A Future We Can Choose

by Paul Gilster on February 10, 2016

The very small may lead us to the very large. Payload sizes, for one thing, can be shrunk as we increasingly master the art of miniaturization, giving us far more bang for the buck. In that sense, we can think about tiny interstellar probes that may one day be sent, as Robert Freitas has envisioned, in waves of exploration, each of them no larger than a sewing needle, but armed with artificial intelligence and capable of swarm-like behavior. Mastering the tiny thus enables the longest of all journeys.

But thinking about small payloads also makes me ponder much larger constructs. Suppose in a hundred years we can work at the atomic level to build structures out of the abundant raw material available in the asteroid or Kuiper belts. It’s possible to imagine enormous arcologies of the kind discussed by Gerard O’Neill that may one day house substantial human populations. In this way nanotech opens the door to renovation in the realm of gigantic colony worlds.

And if one of these colony worlds, eventually exploring ever deeper into the Solar System, becomes so taken with life off-planet that it continues its outward movement, perhaps we’ll see nearby stars explored in millennial time-frames, harvesting Oort Cloud materials and their counterparts among nearby stars. For that matter, could nanotech one day help us build the kind of lens structures Robert Forward envisioned to focus laser beams on departing interstellar craft containing humans? Using these technologies, Forward could work out travel times in decades rather than millennia. The art of the small may work in both these directions.


Image: Don Davis produced this image of a toroidal-shaped space colony for NASA, emphasizing not only its size but its closed ecosystem. Credit: Don Davis / NASA Ames Research Center.

The Next Hundred Years

Closer to our own time, virtual reality enabled by miniaturization and microsatellites may play a large role in how we explore Mars. Robotic bodies, as Emily Lakdawalla points out in a Nautilus essay called Here’s What We’ll Do in Space by 2116, have no need for the mammalian necessities of water and shelter. Putting robots on the Martian surface that serve as avatars for humans in Mars orbit would allow us to map and explore vast areas with minimal risk to life. Now we’re talking building up infrastructure of the sort that may eventually fill the Solar System.

A ‘virtual Mars’ from orbit is one Elon Musk would dislike, given his intention of walking the Martian surface one day, and given the growth of commercial space, it’s possible that private companies will be on the surface before a NASA or ESA-led robotic effort of the kind Lakdawalla imagines might be attempted. But surely there’s a rational mix between human and robotic to be found here. We’ll never tame the questing spirit that drives some to push for manned missions — nor should we — but the advantages of robotics will surely play a huge role in the creation of a human presence around and on whatever bodies we explore in the coming century.

I’m much in favor of Lakdawalla’s ideas on what happens next:

Most of the planets that we’ve discovered beyond the solar system are Neptune-sized, so it would behoove us to understand how this size of world works by visiting one with an orbiter. Uranus is closer, so quicker and easier to get to; but because of its extreme tilt, it’s best to visit near its equinox, an event that happens only once in 42 years. The last equinox was in 2007; I will be sorely disappointed if we do not have an orbiter at or approaching Uranus in 2049. But we may choose to orbit Neptune before we travel to Uranus, because Neptune has an additional draw: its moon Triton, likely a captured Kuiper belt object, and a world where Voyager 2 saw active geysers.


Image: Hubble observations of Uranus, among the first clear images, taken from the distance of Earth, to show aurorae on the planet. Imagine what we could learn with an orbiter in place here. Credit: NASA, ESA, and L. Lamy (Observatory of Paris, CNRS, CNES).

Triton may prove irresistible, especially given what we’ve seen at Pluto, but so too are Kuiper Belt objects like Haumea. This is an interesting place, a fast-spinner (about once every 3.9 hours) that is orbited by two moons, one of them (Hi’iaka) a whopping 300 kilometers in diameter. The scientific interest here is quickened by the belief that Haumea’s oblong shape resulted from a collision, perhaps giving us an opportunity to deeply investigate its composition. In any case, its highly reflective surface seems to be covered with water ice, so perhaps there is some form of cryovolcanism going on here. Triton again comes to mind.

For a look at a Haumea mission concept, see Fast Orbiter to Haumea and Haumea: Technique and Rationale, based on ideas Joel Poncy (Thales Alenia Space, France) presented at the Aosta interstellar conference back in 2009. But in weighing outer system missions, keep in mind as well the search for the putative Planet 9, the discovery of which would doubtless fuel speculation on the kind of technologies that might reach it. Lakdawalla mentions the possibility but, noting that the world would be ten times further out than Pluto, says that it would take a revolution in spacecraft propulsion to get to it in less than a hundred years.

The FOCAL Mission’s Allure

True enough, but the very presence of this intriguing object poses yet another driver for the development of technologies to reach it. So does a target with an equally compelling justification, the Sun’s gravitational lensing focus beginning at 550 AU. A spacecraft sent out from our system in such a trajectory that it would observe gravitational lensing of its target — on the other side of the Sun — could yield huge returns, given the vast magnifying power of the lens. Bear in mind that the focal line in a gravitational lens runs to infinity, so as the spacecraft receded, continuing observations could be made across a wide range of wavelengths.

FOCAL is the name of the mission, given Claudio Maccone’s championing of the concept and the name dating back to the early 1990s, and you can see the design of such a mission in his book Deep Space Flight and Communications: Exploiting the Sun as a Gravitational Lens (Springer, 2009). We continue to explore sail missions with gravity assist and, further in the future, beamed laser or microwave methods to reach the needed velocities.

Meanwhile, FOCAL’s allure is bright: As Michael Chorost writes in The Seventy Billion Mile Telescope, “For one particular frequency that has been proposed as a channel for interstellar communication, a telescope would amplify the signal by a factor of 1.3 quadrillion.” SETI anyone?

