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Appendix B

NOTES



Notes for Thread 1

Gravity Gradient: The difference in gravitational acceleration between Transit Point Station’s center of mass and its endpoints is small—just 0.17 micro-gee or, more specifically, 0.001683 millimeters per second squared. The distance traveled at a fixed acceleration is given by d = 0.5at2, so after twenty-six minutes hovering in midair, Raimy’s car keys will have traveled about two meters.

Launch Window: Technically, the period of days or months when a Hohmann transfer is possible between Earth and Mars is known as a launch “period,” not a launch “window.” A launch window is a period of hours or minutes when conditions are acceptable for launch (for example, due to time-of-day restrictions, i.e., an orientation of the Earth with respect to the celestial sphere, a position of the vehicle along its orbit around the Earth, etc.). Space industry professionals may recognize the error, but the incorrect use of “launch window” has firmly embedded itself in the public vernacular, probably because it just sounds better. So I’m assuming that as more and more private citizens make their way into space, common usage will overwhelm twentieth-century engineering jargon.

St. Joseph of Cupertino Monastery is loosely based on St. Benedict’s Monastery in Snowmass, Colorado, to which my wife has been a frequent visitor across several decades, and with whose members she’s formed many close friendships. The idea of a monastery on the Moon occurred to me during a visit there.

Timelines for Raimy: He graduated high school at nineteen. He spent one year in dive school and submarine school, three years onboard the U.S.S. Jimmy Carter, three years in law school, five years as a prosecuting attorney, three years as a patrolman, and seven years as a detective. Ahead of him in the Mars rankings are world famous billionaire Ian Doerr and world-famous astronomer/author/Ivy League dean Tim Long Chang (now the CEO of National Geographic). Note: Concordia will fly in 2055.


Notes for Thread 2

Andrei Bykhovski was able to hitch a ride to the Moon for the simple reason that carbon and nitrogen are almost totally unavailable in the Lunar regolith. Thus, any permanent habitation on the Moon, however sophisticated, will necessarily be dependent on imports of these two materials. Hydrogen is also quite rare, except in shaded craters of the polar regions. However, since that’s where St. Joseph of Cupertino Monastery is located, its availability is not a huge problem. Because carbon and nitrogen can be found in near-Earth asteroids, at up to seventy-five times their concentrations in Earth’s crust, asteroid mining will likely be a cheaper way to supply these materials than shipping from Earth.


Notes for Thread 3

Thorium Reactors

Depending on the reactor design, a critical mass of thorium is around 1000–3000 kg. However, it’s possible to excite a subcritical reactor with a particle accelerator and thus get by with a lot less fissionable material. How far this technology can be pushed is an interesting question, but 300 kg is a value seen in plausible reactor designs, so that’s what I’ve used in this story.


Mass Driver

The HMI mass driver is ten kilometers long, and has to accelerate its 1000-kg payload to a speed of 2.37 kilometers per second to reach Earth. This requires an average acceleration of 28.1 m/s2 over a period of 8.4 seconds. However, since the acceleration is actually driven by one hundred individual magnets, it can’t be constant. Rather, it’s a “scalloped” curve with one hundred upward-facing peaks. Travel time for the payload is 4.9 days, after which it burns up in the Earth’s atmosphere. By this time, thanks to acceleration from the Earth’s gravity, it’s moving at about ten kilometers per second, so if it’s aimed directly at the Earth’s surface, rather than a grazing shot into the atmosphere, it could reach the ground largely intact, producing an impact crater about forty meters wide and knocking down buildings as much as three hundred meters away from the impact site, with an explosive force equal to about twelve tons of TNT. So while a single mass driver projectile is not as dangerous as even a small nuclear weapon, it’s equivalent to four or five good-sized truck bombs. That’s more than enough of a security threat to make Earthly government nervous, even if they have access to countermeasures.

The main purpose of the mass driver is to get the payload up to Lunar escape velocity. If it has even a small rocket engine, the payload can then be nudged to pass through virtually any point in cislunar space. Actually stopping (or matching orbits) at any point in space is also possible, although the fuel requirements are larger.


Antigravity Bricks

Most aerogels are basically open-celled foams made of glass (or other materials) that are mostly empty space, or rather, mostly air. As such they’re translucent as smoke and incredibly light, though not terribly strong. You can easily crumble a sheet of silica aerogel in your hand, although you need to be careful, because the dust consists of microscopic broken glass. Also, because the material is mostly air with a little bit of glass mixed in, it’s still heavier than air.

But! Imagine if that brittle, open-celled glass foam were replaced with a flexible, closed-cell diamond or graphene one. Such (charcoal gray) gels can be made with densities of just one hundred sixty grams per cubic meter (which is barely any mass at all!), but let’s make ours a bit more robust at, say, six hundred grams per cubic meter. This would be more than strong enough to support the weight of a human being (see, for example, www.nanowerk.com/
spotlight/spotid=52741.php).

