Toward a Soft Machine

When Project Daedalus was being designed back in the 1970s, the members of the British Interplanetary Society who were working on the starship envisioned it being maintained by ‘wardens,’ robots that would keep crucial systems functional over the 50-year mission to Barnard’s Star. Invariably, that calls up images of metallic machines, stiff in construction and marked by a certain ponderous clumsiness. True or false, it’s a view of robotics that has persisted until relatively recently.

But if you’re going to do long-term maintenance on a starship, you’d better be more flexible. And that makes a Tufts initiative interesting not just from a space perspective but for applications in medicine, electronics, manufacturing and more. The Biomimetic Technologies for Soft-bodied Robots project aims to produce machines that draw on the model of living cells and tissues. Five Tufts departments will work with a $730,000 grant from the W.M. Keck Foundation to get the job started.

Check out what’s going on at the university’s Biomimetic Devices Laboratory. The researchers here are calling for us to stop evaluating the line between living and mechanical on the basis of materials. “Many machines incorporate flexible materials at their joints and can be tremendously fast, strong and powerful,” says Tufts biology professor Barry Trimmer, “but there is no current technology that can match the performance of an animal moving through natural terrain.”

Trimmer is a neurobiologist whose work with caterpillars feeds directly into the robot concept. How do you build a simple machine that can move flexibly without joints? Like caterpillars, the new robots are to be soft, but unlike them, the robots will also be capable of collapsing into small volumes, and unlike today’s robots, they’ll be able to crawl along wires or burrow themselves into tiny spaces to do their work. Thus does biology meet nano-fabrication and bioengineering, with results that may prove exceedingly useful for long-haul space missions.

Back to the Daedalus wardens for a moment. They were designed not only to test and repair key onboard systems, but also to operate thousands of kilometers away from the ship as needed, coordinating a variety of experiments through the ship’s main computer. But they were envisioned as weighing five tons apiece and in the thinking of that era, would have been incapable of the kind of adaptive — one could say ‘evolutionary’ — behavior that is suggested by flexible hardware and genetic algorithms.

For software that generates variations in its own code and tests a variety of mutations has been under study for some time — look at the work Jordan Pollack and Hod Lipson have done at Brandeis, for example. Wedding genetic algorithms with a new flexibility in robotic structure promises great things for missions that must proceed without human intervention. Specialized robots will continue to fly on our space missions, but in forms that look less and less like the Daedalus wardens.

And incidentally, if you want to see those Daedalus wardens up close, the best reference is T. J. Grant, “Project Daedalus: The Need for On-Board Repair,” in A. R. Martin, ed. Project Daedalus Final Report. Supplement to the Journal of the British Interplanetary Society, 1978, pp. S172-S179.

A Cometary Transformation

Somehow I missed Mike Brown’s recent thoughts on 2003 EL61, the oddly elongated Kuiper Belt object that’s as big as Pluto along its longest dimension. Fortunately, the BBC recently covered the story. At the American Astronomical Society meeting in Seattle, Brown (Caltech) had discussed the instability of the object’s orbit, pointing out that it is headed for an eventual encounter with Neptune. A possible outcome: Two million years from now, 2003 EL61 may be a comet. “When it becomes a comet,” says Brown, “It will be the brightest we will ever see.”

First Light for COROT

The COROT space telescope doesn’t start scientific observations until February, but the protective cover of the 30 centimeter instrument has now been opened. So far so good. A preliminary calibration exercise — using the constellation of the Unicorn near Orion — delivers data of excellent quality. This news from the European Space Agency should keep exoplanet hunters primed as the search for transiting worlds takes to space. A diagram of COROT’s interesting orbit can be found here.

‘Light Science’ Finds Titan Jet Stream

When I interviewed the Jet Propulsion Laboratory’s James Lesh several years ago, he explained how space scientists could use radio signals to do science. It’s the ultimate technique for taking advantage of what’s at hand. If your spacecraft is moving behind a planet it’s investigating as seen from Earth, the changes to its signal as it disappears behind the disk tell you much about the composition of the planetary atmosphere. “One person’s noise,” said Lesh, “is another person’s signal.”