Then again, suppose Pale Red Dot, now working hard on Proxima Centauri using the HARPS spectrograph at ESO’s 3.6-meter telescope at La Silla, turns up an interesting planet in the habitable zone. Or perhaps David Kipping will find something in the MOST data he is currently working on. As we learned more about such a planet (and other possibilities around Centauri A or B), the idea of turning a FOCAL-like lens upon the stars would become irresistible.


Image: Beyond 550 AU, we can start to take advantage of the Sun’s gravitational lens, which may allow astrophysical observations of a quality beyond anything we can do today. Credit: Adrian Mann.

With all this in mind, though, we can’t forget not only how far we have to go before we’re ready for FOCAL, but how many things we can accomplish much closer to home. Lakdawalla writes:

Some people have suggested floating balloons under the Venusian sulfuric-acid cloud deck to search for active volcanoes, or sending similar balloons under the smog of Saturn’s moon Titan to watch its methane rivers flow and possibly even touch down in a Titanian ethane lake. We’ve dreamed of touring the populations of icy worlds that float ahead of and behind the giant planets in their orbits; many of these worlds have binary companions, and some of them have rings. We’ve suggested setting up lunar bases on polar crater rims where the Sun always shines, and sending rovers into crater bottoms where the Sun never does, where water ice may have been preserved over the age of the solar system.

All true, and I still love the AVIATR concept (Aerial Vehicle for In-situ and Airborne Titan Reconnaissance), a 120 kg airplane fueled by Advanced Stirling Radioisotope Generators (ASRG), which demand less plutonium-238 than earlier RTGs and produce less waste heat. AVIATR could stay airborne in Titan’s benign conditions (benign, that is, because of a dense atmosphere and light gravity) for a mission lasting as long as a year, exploring the moon by powered flight. See AVIATR: Roaming Titan’s Skies for background on the concept. There has been no shortage when it comes to intriguing concepts for exploring Titan.

My belief is that an interplanetary infrastructure will one day lead to our first interstellar missions, but just when those will occur is impossible to know. In any case, building the infrastructure will be so fraught with discovery that every step of the way is cause for celebration, assuming we have the sense to continue the push outwards. That, of course, is an open issue, and I suspect there will never be a time when expansion into space is anything but controversial. As always, I fall back on Lao-Tzu: “You accomplish the great task by a series of small acts.”

Keep working.


Dean Stell February 10, 2016 at 14:51

Thanks for sharing that Don Davis image. I had a jigsaw puzzle of that as a kid. Wish I had it back (or could find another on ebay).

tchernik February 10, 2016 at 15:04

This is the allure of science and technology. Even if nothing revolutionary comes our way. Even if there are no anti-gravity, FTL travels or any of the common tropes of sci/fi in our future. Even then, our future can be incredible and bright.

We can infer it now, because we have seen the torrent of the past, the effects of hundreds upon hundreds of years of human labor and dedication.

We are living in it, in a big, complex, mostly artificial world that would be unthinkable or science fictional for most of our ancestors.

There is simply no telling how far our dabbling in the spaces outside of Earth would take us. As you said: manned missions from Mars’ orbit, making labs and settlements on VR/AR for the final landing. For the people one day working and living in the surface of those planetary bodies that are currently empty of any such life.

Or simply building an incredible extraction/processing/production economy on space based on robots working on the asteroids. The kind of thing that gradually builds up more infrastructure and ensures we have a place to go out there.

And this only needs gradual improvements upon existing technologies. The seeds of this future are already with us, now. It only takes time and directed effort, and the river of human history already shows how that comes to be.

Andrew Palfreyman February 10, 2016 at 15:47

Can we not achieve an ersatz FOCAL mission much closer to home using a synthetic aperture technique? Certainly we can along the ecliptic.

Eniac February 13, 2016 at 14:49

The allure of the solar gravitational lens is its light gathering power, which comes from its enormous extent. Synthetic aperture helps with resolution, only, not light gathering. It does not help if you can resolve an object the size of a whale on an exoplanet if you can capture only one photon every 1000 years actually coming from that whale.

There is no target in the sky that is intense enough to be seen at the resolution that, say, a solar orbit baseline synthetic aperture would provide. Not until you can orbit billions of telescopes with a combined aperture (actual, not synthetic) of astronomical proportions.

Michael February 10, 2016 at 16:25

My favourite by far is the gravity focus point concept and we can view multiple targets of certain stars by moving along an intersecting trajectory. For instance we could view Proxima and Alpha Centauri and there are a few other systems. Use the simulator below and just imagine a SFP telescope in position, I can see 3 to 4 multi-systems.


Another advantage of going out so far is parallax measurements and using other star’s fields of gravity to probe other stars systems if they come in line. And what a view of the central black hole we would get!

Eniac February 13, 2016 at 15:11

I am afraid a FOCAL mission could only be targeted at one particular spot in the sky, with very little potential to changing that once it is determined by the spacecraft trajectory. You could arrange it so that the spot will move over time, covering a (very tiny) arc across the sky, but that arc will be predetermined and cannot be changed by very much.

For a target like Alpha Centauri, the spot could be moved enough to follow a planet, and perhaps switch between A and B, but Proxima would be out of range. It is likely that the first FOCAL missions will be targeted to a nearby galaxy, which can provide many interesting targets close together, and/or the CMB, which is everywhere, to examine its fine structure. When it comes to exoplanet imaging, you need a separate spacecraft for each system, each with an exquisitely fine-tuned trajectory to account for the target system’s proper motion.

