Centauri Dreams
Imagining and Planning Interstellar Exploration
Thoughts on a Different Apollo
Did the Apollo missions produce enough good science to justify their cost? It’s a question Freeman Dyson has speculated on in the past, calling the missions a success because they were “conceived and honestly presented to the public as an international sporting event and not as a contribution to science.” Symbolic of this is the fact that the first item to be unpacked after each landing was the television camera that relayed mission imagery back to Earth. Apollo inevitably labored under the camera’s gaze, but no great scientific discoveries came from it, and the entertainment emphasis inevitably detracted from the missions’ scientific objectives.
Image: Buzz Aldrin leaves the lunar lander in this photo snapped by Neil Armstrong.
What might Apollo have been if it had been conceived from the start to produce good science? Imagine this: Our six Apollo landings put two astronauts each on the surface for a period of several days. At their disposal were two tons of supplies and equipment. For the entire project, Apollo gave us a total of about 50 man-days on the Moon using an aggregate 12 tons of equipment. What if Apollo had produced 40 man-days per ton of equipment instead of the 4 it actually delivered? This could have been achieved by unmanned freight carriers conducting half the landings, providing six astronauts with 60 tons of supplies and equipment, sufficient for 400 days on the Moon.
You wind up with 2400 man-days of exploration instead of the 50 we achieved with Apollo. Let me quote John Cramer on this, because I’m drawing these thoughts from a column he wrote for Analog all the way back in 1988. Dyson had been visiting the University of Washington, where Cramer was then on the physics faculty, and his last lecture there contained these thoughts. Cramer took note of the advantages a much longer stay on the Moon could have brought:
With this much time, Dyson suggested, the Apollo project might have achieved some significant science. There would have been time to explore the lunar poles , to circumnavigate the body, to set up radio-astronomy dishes on the Moon’s radio-quiet back side, to take the time to investigate and theorize and observe and test and probe. There would have been the time and opportunity to bring into play those intrinsically human skills which have lead in previous years-long voyages of discovery to new insights and understanding.
The real Apollo, of course, was carried out in a few days by test pilots operating at a dead run, with one eye on the clock and the other on the prime-time news schedule. There was simply no time for science. Dyson’s revisionist version of Apollo is another road not taken.
The Problem of Premature Choice
Apollo was a success, but on the terms the mission was built around, and it could have been done much better. The Space Shuttle, however, was something much different, an example of what Dyson refers to as the ‘Problem of Premature Choice,’ which he defines as ‘betting all your money on one horse before you have found whether she is lame.’ Translated into bureaucratic terms, this means that a project can become large enough that exploring alternative engineering methods is seen as a waste that could become embarrassing to the public officials who have supported the project all along. Thus one of several alternatives is hastily selected, the rest eliminated, and the premature selection prevents the accurate analysis of the other methods.
Dyson himself has always been an example of independent thinking, but one whose priorities in space exploration favor science, which he thinks should command center stage. As he told his University of Washington audience, the contrast between the Space Shuttle and the International Ultraviolet Explorer (IUE) is instructive. The IUE came with mirror and optics from NASA, a solar power system from ESA, and communications gear from the UK. Countless astronomers and astrophysicists have used it to study tens of thousands of stellar objects in ultraviolet and visible wavelengths, and the IUE was available when supernova SN1987A occurred, providing exceptionally useful light curves that are suddenly back in the news as we try to figure out why neutrinos observed at CERN behaved differently from those from this event.
The IUE, which had been expected to last for three years, ended up serving us for eighteen, being finally shut down in 1996, some eight years after Dyson gave his talk at the University of Washington. The IUE provided a great scientific return in a mission that remains to this day little known. Learning where the payoff is — and deciding what kind of payoff you want to achieve — is key to the process. Looking at NASA’s future as of 1988, John Cramer asked this question:
Will there be further plodding along the dismal path that has lead from the triumph of Apollo to the Challenger Disaster? Will the agency continue to place science far down in the priority queue, going always for the Premature Choice and the job security of mammoth engineering projects? Will NASA continue to withhold any investments in the future, in advanced propulsion technologies, and in new ideas? I hope not.