Of course, that kind of work isn’t limited to radio. Twice on November 14, 2003 Titan passed in front of a star, the events separated by just seven and a half hours. As you would expect, the occultation tracks were different, one visible from the Indian Ocean and southern Africa, the other from the Americas and western Europe. The effects of Titan’s atmosphere on the starlight have, in each case, supplied information about the movement of gases around the frigid world.

This work required observations from multiple locations, because what astronomers were looking for was the shape of the light focused by the gaseous lens of the atmosphere. “It is like the light falling through a glass of water and making bright patterns on the table. The focused light is not perfectly round because the glass is not a perfect lens,” says Bruno Sicardy (Observatoire de Paris). The triangular shape observed indicated an expected flattening of the atmosphere at the north pole, where warmer air from the south was cooling and sinking toward the surface.

Occluded light and Titan

Image: This artist’s impression shows the ‘light curve’ produced by a star passing behind Titan. When such occultation events take place, the light from the star is blocked out. Because Titan has a thick atmosphere, the light does not ‘turn off’ straight away. Instead, it drops gradually as the blankets of atmosphere slide in front of the star, as the light-curve drawn here shows. The way the light drops tells astronomers about the atmosphere of Titan. Credit: ESA. Image by C.Carreau.

The other discovery: a fast jet stream moving at about 720 kilometers per hour. The finding was quickly put to practical use, for the team was able to predict a temperature inversion near 510 kilometers altitude. Fourteen months later, the Huygens probe picked up the jolt of that layer on its accelerometers at precisely the suggested altitude, a validation of what James Lesh calls ‘light science.’ And while this finding relied on chance occultations, we’ll see spacecraft use targeted laser signaling for investigations of planetary atmospheres in the not distant future.

The paper on this work is Sicardy et al., “The two Titan stellar occultations of 14 November 2003,” Journal of Geophysical Research Vol. 111, E11S91 (18 November 2006). The abstract is here.

Tweaking the Past

It was Richard Feynman who proposed that particles like positrons — the antimatter equivalent of the electron — were actually normal particles traveling backward in time. Feynman would develop the idea with John Wheeler, and it continues to resonate with John Cramer (University of Washington), whose ‘transactional’ interpretation of quantum mechanics works with particle interactions that depend upon movement forward and backward in time. In December we looked at an experiment Cramer is developing to study this effect, which is best known as retrocausality.

So it’s nice to see that Patrick Barry’s fine article on Cramer’s work, and retrocausality in general, is available online from the San Francisco Chronicle. Originally written for New Scientist, the article is thus freed from that magazine’s firewall and available for general access. A snippet:

While Cramer last week prepared to start a series of experiments leading up to the big test of retrocausality, some researchers expect reverse causality will play an increasingly important role in our understanding of the universe. “I’m going with my gut here,” says Avshalom Elitzur, a physicist and philosopher at Bar-Ilan University in Israel, “but I believe that when we finally find the theory we’re all looking for, a theory that unifies quantum mechanics and relativity, it will involve retrocausality.”

Also intriguing is a sidebar on the fine-tuning of the physical constants that make life possible. Paul Davies [see below] opines that the universe might be able to tweak its essential parameters through a different kind of retrocausality. The thinking goes like this: If the laws of physics reside within the physical universe, they can only be as precise as the information content of the universe itself. But that content was smaller just after the Big Bang, perhaps offering an imprecision that later observers could influence. In other words, the universe is exquisitely shaped to produce life because life made it so.

Says Davies, “It offends our common-sense view of the world, but there’s nothing to prevent causal influences from going both ways in time.” Fascinating stuff, and the Barry article is a good overview for those of us who find the physics involved completely mind-bending (was quantum mechanics ever anything else?) Cramer’s variation on the classic ‘double-slit’ experiment, well described here, seems to offer the chance to witness an effect before its cause is in place. Needless to say, we’ll keep our eyes on this.

ADDENDUM: I originally referred to Paul Davies as being at Macquarie University, but found out subsequently that he left Australia last September (thanks to Gregory Benford for catching this). Davies is now at Arizona State; more on his work there in a few days.