Michael February 14, 2016 at 11:09

I doubt very much they will have a one shot spacecraft, too expensive, it will more than likely have a powerful on-board engine to move around. And it can be used to view Proxima and Alpha Centauri by moving a few tens of AU along the focus surface in an arc as the sun will be the optical fulcrum point and it can also view countless objects near them.

Eniac February 15, 2016 at 12:15

I think you underestimate the cost of moving “a few tens of AU” along the focus surface. It is not unlike going from Earth to Pluto, except you also have to stop again. You’d need some really advanced nuclear propulsion to do it in a reasonable time. All on top of getting there in the first place.

If there are going to be FOCAL probes at all, they will have to be content with a really, really small field of view, about the size of a close-by star system, or a remote galaxy. Nevertheless, I believe worthwhile missions can absolutely be designed.

Michael February 15, 2016 at 16:07

You must remember that the focus point goes on to infinity, so we can get a really,really good look at say Alpha Centauri and then a while later the Proxima system but with less magnification but still a hell of a lot. And yes we would need a powerful engine to get there, a fission implosion drive would get us there, dirty yes but very powerful and would get us there AND stop.

Eniac February 17, 2016 at 1:26

This would give you two very short observations (days, at most, I would guess) of Alpha Centauri and then Proxima, with years of nothing in between. Not a good deal. If you only have one probe, it is better to send it on a trajectory that follows either A or Proxima, and stays focused on either for many years. You would, after all, want to track the planets in their orbits. Also, even with the solar gravitational lens, photons will still be scarce and you will want time to collect them.

Michael February 15, 2016 at 13:25

Just thinking a bit more about this, not much stops us from having many cheap telescopes, as the magnification is so great, in a large formation communicating via a central telescope/communication module so we can view many objects at once.

Eniac February 17, 2016 at 1:29

Right, multiple instruments is the thing to do. However, cheap they will likely not be, because of the powerful engine that is needed for each.

Michael February 17, 2016 at 15:58

There only need be one engine which carries all the telescopes, once the they are close to the jump off point they are ejected to follow trajectories that would allow observation of other their targets and communication via the central probe for transmission back to Earth. The communication/telescope probe can be slowed to a stop as it has the engine to allow more observation time on special target and further movement. The other telescopes could still observe other targets in their field of view with great magnification.

Alex Tolley February 10, 2016 at 16:47

A third option that bridges humans vs robots is to have human minds uploaded/copied into mechanisms. If that is possible, then this paves the way for miniaturized spacecraft reaching destinations to be explored by human minds. No need to worry about “life support” or worlds in the HZ. All worlds then become possible for exploration or colonization.

Whether this is an option will depend on whether minds can be simulated sufficiently that the simulated mind thinks it is the original, or a reasonable facsimile. That is very much open to question.

I see no reason why a simulation living in a virtual world might not explore the universe, interacting with it via physical devices that are integrated with the mind.

Enzo February 10, 2016 at 17:01

All nice but NASA’s focus is on Mars is a substantial obstacle. The selection of MSL-2 over an Europa or Uranus/Neptune orbiter set back further exploration decades back.
When I looked at the composition of the steering committee of the Decadal Survey, it looked to me that the number of members that declared Mars as their primary interest on their web pages shifted the balance towards Mars. Starting from the chair, of course.
Composition of the committee here :

Paul D. February 10, 2016 at 22:40

It should also be possible to focus neutrinos using the Sun’s gravity. Because these particles can penetrate the sun, they can be focused at a shorter distance by the solar core. There should be a minimum distance where neutrinos with a variety of impact parameters are focused close together (a caustic).

Paul D. February 11, 2016 at 9:39

A reference:


In principle it would be possible to use this technique to observe neutrinos from the cores of nearby stars.

Eniac February 13, 2016 at 15:18

Now all we have to do is orbit a few cubic kilometers of ice between Uranus and Neptune to detect them.

Enzo February 10, 2016 at 22:57

Regarding AVIATAR, hasn’t NASA stopped developing ASRG ?

Also the $425 M TitanMare (also supposedly using ASRG) was deemed too risky but the never-used before fancy sky crane for $2.5B Curiosity mission was not. Funny way of assessing risk I think.

BTW, the white spot on Uranus, on the left picture, clearly bulges out of the globe. Is it an effect of oversaturate pixels ?

Paul Gilster February 11, 2016 at 8:59

Enzo, I just mentioned ASRG as it was part of the original AVIATR proposal, which would now have to be re-configured.

Enzo February 11, 2016 at 20:11

I could be have very well been wrong as these things change back and forth all the times.
However, the re-configuring could prove difficult with the plutonium stash running very low.
This is another “present” oft he Mars program : using scarce plutonium where is not strictly needed (Mars) effectively denying it to where it is necessary (beyond Jupiter).
Maybe there will be an Europa mission now that there’s a general push for it, but anything else (Titan, Uranus/Neptune) is decades away (+traveling time).
After Cassini crashes into Saturn in 2017, apart from the New Horizon fly-by of the KBO, there will not be a single mission, not even on its way to the outer planets. Mars will have numerous orbiters, landers and rovers there and on the way.

Eniac February 13, 2016 at 15:29

The link you posted says that the main reason they terminated the ASRG program was that plutonium is no longer expected to be scarce, since its production is being restarted. This is a good thing for space missions, since the old-fashioned MMRTG has no moving parts and is smaller, too.

Also, there is nothing wrong with prioritizing closer targets over far away ones, and Mars is awfully interesting as planets go.