Choosing the Right Technology
The questions don’t seem to have changed much over the course of the last 23 years, although the scope of our ambitions has been downsized since that even earlier time (1952) when Wernher von Braun proposed a manned expedition to Mars that would have required moving 70 men and 4200 tons of equipment into orbit around the Red Planet, debarking 50 men and 150 tons of equipment to the surface in three ships, using what was essentially World War II technology.
Image: A Chesley Bonestell illustration from a 1952 issue of Collier’s showing his take on the von Braun Mars expedition.
A premature choice would have been dangerous here as well. Among the things Apollo did right was to work with adequate communications channels. Where von Braun chose a 1 kHz bandwidth for the link between the Mars expedition and Earth (essentially allowing the two to communicate via Morse code), Apollo was designed for spectacle and television, and used a communications bandwidth thousands of times broader. Dyson is all about getting the mix right, the right technology (competitively chosen) coupled to serious scientific purpose to achieve a lasting result.
John Cramer’s long-running Alternate View column in Analog can be accessed online. Talking to Cramer at the 100 Year Starship Symposium, I mentioned how useful I had found it over the years, and he told me that the site housing his column had been one of the first to appear on the Internet in Washington, preceding even the Microsoft website. Talk about getting ahead of the curve! Readers will enjoy Dr. Cramer’s take on everything from quantum mechanics to virtual reality over decades of speculation and analysis, a true resource for the interstellar minded. It’s also a source, as this 1988 column showed, of insightful commentary on getting our priorities right.
The Snows of Enceladus
Once again it’s time to catch up with Enceladus, the little moon that has such a huge impact on the planetary system it moves through. We’re learning, for example, how much water vapor is erupting from the features in the moon’s south polar region known as the ‘tiger stripes.’ Cassini measurements (using the Ultraviolet Imaging Spectrograph aboard the spacecraft) had pegged the rate of discharge at 200 kilograms of water vapor every second. New measurements from ESA’s Herschel space observatory match up closely to these findings. Saturn’s E-ring, formed from plume particles, would dissipate in a few hundred years without discharges like these.
You may recall that back in June, Herschel results were announced that showed a huge torus of water vapor circling Saturn itself, one that appeared to be the source of water found in Saturn’s upper atmosphere. More than 600,000 kilometers across and 60,000 kilometers thick, the enormous cloud was produced by Enceladus and picked up by Herschel’s infrared detectors. Water had previously been detected by both Voyager and Hubble in Saturn’s upper clouds, and also spotted by ESA’s Infrared Space Observatory in 1997. These earlier detections had raised the question of how water molecules were entering Saturn’s atmosphere from space.
Studying Herschel’s cloud of water vapor and running computer models that incorporated what we know of Enceladus’ plumes helped researchers put the pieces of the puzzle together. It turns out that most of the water in the torus is lost to space, but enough falls through the rings to enter the planet’s atmosphere to account for the amount of water observed there. Tim Cassidy (University of Colorado, Boulder) is one of those who worked on the data:
“What’s amazing is that the model, which is one iteration in a long line of cloud models, was built without knowledge of the observation. Those of us in this small modeling community were using data from Cassini, Voyager and the Hubble telescope, along with established physics. We weren’t expecting such detailed ‘images’ of the torus, and the match between model and data was a wonderful surprise.”
More in this NASA news release. Meanwhile, we have the announcement at the EPSC-DPS Joint Meeting 2011 in Nantes that ice particles from the plumes also fall back onto the surface of Enceladus, building up areas blanketed by super-fine snow whose present state tells us that the plumes have been active for tens of millions of years or more. We already knew that modeling particle trajectories from the plumes produced accumulation on Enceladus itself — this work was done by Sasha Kempf (Max Planck Institute) and Juergen Schmidt (University of Potsdam) in 2010. The new work, by Paul Schenk (Lunar and Planetary Institute, Houston) relies on a painstaking examination of high resolution images in areas of suspected accumulation.
The result: Smooth terrain with topographic undulations suggestive of buried fractures and craters, and changes in slope along the rims of deeper fractures, all consistent with material coating the top of solid crustal ices. The researchers have been able to apply models of deposition showing that the rate of accumulation of these ice particles is less than a thousandth of a millimeter per year. Because the average layer is 100 meters deep in the area studied, the team calculates tens of millions of years would be needed to accumulate the entire amount.
