Tuesday, March 29, 2011

Storing Fuel in Low Mars Orbit

A human landing on Mars may require fuel to be stored in low Mars orbit (LMO). The motivation for this step arises when mission planners seek to leave the crew's interplanetary propulsion component—that is, the engines that push the crew to Mars—in a highly elliptical "parking" orbit around Mars. For a spacecraft that will return to Earth, a parking orbit is preferable to a lower circular orbit because it requires less fuel to brake into and depart from. In a sense, the vehicle doesn't have to descend as deep into the Martian gravity well. Of course, the crew will then need to travel from Mars parking orbit to LMO and vice versa upon conclusion of the surface mission.

It is in this step—getting from LMO to Mars parking orbit—that a fuel cache in LMO will help out. The amount of fuel required to make this transition can be calculated quite precisely using the Tsiolkovsky rocket equation. It will depend on the type of fuel used, the total change in velocity required, and the mass of the crew, payload, and spacecraft. Since the velocity change needed to achieve an elliptical orbit must be imparted rapidly, the only suitable fuels seem to be traditional chemical rocket fuels. The total change in velocity in an orbital transfer depends only on the sizes of the orbits. A bit less certain is the mass of the crew's spacecraft, so it's best to leave this as a variable.

It is clear from the rocket equation* that using a fuel with 300 seconds of specific impulse (Isp) to impart a 1.2 kilometers per second change in velocity will require an amount of fuel greater than 50% of a spacecraft's non-fuel mass. If the fuel used offers only 250 seconds of Isp, then its weight must correspond to a full 63% of the rest of the spacecraft.

The alternative to storing this fuel in LMO is for the crew to carry it with them to the Martian surface. This would introduce some complications to the fuel's storage: higher temperatures, larger thermal fluctuations, and the shock of landing and ascent. More important, though, is the sheer mass involved. Any mass launched from Mars's surface requires several times as much fuel just to get it into orbit. But this mass and fuel must first be landed on the surface, and this landing requires several times as much fuel as the spacecraft mass and ascent fuel put together! I think that this post-ascent fuel—which is necessary simply to get from LMO to Mars parking orbit—is too much to take to the surface and should be left in orbit.

*see Appendix A

Friday, March 25, 2011

The Central Tragedy of Economics

When I think about how I would like my society to be structured, I am torn between two very different motivations. One is that it be fair; the virtues I would like to see rewarded include ambition, competitiveness, honesty, nonviolence, and intelligence. The other motivation is that my society be functional. It does me little good if fair laws cannot be enforced and the streets are full of violent criminals. For laws to be enforced reliably, a society must be quite stable. For that matter, it must be robust and competitive—if only to defend itself against external enemies.

The central tragedy of economics is that it is impossible to create a society that's both stable and fair. A fair society would surely allow adult individuals to develop their own talents. Whether they needed to manage a lot of wealth to do this would depend on their goals, and would ultimately be up to them to decide. Wealth, however, is not infinite; some mechanism of allocation is required. The free market seems to me a fair and elegant solution to this problem. It would be unfair to punish the nonviolent accumulation of wealth by taking some of it, just as it would be unfair to reward it by adding to it.

But this fairness can be traded for more stability. The most productive citizens, wherever they end up, seem to be most concerned with their own work. They generally are not a threat to the rest of society no matter how much they are abused by it, and so they can be forced to work on behalf of the less creative majority. By contrast, allowing productive citizens to keep the wealth they earn necessarily has destabilizing consequences—those who create nothing of value will fall into poverty and become more violent. The national financial climate could become more volatile as fewer individuals command more of the economic capital. Capitalism, practically by definition, will tend to destroy that which involves no clear victims: the environment. At the end of the day, the field of economics is always a tragedy.