Enzo February 15, 2016 at 5:06

Nothing wrong with “prioritizing” if you want all the stuff listed by Paul to continue to be just fantasies that kept being pushed back into the future..
NASA has allocated > ~ $ 5.6B to Mars alone recently (Curiosity $2.5B, MSL-2 $2B, Maven $700M, Insight >$ 425M).
Nothing else comes even close : as Mars missions keep getting approved, Europa, Titan , Enceladus,Uranus/Neptune only get cancellations and delays.

Eric Hughes February 14, 2016 at 12:31

ORNL is restarting Pu-238 production. First engineering trials were announced a couple months ago.


Michael February 14, 2016 at 13:16

It is a good time to as electronics gets smaller and the thermocouples getting more efficient there should be much more to go around as this stuff is not cheap at $1-2M per kg at the very,very low end!

Enzo February 15, 2016 at 5:13

ESA is also looking at RTGs with Americium :

Unfortunately ESA doesn’t have the same technical capabilities as NASA but they have a much much more scientifically balanced program (i.e. not as Mars obsessed). With an RTG they might be able to do an Enceladus, Titan or Uranus/Neptune mission.

Sean Robert Meaney February 11, 2016 at 0:25

Given we can build an O’Neil cylinder on earth and launch it to space…thirty two billion cubic feet of lift hydrogen capable of lifting a million tons to the edge of space, half of that weight the rocket motors and fuel needed to achieve orbit.

Alex Tolley February 11, 2016 at 12:56

32E9 cu ft of hydrogen may lift 1E6 MT, but only at sea level. Even if the hydrogen was in a separate expandable balloon, your cylinder will reach nowhere near the edge of space. At whatever altitude it reaches, it will then have to attain orbital velocity. What engines had you in mind that only need to consume 50% of the mass of the total vehicle?

I am well aware of JP Aerospace’s floating to space” concept, but there is precious little on how they intend to reach orbital speed with an airship.

Perhaps you can offer some specifics of your suggestion?

Michael February 14, 2016 at 3:54

There is not a lot of info on the engines, which are critical I would think.


NS February 11, 2016 at 3:48

I’d say a fourth option will be “virtual reality” exploration, where robot explorers transmit back enough information to construct virtual worlds that can be experienced by any number of human minds, right here on Earth in the bodies they were born in. Of course speed-of-light issues will limit how interactive the experience will be (or will they? FTL? Drugs?), but certainly many more people will be able to participate in something like that than will be able to be embodied in a robot (even if the latter is possible/desirable).

Alex Tolley February 11, 2016 at 12:43

That may well be the next most immediate approach. We are already building “3D” landscapes of visited worlds, and I see no reason why high resolution 3D maps of cannot be built. Add in a virtual world model and you could definitely “explore” such a world, although it would be limited and partially simulated. But once built, all humanity could spend time in such a simulation, “colonizing”, “terraforming” etc.

It almost seems inevitable such real world inspired virtual worlds will be built.

Eniac February 13, 2016 at 15:40

That’s not really exploration, though. The “virtual reality explorers” will be “exploring” an artificial world that others have put together based on actual data. It is the gathering of that data that is the real exploration, and that needs to be done in situ. The main question is to what extent the actual exploration can be done by machines, how much human control is necessary, and what communication latency is tolerable for that control. Another related question, which Alex brought up, is whether the machines doing the exploration may be controlled in situ by artificial minds that are modeled on actual humans, aka “uploaded” minds.

NS February 14, 2016 at 0:20

I agree that for the purposes of exploration, in part because of communication latency issues machines on very distant worlds will likely need some sort of artificial intelligence. But that level of AI wouldn’t necessarily require an “uploaded mind”. I believe that Alex Tolley is suggesting a way that a human might have the experience of visiting an alien world without going there in a human body, with all the problems that would entail. My view is that there are other ways to accomplish this.

Hiro February 15, 2016 at 20:35

It depends on whether we could achieve universal quantum computing or not; from my personal opinion (not much), universal quantum AI belongs in the biggest class of computational complexity (in term of pragmatic research), hence “uploaded human mind” is no problem. On the other hand, many people don’t buy the idea that human mind could be copied “almost exactly” by ordinary AI machines because lots of people think human “soul” is unique, therefore we can’t attain post-physical form in this universe.

Well, it’s still too early to know when we expand outside our star system by big spaceships which contain lots of useless weight (food, water, animal, tree etc…) or some random PS4 size “mysterious box” which has billions of uploaded human (or artificial) mind living inside several stacks of quantum computer chip.

John Freeman February 11, 2016 at 5:02

Over the last fifteen years I feel like there’s been a real advancement in terms of miniaturisation, in space engine development, and recognition of the powers of both international co-operation and competition to drive achievements; I might actually live to see the FOCAL mission launch in some form! Having people try both robotic and in-the flesh approaches will yield results, probably some them surprising! My money is definitely on the droids, but I could be wrong. I really wish NASA’s wasn’t
such a victim of political winds though.
I’ve always loved the AVIATR idea too (I painted the concept of a Titan air vehicle a few years back, though with a much more fanciful twist http://manyworldsart.blogspot.co.uk/2015/06/a-complete-tower-on-titan-and.html)

Cambias February 11, 2016 at 9:26

It has to be profitable. There will be no permanent presence in space as long as it depends on people back on Earth choosing whether or not to support space exploration. I’d like to see a much stronger focus among the space community on finding ways to make money in space — ways which aren’t simply new wrinkles on “getting the government to pay us.”
Tourism is one obvious answer, but of course tourism ultimately depends on the folks back on Earth. There’s nothing sadder than a tourist town when the tourists have quit coming.
Resource extraction is the way to go. Find things in space that are cheaper than they are on Earth, and come up with ways to make a profit. The Gold Rush built California, oil built Dubai (and Houston), and Pathfinder City on Mars will be built by . . . ?

