by Paul Gilster | Nov 19, 2005 | Advanced Rocketry
Centauri Dreams focuses on the long-term, which almost always means deep space missions and interstellar possibilities. But building an industrial infrastructure in the outer Solar System also means finding much less expensive ways into space, a fact illuminated by the upcoming launch of SpaceX’s Falcon rocket from Kwajalein atoll in the Pacific. CEO Elon Musk talks about building the ‘Ford of space,’ and as noted by Michael Belfiore, Musk went on to say this in a personal interview: “Ford didn’t invent the internal combustion engine. But he found out how to make one at low cost.” Similarly, “We didn’t invent the rocket engine; what we’re trying to do is figure out how to make it low-cost.”
Belfiore’s weblog is a good place to monitor as we approach launch, which is set to occur at 1300 PST on November 25. Also be aware of Jim White’s postings from Kwajalein; White is a member of the FalconSAT-2 satellite team and is reporting on final preparations. Finally, Jeff Foust provides excellent background in a discussion of Musk’s appearance at SpaceVision 2005 in Big Plans for SpaceX.
by Paul Gilster | Nov 19, 2005 | Astrobiology and SETI |
Readers who know of Centauri Dreams‘ fascination with ‘deep time’ will not be surprised that I am working on a side project involving past, not future time. Specifically, a study of the Eocene, that remarkable period beginning some 55 million years ago during which the ancestors of most modern mammals — including the higher primates, such as apes, monkeys and man – appeared.
And if the Eocene, 2/3 of the way back to the age of the dinosaurs, seems like a long reach from interstellar travel, ponder this: the more we learn about how life adapts to changing planetary environments, the better we’ll be able to carry out the hunt for life around other stars. On that score, it’s interesting to see that a team supported in part by NASA’s Exobiology program has determined that Earth’s continents were in place soon after the planet formed. The Earth was not, in other words, a purely ocean world in that era, or a barren, inhospitable place like the Moon.
Analyzing the occurrence of a rare metal element called hafnium in ancient minerals from the Jack Hills in Western Australia, the team, led by Stephen Mojzsis (University of Colorado), found evidence that the rocks it studied dated back 4.4 billion years. “The view we are taking now is that Earth’s crust, oceans and atmosphere were in place very early on,” said Mojzsis, “and that a habitable planet was established rapidly.”
A 2001 study led by Mojzsis and published in Nature had shown the presence of water on Earth 4.3 billion years ago. For more on the scientist’s earlier work, see this NASA story. The current paper is Harrison, Blichert-Toft, Mojzsis et al., “Heterogeneous Hadean Hafnium: Evidence of Continental Crust at 4.4 to 4.5 Ga,” published online November 17, 2005 and available as a preprint via Science‘s ScienceXpress service. A University of Colorado press release is here.
by Paul Gilster | Nov 17, 2005 | Astrobiology and SETI, Culture and Society
Jon Lomberg has a distinction of which few humans can boast — he knows his art will last. As the designer of the cover of the Voyager Interstellar Record, Lomberg created an aesthetic statement that could, in fact, last for a thousand million years. As could the entire sequence of 120 photographs and diagrams that he designed for the Voyager record. And just to show that his interest in deep time isn’t purely space-related, Lomberg also designed a 10,000 year nuclear waste marker for the US Department of Energy. Centauri Dreams appreciates all instances of genuinely long-term thinking, but particularly celebrates the marriage of art with technology in time-frames longer than our civilization.
It seems fitting, then, that when Lomberg turns to SETI issues, he would bring an artist’s eye to the proceedings, which is what he does in an article written with Guillermo Lemarchand (Centro de Estudios Avanzados, Universidad de Buenos Aires). The essay, called “SETI and Aesthetics” and available online, points out that our SETI strategy depends upon the assumed transmission strategies of any civilizations about which we hope to learn. Are there, then, ‘universal’ principles of science and aesthetics that may reasonably be expected among sentient beings?
