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Breakthrough Starshot ‘Sprites’ in Orbit

If Breakthrough Starshot succeeds in launching a fleet of tiny probes to Proxima Centauri in 30 or 40 years, their payloads will be highly miniaturized and built to specifications far beyond our capabilities today. But the small ‘Sprites’ launched into low Earth orbit on June 23 give us an idea where the research is heading. Sprites are ‘satellites on a chip,’ growing out of research performed by Mason Peck and his team at Cornell University, which included Breakthrough Starshot’s Zac Manchester, who used a Kickstarter campaign to develop the concept in 2011 (see Sprites: A Chip-Sized Spacecraft Solution for background on the Cornell work).

Breakthrough Starshot executive director Pete Worden refers to Sprites as ‘a very early version of what we would send to interstellar distances,’ a notion that highlights the enormity of the challenge while pointing to the revolutionary changes that may make such payloads possible. The issues multiply the more you think about them — chip-like satellites in space have no radiation shielding and are susceptible to damage along the route of flight. But missions like these will help us analyze these problems and refine the technology.

Consider communications. In an email yesterday, Mason Peck told me that the Cornell team has juiced up the networking capabilities of the tiny spacecraft. “Now we have them talking to each other in a peer-to-peer network, and this demonstration shows how they synchronize like fireflies,” Peck said, a lovely image that points to what is becoming possible. Instead of a single large probe, think of a cluster of them, a fleet of spacecraft on chips, each carried by a sail. Losses along the route are assumed, but they are overcome by sheer numbers.

And as Peck, himself a key player in Breakthrough Starshot, goes on to point out, we’re beginning to learn how such chips can work among themselves:

This [peer-to-peer networking] capability would allow many of them to share science data, for example, or to create a persistent virtual senor out of many discrete sensors-on-chip. Also, in principle, their transmitting simultaneously could amplify the signals, enabling them to be heard from farther away. Or they could each transmit part of a dataset — say part of a large image.

We’ve never launched fully functional space probes as small as these, each 3.5-by-3.5 centimeter probe built upon a single circuit board and weighing in at just four grams. A Sprite can contain solar panels, computers, communications capability and an array of sensors. The tiny spacecraft’s electronics all function off the 100 milliwatts of electricity each generates.

The Sprites went into space aboard an Indian rocket as supplementary payloads. Now in orbit, the Latvian Venta satellite and the Italian Max Valier satellite, operated by OHB System AG, each have a Sprite attached to the outside, while the Max Valier satellite contains four more Sprites that are be deployed into space for subsequent study of their orbital dynamics.

Breakthrough Starshot is saying that communications from the mission show the Sprites are performing as designed, although Lee Billings, in a Scientific American post, has noted that the Sprites aboard the Max Valier satellite are problematic, with mission controllers thus far unable to establish communications with the external Sprite.

That could mean trouble for deploying the Max Valier’s four internal Sprites, but the stable orbits of the satellites give time for attempted fixes. Zac Manchester tells Billings that controllers have picked up signals from one external Sprite but are not sure which one it is. Even so, adds Manchester: “This is the first time we’ve successfully demonstrated Sprites end-to-end by flying them in space, powering them with sunlight and receiving their signals back on Earth.”

You may recall that Sprites have had their day aboard the International Space Station, being mounted for a long-term experiment outside the station before being returned to Earth undamaged from the exposure. Making a point that resonates with yesterday’s post on deorbiting space debris, Billings adds that the 2014 attempt to put 100 Sprites into orbit aboard a crowd-funded KickSat raised concerns over space debris; in any case, the Sprites were not deployed. Sprites will continue to be tested in space, but for now they will need to operate no higher than 400 kilometers above Earth, below which their orbits decay quickly.

How Sprites will evolve as Breakthrough Starshot continues to examine the technology remains to be seen. But remember that along the way, we have numerous potential uses for the tiny spacecraft here in our own system. Mason Peck has even talked about letting Sprites become charged through plasma interactions and then using a huge magnetic field like Jupiter’s as a particle accelerator to push the chips to thousands of kilometers per second.

That’s actually another way to get a payload to Proxima Centauri, though one that would take decades to get up to speed, and would still require several centuries for the journey. Even so, the idea of swarms of Sprites as interstellar probes, each communicating with the others like fireflies, has a surreal kind of beauty. In the meantime, could we use Sprites for interplanetary missions? Peck pointed out in a 2011 IEEE Spectrum article that the chips could use radiation pressure from the Sun to move around the Solar System. Let me quote him:

If a Sprite could be made thin enough, then its entire body could act as a solar sail. We calculate that at a thickness of about 20 micrometers—which is feasible with existing fabrication techniques—a 7.5-mg Sprite would have the right ratio of surface area to volume to accelerate at about 0.06 mm/s2, maybe 10 times as fast as IKAROS [the Japanese solar sail]. That should be enough for some interplanetary missions. If Sprites could be printed on even thinner material, they could accelerate to speeds that might even take them out of the solar system and on toward distant stars.

Image: Artist’s conception of a cloud of Sprite satellites over the Earth. Credit: Space Systems Design Studio/Cornell University.

Zac Manchester makes the same case, adding that Sprites can also be used to form three-dimensional antennas in deep space to monitor the kind of space weather that can damage power grids and orbiting satellites. Flying aboard larger spacecraft, they could be deployed as a rain of small probes to coat distant planetary surfaces with sensors.

“Eventually, every mission that NASA does may carry these sorts of nanocraft to perform various measurements,” says Pete Worden. “If you’re looking for evidence of life on Mars or anywhere else, for instance, you can afford to use hundreds or thousands of these things—it doesn’t matter that a lot of them might not work perfectly. It’s a revolutionary capability that will open up all sorts of opportunities for exploration.”



Testing out new sail applications is part of a European project called RemoveDebris, which focuses on strategies for dealing with the enormous amount of junk that is piling up around the Earth. Run by the Surrey Space Center at the University of Surrey (UK) and the Von Karman Institute of Belgium, the work takes note of the fact that, from flecks of paint to inactive satellites to spent rocket boosters, our planet is orbited by about 7000 tonnes of material. If you want to visualize that amount, it’s the equivalent of 583 London buses, according to this SSC news release.

You may recall that in the film Gravity, a Space Shuttle is destroyed by space debris. But the issue is hardly confined to Hollywood imaginings. Jason Forshaw is Surrey Space Centre project manager on the RemoveDebris team:

“Various orbits around the Earth that are commonly used for satellites and space missions are full of junk, which is a significant danger to our current and future spacecraft. Certain orbits – which are commonly used for imaging the earth, disaster monitoring and weather observation – are quickly filling up with junk, which could jeopardise the important satellites orbiting there. A future big impact between junk in that orbit could result in a real life ‘Gravity-like’ chain reaction of collisions.”

A scary thought, but as you would imagine, my interest for Centauri Dreams is primarily in terms of that interesting sail deployment. Funded by the European Commission, the Surrey effort, called InflateSail, has demonstrated inflatable sail deployment techniques and will be testing deorbiting sail technologies from a small satellite. Launch occurred on June 23, with deployment shortly after the CubeSat carrying the sail achieved orbit.

The sail is designed to demonstrate the effectiveness of a drag sail at causing satellites to lose altitude and burn up in the atmosphere. The satellite uses a cool gas generator to inflate a one-meter long boom. After boom inflation, a motor extends four carbon booms that extract the 10-meter square sail. In future use, such a sail could be carried aboard a satellite and deployed at the end of its life, to ensure that it does not join the ranks of space debris.

Image: The InflateSail mission has successfully tested both inflatable and ‘deorbit sail’ technologies in space from a small nanosatellite. Credit: University of Surrey.

You may recall that NASA launched a small sail called NanoSail-D2 in 2010 that eventually re-entered the atmosphere after 240 days in orbit. Its deployment from the FASTSAT satellite in which it launched did not occur on time, but the sail later ejected and deployed three days later, a follow-up to an earlier NanoSail-D that was lost during the launch attempt. In addition to testing systems for sail deployment, NanoSail-D2, like InflateSail from the SSC, was designed to explore deorbiting measures that could be applied to space debris.

