Do you prefer real-world settings or "science fantasy"?

[Nyrath]

I seriously doubt there's 10,000 star systems PERIOD within 100 lightyears of our system leave alone 10,000 ones that actually have habitable planets. Or planets PERIOD.

According to the best figures I have available, a sphere with a radius of 100 light years centered on Sol should contain roughly 10,000 stars. With a large error bar, of course. (between 8.33x10^-2 and 8.67x10^-2 stars per cubic parsec)

If you accept Dr. Jill Tarter's paper on stars likely to host a planet that some conceivable form of life could survive on, there would be very very roughly about 2000 such stars.

[Nyrath]

Getting back on topic, I recently found this little quote:

Copernicus’ Law of Science Fiction: Bending the laws of physics out of service to the story is fine, doing it out of ignorance is unconscionable.

[Junghalli]

I'm not entirely convinced you could brake on an interstellar medium for long enough to really make relativistic flight with high mass craft reasonable. If someone could do the calcs that'd be grand, but don't bussard scoops only start being able to scoop shit up at a good fraction of C (meaning braking on interstellar hydrogen via this wouldn't work below that speed either)? Are mag sails any better in this respect?

Estimates for how fast a Bussard ramjet would need to be going for the scoop to work vary between .01-.06 c according to Atomic Rocket. A magsail brake that shaved off the need for external fuel above the last .06 c of decelleration would still be enormously useful. If your starting velocity is .9 c, for instance, I calculate you would need to carry more than 700 times as much fuel to decellerate without a magsail as you would need with it, and that's just based on kinetic energy, without factoring in the mass ratio death spiral problem (past a certain point you end up using up most of your fuel to accelerate the rest of your fuel instead of your ship).

At any rate, you can find good information about magsails here. The section where they discuss braking starts on page 26. They calculate 30 years for a 1 ton (+968 kg for the magsail brake loop) probe to decellerate from .1 c to ~300 km/s using a magsail with a radius of 28 km, so apparently it works down to at least that speed. That's rather slow decelleration, but reasonable for a voyage lasting hundreds of years anyway. Decellerating from 300 km/s would be easy with a number of plausible secondary propulsion systems. Performance increases sharply with speed, so decellerating from higher fractions of c would not add much decelleration time. They also give the magsail drag formula:

A MagSail field will also deflect ionized material in the interstellar medium (ISM), and will therefore
produce drag when active. The magnitude of this drag can be estimated by treating the MagSail as a
dipole, which will form a magnetosphere whose size is set by equilibrium between the dynamic pressure of
the ISM and the magnetic field pressure. The drag force is calculated to be:
Fdrag = 1.175 π (Ni mi μ1/2 I r2 V2)2/3
where Ni and mi are the number density and mass of ISM ions, and V is the vehicle velocity through
the ISM, nominally 0.1c = 3 x 107 m/s.
For the baseline 100 meter loop, and with an assumed density of the ISM of 105 ions/m3, the drag is
33.6 N.

The paper is also a good introduction to the sailbeam concept, which is basically like a laser lightsail only instead of shining a laser directly on the ship you use the laser to send a bunch of tiny sails flying at the ship, and the ship uses an onboard laser to turn them into ionized gas which hits the magsail and pushes it forward. It saves you the engineering difficulties of having to build a laser capable of pushing a ship at light year distances.

-------

It is also a matter of the audience's preconceptions and expectations. If they are fed up on interstellar alliances and galactic empires a realistic polity will inevitably look small.

One good way to counteract this would be to show the great scale and diversity that you could fit into a single solar system. You could easily support more people in a single system than many "galactic empires" probably do in all their vast dominions. Of course, as I said, if you drop the idea that everything has to happen on the scale of natural human lifetimes then you can easily have vibrant interstellar settings.

I generally avoid writing nonhuman viewpoint characters, for the simple reason that their mindset will logically be completely alien from that of humans like myself.