If so, these are surely what any intelligent race would use when attempting to make contact with other civilizations, for random transmission strategies would make the odds of contact so small as to be insignificant. SETI researchers have done much with scientific deductions, such well known variables as selecting the best frequencies (i.e., the famous ‘waterhole’ wavelengths), choosing the best target stars, deducing the best interstellar bandwidth, and so on. But what about elegance and design?
Image: A Lomberg image from COSMOS. This frame from the original television series storyboards shows the galactic center setting behind the disk of the galaxy as we enter the Milky Way.
Lomberg wants to expand our list of SETI factors by studying universal symmetries, which appear widely not only in nature but also in human artwork. Here he discusses radial symmetry, an arrangement based on radii emanating from a common center:
In Earth’s biosphere radial symmetry is found throughout many phyla and kingdoms, from the shells of radiolarians to the growth patterns of colonial algae, from the lotus flower to the octopus, from the spider’s web to the human eye.
In human art radial symmetry is one of the commonest design motifs in the world, equally obvious in the stonework of Gothic and Aztec masons, in the symbols of Chinese and Navajo people, in the religious iconography of Tibet and family crest design in Japan. Indeed, mandala patterns are among the few designs found in almost every human culture known…
Applying radial symmetry to SETI, Lomberg’s belief is that a commonly recognized unique point would be any center which both civilizations (transmitting and receiving) have in common. In the Milky Way, that unique point is the center of the galaxy. “If there are many transmitting civilizations in the galaxy, some other civilizations may exist along the same radius as the Sun,” he adds. “These civilizations would therefore occupy a privileged position over other galactic locations from the point of view of symmetry. Radial symmetry thus offers a solution to the question of where in the sky interstellar beacons might preferentially be directed and found.”
A reasonable deduction, then, is that the search for interstellar beacons should be concentrated in a deep field survey along the radius connecting between us, the galactic center and the galactic anti-center, offering a field of 108 stars and increasing the time we could spend on candidate sources dramatically by reducing the field of view. Another benefit is to simplify the question of relative motion by relating it to the galactic barycenter as a common rest frame.
This is a rich paper that goes on to explore both the omnipresence of Phi (the constant of proportionality, also known as the Golden Section and the Divine Proportion), and forms of bilateral symmetry found throughout the biosphere, considering what they may tell us about creating a strategy for communicating with radically different cultures in a refined, targeted SETI hunt. Lomberg, who is well known as the principal artistic collaborator of Carl Sagan and chief artist for the COSMOS television series, infuses SETI possibilities with aesthetic concerns that seem an entirely reasonable extrapolation of what an advanced culture might choose to deliver in a galaxy-spanning signal.
For more on Lomberg’s thinking, be aware of an upcoming interview on the Australian Broadcasting Corporation’s Science Show, to be aired Saturday the 19th and available over the Net.
by Paul Gilster | Nov 16, 2005 | Missions, Sail Concepts
Among the curious features of a gravitational lens is the way it focuses electromagnetic waves. Supposing we could build a spacecraft like Claudio Maccone’s FOCAL concept, a vehicle designed to reach the Sun’s gravity focus at 550 AU. From that vantage, the electromagnetic radiation from an object occulted by the Sun (i.e., on the other side of the Sun from the spacecraft), would be amplified by a factor of 108. Such amplification could be exceedingly useful for astronomy at all wavelengths, and even for SETI.
But note this key difference between a gravity focus and its optical counterpart: in an optical lens, the light diverges after the focus. Light focused by the Sun’s gravitational lens, however, stays fixed along the focal axis as you move to distances greater than 550 AU. Quoting Maccone: “It is true that one does not have to stop FOCAL at just 550 AU, because every point along the straight line trajectory beyond 550 AU still is a focal point.”
It was in the 1980s that Alenia Spazio, an Italian aerospace company based in Turin, began looking into a mission that would evolve through successive iterations into FOCAL. The mission was originally conceived as an inflatable radio telescope that was christened Quasat. In regular meetings that explored the concept in the following decade, the uses of inflatable technologies for a mission to the gravity focus were analyzed. Gregory Matloff, for example, studied an inflatable solar sail with reflective metallic layer facing the Sun. Matloff’s baseline sail would have had an area of 10,000 square metres and a total mass of less than 100 kg. Time to reach the gravity focus: about 60 years.