Tuesday, March 22, 2011

Review: The Moon Is a Harsh Mistress

Robert A. Heinlein's The Moon Is a Harsh Mistress tells of a popular revolt against the incompetent and oppressive authority of a lunar colony. Political themes are central to the book, but it also explores a revolutionary space launch technology: the mass driver. A mass driver is sometimes called an electromagnetic catapult because it would use electricity to accelerate a vehicle along an inclined track, such that the vehicle would gain enough momentum to be cast into orbit. The story considers the possibility of building such a superstructure up the west side of a mountain—so as to take advantage of Earth's rotation. Heinlein is at his best with this kind of vision.

The Moon Is a Harsh Mistress by Robert A. Heinlein bookRead more reviews on AmazonThe novel also explores polygamous family structures—the author's main point being that a variety of relationships based on free association can be mutually beneficial. It is a good point, but it's one that's more idealogical than practical.

Given the book's chatter on libertarian ideology, I expected Heinlein to get his economics straighter. The whole viability of the colony relies on a net export of wheat. Worse, this wheat is grown artificially in tunnels excavated in the lunar surface. I can imagine a space colony building wealth by exporting something valuable to Earth, but that something is not food.

Other problems with the plot include Mike, a superintelligent computer. Mike has a completely human psychology and Heinlein does not attempt to explain how. The workings of Heinlein's utopia are also worth scrutinizing—the lunar colonists eventually establish a justice system that is enforced not through laws, but through local mobs which must be hired. This society seems more anarchist than libertarian.

Heinlein tells the story using a hybrid Russo-English grammar that omits articles like "the". This literary device—perhaps used to evoke sentiments of the Bolshevik Revoltion and the Cold War—seems innovative for the first few pages, annoying for the next hundred, and tolerable for the rest of the novel. It becomes more acceptable when characters are actually speaking and less so during, say, aesthetic descriptions of the landscape, which are, incidentally, in short supply. Still, The Moon Is a Harsh Mistress is an example of science fiction that genuinely strives to take itself seriously.

Friday, March 18, 2011

On the Rare Earth Hypothesis

The Rare Earth hypothesis claims that conditions for complex life in the universe are rare. It is one resolution to the Fermi Paradox—the apparent lack of extraterrestrial intelligence despite the existence of numerous extrasolar planets. The original advocates of this theory predict that simple life is fairly abundant in the universe, but that multicellular organisms are almost always prevented from evolving. There are many factors offered, ranging from the galactic level to the planetary, that could keep a biosphere primitive.

Perhaps the most convincing tenet of the Rare Earth hypothesis is the idea of a galactic habitable zone. The habitable zone is not a new concept in astronomy, but it has usually referred to the region around a star. Might there also be zones of a galaxy that are unsuitable for life? The center of the Milky Way is believed to be flooded with harmful radiation, while the outskirts lack the heavier elements—carbon, nitrogen, oxygen—that are found in living things. The spiral arms contain solar systems that frequently disturb each other with celestial impacts and supernovae; in fact, there may even be a correlation between Earth's mass extinctions and its passage through the Milky Way's spiral arms. It seems there must be entire galaxy types that are hostile to life. Though the boundaries of a galaxy's habitable zone may currently be less certain than a star's, it stands to reason that such a zone is meaningful.

Other factors of the Rare Earth hypothesis seem to be essentially conjecture. For instance, I don't quite understand the importance of plate tectonics in the development of complex life. Couldn't mere volcanism provide environmental variation and mineral recycling? It's also unclear to me whether a large moon is necessary to stabilize a planet's axial tilt. The tilt of a planet's axis is what causes seasons, which do seem to allow more biological variation—clearly helpful if complex life is to evolve. There may be some holes in the Rare Earth hypothesis, but they must be addressed scientifically. We must not let our excitement about the possibility of extraterrestrial life cripple our capacity to be objective.