Uploads could still be quite human mentally. They would only become inhuman mentally if they deliberately modified the brain simulator program to make them so. It's pretty plausible that most of them would choose not to do that - I imagine people with no attachment to their mental humanity would be considerably rarer than people with no attachment to their physical humanity.

Of course for the kind of setting I was talking about there are other options, like showing the war from the perspective of some third party caught in the middle of it.

I can see the point you are making, but in the end that is not really a limitation on soft sci-fi, merely on writer imagination. You can have every kind of uploading, "super intelligence", nano-gizmos or other AI-wankery in a soft setting as well (say, the Culture or OA as examples) and explore the realistic consequences of those things in such environs. The breaking point is really that in a soft story you can have any realistic story element and any unrealistic one, while in a "hard" such you are restricted to the realistic ones only. Therefore by definition it is more restricted; soft sci-fi only grants more options, but removes none.

That is true. I don't dispute that it is more limited, I dispute that it's some kind of creative straightjacket that severely limits what the author can do. There's still lots of things you can do within the limits of hard science.

[Junghalli]

Correction in my reply to Batman: a laser lightsail has thrust of 6.7 newtons per gigawatt, not 1 newton per 6.7 gigawatts. The required energy and area for the solar panel should therefore be divided by 6.7 from my estimates.

reference.

[adam_grif]

Had no idea the Bussard scoop could operate at such low velocities. For some reason I had it in my head you had to be something like 20% of C to get it running.

So if we can get down to <1% C with the mag-sail drag, that makes stationary positions providing acceleration then ships slowing down under their own power much more reasonable over interstellar distances.

The other day I got all depressed because I read somewhere that an objects KE exceeds it's rest mass converted to energy at .94 C (or somewhere around there), meaning to accelerate a mass of X up to that speed you need X/2 matter combined with X/2 antimatter, not counting the excess you need to accelerate the fuel up with it, and assuming magical 100% conversion efficiency.

If you had to slow down under power the whole way you'd thus need to carry >X antimatter and >X matter to ship X cargo. Which is a ridiculous amount. Otherwise you're forced to go between fixed positions with some kind of beam powered acceleration and deceleration, meaning you'll only ever be boldly going where many men have been before.

But this is good news, yes.

[Shinova]

Prefer soft sci-fi because of the bigger variety of possible settings, and because big honkin space guns and wonked psychic powers of doom are AWESOME.

[bz249]

I prefer stories where characters/groups have beleivable (hard) motivations and goals instead of doing unreasonable (soft) things. That's where most so-called hard sci-fis fail, by keeping the physics "hard" (by the way from late eighteenth century point of view steampunk is hard sci-fi while yesterdays BBC World News are soft sci-fi) they just make setting which are nonsense from economical point of view.

[RedImperator]

they just make setting which are nonsense from economical point of view.

Wait, what? Soft sci-fi more often than not transplants 21st century Earth economics (or the Gilded Age, or the high middle ages, or the Roman Empire) into a setting full of magi-tech and an entire galaxy's worth of natural resources, and you're bitching about hard sci-fi not having realistic economics?

[bz249]

they just make setting which are nonsense from economical point of view.

Wait, what? Soft sci-fi more often than not transplants 21st century Earth economics (or the Gilded Age, or the high middle ages, or the Roman Empire) into a setting full of magi-tech and an entire galaxy's worth of natural resources, and you're bitching about hard sci-fi not having realistic economics?

For example interstellar travel is really stupid thing, or doing anything in space other than tying yourself to a certain dustball. Moving things in space are tremendously costly (or it take millions of years), that's why moving anything is a really bad idea. There is hardly anything out there worth the cost of transportation with any plausible drive we could have since it requires more resources than the amount of resource it can offer. One must really think hard why to do anything in space under those settings (apart from one way trips to build a colony somewhere).

[Junghalli]

For example interstellar travel is really stupid thing, or doing anything in space other than tying yourself to a certain dustball. Moving things in space are tremendously costly (or it take millions of years), that's why moving anything is a really bad idea. There is hardly anything out there worth the cost of transportation with any plausible drive we could have since it requires more resources than the amount of resource it can offer. One must really think hard why to do anything in space under those settings (apart from one way trips to build a colony somewhere).

