Notes & Queries 8/19/09

by Paul Gilster on August 19, 2009

On Returning to the Moon

Interesting to see that the recent debate in the pages of The Economist on whether or not we should return to the Moon has reference to the outer Solar System. The debate pits Gregg Maryniak (James S. McDonnell Planetarium, St. Louis) against Mike Gold (Bigelow Aerospace). Normally the Moon is off our agenda in these pages because of our focus on the outer system and beyond, but my friend Frank Taylor noticed that among Maryniak’s arguments for a return to the Moon was its utility as a staging point.

Specifically, Maryniak argues that in addition to its other uses, the Moon lets us get our ‘space legs’ by learning about shielding human crews and ‘living off the land’ in a deeply inhospitable place. All of this may well lead to lunar power stations or the collection of Helium-3 for fusion projects, a developing technology with profound implications. Writes Maryniak:

Once we have the ability to capture and transmit energy at the megawatt and gigawatt levels we will see fast solar system travel. By beaming power to future space travelers we can free them from the intrinsic limitations of the chemical energies embedded in their propellants. Having both abundant energy and materials available in free space will also enable such useful things as cleaning up orbital space debris and mitigating the threat of Earth impact from asteroids and comets. The use of lunar materials and later asteroid and comet resources will ultimately enable probes beyond our solar system.

The whole debate, won by Maryniak by a vote of 61 to 39 percent, is well worth reading, and is particularly worth considering in light of recent arguments by Buzz Aldrin and others that Mars is the preferable next step.

Alien Worlds on the TV

A quick note that the National Geographic Channel will be offering two shows of interest this weekend. Alien Earths is a look at exoplanet possibilities with astrobiological implications, including exotic places like those shown in the accompanying video that find ways to support life in the absence of a star.

The other show is Naked Science: Hawking’s Universe, a look at the many contributions this extraordinary physicist has made to our understanding of the universe. Check local listings for Sunday, August 23rd for these.

Dark Energy or Spacetime Waves?

I’ve been working my way through a preprint of a paper arguing that dark energy is not what many scientists think. Joel Smoller (University of Michigan) and Blake Temple (UC-Davis) believe that an expanding wave moving through spacetime could be the reason why distant galaxies appear to be accelerating as they move away from us. The dark energy debate centers on the idea that dark energy fuels the acceleration, but Smoller and Temple will have none of it. Quoted on Space.com, Temple notes:

“We’re saying there isn’t any acceleration. The galaxies are displaced from where they’re supposed to be because we’re in the aftermath of a wave that put those galaxies in a slightly different position.”

What’s interesting about this is that it allows us to explain the anomalous acceleration with the confines of classical general relativity, seeing the anomaly as not an acceleration at all, but what the authors call a ‘correction to the Standard Model due to the fact that we are looking outward into an expansion wave.” Here’s more (note that I’m quoting from the preprint, not the published paper):

Unlike the theory of Dark Energy, this provides a possible explanation for the anomalous acceleration of the galaxies that is not ad hoc in the sense that it is derivable exactly from physical principles and a mathematically rigorous theory of expansion waves. In particular, this explanation does not require the ad hoc assumption of a universe filled with an as yet unobserved form of energy with anti-gravitational properties in order to fit the data.

Those possible ‘anti-gravitational’ properties naturally arouse the interest of propulsion-minded people, implying exotic new forms of transportation. But only if the enigmatic dark energy actually exists to serve as a model. Clara Moskowitz’ story in Space.com notes how may tests the new theory will need to pass before it will become convincing. Thus Mario Livio (Johns Hopkins University), who says that a model like this must be able to predict properties of the universe that astronomers can measure, and adds “To only produce an apparent acceleration is in itself interesting, but not particularly meaningful.”

The paper is Smoller and Temple, “Expanding Wave Solutions of the Einstein Equations that Induce an Anomalous Acceleration into the Standard Model of Cosmology,” Proceedings of the National Academy of Sciences, published online August 17, 2009 (abstract). A preprint is available.

