This episode is sponsored by Brilliant
The trick to designing any machine, especially a spacecraft, is knowing what its purpose
and mission are⌠unfortunately science fiction provides us with few ships designed with those
concepts in mind. So today weâll be looking at spaceship design
from modern ships to those of the distant future, to some that might never exist outside
of science fiction. Weâll also be deconstructing some sci-fi
designs to see if they really make that much sense, and[a] examining some real-world design
elements that are specific only to modern spacecraft. Right now every spacecraft is designed to
be as light as possible, because every kilogram costs a lot of money to get into space. Also, spacecraft are most commonly lost in
the launch phase, so if you want to assemble a bigger ship or station in orbit, you need
a lot of launches, each of which might blow up on the pad or shortly after launch, and
even for automated launches, that results in in missions exceeding budgets and introducing
big delays. And so, in modern space exploration, if you
can make a hammer that weighs half as much but costs a hundred times as much, you send
that expensive hammer up instead of the cheaper and heavier one. The major paradigms of modern spaceship design
are extreme quality control, ultra-reliability, and the minimization of your mass, because
failure is not an option. If a rare manufacturing defect in a half-penny
resistor can disable a circuit that disables your $100 million probe, youâll spend thousands
of dollars making sure that half-penny resistor works right. This stands in contrast to the standards to
which most mass produced items are held, where cost usually is a bigger concern than reliability
or redundancy. You generally donât pay 10 times as much
for an appliance that will last twice as long or is half as likely to malfunction. As a result, our perception and attitude towards
modern terrestrial industry can warp our understanding of spacecraft design. A good example is addressing the issue of
radiation. Most spacecraft rely on thin, but dense, shielding
made usually of lead, gold foil or water, but other materials such as uranium can work
as well. Thick shielding adds cost due to the weight,
for fairly little added benefit. Another thing we have to consider is that
not all of the ship needs to be shielded, only the areas which have vulnerable computer
systems or lifeforms do, which saves on weight and cost. We can also look to technological solutions
to eliminate the cost and weight of shielding. For example, magnetic fields strengthened
with ionized gases like xenon have been proposed for shielding against cosmic radiation, as
they are able to deflect charged particles away from the crew. However these also come with trade offs - such
a device consumes more power, so you have to have a bigger power source, which means
more mass as well. Of course, a more efficient power source can
help solve that issue, and a total and cheap cure for cancer would minimize the need for
shielding humans too. A different approach is to incorporate other
components of your mass into your shielding. For example, water is a fantastic radiation
shield - thatâs one reason why we use it to shield radioactive material here on earth;
you can design a spacecraftâs storage for water and waste to double as your radiation
shielding. Aerogels also offer a lightweight approach
to shielding while having a minimal effect on mass, though the larger or faster the projectile,
the thicker the layer of aerogel or the incorporation of a denser layer working in tandem. Of course, if youâve already well established
yourself in space, and need to protect habitatsâ long term inhabitants from radiation, you
can always simply pile mass around your habitat. An established space industry can take advantage
of low-gravity bodies like small moons or asteroids to save on launch costs, making
thicker shielding practical. Some of our habitats and spacecraft are likely
to be built into existing small, rocky bodies as well, which will mean they come with their
own free shielding. Perhaps the most important factor though,
especially for spaceships, is the square-cube law. If you make something bigger by simply expanding
its geometry, the surface area will rise with the square of that increase while the volume
rises with the cube of that value. Double a sphereâs radius, and it has four
times the surface area, but eight times the volume. Make a cylinder ten times bigger along its
long axis and radius, and it gets a hundred times the surface area and a thousand times
the volume. If we want a space station that can hold a
thousand times as much cargo or personnel, we make it ten times bigger, which also gives
it a hundred times the surface area, and by default a thousand times the mass. But itâs not really necessary to make my
shielding ten times as thick, we only need to extend it over one hundred times as much
