by Paul Gilster | Jul 13, 2006 | Autonomy and Robotics
We don’t talk as much as we might about computer autonomy here, perhaps because it’s obvious that the biggest challenge facing interstellar flight is propulsion. But it’s clear that we need computer systems with fully autonomous characteristics on the kind of decades-long robotic missions that might eventually be flown. We’ll want such probes to have human-like traits of curiosity and judgment, as well as repair and maintenace capabilities for the long journey.
It’s interesting to see, then, that Cambridge, MA-based BBN Technologies, which played such a pivotal role in the development of the ARPANET and later Internet protocols, has just received funding to create a so-called ‘Integrated Learner.’ Working to the tune of $5.5 million from the Defense Advanced Research Projects Agency (with a possible total of $24 million over four years), BBN’s first phase effort will be to create a reasoning system that can apply itself to advanced tasks and master principles of the kind we all refer to as ‘common sense.’
“This program attacks one of the biggest problems in AI,” said Mark Berman, vice president, BBN Technologies. “The Integrated Learner will combine traditional machine learning techniques with an AI reasoning system capable of understanding behavior it observes only once. This ambitious goal is necessary because, for many of the current and future complex military tasks that could benefit from automation, there simply are not many examples in existence. Although there has been some research into this area, this will be the first deployed system with the capacity to apply general knowledge and reasoning to a task.”
Up first is research on military medical logistics planning, involving a simulation of the evacuation of wounded soldiers to various hospitals out of the combat theater. But the larger picture relates to building digital systems that can learn complicated tasks and apply the acquired skills broadly. Computer learning isn’t particularly captivating until you see it in context, but go read Greg Bear’s wonderful Queen of Angels (Warner Books, 1990) and you’ll see a malleable, motivated AI system built into the world’s first probe to Alpha Centauri, and learn what happens to a truly adaptive system once it begins to fathom the true meaning of its mission.
by Paul Gilster | Jul 12, 2006 | Culture and Society, Missions
The possibility of deflecting an incoming asteroid became more problematic in early July. That’s when David Polishook and Noah Brosch (both of Tel Aviv University) presented evidence that the number of binary asteroids near the Earth might be much higher than originally thought. Binaries might, in fact, comprise more than fifty percent of all NEAs. Now we’re talking about moving two objects instead of just one, an indication that asteroid-nudging is more tricky than we thought.
The paper “Many binaries among NEAs,” available here, was presented at NASA’s Near-Earth Object Detection, Characterization, and Threat Mitigation workhop in Colorado. It’s a reminder that the environment incessantly nudges technological civilizations to extend their capabilities. Jose Garcia recently commented here on a story about the New Worlds Imager ‘starshade’ concept, noting that experience with starshades could come in handy in future attempts to mitigate the effects of global warming by covering up parts of our own star.
Far fetched? In today’s terms, sure, but thinking ahead is what this is all about, and who knows what a technological race might accomplish with starshade technology in an attempt to keep its home world habitable. We seem to live in a universe that pushes us toward Kardashev Type II status, defined as a civilization that can exploit all the energy of its star. Could adjusting our Sun’s effects upon the Earth be a faint harbinger of such an outcome? I suspect evolution from Type I (harnessing the power of an entire planet) and on to Type II is all but essential for any species to survive over genuinely long time frames, its home planet challenged by all the menaces of solar system living.
On the starshade front, I notice that BBC has now picked up the Webster Cash story, drawing on an interview with Cash and the paper he recently wrote in Nature. Here Cash reiterates his belief that the fastest way to accomplish a planet-finder mission with this technology is to follow the James Webb Space Telescope, launching several months after it and using it to collect starshade observational data.
One problem is noted by Timothy Naylor (Exeter University), who points out the need for keeping shade and telescope in precise alignment. It’s tricky business, especially given the time frames involved. “If you are trying to collect the light from a planet then you are going to have to stare at it for a relatively long period of time to do anything really useful,” says Naylor, a good point and one we’ll address in a future article.
by Paul Gilster | Jul 11, 2006 | Deep Sky Astronomy & Telescopes |
Supernova remnant RCW103 is not exactly a new discovery. In fact, it was found over 25 years ago, the survivor of an explosion that took place in the early days of the Roman empire, though visible only in southern skies. And as you would expect, the area in question looks to be fairly standard issue for a supernova aftermath: a rapidly spinning neutron star and a surrounding bubble of material ejected by the explosion.