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{ 21 comments }

NS August 19, 2009 at 19:08

Gold basically wants NASA to become a promoter of the commercial aerospace industry. Irrespective of whether the Moon ever provides the benefits that Maryniak envisions, Gold’s arguments are worthless. Maryniak wins by forfeit.

Peter August 20, 2009 at 8:40

There would be great advantages to building a telescope on the far side of the moon, but other than that I don’t see any point in going back- we don’t need to go there to mine Helium or anything else, and I don’t see how the moon or Mars is to be a stepping stone to interstellar flight; it will always be cheaper to do experiments and engineering in earth orbit or in labs right here. Outrageously expensive colonies wouldn’t actually advance science a whole lot, and they would do nothing to stem our population growth/ environmental problems since only a tiny fraction would ever want to live there.

Other than a lunar telescope, I suppose that colonies serving as hotels for space tourists could benefit interstellar missions if the money from that were channelled directly into that kind of research. Barring that, it’s time we stopped wasting billions and look beyond our immediate neighborhood.

Ronald August 20, 2009 at 9:01

Ref. the moon and its utilization: probably the most quoted commercial rationale for settling and exploiting the moon is the occurrence of Helium-3 for (future) nuclear fusion.

However, I wonder whether the concentration of this is high enough to justify its exploitation. I understood that its concentration is only about 0.01 to 0.1 ppm.
It may appear that Helium-3 extraction from the outer layers of Saturn and/or Uranus is more feasible.
I also learned that natural gas here on earth contains a certain (though very low) concentration of He-3, about 0.005 to 0.05 ppm.

Of course remains the enormous value of the moon for astronomy and as a launch platform.

James M. Essig August 20, 2009 at 9:17

Hi Paul;

I defiinately think we can do 1 Gw to 10 Gw via laser, rf beam, nuclear rocket etc. If I am not mistaken, the Saturn V rocket developed some ~ 200 million hourse power using the Power = d (Int Fdx)/dt simple calculation. This is about (200 million)(746)watts or about 150 Gigawatts.

Lunar lasers powered by Helium 3 reactors would indeed offer a great means to propell manned craft out into the Oort Clould and also to our stellar neighbors.

If I am not mistaken, some sort of Strategic Defense Initiative experiment to test lasing accuracy shined a laser beam off of a 1 foot or so wide mirror attached to the space shuttle in orbit and held its position for a significant amount of time, all from an Earth based location that was at least hundreds of miles away if not a thouasand miles or so distant.

I definately think we could work out the aiming requirements for a 10 Gw laser or even a 1 Tw to 10 Tw laser powered by a Helium 3 Fusion reactor system. At 10 Tw, assumming that the beam could be utilized with atleast 33 percent efficiency, after ten years of shine time, a total of 10,000 kg [C EXP 2] of kinetic energy could be delivered to the craft. For a 1,000 metric ton space craft, this works out to a gamma factor of about 1.01 and a velocity of about 0.2 C (I wish I had my calculator handy). Electrodynamic breaking could slow the craft down or perhaps a reverse thrust ion rocket could do the same, even an ion rocket powered by the laser.

I cannot not think of a better use for Helium 3 which might otherwise find some use in nuclear weapons fusile material.

ljk August 20, 2009 at 10:13

Dual Orion capsules studied for manned asteroid missions

BY CRAIG COVAULT

SPACEFLIGHT NOW

Posted: August 17, 2009

A manned asteroid mission using two Orion spacecraft, docked nose-to-nose to form a 50-ton deep space vehicle, is being studied by Lockheed Martin Space Systems as an alternative to resumption of U.S. lunar landing missions.

The Orion asteroid mission concept is being unveiled just as the Presidential committee reviewing U.S. human space flight is citing asteroid missions after 2020 as a less costly alternative to NASA’s proposed lunar landing infrastructure.

Results of the review will be briefed to President Obama by Norman Augustine, committee chairman, by the end of August.