Dani Eder February 11, 2016 at 17:09

@Cambias: “Resource extraction is the way to go. Find things in space that are cheaper than they are on Earth, and come up with ways to make a profit.”

Global space industry was $323 billion in 2014

http://www.sia.org/wp-content/uploads/2015/06/Mktg15-SSIR-2015-FINAL-Compressed.pdf (page 7)

Today we have to write off a satellite if it runs out of fuel or a critical part breaks, and launch is still very expensive. The market for refueling, repairing, and servicing the 1250 satellites in Earth orbit is worth billions a year. Space resources can supply the fuel, and support maintenance operations. We just have to get the cost to be a few less billions than the customers are willing to pay.

Beyond servicing the existing satellite market, there are new markets if you can deliver the supplies. For example, food, air, and water for a space hotel is expensive if you have to bring it all from Earth. Obtained from asteroids or the Moon, the mass return ratios can be in the 100’s to 1.

NS February 14, 2016 at 0:38

The problem is the huge up front investment with no near-term return that will be required to make these space resources available. There just doesn’t seem to be what someone here called low-hanging fruit to get the interest of either private industry or government in making that kind of effort.

Michael February 11, 2016 at 11:25

It has always been a personal bug of mine when we think of these ‘longtime’ migrations. Firstly we will not be beyond communication with the Earth, there are two ways we can communicate, by light and even probes with massive memory relays to these ‘longtime’ boats. Secondly its more than likely faster craft will be designed and go passed them at which point people can be picked up along the way in faster and faster craft.

It will be anything but lonely!

Eniac February 13, 2016 at 15:49

Unfortunately, it will be very difficult for the faster craft to “pick up” people along the way. Precisely because they move so much faster….

It will be possible, though, to send communications. Something like: “Hi, guys! Sorry, guys! Bye, guys!”

Michael February 14, 2016 at 11:28

The slower craft only need drop the excess ship mass and power up the engines with a small crew in a much lighter craft, easily catchup.

Eniac February 15, 2016 at 12:21

Sounds easier said than done to me….

Michael February 15, 2016 at 23:42

I think almost everything said on this forum is easier said than done. Now if we don’t build faster ships we can simply carry on with the one we have, it gives us an option is all I am saying.

Samuel February 11, 2016 at 12:14

“There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy”

I feel we have hit a stage where we can no longer imagine the new. I constantly hear, “everything that can be imagined has been” and that there is nothing new, I have to disagree, there’s plenty we haven’t imagined yet, if nothing else the universe will keep teaching us that!

Michael Chorost February 11, 2016 at 14:20

I agree that postbiological exploration is much likelier than us humans making the trip to distant destinations with our fragile, water-filled bodies. Pushing water and life-support systems around is so expensive that I think our AI descendants are much more likely to be able to undertake such voyages. They can also withstand much more acceleration. Dan Simmons’s “Ilium” makes use of a “scissors” made by using Jupiter’s magnetic field to accelerate AI bots in spacecraft to tremendous velocities (and they happily discuss Proust along the way.) As for me: my vote is for the Titan boat, though I’ve heard that Titan’s seasons aren’t propitious for a voyage in the next decade or two.

Michael February 13, 2016 at 7:36

My vote would be for a neutrally buoyant nuclear powered glider, perhaps we could make this super light glider in LEO first and then drop it into Titans atmosphere. Been ultralight it should not require such a heavy heat shield just be required to handle the high G loads, an orbiter will deal with the communication systems.

Perhaps one day we will control Jupiter’s magnetic environment and have a powerful accelerator, there is an enormous amount of energy available in its field. With Jupiter’s field we can move about in it using a small coil and even gain energy from it, less need for Pu238. I think with any future Jupiter orbiters they should send a simple design concept prototype with it to test it out.

Robert February 11, 2016 at 14:57

In the 1970’s NASA supported ‘Summer Studies’ on space colonies. O’ Neil served as the Technical Director of the 1975 study and as Study Director of the 1977 study. These studies produced the technical and economic framework necessary to build such space colonies with the then existing technological base.

The 1975 Study:

The 1977 Study:

The NSS Library of studies and books:

It may interest readers here to know that K. Eric Drexler, the ‘father’ of the modern concept of molecular nanotechnology, was a student and disciple of
O’ Neil. Drexler gives credit to Feynman for originating the concept but it was
really Drexler who put teeth on the concept, as it was developed by him for his PhD thesis under the late Marvin Minsky at MIT. Drexler was a student participant in the 1975 study referenced above.

Robert February 11, 2016 at 15:03

The ‘mass driver’ concept developed by O’ Neill’s group is far superior. Materials are mined on the Lunar surface and shot to the Lagrange points using solar energy and electromagnetic rail guns.

Dani Eder February 11, 2016 at 17:16

The mass driver may be more efficient for large scale materials delivery – Island One required a million tons a year. For starter scales, a centrifugal catapult works. That’s a rotating centrifuge arm driven by an electric motor and solar panels. Orbit velocity is low enough on the Moon that the tip of the arm can reach it, releasing a package at the right time to meet a collector in orbit. A tug then goes from low Lunar orbit to a higher location that gets full sunlight.

For maximum efficiency, you want two rotating arms. One then serves as the generator for the other, while slowing down to load the next payload. Basically it’s a flywheel energy storage system.

Eniac February 13, 2016 at 16:06

I don’t think you have to slow down to load the next payload. You can attach them at the hub, and let them slide/roll outwards under centrifugal force. This gives you an extra sqrt(2) in velocity, very high throughput, and near-perfect energy efficiency. If a simple roller will not take the speed, a gas cushion or magnetic levitator will.

Such a simple device is far superior to O’Neils magnetic drivers in any respect I can think of.

