by Paul Gilster | Aug 11, 2008 | Advanced Rocketry |
It’s safe to say that Franklin Chang-Diaz knows what he’s talking about when he discusses the space experience. An astronaut who has logged seven flights and over 1600 hours in space (a period that includes three spacewalks), Chang-Diaz has been making even more impressive news in recent times with his Ad Astra Rocket Company, where the VASIMR (Variable Specific Impulse Magnetoplasma Rocket) is under development. It’s heartening to think of VASIMR undergoing space-based tests, a future that is now in the cards with the news that NASA has plans to test the VASIMR engine aboard the International Space Station.
We naturally think long-term here, but VASIMR’s uses in potential missions to Mars (Chang-Diaz talks about a 39-day trip to the planet!) and beyond will first have to be shaken out in near-Earth orbit. But ponder a VASIMR gradually becoming operational, mounting missions to communications satellites that are now economically all but unreachable. Indeed, VASIMR sets up the potential for servicing a wide range of space technologies, keeping them viable even as we move back to the Moon and find the need to service and re-supply a colony there, a tricky and expensive process with chemical rockets.
This is heady stuff that’s coming in the short term. Here’s what Chang-Diaz told an interviewer late last year, when asked about timelines for the technology:
We are on a fast track to complete the first flight-like VASIMR prototype, the VX-200 by early 2008. This device will be in all ways identical to the flight engine but will not fly. We plan to complete the characterization of this prototype by mid 2008 and begin the design of the VF-200-1 and the VF-200-2, the first flight engines, which will be ready for flight in late 2010 and 2011 respectively. By 2012 we expect to have both engines operating in space in two different venues. By the middle of the next decade we plan to fly more powerful engines in a lunar cargo vehicle, which is presently in our drawing boards. This vehicle could enable economically sustainable re-supply services to the Moon colonies and also be used to access space resources such as water and metals on comets and near Earth asteroids. By the end of the next decade, Ad Astra plans to begin construction of a lunar rocket test facility that will enable us to fully test the very powerful VASIMR rockets needed for missions to Mars and beyond. These rockets require a vacuum and a suitable facility large enough is not practical to build on Earth.
Using plasma heated by radio waves and channeled magnetically, VASIMR offers major benefits in fuel efficiency and thrust in a system that can be adapted for robotic cargo missions as well as faster manned operations. The ISS would not only provide the venue for early testing in space but also point to a major future use, the maintenance of large structures in orbit without burning far more inefficient rocket fuel to do the job. At the ISS, the plasma drive would draw its power from solar panels, but the kind of output needed for a mission to Mars would inevitably demand an onboard nuclear powerplant.
Thus we circle back to the nuclear issue, an obvious political problem that has plagued the development of space systems designed for operations far from the Sun. Remember the fear inspired by Cassini’s 1999 Earth flyby on its way to Saturn? Cassini’s radioisotope thermoelectric generators (RTGs) have to be used in venues where the Sun’s rays are weak, but anti-nuclear activists spoke of an environmental catastrophe if the craft hit the Earth. The obvious success of the mission has only put the nuclear question on hold rather than answering it. Mars in 39 days is a grand concept, but it means a nuclear option is in play that will generate more than its share of renewed protests. Brace yourself.
by Paul Gilster | Aug 9, 2008 | Culture and Society |
The latest Carnival of Space is now available at the Mars Odyssey blog, where Nancy Houser has gathered space-themed materials from the past week, many of them dealing with the question of perchlorates on Mars and the implications of that possible discovery. I’ll send you straight to the Carnival for the perchlorate story, where many bloggers dissect it. My usual practice is to focus on Carnival items that connect to our theme here on Centauri Dreams — articles about deep space starting with the outer planets and moving to regions beyond. This week the entry that fits that bill is Brian Wang’s article in NextBigFuture on radiation shielding.
Although Brian couches this work in the context of solutions to radiation exposure following nuclear attacks, it’s also true that a drug that is 5000 times more effective at reducing the effects of radiation injury than the drugs we currently use has interesting space implications. The experimental drug, intriguingly named Nanovector Trojan Horses (NTH), is based on single-walled carbon nanotubes that are coated with antioxidant compounds commonly used as food preservatives. In this setting they seem to dampen the effects of serious radiation exposure.