Full article here:

http://www.spaceflightnow.com/news/n0908/17orion/

Ronald August 20, 2009 at 10:45

Peter: “it will always be cheaper to do experiments and engineering in earth orbit or in labs right here”.

I wonder, maybe this is ultimately a matter of scale: at (very) large scales of industrial operation it might actually be more feasible to establish a base on the moon. Especially if the required resources can be found on the moon (living off the land concept) instead of having to keep sending them up from the gravity well of earth.

James M. Essig August 20, 2009 at 11:48

Hi Folks;

I am really intrigued about the prospect of Lunar He-3 powered lasing stations since we will be going back to the Moon by 2020 with plans to permanently set up shop there.

If a 1,000 Terawatt laser beam could be generated by Lunar based nuclear fusion reactors,, and the system efficiency was 33 percent, in just 10 short years, a 1,000 metric ton space craft could reach a terminal gamma factor of 2 or a velocity of 0.867 C. A 100 Terawatt laser could accelerate a 1,000 metric ton space craft to a gamma factor of 2 in 100 years Lunar time.

As human life expectancy increases, perhaps to 120 years or more if researchers in the field of anti-aging medicine have their way, we should be able to reach any of the stars within a 100 light year radius of Earth in about 60 years ship time assuming the 1,000 Terawatt, 10 year acceleration scenario described above. The number of stars with 1,000 light-years of Earth is about 15,000.

We should as a civilization take seriously the opportunity that Lunar Helium-3 powered lasing facilities can afford us in our travel among the stars.

Peter August 20, 2009 at 12:50

Jim:

You definitely need to stop spelling ‘definitely’ with an a.
And we don’t need to go to the moon to mine Helium3. I would make the argument why, but Dr.Bussard in his final interview made the case much better than I ever could. The link to that interview appears to be dead, but I’ll upload it if I have the time and no one else can locate it.

hiro August 20, 2009 at 13:03

The major problem is that we don’t have any practicable and efficient fusion reactor, so going back to the moon for He3 is not a right reason. I remember people in the 70s said that we would have fusion technology in 20-30 years. Now some of us repeat the same thing again, I just wonder whether we’re able to do it this time.

andy August 20, 2009 at 13:27

Why would helium-3 be useful? There’s no compelling reason to extract it right now… fusion fuels are not much good without a useful fusion reactor to use them in, and such devices are notable for their absence in today’s world… always another couple of decades away…

andy August 20, 2009 at 13:53

Incidentally I do like the way that in the video all the depictions of “starless” planets are lit up to imply a strong nearby lightsource. Like, say, a star.

James M. Essig August 20, 2009 at 14:09

Hi Peter, hiro, and andy;

Peter, I will make every effort to spell “definitely” correctly. Grins and Giggles! In grade school, I had a strong tendency to cause my spelling bee team to loose contests.

You folks make some great points. I too have been dissapointed with the ever looming development of nuclear fusion reactors over the previous 35 years. The moon might best be mined for nuclear fission fuels since we know how to do nuclear fission. Nuclear fission fuel does not offer as great of Isp nuclear fusion rocket fuel, however, perhaps refined and optimized fission powered space craft can get us to the stars as well. The journeys will be longer with fission fuel, but if we can medically enhance human life expectancy significantly, I think the future taxpayers would support such systems.

Tulse August 20, 2009 at 14:31

It seems to me that the only attractive feature of He3 fusion is that it is (relatively) aneutronic. However, the proton-boron reaction is also aneutronic, and my guess is that solving the problems of making that reaction feasible are much much simpler than setting up industrial scale mining operations on the moon. Indeed, there are several small-scale companies working on devices using this reaction right now, whereas I’d guess doing even the basic research on He3 fusion is challenging due to the lack of fuel.

Tom August 20, 2009 at 16:11

Mario Livio (Johns Hopkins University) says that a model like this must be able to predict properties of the universe that astronomers can measure, and adds “To only produce an apparent acceleration is in itself interesting, but not particularly meaningful.”