Image: Perspective view of “snow” covered slopes of Enceladus. This heavily fractured terrain lies north of the edge of the active south polar region. The largest of these fractures in the foreground is roughly 1 kilometre wide and 300 meters deep (0.6 miles wide and 1000 feet deep). The fainter dimples on the plateaus are actually older craters and fractures that appear to be covered by thick accumulations of fine particulates, sub-millimetre sized ice grains falling to the surface from the giant plumes to the south. At 12 meters per pixel (~40 feet) this view is one of the highest resolution images Cassini has obtained of Enceladus. Perspective rendering of the surface is derived from colour imaging a stereo topography of Cassini images, produced by D. Paul Schenk (Lunar and Planetary Institute, Houston). See also this ESA news release.
And so we can now talk about the ‘snows of Enceladus.’ They’re important, for their steady accumulation tells us that the heat source that drives the plumes and maintains any liquid water found under the ice crust must have been there for a long time. Schenk says the particles found here are roughly a micron or two across, making them finer than talcum powder that “would make for the finest powder a skier could hope for.” A pleasing thought, but Centauri Dreams assumes the scientist is even happier with the prospect that Enceladus’ snows will help us understand the internal heating mechanism that drives the plumes. What we need now is more high resolution imagery of a world few would have suspected would turn out to be so compelling.
Updating the 100 Year Starship Symposium
I’ve got an out of town speaking gig today and am pressed for time, so this may be a good occasion for something I needed to do anyway for the record, which is to highlight the papers given by Tau Zero Foundation and Project Icarus people at the recent 100 Year Starship Symposium. Most of the following were delivered as individual talks, although some were presented in panels. If you’re interested in reading the papers each author prepared for the conference, many (but not all, evidently) are to be published in the Journal of the British Interplanetary Society. I’ll deliver publishing details when they become available.
Here are the presentations of those associated with Tau Zero:
- E. Davis, “Faster-Than-Light Space Warps, Status and Next Steps”
- K. Denning, “Inertia of Past Futures” (anthropology)
- P. Gilster, “The Interstellar Vision: Principles and Practice”
- G. Landis, “Plasma Shield for an Interstellar Vehicle”
- C. Maccone, “Sun Focus Comes First, Interstellar Comes Second (Mission concept)”
- J. Maclay, “Role of the Quantum Vacuum in Space Travel”
- G. Matloff, “Light Sailing to the Stars”
- M. Millis, “Space Drive Physics, Intro and Next Steps”
- M. Millis, “Cockpit Considerations for Inertial Affect and FTL Propulsion”
- R. Noble, “Small Body Exploration Technologies as Precursors for Interstellar Robotics”
- S. White, “Warp Field Mechanics 101”
You may also be interested in Slate‘s take on the Symposium, which focuses on some of the breakthrough propulsion concepts at the far edge of the speculative frontier. The Smithsonian’s blog also carried an update about the conference, while MSNBC offered up a look at possible starship destinations, a major interest as we continue to lack planetary data for nearby stars. Finally, I loved Gregory Benford’s article describing the 100 Year Starship Symposium: The First Hard Science Fiction Convention.
