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Beta and Higher Patron Notice for 02/07/2020

🕑 Added 2020-02-08 01:44:30 +0000 UTC

Comments

Nyrath

Ah, yes, your analysis shows that once again I do not know what I am talking about. I will probably delete my section and with your permission add your analysis to the paragraph you indicated.

Maximilian Crichton

I have some issue with the explanation for why torchships are so hard to make. Firstly, the two formulae presented aren't really antagonistic. In fact, they're slightly different arrangements of the same equation, and what's more it's an equation which does not actually constrain their behaviour. To see what I mean, let's look at the first equation: F = m_dot*I_sp*g_0 In a rocket engine, I_sp and m_dot are design variables, decided upon by the engineer. Suppose I held m_dot constant and increased I_sp? Then both I_sp and thrust would simply increase in proportion to each other, in accordance to the first equation. This works too if I hold I_sp constant and increase m_dot (effectively how today's rocket engines throttle), or if I use the reversed form of the equation: I_sp = F/(m_dot*g_0). There's nothing in either equation preventing me from simply dialling m_dot and I_sp up to 11 and achieving a torchship. (There is a limit to F, but that only becomes relevant when you already have torchships) What actually constrains m_dot and I_sp and prevents you from creating a magitech torch drive is, as you've mentioned elsewhere in the torchship page, the waste heat problem. Every space propulsion system will generate waste heat due to inefficiencies, and there is a physical limit to how much heat the spacecraft can reject. Dividing by the efficiency, this tells us there is a maximum power level for the thruster P, and this power level relates to our design variables m_dot and I_sp through the equation: P = 0.5*m_dot*(g_0)^2*(I_sp)^2. The fact that P is constant creates the tension between I_sp and m_dot you were driving at. If my spacecraft can only run at a power level P, then the product of m_dot and the square of I_sp cannot exceed a certain level. If I quadruple m_dot, I_sp must reduce by half (and thrust will double) to preserve the power level P. Hence, it is this low value of P, limited by heat rejection constraints and our anemic energy sources, which make a torchship hard to make. With such a low power level, you either get boatloads of thrust and horrible I_sp (chemical rockets) or a spoonful of thrust and excellent mileage (electric rockets). The advances necessary to actually make a torchship will require raising this P level into the terawatt range, while trying to safely contain this continuously detonating atomic explosion inside your engine. At the moment, almost none of our materials, engineering methods, or energy generation devices, are up to the task.

John

The bit about coffee reminded me of some of the background work I'm doing for my SFRPG: Pastoral. The planet is 90% water, and the 10% land is scattered mostly near the poles due to the rotational bulge of the oceans. The place where the game is set, Veneto Island, represents about 5% of the dry land. But it's mostly covered in trees, bamboo covers three quarters of the island, and various hardwoods cover the rest, except for a few locations. It's all hilly and full of gullies, eroded out fjords and the like. All this means that there is precious little land for farms, so they have resorted to floating farms: large scale barges that grow most of the crops for the colonists, along with some extensive hydroponics operations for crops best suited for that method of production. And all this means is that there is no space for "luxury" crops like coffee or tea. That means every coffee bean and tea leaf was imported from Earth. None of the local flora has ever developed caffeine in any shape or form, at least in the ocean regions the colonists have investigated. So it's all imports, with a few grow ops on the island producing even more expensive local coffee, which has a bigger market back on Earth! The other thing imported to the planet is processed fish: tuna, salmon, and other species. Due to the low salt levels in the planet's oceans (and the presence of salts other than NaCl) Terran sea life won't do well without a lot of genetic tinkering. But sea life that migrates a lot, end up entering the CO2 rich waters outside the terraformed regions of the planet and die. So, processed tuna, salmon, etc. get shipped to Pastoral as well as coffee and tea. That doesn't mean that there's no sea food for the colonists, there's plenty. The native sea life is edible and nutritious for the most part. You still need to take your supplements, but there's plenty to eat. (And while you can vat grow tuna, salmon, etc. it's nothing like the meat on an actual fish. Yes you can "make it like real meat" but it's expensive and you're virtually growing an actual fish instead of just it's meat.)