Same reason we send space probes to Mars. We want to see what's there, and it's a trivial expenditure compared to the resources a civilization that exploits even 1% of the resources of our solar system would have access to. And once you have visited a system travel there need not be expensive if you ditch the really kind of silly concept that you must transport living humans. Upload their mind states and send them on a comm laser.

[bz249]

Same reason we send space probes to Mars. We want to see what's there, and it's a trivial expenditure compared to the resources a civilization that exploits even 1% of the resources of our solar system would have access to. And once you have visited a system travel there need not be expensive if you ditch the really kind of silly concept that you must transport living humans. Upload their mind states and send them on a comm laser.

Yes since we've never been on the Mars what is out there might be interesting. Now imagine if we had sent probes to one houndred systems.. and we find exactly nothing there. You should not, the physical laws are the same, the elements are the same. Star systems would be well... the same. Would one send a probe for the next one? Or how many people going yearly to Bumbfuck, Idaho on touristic purposes (a trivial expenditure at our current technological level)?

Also it is interesting how to exploit 1% of the resources of the Solar System based on our knowledge. Since space travel is a very energy inefficient (simply because of conservation of momentum and energy), digging here on Earth would always be the economical solution. Unless we have:
- a way different method of propulsion (some whacky reactionless drive)
- energy would be costless (and even than, digging here on Earth would be the better option)
it is rather difficult to imagine some self-sustained colonization of the Solar System.

[Junghalli]

Yes since we've never been on the Mars what is out there might be interesting. Now imagine if we had sent probes to one houndred systems.. and we find exactly nothing there. You should not, the physical laws are the same, the elements are the same. Star systems would be well... the same. Would one send a probe for the next one? Or how many people going yearly to Bumbfuck, Idaho on touristic purposes (a trivial expenditure at our current technological level)?

There can't be anything interesting in other solar systems? Different planetary configurations can't be scientifically interesting (most of the exoplanets we've found do not look like planets in the solar system)? Alien ecologies can't be interesting? Intelligent aliens can't be interesting? You must be easily bored.

Also it is interesting how to exploit 1% of the resources of the Solar System based on our knowledge. Since space travel is a very energy inefficient (simply because of conservation of momentum and energy), digging here on Earth would always be the economical solution. Unless we have:
- a way different method of propulsion (some whacky reactionless drive)
- energy would be costless (and even than, digging here on Earth would be the better option)
it is rather difficult to imagine some self-sustained colonization of the Solar System.

At this point I could start bringing up hypothetical scenarios by which space colonization would be profitable, but that actually isn't necessary. All you need is AI + Von Neumann machines + people who have any interest in exploiting the solar system for any reason. AI and Von Neumanns are pretty hard SF and the combination is Kryptonite to a lot of our assumptions about how economics works* (since it has the potential to easily give every human basically a giant army of perfectly obedient robots).

* Well, not exactly. Technically, it doesn't fundamentally change anything. But it does have the potential to turn every human into the equivalent of a billionaire, provided sufficient raw resources are available.

[bz249]

For example interstellar travel is really stupid thing, or doing anything in space other than tying yourself to a certain dustball.

Another person not thinking with habitats!

Why should I, materials have to be moved there, so better start with an already existing asteroid (a dustball). It is way cheaper to construct anything where the resources are, than to mine the resources and move to somewhere else. Unless of course cost is of no importance.

Moving things in space are tremendously costly (or it take millions of years), that's why moving anything is a really bad idea.

Two errors:

Poor logic: just because something is costly doesn't mean it is a bad idea. The benefit may outweigh the cost.