Papers and presentations from the Icarus team in Orlando were plentiful indeed:
- J. Benford, “Recent Developments in Interstellar Beam-Driven Sails”
- B. Cress, “Icarus Interstellar’s New Icarus Institute for Interstellar Sciences”
- A. Crowl, J. Hunt, “How an Embryo Space Colonization (ESC) Mission Solves the Time-Distance Problem”
- J.R. French, “A Review of the Daedalus Main Propulsion System”
- R. Freeland, “Fission-Fusion Hybrid Fuel for Interstellar Propulsion”
- P. Galea, “Machine Learning and the Starship: A Match Made in Heaven”
- A. Hale, “Exoplanet Studies for Potential Icarus Destination Stars”
- A. Hein, “Technology, Society and Politics in the Next 100-300 Years: Implications for Interstellar Flight”
- A. Hein, K. Long, “Exploratory Research for an Interstellar Mission: Technology Readiness, Stakeholds and Research Sustainability”
- R. Obousy, “A Review of Interstellar Starship Designs”
- R. Obousy, “A 21st Century Interstellar Starship Study”
- M. Stanic, “Fusion Propulsion Comparison”
- R. Swinney, “Initial Considerations in Exploring the Interstellar Roadmap”
- R. Swinney, “Navigational and Guidance Requirements of an Interstellar Spacecraft”
- A. Tziolas, “Long Term Computing”
- A. Tziolas, ” Starflight Academy: Education in Interstellar Engineering”
Also, be aware that Ian O’Neill is continuing his coverage of the Icarus study, the latest article being a look at sex in space that circles around to starship design. Icarus team member Tiffany Frierson gives us her personal perspective on the conference (and it was a pleasure to meet Tiffany, who was often to be found circulating near the Icarus and Tau Zero tables snapping photos). Athena Andreadis presents an insightful look at the conception and preconceptions of the conference in If They Come, It Might Get Built. Finally, Centauri Dreams contributor and Astronomy Now editor Keith Cooper offers up his own take on starship design and fusion propulsion in an excellent essay that delivers helpful background and segues into the Icarus team’s thoughts on fusion’s future between the stars.
A New Slant on ‘The Planet of Doubt’
Among all the planets, Uranus seems to get the least play in science fiction, though it does have one early advocate whose work I’ve always been curious about. Although he wrote under a pseudonym, the author calling himself ‘Mr. Vivenair’ published a book about a journey to Uranus back in the late 18th Century. A Journey Lately Performed Through the Air in an Aerostatic Globe, Commonly Called an Air Balloon, From This Terraquaeous Globe to the Newly Discovered Planet, Georgium Sidus (1784) seems to be reminiscent of some of Verne’s work, even if it pre-dates it, in using a then cutting-edge technology (balloons) to envision a manned trip through space.
Image: Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which it is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory.
When ‘Vivenair’ wrote, Uranus had just been discovered (by William Herschel in 1781). The author used it as the occasion for political satire, and not a very good one, according to critic James T. Presley, who described it in an 1873 article in Notes & Queries as ‘a dull and stupid satire on the court and government of George III.’ Vivenair evidently put the public to sleep, for Uranus more or less fades from fictional view for the whole of the 19th Century. More recent times have done better. Tales like Geoff Landis’ wonderful “Into the Blue Abyss” (2001) bring Uranus into startling focus, and Larry Niven does outrageous things with it in A World Out of Time (1976). But although it doesn’t hold up well as fiction, Stanley G. Weinbaum’s story about Uranus may sport the most memorable title of all: “The Planet of Doubt” (1935).
What better name for this place? The seventh planet has a spin axis inclined by a whopping 98 degrees in reference to its orbital plane — compare that to the Earth’s 23 degrees, or Neptune’s 29. This is a planet that is spinning on its side. Conventional wisdom has it that a massive collision is the culprit, but the problem with that thinking is that such a ‘knockout blow’ would have left the moons of Uranus orbiting at their original angles. What we see, however, is that the Uranian moons all occupy the same 98 degree orbital tilt demonstrated by their parent.
New work unveiled at the EPSC-DPS Joint Meeting in Nantes, France is now giving us some answers to this riddle. A team led by Alessandro Morbidelli (Observatoire de la Cote d’Azur) ran a variety of impact simulations to test the various scenarios that could account for Uranus’ tilt. It turns out that a blow to Uranus experienced when it was still surrounded by a protoplanetary disk would have reformed the entire disk around the new and highly tilted equatorial plane. The result would be a planetary system with moons in more or less the position we see today, as described in this news release.
But this is intriguing: Morbidelli’s simulations also produce moons whose motion is retrograde. The only way to get around this, says the researcher, is to model the Uranian event not as a single impact but as at least two smaller collisions, which would increase the probability of leaving the moons in their observed orbits. Given all this, some of our planet formation theories may need revision. Says Morbidelli:
“The standard planet formation theory assumes that Uranus, Neptune and the cores of Jupiter and Saturn formed by accreting only small objects in the protoplanetary disk. They should have suffered no giant collisions. The fact that Uranus was hit at least twice suggests that significant impacts were typical in the formation of giant planets. So, the standard theory has to be revised.”