I disagree with Mario. What is more likely, that a large gravitational wave is travelling through the universe, or that 90% of the universe is made up of something we don’t know who’s properties exist only to fit with observations. It is very meaningful that we could get the same observations by being a bit smarter in how we apply general relativity. I’ve also wondered whether the rotation speed disparity with rotating galaxies isn’t also the effect of the galaxy arms ‘surfing’ on the gravity waves that circulate outwards, rather than requiring the galaxy be 90% dark matter.

ljk August 20, 2009 at 22:11

Dark Energy

Authors: Aruna Kesavan

(Submitted on 20 Aug 2009)

Abstract: Dark energy is one of the mysteries of modern science. It is unlike any known form of matter or energy and has been detected so far only by its gravitational effect of repulsion.

Owing to its effects being discernible only at very very large distance scales, dark energy was only detected at the turn of the last century when technology had advanced enough to observe a greater part of the universe in finer detail.

The aim of the report is to gain a better understanding of the mysterious dark energy. To this end, both theoretical methods and observational evidence are studied.

Three lines of evidence, namely , the redshift data of type Ia supernovae, estimates of the age of the universe by various methods, and the anisotropies in the cosmic background radiation, build the case for existence of dark energy.

The supernova data indicate that the expansion of the universe is accelerating. The ages of the oldest star clusters in the universe indicate that the universe is older than previously thought to be. The anisotropies in the cosmic microwave background radiation suggest that the universe is globally spatially flat.

If one agrees that the dynamics of the geometry of the universe is dictated by its energy-momentum content through Einstein’s general theory of relativity, then all these independent observations lead to the amazing conclusion that the amount of energy in the universe that is presently accounted for by matter and radiation is not enough to explain these phenomena.

One of the best and simplest explanations for dark energy is the cosmological constant. While it does not answer all questions, it certainly does manage to explain the observations.

The following report examines in some detail the dark energy problem and the candidacy of the cosmological constant as the right theory of dark energy.

Comments: Master’s Thesis 82 pages

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Cite as: arXiv:0908.2852v1 [astro-ph.CO]

Submission history

From: Joseph Samuel [view email]

[v1] Thu, 20 Aug 2009 04:19:52 GMT (1773kb,D)

http://arxiv.org/abs/0908.2852

Ronald August 21, 2009 at 5:46

Peter: even if the moon appears to be a poor source of He-3 (see my previous posts) it may still be an excellent platform for manufacturing and/or assembling and/or launching He-3 powered-laser-driven spacecraft.

The idea that this will always be better/cheaper from an orbit in space might be very wrong, depending, again, on availability of lunar resources (for local construction, i.e. other than just He-3) and economics of scale etc.

So James may still be very right about his lunar-laser-launches, even if and when the energy source would imported from somewhere else (the outer solar system).

But then again, our descendants will most probably be laughing their heads off, when they read about our primitive ideas concerning propulsion, since they will, of course, be utilizing anti-gravity drives, what else ;-)

george scaglione August 21, 2009 at 12:49

ronald,my god! you are so right! lol on another part of this site i just (a couple of days ago) said something about gravity drives being the thing of the future! anti gravity,yes also, a slightly different bent on that same basic idea.also our primative ideas concerning propulsion will WITHOUT A DOUBT be laughed at.it just occured to me the other day when i was watching a tv show explain how we need to launch more fuel to sustain the weight of the fuel we are launching!!!!! thank you very much and well said,your friend george

Doug M. August 25, 2009 at 22:51

Speaking only for myself here: there are so many problems with “mine the Moon for Helium-3!” that it has become, for me, a marker that says “I have not looked at this seriously! and probably don’t want to.” Let me try to explain why.

1) We have not actually ever detected Helium-3 in lunar rocks. We reasonably assume it should be there from interaction with the solar wind, but at the moment that’s just an assumption.

2) The amount of Helium-3 we expect to find in the lunar crust is very tiny — less than one part per million. Extracting useful quantities would require processing megatons of lunar regolith, consuming a surprisingly high percentage of the energy gained from fusing it.