But look again, as an Italian team using the European Space Agency’s XMM-Newton x-ray satellite has done, and you spot some anomalies. The scientists, based at the Istituto Nazionale di Astrofisica (INAF) in Milan, find that emissions from the central source of the explosion repeat on a cycle of 6.7 hours, far longer than would be expected from such a neutron star. Another oddity is that the spectral properties found in these observations differ from another set of data made just five years ago with the same XMM-Newton equipment.
So what we have is an object embedded in a supernova remnant that acts more like a multimillion year old neutron star than one that is no more than two millennia old. “RCW 103 is an enigma,” said Giovanni Bignami, director of France’s Centre d’Etude Spatiale des Rayonnements (Toulouse), and co-author of a paper on the find. “We simply don’t have a conclusive answer to what is causing the long X-ray cycles. When we do figure this out, we’re going to learn a lot more about supernovae, neutron stars and their evolution.”
Possible explanations include a magnetar, or magnetized neutron star, whose magnetic field lines slow the object’s rotation, perhaps influenced in this case by a debris disk. Or we could be looking at a binary system, one in which a normal star somehow stayed bound to the object created by the supernova explosion. In either case, anomalies remain that may tell us much about how neutron stars evolve, especially since this system is a million times younger than other x-ray binary systems with low-mass companions.
The paper is De Luca, Caraveo, Mereghetti et al., “A long-period, violently-variable X-ray source in a young Supernova Remnant,” which ran in Science Express on July 6, 2006, with abstract available here.
by Paul Gilster | Jul 10, 2006 | Missions |
Good space science comes from unexpected quarters. When I interviewed the Jet Propulsion Laboratory’s James Lesh about his thinking on communicating with a probe around Alpha Centauri, he pointed out how much can be gained by simply studying the signal sent by a spacecraft. Here in the Solar System, we’ve seen how that signal is affected by passing through a planetary atmosphere as the vehicle moves behind a distant world, an event that tells us much about the atmosphere in question. So in many cases it’s not just the data carried by the communications signal, but how that signal behaves, that tells the tale.
Can we imagine something similar around Alpha Centauri? Lesh envisaged a 20-watt laser communications system sending data from a sophisticated probe. But a new paper takes a different approach, imagining a fast probe moving at relativistic speeds, one that would announce its arrival in the Centauri system and create effects that could be studied from Earth. At 10 ounces, such a probe wouldn’t carry instrumentation (at least, not until our nanotechnology becomes more sophisticated), but it would be the first manmade object ever to reach another star, and it might teach us valuable lessons about the art of starflight.
The authors, Wade Hobbs Jr. (a researcher at the Library of Congress) and Daniel Junker, a spaceflight consultant in Arlington VA, presented this work at the Fourth International Symposium on Beamed Energy Propulsion in Nara, Japan. Much of their effort is devoted to assessing the parameters of the journey in relation to the power of the laser that would drive it. They propose a matrix of laser beams on Earth’s surface, a further reduction in cost over previous beamed energy concepts for space-based lasers. Such a system would allow the probe, the duo calculates, to reach the Centauri stars in between five and ten years.
Confirming the probe’s arrival depends upon detecting the effects of this relativistic craft as it impacts the dust ring surrounding the Centauri system, looking for data anomalies via x-ray instruments like COAST (the Cambridge Optical Aperture Synthesis Telescope) or the Compton x-ray telescope. Other detection methods are also discussed, including tiny but forseeable laser options, or planned collisions between sequentially launched probes timed to coincide with their arrival in Centauri space, the latter perhaps more detectable from distant Earth.
Centauri Dreams‘ take: Lightweight probes bring back memories of Robert Forward’s ‘Starwisp’ mission, an unmanned, microwave-driven mesh a kilometer in diameter that would weigh no more than sixteen grams. Forward hoped to put microchips at each intersection in the mesh and push Starwisp with a 10-billion watt microwave beam, reaching Centauri in 21 years and beaming back images of the encounter. The idea fell apart when Geoffrey Landis demonstrated that the needed microwave power would simply turn the Starwisp mesh into slag, but it seemed a grand notion in its day.
The Junker/Hobbs probe, by sharp contrast, seems a flyable mission, a major question being whether it is worth our while to send a probe whose sole contribution to science would be in our measurements of its effects on the Centauri debris disk. The thinking here, though, is that there is another reason for such a probe.
The Tau Zero’s Foundation’s motto is ad astra incrementis, meaning we go to the stars one step at a time, hoping that each step is bigger than the last. More valuable than the science the probe could show us in the Centauri system is what we would learn from the first attempt to accelerate a craft to relativistic speeds. That this could be accomplished at much lower cost than previously believed puts such a mission into the realm of the forseeable. In other words, get something there, examine what you have learned in the attempt, and then build the next iteration, bigger and better.
