by Paul Gilster | Dec 7, 2005 | Outer Solar System |
Back in the heady early days of Project Orion, Freeman Dyson was already thinking about an advanced interplanetary vehicle that could take a 1300-ton payload to Saturn. His target was Enceladus. “We knew very little about the satellites in those days,” Dyson said. “Enceladus looked particularly good. It was known to have a density of .618, so it clearly had to be made of ice plus hydrocarbons, really light things, which were what you need both for biology and for propellant, so you could imagine growing your vegetables there…”
The quote is from George Dyson’s Project Orion: The True Story of the Atomic Spaceship (New York: Henry Holt, 2002), which belongs on the shelves of anyone interested in the human future in space. And it always comes back to me when I hear more Cassini news from Enceladus, and think how feasible it once seemed (in the 1960’s!) to go straight to the outer planets. Talk about audacity — Orion would set off atomic bombs behind a pusher plate to drive a ship so massive that designer Ted Taylor wanted to include a 4000-lb barber’s chair for the crew, just to make the point that he wasn’t worried about payload.
The latest Cassini news may not be quite that audacious, but as this image reveals, it’s an indication that we still have a lot to learn about Enceladus. Backlit by the Sun, the image shows sprays of fine material coming from the south polar region, clear evidence that the moon is geologically active. Current thinking is that these ‘jets’ come out of the warm fractures scientists have dubbed ‘tiger stripes.’ Stretching at least 300 miles above the surface of Enceladus, these plumes are known to contain water vapor and icy particles.
Image: Recent Cassini images of Saturn’s moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. Credit: NASA/JPL/Space Science Institute.
And what a surprise would have met our 60’s era Project Orion explorers if they had ever launched the Saturn mission. From a Jet Propulsion Laboratory news release:
“I think what we’re seeing are ice particles in jets of water vapor that emanate from pressurized vents. To form the particles and carry them aloft, the vapor must have a certain density, and that implies surprisingly warm temperatures for a cold body like Enceladus.”
That thought is from Caltech’s Andrew Ingersoll, but it was left to imaging team member Torrence Johnson at JPL to go the final step, noting the resemblance of Enceladus to a ‘huge comet,’ a body whose energy, however, comes not from sunlight but internal heating by radioactivity and tides. Enceladus’ role in supplying material to Saturn’s E ring becomes more significant with each new Cassini pass. It’s a shame we had to wait so many years after the demise of Project Orion to see these things close up, but we can hope that research in areas like antimatter-initiated microfusion or Steve Howe’s antimatter sail may eventually get us there without the baggage of nuclear weaponry.
by Paul Gilster | Dec 6, 2005 | Exoplanetary Science
Seeing a planet around another star means finding a way to mask the overwhelming glare that swamps the faint image. The job is, as a news release from the American Institute of Physics reminds us, something like trying to see the light of a match held next to an automobile’s headlight from a distance of 100 meters. Consider that the Earth is ten billion times less bright than the Sun at optical wavelengths and you see the enormity of the problem.
Among the possible solutions is an approach taken by Grover Swartzlander and his colleagues at the University of Arizona. Swartzlander eliminates excessive starlight by feeding it through a helical ‘mask’ — a kind of lens. The result is what the team calls an optical vortex coronagraph. From the news release:
The process works in the following way: light passing through the thicker and central part of the mask is slowed down. Because of the graduated shape of the glass, an “optical vortex” is created: the light coming along the axis of the mask is, in effect, spun out of the image. It is nulled, as if an opaque mask had been placed across the image of the star, but leaving the light from the nearby planet unaffected.
Laboratory trials so far seem promising, with the light from mock stars reduced by factors of 100 to 1000 even as light from the nearby ‘planet’ was unaffected. This image gives some sense of the optical vortex at work.
Image: These laboratory images demonstrate how the optical vortex coronograph operates. They were obtained with a green “star” and red “planet” (point light sources). (a) shows how the green light is “spun out,” while the red light remains unaffected. Images of the point sources are shown when large (b) and small (c) apertures are used to limit the transmission of light from (a). Credit: Grover Swartzlander, University of Arizona.
For more, a preprint of an article slated to appear in mid-December in Optics Letters is available (PDF warning).
by Paul Gilster | Dec 5, 2005 | Culture and Society |
by Gregory Benford
(Centauri Dreams note: Gregory Benford was kind enough to send along the following, which is the text of a speech he delivered at the Advanced Space Propulsion Conference in Aosta, Italy last June. A modified version of this talk is to appear shortly in the Journal of the British Interplanetary Society. Dr. Benford’s extraordinary career as physicist and science fiction author needs no introduction here, but Centauri Dreams readers are also urged to have a look at his new Benford & Rose Web site, written in collaboration with UC-Irvine professor of ecology and evolutionary biology Michael R. Rose. Herewith Dr. Benford’s thoughts on space exploration as human imperative).