The NTH work (led by James Tour at Rice University) raises the question of how useful radiation shielding becomes as we move out into the Solar System. It’s commonly assumed that a human presence on the large Jovian moons, for example, is all but ruled out by intense radiation there. But future breakthroughs in radiation shielding and treatment, perhaps one day leading to turbo-charged vaccines against radiation damage, could help change that picture and allow scientists to function in such settings. Boots on the ground in places like Europa may no longer be completely inconceivable, and given what we may find there or, perhaps, on Callisto or Ganymede, that could be useful news indeed.
by Paul Gilster | Aug 8, 2008 | Astrobiology and SETI |
‘Hanny’s Voorwerp’ may soon enter the astronomical lexicon as a reference to anomalous objects in deep space. ‘Hanny’ is Hanny van Arkel, a 25-year old Dutch school teacher and participant in the Galaxy Zoo project, where she and 150,000 other volunteers worldwide help to scan galaxy images online. ‘Voorwerp’ is the Dutch word for ‘object,’ in this case a conglomeration of gas heated to about 10,000 degrees Celsius and marked by a hole in its center. The suspicion grows that van Arkel has stumbled upon an entirely new class of astronomical object.
Out of such finds does the work of a computer-armed volunteer become fodder for the Hubble Space Telescope, which will soon have ‘Hanny’s Voorwerp’ under observation. The object is apparently being illuminated by a source we cannot see, leading the Galaxy Zoo team to look at the nearby galaxy IC 2497. The quasar at the heart of this galaxy seems to have shut down some time in the past 100,000 years — at least, that’s the theory — while its ‘light echo’ persists in our view of the Voorwerp. Chris Lintott, an organizer of the Galaxy Zoo project, puts it this way:
“From the point of view of the Voorwerp, the galaxy looks as bright as it would have before the black hole turned off – it’s this light echo that has been frozen in time for us to observe. It’s rather like examining the scene of a crime where, although we can’t see them, we know the culprit must be lurking somewhere nearby in the shadows.”
Image: ‘Hanny’s Voorwerp’ : the green blob of gas [center] believed to be a ‘light echo’ from the bright, stormy centre of a distant galaxy that has now gone dim. Credit : Dan Smith, Peter Herbert, Matt Jarvis & the ING.
But what caused the hole 16,000 light years across that lies at the center of Hanny’s find? Chances are we’ll be pondering that for some time, with growing interest in what Hubble will see. What a boost for the Galaxy Zoo, which has produced 50 million classifications for a set of one million images online. And what a reminder, too, that at their present state of development, computers aren’t always as capable as people at finding unusual patterns. What they have allowed, of course, is the fecund networking that makes such an exciting project possible.
And if you’re thinking about anomalous objects in deep field images, you should ponder a question Adam Crowl asked recently on his Crowlspace site. Supposing a species somewhere in the universe attains a ‘Singularity’ state and is able to render itself essentially immortal, what will it then do for energy? We may be able to conceive of machine-based intelligence gaining a kind of immortality, and perhaps even the uploading of a biological creature’s consciousness, but stars aren’t immortal, as the inexorable physics of fusion attest.
Adam looks at two recent papers that consider how stellar lifetimes might be extended (see his site for the references), none of them stranger than the black hole quasi-star, which he explains thus:
A star is essentially an object in which the pressure created by inward pull of gravity is counteracted by the outward pressure of escaping electromagnetic energy – either indirectly as particle agitation (what we call ‘heat’) or directly as radiation pressure. Inside a quasi-star the hot layers of gas above the black hole are bloated into a heat-pressure supported radiating surface, a luminous star, by the energy of infalling matter. As matter falls into a black hole it can lose up to ~5.7% of its mass energy as radiation – this is more efficient than a star’s piddling 0.7% energy production via nuclear fusion.
The downside? Violent instability as the result of stellar opacity, which can cause the gaseous envelope around the star to be blown away, exposing the accreting black hole beneath. But maybe there’s another way, a star that actually uses dark matter in the form of WIMPs — Weakly Interacting Massive Particles — to the density of about a billion per milliliter. Now this gets interesting indeed:
…with the right density of WIMPs (about a billion per millilitre) a 20 Solar Mass star can be ‘frozen’ and still be happily burning on the Main Sequence for as long as the current age of the Universe. That’s a life extension of about ~2,000 fold, so it’s definitely enticing to imagine ETIs shepherding Dark Matter into the Galactic Core and giving their stars a life-extension. With a mass-energy conversion efficiency of ~60% the Galaxy’s 1.2 trillion Solar Masses of Dark Matter could keep its stars burning at 30 billion Solar Luminosities (current output) for ~350 trillion years. Much of that luminosity is from over-active O, B and A stars, so the useful light level is more like ~3 billion, thus 3.5 quadrillion years of starlight is available for all to bask in. Not forever, but substantially better than the darkness awaiting the natural Galaxy in that epoch.
Dark matter as an energy source for an advanced civilization takes us way out on a speculative limb, but it’s also an energizing way to ponder our options in next-generation SETI. For if such long-lasting stars, imagined either as ‘quasi-stars’ with black holes at their center or as ‘dark stars’ using the annihilation of dark matter, could be created, what would be their most obvious signature? Would there be a quick way to identify them, something that sets them apart from the wide range of other stellar objects? Or would they, like ‘Hanny’s Voorwerp,’ languish in archival records until dug up by a researcher noting an anomaly?
by Paul Gilster | Aug 7, 2008 | Exoplanetary Science |
A supercomputing cluster operated by a team at Northwestern University is giving us fresh simulations of the birth of planetary systems, with results that may dismay terrestrial planet hunters. For if this work is correct, the ‘rare Earth’ hypothesis is back, this time bolstered by computer models that are the first to simulate the formation of planetary systems all the way from earliest dust disk to full-fledged solar system.