Ok let us start from the very principles: the conservation of momentum and energy. If we have a spaceship, the following equations will hold for a burst (in center of mass system).

m(fuel)*u(fuel)=M(ship)*v(ship)

from that v(ship)=m(fuel)/M(ship)*u(fuel)

The kinetic energy you gave to the fuel (lets calculate in a classical way, because it is easier)

0.5*m(fuel)*u(fuel)^2

The kinetic energy of the ship

0.5*M(ship)*v(ship)^2=0.5*m(fuel)*u(fuel)^2*[m(fuel)/M(ship)]

So a burst of rocket drive have an energy efficiency of m(fuel)/[M(ship)+m(fuel)]

For any normal spaceship design, the mass of the ship outweight the mass of the fuel by orders of magnitude, (unless you have a gun-like system... but then stopping at the destination would still be an issue). Thus you can expect a very poor energy efficiency.

Incorrect premise: moving things in space are not in fact tremendously costly, nor does it take millions of years. Consider that we have landed men on the moon and brought them back - alive - in the real world.

Cost of course matters nothing when we think about exploration, going to the Moon would have worth any price that time, since the thing was about going there. In the meantime, the astronaut brought back 381 kgs of lunar stone, for a mere 145.000.000.000$ (current value).

Okay they have to maneuver in and out of Earth gravity well, but using plausible scientific principles there is no way that you can apply enough delta v on anything for a reasonable cost, for the simple reason that most of the energy is wasted on accelerating the fuel.

There is hardly anything out there worth the cost of transportation with any plausible drive we could have since it requires more resources than the amount of resource it can offer.

Circular logic. Let me reword it: Since it costs more than the benefit can be, there is no benefit out there worth the cost.

What is out there which is unavailable in Earth for less of an investment? If there are no unknown elements* (there aren't), alloys (there aren't) and molecules (there aren't). Then all you have to compare the cost of transportation, and it is high and it would remain high if you want reasonable timescales**. Reasonable timescales means: the material would still needed by the time it arrives; and the group which launched it would still exists.

*you may say He3 isotope, but it is such an abysmal quantity, that even it is worth collecting, it is better used where it is.

**by applying a very small delta v the cost could be reduced, but the price is the package will arrive very late

One must really think hard why to do anything in space under those settings (apart from one way trips to build a colony somewhere).

Science (doing this today), tourism (doing this today, though it isn't profitable yet), living space (habitats), energy (solar power satellites - a company is planning to do this today, and the only reason we aren't doing it now is coal remains so cheap).

Raw materials from space could be used to support the other goals; mining the moon to build habitats, capturing asteroids to build solar power satellites, etc.

Science: can be done, sure it is not cost sensitive.
Tourism: can be done for sure it is for the rich people it should not be cost sensitive.
Colonization: possible, but only as one way trips, go there, live there and be forgotten.
Space mining: cheaper to use wherever it is, then you don't have to add an inefficient transportation system
Power satellites: that will never happen, unless we will have too much energy to lob something there (that case there is no need for those satellites) or we have too little energy to put something up there. If you would like to replace just one large nuclear reactor you need something of 4x4 km2.

[bz249]

Yes since we've never been on the Mars what is out there might be interesting. Now imagine if we had sent probes to one houndred systems.. and we find exactly nothing there. You should not, the physical laws are the same, the elements are the same. Star systems would be well... the same. Would one send a probe for the next one? Or how many people going yearly to Bumbfuck, Idaho on touristic purposes (a trivial expenditure at our current technological level)?

There can't be anything interesting in other solar systems? Different planetary configurations can't be scientifically interesting (most of the exoplanets we've found do not look like planets in the solar system)? Alien ecologies can't be interesting? Intelligent aliens can't be interesting? You must be easily bored.

If alien ecologies exist at all... currently we can not even make an educated guess about if we are not alone at all. The only parameter we know in the Drake-formula, is the number of stars. About the others we can not make even an educated guess. The number of planets we can estimate in the not-so-far future.