There are three forms of chimpanzees: the common chimp, the bonobo, and us. We are the only chimp who got out of Africa. That experience reflects and probably laid down the deep human urge—indeed, our signature: the urge to restlessly move on, explore, exploit. Natural selection gives us a gut imperative that plays out physically and culturally, our goal: the expansion of human horizons.
Human history has favored both the spatial and cultural expansion. Fresh prospects yield new perspectives. Life springing from the sea to land was similarly favored. We now stand on a beach, our world, timidly dipping a toe into the sea of space.
We stare into this ocean of night and imagine we are the Columbus generation. I fear we may be the Lief Eriksons.
Curiosity drives us at this early stage. This is proper and intrinsic. The grandest question we can solve in our generation is to find whether life began and survives on Mars. With a mass the tenth of ours, it cooled off first and did not suffer the impact by a Mars-sized object that Earth did, forming our uniquely large moon. We know it had early wet days and much liquid erosion. Did life arise and migrate beneath the soil, perhaps persisting still?
Meteor impacts transfered matter from Mars to Earth far more often than the reverse. Microbial life could survive the trip and seed our early seas. We may be Martians.
Even more exciting, Mars may harbor a different type of life, not even DNA based. If so, life is probably common in our galaxy, because it arose twice in a single solar system, a powerful argument.
I know no biologist who thinks we can settle this point without smart exploration—by humans. Robots are just not up to it. A manned expedition to Mars would be one of the great defining events of this century, as Apollo’s moon landing was in the last. It would be thrilling, dangerous, and witnessed by all humanity, with daily fresh vistas. We would come to know the small crew better than our neighbors. Unlike Apollo, their scientific curiosity would be crucial to their character.
This strong link between exploration and science suggests the next phase of our ventures into space— finding resources and living there. Lief Erikson did not live off the land, but the later Europeans did. This was critical to their persistence.
We do not now live in space; we camp there. The space station never addresses the two crucial elements needed to explore the planets—a closed, renewable biosphere, and centrifugally made gravity. Without those, we will go nowhere beyond our moon.
NASA plans to return to the moon in twice the seven years it took us before. Mars comes a decade later, so no astronaut now working can hope to go. This is a plan for failure. By 2015 the US Federal budget comes under severe strain from the retirement and medical plans in place. Agencies which spend money in jobs programs producing “luxuries” like a space program will suffer. Meanwhile, new global problems will loom.
Very probably, climate change driven by fossil fuel emissions will worsen. Currently, carbon dioxide levels rise along a curve predictede by economists decades ago. China, India and other ambitious countries pay no heed to nations that, in their view, never gave up easy energy sources when it hurt them economically. This pattern will persist.
To solve global problems, think globally. The easiest and cheapest way to cool our world is by reflecting more sunlight back into space. Clouds do this best. Producing them over the tropical oceans, which absorb most of the sun’s bounty, is cheap, using technologies developed many years ago. We can do more, too, in our own lives. Our own habitation covers about 1% of North America and 3% of Europe. We can reflect sunlight from them at little cost. Lightening roof colors, mixing sand and glass into asphalt, and similar measures can also lower the cooling costs in summer, saving fossil fuels and paying for themselves. A US Department of Energy study showed this a decade ago, but was ignored.
To monitor all this takes global monitoring from space. So will gathering resources from beyond our moon. In the second half of this century, metals will become harder to find in the Earth’s crust, and more costly and damaging to extract. There are plenty of metals in the asteroid belt. Inevitably, we will need them. Bringing them to Earth, smelting them in high orbits—all this could help fuel an expansion of the global economy.
We certainly need such expansion, while minimizing the impact of our growing numbers. Indeed, the greatest agenda of this century will be the expansion of human horizons by uplifting the bulk of humanity to a standard of living enjoyed by the advanced nations. That would complete the promise begun 500 years ago by the first European expansion, following on Lief Erikson without knowing his role in their own history.
We will need those informed minds. We forget that most of humanity still labors in routine manual labor, walking behind a plow or assembling in a factory. What Einsteins or Beethovens are doing that now, dreaming of a better life?
Only by expanding their conceptual horizons through a modicum of prosperity can we liberate our species from drudgery.
Frontiers breed liberty. They make possible freedom of movement and ideas. A fundamental revolution in human destiny began half a millennium ago with the European breakout onto the oceans of Earth. That opened new cultural vistas after centuries of little progress and few freedoms. Room to breathe and think anew is not sufficient to ensure progress, but it is essential.