Tuesday, March 15, 2011

9/11 and the Religious Paradigm

People commonly understand the motives for the September 11th attacks as earthly motives: to resist the U.S. presence in Saudi Arabia, America's support of Israel, or even the existence of freedom. Rarely do we examine the psychological perspective of the hijackers. Why would they would sacrifice their lives to achieve these goals if they won't be alive to experience the results? We often dismiss terrorists as monsters we can't relate to, but this is an abandonment of the scientific method. "Monsters" don't exist; there are only animals that behave in violent ways.

Though the 9/11 hijackers were very religious, it's not correct to say the atrocities were caused by religion. What religion can do is influence one's personal paradigm—one's conception of what is real. If a terrorist believes he might spend eternity with 72 virgins, then this is part of his paradigm. It's what he takes seriously and bases his actions on, actions that are trigged by the same basic biological impulses shared by all humans. His paradigm can help explain his behavior whether or not there's any truth to it.

There's little reason to assume humans would be more peaceful if a cosmic paradigm prevailed, but I do think they would be less willing to sacrifice themselves. After all, self-sacrifice can be rationalized as an investment for someone with a religious paradigm. People have been sacrificing themselves and each other for millennia, and it's tied to belief in an afterlife far too often. Perhaps it's time to examine the results of the religious paradigm for what they are.

Saturday, March 12, 2011

Review: Banquet Piece with Ham

Willem Claesz Heda was a 17th-century Dutch painter who specialized in breakfast scenes like Banquet Piece with Ham. The artist used a sharply limited set of colors and rendered his compositions in excruciating detail. He produced an almost photographic realism that would have been all the more impressive in his own time. The subject of the painting is largely self-contained, with the diagonal stream of light the only explicit reference to an outside world. Nonetheless, the viewer can uncover tiny reflections of the studio's windows in the wine glass on the left.

Banquet Piece with Ham by Willem Claesz Heda art
The piece was completed in 1656, near the height of the Dutch Golden Age—a time period that saw the Dutch Republic dramatically rise in economic and political power. New wealth spawned a new class of entreprenuers, who feasted on the luxuries depicted in Heda's work, as well as a new a class of artists to record their exploits.

Paintings like Heda's are often called vanitas because they contain objects that symbolize the emptiness of human vanity. Banquet Piece with Ham depicts numerous items of high luxury, but they are chaotically strewn about as if the diners left abruptly. Similarly, it is said, can this life pass abruptly—leaving all of our vanity as discarded as the dishes on this table.

Though Heda rendered this alluring scene meticulously, its effect seems to be lost on our generation. We are saturated with appealing images on a minutely basis, the mildest of which would be some ham, lemon, and oysters. In 1656—more than 150 years before the first photograph—I think this image would have stood out as extravagant and seductive.

Tuesday, March 8, 2011

Who Needs a Heavy Lift Launch Vehicle?

Space agencies and corporations alike have expressed interest in developing a heavy lift launch vehicle (HLLV). Though the terminology varies, I am referring explicitly to launch vehicles that can lift more than 50,000 kilograms (kg) to low Earth orbit. These are sometimes referred to as "super heavy lift" launch systems, probably because they would be among the most powerful rockets ever flown. As far as I am aware, only three launch vehicles ever lifted more than 50,000 kg to space: the Saturn V, the Space Shuttle, and the Soviet Energia rocket. The Saturn V could lift 118,000 kg, while the Space Shuttle and Energia could lift about 100,000 kg including the mass of their reusable orbiters.

Ares V rocket concept
The Ares V rocket was to lift more mass
than any other launch vehicle in history
The problem with HLLVs is that they're not an economical way to lift mass into orbit. These enormous launch vehicles have a great deal of structure that does not end up in orbit because they have to be made of strong, heavy materials. Smaller rockets can be made of lighter materials because they do not need to support all that weight—both payload and fuel—above them. An HLLV will also typically require much more sophisticated engines to generate the thrust necessary to reach space. This added complexity can quickly introduce new costs as developers seek to match the reliability of smaller, more manageable rockets.