If aliens exist it is a different setting. Then it might be interesting of going there. But to see rocks, well

[Junghalli]

What is out there which is unavailable in Earth for less of an investment? If there are no unknown elements* (there aren't), alloys (there aren't) and molecules (there aren't).

http://www.tricitiesnet.com/donsastronomy/mining.html

There are 22 metallic elements present in C-Type asteroids which exceed (sometimes to an astonishing degree) the percentages found in the Earth's crust. And nearly all of them are important and/or scarce on Earth. They range from Copper (about 1.5 X Earth Crust Abundance (ECA)), to Platinum (27 X ECA), to Tellurium (2100 X ECA).
<snip>
Any element valued at $500,000 per M.T. ($500 per kg. or about $227.50 per lb.) or more (22 elements) would be a likely candidate for export to Earth.

You may also want to check out PERMANENT.

Of course, if we (reasonably) assume a future with AI and Von Neumanns we do not need a profit motive. If every person on Earth had resources comparable to billionaires today you would have no shortage of eccentrics willing to launch constructors into the asteroid belt because they think space exploration is cool. And if there aren't enough resources on Earth for everyone to have that level of wealth even with that technology, well, that's a material incentive for developing space right there.

Tourism: can be done for sure it is for the rich people it should not be cost sensitive.

It is reasonable to imagine future scenarios in which the average citizen would be "rich" by our standards. After all, leaving aside for a moment the Von Neumann this and Intelligent Explosion that, the average Westerner today is rather wealthy by the standards of the Middle Ages.

Colonization: possible, but only as one way trips, go there, live there and be forgotten.

Set up a mind uploading/downloading system at the colony. Hook it up to a comm laser. People can come and go very cheaply, assuming the uploading and re-cloning procedure isn't expensive (eventually it could probably be made cheap with economies of scale and engineering experience and the like; it is complex but does not require great energy or rare elements).

If alien ecologies exist at all... currently we can not even make an educated guess about if we are not alone at all. The only parameter we know in the Drake-formula, is the number of stars. About the others we can not make even an educated guess. The number of planets we can estimate in the not-so-far future.

We are talking about science fiction. It is up to the author whether he wants to have aliens or not.

If aliens exist it is a different setting. Then it might be interesting of going there. But to see rocks, well

I think some scientists might be rather interested in seeing rocks from different star systems. In a civilization with Von Neumanns or an appreciable percentage of the solar system's resources under exploitation that can be sufficient reason to send ships to the stars.

[Peptuck]

But to see rocks, well

Hey, rocks and geology are actually pretty interesting. Take a geology course sometime.

[Nyrath]

For any normal spaceship design, the mass of the ship outweight the mass of the fuel by orders of magnitude, (unless you have a gun-like system... but then stopping at the destination would still be an issue). Thus you can expect a very poor energy efficiency.

Ummmm, you lost me there.

For most realistic designs, one typically has the mass of the propellant/fuel outweighing the mass of the ship by a factor of three or so, not the other way around. And not by orders of magnitude.

An economical spacecraft would have a mass ratio of about 4, which is a propellant fraction of 75%. A mass ratio below 2 (propellant fraction of 50%) is almost unheard of.

[bz249]

For any normal spaceship design, the mass of the ship outweight the mass of the fuel by orders of magnitude, (unless you have a gun-like system... but then stopping at the destination would still be an issue). Thus you can expect a very poor energy efficiency.

Ummmm, you lost me there.

For most realistic designs, one typically has the mass of the propellant/fuel outweighing the mass of the ship by a factor of three or so, not the other way around. And not by orders of magnitude.

An economical spacecraft would have a mass ratio of about 4, which is a propellant fraction of 75%. A mass ratio below 2 (propellant fraction of 50%) is almost unheard of.

Yes, but the fuel is not expended in one short burst, so you accelerate most of the fuel throughout the process. In any given time the ratio of the expended fuel versus the rest of the system is rather small.

[bz249]

So for Vulcain-2 (the main engine of Ariane-5) it is a mere 230kg/s

http://en.wikipedia.org/wiki/Vulcain

Or for the F-1 it is (the main engine of the of the Saturn-V) 5x2600kg/s

http://en.wikipedia.org/wiki/F-1_%28rocket_engine%29

[Batman]

Um-this changes the fact that the vast majority of the mass IS fuel and thus the fuel DOES outmass the vehicle itself-how, exactly?