The Surrey sail is in orbit and returning data to ground controllers. Drag produced by the sail will gradually lower its altitude for re-entry, causing it to burn up in the atmosphere. Craig Underwood, who is in charge of the Surrey Space Center’s environments and instrumentation group, is principal investigator for the mission. Says Underwood:

“We are getting tremendous data from the spacecraft, which have already given new insights into these key deorbiting technologies in the real space environment. InflateSail heralds yet another successful CubeSat mission for the space engineering and academic team at the SSC. It also demonstrates how we can effectively help reduce space junk, and later this year we will launch one of our flagship missions, RemoveDebris – one of the world’s first missions to test capturing of artificial space junk with a net and harpoon.”

Centauri Dreams’ take: The more experience we gain with sail deployment and operations, the better. In this case, we are looking at near-term sail applications to solve a serious problem for spacecraft near the Earth. But remember the success of Japan’s IKAROS mission at going interplanetary and testing sail deployment, navigation and data return. Early in the next decade, if all goes as planned, a new sail from JAXA spanning 50 meters to the side will deploy and head for Jupiter to study its trojan asteroids.

The future of sail technologies seems bright, particularly as we gain experience and begin to explore beamed energy possibilities. The fact that the Surrey Space Center has successfully deployed an inflatable sail from the small CubeSat in which it was contained is an encouraging nod to the continued development of sails for near-Earth use. As we master these technologies, we’ll apply them to missions deep into the Solar System and beyond.



SailBeam: A Conversation with Jordin Kare

Looking around on the Net for background information about Jordin Kare, who died last week at age 60 (see yesterday’s post), I realized how little is available on his SailBeam concept, described yesterday. SailBeam accelerates myriads of micro-sails and turns them into a plasma when they reach a departing starship, giving it the propulsion to reach one-tenth of lightspeed. Think of it as a cross between the ‘pellet propulsion’ ideas of Cliff Singer and the MagOrion concept explored by Dana Andrews.

So I thought this morning to offer you some thoughts about SailBeam and its genesis from the man himself. I interviewed Jordin back in early 2003 in a wide-ranging discussion that took in most aspects of his work. He was an easy interview — all I had to do was offer the occasional nudge and he would take off. I found him engaging and hugely likeable. What follows is a fraction of the entire interview, the part that focuses primarily on SailBeam and a bit on Kare himself. I’ve edited it but in general preferred to let Kare’s own voice come through. The images I use here are from Jordin’s “SailBeam Space Propulsion by Macroscopic Sail-type Projectiles,” a presentation he delivered at the 2001 NIAC workshop in Atlanta.

PG: Your work with NIAC on the SailBeam concept takes sail technologies down a new path. Tell me how SailBeam and the NIAC report came about.

JK: I am an astrophysicist by background. I worked at UC-Berkeley and got a doctorate there in 1984. For most of the time since, I’ve been an aerospace engineer, dividing my identity between physicist and engineer. A lot of what I’ve worked on in this area are advanced propulsion projects. So I’ve been involved in a community of people who do exotic propulsion things.

One of the things that’s always in my mind is doing advanced interstellar propulsion. In this case, I’d been aware of ideas for doing laser and microwave sails for interstellar propulsion. Bob Forward did prototypical work on that. I’d been involved in couple of workshops where he talked about the concept, one at the Jet Propulsion Laboratory a couple of years back.

Along those lines, I had realized that there’s a scaling law to how laser sails worked. If you took a laser sail and tried to get to a certain velocity with a certain size laser and certain size sail, and then you took that sail and cut it into several pieces and accelerated those one after another, you could get the same amount of mass to the same velocity in the same amount of time, but you could use a smaller laser because the sail doesn’t accelerate over as long a distance.

That was interesting but not very useful. And then I thought about work that Geoffrey Landis had done about using sails not made of metal foils. The trouble with small sails is that you’re pushing them harder, accelerating faster. And if you’re using metal sails, you can’t do much of that before they just melt. Landis had pointed out you could push harder on dielectric sails.


PG insert: A brief bit of background on this. The problem with metal films is that they have low emissivity. A small sail made of such materials overheats under the beam. High emissivity materials with higher melting temperatures are needed. Dielectrics are non-conductive materials that will emit a lot but absorb little of the radiation impinging upon them. Silicon carbide is a dielectric, as is aluminum trioxide and, Kare’s favorite, diamond. But back to the interview.


JK: Dielectric sails that are a thin layer of transparent material reflect better than metal foil sails because they have a different index of refraction [describing how light propagates through a particular medium], like the reflection off the surface of a piece of glass, or reflection off a metal film. Forward noted that dielectric sails could potentially have higher acceleration.

My mental light bulb went on and said I know from working in laser technology and other areas I work on, that you can make very low absorption dielectric materials. If I can make very high quality, very low absorption dielectrics, I could push them really hard. Now instead of thinking in terms of taking a sail and dividing it into ten pieces, I can divide it into a million pieces. I started doing calculations and realized that this made sense as a propulsion system.

I started pulling in pieces from other projects I’ve worked on. This got to the point where I could make a rough design of the system concept and started telling my associates about it. I did a quick presentation at a meeting of space people that we exotic propulsion people go to — the Space Technology and Applications International Forum every January in Albuquerque.

I was describing the SailBeam idea to Bob Forward and he was the one who said you should get some money out of NIAC to study this further; he’d been involved with reviewing stuff for NIAC. I knew other people who had worked with them, so I went to the next NIAC workshop and did a proposal for the following round. When I looked at the kinds of things NIAC was supporting, SailBeam fit with the tenor of their proposals.

PG: Of course the whole idea of sail technologies is changing.

JK: It is for sure, and we have to distinguish between solar and laser sails, or beamed energy sails. The idea of solar sails has been around for a long time. And there have been many changes of direction. They used to look primarily at metallic sails for solar sail missions, usually metallic sails coated on a plastic film. But people who were really aggressive thought in terms of free-standing metal sails. Just in the last couple or three years, carbon-carbon has emerged. Here we have carbon fibers fused together to make an open lattice material that is as lightweight as anything they were ever hoping for out of metal-coated plastics, and much easier to handle. Carbon-carbon also takes much higher temperatures than plastic film.

Suddenly the solar sail people began looking at Sundiver missions, where they fly a solar sail and let it drop close to the Sun, flying edge on until it gets well inside the orbit of Mercury and then turning it face-on to the Sun for that propulsive kick. This gives you much higher velocities than anything we’ve done today, something like 100 or 200 kilometers per second, which means this has application for missions far past Pluto. This kind of velocity lets you begin to talk about thousand astronomical unit missions, a true interstellar precursor.

PG: Missions to another star demand even more. A lot more.

JK: True. Bob Forward was working at Hughes on some of the earliest lasers back in the 1960s when he first came up with the beamed sail idea. His idea was that if you have a laser or microwave beam, you can focus much more energy over a longer distance than you can with sunlight. You can use the same light pressure that solar sail people are talking about to get much higher velocities. Forward came up with this thing called Starwisp [a microwave-driven wire-mesh sail about a kilometer in diameter with a flight time of 20 years to Alpha Centauri — see The Case for Beamed Sails].

Forward realized there were problems with the basic Starwisp concept. One that always bothered me was how Bob was going to get any useful information out of this Starwisp. He talked about having little sensors at the intersections of this fine wire mesh, magically having them turn into a large telescope aperture. I was never quite clear how that actually worked.

So that was his first notion of a very high velocity sail. Forward also came up with concepts for laser sails, in particular the multistage laser sail that would be able to decelerate at destination by splitting off part of the sail and using that to reflect the beam back onto a separate section. A lot of people were interested in that and the idea got used in a lot of science fiction, including Bob’s own writing.

I’ll mention there’s a paper Bob Forward wrote for a workshop I ran at Livermore in 1986, when we were looking at non-interstellar laser propulsion applications. His paper was “Laser Weapon Target Practice with GeeWhiz Targets.’ And in there he talked about a sail that was made of multiple layers of diamond film. I had almost forgotten about this when I came up with my notion of the SailBeam. He had the idea of using dielectric reflectors by way of getting to extremely high performance in a sail.