3) We do not know how to make a fusion reactor.

4) If we did, it probably would not be a Helium-3 fusion reactor, since this is not the easiest sort of fusion reaction to sustain and contain. By the most optimistic projections, Helium-3 fusion would be a second generation reaction.

5) The main attraction of Helium-3 is that it can be used in a fusion reaction that is aneutronic. However, the reaction most commonly proposed for lunar Helium-3 (fusing it with deuterium) is not, in fact, aneutronic. The aneutronic one (fusing two Helium-3 nuclei to create deuterium and an alpha particle) is much harder.

6) There are other aneutronic reactions, most notably the one involving an isotope of Boron that’s tolerably common here on Earth. The boron one is slightly trickier than the Helium-3 one, but only slightly. For lunar Helium-3 to be attractive, you have to imagine a future whose fusion capabilities fall into a very narrow window.

7) Just to drive this point home: Helium-3 is not a better fusion fuel in terms of cost or ease of reaction. The only good thing about it is, you can use it in a reaction that doesn’t produce neutrons. That’s good because it means no nuclear waste. But it’s not /that/ good, because all the plausible first-generation fusion reactions produce relatively modest amounts of nuclear waste.

8) Helium-3 can be found on Earth. It’s present in several parts per million of terrestrial helium. With a fairly modest effort we could isolate several tons of the stuff from current natural sources of Helium (i.e., natural gas). The cost of this would be several orders of magnitude less than going to the Moon for it.

9) Helium-3 can also be created artificially. The cheapest way (if you have the patience for it) is to create a bunch of tritium, since tritium decays naturally into Helium-3 with a half-life of 12 years. Pure tritium currently costs around $50,000 per gram, but (a) this could certainly be dropped by at least an order of magnitude if there were serious demand for tritium in quantity, and (b) you don’t need pure tritium to produce helium-3. Impure tritium-containing sludge will do just fine — you just catch the helium-3 as it outgasses — and many nuclear reactors produce exactly this. So, terrestrial commercial production of Helium-3, though very expensive, would still be cheaper than almost any imaginable scenario for getting Helium-3 from lunar regolith.

10) Cost of transporting mining equipment to the Moon + cost of building a fusion reactor on the Moon = $BIGNUM. A future society that can spend this sort of money, and that has the technology to make this plausible, is not going to be so starved for energy that it needs to mine Helium-3 from the Moon. To make this even remotely plausible you need to use fairy-dust-and-unicorn levels of handwavium. It’s like setting up giant whale-breeding lagoons all over the world so that we will always have access to whale oil to replace gasoline. It’s that level of whack.

So, again, no offense, but lunar Helium-3 is one of those tropes that really really needs to die. Someone proposed it 30 years ago, and then people seized on it as a reason to go back to the Moon, but it isn’t. It just isn’t. Find other reasons, yes? But that one, no.

Doug M.

ljk September 9, 2009 at 11:53

Rendering Dark Energy Void

Authors: Sean February, Julien Larena, Mathew Smith, Chris Clarkson (Univ. Cape Town)

(Submitted on 8 Sep 2009)

Abstract: Dark energy observations may be explained within general relativity using an inhomogeneous Hubble-scale depression in the matter density and accompanying curvature, which evolves naturally out of an Einstein-de Sitter model.

We present a simple parameterization of a void which can reproduce concordance model distances to arbitrary accuracy, but can parameterize away from this to give a smooth density profile everywhere.

We show how the Hubble constant isn’t just a nuisance parameter in inhomogeneous models because it affects the shape of the distance-redshift relation. Independent Hubble-rate data from age estimates can in principle serve to break the degeneracy between concordance and void models, but the data is not yet able to achieve this.

Using the latest Constitution supernova dataset we show that robust limits can be placed on the size of a void which is roughly independent of its shape. However, the sharpness of the profile at the origin cannot be well constrained due to supernova being dominated by peculiar velocities in the local Universe. We illustrate our results using some recently proposed diagnostics for the Friedmann models.

