by Paul Gilster | Jun 26, 2007 | Breakthrough Propulsion, Exotic Physics |
Four trips to the Moon a day? That’s one capability of a theoretical vehicle discussed in last January’s newsletter from the American Institute of Aeronautics and Astronautics. I hadn’t realized the AIAA was putting these newsletters online until I saw Adam Crowl’s post on Crowlspace discussing the above possibility. Adam notes that a vehicle powered by a so-called Mach-Lorentz Thruster (MLT) of the sort being studied by James Woodward (California State University, Fullerton) could not only make the four lunar trips a day but deliver almost 3000 tons of cargo a year.
The AIAA story, adapted by Paul March from his later presentation at the 2007 STAIF meeting (Space Technology and Applications International Forum) in Albuquerque, presents several startling scenarios, all of which come down to our understanding of inertia. Go back to the days of Isaac Newton and inertia is seen as an inherent property that causes a body to resist acceleration. Inertia means a body at rest will oppose anything that tries to get it into motion. And if it is already moving, inertia is that property that resists attempts to change the magnitude or direction of its velocity. [Addendum: Slightly changed from the original; see Jimmy Cone’s comment below].
But what causes inertia? Woodward, a professor of history as well as physics at Fullerton, sees inertia as the result of all objects in the universe — even the most distant — acting on an accelerated object. The concept is based on Mach’s Principle (named for 19th Century Austrian physicist Ernst Mach), and it may remind you a bit of some of our discussions about John Cramer’s Transactional Interpretation of quantum mechanics. Perhaps pushing on an object causes a gravitational disturbance that moves into the future, ultimately causing all other matter to move infinitesimally, creating a disturbance that moves backward in time and converges on the original object.
And thus you have one explanation for inertia. To say this is controversial is to belabor the obvious — among the scientists who abandoned Mach’s view was Einstein. But Woodward goes on, using Mach’s ideas, to show that objects undergoing acceleration experience transient fluctuations in their mass. Can these variations help us create spacecraft that expel no propellant? Woodward has been working on the concept since 1990, and the AIAA article offers a good introduction to his investigations. Here Paul March discusses the mass fluctuations under discussion:
The M-E [Mach Effect] is based on the idea that when a mass is accelerated through a local potential field gradient, its local rest mass is momentarily perturbed about its at-rest value. These resulting acceleration induced “mass fluctuations” used in conjunction with a secondary force rectification signal can then be used to generate an unbalanced force in a local mass system, which can accelerate a payload or generate energy. Local system energy and momentum conservation is maintained by interactions with all the distant mass in the universe. Therefore to accelerate a spacecraft here, the Machian interpretation of inertial reaction forces means that each star or other distant matter in the universe will move in the opposite direction of the locally accelerated mass in response here – even if only on an extremely small scale. Conservation of energy and momentum must be maintained globally, but nature doesn’t say how big the system box has to be, nor when the accounting has to be done.
Woodward’s continuing experiments at the ‘tabletop’ level have been provocative, and John Cramer investigated mass fluctuation under the auspices of the Breakthrough Propulsion Physics program in the late 1990s, although, as March notes, with inconclusive results. March goes on to the crux of things in describing a thruster built on these principles:
Assuming that mass fluctuations really do exist, in theory an M-E thruster can be built using externally applied forces that can push on the device’s “active” mass when it is lighter and then pull on this active mass when it is heaver in a cyclic manner, thus generating a net time-averaged force per Newton’s F=ma relationship.
Build a true Mach-Lorentz Thruster — assuming such a thing is possible — and if the technology scales the way Woodward believes it must, the outer Solar System is reachable in less than a month. In fact, the travel times are limited largely by the accelerations a human crew could endure. Clearly, the implications for interstellar missions are interesting indeed. But we’re a long way from building such devices. Indeed, conclusively verifying the viability of the thruster principle is still a work in progress, much less building larger MLTs to examine scaling issues.
Woodward’s ideas continue to be investigated. Peter Vandeventer has collected a number of non-published papers on his Woodward Effect site, while Woodward’s own home page offers useful background studies. Given the scope of the challenge of reaching the outer planets with human crews — much less the closest stars — it’s clear that major breakthroughs have to occur to replace conventional rockets and their bulky propellants. We’ll know one day if Woodward’s contribution to breakthrough propulsion physics can provide the answer. Right now we’re still trying to see if MLTs and the the Mach Effect itself make sense.
by Paul Gilster | Jun 25, 2007 | Deep Sky Astronomy & Telescopes |
Putting an enormous radio telescope on the far side of the Moon has so many advantages that it’s hard to imagine not doing it, once our technology makes such ventures possible. Whatever the time frame, imagine an attentuation of radio noise from Earth many orders of magnitude over what is possible anywhere on the near side, much less on Earth itself. In a recent telephone conversation, I discussed these matters with Italian space scientist Claudio Maccone, whose work on a mission to the Sun’s gravity focus we’ve examined in these pages before.