I use artificial diamond as the best material for my sail. So Bob, as was usually the case, had some of the same pieces considerably earlier than anyone else. But he also had much thicker sails with more layers and wasn’t trying for quite such high performance. He was talk about building something that could fly at perhaps 100 kilometers per second using the types of laser we were talking about building for strategic defense.

The problem with his interstellar propulsion scheme, and everyone agreed it was a problem, was the scale that was required. Because Bob Forward wrote about 10,000 kilometer diameter Fresnel zone plate lenses. He would show an artist’s conception of the lens hanging next to the Earth, and it was the same size as the Earth! The sail by itself would be a hundred or thousand kilometers in diameter, and the lasers were in the terawatt category. It was clear that in principle it would work, but it was, to say the least, a monumental engineering task.

We all wondered if we could do this better somehow. At a workshop out at the Jet Propulsion Laboratory, Geoff Landis ran the session on laser sails and we looked at how you could make smaller sails, asking what was the smallest sail you could build and still do interesting missions. We were still looking at a single laser pushing a single sail.

It was hard to come up with something buildable and still interesting, but Landis had looked at optimizing sails in terms of choosing the best possible material. He was the one who pointed out there was this notion of designing not with multiple layers of dielectric that Bob Forward had put into his ‘gee whiz targets’ paper, but with a single layer of dielectric a quarter wavelength thick. That plus the scaling property that I had been thinking about were some of the ingredients that led to the SailBeam.

PG: SailBeam works by turning your micro-sails into plasma to push the departing spacecraft.

JK: This is where Dana Andrews’ work with magsails was so critical. The notion of putting magnetic coils on a spacecraft, essentially a magnetic loop, and making a magnetic field around it to deflect the solar wind, the stream of charged particles from the Sun. I had done some work for Dana on MagOrion, a notion of making the magnetic field strong enough that you could set off an atomic blast behind the spacecraft and deflect the plasma produced by the bomb.

PG: This was the Project Orion idea applied to magsails.

JK: Exactly. The magsail replaces what would have been a physical sail. The idea was designed originally for cruising around inside the Solar System. But magsails and all these other threads tie together — remember that the original invention of the magsail came when Dana Andrews and Bob Zubrin were trying to figure out if they could make the Bussard ramjet work. They wanted to see what you could do if you were trying to collect interstellar hydrogen with a magnetic scoop. And what they discovered is that they couldn’t make a Bussard ramjet work, because the magnetic fields always ended up deflecting the ionized hydrogen at high velocity. What that turns into is a very good drag brake.

Tweaking the numbers a bit, they could make it be a drag break against the solar wind, which is flying along at a pretty good velocity in the Solar System, 75 K per sec or so. So they could fly around on the solar wind. But all this originated from looking at another interstellar propulsion concept. These ideas build on each other; they’re hybrids.

So I had been working on MagOrion, had done designs of the field coils for Dana Andrews, and that was another piece, because I wondered if I can accelerate little bitty sails and do this scaling of launching a million little sails instead of one big sail, what do I do with them? They are too small to be useful individually. Well, I can use them like a MagOrion. I can turn them into blobs of ions and bounce them off a magnetic field at the vehicle. So I got to pull in yet another piece from things that other people had come up with that I adapted for my own design.

PG: You also applied magsail to deceleration in the target stellar system.

JK: Exactly. One of the things that Dana and Bob Zubrin had pointed out in the past is that a magsail worked as a way of decelerating interstellar spacecraft. I’m carrying a magsail anyway, so Dana and I collaborated on an IAF paper on slowing down a SailBeam vehicle at the far end. Now we had both a way of accelerating and reusing some of that hardware to stop at the far end.

PG: This seems like a more realistic way to do it than Forward’s ‘staged sail’ concept.

JK: I think it is. The one limit on it is that it is not a very fast braking system. It does take tens of years to stop. And it doesn’t bring you down to a full stop. That’s because the force you get to slow down varies with how fast you’re going. So the slower you’re going, the less you slow down. At some point, the time it takes to slow down from a tenth of the speed of light to one percent of the speed of light isn’t too bad, but it takes progressively longer to slow down the rest of the way. You can argue design details as to whether you can get down slow enough that you can then come to a stop by braking against the wind from whatever star you’re approaching. That gives you an extra 75 or 100 kilometers per second for the wind velocity to work against.

Or maybe you’re going to have to carry some system like nuclear electric to slow you down the last 100 kilometers per second. Forward’s sail in principle would let you come to a complete stop or reach any final velocity you wanted to. But it does seem like a very difficult thing to do. It’s in the category of ideal technology. It’s pretty hard to see how you’d actually build it.

PG: You talk about using relay lenses along the acceleration path for your micro-sails. How does this system improve the original design?

That was something i realized late in the process of doing the design. My little sails accelerate over short distances by comparison to Forward’s big sail concepts, a few tens of thousands of kilometers. The problem with pushing a big sail is that I have this one big lens that has to focus the light on the sail some large distance away. How about if I take a smaller lens and use it to focus light, but then I put another lens at a place where the beam spreads out again. And I put another lens out and focus the beam yet again. So I have this spaced series of lenses.

It’s pretty easy to show this is not a useful thing to do if you’re trying to accelerate a large sail over a light year. Partly because you have to put the intermediate lenses a large fraction of a lightyear away and partly because you don’t gain when the lens and the sail are about the same size. There’s no advantage to it; you end up having the same amount of material in multiple lenses as you would in one big lens. Geoff Landis did a paper to show why it doesn’t work.

With my situation, though, I was only accelerating things for a few tens of thousands of kilometers. I had been thinking I’ll do this with one big telescope, a 500 meter telescope. But at some point I realized I’m taking this 500 meter telescope and focusing the beam on this little tiny sail. If I were to try to focus on another lens, another telescope, i could do that easily. I’m only accelerating over a short distance, so I can physically put a telescope forty thousand kilometers away; it’s not like I have to put it half a light year away.

So I realized I could build a 50 meter telescope and have 10 of them. Because of the way the numbers work out, because I’m focusing on a very small object, it turns out I gain in terms of the total area of the telescopes. I can make ten telescopes each a tenth of the diameter and spaced one tenth of the way along the path. And end up using, since each telescope is a tenth of the diameter, a hundredth of the area. So I can have ten times the total material of the telescopes.

Now I had gotten the lens down from 10,000 kilometers to a few hundred meters. Which certainly helps. Look, Bob Forward figured out a way you could get to the stars using known physics. Cliff Singer talked about using particle accelerators for ‘pellet’ propulsion. Both these notions left us huge engineering problems. What Geoff Landis and I both did was to say, can we do better from an engineering standpoint. Can we make this something we can actually build.

What I like best about Sailbeam is that as far as I know right now, it is the most engineering-practical way to get up to a tenth of speed of light.

PG: These sails get up to speed, shall we say, quickly.

JK: Yes. In some of the designs they go from zero to light speed in about a tenth of a second. That’s pushing it and in the design that’s in the final proposal, they take about three seconds. I love showing that slide — it shows what the limiting acceleration would be for an ideal microsail and it’s like 30 million gravities, or zero to lightspeed in .97 seconds. But even backing up because of materials properties, you’re talking about accelerating at hundreds of thousands of gravities and getting up to a large fraction of lightspeed in a few seconds.

PG: And you’re pushing, in an ideal scenario, an interstellar probe of what size.

JK: The baseline is a one ton probe. There really is nothing, you probably can’t go a lot smaller than that, though i wouldn’t swear you couldn’t build a one kilogram probe. But even with sophisticated miniaturization, it becomes hard to make a useful probe that’s much smaller than a ton. So I tend to look at that size scale. On other hand, there isn’t an upper limit. You could build much bigger probes, but they would cost more to build the lasers to launch them. The laser power you need is proportional to the mass.

PG: Up to near lightspeed in a second! You seem to be somebody who enjoys pushing the boundaries.

JK: It’s definitely a lot of fun to do. The interesting part of my work is coming up with new schemes and combinations to see if they work. The flip side is that interstellar flight is such a hard problem that you don’t get the satisfaction of something you expect to see built.

PG: Interstellar flight is all about long time frames. Even mission durations of 50 to 100 years are wildly beyond our current capabilities. So how do you cope with this perspective — long-term thinking isn’t something our culture has much patience with.