Comments: 13 pages, 14 figures

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)

Cite as: arXiv:0909.1479v1 [astro-ph.CO]

Submission history

From: Sean February [view email]

[v1] Tue, 8 Sep 2009 13:22:34 GMT (1484kb)

http://arxiv.org/abs/0909.1479

ljk September 22, 2009 at 13:11

Lunar Outgassing, Transient Phenomena & the Return to the Moon, II: Predictions and Tests for Outgassing/Regolith Interactions

Authors: Arlin P.S. Crotts, Cameron Hummels

(Submitted on 21 Sep 2009 (v1), last revised 22 Sep 2009 (this version, v2))

Abstract: We follow Paper I with predictions of how gas leaking through the lunar surface could influence the regolith, as might be observed via optical Transient Lunar Phenomena (TLPs) and related effects. We touch on several processes, but concentrate on low and high flow rate extremes, perhaps the most likely.

We model explosive outgassing for the smallest gas overpressure at the regolith base that releases the regolith plug above it. This disturbance’s timescale and affected area are consistent with observed TLPs; we also discuss other effects. For slow flow, escape through the regolith is prolonged by low diffusivity.

Water, found recently in deep magma samples, is unique among candidate volatiles, capable of freezing between the regolith base and surface, especially near the lunar poles. For major outgassing sites, we consider the possible accumulation of water ice.

Over geological time ice accumulation can evolve downward through the regolith.

Depending on gases additional to water, regolith diffusivity might be suppressed chemically, blocking seepage and forcing the ice zone to expand to larger areas, up to square km scales. Ice areas could reach large sizes near the poles. We propose an empirical path forward, wherein current and forthcoming technologies provides controlled, sensitive probes of outgassing.

Understanding lunar volatiles seems promising in terms of resource exploitation for human exploration of the Moon and beyond, and offer interesting scientific goals in its own right, but many of these approaches should be practiced in a pristine lunar atmosphere, before significant confusing signals likely dominate when humans return to the Moon.

Comments: (For Correctly Formatted Figures, See: this http URL) 47 pages LaTeX, 9 figures. Resubmitted to The Astrophysical Journal on Sep. 2nd, 2009. Originally submitted June 27th, 2007 (see arXiv:0706.3952 & arXiv:0706.3954)

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:0909.3832v2 [astro-ph.EP]

Submission history

From: Arlin Crotts [view email]

[v1] Mon, 21 Sep 2009 18:21:53 GMT (3384kb)

[v2] Tue, 22 Sep 2009 11:01:59 GMT (3367kb)

http://arxiv.org/abs/0909.3832

ljk September 28, 2009 at 8:36

http://antwrp.gsfc.nasa.gov/apod/ap090928.html

Water Discovered on the Moon

Credit: ISRO/NASA/JPL-Caltech/USGS/Brown U.

Explanation: Water has been discovered on the surface of the Moon. No lakes have been found, but rather NASA’s Moon Mineralogy Mapper aboard India’s new Chandrayaan-1 lunar orbiter radios back that parts of the Moon’s surface absorb a very specific color of light identified previously only with water.

Currently, scientists are trying to fit this with other facts about the Moon to figure out how much water is there, and even what form this water takes. Unfortunately, even the dampest scenarios leave our moon dryer than the driest of Earth’s deserts.

A fascinating clue being debated is whether the water signal rises and falls during a single lunar day. If true, the signal might be explainable by hydrogen flowing out from the Sun and interacting with oxygen in the lunar soil. This could leave an extremely thin monolayer of water, perhaps only a few molecules thick. Some of the resulting water might subsequently evaporate away in bright sunlight.

Pictured above, the area near a crater on the far side of the Moon shows a relatively high abundance of water-carrying minerals in false-color blue. Next week, the new LCROSS satellite will release an impactor that will strike a permanently shadowed crater near the lunar south pole to see if any hidden water or ice sprays free there.

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