The Probe and the Particle Beam

by | Apr 2, 2014 | Sail Concepts | 13 comments

For those wanting to dig deeper into Alan Mole’s 1 kilogram interstellar colony probe idea, the author has offered to email copies of the JBIS paper — write him at RAMole@aol.com. For my part, writing about miniaturized probes with hybrid technologies inevitably calls to mind Freeman Dyson, who in his 1985 title Infinite in All Directions (Harper & Row) discussed a 1 kilogram spacecraft that would be grown rather than built. Here’s Greg Matloff’s description of what Dyson whimsically called ‘Astrochicken’:

Genetically engineered plant and animal components would be required in Astrochicken. Solar energy would power the craft in a manner analogous (or identical) to photosynthesis in plants. Sensors would connect to Astrochicken’s 1-gm computer brain with nerves like those in an animal’s nervous system. This space beast might have the agility of a hummingbird, with ‘wings’ that could serve as solar sails, sunlight collectors and planetary-atmosphere aerobrakes. A chemical rocket system for landing and ascending from a planetary surface would be based upon that of the bombardier beetle, which sprays its enemies with a scalding hot liquid jet.

The passage is from Matloff’s Deep Space Probes (2nd ed., Springer, 2006), which goes on to discuss the need to master nanotechnology so that we can manipulate objects on the scale of atoms. He even speculates, citing Alan Tough, that nanotechnology could produce a hyperthin communication antenna for relaying information to Earth from an interstellar probe, constructing it from resources in the destination star system. And he cites Anders Hansson’s 1996 paper in JBIS that sketches an interstellar Astrochicken, one with

…miniaturised propulsion subsystems, autonomous computerised navigation via pulsar signals, and a laser communication link with Earth. The craft would be a bioengineered organism. After an interstellar crossing, such a living Astrochicken would establish orbit around a habitable planet. The ship (or being) could grow an incubator/nursery using resources of the target solar system, and breed the first generation of human colonists using human eggs and sperm in cryogenic storage.

Infrastructure for the Probe

Just as Project Icarus is an attempt to update the Daedalus design of the 1970s, Alan Mole’s work re-examines ideas like these in light of recent work. Yesterday we looked at the trends he thinks make probes with this degree of miniaturization possible. For getting the probe to destination at 0.1 c, he relies on a magnetic sail which draws on studies performed by Dana Andrews in the 1990s. Andrews was talking about a 2000 kg payload, but Mole’s 1 kg payload could be accelerated at 1000 g to cruising speed, with an acceleration distance he calculates at only 0.3 AU, using 1/9th the kinetic energy of the Andrews probe.

To push the magnetic sail a particle beam produced by an accelerator is demanded. Here is Mole’s description:

The probe interacts with the beam by having a magnetic sail, a loop of superconducting wire. This is ejected from the probe and a large current introduced. The magnetic field repels all parts of the wire, so it naturally inflates to a circular loop. For one kg and 0.1 c the acceleration distance is only 0.3 AU and the loop diameter…is just 270 m. After cruise, it is possible to slow the probe by reintroducing a current into the sail and using “friction” from interstellar magnetic fields. This method seems to scale successfully.

The beam generator in Earth orbit would be powered by beamed power from the Earth’s surface. Mole describes the installation as ‘an orbital solar power farm in reverse,’ with the advantage of tapping directly into Earthbound power resources. He points out that NASA drew up studies of a Solar Power Satellite system in 1981, coming in at a cost of about $4 billion to beam power to Earth by microwaves. The Mole plan reverses the process to power an orbital beam generator that would accelerate the magsail, with an estimated beam generator cost of $17 billion.

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Image: We’ve long imagined beaming power down to Earth to tap the Sun’s abundant energies. But is there a case for beaming power up to drive an interstellar beam technology? Credit: Mafic Studios/National Space Society.

Mole believes the cost of such a beam generator might actually come in considerably lower than $17 billion, but the appendix to his paper shows a wide range of possible costs. In a recent email, Mole wrote me that he is offering a stipend of $5000 (negotiable) for a suitable expert to design and produce cost estimates for the beam generator. Those interested should apply to Mole directly at the email address given at the top of this article. The cost estimates are significant, to say the least, and getting them right should illustrate the value of moving to a smaller probe.

In terms of energy use, by Mole’s figures, a 2000 kg probe of the sort Dana Andrews discussed in his 1994 paper, would require 560 times the US capacity for power generation today. A 1 kg probe would require 28 percent of the US generating capacity, making it far more feasible for a civilization at our stage of development over the next fifty years. The author adds:

Large probes and worldships inspire readers to imagine the vast civilizations that could afford them, but not to start work in hopes of seeing them launched in the readers’ lifetimes. In contrast, a 1 kg probe is plausible for the present civilization. If discussion begins now such a probe could be launched in fifty years.

Sail technologies, whether beamed by microwave, laser or particle beam, come to the fore in discussions like these because we’re already beginning to build experience with solar sails in space. Laboratory experiments have shown that sail beaming works, with the added benefit — shown in Greg and Jim Benford’s experiments — that materials can undergo ‘desorption,’ providing additional acceleration. Now we need to learn how well particle beams can drive a magnetic sail because, like all these sail concepts, this one requires no propellant aboard the spacecraft, a huge plus given the challenge of pushing even a 1 kilogram payload to a tenth of lightspeed.