Michael February 14, 2016 at 4:22

You would need to counter act the momentum change of the released object, it would require firm foundations. Now there is no need to attach them to the arms if they are of a tubular construction, they can be fed through the hub as you state and down the multiple tubes to be flung out. A small amount of solar thermally heated oxygen, a by-product of mining operations, could be used to start the ball rolling so to speak.

Mark Zambelli February 15, 2016 at 13:05
Eniac February 17, 2016 at 1:38

It says there “The Slingatron is styled around a modified version with a constantly-extending string, but replaces the fragile string with a steel track.”

It could be argued that a steel string is actually less fragile than a steel track. Certainly it is simpler and lighter. As far as I can see, this “modification” provides only disadvantages.

Robert February 11, 2016 at 15:22

Readers may also be interested in Robert Freitas’ classic 1980 NASA/ASEE summer study ‘Advanced Automation for Space Missions’. He describes a self-replicating automated Lunar factory system. The heart of it is chapter 5. Of course such a system could be very useful in constructing large structures in space (as long as it doesn’t get out of control!).


Dani Eder February 11, 2016 at 17:19

You may be interested in my work derived from the AASM study, but generalized to any location:


The book is incomplete, but there should be enough there to understand the concept.

Robert February 12, 2016 at 15:59

Yes, thanks!

Alex Tolley February 12, 2016 at 17:54

No mention of P K Dick’s scifi short – “Autofac”? Dick wrote a number of stories that had self constructing and replicating factories.

Robert February 15, 2016 at 15:35

There is also ‘Kinematic Self-Replicating Machines’ by Freitas and Merkle,
Landers Bioscience, 2004.

Robert February 15, 2016 at 15:37

Landes Bioscience

Eniac February 17, 2016 at 2:07

This (KSRM) is a fascinating summary of the field, which has been curiously inactive in the last decades. Dani Eder’s Wikibook is, in my opinion, a much needed attempt to revive the concept, which I believe went dormant after Drexler and Freitas went off to develop the much more fantastic (and much less feasible) nano-assemblers.

I completely agree with Dani that this technology should be developed on Earth, first. Perhaps with the goal of self-replicating solar cell factories / power plants in the desert, with sand and rock as raw material. Once that works, the hardest part is done, not to mention an important Earthly problem solved. The next goals could then be adapting the processes to vacuum and zero-g conditions, and miniaturization of the “seed” so it can be launched at reasonable expense. Perhaps with an asteroid as raw material.

The advantages of starting on Earth are immense: The development can involve hardware stores and engineers with toolboxes; no space launches or teleoperated robots needed.

Robert February 17, 2016 at 13:50

Nano-assemblers as a field of study was crushed out of existence by people like Nobel prize winner Richard Smalley with wrong headed and unfounded criticisms of something he did not comprehend.

Drexler and Smalley had a public debate over the feasibility of assemblers many years ago. On every technical point, Drexler’s arguments won, yet Smalley’s arguments prevailed with the vast majority of those who control the budgets and the flow of science. Assemblers were considered an embarrassment and a distraction to the mainstream. Perhaps the concept was too popular among the public at large which is always a death blow to ‘serious’ researchers.

We don’t have the best science possible or the best engineering possible because the funding process fails us. It’s way too conservative and self serving. It vastly reinforces the status quo.

Alex Tolley February 17, 2016 at 15:06

There is quite a nice review of the debate and follow up on Wikipedia.
I think it is fair to say that:
1. Drexler’s initial ideas and images of machines cannot be made to work. As Smalley notes, biology can do many things, but it cannot make crystals of titanium.
2. Despite the marketing of “nano” everything, there are no examples of even crude assemblers, let alone the scifi “nanites”, which remain magic pixie dust.

What has been fruitful is reengineering biology to make new compounds and materials that can be made by biology, as well as using biology to create functional “devices”. An example is the use of antibodies to deliver chemotoxic compounds to cancer cells by binding to unique proteins, sparing non-cancerous cells.

Computationally, the best way that I have seen biology be used to do computations is to engineer DNA replication and modification processes so that “if-then” rules can be implemented. It is crude and only works for a few rules, but this can be made useful for diagnostic purposes. MIT’s bio-brick catalog of parts is a good step towards standardizing components to mimic the electronics industry approach.

Robert February 18, 2016 at 14:24

Thanks for the response.

Given the Wikipedia treatment of Randy Mills (of hydrino fame) forgive me if I do not find it a very reliable source for anything even remotely controversial.

As to your first point, Smalley’s point about biology is simply irrelevant, as were most of his points. Drexler’s designs could work in principle, which is the point. Criticism as to not knowing exactly how to build them at the moment misses the point entirely. Not many know but Drexler received a PhD from MIT under Marvin Minsky exactly dealing with the theory and calculations of why such devices could work. It’s published in the book Nanosystems. An online version of his thesis is here;


Consider that folks we mentioned recently here, Freitas and Merkle both agree with and have long worked with Drexler.

Your second point ‘there are no examples of even crude assemblers’ seems to be saying that if there are no examples now that proves there can be no examples ever? Assemblers are an idea, an engineering concept. They will never exist unless people try to build them. That will never happen if people claim that would be impossible because they don’t exist.

Starships don’t exist so we should give up trying to design them?

Alex Tolley February 18, 2016 at 19:13

Drexler’s designs could work in principle, which is the point.

Probably not. That was Smalley’s point, I believe. We have techniques to place individual atoms, as well as existing chemistry, yet even simple machines, e.g. gears, rotating shafts, have not yet been built. What we do have working is the use of biology and chemistry, that can build quite complex structures. We also know that rotating shafts can be built of proteins working in an aqueous environment, because that is how cilia can rotate for movement.