area, and now shielding accounts for a tenth the proportional mass that it did on the smaller
version. And many other aspects of my ship also wonât
need to scale up by 1000 either. So, I probably donât need a thousand times
as many spare parts for instance, even if I do need a thousand times as many components--which
I probably wouldnât anyways. You will always need two of any critical component
or part, but that doesnât necessarily mean you need two-thousand of them just because
you have a thousand times as much space. For spaceships, bigger is often better. In other words, once you start making ships
of a certain size, even if mass is still a big concern, radiation shielding really stops
being an issue. Even on interstellar ships plowing through
the void at relativistic speeds, you really only need to increase your shielding on the
nose of the craft. The easiest way to do this is to simply keep
your spare fuel and water supply up front to soak up radiation. Hydrogen and water ice mostly wonât be harmed
by it, and they will be stored in thick volumes, so you can design long and skinny ships with
the front, thick shielding being proportionally smaller, reducing how much proportional mass
youâre pushing around. So thatâs our most likely layout for spaceships,
they are skinny and long. This does not necessarily mean you build ships
like long, ultra-thin wires, but you will generally want to optimize the shape of your
spacecraft by employing a minimum longitudinal cross-section. A spear, needle, or arrow shape is preferred,
not a blocky one. Generally it would be symmetric too, though
they donât necessarily need to be aerodynamic. Thereâs no air in space to cause drag; however,
if youâre moving at highly relativistic speeds, the near-vacuum of the interstellar
medium actually acts like a gas, though weâll come back to that later. With that in mind you could easily introduce
a lot of protrusions such as antennae, shielding, extra habitation pods, and so on, which destroys
the image of a nice, sleek hull. Not every location or area on a ship needs
the same level of protection, for example, you donât particularly care if a random
bit of space debris slams into an antenna, as such hardware is easily replaced or can
even be manufactured on the ship. Indeed you might use less armor and shielding
on spare water and fuel tanks to ensure any debris doesn't fragment upon impact. That could cause a large exit wound, and which
means your fuel or water will be lost to the void. If you can ensure debris only punches a small
hole in those tanks, the leakage could be kept minimal during the tiny amount of time
it would take to patch that small puncture, especially if you have a self-sealing material
for the tanks. Indeed, perhaps such a self-sealing tank might
leak an average of a few hundred kilograms to these minor punctures during the voyage. However, if you were to use a more heavily
armored tank, youâd have to attach many thousands of kilograms of additional armor,
adding to your shipâs mass, and increasing your fuel bill. In this case, youâd want to go with the
thinner tanks and just absorb the minor losses, because itâs an overall net gain. You are also very likely to have a lot of
modular, reconfigurable, or retractable segments or pods on your ship. During the shipâs construction, you wonât
be fighting air resistance or the drag of gravity, but once you embark on your journey,
during your acceleration phases, you will effectively be back under gravityâs thumb. Of course the robustness of your ship design
will need to consider the level of acceleration, and deceleration you intend to use. Short trips may accelerate harder for a brief
time, whereas longer journeys may opt for a protracted, but lower and more efficient
acceleration. Once the acceleration phase ends and you begin
your coasting phase, which will be the majority of your trip, thereâs no reason why you
canât begin to expand outward, adding segments and pods and extrusions of all types, but
this must be measured against the fact that you will be increasing your shipâs cross
section. If you wish to expand, you must decide how
much radiation shielding and anti-collision armor youâll give to each extrusion. However, while youâre cruising, you even
have the option to trail things behind your ship; maybe you detach your power generator
and instead drag it behind you, apart from the ship, so whatever waste it produces can
be ejected into space, instead of remaining part of your shipâs mass. You can reel the reactor back in when itâs
time to fire your engines for your deceleration phase. Thereâs also the option to trail a radiator
behind you, to help dissipate the excess heat all of your shipboard activities will generate. Indeed, interstellar craft might sport many
thin radiating fins protruding from the hull. You could even add things to the front--radar,
anti-collision lasers, or thin sails sent drifting in front of you to absorb collisions