The paper we’ve been discussing is Mole, “One Kilogram Interstellar Colony Mission,” Journal of the British Interplanetary Society Vol. 66, No. 12, 381-387 (available at the site). The Dana Andrews paper referred to above is Andrews, “Cost considerations for interstellar missions,” Acta Astronautica 34, pp. 357-365,1994. The Hansson paper is “Towards Living Spacecraft,” JBIS 49 (1996), 387-390.

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Small Probes, Hybrid Technologies

by | Apr 1, 2014 | Culture and Society | 20 comments

Reducing the size of a starship makes eminent sense, and as we saw yesterday, Alan Mole has been suggesting in the pages of JBIS that we do just that. A 1 kilogram interstellar probe sounds like it could be nothing more than a flyby mission, and with scant resources for reporting back to Earth at that. But by Mole’s calculation, a tiny probe can take advantage of numerous advances in any number of relevant technologies to make itself viable upon arrival.

Just how far can nanotech and the biological sciences take us in creating such a probe? For what Mole proposes isn’t just an automated mission that uses nano-scale ‘assemblers’ to create a research outpost on some distant world. He’s talking instead about an actual human colony, one whose supporting environment is first guaranteed by nanobots and, in turn, the robots they build, and whose population is delivered through the hatching of human embryos or perhaps even more exotic methods, such as building humans from DNA formulae stored in memory.

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Let’s look at some of the factors the author lists, and bear in mind that we are trying to sketch out the shape of technologies that will have advanced in ways we can’t predict by the time such a probe is ready to fly, even if we allow it the relatively short time-frame (by interstellar scales) of fifty or sixty years of development before launch. From the “One Kilogram Interstellar Colony Mission” paper, here are the key points:

1) Increases in memory density show no sign of slowing. Mole cites small media memory chips that will soon carry two terabytes, but I’d point to Charles Stross’ fascinating discussion of ‘memory diamond,’ which sets theoretical limits on memory density by manipulating carbon atoms. If we need to pack vast amounts of memory into tiny spaces, the future is increasingly bright.

2) Within fifty years, nanotechnology may be able to produce tiny machines — nanobots — capable of complex tasks including self reproduction. The key question then becomes, can such technologies build humans? Mole recognizes the size of the challenge:

“Whether nanomachines can build full humans is unknown. It is physically possible — nature does it when a single fertilized egg cell grows into a human or animal. The DNA of a bacterium has been produced from stored ones and zeros in a computer. Granted, this required a full laboratory of equipment, but in five decades nanobots may be able to do it.”

3) I would feel better about the nanotechnology cited above if we took that fifty year restriction out of the equation, but even without humans ‘built’ by nanotech, we still have the option of sending embryos. Here the relevant citation is a 1989 Japanese project to incubate a goat fetus in an artificial womb, where the fetus grew to birth size but did not survive. Using vast numbers of human embryos on a colony ship, to be raised by robots at destination (robots that have themselves been built by nanobots), allows humanity to spread without large ships and without the need for hibernation (the large ships may be less feasible than the hibernation).

4) That Mole’s proposal is audacious is underlined by the fact that artificial intelligence may be its least controversial feature. Not everyone agrees with Ray Kurzweil that within three decades we’ll be able to essentially duplicate a human mind and run it as a program on a computer. But watching the trends in memory and recent work in brain architecture, including the Blue Brain Project, makes the prospect of uploaded minds at least possible. In any event, we are talking about running some kind of artificial intelligence on tiny CPUs that can manage the activities of nanobots as they build androids that go on to create a human colony. We’re in Singularity territory now, and in the nature of things, that makes predictions tricky indeed.

All of this grows out of a foundation of thinking that combines biology and silicon in interesting ways. Back in June of 1999, then NASA administrator Daniel Goldin spoke before the American Astronomical Society. It had been two years since he announced (in the same year that the Pathfinder probe landed on Mars) that reaching another star would be a new goal for NASA. That was startling enough, but Goldin went on to speak about a combination of lightsail technologies, artificial intelligence advances and hybrid systems tapping advances in biology.

It was an exciting time, even if the interstellar vision was quickly submerged in NASA’s more immediate goals and the ever present challenge of funding work in low Earth orbit. But Goldin’s probe — he described it as a space vehicle about the size of a Coke can — was meant to build itself by scavenging an asteroid, using the abundant supplies of carbon, iron and other materials such an object could provide. Mole’s paper reminded me of Goldin’s quote from that time:

“This reconfigurable hybrid system can adapt form and function to deal with changes and unanticipated problems. Eventually it will leave its host carrier and travel at a good fraction of the speed of light out to the stars and other solar systems… Such a spacecraft sounds like an ambitious dream, but it could be possible if we effectively utilize hybridized technologies.”

With Goldin as with Mole, the intent was to craft a starship without the need to push thousands of tons of payload, using the ability of technology to build and extend itself with local materials. In any case, we’re getting better and better at working with small spacecraft. Consider the Viking landers, each of which massed about 1200 kilograms (the Viking orbiter was 2300 kg). Mars Pathfinder’s lander came in at 100 kilograms, while the Sojourner rover itself massed only 12 kg.

Freeman Dyson laid out a concept for a 1 kilogram probe back in 1985 that set the stage not only for increased miniaturization but the fusion of biology with digital tech. Tomorrow I’ll get into some of Dyson’s ideas as a way of framing what Alan Mole is discussing, and then we need to focus in on the propulsion question. Getting anything — even something as small as a 1 kilogram probe — to another star is an extraordinary undertaking. But finding ways to leave the propellant behind can make it more feasible.

The paper under discussion is Mole, “One Kilogram Interstellar Colony Mission,” Journal of the British Interplanetary Society Vol. 66, No. 12, 381-387.

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