Your second point ‘there are no examples of even crude assemblers’ seems to be saying that if there are no examples now that proves there can be no examples ever?

All I am saying is that the devices suggested by Drexler have not materialized as I indicated above, and certainly nothing like the computationally smart devices like robots that can assemble other objects. That doesn’t mean that they are impossible, just that no one has managed even a simple machine based on macro engineering designs, whilst biological inspired machines have be created (or tweaked).
Critics like Smalley would argue that these designs cannot work in principle, which is a strong claim, and might run afoul of Clarke’s 1st law.

Eniac February 19, 2016 at 13:20

I agree with Robert (and Drexler) that the nanomachines could work in principle. Alex, though, has a point in that we are not very far along in actually building any. The reason we can’t is we do not have suitable tools, and we do not have the tools because they themselves would be nanomachines. It is a chicken and egg problem that will eventually be solved, perhaps using biologically inspired tools. However, macroscopic, kinetic, self replicating machines can be made in a machine shop, all the tools are available. We can start building them now, really.

This is what I meant when I said “which I believe went dormant after Drexler and Freitas went off to develop the much more fantastic (and much less feasible) nano-assemblers”. It is the turning of Drexler and Freitas to nanotechnology that stopped self-replicating machines in their tracks. The Smalley controversy is incidental, further delaying even nano-machines, perhaps, but the real damage to the development of self-replicating technology was done by Drexler’s change in focus.

Alex Tolley February 19, 2016 at 16:56

We are seeing additive printers and other fabbing devices make most of the components to replicate, at least with a robot to do the assembly.

We also know that self replication is possible, both with designed engineering and of course, living systems. Simple, non-living things can also replicate.

In principle I see no objection to having self replicating things, although it seems to me that life does it superbly well, and may continue to be the supreme self-replicator, even when star ships can be built.

Eniac February 21, 2016 at 2:03

Life works well on Earth, but it’s use of relatively rare primary resources (volatiles like water and CO2) and it’s fragile substrate (aqueous solution) make it ill-suited for space. Rock is a more commonly available resource, and machinery made from ceramics, glass and steel a more robust substrate. Rock is almost entirely made from metal and oxygen (counting silicon as a metal), and so are ceramics, glass and steel.

Robert February 20, 2016 at 15:53

What really happened is that Drexler made the term ‘nanotechnology’ so popular it was co-opted by people doing standard chemistry or companies making powders and such things. Then, there was a concerted effort to delegitimize Drexler’s vision as ‘fringe’ in order to keep the money flowing.

Stick the word ‘nano’ in your proposal and you are good for even more funding…

Robert February 19, 2016 at 14:44

Smalley was motivated to cast doubt on Drexlers’s vision because he felt it threatened support for ‘serious’ research into nanotechnology. Perhaps the Drexlerian dream is more akin to building a real intersteller ship, further off than I hoped it would be but possible in principle. Simulations show its possible in principle based on hard science.

Here is a small step;


I have often wondered if the goal of true molecular sized device is making things a lot harder. The building block approach at a meso scale would effectively allow the same benefits with far less effort in design and construction. I think a lot of work is moving in that direction.

Alex Tolley February 19, 2016 at 16:50

Note that this uses chemistry, not nano assembly (positioning atoms). I fully endorse this approach to nano machines as it uses known techniques in novel ways.

Robert February 20, 2016 at 15:39

Chemistry is atomically precise by definition. Even a positional assembler would use chemistry with some mechanical force substituted for random alignments. Also, mechanical positioning of atoms has been done millions of times in experiments over the last few years.

They have always said that there are many potential pathways to a true molecular manufacturing capability.

Eniac February 21, 2016 at 1:50

Yes, exactly, except I think mini, or “toy” scale is the best bet. Forget about nano, meso, or even micro scale. The mini scale is best because we have all the tools we need, and we can do manually whatever we do not have programmed the robots for, yet.

Robert February 22, 2016 at 14:39

But the concept really makes sense when the parts can be made in bulk dirt cheap. That is something more likely done at the meso scale with bulk chemistry than at the toy scale in my opinion. But I’m not dogmatic on the issue.

Eniac February 19, 2016 at 21:14

“Given the Wikipedia treatment of Randy Mills (of hydrino fame) forgive me if I do not find it a very reliable source for anything even remotely controversial.” Are you implying that there is reason to believe this hydrino business is not an elaborate fraud?

Robert February 20, 2016 at 15:31

I have followed his career since 2000 and no, he’s no fraud. He is a modern day Tesla figure, wholly devoted to his discovery which, ultimately will be widely recognized because it happens to be real.

Eniac February 21, 2016 at 0:49

I admire the steadfastness of your belief, having followed this work for 16 years without any demonstrable success. You must have noted countless promises of working devices coming real soon, none of them ever materializing.

“Energy level lower than ground state” is an obvious contradiction in terms. You don’t even need to be a physicist to see that, it is in the semantics. There is no energy to be had, here.

And don’t get me started on “Tesla figures”. The mention of Tesla is (unfortunately) one of the best advance indicators of fraudulent science. Tesla may have been off the rocker a bit, later in life, but he does not deserve this.

Robert February 22, 2016 at 16:22

You made three point and I would like address each one.

First, the engineering of what they are trying to do is hard. Almost impossible, especially with just one guy and his support team. Sure, there have been numerous setbacks but also progress. It’s more akin to a complex processes like fusion (though it’s definitely not fusion of any kind). How long have the fusion guys been working on a practical device? Around 2000, the energy levels were milliwatts. Now, the process is in the kW range and higher. The engineering is quite challenging.