and minimize damage to the actual ship. But then again, maybe not, because while losing
an antenna or radiating fin or a few scraps of a thin fuel or water tank might not be
a big deal, the fact is that the debris destroying your antennae is moving extremely fast, relative
to your ship. Even small pebble- or sand grain-sized particles
are essentially bombs at interplanetary speeds - and at interstellar speeds, those grains
are atomic bombs. Any ships coming into an inhabited system
might need to retract such flimsy protuberances. Should a radiating fin or antenna be knocked
off your ship by interplanetary debris, at the speed youâll be moving, even as you
decelerate from interstellar speeds into the system, your lost equipment just became an
entire nuclear arsenalâs worth of kinetic energy, rocketing towards your intended destination. Just imagine some space freighter decelerating
into a densely inhabited system; it would be disastrous to essentially nuke the world
you spent decades, or even centuries, to reach, with a loose or broken piece of hardware--so
all of your protuberances and extrusions need to be pulled in to minimize your shipâs
cross section again when you are in a system, in interplanetary areas. Unless of course you are an invading fleet,
in which case all that potential debris becomes your targetâs problem rather than yours. Though speaking of space freighters, those
are probably one of those things youâd only see in science fiction - specifically of the
giant mega-freighters plowing through deep space variety. Thereâs plenty of room for freighters, but
if weâre talking about moving large quantities of raw materials around, realistically, those
huge container freighters really arenât the best way to ship your resources. Instead, youâd attach a small ship to a
large payload, essentially a slowboat, meekly cruising back towards the world or habitat
or station that requires the materials, taking many years to arrive. A megaton of iron is just as valuable when
it is on its way as it is the moment you acquire it. Letâs consider 3 likely cargos of raw materials
one might haul around in the future. Ice, Gas, and metal ores. Letâs start with ice. Water in any form is rare in the inner system--outside
of Earth, of course--but out past the asteroid belt, past the âfrost line,â there are
innumerable icy bodies, asteroids, comets, and ice-covered moons around the gas giants. This makes the concept of transporting large
quantities of water very logical; if youâre building rotating habitats in the inner system,
youâll need that water to be shipped in. However, those icy bodies arenât entirely
pure water ice--they typically also contain chemicals such as frozen ammonia, methane,
and so on--a little perk, resources that can be put to other uses. If your shipâs job is pushing ice out from
Saturnâs Rings or the Kuiper Belt, thatâs exactly what you would do: push it. You wouldnât cut the icy body into pieces
and haul them into a massive freighter, youâd simply attach your ship, which is probably
rather small, to the icy body and use your engines to accelerate the body towards your
destination. However, you really arenât just shoving
the cargo--you donât want to send a comet rocketing into the inner system on a ballistic
trajectory. You will probably arrive at the ice with equipment
that is basically a set of extra engines and a protective wrap. As you push the ice in-system, if it is unprotected,
it will start to melt and outgas--which is what gives us those beautiful comet tails
we all know. So youâll want to wrap the ice in some sort
of thermal protection--something that will keep the ice cold and frozen even as you approach
the warmer inner system. Youâll want the wrap to maintain some pressure
inside, so that any phase changes that do occur will be the ice melting into a liquid,
instead of sublimating into a vapor. The wrap will also probably be reflective,
especially to infrared radiation. While comets are beautiful to see, in this
situation, we definitely want to avoid losing all that precious water. However, any sublimation and outgassing could
make handy propellants to push that comet around, and an alternative to wrapping the
comet. You could follow the comet closely and collect
the gas and vapor so you donât lose those resources to the vacuum. Once collected, you have many options for
using these gasses: process the mix and separate all the molecules. Electrolyze the water to get the hydrogen
to dump into your fusion drive or reactor. Or perhaps your ship has great mirrors or
solar sails, which you can use to reflect and focus an energy beam at the comet to sublimate
the ice into natural propellant. This superheated gas and vapor would push
the comet in-system quite powerfully, and would get to its destination more quickly. However, this method requires some decision
making; how much of that material are you willing to lose in order to get the comet