Now imagine that instead of air, the structure is filled with hydrogen, with a sea-level buoyancy or lifting force of about twelve hundred grams per cubic meter. Graphene and diamond are both “sticky” to hydrogen molecules and have been used to store them in bulk (see www.researchgate.net/publication/235637852_
Hydrogen_Storage_in_Diamond_Films and link.springer.com/
article/10.1134/S1995078020030027), so we can assume most of the gas won’t leak out immediately. However, just in case, let’s add a thin, impermeable, inelastic shrink wrap to hold it all together when compressed.

The result is an “antigravity brick” that’s strong enough to build things out of, and yet “weighs” negative six hundred grams. It would literally fly up into the sky if you let go of it, and one hundred and fifty of them glued together would be enough to lift a good-sized person, clothes and all.


Notes for Thread 4

Earth-Sun Lagrange Point 1 Shade

The Earth-Sun Lagrange 1 (ESL1) Shade has a radius of two hundred sixteen kilometers. Since it’s only a fraction of a millimeter thick, there is not room for a lot of fancy photovoltaic layers, so its initial photovoltaic conversion efficiency is only around one percent. However, this is still sufficient to generate 1.47 terawatts of continuous electrical power—more than the entire United States circa 2022. Unbeknownst to anyone outside of ESL1 Shade Station, ongoing improvements to the Shade, in the form of additional coated layers, are improving this efficiency as time goes on. As seen from Earth, the Shade subtends an angle of 0.158 degrees (roughly three percent of the width of the Sun), and blocks 0.1 percent of the solar energy that would otherwise strike the Earth. Eventually, observers on Earth and elsewhere will begin to notice the shade is becoming more opaque.


Igbal Renz’s Spaceship

Brother Michael is correct that Renz Ventures has more than enough antimatter to reach any point in the solar system, and return, within the specified two-year mission duration. However, a mission headed outside the solar system first has to answer one question: where exactly is the outer edge? The orbit of Neptune is roughly thirty AU (“astronomical units”) from the Sun. The Kuiper Belt—a very loose swarm of comets in elliptical orbits—spans between forty and sixty AU. The “bow shock,” where the solar wind begins to be affected by the galactic wind, occurs at one hundred AU, and the heliopause, where the solar wind stops altogether, occurs at about one hundred twenty-five AU. However, if you cross the heliopause, you’re still not there, because the Oort cloud (an even looser swarm of comets orbiting the sun really, really slowly) begins at around ten thousand AU (or 1.7 percent of a light-year), and continues all the way out to one hundred thousand AU (or 1.58 light-years). If you’re headed toward Alpha Centauri, the light from that system will be brighter than the light of Sol once you’ve reached a distance of about 1.0 light-years, and if you’re headed for Sirius, it will become brighter than Sol at about 1.5 light-years. In other words, the solar system has a number of different “edges,” some easier to reach than others.

Let’s say, for example, we decide to go to the inner edge of the Oort cloud. A quick back-of-the-envelope calculation shows that (for example) a starship weighing one million kilograms, accelerating continuously at 1 m/s2, could get there in roughly seven months, at an ending velocity of six percent of the speed of light. Assuming total conversion of antimatter into kinetic energy, you’d need 1.9 tons of the stuff for the outbound journey, and an equivalent amount to turn around and come home.


Notes for Thread 5

The effects of the MSL1 magsat are perhaps the most speculative element of this story. From the distance of Mars-Sun Lagrange Point 1, it should actually be fairly easy to deflect a significant portion of the solar wind; the Earth does this with a fairly weak magnetic field of 3 x 10-5 Tesla (or ~3 gauss). By contrast, the electromagnet in an ordinary MRI scanner can be up to three Tesla (thirty thousand gauss), though it’s generated in a much smaller volume of space. The Earth generates its field with gigantic layers of molten iron flowing past each other at different speeds, so the field geometries are really not that similar, especially close to the planet. However, the field strength of the Earth’s dynamo drops off with the square of the distance, just like Miyuki’s fusion magnet, and still manages to keep our atmosphere from being stripped away by charged particles. The MSL1 magsat could potentially have an even stronger effect.

Blocking the solar wind would in fact cool the outer regions of Mars’ atmosphere, which right now sizzles with energetic collisions. At this time there’s no evidence this would have a dramatic effect on the atmosphere’s deeper layers—I made that up—but the Martian atmosphere is so thin that very small absolute changes could still wind up having large percentages attached to them. Now, according to the ideal gas law, a thirty percent reduction in the volume of Mars’ atmosphere, with no pressure increase, should result in thirty percent higher temperatures as well. However, as we’ve seen here on Earth, real atmospheres are not ideal gases, but complex systems that can produce head-scratching results. Alien atmospheres will no doubt have surprises of their own, especially if we start artificially mucking with them.

By the way, this would be a remarkably easy experiment to perform. As space exploration budgets are increasingly decoupled from risk-averse national governments, it seems likely that someone will eventually try it.


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