[Talk738kno]

A solar system can be a big place by itself to human sensibilities, but on any cosmic scale it is utterly insignificant.

Everything is utterly insignificant on any cosmic scale. Take Star Wars' "Galactic" Empire. On the higher end of the estimates, they have millions of systems.

A galaxy has hundreds of billions of stars. Being as generous as possible, the Empire is still a fractional percentage of the galaxy. And, of course, the galaxy is just one of billions of its siblings.

According to the Star Wars saga edition core rulebook, the economy of the galexey runs on billions of worlds.

[Lord of the Abyss]

What is out there which is unavailable in Earth for less of an investment?

Room. Unowned resources on a very large scale. A realistic hard sci-fi future would include such things as AI and Von Neumann machines; which means that individual citizens or small groups can, if allowed, pursue projects on enormous scales. Earth, with billions of people is just too small and restrictive for that sort of thing; people would object if you had a legion of replicating robots disassemble a mountain range for your projects. In space, there's a huge amount of, well, space. You can indulge in large scale projects, do all sorts of things that would be hugely environmentally destructive on Earth, and in general do things that would never be allowed on a world crowded with billions.

[bz249]

Destructionator XIII:

Earth-Mars transit, delta_v on a Hohman transfer: 5.5km/s

thus: having 10% energy efficiency for our rocket, means that one kg on material making the transfer requires: 0.5*5500*5500*10=151MJ energy or 3.2kg of gasoline. Name me one raw material from which you can't get here on Earth 1kg for 3.2kg of gasoline invested in mining and refining! Because that make something economically competitive, to do that easier and cheaper.

Moonshot: Space flight, at our current level, is a fucking hobby (except some surveillance satellites), hobbies does not have to be economical. People are spending on hobbies, they do not have to turn profit. Sending a man to the Moon and back was just for doing that. They made exactly nothing there (nothing which have any serious importance from scientific, economical or technoligal point of view) and we have not send anyone in the last 36 years, and we will not send anyone in the next 10 at least. Because after been there, done that it have fallen out of fashion (happens with hobbies sometimes).

[bz249]

Room. Unowned resources on a very large scale. A realistic hard sci-fi future would include such things as AI and Von Neumann machines; which means that individual citizens or small groups can, if allowed, pursue projects on enormous scales. Earth, with billions of people is just too small and restrictive for that sort of thing; people would object if you had a legion of replicating robots disassemble a mountain range for your projects. In space, there's a huge amount of, well, space. You can indulge in large scale projects, do all sorts of things that would be hugely environmentally destructive on Earth, and in general do things that would never be allowed on a world crowded with billions.

Okay enviromentalism can be an issue. Rich people/society (with very large energy and material budget) can choose to do inefficient thing for enviromental protection/artistic/entratainment... purposes.

[GrayAnderson]

To address the initial question of the thread, I prefer my sci-fi on the harder side, but with a dose of familiarity. If a world is too alien or unfamiliar, I simply have trouble working with it.

That said, I don't mind a few in-built fudges to make the setting/concept work as long as the author "declares their variables" fairly early on and doesn't start sneaking things in after the fact. Basically, I'm willing to work with a slightly more fantastic setting if, after the initial declaration of the setting, the author/director does their best to make it "hard" within the context of the fudge they've set up...though there's a limit on how far I'm willing to let you fudge things before I lose interest. I'm also willing to cut some slack to outdated science (i.e. what you tend to find in H. G. Wells stuff) as well.

Edit: An example of what I like is Stuart's Salvation War series, because once you get beyond the initial conceit, the story is about as hard as anything out there. By contrast, I've had increasing trouble with Star Wars, and even with parts of the Ender's Game series, because of issues with the author(s) not making up their mind about what rules they want to apply. George Lucas is particularly bad in this regard.