to its destination faster? You might of course do this entirely automated,
but if you need on-site crew, they need a place to live, and youâre never going to
be in a rush on ice, since the slower you go the higher your profit, minus the cost
of salaries and equipment maintenance, which Iâd imagine will be the dominant factors
in deciding how slow you can push ice. Theyâre going to want to make a bit of a
home out of that place, and of course might carve in ice tunnels or extract minerals to
build more stuff â icy bodies typically have plenty of rock mixed in there too. This gets one thinking about ore freighters
as well. Now you might opt to move a metal or carbon
rich asteroid this same way. If thatâs the case, given that many a freighter
or colony ship might also be a mobile refinery and factory, they might not be moving raw
materials but instead be making stuff out of them or refining as they go. I should also note that ship hulls and space
habitat hulls are likely to be fairly generic, so you might start moving an asteroid and
turning bits of it into a ship plating and end with a classic big space freighter full
of a mix of ore, refined metal, and manufactured goods, all surrounded by cheap, standardized
hull plating you could also sell at your destination. One-use freighters in a sense, with a core
ship for the crew and sophisticated components you couldnât make en route. As to moving gas, the reality is that you
probably would not, in favor of pressurizing and cooling it enough to be a liquid or solid. A great big balloon is going to leak on you,
both from all the extra debris it might be punctured by from its larger size, and because
any container has to be able to keep tiny gas molecules from slipping through, and thatâs
very hard to do with hydrogen for instance since its smaller than the atoms of the container
material. So a gas freighter might end up looking a
bit more like our classic image as it probably would be a ton of tanks filled with gas or
liquid strapped to a ship. That crew doesnât really need much room
compared to the sizes involved, especially in terms of the habitat drum. This is all assuming you even need a crew
but as we often mention on this show, the concept of a sophisticated ship computer able
to replace a human crew doesnât necessarily mean its âunmannedâ. By and large you donât need much brains
for navigating space but many of the other tasks might start edging into an area where
you need something animal-smart, and if it needs human-smart, you use a human. Or a person anyway, even if they might never
have been born in the classic sense. Artificial intelligence is a rather vague
concept when you get to higher levels. Whether itâs an unmanned ship or a manned
one, and for all the vagueness of that term in a futuristic sense, a ship is always going
to have a computer on board. What else does it need? Well air and water and warmth if anything
biological is in play, and a means to clean and recycle both. Itâs tempting to assume spaceships will
always have gardens or hydroponics onboard if people are on board, but plants arenât
the most mass-efficient way to scrub carbon dioxide out of the air. Short-run ships or those that need to accelerate
fast like a warship probably wouldnât bother. For everyone else, it offers at least a supplement
of fresh food and something green to look at. Your crew needs to bring some home along though,
and will always try to, within the limitations of the ship and mission. A ship that needs to be able to accelerate
very fast and suddenly might have problems keeping a garden or hydroponics bay going
so it doesnât get smashed around by the sudden jerks or effective high-gravity, but
I suspect that would simply results in lots of inventions to make it practical rather
than abstaining from having them. When it comes to living quarters, âas close
to home as possibleâ will always apply, and where it canât we either do our best,
go without, or modify ourselves for it to not matter. That could be a minor thing like everyone
wearing sunglasses and sunscreen because the ship or work environment in space was heavily
flooded with UV light, or more likely the reverse, having sunrooms you could sit in
that let you soak up the rays while the ship tended to be otherwise dim. Alternatively it could be big stuff like modifying
a human to not need gravity, or handle gravity and acceleration better, or even uploading
minds into computers or cyborgs to handle extreme conditions like acceleration or radiation. Ships that spend a lot of time cruising or
only undergo weak long accelerations like an ion drive , rather than fast burns like
chemical rockets, are generally going to be able to have a much more regular layout of
things like dining and food preparation and bathrooms and gardens. Alternatively, ships that do have to be ready
for rapid burns need to have very specialized and specific places for eating, drinking,