JK: It’s certainly something that is pretty rare in our society. Although I am occasionally amazed because on the one hand people don’t think long term, and then, on the other hand, I see people worrying about things like Social Security going bankrupt in thirty years. We have no idea of what the economy is going to be like in thirty years. So there are a few places in our society where people do think long term, but most of them don’t seem to me to be. Actually this is an interesting phenomenon.

PG: The notion of working on projects where you won’t get results in a lifetime or more is rare indeed. But from talking to you, I get the idea that you would be pleased to think that something you did today would contribute to a mission that might not launch until you and I are both gone.

JK: That’s absolutely true. I would be delighted if when I am old and gray, I discover that people are just starting to work on building something like SailBeam and are referring to me as having come up with the idea, or part of the idea. It’s not that I can’t imagine this SailBeam concept actually being launched within my lifetime — it’s not impossible — but it’s as much as I can reasonably expect to hope that in my time on Earth we’ll maybe be getting started on it.

PG: You’re also a science fiction fan.

JK: Yes. No fiction of my own rather than the occasional song. But I do often point out that I write both science fiction and fantasy. It’s just that the science fiction is usually titled ‘technical proposal’ and the fantasy is titled ‘budget proposal.’ I have never turned pro like Geoff Landis.

Certainly I’ve been an SF reader since way back when. I will note in fact that if there was any single book that turned me onto the notion of engineering interstellar flight, it would be the book Tau Zero by Poul Anderson. That was the one that got me going, stimulating a lot of interest in interstellar flight as something that we might actually make happen.


Jordin’s report on SailBeam concepts is “High-Acceleration Micro-Scale Laser Sails for Interstellar Propulsion,” Final Report, NIAC Research Grant #07600-070, revised February 15, 2002 and available here. And see Geoffrey Landis’ “Optics and Materials Considerations for a Laser-propelled Lightsail,” presented at the 40th International Astronautical Federation Congress, Málaga, Spain, Oct. 7-12, 1989 (full text).



Remembering Jordin Kare (1956-2017)

We’ve just lost a fine interstellar thinker. Jordin Kare has died of aortic valve failure at age 60. While Kare played a role in the Clementine lunar mapping mission and developed a reusable rocket concept in the 1990s that he thought could be parlayed into a space launch system (in typical Kare fashion, he called it “DIHYAN,” for ‘Do I Have Your Attention Now?’), it is through a laser sail system called SailBeam and a ‘fusion runway’ concept that he will most likely be remembered among those who study starflight. But he was also an active science fiction fan, ‘filksinger’ and poet whose name resonates wherever science fiction fans gather.

To science fiction writer Jerry Pournelle, who remembered Kare to a small mailing list over the weekend, it was a song called ‘Fire in the Sky’ that first came to mind. The first verse:

Prometheus, they say, brought God’s fire down to man
And we’ve caught it, tamed it, trained it since our history began
Now we’re going back to Heaven just to look Him in the eye
And there’s a thunder ‘cross the land and a fire in the sky

The song is a rousing tribute to outward yearning, written by a man who was a regular at science fiction conventions, where he achieved his fame as a singer. If you’re not familiar with the term ‘filksinger,’ it emerged in the musical community that evolved inside science fiction fandom. Kare was prolific at the genre and released two albums of his own work: Fire in the Sky (1991) and Parody Violation: Jordin Kare Straight and Twisted (2000). He was also a partner in Off Centaur Publications, a commercial venture specializing in such music. Pournelle liked ‘Fire in the Sky’ enough to feature it in the novel Fallen Angels (Baen, 1981), which he wrote with Larry Niven and Michael Flynn.

Image: Astrophysicist and space systems consultant Jordin Kare, who died on July 19.

As a physicist and aerospace engineer, Kare focused primarily on laser propulsion, both from ground-to-orbit and deep space perspectives. A long-time researcher at Lawrence Livermore National Laboratory, he put together an early laser propulsion workshop at LLNL in 1986; his work on laser launch from ground to orbit drew support from the Strategic Defense Initiative.

Kare left Livermore in the mid-90s to become a consultant specializing in spacecraft design. I ran into him through reports he did for what was then called the NASA Institute for Advanced Concepts, where he wrote about launch prospects using laser arrays, and reshaped laser sail concepts for speed and efficiency. I highly recommend you take a look at his “High-Acceleration Micro-Scale Laser Sails for Interstellar Propulsion” report for NIAC in 2002 (citation below). He would go on to become chief scientist in beamed power company LaserMotive.

In the interstellar community, it may be SailBeam that stands as his primary legacy. At a time when Robert Forward had studied vast lightsails hundreds of kilometers across, Kare went the other direction. He had realized that Forward’s sails demanded gigantic optical systems including in one instance a Fresnel lens in the outer Solar System that would be the size of a planet (this was to be used to collimate the powerful laser beam from the inner system). Why not power down and aim for a system far less complex by shrinking the sails themselves?

The gist of the idea is this: Kare’s tiny sails, made of diamond film and pushed by a multi-billion watt orbiting laser, could be accelerated much closer to their power source than Forward’s sails and brought up to a substantial fraction of lightspeed within seconds. Kare coupled sail concepts with Cliff Singer’s pellet propulsion, reasoning that his tiny sails could intercept a large interstellar probe and become a source of propulsion as they were vaporized into plasma.

Aerospace engineer Dana Andrews worked with Kare on various magsail concepts and wrote about SailBeam himself in a paper cited below. Andrews pointed out that SailBeam solved a key problem in particle beam propulsion — a neutral particle beam will disperse as it travels. A stream of tiny sails driven by laser will not. You might see some crossover here with another concept Andrews and Kare both studied called MagOrion, which would use plasma pulses from small nuclear explosions to drive a starship deploying a magnetic sail.

Kare’s fame also rests on the concept of a fusion runway, which he saw as a long string of pellets deployed ahead of a departing spacecraft. The vehicle, moving several hundreds of kilometers per second initially, would begin encountering fusion pellets with enough velocity to light up its main engines. A cruising velocity of 30,000 kilometers per second, he believed, was possible with a runway strung over a tenth of a light year (I wrote about this one recently in A Fusion Runway to Deep Space?) and had an interesting conversation with Kare about it.

More about that conversation tomorrow, because I would like to bring Kare’s own words into the mix. For now, Kare’s rousing finale to the song with which I began this piece:

Now the rest is up to us – there’s a future to be won
We must turn our faces outward, we will do what must be done
For no cradle lasts forever, every bird must learn to fly
And we’re going to the stars, see our fire in the sky
Yes, we’re going to the stars, see our fire in the sky

The Andrews paper is “Interstellar Propulsion Opportunities Using Near-Term Technologies,” in Acta Astronautica Vol. 55 (2004), pp. 443-451. Jordin Kare’s report on SailBeam concepts is “High-Acceleration Micro-Scale Laser Sails for Interstellar Propulsion,” Final Report, NIAC Research Grant #07600-070, revised February 15, 2002 and available here.



METI: A Response to Steven Johnson

Yesterday’s post dwelt on an article by Steven Johnson in the New York Times Magazine that looked at the issue of broadcasting directed messages to the stars. The article attempted a balanced look, contrasting the goals of METI-oriented researchers like Douglas Vakoch with the concerns of METI opponents like David Brin, and fleshing out the issues through conversations with Frank Drake and anthropologist Kathryn Denning. Johnson’s treatment of the issue prompted a response from a number of METI critics, as seen below. The authors, all of them prominent in SETI/METI issues for many years, are listed at the end of the text.

We thank Steven Johnson for his thoughtful New York Times Magazine article, which makes it clear that there are two sides to the METI issue. We applaud his idea that humankind needs a mechanism for decision-making on long-term issues that could threaten our future.

As Johnson implies, deliberately calling ourselves to the attention of a technological civilization more advanced than ours is one of those issues. What we do now could affect our descendants.

As Johnson asks, who decides? Without an agreed approach, the decision to transmit might be made by whoever has a sufficiently powerful transmitter.

Astronomers have given us an additional reason for addressing this question: the discovery of thousands of planets in orbit around other stars, increasing the probability that life and intelligence have evolved elsewhere in our galaxy.