Or perhaps better but not bigger. For we are advancing into an era when nanotechnology will make tiny probes that carry significant instrumentation possible. The Junker/Hobbs probe could be seen as a forerunner of equally small (and smaller) vehicles that sacrifice little in terms of the science they can do. It may be possible one day to send the kind of probe nanotech pioneer Robert Freitas talks about, a vehicle the size of a sewing needle capable of reaching its target and constructing a scientific base via assembler technologies on, say, a moon or asteroid in the Centauri system. Small may, in fact, be better when the speeds demanded are a significant fraction of light speed.
The paper is D. Junker and W. D. Hobbs, Jr., “Sending a Probe to Alpha Centauri on a Voyage of Five to Ten Years,” AIP Conference Proceedings Volume 830 (May 2, 2006), pp. 605-611 (abstract available here).
by Paul Gilster | Jul 8, 2006 | Exoplanetary Science |
We may not have images of terrestrial planets around another star yet, but many things can be learned about such worlds by computer simulation. A team of British astronomers, for example, has examined known exoplanetary systems in hopes of isolating those in which Earth-like worlds could exist in stable and habitable orbits. This is tricky business, because the massive planets present in almost every exoplanetary system we know about could disrupt such orbits long before life might have a chance to form on any worlds there.
It’s also tricky because to determine which systems could have life-bearing planets requires you to figure out the location of the habitable zone in each. Researchers Barrie Jones, Nick Sleep and David Underwood (Open University, Milton Keynes, UK) here use the classical definition of habitable zone: the distances from a star where water at the surface of an Earth-like planet would be in liquid form. Not surprisingly, they find that the question of planetary migration looms large in their analysis.
If a gas giant orbits well inside the habitable zone around a given star, and if that planet has reached its position by migration through the habitable zone, then Earth-like worlds may be far less common than would otherwise be the case. Here’s a good precis of research on the migration question, as presented in the UK team’s discussion of why habitable planets, depending upon the effects of migration, might be found in a mere 7 percent of the systems surveyed. From the paper:
The decrease to 7% demonstrates the importance of understanding how readily or rarely at least one ‘Earth’ can form in the HZ after a giant planet has migrated through it. This urgent question has received some attention. Formation in 47 Ursae Majoris has been examined by Laughlin et al. (2002). They have shown that Earth-mass planets could form within about 0.7 AU of the star, which is interior to the HZ, and possibly a bit further out in the inner HZ. It is the proximity of the inner giant planet to the HZs that hinders formation, by stirring up the orbits of the planetesimals and planetary embryos. Armitage (2003) concluded that post-migration formation of ‘Earths’ might be unlikely, though he concentrated on the effect of giant migration on planet-forming dust rather than on planetesimals and planetary embryos. On the other hand, Mandell and Sigurdsson (2003) have shown that when the HZ is traversed by a giant planet, a significant fraction of any pre-formed terrestrial planets could survive, eventually returning to circular orbits fairly close to their original
positions. An optimistic outcome has also been obtained by Fogg and Nelson (2005), who have shown that post-migration formation of ‘Earth’ from planetesimals and planetary embryos is fairly likely. Fogg and Nelson’s work is the most comprehensive to date, and gives cause for optimism…
That the migration issue is the hinge of this study is shown in the authors’ summary. They find that of the 152 known exoplanetary systems (as of 18 April 2006), 60 percent offer safe habitable zone orbits for Earth-like planets. A second analysis of 143 of these systems shows that 50 percent would have provided sustainable orbits in the habitable zone for at least a billion years. So the question of how giant planets got closer to their stars than the habitable zone becomes crucial. And if migration through the habitable zone rules out the formation of Earth-like worlds, we are left with that discouraging 7 percent number instead of the much more robust 60 percent.
Centauri Dreams‘ take: The effects of migration will merit much future work, but may become somewhat less pressing if we find that ‘hot Jupiters’ are the exception rather than the rule. Right now the observational bias is built into our methods; massive planets close to their stars are more readily detectible. We have yet to establish any sort of workable ‘norms’ for solar system formation against which to measure such systems, but migration may turn out to be of less interest if we start routinely identifying systems where the gas giants are found well outside the habitable zone.
The paper is Barrie, Sleep and Underwood, “Habitability of known exoplanetary systems based on measured stellar properties,” now accepted for publication in The Astrophysical Journal and available here.
