Random SF Science Questions

[Cancer]

Re: Random SF Science Questions

 

Any moon of a gas giant that's large enough to have an atmosphere will be in synchronous rotation.

 

Moons that aren't in synchronous rotation will be small, and/or very distant from the GG.

[Yansuf]

Re: Random SF Science Questions

 

GDW in its game 2300AD had several books about a moon of a gas giant that was habitable. The moon was called Aurora, it was tidally locked, but the "twilight zone" was habitable.

I never actually checked their science, but it was my understanding that it was valid.

[Basil]

Re: Random SF Science Questions

 

Photons have much smaller mass than the various gas particles that make up the solar winds - and solar sails are photon powered.

However, particles are SO much rarer than photons, that they have nearly no effect on a light sail in comparison.

[Basil]

Re: Random SF Science Questions

 

Thus, the "day" (the period of the star's apparant period) would be days long, which would lead to ferocious weather, and thus difficult to live there.

I agree with everything you have here, except that I don't understand why long "days" make for severe weather. An earth-mass moon in orbit around Jupiter-mass planet with an orbital period (and hence "day", assuming the moon orbit and planet orbit are approximately coplanar) of about a week

Weather is caused by unequal heating of the surface of a planet (or habitable moon, in this case). The more unequal the heating, the worse the weather. With a "day" of a week, the winds would be devastating. Think of a planet with non-stop hurricanes everywhere, and you get the picture.

 

Minor comment ... you slipped a decimal place there (Titan is 0.022 Earth masses)' date=' but correcting that error actually strengthens your argument.[/quote']

Note, however, that Titan's surface gravity is .147 that of Earth, so the disparity is not as much as one might think.

 

Still, that's less than Luna's surface gravity, so I don't see a Titan- (or Luna-) sized body holding an atmosphere at Earth-like temperatures.

 

No argument here. Because Jovian planets have such hugely strong magnetic fields' date=' I think a strong geodynamo in the "moon" would be essential for any life that might get going there, even if it is outside the principal radiation belts of the gas giant planet it was orbiting.[/quote']

Another reason for a goodly-sized moon: You need enough size to keep/generate enough internal heat to make the body geologically active, and enough size to retain enough water so the geological activity shows up as tectonics. Otherwise, the inorganic carbon cycle stops, and eventually the atmosphere is full of carbon dioxide. That, of course, leads to a runaway greenhouse scenario, and no life can survive (or evolve into existance) because the surface is too hot.

 

If you imagine the moon being so far from the star that it needs that much CO2 to bring the temperature up into the habitable range, life must remain at the pre-photosynthesis level; photosynthesis will pull CO2 out of the air, dropping the temperature to sub-0 (Celcius) levels rather quickly.

 

So again, you'll need a nearly-Earth-sized moon of a GG---which likely means a great big GG.

 

BTW, sychronous rotation is not the only from of gravitational lock. The moon could, for example, rotate three times for every two times it revolved around the GG. Which could shorten the "solar day" down to more reasonable levels.

[Curufea]

Re: Random SF Science Questions

 

???

Ripples of what? Solar sail act by light pressure. Very low light pressure at that. any variation in light pressure will be negligible. Yes, planets would reflect sunlight, but you're comparing that to the overwhelming light coming directly from the sun is like comparing the north wind to a house fan.

If you are talking about ripples in the stream of charged particles, that has already been addressed above. Also negligible.

If it something else entirely, I'm not getting your meaning.

 

Keith "perplexed" Curtis

Gasses/particles, yes. Not photons. The closer you get to planets with atmospheres - or to suns, the less vacuum there is.

[gojira]

Re: Random SF Science Questions

 

Gasses/particles' date=' yes. Not photons. The closer you get to planets with atmospheres - or to suns, the less vacuum there is.[/quote']

 

Hmm, I don't think this is correct. Conventional wisdom says that after you pass some point above a planet you are in space. The accepted limit for Earth is about 115 miles above the surface. From that point on, it's all hard vacuum.