disposing of waste, and even sleeping. You might need to strap in. If the ship needs to be able to rapidly accelerate
on short notice, you need padded walls or airbags in them, because a sudden 5-g burn
might slam someone into the ceiling or wall of a corridor hard enough to shatter their
bones. You might go the other way though and include
padded suits instead, or pad objects that might not be secured. Pet collars on such a maneuverable spaceship,
and Iâm sure most with crews would have pets too, would likely feature air bags or
balloons that could act as impromptu life support bubbles. Amusingly a coffee cup might have an accelerometer
in it that triggered a lid and blew out a balloon, many tools might too. We often see boarding parties in science fiction
fighting through corridors, but less so debris bouncing around or the combatants trying to
blast or squirm through corridors that have blown out airbags down their length. On any such ship though, every bit of equipment
is going to be secured when not in use and likely attached to tethers even when in use. A hammer or screwdriver kicked down a corridor
by a rapid burn is a lethal object. Such ships wouldnât have large rotating
sections much either. We often picture stations or ships that provide
gravity by rotation as being the whole thing rotating, but as weâve noted in other episodes,
usually the rotating section would be inside a larger superstructure, and on a ship, except
a classic slowboat generation ark ship, that rotating drum is likely to be only a small
part. They are a place for sleeping and relaxation
or stationary work, like offices, kitchens, or workshops. A ship doesnât have to have only one drum
though, it can have several of various sizes, even nested inside each other and providing
different levels of gravity. Your issue there is that the smaller in diameter
a drum is, the more times per minute it needs to rotate to produce the same gravity. Evidence suggests 2 RPM is beneath our threshold
to feel nauseous but more RPMs are probably easy to acclimate to. That limits how small a drum can be, though
it can be smaller if you donât need full gravity and odds are some small workshop in
a distant corner of a ship only needs enough gravity so stuff falls and things feel up
and down, moon gravity might be enough. Propulsion is important for how a ship will
be laid out inside, but of course itâs a big deal for overall ship configuration too. Indeed in the case of a ship attempting to
achieve high delta-v, meaning a high cruise velocity, the so-called propulsion bus may
have to represent the bulk of total mass: the âpayloadâ, where youâd have crew
quarters, cargo and life support, would look relatively small even if itâs in the thousands
of tons, and it would be dwarfed by the engines, waste heat removal systems / radiators, and
the fuel tanks, which may be the largest part of the ship, to obtain a high mass ratio. Letâs talk a little more about streamlining
the outside of ships though. For the most part, as I mentioned earlier,
ships donât need be streamlined other than to cut down on overall mass and cross section,
and might feature a lot of retractable equipment in exterior bays so you could store them under
more cover when not in use and make it easier to get at them for repairs, be it antennas
or radiators or sensors or big point-defense guns. Weâve got some special cases for streamlining
though. Needless to say if you want your ship to be
able to land on a planet or move into a gas giant it needs streamlining. Such ships have an excuse for more of the
jet or plane look, as they have to deal with lift since they are going through air and
gravity fields. However space is not a true vacuum and at
high enough speeds even in intergalactic space, as close to true vacuum as you can get outside
a lab, it can act like air giving drag and friction, though not lift, or much anyway. If youâre flying above a galaxy at ultra-relativistic
speeds you might get a tiny amount of lift you needed to account for. This does mean relativistic ships want to
have a nose on them, so that if stuff hits, it deflects away, rather than just impacting
against a flat wall. Of course at such speeds even a grain of sand
is like a big bomb but it still helps to have that nose-cone, and I was apparently rather
unintentionally ambiguous about that in our Interstellar Travel Challenges episode where
we looked at the issues and options for ships moving at a decent percentage of light speed. I also mentioned there that you probably would
never want to build a ship that ever went anywhere near light speed, but there are cases
and setups where that would make sense. All the gas and dust lying around will be
acting as drag, and even a ship with infinite fuel, either by some magic clarketech or by
a pushing laser, will eventually reach a maximum speed where the ship drive or pushing laser
equals out in thrust to the drag of the interstellar or intergalactic medium
