by Paul Gilster | Aug 12, 2006 | Culture and Society |
It was Tennyson whose narrator, recalling youthful wanderings and celestial vistas in the poem ‘Locksley Hall,’ wrote about ‘the fairy tales of science, and the long result of Time.’ That long result is something we seldom look at in our feverish and accelerated world, but in these closing paragraphs from a book written with Chesley Bonestell in 1972, Arthur C. Clarke thinks about the Pioneer spacecraft, the distant future and the things that may survive man. For the Pioneers will keep going.
“As our space-faring powers develop, we may overtake them with the vehicles of a later age and bring them back to our museums, as relics of the early days before men ventured beyond Mars. And if we do not find them, others may.
“We should therefore build them well, for one day they may be the only evidence that the human race ever existed. All the works of man on his own world are ephemeral, seen from the viewpoint of geological time. The winds and rains which have destroyed mountains will make short work of the pyramids, those recent experiments in immortality. The most enduring monuments we have yet created stand on the Moon, or circle the Sun, but even these will not last forever.
“For when the Sun dies, it will not end with a whimper. In its final paroxysm, it will melt the inner planets to slag and set the frozen outer giants erupting in geysers wider than the continents of Earth. Nothing will be left, on or even near the world where he was born, of man and his works.
“But hundreds — thousands — of light-years outward from Earth, some of the most exquisite masterpieces of his hand and brain will still be drifting down the corridors of stars. The energies that powered them will have been dead for aeons, and no trace will remain of the patterns of logic that once pulsed through the crystal labyrinths of their minds.
“Yet they will still be recognizable, while the universe endures, as the work of beings who wondered about it long ago and sought to fathom its secrets.”
Arthur C. Clarke and Chesley Bonestell, from Beyond Jupiter: The Worlds of Tomorrow (New York: Little, Brown), 1972.
by Paul Gilster | Aug 11, 2006 | Asteroid and Comet Deflection, Missions |
With the recent knowledge that half of all near-Earth asteroids are binaries, the stakes go up in the race to develop technologies to prevent potential impacts. But is the best solution what Centauri Dreams has always advocated, to intercept the approaching object as far from Earth as possible and alter its trajectory? A new paper suggests an alternative strategy: why not capture a nearby asteroid and put it into an Earth-bound orbit to use as a shield?
Such an asteroid could then be moved as needed to absorb the impact of any collision that would otherwise hit the Earth. The work of Didier Massonnet and Benoît Meyssignac (Centre National d’Etudes Spatiales, France), the paper argues that an asteroid between 20 and 40 meters in diameter, which the two nickname ‘David’s stone,’ could destroy a much larger incoming object under proper targeting conditions. The problem becomes finding the right asteroid. From the paper:
We…have a detection challenge: we seek an asteroid small enough to be manoeuvred “easily”—i.e. within a 10-year time frame and with a typical ΔV which we set at 50 m/s—while large enough to ensure the destruction or the deviation of Goliath. David must be energetically close to the Earth, which means that its initial semi major axis is close to one astronomical unit and its eccentricity as well as its inclination are small. David may be too small to be easily detected by optical means, in addition of being often in the angular vicinity of the Sun. The best way to detect efficiently such an asteroid might be by radar survey.
How to capture such an object? The authors point out that in terms of thrust, a large mass with a low ejection velocity is as efficient as a low mass with a large ejection velocity. Their solution is a robotic catapault that collects samples from the asteroid and throws them into space. The propellant becomes the material of the asteroid itself, with solar arrays generating power for the operation. Ingeniously, the paper suggests a ‘hopping’ catapault device that could compensate for the slow rotation of the asteroid while maintaining the average torque delivered to the asteroid close to zero.
Image: Is this a scenario we can prevent? The art of asteroid manipulation near the Earth may hold the answer. Credit: NASA.
And they offer up a good candidate for the David’s stone in the asteroid 2000SG344, whose passage near the Earth in 2029 offers a relatively straightforward capture scenario. On station orbiting either the L1 or L2 Sun-Earth Lagrangian points, the asteroid would protect Earth from incoming material with a reaction time of about eight months. Significant here is that Massonnet and Meyssignac’s method would be the only solution to a short-notice threat such as a cometary nucleus.
Another benefit is that with the installation of proper equipment, a nearby asteroid could be exploited to produce propellants for manned exploratory missions. Producing fuel like liquid oxygen in such a location would dramatically alter the lifting requirements for long-range flights and could be practical even factoring in travel requirements to retrieve the fuel:
This oxygen could then be loaded into the tanks of a planetary mission which would first reach an EET [Earth-escape trajectory] toward this Lagrangian gas station and then come back close to the Earth, still on an EET, in the proper position for its final acceleration to a planetary trajectory. If a chemical propulsion is used for the exploration of Mars, up to 80% of the mass of the mission could be liquid oxygen, thus offering a similar gain in heavy lifting requirements. The 240-day or so detour to the asteroid does not necessarily apply to the exploration crew which could join the spacecraft when it grazes Earth again on its way back. If necessary, a different crew could manage the refill and enter the earth atmosphere directly on the way back from the asteroid. The cost in ΔV would virtually be zero.