 

(I read math books for fun. I'm currently plowing through a book used to teach NASA engineers during the Apollo space program, Fundamentals of Orbital Dynamics, and that's the value they use.)

 

If you compare that with the diameter of the Earth, about 8000 miles, you can see that the atmosphere hugs the planet pretty closely.

 

I'm not going to even talk about gasses close to a star. Anytime you are close enough to a star to have the "gasses" affect your maneuvering, I think realistically you've burned up a long time ago.

[Thia Halmades]

Re: Random SF Science Questions

 

New Topic: As a novice of physics theory, I get to putz around and discuss things like gravity, mass, particles, waves, etc. Reading up on it gives me an edge when doing 'hard' sci-fi, and making my rubber sci-fi more plausible. So here's one I just don't get (it's actually a set of questions which y'all can answer as you see fit). Please be advised prior to answering: I have a lot of ideas down, but not a lot of terminology. I will need answers in something approaching blue-collar explanations. I'm a writer, not a scientist.

 

Light: It's both a particle AND a wave, IIUC. Bright enough light hurts people! A really bright focused light is called a LASER. LASERs are all around us now - our CD/DVD players, we use IR to control our garages (not technically a LASER, but certainly an application of light as a communication device) and so on. Light can do many things, including decode, encode, and transmit data.

 

- How much power would you need, in hard science terms, to create an actual, functional, energy weapon? If you were to propose said energy weapon to a government, what would be the first reasonable step? Would it be a LASER? Would it be a variation on a Particle Projection Cannon? Would it be nuclear powered?

 

- Rail Guns use a totally separate, but equally common force; magnetics. I've read many of the magnetics articles that have been posted and I'm proud to say I understand wht they say prior to the math. How reasonable is a Mass Driver? is a chemical weapon (by chemical I mean a pistol; a chemical reaction driving a piece of lead) that much more efficient in the long run, or is it only efficient right now?

 

- What level of technology is needed to mass produce an energy/mass driver weapon? What side effects would an early weapon of its type have on its user?

[Nyrath]

Re: Random SF Science Questions

 

- How much power would you need' date=' in hard science terms, to create an actual, functional, energy weapon? If you were to propose said energy weapon to a government, what would be the first reasonable step? Would it be a LASER? Would it be a variation on a Particle Projection Cannon? Would it be nuclear powered?[/quote']

Lasers are Coherent light, where the waves are all in step.

 

For laser sidearms, read this:

http://www.projectrho.com/rocket/rocket3l.html#laserpistol

 

Your questions:

 

Power needed: approximately one kilojoule per shot.

 

Proposing to government: See Frank Herbert's "The Committee of the Whole." The inventors mail copies of the plans to everybody they know, in all the nations they know. Then they go to testify before Congress. Otherwise they'd be locked up in a top secret military lab for the rest of their lives.

 

Laser or Particle beam?: It could be either, but lasers are a more mature technology.

 

Nuclear powered: No need. A lead-acid battery could manage in a pinch.

[Zeropoint]

Re: Random SF Science Questions

 

If you want a good source of easy-to-understand, scientifically valid information about sci-fi topics, allow me to reccomend the Atomic Rocket site. They have detailed information about potential sci-fi weaponry.

 

 

I don't have hard numbers, but I'd be surprised if conventional firearms were highly efficient in terms of the total energy of the gunpowder vs. the kinetic energy of the projectile. They do, however, have other things going for them:

 

They are a mature technology, with all the kinks worked out long ago.

The ammunition is self-contained and can be easily broken down into single shots.

A wide variety of bullets can be used for different applications.

The energy is delivered in a form which is quite effective at causing lethal trauma to humans.

They are relatively simple mechanical devices, reliable and easy to maintain.

They can be silenced. (a weapons-grade laser CANNOT, at least not in an atmosphere)

[gojira]

Re: Random SF Science Questions

 

- What level of technology is needed to mass produce an energy/mass driver weapon? What side effects would an early weapon of its type have on its user?

 

Some guy in Australia has a rail gun now, with working prototypes. He's trying to sell it to the US military. A rail gun has few moving parts than a conventional firearm, doesn't use propellant, so the shot is denser and has more kinetic energy and range than a conventional weapon.