“Energy level lower than ground state”
If there was truly ‘no energy to be had there’ from the hydrogen atom ‘ground state’, all of chemistry would be impossible. When two hydrogen atoms bond to make an H2 molecule, the reaction is exothermic. Each hydrogen atom gives up a little of its ‘ground state’ energy to form the new ‘ground state’ of the molecule. Thus each electron is on average closer, more tightly bound to each proton. The average energy of each electron is -15.4ev, not -13.6ev. This is precisely because some if that ‘no energy to be had’ ground state energy is given up to a third body in the non-photonic three body process which forms the molecule. Mills just carries this process further. In Mills’ view, what we traditionally call the ground state is the first of a series of stables states, the one excited states decay to. You can consider it the photonic ground state. The contradiction exists, but only in the terminology.

“Tesla figures”
It’s a superficial indicator. If Mills is correct, he both predicted and discovered the hydrino state. If he is successful, he will have developed it into a useful technology. That would make him more like Einstein and Tesla combined.

Phil February 11, 2016 at 18:48

“BTW, the white spot on Uranus, on the left picture, clearly bulges out of the globe. Is it an effect of oversaturate pixels ?”

Enzo, that is a composite picture and the white spots are auroral emissions detected a few years ago. Uranus has weird auroral spots, but it also has a weird magnetic field. Its one reason my personal next flagship mission would be long lived orbiter and probe to the Uranian system.


Enzo February 12, 2016 at 1:02

Thanks for the explanation.

There was a proposed New Frontier mission to Neptune (flyby),not quite an orbiter (and not Uranus) but a relatively cheap substitute instead of waiting another 20-30 yrs.
Unfortunately :
“Argo, the last proposed mission to Neptune, was grounded because NASA didn’t have enough plutonium to power all of its spacecraft, according to one of its designers.
Candice Hansen of the Jet Propulsion Laboratory says there was a special launch window from 2015 to 2020 that would put Argo at Neptune in a decade thanks to gravity assists from Jupiter and Saturn. That timeline is now impossible to meet. ”


Also mentioned by Emily Lakdawalla of the Planetary society :
“It’s a neat idea. It can’t happen in the next New Frontiers opportunity because the U.S. doesn’t have enough plutonium available for the next New Frontiers to be nuclear-powered.”

Which brings me back to how damaging NASA’s Mars obsession is to planetary science (see also above).

John Frazer February 19, 2016 at 6:18

Re: the FOCAL mission.
In their articles on the anti-proton triggered nuclear pulse rocket, the Penn St physics depart mentioned that at 520AU, s the Sun’s gravitational lens to the distance of the center of the Galaxy. Of course, it has to be fixed in the appropriate direction, so to view different places, it’s a different place. You have different focal lengths, I presume. IDK how that distance works out for viewing deep intergalactic space compared to nearer stars.

Forward’s Starwisp probes can thoroughly map local interstellar space. Especially with SSPS arrays devoted to illuminating the target star system or region as the tiny mesh probe is going through.

A large habitat or space city (a “macrolife” unit) can only move as fast as you want to push a cometary chunk so that by the time you’re eaten and processed it, you’re nearing matching trajectories/closing distance with another.
That’s not a “ship”. A large habitat is mobile, but only about as much as a small-ish asteroid is. You can push it with an EM catapult throwing rock dust mining slag, but it’s not going anywhere in a hurry. If you want to put more drastic technologies to the task, you still are always pushing all of the GCR shielding of such a hab. A hundred million tons is fairly lean for habitat hull strength. Build it like a bunker. You’ll be pushing a (slowly dwindling) flying icy mountain with it.

O’Neill or “Kalpana” type colonies in the Oort halo aren’t alone. Kids born on one have a choice through school life of seeing other places. If they’re close enough to the inner Solar system, even the Earth.
Dyson speculated about what we could realistically expect to do with even the crude H-bomb powered Orion. 40million+ ton ship with delta-V of .1C is a lousy starship, but it allows fairly ready travel among university town at different cometary bodies & observatories. Moves 200 AU in 34 days during mid-course coasting.
Especially if ports of call can provide them with propellant for the next leg of their trip (plastics or metals from ISRU at a colony, work well). It burns a kilo or so of weapons-grade Pu in the triggers of the tens of megaton H-bombs of the pulse unit, but each is 1300 tons of stuff to be vaporized and shot at the aft end of the ship to push it. It carries thousands of them, so for future trips it helps if the ship only has to carry the bombs, and not the propellant.
Imaginable if far-out with early ’60s tech.
It would be interesting to see what a big SC wire hoop for a magsail could do for helping make this sort of ship more practicable. No physical interaction between the plasma and the ship, and huge capture angle and long compression/rebound of the field and the physical wire for each pulse.

mike4ty4 February 22, 2016 at 6:00

I notice discussion about molecular assemblers — whether they’re feasible or not, what they can do. It is interesting to point out that if you could construct some form of molecular assembler, then that would provide yet another way to colonize with humans: you send a very compact ship that contains only the very raw materials for building life (basic molecules and elements), nano-assemblers, macro-assemblers, artificial wombs, and computers loaded with blueprints for bases and living cells. When it arrives, it starts building a base using the macro-assemblers, then it creates the people to occupy the base by using the nano-assemblers to assemble a zygote from the raw organic materials. The artificially-fabricated zygotes are then inserted into the artificial wombs and develop into babies, which are then nursed by robo-mommies and robo-daddies to be raised to be the first colonists. This way you don’t need to bother with trying to make some giant “arkship” or whatever, don’t need to worry about radiation, etc. (because these are just raw materials, they are much more robust to radiation than actual living tissue)

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