Day One, Day Two, Day Three, Day Four.
My final day of the World Science Fiction Convention started out with a panel on worlds with Two Suns in the Sky. This was a discussion of a few hypothetical concepts and largely-unvalidated models that are nonetheless the best we can do. These include Niven's notion of a planet with an off-center core, and planets which orbit in a Figure-8.
Trying to determine the properties of a planet about another star is difficult. We can obtain the mass and approximate density from orbital characteristics, but finding chemical composition requires huge telescopes to do spectroscope. A related instrument limitation is that the Kepler Space Telescope can only find about 3% of possible exoplanets around target stars, as the ecliptic must pass between their star and our own.
For a close binary pair, it's estimated that two stars about 80% of Sol are the most likely to produce a habitable planet. Binary systems are much more likely to eject planets than single star systems. (About 30% of star systems are binary.) The minimum stable orbit radius is about 2-4 times that of the stars. It's not necessary for the planet to have formed there.
Is Asteroid Mining Feasible? The next panel set out to answer that question. The first question is which asteroids you're trying to mine. Near-Earth Objects are much easier to reach than the Asteroid Belt. The next question is what you want to mine. Are you searching for water or rare minerals. For the latter, it may just be cheaper to mine them on Earth until an adequate industrial base is built up in space. Note, too, that asteroids are not subject to many of the geophysical and geochemical processes which produce terrestrial ore deposits.
Water and other volatiles would be valuable as chemical propellants. Refueling satellites would be an obvious near-future application, but there's a sort of chicken and egg problem. Until the technology is developed, no one will build satellites with refueling capability. But the technology won't likely be developed until there's a market. Many companies don't appear to be grappling with this economic problem. A business plan emphasizing spin-off applications is desirable as it aids profitability and reduces the capital investment.
There's also legal implications. The Outer Space Treaty is quite vague about the use of off-world resources. It probably won't get resolved until prosecutions begin. Another interesting fact is that, according to one panelists, Americans and Australians are the primary supporters of space mining. Those from other nationalities are often opposed (though Luxembourg is investing in such technologies). Canada may tag along, but this seems to be mostly an Anglospheric obsession.
A higher-level concern is that asteroidial resources contribute to our current linear, one-pass economy, reducing pressure to develop more sustainable infrastructure. However, in space the perspective is different. Dragging materiel up from the gravity well is both expensive and requires considerably more structural strength than machines manufactured on orbit would.
More futuristic questions were considered by Jordin Kare's talk on SailBeam and the Bussard Buzz Bomb, two hypothetical technologies for reaching the stars within a human lifespan. His goal is a 50-year time horizon, which requires reaching speeds of at least 0.1c. Nuclear fission propulsion doesn't get us a tenth of the way there, even with staging. Fusion would be slightly better, but we still don't have that technology and only marginally improves the situation.
Using external energy gets us around the rocket equation, but most approaches to this don't allow us to slow down at the other side. Flying through an alien star-system at cruising velocity isn't really worth it, and this is the key limitation of the standard laser-driven sailship. Additionally, Robert Forward's original design had to be over a kilometer across, with a laser a thousand times that size. Dividing it into many smaller sails reduces the laser requirements but also the payload, down to a few milligrams. Considering any data sent back would need to be transmitted by laser, there's really not a whole lot there.
SailBeam is a way around this, by using multiple one-meter sails launched in succession, transferring momentum to one-another. One major aspect of this is that it requires a different material. The enormous heat flux of the laser blast, combined with tremendous accelerations, rules out metals. Dr. Kare proposes using a dielectric material, which will either reflect or retransmit most of the energy without absorbing. By his calculations this design would allow a sufficiently large laser to accelerate the sailship from zero to lightspeed in a few seconds (ignoring relativity).
There's still a lot of engineering problems to work out, of course. Guidance is one--trying to rendezvous one-meter objects across light-weeks of space would be a real challenge. Control is another--spin stabilization would require about 600,000 rotations per minute. Laser guidance, exploiting high-velocity dust impacts, and shedding small amounts of mass are possibilities to pursue.
Finally, the sail-probe would use a magnetic sail to slow down, dragging against the interstellar medium. This uses a similar technology to another proposed starship design, the Bussard Ramjet. Unfortunately, we now know that the interstellar medium is too thin for the Bussard Ramjet to produce adequate thrust. The magnetic fuel scoop would end up producing more drag than the engine thrust, just like the SailBeam. However, it's possible to seed the route leading out of the solar system with pellets of fusion fuel. Guiding these into the combustion chamber would need a much smaller scoop, which could be repurposed as a small shield once reaching cruising velocity. A "runway" a few light-days long would be adequate, which the ship would cover in a few weeks time. By the end, it would be experiencing about 30 fusion explosions per second.
The next panel I went to was about Human Culture in Remote Space Settlements, which by and large didn't really address the question. For me, it raised another: what makes a panel work? Does it depend on the moderator? A coherent question? Relationships between the panelists? We don't know.
I did take away a few good points, however. One is that many of the worlds around nearby stars are likely to be tidally locked, which poses a challenge to colonization. It's quite possible that fixating on planets is the wrong approach, when we could much more easily build nice, comfortable space colonies from the resources of the system. This solves the problem addressed in the generation ship panel on Friday, asking why colonists would bother getting off the ship.
Another thing discussed was the notion of athletics in space colonies. There would be the normal sports we know, combined with low-gravity and zero-gravity activities that are yet to be invented. Depending on the size of the habitat, some of them may need to be adapted to account for Coriolis forces. Physics class will be very different in an O'Neill Cylinder or Stanford Torus.
The afternoon's main attraction was a chat between George R. R. Martin, Pat Cadigan, and Michael Swanwick reminiscing about the first MidAmeriCon in 1976. I jotted down a few things, but won't try to condense them into something coherent.
The final event I went to was dialog on asking Can Hard Science Fiction be too Hard? The answer is: it depends on your readers. Different people have different preferences and levels of scientific literacy--whose your target audience?MidAmeriCon I memories dialog #MAC2 pic.twitter.com/t8QK7yV556— Nathaniel M. Routh (@NathanielMRouth) August 21, 2016
Appreciate the limits of infodumps, and ask if you should explain your work in the text. There's a sort of taboo against putting equations in your books, but some readers really like that sort of thing. Part of the problem is dislodging popular misconceptions before inserting the truth of the matter.
Science fiction shouldn't really be hard for hardness' sake. Real-world difficulties should cause difficulties for your characters. A common example is the lightspeed delay. Just because a story is set in space and deals with that doesn't mean it has to be a Mohs 11.
Many readers will forgive small errors if you get the big stuff right. Asimov said that there's a relativity of wrong, and he was right. Our modern models are true in broad strokes, but many of the details may change as the scientific method continues its process of refining and revising. If you reach the limits and veer into speculation, be honest about it. Speculative physics, biology, or psychology can still make for a great story.
That's the final report. WorldCon was a great experience, but it was also a lot of work. I'm almost relieved to be back at engineering school.