METI is not scientific exploration. It is an attempt to provoke a reaction from an alien civilization whose capabilities and intentions are not known to us.

The most likely motivation for alien intervention is not a wish to exploit Earth’s territory or resources, but the potential threat posed by a new space-faring civilization — us. Scientists and engineers already are designing Humankind’s first unmanned interstellar probes. Some might be visiting nearby stars less than a century from now.

Image: Taken by the Advanced Camera for Surveys on the Hubble Space Telescope, this image shows the core of the great globular cluster Messier 13, to which a message was beamed in 1974. Credit: ESA/Hubble and NASA.

Though altruism may be a noble goal, human history suggests that it rarely extends beyond one’s own species. We have not been very altruistic toward dolphins, whales, or chimpanzees.

What mechanism can we devise for what Johnson calls global oversight of METI? In the 1970s conferences at Asilomar assessed dangers from the then theoretical notion of genetic engineering. The resulting compromises improved laboratory safety while allowing continued research in this field under an agreed set of rules.

In the 1980s, some of us proposed a first step toward agreed rules through the document known informally as the First SETI Protocol, which calls for consultations before responding to a detected alien signal. (That protocol has been endorsed by most SETI researchers, but has not been adopted by government agencies.) An attempt to gain consensus on a second protocol calling for consultations before the transmission of powerful, human-initiated signals foundered on a basic disagreement that is mirrored in today’s METI debate.

Seventeen years ago, the International Academy of Astronautics presented a proposal to the United Nations for an international decision-making process for sending such communications. The U.N. noted the report and filed it.

Plans to send powerful targeted messages to nearby solar systems have brought this issue back to our attention. The underlying issue has not changed. As renowned Chinese science fiction writer Cixin Liu wrote, “I’ve always felt that extraterrestrial contact will be the greatest source of uncertainty for humanity’s future.” Let’s address that issue as rationally as we can.

Gregory Benford, astrophysicist and science fiction author

James Benford, radio astronomer

David Brin, astrophysicist and science fiction author

Catharine A. Conley, NASA Planetary Protection Officer

John Gertz, former chairman of the SETI Institute

Peter W. Madlem, former board member of the SETI Institute

Michael Michaud, former diplomat, author

John Rummel, former Director, NASA Planetary Protection Office

Dan Werthimer, radio astronomer



Wrestling with METI

If we were to send a message to an extraterrestrial civilization and make contact, should we assume it would be significantly more advanced than us? The odds say yes, and the thinking goes like this: We are young enough that we have only been using radio for a century or so. How likely is it that we would reach a civilization that has been using such technologies for an even shorter period of time? As assumptions go, this one seems sensible enough.

But let’s follow it up. In an interesting piece in the New York Times Magazine, Steven Johnson makes the case this way: Given the age of the universe, almost 14 billion years, that means it would have taken 13,999,999,900 years before radio communications became a factor here on Earth. Now let’s imagine a civilization that deviates from our own timeline of development by just one tenth of one percent. If they are more advanced than us, they will have been using technologies like radio and its successors for 14 million years.

Assumptions can be tricky. We make them because we have no hard data on any civilization outside our own. About this one, we might ask: Why should there be any universal ‘timeline’ of development? Are there ‘plateaus’ when the steep upward climb of technological change goes flat? Soon we have grounds for an ever deeper debate. What constitutes civilization? What constitutes intelligence, and is it necessarily beneficial, or a path toward extinction?

Image: The Arecibo Observatory in Puerto Rico, from which a message was broadcast to the globular cluster M13 in 1974.

Airing out the METI Debate

I want to commend Johnson’s piece, which is titled “Greetings, E.T. (Please Don’t Murder Us.” As you can fathom from the title, the author is looking at our possible encounter with alien civilizations in terms not of detection but of contact, and that means we’re talking METI — Messaging Extraterrestrial Intelligence. What I like about Johnson’s treatment is that he goes out of his way to talk to both sides of a debate known more for its acrimony than its enlightenment. Civility counts, because both sides of the METI issue need to listen to each other. And the enemies of civilized discussion are arrogance and facile assertion.

It was Martin Ryle, then Astronomer Royal of Britain, who launched the first salvo in the METI debate in response to the Arecibo message of 1974, asking the International Astronomical Union to denounce the sending of messages to the stars. In the forty years since, about a dozen intentional messages have been sent. The transmissions of Alexander Zaitsev from Evpatoria are well known among Centauri Dreams readers (see the archives). Douglas Vakoch now leads a group called METI that plans to broadcast a series of messages beginning in 2018. The Breakthrough Listen initiative has also announced a plan to design the kind of messages with which we might communicate with an extraterrestrial civilization.

All of this will be familiar turf for Centauri Dreams readers, but Johnson’s essay is a good refresher in basic concepts and a primer for those still uninitiated. He’s certainly right that the explosion of exoplanet discovery has materially fed into the question of when we might detect ETI and how we could communicate with it. It has also raised questions of considerable significance about the Drake Equation; specifically, about the provocative term L, meant to represent the lifespan of a technological civilization.

Johnson runs through the Fermi question — Where are they? — by way of pointing to L’s increasing significance. After all, when Frank Drake drew up the famous equation and presented it at a 1961 meeting at Green Bank (the site of his Project Ozma searches), no one knew of a single planet beyond our Solar System. Now we’re learning not just how frequently they occur but how often we’re likely to find planets in the habitable zone around their stars. The numbers may still be rough, but they’re substantial. There are billions of habitable zone planets in the galaxy, so the likelihood of success for SETI would seem to rise.

And if we continue to observe no other civilizations? The L factor may be telling us that there is a cap to the success of intelligent life, a filter ahead of us in our development through which we may not pass, whether it be artificial intelligence or nuclear weaponry or nanotechnology. METI’s critics thus worry about planet-wide annihilation, and wonder if a limiting factor for L, at least for some civilizations, might be interactions with other, more advanced cultures. Far better for our own prospects if the ‘filter’ is behind us, perhaps in abiogenesis itself.

Hasn’t our own civilization already announced its presence, not just through an expanding wavefront of old TV and radio shows but also through the activity of our planetary radars, and the chemistry of our atmosphere? After all, even at our level of technology, we’re closing in on the ability to study the atmospheres of Earth-class planets around other stars. If this is the case, are we simply being watched from afar because we’re just one of many civilizations, and perhaps not one worth communicating with? METI proponents will argue that this is another reason to send a message: Announce that, at long last, we are ready to talk.

The counter-argument runs like this: A deliberately targeted message is a far different thing than the detection of life-signs on a distant planet. The targeted message is a wake-up call, saying that we are intent on reaching the civilizations around us and are beginning the process. Passive signal leakage is one thing; targeting a specific star implies an active level of interest. And the problem is, we have no way of knowing how an alien culture might respond.

Procedures for Consensus

In his article, Johnson is well served by the interviews he conducted with with Frank Drake (anti-METI, but largely because he would prefer to see METI funding applied to conventional SETI); METI proponent and former SETI scientist Vakoch; anti-METI spokesman and author David Brin; and anthropologist Kathryn Denning, who supports broad consultation on METI. Johnson does an admirable job in summarizing the key questions, one of which is this: If we are dealing with technologies whose use has huge consequences, do individuals and small groups have the right to decide when and how these technologies should be used?

I think Johnson hits the right note on this matter:

Wrestling with the METI question suggests, to me at least, that the one invention human society needs is more conceptual than technological: We need to define a special class of decisions that potentially create extinction-level risk. New technologies (like superintelligent computers) or interventions (like METI) that pose even the slightest risk of causing human extinction would require some novel form of global oversight. And part of that process would entail establishing, as Denning suggests, some measure of risk tolerance on a planetary level. If we don’t, then by default the gamblers will always set the agenda, and the rest of us will have to live with the consequences of their wagers.

Easier said than done, of course. How does global oversight work? And how can we bring about a discussion that legitimately represents the interests of humanity at large?