But another way to reduce travel time does exist, as suggested by Maccone. Imagine not one but two flybys of Jupiter. The first close pass slingshots the probe to a perihelion extremely near the Sun, where the sail is deployed for maximum acceleration. The probe then makes the second flyby of Jupiter and receives an even greater boost in velocity. Significantly shortening that 60 year flight time, and the possibility of continuing to make enhanced observations along the focal axis after 550 AU, makes the idea of a FOCAL mission all the more compelling.
It is here that the FOCAL concept recalls earlier NASA studies like the Jet Propulsion Laboratory’s Thousand Astronomical Units (TAU) mission, conceived in the 1980s and designed to double FOCAL’s distance from the Sun. In both concepts, the scientific payoff would be immense in the form of observations of the heliosphere and heliopause as well as the interstellar medium itself. However, FOCAL must be considered an evolutionary step forward from the TAU concept, with a potential for astronomical breakthroughs available to no other technology. It would be the first interstellar precursor mission designed as such, and a symbol of mankind’s commitment to galactic exploration.
Needless to say, FOCAL remains only a concept at this stage, but this is how missions are built, by the labors of scientists producing papers and advocating in the journals and at conferences the scientific payoff that will justify funding their concepts. We will be having a lot more to say about FOCAL. Meanwhile, see Claudio Maccone’s The Sun as a Gravitational Lens: Proposed Space Missions (Aurora, CO: IPI Press, 2002). The Matloff paper is “Solar Sailing for Radio Astronomy and SETI: An Extrasolar Mission to 550 AU,” Journal of the British Interplanetary Society Vol. 47, pp. 476-484 (1994).
by Paul Gilster | Nov 15, 2005 | Asteroid and Comet Deflection, Outer Solar System |
The Discovery Channel’s news site offers a brief story about changing the course of an Earth-threatening asteroid. Specifically, the story focuses on a paper in the November 10 issue of Nature by Edward Lu and Stanley Love that offers a new method of avoiding an impact without even touching the asteroid. Previous options had included docking a spacecraft to the asteroid and applying steady thrust to change its course, but that method seems like a long-shot considering how tricky it is to get a conventional rocket to such an object with fuel to spare for an extended burn.
What Lu and Love discuss is a 20-ton spacecraft that would actually use the weak gravitational force between asteroid and ship to effect a change in the asteroid’s orbit. In essence, the spacecraft would use nuclear-electric thrusters to maintain a fixed position above the asteroid. If such a mission were flown years in advance of an asteroid impact, the force exerted should be enough to change the expected impact into a not-so-near miss.
Image: A space tractor at work, using nuclear-electric propulsion to establish a fixed position above an asteroid. Credit: Dan Durda/FIAAA/B612 Foundation.
The paper is Lu, Edward and Love, Stanley G., “Gravitational tractor for towing asteroids,” Nature Vol. 438, pp. 177-178 (10 November 2005). An abstract can be found here.
Centauri Dreams‘ take: The use of gravity as a ‘towline’ is ingenious and just the kind of realistic thinking we need when contemplating a potential mission of this magnitude. Conventional rocketry simply isn’t up to the challenge, but nuclear electric propulsion is theoretically sound and capable of maintaining the kind of low levels of thrust needed for asteroid station-keeping.
But another issue is at work here. Such gravitational nudging will only work if we can reach Earth-threatening objects well in advance of potential impacts. That calls for beefed up detection systems for objects that might threaten the planet, and also robust research into advanced propulsion to get us to such objects in a hurry, even if we initially detect them a long way from Earth. Closer to home, a mission like that envisioned by Lu and Love could conceivably be used to deflect the course of asteroid 99942 Apophis, which will make a near miss in 2029 and could threaten the Earth again in 2036.
As always, the B612 Foundation deserves your attention for its work in educating the public about potential asteroid collisions. And be aware that the testimony of B612’s Rusty Schweickart and Edward Lu before the Senate Subcommittee on Science, Technology, and Space of the Senate Commerce Committee (7 April 2004) is available along with other papers on the B612 Foundation’s news page.