More than a hundred simulations using exoplanet data collected over the last fifteen years went into the modeling of dust, gases and the effects of gravity. Planetary systems do seem to have a few things in common, among them a violent birth. The Northwestern team found that the dynamics of the early gas disk push nascent planets inexorably toward their central star. There they may be consumed in the star or subjected to collisions with other objects as each accumulates mass. Dynamical resonances can occur that produce increasing orbital eccentricity, with planets occasionally flung into deep space. The young system emerges out of this flux and bears the inevitable stamp of these interactions.
Frederic A. Rasio, senior author of the paper on this work, notes that the violent history of early planetary growth makes producing a relatively sedate solar system like ours problematic. A massive gas/dust disk tends to give rise to ‘hot Jupiters’ and highly eccentric orbits. A low-mass disk produces ice-giant planets no larger than Neptune. Is it possible that our mix of small, rocky worlds, ice giants and gas giants in circular outer orbits really is an exception in the galaxy? Says Rasio:
“We now better understand the process of planet formation and can explain the properties of the strange exoplanets we’ve observed. We also know that the solar system is special and understand at some level what makes it special. The solar system had to be born under just the right conditions to become this quiet place we see. The vast majority of other planetary systems didn’t have these special properties at birth and became something very different.”
A rare Earth is, of course, another way to answer the Fermi ‘where are they’ question. They’re not here because they don’t exist, or at least, not in appreciable numbers, and the reason for that is that planets capable of producing intelligent life hardly ever form. It’s a depressing thought for those of us excited by the prospect of future contact, but one that should be placed in a certain perspective. For while it is true that other planetary systems we’ve found tend to look much different than ours, it’s also true that we don’t yet know as much as we need to know about these systems. We do not, for example, know how many other planets we have yet to find in them, or how many of these may be potentially habitable.
Future space-based missions should help us sort that out. Until then, my view is that these powerful simulations do exactly what good science is supposed to do — they work with the best available data and draw conclusions that will be subject to further observation and refinement. Just as the sheer number of ‘hot Jupiters’ came as a surprise to most astronomers, so may the presence of terrestrial worlds in hot Jupiter systems, or their possible existence around close binaries like Centauri A and B, force us to look anew at our formation theories. We’ll see how this latest take on the ‘rare Earth’ hypothesis develops as our data increase and we have closer looks at systems we are only beginning to characterize.
The paper is Thommes et al., “Gas Disks to Gas Giants: Simulating the Birth of Planetary Systems,” Science Vol. 321, No. 5890 (8 August 2008), pp. 814-817 (available online).
by Paul Gilster | Aug 6, 2008 | Astrobiology and SETI |
Imagine a form of life so unusual that we cannot figure out how it dies. That’s exactly what researchers are finding beneath the floor of the sea off Peru. The microbes being studied there — single-celled organisms called Archaea — live in time frames that can perhaps best be described as geological. Consider: A bacterium like Escherichia Coli divides and reproduces every twenty minutes or so. But the microbes in the so-called Peruvian Margin take hundreds or thousands of years to divide.
“In essence, these microbes are almost, practically dead by our normal standards,” says Christopher H. House (Penn State). “They metabolize a little, but not much.”
House goes on to discuss what a slow metabolism may imply about environments outside our own planet. Imagine hydrothermal vents on Europa, where the energy ration may be slim. For that matter, with Phoenix still working its magic at the Martian pole, imagine subsurface aquifers on that planet whose energy resources may be just enough to keep microbes like these alive. And ponder the implication for life’s survival anywhere, for the sub-ocean floor may be the most bulletproof place on a planet, even when an incoming asteroid is substantial.
It seems remarkable to think that a large percentage of life on Earth — perhaps one-third of the planet’s biomass — may exist in forms that have yet to be subjected to laboratory analysis, but at least in this unusually active area off Peru, where organic materials are continually being deposited, microbes adapted to a far different kind of life than we are familiar with are flourishing. Reader Hans Bausewein, who sent links to this story, noted the tenacity of life that these results suggest. Get the process rolling and it seems to spread into every possible niche, at least on Earth, and the betting here is that the story is similar on other worlds.
The paper is Biddle et al., “Metagenomic signatures of the Peru Margin subseafloor biosphere show a genetically distinct environment,” Proceedings of the National Academy of Sciences, Vol. 105 No. 30 pp. 10583-10588 (July 29, 2008). Abstract online. Summary in this Penn State news release.