The paper is Massonnet and Meyssignac, “A captured asteroid: Our David’s stone for shielding earth and providing the cheapest extraterrestrial material,” in Acta Astronautica 59 (2006), pp. 77-83.
by Paul Gilster | Aug 10, 2006 | Exoplanetary Science |
Centauri A and B continue to stand out as likely venues for terrestrial planets. What a change since the days when it was thought orbits in binary systems like this one would be completely unstable. Today we believe that both the major Centauri stars could support small, rocky worlds within about 4 AU, and that such planets are as likely, if not more so, to form there as around our own Sun. The latter insight emerges directly from the work of Elisa Quintana and Jack Lissauer.
Add to that two other factors: At UC-Santa Cruz, Greg Laughlin and Jeremy Wertheimer have shown that Proxima Centauri could perturb the debris disk surrounding the Centauri stars enough to deliver volatiles to inner worlds there. Laughlin has been arguing the Centauri case for some time now, discussing not just the Proxima factor but pointing as well to the metallicity of Alpha Centauri, which is high enough to provide the kind of materials needed to form planets analogous to Earth.
Keen on detecting such a planet, Laughlin now advocates a radial-velocity investigation of Centauri B, toward which end he has been working up detailed feasibility studies. The method: model terrestrial planetary systems in stable orbits using accepted accretion models, then work out hypothetical observing strategies. The radial velocity measurements thus produced are fed to the downloadable systemic console for manipulation.
So far, so good. In fact, working with this data at the highest time resolution produces clearly readable planetary signatures. “The peak at 351 days corresponds to an Earth-mass planet,” Laughlin writes. “The three neighboring peaks correspond to smaller planets having masses on the order of Mars.”
Remember, these planets are simply simulations. But detecting Earth-like worlds in Centauri space looks to be a workable proposition provided we have time and resources to make the needed observations (Laughlin worked with 96,464 radial velocities obtained in a simulated five-year observing run). And there are numerous complications, not the least of which involve the proximity of Centauri A. Can a special purpose telescope be built to handle these observations, given that existing instruments aren’t going to let themselves be comandeered for the length of time required? Laughlin promises more on system modeling and telescope strategy soon.
by Paul Gilster | Aug 9, 2006 | Exoplanetary Science |
Gravitational microlensing is a fascinating way to find exoplanets, provided you’re not worried about nearby targets. For the best way to do microlensing of this sort is to work with a crowded starfield, which means looking toward galactic center, where stars are numerous and distant enough that their lensing events can be studied. You’re hoping to find a star that passes in front of another as seen from Earth, in which case the gravity of the foreground star sets up the gravitational lensing effects that magnify the light of the background star.
Thus OGLE-2003-BLG-235L, which displayed a planetary companion that was discovered in 2003 using ground-based observations. The oddity here is that while the planet produced an additional brightening of the background star, thus confirming its existence, astronomers weren’t sure about the identity of the star it circled. It has taken two years and new observations by the Hubble Space Telescope to pin down OGLE-2003-BLG-235L — the foreground star — as the parent star of this particular planet, and to characterize its properties.
Image (click to enlarge): A blowup of the target (lower left) reveals the light of two stars: a foreground star and a background star superimposed on each other. The background star is the brighter, solar type star, and the foreground star is the fainter star. The motion of the foreground star, as it drifts past the more distant background star is apparent in the Hubble image taken in 2005, even though it is below Hubble’s resolution. Credit: NASA, ESA, D. Bennett (University of Notre Dame), and J. Anderson (Rice University).
A brief aside on nomenclature: The star’s designation depends on which catalog you use. OGLE-2003-BLG-235L draws on the database of the Optical Gravitational Lensing Experiment (OGLE), while the Microlensing Observations in Astrophysics (MOA) project designates the star as MOA-2003-BLG-53L. MOA is a New Zealand-based microlensing experiment that has been in place since 1995.
In the absence of a more user-friendly name, here’s what we now know about this system: The planet is roughly 2.6 Jupiter masses and in a Jupiter-like orbit around its star. OGLE-2003-BLG-235L itself is 63 percent the mass of our Sun, making it hotter and more massive than the average field star in our galaxy, which is about 30 percent Sol’s mass. The distance from Earth is 19,000 light years. Hubble could distinguish the light of the two stars because the foreground star is a different color than the background one; red and blue filters allowed astronomers to enhance the visibility of the event.
by Paul Gilster | Aug 9, 2006 | Autonomy and Robotics |
Igor Aleksander (University College, London) is a specialist in neural systems engineering who is working on emerging consciousness in machines, a process he calls ‘more basic’ than artificial intelligence. Velcro City Tourist Board offers up an interview with Aleksander that gets into models of the mind and the meaning of consciousness itself. A snippet:
“There’s one important principle involved in the computational modelling of consciousness: being conscious does not mean being a living human, or even a non-human animal. For an organism to be conscious is for it to be able to build representations of itself in a world that it perceives as being ‘out there’, with itself at the centre of it. It is to be able to represent the past as a history of experience, to attend to those things that are important to it, to plan and to evaluate plans – these are the five axioms.”
For more on conscious machines and links to Aleksander’s axioms, read the whole story. We’ll see the benefits of such work showing up in spacecraft that make decisions and manage research in environments increasingly remote from Earth-based support. An intelligent probe may or may not achieve consciousness in a recognizably human sense, but our initial wave of interstellar robotics will depend on systems with human-like traits of awareness and flexibility. All of which may leave the question of consciousness as a matter for philosophers to decide.