Consultation also meets an invariable response: You can talk all you want, but someone is going to do it anyway. In fact, various groups already have. In any case, when have you ever heard of human beings turning their back on technological developments? For that matter, how often have we deliberately chosen not to interact with another society? Johnson adds:

But maybe it’s time that humans learned how to make that kind of choice. This turns out to be one of the surprising gifts of the METI debate, whichever side you happen to take. Thinking hard about what kinds of civilization we might be able to talk to ends up making us think even harder about what kind of civilization we want to be ourselves.

The METI debate is robust and sometimes surprising because of what doesn’t get said. Under the frequent assumption that human civilization is debased, we assume an older culture will invariably have surmounted its own challenges to become enlightened and altruistic. Possibly so, but without data, how can we know that other civilizations may not be more or less like ourselves, in having the capacity for great achievement as well as the predatory instincts that can cause them to turn on themselves and on others? Is there a way of living with expansive technologies while remaining a flawed and striving culture that can still make huge mistakes?

We can’t know the characteristics of any civilization without data, which is why a robust SETI effort remains so crucial. As for METI, I’ll be publishing tomorrow a response to Johnson’s article from a group of METI’s chief opponents exploring these and other points.



Keeping an Eye on Ross 128

Frank Elmore Ross (1874-1960), an American astronomer and physicist, became the successor to E. E. Barnard at Yerkes Observatory. Barnard, of course, is the discoverer of the high proper motion of the star named after him, alerting us to its proximity. And as his successor, Ross would go on to catalog over 1000 stars with high proper motion, many of them nearby. Ross 128, now making news for what observers at the Arecibo Observatory are calling “broadband quasi-periodic non-polarized pulses with very strong dispersion-like features,” is one of these, about 11 light years out in the direction of Virgo.

Any nearby stars are of interest from the standpoint of exoplanet investigations, though thus far we’ve yet to discover any companions around Ross 128. An M4V dwarf, Ross 128 has about 15 percent of the Sun’s mass. More significantly, it is an active flare star, capable of unpredictable changes in luminosity over short periods. Which leads me back to that unusual reception. The SETI Institute’s Seth Shostak described it this way in a post:

What the Puerto Rican astronomers found when the data were analyzed was a wide-band radio signal. This signal not only repeated with time, but also slid down the radio dial, somewhat like a trombone going from a higher note to a lower one.

And as Shostak goes on to say, “That was odd, indeed.”

It’s this star’s flare activity that stands out for me as I look over the online announcement of its unusual emissions, which were noted during a ten-minute spectral observation at Arecibo on May 12. Indeed, Abel Mendez, director of the Planetary Habitability Laboratory at Arecibo, cited Type II solar flares first in a list of possible explanations, though his post goes on to note that such flares tend to occur at lower frequencies. An additional novelty is that the dispersion of the signal points to a more distant source, or perhaps to unusual features in the star’s atmosphere. All of this leaves a lot of room for investigation.

We also have to add possible radio frequency interference (RFI) into the mix, something the scientists at Arecibo are examining as observations continue. The possibility that we are dealing with a new category of M-dwarf flare is intriguing and would have obvious ramifications given the high astrobiological interest now being shown in these dim red stars.

All of this needs to be weighed as we leave the SETI implications open. The Arecibo post notes that signals from another civilization are “at the bottom of many other better explanations,” as well they should be assuming those explanations pan out. But we should also keep our options open, which is why the news that the Breakthrough Listen initiative has now observed Ross 128 with the Green Bank radio telescope in West Virginia is encouraging.

No evidence of the emissions Arecibo detected has turned up in the Breakthrough Listen data. We’re waiting for follow-up observations from Arecibo, which re-examined the star on the 16th, and Mendez in an update noted that the SETI Institute’s Allen Telescope Array had also begun observations. Seth Shostak tells us that the ATA has thus far collected more than 10 hours of data, observations which may help us determine whether the signal has indeed come from Ross 128 or has another source.

“We need to get all the data from the other partner observatories to put all things together for a conclusion,” writes Mendez. “Probably by the end of this week.”

Or perhaps not, given the difficulty of detecting the faint signal and the uncertainties involved in characterizing it. If you’re intrigued, an Arecibo survey asking for public reactions to the reception is now available.

I also want to point out that Arecibo Observatory is working on a new campaign to observe stars like Ross 128, the idea being to characterize their magnetic environment and radiation. One possible outcome of work like that is to detect perturbations in their emissions that could point to planets — planetary magnetic fields could conceivably affect flare activity. That’s an intriguing way to look for exoplanets, and the list being observed includes Barnard’s Star, Gliese 436, Ross 128, Wolf 359, HD 95735, BD +202465, V* RY Sex, and K2-18.

A final note: Arecibo is now working with the Red Dots campaign in coordination with other observatories to study Barnard’s Star, for which there is some evidence of a super-Earth mass planet. More on these observations can be found in this Arecibo news release.



Making Optical SETI Happen

Yesterday I made mention of the Schwartz and Townes paper “Interstellar and Interplanetary Communication by Optical Masers,” which ran in Nature in 1961 (Vol. 190, Issue 4772, pp. 205-208). Whereas the famous Cocconi and Morrison paper that kicked off radio SETI quickly spawned an active search in the form of Project Ozma, optical SETI was much slower to develop. The first search I can find is a Russian project called MANIA, in the hands of V. F. Shvartsman and G. M. Beskin, who searched about 100 objects in the early 1970s, finding no significant brightness variations within the parameters of their search.

If you want to track this one down, you’ll need a good academic library, as it appears in the conference proceedings for the Third Decennial US-USSR Conference on SETI, published in 1993. Another Shvartsman investigation under the MANIA rubric occurred in 1978. Optical SETI did not seem to seize the public’s imagination, perhaps partially because of the novelty of communications through the recently discovered laser. We do see several optical SETI studies at UC-Berkeley’s Leuschner Observatory and Kitt Peak from 1979 to 1981, the work of Francisco Valdes and Robert Freitas, though these were searches for Bracewell probes within the Solar System rather than attempts to pick up laser transmissions from other star systems.

Image: Harvard’s Paul Horowitz, a key player in the development of optical SETI. Credit: Harvard University.

This was an era when radio searches for extraterrestrial technology had begun to proliferate, but despite the advocacy of Townes and others (and three conferences Townes helped create), it wasn’t until the 1990s that optical SETI began to come into its own. Charles Townes himself was involved in a search for laser signals from about 300 nearby stars in the ‘90s, using the 1.7-meter telescope on Mt. Wilson and reported on at the 1993 conference. Stuart Kingsley began an optical SETI search using the 25-centimeter telescope at the Columbus Optical SETI Observatory (COSETI) in 1990, while Gregory Beskin searched for optical signals at the Special Astrophysical Observatory run by the Russian Academy of Sciences in the Caucasus in 1995.

Optical SETI’s advantages were beginning to be realized, as Andrew Howard (Caltech) commented in a 2004 paper:

The rapid development of laser technology since that time—a Moore’s law doubling of capability roughly every year—along with the discovery of many microwave lines of astronomical interest, have lessened somewhat the allure of hydrogen-line SETI. Indeed, on Earth the exploitation of photonics has revolutionized communications technology, with high-capacity fibers replacing both the historical copper cables and the long-haul microwave repeater chains. In addition, the elucidation (Cordes & Lazio 1991) of the consequences to SETI of interstellar dispersion (first seen in pulsar observations) has broadened thinking about optimum wavelengths. Even operating under the prevailing criterion of minimum energy per bit transmitted, one is driven upward to millimetric wavelengths.

In the late 90’s, the SETI Institute, as part of a reevaluation of SETI methods, recommended and then co-funded several optical searches including one by Dan Werthimer and colleagues at UC Berkeley and another by a Harvard-Smithsonian team including Paul Horowitz and Andrew Howard. The Harvard-Smithsonian group also worked in conjunction with Princeton University on a detector system similar to the one mounted on Harvard’s 155-centimeter optical telescope. A newer All-Sky Optical SETI (OSETI) telescope, set up at the Oak Ridge Observatory at Harvard and funded by The Planetary Society, dates from 2006.

Image: Dan Werthimer, chief scientist at the Berkeley SETI Research Center. Credit: UC-Berkeley.