It seems the only redeeming aspect of HLLVs is the capability to launch huge payloads in one piece. Even if it were more expensive per kilogram to use an HLLV than a smaller alternative, there may be some spacecraft that cannot be split into two launches. However, I cannot imagine many payloads that fit this description. Unpressurized space modules can often be folded up and deployed once in space, while pressurized modules can fit inside smaller launch vehicles if they are made to be inflatable—like the modules under development by the company Bigelow Aerospace. If these separate modules could autonomously rendezvous and dock with each other after reaching orbit, who would pay extra to use a heavy lift launch vehicle?

Saturday, March 5, 2011

I Think Ancestry.com Stock Will Go Up

Ancestry.com seems to gain little recognition as a serious money-making business. This is understandable though, because such a service has never been offered before and people are reluctant to trust something new. But if it really can grow its profits, and people don't recognize this yet, then there's an opportunity to buy the stock now while it's cheap ($33.75 at the time of writing).

There's no need to prove selling genealogy information is a sound business plan because Ancestry.com is already profitable—and it has been for years. In fact, the company has already paid off all of its long-term debt. It is the largest company of its type and is the clear front-runner in this competition. Since it has already set itself up and put together a large database, it stands to reason that new subscribers will bring in more revenue but will not increase costs much. Does it really cost that much to let another subscriber access the database? The amount of money Ancestry.com can make seems to be limited only by the final number of people willing to pay for a subscription. The company's CEO, Tim Sullivan, said, "The real question is: Is this a 2 million, 3 million, 5 million or 10 million subscriber category?"

The final size of this market will be large because genealogy is a universal interest. Nearly every primitive society worshiped its ancestors, and this is evidence that the interest is biological and not cultural. One's ancestors are interesting because they are part of the puzzle of one's own origins and identity—and these questions are important to every thinking human in every culture. With this in mind, it's not all that surprising that people have described Ancestry.com's service as "addicting".

Disclosure: the author owns shares of Ancestry.com (ACOM)

Wednesday, March 2, 2011

Review: God Is Not Great

Christopher Hitchens's God Is Not Great brings literary talent to a subject all too often bogged down by abstruse philosophical language. His case against religion is primarily a moral one; he examines the practical results of religion on improving man's condition, which are not impressive. To a lesser extent, he exposes the contradictions of religious teachings, such as Moses's ten commandments alongside his order for parents to stone their insubordinate sons to death. There is little that is new in this book, but the author certainly puts known material together in a fresh, articulate way. He commands a great deal of cultural knowledge and lends an impression of intellectual authority.

God Is Not Great by Christopher Hitchens bookRead more reviews on AmazonThere's something of a double standard, though, in Hitchens's attribution of altruism to innate human decency and barbarism to religion. It can't go both ways—our behavior either stems from religion or it doesn't. But if religion is man-made, then it can't be the fundamental source of any behavior.

Hitchens is a polemicist; he could have crafted a more eloquent title than "god is not Great" but it wouldn't have enraged so many theists. And in doing so he may have ensured he'd be preaching to the choir. Only a portion of this book—the critique of religion's logic—could steer the religious moderate away from religion, for this group is likely to feel affirmed by Hitchens's criticism of extremism. The fact is that most people nowadays don't pressure their children into believing, burn witches at the stake, or join holy crusades. They are religious because it enriches their lives with a shred of meaning and community. This is not to say that Hitchens's strategy won't work; it may be that stirring up trouble is the most effective way to bring attention to the issue.

Hitchens misses the point on Nietzsche's phrase "God is dead". Nietzsche was talking about the resulting crisis in values as Christianity was shed from the European mind, a crises that Hitchens is only partially successful in addressing. He speaks of the sense of awe and wonder at the mechanistic cosmos, which I think provides a powerful but insufficient purpose of life. As the title implies, God Is Not Great is best an argument against religion than an argument for any replacement.