Even if you do reach highly relativistic speeds, you have a new problem, because even if you
can clear out every speck of debris in front of you, that ambient radiation everywhere
in the universe becomes a problem. A really skinny ship with a magic stardrive
can potentially get insanely fast, but would rely on technology we have not even an inkling
of yet, and maybe ever. A pushing laser can be done though but introduces
a new problem. A great big sail or mirror on the back also
massively increases your ships cross section. The better you can focus that beam the smaller
that cross section can be, but even if you can pull off a long relay of pushing stations
so the beam is always tight, you still get an issue with light red shifting, and blue
shifting. The faster youâre going, the more red-shifted
the pushing beam will be, and thus the weaker it is and the less thrust it offers. On the flip side, all the ambient radiation
youâre plowing through will be more blue shifted, and thus provide more thrust against
you. Inside a galaxy this radiation drag is going
to be way less than from all the gas and dust, even keeping in mind that thereâs a lot
more ambient radiation from all those stars. Out in the intergalactic void though you still
have to tackle Cosmic Background Microwave Radiation, which is evenly dispersed everywhere. Far, far in the distant future this will grow
ever weaker, as it redshifts as the Universe expands, but right now it places a barrier
at about a gamma of 133, according to calculations by Colin McInnes in his book âSolar Sailingâ,
where the red shifted pushing beam and the blue-shifted CMB radiation equalize out. Gamma by the way is the term for the Lorentz-factor
in Special Relativity, weâve discussed that more in other episodes but for a quick abridged
version, this is how much time slows down for you relative to the outside universe or
how much of your total energy is in kinetic motion rather than mass energy. A gamma of 133 would mean 133 seconds would
pass on other peopleâs clocks for every second you experienced, or basically a bit
over two minutes for each of your seconds. It also means youâd be moving at 99.9972%
of light speed. In other words, if you were making the trip
to the Andromeda Galaxy at this speed, 2.5 million light years away, you would personally
experience only 19,000 years on the voyage. At that speed incidentally the light from
any signal sent when you left would only arrive about a century before you on your 2.5 million
year journey. I doubt you could ever get to that speed,
but it does mean that even if you do, your intergalactic crews still either need radical
life extension or very-multi-generation-ships for the trips. Even frozen crews, as we mentioned in Sleeper
Ships, need special measures to be taken to avoid being killed by buildup of radiation
damage from the tiny amounts given off by the radioactive potassium isotopes in your
bones and other isotopes in your body. Such ships can start slowing by just cutting
off their pushing laser. Slowing down cost fuel and energy, so you
want to get all the freebies you can, and at these speeds youâd start by slowing using
ambient blue-shifted energy, then cosmic gas and dust, then hopefully by vanguard probes
hitting stars ahead of you and building pushing lasers to slow you, using the technique we
discussed in Exodus Fleet. Magnetic sails can also help you with deceleration,
their effectiveness increases with initial speed, and even todayâs proposed designs
could allow a braking rate of several milligees, though it may be less in intergalactic space
due to its lesser density. The faster youâre going though, the more
each mote of dust or photon you collide with reduces your speed, and here we see yet again
how much ship design has to vary with things specific to purpose rather than technology
available let alone any constant rules of ship design that apply across all levels of
mission purpose, technology, and aesthetics. Iâll also note though before we close out
that what we think of as a cool looking spaceship, or machine, often is altered by our exposure
to it. When you get around to a rocket or a jet or
a sportscar donât look that particularly awesome until you know what they can do, and
your mind tends to start altering what you think is cool to look at. Your default spaceship is likely to look a
lot more boring and plain than what we see in scifi, but our descendants in the future
might think those designs look pretty cool. Iâd like to have spent some time looking
at a lot of the classic scifi spaceships we see and talking about what their flaws and
window dressing was, but we should wrap up here for the sake of brevity and Iâll just
give a quick shout out to Spacedock as a fun channel to look into the pros and cons of
all those schematics of spaceships from our favorite shows and films. Science and technology and purpose ultimately