At Berkeley, the optical SETI effort is led by Werthimer, who had built the laser detector for the Harvard-Smithsonian team. Optical SETI efforts from Leuschner Observatory and Lick Observatory were underway by 1999. Collaborating with Shelley Wright (UC Santa Cruz), Remington Stone (UC Santa Cruz/Lick Observatory), and Frank Drake (SETI Institute), the Berkeley group has gone on to develop new detector systems to improve sensitivity. As I mentioned yesterday, UC-Berkeley’s Nate Tellis, working with Geoff Marcy, has analyzed Keck archival data for 5,600 stars between 2004 and 2016 in search of optical signals.

Working in the infrared, the Near-Infrared Optical SETI instrument (NIROSETI) is designed to conduct searches at infrared wavelengths. Shelley Wright is the principal investigator for NIROSETI, which is mounted on the Nickel 1-meter telescope at Lick Observatory, seeing first light in March of 2015. The project is designed to search for nanosecond pulses in the near-infrared, with a goal “to search not only for transient phenomena from technological activity, but also from natural objects that might produce very short time scale pulses from transient sources.” The advantage of near-infrared is the decrease in interstellar extinction, the absorption by dust and gas that can sharply impact the strength of a signal.

Image: Shelley Wright, then a student at UC-Santa Cruz, helped build a detector that divides the light beam from a telescope into three parts, rather than just two, and sends it to three photomultiplier tubes. This arrangement greatly reduces the number of false alarms; very rarely will instrumental noise trigger all three detectors at once. The three-tube detector is in the white box attached here to the back of the 1-meter Nickel Telescope at Lick Observatory. Credit: Seth Shostak.

I might also mention METI International’s Optical SETI Observatory at Boquete, Panama. The idea is to put the optical SETI effort in context. With the SETI Institute now raising money for its Laser SETI initiative — all-sky all-the-time — the role of private funding in making optical SETI happen is abundantly clear. And now, of course, we also have Breakthrough Listen, which in addition to listening at radio wavelengths at the Parkes instrument in Australia and the Green Bank radio telescope in West Virginia, is using the Automated Planet Finder at Lick Observatory to search for optical laser transmissions. Funded by the Breakthrough Prize Foundation, the project continues the tradition of private funding from individuals, institutions (the SETI Institute) and organizations like The Planetary Society to get optical SETI done.



Detection Possibilities for Optical SETI

The Laser SETI campaign we looked at on Friday is one aspect of a search for intelligent life in the universe that is being addressed in many ways. In addition to optical methods, we look of course at radio wavelengths, and as we begin to characterize the atmospheres of rocky exoplanets, we’ll also look for signs of atmospheric modification that could indicate industrial activity. But we have to be careful. Because SETI looks for evidence of alien technology, it is a search for civilizations about whose possible activities we know absolutely nothing.

So we can’t make assumptions that might blind us to a detection. Getting the blinders off also means extending our reach. If successful, the Laser SETI project will do two things we haven’t been able to do before — it will scan the entire sky and, because it is always on, it will catch optical transients we are missing today, and tell us whether any of these are repeating.

In radio terms, think of the famous WOW! signal of 1977, detected at Ohio State University’s Big Ear radio telescope. Seeming to come out of the constellation Sagittarius, it fit our ideas of what an extraterrestrial signal could look like, but we can’t draw any conclusions because we’ve never seen it again. If the signal intrigues you, Robert Gray’s book The Elusive WOW (Palmer Square, 2011) goes into it in great depth, including Gray’s 1987 and 1989 attempts to find it. Gray would search again in the mid 90’s using the Very Large Array, and again in 1999 with the University of Tasmania’s Mount Pleasant Radio Observatory, with null results.

The Elusive WOW is a splendid page-turner that captures the drama of the hunt. It also reminds us how frustrating a transient can be — here today, gone in moments, never seen again. Did the WOW signal reappear at some time that we weren’t pointing our instruments at it? Is it repeating on some schedule we haven’t figured out?

All-sky surveys like Laser SETI weren’t on the mind of Giuseppe Cocconi and Philip Morrison when they wrote their ground-breaking paper “Searching for Interstellar Communications” in Nature (1959), one that is mostly commonly cited as launching SETI. But for optical SETI’s origins, we can look back with equal admiration at R. N. Schwartz and Charles Townes’ “Interstellar and Interplanetary Communication by Optical Masers,” which ran two years later in the same journal. The author’s vision encapsulates the idea:

We propose to examine the possibility of broadcasting an optical beam from a planet associated with a star some few or some tens of light-years away at sufficient power-levels to establish communications with the Earth. There is some chance that such broadcasts from another society approximately as advanced as we are could be adequately detected by present telescopes and spectrographs, and appropriate techniques now available for detection will be discussed. Communication between planets within our own stellar system by beams from optical masers appears a fortiori quite practical.

Image: Charles Hard Townes, at the National Institute of Biomedical Imaging and Bioengineering’s 5th Anniversary Symposium, held in June 2007. Credit: NIBIB.

Optical SETI Scenarios

We saw Friday that a petawatt laser of the kind that has been built at Lawrence Livermore National Laboratory could be transformed into an optical SETI beacon, working in conjunction with a huge mirror like that found on our largest telescopes. Indeed, the Sun can be outshone by a factor of 10,000, a bright and, one would assume, obviously artificial beacon. But the complexities involved in targeting another star — and aiming the beam to lead the moving target, one that will be many light years away, make targeted laser beacons difficult.

Surely the challenges of laser beacons — not to mention their cost — could be overcome by advanced civilizations, although the idea of a less targeted beacon seems to make more sense; i.e., a beacon that sweeps a region of the sky on a recurrent basis, assuming the intent here is simply to announce the presence of the extraterrestrial civilization as widely as possible. But perhaps it’s much more likely that, if we do detect a laser signal from another civilization, it will be in the form of a chance interception of a technology at work.

Image: The power of laser technology even today. Credit: Eliot Gillum/SETI Institute.

Detecting communications within an exoplanetary system presents serious problems of geometry, given that these optical beams would be broadcast to specific targets and are unlikely to be pointing by chance at the Earth. But there is a scenario that could work: We’ve learned all about exoplanet detection through planetary transits from the Kepler mission. A planetary system that was co-planar with our own could produce a communications beam between its own planets that swept past us with each orbital revolution. Even then, the target planet would likely absorb enough of the signal that detection would be unlikely.

But there are other kinds of detections. James Guillochon and Abraham Loeb have looked at the possibility that beaming to interstellar sailcraft would produce leakage that might be observable to our detectors (see SETI via Leakage from Light Sails in Exoplanetary Systems). Both interplanetary as well as interstellar transportation systems leave possible signatures.

And consider Boyajian’s Star (KIC 8462852), whose odd light curves drew it to the attention of citizen scientists at the Planet Hunters project and subsequent worldwide scrutiny. Numerous natural phenomena have been put forward to explain what we are seeing here, but light curves like this could also be the sign of an extraterrestrial civilization working on some kind of massive project (a Dyson sphere inevitably comes to mind, but who knows?)

It made sense, then, to make Boyajian’s Star a SETI target, which is why the SETI Institute used the Allen Telescope Array to search for radio emissions, a two-week survey that produced no evidence of artificial radio signals coming from the system. For more on this investigation, see Jim and Dominic Benford’s Quantifying KIC 8462852 Power Beaming, which analyzed the ATA results at radio wavelengths. But note the following, which summarizes what the Benfords believe would be detectable given the instruments used in the attempt. As you can see, not all detectable signals would come from power beamed, for example, to an interstellar mission. Some of them definitely include applications within the target system:

  • Orbit raising missions, which require lower power, are not detectable at the thresholds of the Allen Array.
  • Launch from a planetary surface into orbits would be bright enough to be seen by the 100 kHz observations. However, the narrow bandwidth 1 Hz survey would not see them.
  • Interplanetary transfers by beam-driven sails should be detectable in their observations, but are not seen. This is for both the narrow 1 Hz and for the “wideband” 100 kHz observations.
  • Starships launched by power beams with beamwidths that we happen to fall within would be detectable, but are not seen.

Image: Power beaming to drive an interstellar lightsail. Credit: Adrian Mann.