The questions thus raised by the ‘planet of doubt’ may prove helpful in understanding how giant planets evolve. More on this when the paper becomes available.
Earth’s Oceans: A Cometary Source After All?
Getting water into the inner Solar System is an interesting exercise. There has to be a mechanism for it, because the early Earth formed at temperatures that would have caused any available water to have evaporated. Scientists have long speculated that water must have been delivered either through comets or asteroids once the Earth had cooled enough to allow liquid water to exist. The former was preferred because the water content in comets is so much higher than in asteroids.
But the theory had problems, not the least of which was that comets studied in this regard showed deuterium levels twice that of Earth’s oceans. The ratio of deuterium and hydrogen, both made just after the Big Bang, can vary in water depending on its location because local conditions can affect the chemical reactions that go into making ice in space. A comparison of the deuterium to hydrogen ratio in extraterrestrial objects can be compared to water found in Earth’s oceans to identify the source of our water. Now comet Hartley 2 swings into the picture, for researchers have announced that its hydrogen/deuterium ratio is similar to Earth’s oceans.
Image: This illustration shows the orbit of comet Hartley 2 in relation to those of the five innermost planets of the Solar System. The comet made its latest close pass of Earth on 20 October last year, coming to 19.45 million km. On this occasion, Herschel observed the comet. The inset on the right side shows the image obtained with Herschel’s PACS instrument. The two lines are the water data from HIFI instrument. Credit: ESA/AOES Medialab; Herschel/HssO Consortium.
So how do you measure the hydrogen/deuterium ratio in the water of a comet? The answer is an instrument called HIFI, which operates aboard the European Space Agency’s Herschel infrared space observatory. HIFI (Heterodyne Instrument for the Far Infrared) is a high-resolution heterodyne spectrometer developed in The Netherlands that covers two bands from 480-1250 gigaHertz and 1410-1910 gigaHertz. Herschel was examining the comet’s coma, which develops as frozen materials inside vaporize when the comet moves closer to the Sun.
Remember, previous comet studies had found hydrogen/deuterium ratios different from our oceans. The difference between these comets and Hartley 2 may be that Hartley 2 was formed in the Kuiper Belt, whereas other comets studied in this regard are thought to have first formed near Jupiter and Saturn before being flung out by the gravitational effects of the gas giants, returning millions of years later for their pass around the Sun. The hydrogen/deuterium ratio we see in water ice may well have been different in the Kuiper Belt than in ice that first formed in the inner system, where conditions are much warmer. Further comets studies may confirm the idea.
Says Dariusz Lis (Caltech):
“Our results with Herschel suggest that comets could have played a major role in bringing vast amounts of water to an early Earth.This finding substantially expands the reservoir of Earth ocean-like water in the solar system to now include icy bodies originating in the Kuiper Belt.”
Surely the early oceans were the result of both comet and asteroid impacts, but the new findings point back to comets as major players. Even so, we have plenty of work to do to understand the role of the lightest elements and their isotopes in the early Solar System. Six comets besides Hartley 2 have been examined for hydrogen/deuterium levels, all with deuterium levels approximately twice that found in Earth water. Kuiper Belt comets were once thought to have even higher deuterium levels than Oort Cloud comets, an idea the Hartley 2 results have now refuted.
The team led by Paul Hartogh (Max Planck Institute for Solar System Research) has also used the Herschel Observatory to measure the hydrogen/deuterium ratio in comet 45P/Honda-Mrkos-Pajdusakova, another Kuiper Belt comet whose data is now under analysis, so we may soon have new data to add to this story. The paper is Hartogh, “Ocean-like water in the Jupiter-family comet 103P/Hartley 2,” published online in Nature 5 October 2011 (abstract).
And there is further news out of the joint meeting in Nantes, France, of the European Planetary Science Congress and the American Astronomical Society’s Division for Planetary Sciences, where this work was announced. As noted in this article in Nature, a new study of the Sun-like star Eta Corvi, which is roughly the same age our Sun was during the Late Heavy Bombardment (when most water is thought to have been delivered to the Earth), shows that the star has an inner ring of warm dust that is rich in carbon and water. Team leader Carey Lisse (JHU/APL) thinks we’re seeing the traces of one or more Kuiper Belt-class comets being flung into the inner system, colliding with a planet there to form the ensuing ring of material.
