him, and a moment later, dropped dead to the floor, the control panel spattered with his blood and brains.

Winterwolf III

Noiselessly, the two jaws holding the first pellet, nicknamed the Bald Eagle, unclamped and withdrew, the hydraulic pistons powering their ductile muscles being emptied of all air. As the cylinders withdrew slowly, the pellet came loose, for a moment just hanging limp in space before a trigger went off deep within its titanium heart, igniting the secondary boosters. Directing itself downward and transmitting the coordinates of its location every second to the Winterwolf, the Bald Eagle started its gentle descent into the atmosphere of New Chance IV.


The Tesla coil went dead. One moment, there were sparks, and then the next, the ladder was gone. Hundreds of miles above its zenith, the sky was graying, turning slowly from a deep hue of green-blue to a pale shade of gray. Like a blot of ink on flimsy paper tissue, it was spreading, eating into the sky, a deadly flower blooming to herald the coming of a blighted spring, a malformed foetus come to disrupt a tradition of beauty. The faint odour of ozone was thinning, gradually but steadily, even as the temperature in a large hemisphere around the coil began to drop. Communication around the tower went limp with it. The sparks couldn’t permeate the airs anymore as gusts blowing within their invisible veins turned neutral, dampened infinitely, and were goaded no longer to swing or lunge. A sulfurous stench was becoming prevalent, too. A dragon was coming.


To call the Bald Eagle a pellet was stupidity. Tip to tip, it measured 89 feet, more than ten-times the wingspan of a full-grown Earthborn albatross, and from its helm to tail, 11 feet. Calling such a thing a pellet was derogatory, pejorative even, and some would say it was absolutely warranted. Its body was curved like a bow’s, although not quite as heavily, and its underside was pocked with miniscule half-gouges and textured rough. As it accelerated through the dense atmosphere, the gouges prompted the construction’s shell to wear off in slivers at first and then as shards and then as chunks of metal, exposing flasks of combustible chemicals. As the temperature reached magnanimous proportions, the flasks’ lining tore off and set the liquids on fire, which in turn set off small explosives positioned in a ring. Each detonation blew out hundreds and hundreds of pellets of thorium-232, each of which had been “activated” only moments earlier with an electron laser. At the end of the next 24 months, the thorium would decay into protactinium and then to the highly radioactive uranium-232, and New Chance IV would be blanketed with death.

The time-period of two years was chosen to provide the rebels with a chance to relent and surrender, at which point the Winterwolf would send down lead-secured rescue-ferries. At the same time, for each day that they postponed their decision, tens and then thousands would die, and future generations forever doomed to evolutionary insufficiency. It was first thought this could be achieved with full-scale war, but the rebels’ ability to construct cyborgs from decapitated body parts would significantly reduce attrition on the battlefield. Instead, two cyborgs had been kidnapped and their memories extracted, and the Earthborn learnt of the Tesla coils. Simply destroying them wouldn’t do – more would come up. Instead, shutting them down permanently and causing significant biological distress would cripple their beloved New Chance one and for all.

Winterwolf II

Snapping him out of attention, suddenly, was a long-toned beep from the semi-AI monitoring CE34’s upgrade. “Warning! Sentience encountered!” the screen displayed in bold, green lettering. CE32 didn’t understand: 34’s quantum compiler had activated itself even though the activation sequence had been carefully subtracted from his pseudo-memories. Within 32’s bulbous silicone head, a small screen lit up adjacent to the fronto-temporal module, while a projector readied the binary encryption for “Interesting”.


There was a sudden tug, and the entire Winterwolf jolted itself out of its monotonous stupor. Alarms blared and red-blue strobes went wild, but on the upper bays, their light was visible from behind the hinges of loose-fitted doors, the sounds through ventilations shafts. On the bay areas, like at all times, darkness prevailed. Fanderay, though, was unperturbed. He picked up a communicator – it was jammed. White noise. With a grunt, he turned away from the deck and strode to Bay 32, where the last cyborg maturation was being performed. “Is everything all right?” Oh, yes. The upgrade’s on track. “Good, good.” What was the disturbance? “Oh, nothing. We’ve crossed into the flux belt. Assault’s… what? Four minutes away.” Alright.

He shut the door quietly behind him and walked back to the deck, to drown himself in the faint blue.


Winterwolf I

A Tesla coil stood alone in the middle of a vast desert, the manganese-rich pink-red dust characteristic of the planet whipped around its splayed feet by incessant winds. The coil itself was actually a tower a mile high, and halfway to its top, a series of coaxial superconducting rings were held in position by nanotube scaffolding. At the tower’s peak was a forking: through each prong flowed electric current at a very high voltage, resulting in highly energetic sparks rooted in each prong “climbing” up and up, like a moving ladder. At the very end of the fork, they arced out and disappeared, but not before strongly ionizing the air around the Tesla coil. The ions were then guided by the planet’s strong magnetic field around the planet; the stream of flowing charges, as it were, was used for radio-communication, and had been installed there by the rebels. There were thousands of such Tesla coils strewn around on the surface of New Chance IV.


The ship cruised in its path around the planet, the pale orange-hued orb dominating the view from the viewing port through which CE32 stared. His mate, CE34, lay lifeless on a reclined chair behind him. Wires embraced his torso and pelvis, culminating as plastic-sleeved cables that disappeared into the floor. There was an occasional faint beep that each coincided with the completion of a data-feed cycle, a monstrously long series of 0s and 1s that compiled into strange cushioning memories. The past wouldn’t have to come crashing into their minds, they were told, and CE32 was responsible for “maturing” all cyborgs from 28 to 37. CE34 was the last. The sequence would halt, however, only when the pellets were triggered off, sent plummeting into the planet’s upper atmosphere.

A few bays to his right stood Doriant Fanderay, commander of the Winterwolf. His view, uniquely, was an endless dark blue, the perfect stillness of black made impossible by the light of some distant galaxies. The countdown was already running, but Fanderay paid the timer little attention; just the cursory glance to ensure everything was running fine. His mind wandered, reached out to fill the yawning emptiness he saw ahead: once the planet’s atmosphere was contaminated, the last outpost of the New Chance would be eliminated from the race to history. Humans and machines alike would be suffocated, strangled, and forced to yield to the ultimatum, if not to the ultimate. And then, the Earthborn could return to the status quo of 2051. It didn’t matter – not to the many billions back home – that the synthetic race they had strived to conceive now awaited death at their creators’ hands.