take center stage on design, and if you want to contemplate how a spaceship might be designed
properly, it helps to have that science background. Iâd also say though, and it's an approach
we favor here on SFIA, that we already know itâs beneficial to have a science background
and the important part is learning and practicing with that knowledge on fun topics. Thatâs something our friends at Brilliant
excel at. Brilliant is a problem solving website and
app with a hands-on approach, and not only do they have over 50 courses to help you learn
new science and math, but they also have daily challenges that can reinforce and strengthen
material in your head. They make it fun and interactive though, because
we not only find it easier to set aside time to learn when itâs fun, but we learn better
that way too. They also appreciate that we often have to
squeeze our learning in when we have time, so they have a great mobile app that lets
you access their courses on the go and use them even when your internet connection is
spotty. If youâd like to learn more science, math,
and computer science, go to brilliant.org/IsaacArthur and sign up for free. And also, the first 200 people that go to
that link will get 20% off the annual Premium subscription, so you can solve all the daily
challenges in the archives and access dozens of problem solving courses. We were looking at spaceship design today
and how that might get us out in the solar system and eventually the galaxy. Next week weâll be exploring the possibility
that we might not ever get out there, either because we canât design the ships or we
kill ourselves off first or some other worrisome notions as we return to our Fermi Paradox
Great Filters series to look at Late Filters, things that might prevent civilizations as
advanced as ours already from going the full distance to be galactic empires. The week after that, weâll have our poll-winning
topic, âGods & Monsters: Space as Lovecraft envisioned itâ, which beat out itâs 4
competitors, and thank you to the over 16,000 folks who voted in that poll. For alerts when those and other episodes come
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have a Great Week!
Praised be Arthur. Awesome.
Arthur, could you please look at ongoing UFO talk, and openly speculate (reductio at absurdem, et.al.) what we know about aliens visiting the solar system (what would be possible, what would be ridiculous) and "sherlock holmes" backwards from existing UFO reports so that IF, YES we are being visited, what can we conclude from that premise to be true and what not true?
Well, shoot. He kind of teased at the beginning that he'd be reviewing different sci-fi ship designs. I was really looking forward to hearing his take on various designs.
I do subscribe to Spacedock, and love his breakdowns of ship designs.
I think the ship that best matches Isaac's points is the Discovery from 2001:A Space Odyssey. Long, symmetrical design with the hab section kept far away from the radiation of the muon-catalyzed, aommonia-fueled fusion engines.
I can think of four categories of spaceships
I didn't know about the background cosmic radiation imposing a speed limit. That's fascinating - I knew about the conventional drag for any starship that makes it riskier to push speeds above about 10-20% of light speed, but not that.
I figure any crews that make an interstellar trip will definitely be effectively immortal, and they'll have medical treatments to prevent them from getting bored no matter how many times they do the same routine over and over again. That specific type of behavioral modification is something we tend not to think about, but it always seemed likely to me for particularly tedious crewed space trips.
I'm confused by the statement that volatiles for cylinder habitats would be transported to near-Earth construction sites by attaching engines to small moons. Only a fraction of any moon is going to be the volatiles you're interested in. Lots of that moon will be junk like silicon and oxygen. Plus, like he said, you will need to cover the whole dumb thing in insulation or suffer considerable losses during transit. Time is a critical resource in any construction project. Often time is so valuable that you're willing to spend a lot of energy to save a small amount of time.
From that perspective, I think it probably would make sense to use freighters to move purified shipments of volatiles.
A second option would be to complete the habitat hardware build, staff it with people, and then fly the whole thing beyond the frost line to pick up volatiles.
Probably the most likely option would be to purify small containers of volatiles, and then to fire them toward the inner solar system via a mass driver. At the destination, the containers are either "caught" by a stationary facility (if you can manage the precision needed), "caught" by a mobile tug with a fusion engine, or decelerate themselves using the volatiles as fuel.