Plausibility In Science Fiction

     Now and then, a reader will write to me about something scientifically or technologically disputable in one of my books. That readers don’t always manage to “suspend disbelief” while reading a science fiction novel doesn’t come as a surprise. However, one recent observation was a reminder that the ability to accept a novelist’s “handwavium” varies from reader to reader.

     One correspondent took issue with the use of a catapult to deliver cargo to a celestial body. The precedent for such a delivery system appears in Heinlein’s The Moon Is A Harsh Mistress:

     “Manuel, you asked us to wait while Mike settled your questions. Let’s get back to the basic problem: How we are to cope when we find ourselves facing Terra, David facing Goliath.”
     “Oh. Been hoping that would go away. Mike? You really have ideas?”
     “I said I did, Man,” he answered plaintively. “We can throw rocks.”
     “Bog’s sake! No time for jokes.”
     “But, Man,” he protested, “we can throw rocks at Terra. We will.”

     It was a brilliant concept. However, it has requirements that one must observe in the real world:

• Very low surface gravity on the “throwing” end;
• Greater and well-mapped gravity on the “receiving” end;
• A high-accuracy “thrower;”
• The thrown item must be able to make minor course adjustments in flight.

     I violated all of those requirements in Freedom’s Fury. I hoped my readers would let me get away with it for the sake of the story. Sadly, one such reader was a physicist. Of course he clucked at me: “You should have known better, Fran!” I must admit that I did. I hoped to “pull a fast one” that would slide past the reader.

     But I can preen over one thing, at least. There’s a fifth requirement, which my correspondent failed to mention: the “thrower’s” atmosphere must not be thick enough or deep enough to rob the projectile of the necessary velocity. Hope’s atmosphere, like that of Earth, is far too dense and deep for a catapult-launched projectile to reach the Relic.

     Here on Earth’s surface, we seldom take note of atmospheric resistance to the travel of an airborne object. (I did; I used to throw a screwball.) Nevertheless it’s there and significant, which is why car designers keep refining the noses of cars. It must be accounted for in artillery calculations and ground-to-ground missile trajectories. As regards reaching orbit from the surface of an Earthlike world… forget it!

     That made this story all the more poignant:

     Outside of several mentions in the Rocket Report newsletter dating back to 2018, Ars Technica has not devoted too much attention to covering a novel California space company named SpinLaunch.
     That’s because the premise is so outlandish as to almost not feel real. The company aims to build a kinetic launch system that spins a rocket around at speeds up to 4,700 mph (7,500 km/h) before sending it upward toward space. Then, at an altitude of 40 miles (60 km) or so, the rocket would ignite its engines to achieve orbital velocity. Essentially, SpinLaunch wants to yeet things into space.
     But the company was no joke. After being founded in 2014, it raised more than $150 million over the next decade. It built a prototype accelerator in New Mexico and performed a series of flight tests. The flights reached altitudes of “tens of thousands” of feet, according to the company, and were often accompanied by slickly produced videos.
     Following this series of tests, by the end of 2022, the company went mostly quiet. It was unclear whether it ran out of funding, had hit some technical problems in trying to build a larger accelerator, or what.

     [Applause to our favorite Graybeard for the tip.]

     Getting a good distance away from Earth’s surface is hard. That’s why rockets are always huge: they need a lot of fuel, and there’s nowhere along the way to “refill.” (If you don’t like it, talk to this guy. I doubt he liked it either.) The idea of using a “thrower” to overcome at least part of the difficulty was attractive. It wasn’t necessarily doomed to fail. But as matters stand, it will remain impractical for the foreseeable future, for reasons given in the article and others not mentioned.

     Sigh. I really would like to see more progress made in the technology of space travel. It would make my science fiction, and that of others that I enjoy, so much more plausible!