But let’s move back into the optical. Nate Tellis (UC-Berkeley) recently worked with astronomer Geoff Marcy to analyze Keck data archives on 5,600 stars observed between 2004 and 2016, using a computer algorithm fine-tuned to detect laser light (see A Search for Laser Emission with Megawatt Thresholds from 5600 FGKM Stars,” preprint here). The search was an excellent way to put thousands of hours of accumulated astronomical data to work — who knows what discoveries may lurk within such datasets? As a part of the effort, the astronomers studied Boyajian’s Star, again finding no detectable signals. Potential candidates that did emerge in the survey all turned out to be the result of natural processes.

But power beaming is a possible observable as any local civilization goes about moving things around in its own system. Leakage from a beamed power infrastructure is something we’ve focused on here frequently (see, for example, Power Beaming Parameters & SETI re KIC 8462852). Power beaming could be what enables a space-based infrastructure, one that would be capable of large-scale engineering and also of producing the kind of power beams that could drive spacecraft at high velocity to other stars.

But we needn’t exclude communications entirely. Jim Benford has pointed out that any civilization using large-scale power beaming would be aware that its activities could be visible to others. If it had the desire to communicate on such a random basis, the ETI civilization could embed a message within the beam. A kind of interstellar message in a bottle, thrown into the cosmic sea with each sweeping power beam that does local work.

All of this should reinforce the key issue that the Laser SETI project addresses — such beams, working within their own planetary system, would appear in our sky as transients. We return to the core issue, the need for an all-sky survey that observes continuously. Making no assumptions about any desire to communicate, such a survey nonetheless is capable of spotting the signs of a working civilization going about its business. It should, I would wager, also pick out new astrophysical phenomena that will add to our knowledge of the galaxy.



Laser SETI: All Sky All the Time

The SETI Institute’s just announced Laser SETI funding campaign intends to put into practice what SETI researchers have been anticipating for decades, an all-sky, all-the-time observing campaign. The Institute’s Eliot Gillum and Gerry Harp are behind the project, backed by an impressive list of advisors, with the intention of using optical SETI methods to look for signs of extraterrestrial civilizations. In doing so, they’re reminding us how we’ve done SETI, how we can surmount its current limitations, and what a SETI of the future will look like.

Think about how SETI has evolved since the days when Frank Drake created Project Ozma at the National Radio Astronomy Observatory at Green Bank (WV). Fresh with the insights of Giuseppe Cocconi and Philip Morrison, who examined radio methods and suggested a search for signals near the 21 centimeter wavelength of neutral hydrogen, Drake turned a 26-meter radio telescope to examine the nearby Sun-like stars Tau Ceti and Epsilon Eridani.

Would SETI be a matter of looking at specific stars at certain wavelengths? Immediately the list of questions began to grow. Once you have chosen a target (and there are 18 million stars within 1000 light years), how long do you need to examine it before moving on to another? For that matter, are radio wavelengths optimal? And if our method is to look at particular places at particular times, how would we detect periodic signals that are on no schedule we can hope to predict? What do we miss in between?

Image: The view toward Messier 24, the Sagittarius star cloud. We are looking for signals amidst immensity. Credit: Hubble Heritage Team (AURA/ STScI/ NASA).

All Sky All the Time

We started doing SETI at radio wavelengths at a time when there were no operational lasers, but today we can look at the experience of our own civilization to see how high-capacity fibers have changed the way we communicate. As we add laser methods to SETI, we begin looking for the kind of monochromatic optical signal that nature does not tend to produce. We also look on timescales of nanoseconds, for no natural sources produce nanosecond pulses.

Configured to serve as a beacon, the Helios laser at Lawrence Livermore National Laboratory could outshine our own Sun by a factor of 10,000. Couldn’t an ET civilization do the same?

But of course we have no way of making assumptions about what an alien civilization might do. We may not receive a beacon at all. We may find ourselves intercepting alien communications or activities like power beaming that produce optical signatures but are not intended as communications. For that matter, here on Earth we use powerful radars (think Arecibo) to examine near-Earth asteroids as we assess impact possibilities. The beams from these searches should be detectable, but would appear in an alien sky as a transient.

So we have to get away from the assumption that any extraterrestrial civilization will be ‘always on,’ just waiting for us to detect it. Searching with instruments pointed at specific targets and limited by short ‘dwell’ times (how long we remain on that target), we wouldn’t find the great bulk of transients that could be telltale evidence of other civilizations. We’re just now learning, for example, about Fast Radio Bursts (FRBs), millisecond radio pulses thought to occur in their thousands every day and still poorly understood. Because they appear as transients, we’ve only catalogued a handful. SETI sometimes detects radio transients that never, to our knowledge, reoccur. Or perhaps some do, but we aren’t looking then.

Current methods are, to use Paul Shuch’s phrase, looking at the sky through a soda straw. Laser SETI proposes to put an end to that limitation with new detectors that will become the basis of observatories that will one day provide global coverage of the entire sky.

Moreover, the detector Eliot Gillum talked about in last year’s Breakthrough Discuss meeting, is not hypothetical. The design has been turned into a prototype and tested with sky observations to validate the methods and analyze performance. The Laser SETI campaign on Indiegogo seeks to raise the funds needed to produce a minimum of two cameras, enough to localize targets on the sky and examine the algorithms used in signal detection.

Pushing Imaging Technologies in SETI’s Direction

Laser SETI’s technology involves cameras with a wide field of view that use ‘drift scanning’ methods (a fixed camera tracking the celestial scene as it passes above). The camera is a charged coupled device (CCD), a familiar technology widely used not only in astronomical observations but also in cell phone cameras and numerous scientific applications. Photons striking a CCD’s light-sensitive elements generate a charge that can be read by electronics within the device and turned into a digital copy of the light falling onto the surface.

But that just begins the story. Remember, we’re talking about the night sky moving across the camera’s fixed field of view. Laser SETI thus incorporates what is called Time-Delay Integration (TDI), a CCD readout technique used in many applications to capture images of fast-moving objects. TDI can preserve both sensitivity and image quality even when dealing with fast relative movement, with photo-charges constantly being shifted down the CCD detector from pixel to pixel as they record changes to the light pattern being observed.

In TDI work as it is normally used — this might be, for example, in factories for quality control — the shift rate within the CCD matches the rate of the target being imaged. But Laser SETI’s new technology uses TDI in an entirely novel way. Instead of producing a normal working image, the idea is to overclock the TDI so that the ‘scene’ — the sky above — becomes smeared out and spread over the entire CCD. The beauty of this is that while the background sky loses definition, any transient pulses that appear show up as a single point.

Reading out the camera at over 1000 times per second, the detector also employs a transmission grating that spreads each point source into two spectra, allowing a single color of light to be distinguished from other kinds of sources. Gillum and Harp’s methods demand two cameras, the second looking at the same field of view but turned 90 degrees sideways. The coordination between the two instruments allows the software to recover accurate sky coordinates for any transient being observed. Putting four cameras at a given site, coupled the same way (two per field of view), allows the entire night sky to be covered.

Image: The first detector. The CCD camera is at the base, the lens atop it, and the transmission grating at the top beneath the hood. Two of the major three components here are off-the-shelf, keeping costs low. Credit: SETI Institute/Eliot Gillum.

Moving Laser SETI Worldwide

You can see what all this is building toward. The Indiegogo project’s intent is to raise the money for two cameras, but further funding takes us toward multiple site operations. The entire sky can’t be seen from any one part of the globe, but six observatories could cover all of it, with eventual secondary observatories adding valuable statistical validation, and also necessary sky coverage during times when the weather is inclement at any one site.

Have a look at the Laser SETI campaign for further background. The low cost of these detectors is significant. And bear this in mind. When we look at particular points in the sky, we have to be lucky enough that the signal we seek is available just then, just there. Looking everywhere all the time, we see the brightest signals in the sky whenever they appear.

In the entire history of radio astronomy, it has taken us until now to detect Fast Radio Bursts. What else are we missing? As Eliot Gillum pointed out in a recent presentation, we have no way of knowing what any extraterrestrial civilization may be doing, but we can say this: If their activity is bright but intermittent, all previous and current searches very likely won’t find it.

That’s why we need to look at the entire sky all the time.