Having just completed a week at Rutgers attending its Symposium on Lunar Settlements, Maccone anticipates the publication of his new paper on the lunar far side and its scientific potential — I’ll have to put off the specifics of those interesting ideas until the paper actually appears. But do ponder the implications of a radio observatory conceivably able to probe extrasolar planets. As a news item in New Scientist explains:
The interaction of charged particles such as electrons with the magnetic fields of extrasolar planets should produce low-frequency radio waves. They could provide information on the interiors of extrasolar planets, as the internal structure and composition governs the strength of the magnetic field.
How to build such an array and, even more to the point, just where to put it is a subject we’ll take up soon in relation to Maccone’s work. But with science on the Moon’s surface in mind, the news of what appears to be a breakthrough in liquid mirror technology for use in an entirely different kind of telescope catches the eye. Ermanno Borra (Laval University, Quebec) and team seem to have conquered the temperature problem, allowing the possibility of building telescopes with large, liquid apertures on the lunar surface.
Setting up a rotating frame containing liquid mercury is a proven technique for constructing high-precision mirror-like surfaces, but at lunar temperatures, the substance freezes. Borra’s group uses complex salts in the form of so-called ‘ionic liquids’ whose freezing point is below ambient lunar temperatures. A fine layer of chromium particles is deposited on the liquid followed by a layer of silver particles. Here we’re talking not radio telescopes, as in Maccone’s work, but an optical and infrared instrument, and one of fantastic precision compared with what is available today.
A quick look at the team’s recent paper reveals the concept: an optical instrument with infrared capabilities with an aperture up to 100 meters in size. That allows observations of objects anywhere from 100 to 1000 times fainter than what the James Webb Space Telescope will see. Pete Worden, director of NASA Ames and a co-author of the paper, says of the concept, “In this case we have shown how the moon is ideal (for) using liquid mirror technology to build a telescope much larger than we can affordably build in space.”
The paper is Borra et al., “Deposition of metal films on an ionic liquid as a basis for a lunar telescope,” Nature 447, 979-981 (21 June 2007), abstract available. A New Scientist story on Borra’s work is also available. It should be noted that this is yet another project funded by NASA’s Institute for Advanced Concepts, whose record at advancing cutting-edge ideas like this from raw speculation into the realm of proven laboratory work is well established. Without NIAC, how will the next generation of advanced concepts gain financial traction?
by Paul Gilster | Jun 23, 2007 | Outer Solar System |
With launch of the Dawn mission to Ceres and Vesta coming up on July 7, NASA has announced a news conference for next Tuesday, the 26th, to discuss details of the four year journey to the asteroids. Held at NASA headquarters, the event is due to be streamed on the agency’s homepage. The Hubble Space Telescope, meanwhile, has provided these images, shown below as a montage, of the two target asteroids. The debris of the asteroid belt, which may house 100,000 or more asteroids as large as ten kilometers across, provides an idea of the kind of materials available for planet-building some 4.6 billion years ago.
For those who follow robotic missions with fascination for the rapid strides in technology they represent, consider that Dawn is the first mission sent to orbit two different targets. Vesta will be the first, in 2011, with Ceres following in 2015. The Vesta image (on the right) shows the asteroid’s southern hemisphere, which is dominated by an impact crater so large that the distance across it is almost equal to the asteroid’s diameter. About the size of Arizona, Vesta produced fifty smaller asteroids from the impact that are often referred to as ‘vestoids.’
Image: These Hubble Space Telescope images of Ceres and Vesta show two of the most massive asteroids in the asteroid belt, a region between Mars and Jupiter. The images are helping astronomers plan for the Dawn spacecraft’s tour of these hefty asteroids. Credit: For Ceres, NASA, ESA, and J. Parker (Southwest Research Institute). For Vesta, NASA, ESA, and L. McFadden (University of Maryland).
Ceres, seen on the left, shows the presence of dark and bright regions probably related to topographic features. The small world is thought to hold thirty to forty percent of the mass in the asteroid belt, with water possibly occurring beneath its surface. Or maybe we should call this a ‘dwarf planet,’ as planet-definers like the IAU prefer to do. Ceres is round and thus planet-like, but it does not sweep debris out of its orbit. However we describe it, this first asteroid to be discovered (in 1801) should tell us much about asteroid structure, and the comparison with New Horizons data from Pluto may help us decide whether the ‘dwarf planet’ category is sufficient to cover both of these small worlds.
by Paul Gilster | Jun 22, 2007 | Exoplanetary Science |
Speaking of bio-signatures, as we did at the end of yesterday’s post on planetary atmospheres, take note of the Virtual Planet Laboratory, a working group at the Jet Propulsion Laboratory that is trying to figure out what life’s markers might look like across a wide range of biological types. The most obvious signature for life itself is the presence of unusual combinations of things. A world without life shouldn’t, for example, give us strong signatures in both methane and oxygen simultaneously.