Resonance and Probability Around Kepler-18
Three planets recently discovered through Kepler data provide an interesting take on how we look at smaller planets. Not that the planets around the star designated Kepler-18 are all that small — two of them are Neptune-class and one is a super-Earth. But what is becoming clear is that given the state of our current technology, we’ll have to get used to a process different from planet verification as we move to ever smaller worlds. The technique is being referred to as planet validation — it helps us determine the probability that the detected object could be something other than a planet.
Image: The orbits of the three known planets orbiting Kepler-18 as compared to Mercury’s orbit around the Sun. Credit: Tim Jones/McDonald Obs./UT-Austin.
The new system shows how this works. Kepler-18 is a star similar to ours, about 10 percent larger than the Sun and with 97 percent of the Sun’s mass. Around it we have Kepler-18 c and d, which turn up through transits. Planet c has a mass of about 17 Earths and is thought to be some 5.5 times the size of Earth. Its orbit takes it around Kepler-18 in 7.6 days. Kepler-18 d is 16 times as massive as the Earth, 7 times Earth’s size, and orbits its primary in 14.9 days. These two Neptune-class worlds are, interestingly enough, in a 2:1 resonance: Planet c orbits the star twice for every single orbit of planet d. The demonstrable resonance is ample proof that these are planets in the same system and not something else mimicking a planetary signature.
But the super-Earth, Kepler-18 b, is something else again. A team led by Bill Cochran (University of Texas at Austin) went to work with the 5-meter Hale Telescope at Palomar, aided by adaptive optics, to examine Kepler-18 to see whether the transit signal they thought to be a super-Earth was genuine. Finding no background objects that could have influenced the finding, they were able to calculate the odds that Kepler-18 b is not a planet at 700 to 1. Cochran thinks this process of planet validation is going to become much more significant as Kepler brings in new data:
“We’re trying to prepare the astronomical community and the public for the concept of validation. The goal of Kepler is to find an Earth-sized planet in the habitable zone [where life could arise], with a one-year orbit. Proving that such an object really is a planet is very difficult [with current technology]. When we find what looks to be a habitable Earth, we’ll have to use a validation process, rather than a confirmation process. We’re going to have to make statistical arguments.”
So we can with a high degree of probability rule out any of the objects — stars, background galaxies — that might in any way compromise the transit data. The planetary signature of the super-Earth seems real enough, though established in a different way than Kepler-18 c and d, whose gravitational interactions can be readily demonstrated. The planet is thought to be 6.9 times Earth mass and twice Earth’s size. All three worlds orbit much closer to their parent star than Mercury does to the Sun, the super-Earth Kepler-18 b being the closest, with a 3.5 day period.
We can also deduce an interesting possibility about Kepler-18 b, as noted in the paper:
The inner, 3.5-day period planet Kepler-18b, is a super-Earth that requires a dominant mixture of water ice and rock, and no hydrogen/helium envelope. While the latter cannot be excluded simply on the basis of the planet’s mass and radius, the evaporation timescale for a primordial H/He envelope for a hot planet such as Kepler-18b is much shorter than the old age derived for the Kepler-18 system, and such a H/He envelope should not be present. Thus, despite its lower equilibrium temperature, Kepler-18b resembles 55 Cnc e and CoRoT-7b… Kepler-18b, together with 55 Cnc e… are likely our best known cases yet of water planets with substantial steam atmospheres (given their high surface temperatures).
The discovery was announced at a joint meeting of the American Astronomical Society’s Division of Planetary Science and the European Planetary Science Conference in Nantes, France. More on the Kepler-18 results in this news release from the University of Texas at Austin. Look for these results in an upcoming issue of the Astrophysical Journal Supplement Series devoted to Kepler, which will appear in November. The paper is Cochran et al., “Kepler 18-b, c, and d: A System Of Three Planets Confirmed by Transit Timing Variations, Lightcurve Validation, Spitzer Photometry and Radial Velocity Measurements” (preprint).
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