Friday, October 2, 2015

Tall Ships and Trading Posts: Economics and MacGuffinite

Apologies for such a long pause between post, RocketFans, but I have had an appalling number of Doctor's appointments in the last week.  Next week is just as bad, but that doesn't mean I can't squeeze in a post about our lovely Tall Ships in between long waits without wi-fi.
My week.
Anyways, to return to the topic at hand, I have played with the specs of my Tall Ships and Spacecoaches a little bit more, in order to get numbers I like better.  Mainly, I've manipulated mass ratios, altered the number of thrusters, and other minor tweeks in order to get designs I, as a writer, would like for an interplanetary wagon train to Mars:

Tall Ship with Star Destroyer for scale.  Just to put thing into perspective...

Tall Ship:
Dry Mass: 2164 tons
Wet Mass: 6656 tons
Mass Ratio: 4
Delta V: 13600 m/s
Acceleration: 0.005 m/s^2
Travel Time to Mars: 7.1 Months

Dry Mass: 794 tons
Wet Mass: 3176 tons
Mass Ratio: 4
Delta V: 13600 m/s
Acceleration: 0.007 m/s^2
Travel Time to Mars: 13.6 Months

Yes, the Spacecoaches take twice as long to travel despite having a higher acceleration.  These are just basic figures; the burn duration on the Tall Ship, for example, is almost three times that of the Spacecoach.  I justify the excess this way:  The Tall Ships trim their burns to keep pace with the Spacecoaches, and use the extra propellant for emergency burns, space taxi service from the fleet to the showboat, and emergency remassing of damaged craft.

They are perfect for my needs.  We have a wagon train to Mars, that will get there in a bit over a year, allowing for stories in SPAAACE! about life in a constellation to Mars and whatnot, and having a central Tall Ship that is the center of all the action, like a Miss Kitty's in the Dodge City of space. 

But. I am a writer of Hard science fiction, and therefore need more justification for my spacecraft designs that "it fits the story I want to tell"  Let's all remember Ray's Rule of Science Fiction:  "Soft Science Fiction tries to make technology fit the imagination, and Hard Science Fiction tries to imagine what fits the technology."  So, If I want to keep my Hard SF street cred, I must justify such robust spacecraft in the hands of middle-class starry-eyed pioneers who sold off their meager assets to Go To Mars.  If you'll bear with me, I'll provide just such a justification, and as a bonus give you those L5 colonies they talked about in the 70s free of charge.

Okay, as a first step in our journey to make Tall Ships realistic, let's put them into context by reviewing our basic assumptions:

1. The cost of natural gas from Saturn's moon Titan is less than the cost of oil drilling on Earth, when you factor in the cost of wars over oil bearing territory.
2. A future war between China and the United States will result in Kessler's Syndrome from the  destruction of the US satellite network.
3. Nuclear Pulse Propulsion vehicles will be the best equipped to go into space and establish a manned communications network of heavily armored space stations.
4. A NPP Spacecraft has enough Delta V to go to Saturn.
5. An NPP expedition will be dispatched to Titan by nations that cannot afford to fight for oil sands but can afford a spacecraft.
6.Once Kessler's Syndrome thins out enough to allow regular space travel, there will be a demand for it from the general public.

That last is an assumption based on the idea that we really want what we can't have.  This seems like a decent bet - just look at the current furor over the defunding of the commercial crew program.

So, how do we translate those assumptions into a wagon train to Mars?

First of all, the cost of the spacecraft must be reasonable.  The most likely method of obtaining a reasonably priced spacecraft, for my money, is to obtain them second-hand.  There's ample precedent for this; the 747, $300 million per aircraft new, goes for about the cost of a new Ferrari right now.  At that kind of price schedule, a family could easily afford to replace their house with a Spacecoach and fly off to Mars.  Unfortunately, In order to have Spacecoaches' price drop as dramatically as the 747, They would have to make as many Spacecoaches as Boeing did the 747.  Optimist that I am, I don't see the Martian Run ever needing that many Spacecoaches.

So I consulted the numbers for my two ships, both written on their own index cards, hoping for inspiration.  I thought about their Delta V, they could go all the way to Ceres if you had the patience.  I figure the demand for single-family spacecraft to the Belt will be even less than the same to Mars, so that was no help.  Next, I concentrated on the engine type I chose, the Microwave Electrical Thruster.  I love these engines!  They are perfect for the mission of a Spacecoach - no moving parts, the ability to double as mining drills, and an absurdly small mass flow.  Seriously, the mass flow for a 400 engine array is only one kilo per second - an infinitesimal 2.5 grams per thruster.  I had to check these numbers more than once before I believed them.  Because the output is low pressure steam, not liquid water, the entire array can get away with small mass flows.  With the propellant mass of the modest Spacecoach design 2.3 million kilos, you can have a burn duration of over a million seconds before flip-and-brake.  That's a burn for days...

That's when I realized, for a trip to Mars the Spacecoach may use a long, slow burn, but for a trip to the Moon, it would be a constant boost rocket.

The Bachristochrone Duration for a trip from LEO to Luna's orbit at the Spacecoach's acceleration is only 414,039 seconds - well under half the maximum burn duration of our example. Our example also has a massive payload capacity, as a pioneer's wagon, so we can convert some into passenger accommodation. So, the Spacecoaches I'll use for my theoretical trips to Mars were originally meant Luna Express ships, carrying passengers cheaply into lunar orbit.

As cool as a second-hand Lunar Express sounds, we're only half-way done, RocketFans.  We've made our ships economical, but only if there's something really important in Lunar orbit that requires a substantial human presence.  In other words, we need MacGuffinite.

Remember when I said you could have the L5 colonies of old as a bonus?  I meant it.  If you followed the link above, then you may have noticed that "Petroleum Mining" is already listed.  See, the megatons of Titanian methane have to end up somewhere. The most logical place would be the two stable LaGrange points in lunar orbit, because anything at those points will stay there until you're good and ready to go fetch them.  You could try to put the methane shipments directly into Earth orbit, but after having suffered through Kessler's Syndrome once,  I doubt anyone will be willing to try.  So that's the "really important stuff in lunar orbit" part.

 And while Saturn is far enough away to be nearly imaginary to some people, you can see the Moon, and just knowing that all the oil you would ever need is right there will be more than enough incentive to go get it.  But not everyone will want to pay the Titan Oil Co. for the privilege of getting orbital oil.  There will be nations that just want to take it. Which means the oil will be defended.  There will be nations trying to sabotage the oil recovery of their rivals; they must be stopped. The powers that be on Terra that stand to lose billions as their petroleum becomes too expensive to compete may also try to interfere. And the UN, whose Security Council has two of the original sponsors of Titan Oil as members, will be on hand to make sure everyone plays nice.

That's the "substantial human presence" part.

So Spacecoaches were the cheap express ships to L5 and Luna, and Tall Ships were the overpowered, over remassed versions on hand for search and rescue, mass transits and charters.  As power stations were built to support the colonies, beam-riders replaced the gigantic solar sailers, which became less economical to run. These were bought up second-hand by settlers moving rimward, toward Cape Dread, Mars, and the beyond.  With colonies from L5 to around Saturn already, anything in between seems possible.


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