Meanwhile, my friends jump off bridges on giant bungee cords and run hundreds of miles in desert heat — for fun. Around us in the extreme entertainment culture there are ample signs of a society with far too much spare time on its hands, and no sense of new horizons.
Space is, as the cliché goes, the final frontier — because it is infinite. But it takes courage, bravery and imagination. We cannot have a future that we do not first imagine. That is why we must explore and then open to our use the beckoning lands beyond our sky. They are the horizons our species needs and was born to win.
by Paul Gilster | Dec 3, 2005 | Deep Sky Astronomy & Telescopes |
The Hubble Space Telescope used its Wide Field and Planetary Camera 2 to create the image below, which is actually made up of 24 separate exposures — this is said to be the highest resolution image of the Crab Nebula ever made. Be sure to click on the image to explore it in detail. I had planned to use an intriguing Robert Forward quote for today’s entry (Saturday’s are usually a day for reflections and overviews), but this image was just too pretty to resist.
The Crab Nebula is about six light years wide, the remains of a supernova that is reliably dated at 1054 as witnessed by both Chinese and Japanese astronomers. Recall that the distance from the Sun to the primary Centauri stars is 4.3 light years and you get a sense of scale here. The filaments you’re seeing are primarily hydrogen, lit blue from within by a spinning neutron star that is the remaining core of the supernova. The neutron star emits twin beams of radiation that pulse 30 times a second due to its extreme rotational rate.
For more, click here for a fact sheet on the Crab Nebula.
by Paul Gilster | Dec 2, 2005 | Missions, Sail Concepts
Proposals for realistic interstellar missions are not a new thing; in fact, several concepts grew out of work in the early 1980’s at the Jet Propulsion Laboratory, starting with the ‘Thousand Astronomical Units’ (TAU) mission, and extending to recent studies on the mission commonly referred to as the Interstellar Probe. By ‘interstellar,’ I mean journeys not to a nearby star but (a much needed first step) a journey to the interstellar medium beyond the heliosphere, that region carved out by the influence of the Sun’s solar wind. We have one vehicle there now, as Voyager 1 seems to be crossing the heliopause into true interstellar space. What we need to ponder next is how to build a spacecraft specifically designed for heliopause studies.
A team of European researchers is now tackling the job. Designed as part of the European Space Agency’s excellent Technology Reference Studies, the Interstellar Heliopause Probe is put forth as a mission to reach 200 AU within 25 years, using a variety of near-term technologies including a solar sail.
Numerous questions about payload, communications and spacecraft autonomy come out of this work, but the big issue remains propulsion. ESA considered three candidate systems:
Chemical propulsion, using one or two Earth gravity assists to reach Jupiter, followed by a close solar flyby with propulsive maneuver at perihelion (rejected because of the high thermal requirements and lack of sufficient specific impulse to push a useful payload);
Nuclear electric propulsion, using a close Jupiter flyby and extended low-thrust cruise, with specific impulse in the range of 5000 to 20,000 seconds and a thrust sequence lasting as long as 20 years. This one was derailed by power issues, especially the mass requirements of the needed nuclear reactor.
Solar sailing, the method of choice, using the momentum of photons to achieve low acceleration without propellant. ESA is investigating both square and spinning disk sails for the job. To give an idea of the size requirement, the square sail demands about 260 x 260 meters at a sail thickness of 2 microns; the spinning sail allows a reduction to a radius of 140 meters, but demands a sail thickness of 1 micron. To achieve the needed acceleration to reach 200 AU in 25 years, the spacecraft would make a close Solar pass.
So where do we stand on making solar sailing a reality? The largest sail deployment has been on the ground, in the form of an ESA/DLR (Deutsches Zentrum für Luft- und Raumfahrt) tests, while spinning disk deployments have recently been demonstrated at the Jet Propulsion Laboratory. The Russian Znamya ‘mirror’ is the only space-based sail deployment, and it revealed significant issues in need of resolution. Clearly, we have much to learn about preventing ruptures and damage to delicate sail coatings, not to mention retaining the sail’s optical properties during a solar pass that closes to 0.25 AU.
The paper is Lyngvi, A., Falkner, P. et al., “The interstellar heliopause probe,” Acta Astronautica 57 (2005), pp. 104-111.
Centauri Dreams‘ take: The consensus about sail technologies for our interstellar precursor work seems to be firming up, and we are not so many years from seeing sail deployment tests in space. Note the key fact that the length of even the most optimistic missions (and 25 years to 200 AU is quite optimistic) presupposes a mission that effectively occupies the career of the researchers who design, build and fly it. Add the extensive testing and development needed to create such a spacecraft to the quarter century flight time and you can see why deep space research demands long-term thinking, a product in short supply given our ephemeral political and economic cycles. Probing interstellar space turns out to be a matter of will as much as technology.