We looked at this subject in an April post, but a recent news release prompts me to put it back into play. The work is highly theoretical, proceeding as it does with no current examples of extrasolar planetary spectra from terrestrial-class worlds to look at. But we can begin with photosynthesis and its variants, as discussed here by Robert Blankenship (Washington University, St. Louis), a member of the group of researchers:
“When you consider another world you’ve got to find that life there depends on photosynthesis in the broad sense, but it’s probably not identical to the way that photosynthesis works here. You’ll need molecules that absorb light that are highly colored, but whether they have the same green colors we know on Earth is unlikely.”
Plants that are black instead of green? Blankenship thinks they’re possible. It’s wonderful to think about what Chesley Bonestell might have come up with to illustrate such concepts, but Doug Cummings’ work below handles odd foliage colors nicely. And Blankenship points out that chlorophyll isn’t as efficient as it might be in harnessing light’s energies. A black molecule could absorb all the ambient light, depending on the spectrum of light impinging on the planetary surface. The size and intensity of the star in question obviously become key players here.
Image: An artist’s conception of multi-colored plants on a distant world. Credit: Doug Cummings, Caltech.
“Apparently the vegetable kingdom in Mars, instead of having green for a dominant colour, is of a vivid blood-red tint,” wrote H.G. Wells in The War of the Worlds, an 1898 novel whose landscape speculations now can be extended to other solar systems, Mars having failed in the vegetation department. In a recent paper, the researchers speculate that among the best candidates for the study of biomarkers are M-class stars, red dwarfs like Barnard’s Star, Proxima Centauri and the widely touted Gliese 581:
Biosignatures — both atmospheric and surface — on planets around M stars may actually be easier to detect than those around F, G, or K stars. The modeled atmospheres of M star planets of Segura, et al. (2005) reveal that low UV radiation from quiescent M stars could result in higher concentrations of biogenic gases CH4, N2O, and CH3Cl. Tinetti, et al. (2006) found the “red edge,” shifted to the NIR, to be easier to detect through modeled clouds than the plant red edge. These prospects to detect life should motivate continued investigations into M star atmospheres and the spectral adaptations of extrasolar photosynthesis.
The ‘red edge’ in question can be helpful because as you push into the near-infrared (NIR), chlorophyll becomes much more reflective (this begins at wavelengths in the area of 700 nm and greater). Thus foliage can throw an interesting signature at these wavelengths, telling us that there is a method of light capture and energy storage at work on a distant world. The same paper cited below also goes into M star flare activity and its effects on plants pushing into deeper water for flare protection.
The paper, of which Blankenship is a co-author, is Kiang et al., “Spectral signatures of photosynthesis II: coevolution with other stars and the atmosphere on extrasolar worlds,” Astrobiology 7 (2007), pp. 252-274 (abstract). See also Kiang et al., “Spectral signatures of photosynthesis I: Review of Earth organisms,” Astrobiology 7 (2007), pp. 222-251 (abstract).
by Paul Gilster | Jun 21, 2007 | Exoplanetary Science |
Where does the Solar System keep its water? Beyond Mars, the trend seems to favor more and more water content the farther out we go. Thus Jupiter, which is considered depleted in water, is eclipsed in these terms by Saturn, though that planet has less water than other volatiles. Move on to Uranus and Neptune and you get into serious water enrichment. “The farther out you go in the solar system, the more water you find,” says Bruce Fegley (Washington University, St. Louis).
Fegley’s work, discussed at the Chicago meeting of the American Chemical Society last March, points to a compelling theory about the outer planets: From Jupiter to Neptune, these are worlds whose atmospheres are ‘primary,’ drawn directly from the solar nebula as the planets of our Solar System were forming. Just as the Sun is rich in hydrogen and helium, Jupiter likewise shows large amounts of hydrogen and helium, though less carbon, nitrogen and oxygen than the other gas giants.
Observations of methane, hydrogen and carbon monoxide help us calculate the water vapor abundance on a given world. By the time you get to Uranus and Neptune, it becomes clear from such studies that the water content is considerable. And what of Earth and the other inner planets? Here’s Fegley’s take:
“On the other hand, the terrestrial planets Venus, Earth and Mars have secondary atmospheres formed afterwards by outgassing — heating up the solid material that was accreted and then releasing the volatile compounds from it. That then formed the earliest atmosphere.”
Where all this ties into exoplanet studies is that Fegley thinks his methods can help us study the likely atmospheric composition of Earth-like planets in other solar systems. This Washington University news release quotes the scientist again on what we might find out there:
“Because the composition of the galaxy is relatively uniform, most stars are like the sun — hydrogen-rich with about the same abundances of rocky elements — we can predict what these planetary atmospheres would be like. I think that the atmospheres of extrasolar Earth-like planets would be more like Mars or Venus than the Earth.”
And here’s why: We get abundant oxygen on Earth because of photosynthesis, without which we would be engulfed in nitrogen, carbon dioxide and water vapor. All of which makes spectroscopic studies of exoplanet atmospheres — something we’ll be doing on Earth-size planets in the not distant future — a project of no little significance. For if we know what we ought to find there, and if we find things like oxygen and a reduced gas like methane or nitrous oxide in unusual quantities instead, we’ll have a bio-signature that should launch a thousand dissertations.