 

I get the impression that the real problem with his rail gun weapon is he owns the patents, and there's no way an American company can make money on it. So it's being tied up in red tape.

 

 

EDIT: changed "mass driver" to "rail gun." Per Wikipedia, a mass driver is a launch device for space ships. A rail gun is a weapon.

[austenandrews]

Re: Random SF Science Questions

 

They can be silenced. (a weapons-grade laser CANNOT' date=' at least not in an atmosphere)[/quote']

Ye of little faith! "Cannot" has no place in SF; instead consider "how hard?"

 

Btw thanks everyone for the responses to my solar sail post. I'm taking your answers and doing more research. If I have more questions, hopefully they'll be reasonably informed.

[Pogo]

Re: Random SF Science Questions

 

Bright enough light hurts people! A really bright focused light is called a LASER.

The light does not have to be focused, though it often is. The light is coherent and monochromatic. This means that the crests and troughs of the waves line up with each other and that the light is all the same frequency (there's actually a spread of frequencies, but it's small).

 

- How much power would you need, in hard science terms, to create an actual, functional, energy weapon?

 

Nyrath has already provided a link. One problem mentioned by Dr. Schilling in that link is more general. Lasers produce a plasma when they start to vaporize things, and plasmas can act as mirrors, sending the photons away from their intended target, so you really want to pulse the light. It is probably true that the steam from a human body will scatter even more light, and that's why the good doctor left this out.

[Nyrath]

Re: Random SF Science Questions

 

One problem mentioned by Dr. Schilling in that link is more general. Lasers produce a plasma when they start to vaporize things' date=' and plasmas can act as mirrors, sending the photons away from their intended target, so you really want to pulse the light. It is probably true that the steam from a human body will scatter even more light, and that's why the good doctor left this out.[/quote']

 

That turns out not to be the case. The good doctor did address the problem of steam.

 

from http://www.projectrho.com/rocket/rocket3l.html

The key to making a laser do bullet levels of damage is pulsing the laser. The first pulse creates a steam explosion and a shallow crater in the skin of the hapless pirate. By careful timing' date=' the second pulse arrives after the steam from the first pulse has dissipated and creates a second crater at the bottom of the first. If you don't delay the pulses, the cloud of steam interferes with laser beam, protecting the target. [/quote']

 

The plasma clears away easily in that time frame; debris is the real issue' date=' and the driving force between the 5 microsecond pulse rate. That allows roughly 90% of the debris to clear the beam path, assuming a 1mm beam and instantaneous 1J pulses. 1 joule every 5 microseconds is optimal against soft tissue, other materials will want different pulse trains.[/quote']

[Yansuf]

Re: Random SF Science Questions

 

Standard firearms are "projectile weapons propelled by gas expansion from a chemical reaction." As has been mentioned in a previous post, these are a mature technology and are efficient. In fact, they are so good that the Gyrojet company went out of business; its products couldn't compete.

 

The advantage of electro-magnetic propelled projectile weapons (rail guns, coil guns, or "gauss weapons") is potentially much higher muzzle velocities. The maximum muzzle velocity of "gas expansion" firearms is limited by the "detonation velocity" of the propellent. The gauss weapons have no such limitation.

 

I believe current rail guns (in laboratory) can achieve two miles per second muzzle velocity, actual guns can only (in practice) get about half that.

While both can be improved, the potential for the gauss weapons is much more, which is why the US (and probably many other nations) are working on it.

 

However, this is not important for small arms. Current US research is designed for improved tank/anti-tank weapons.

 

It is likely gauss weapons will be field tested on armore vehicles in a decade or so.

 

Of course, Lasers were field tested on a USN Destroyer in the late 1990's. I believe the reason that they were not brought into service was reliability problems in the nautical environment.

[Guest Schwarzwald]

Re: Random SF Science Questions

 

Lasers are Coherent light, where the waves are all in step.

 

For laser sidearms, read this:

http://www.projectrho.com/rocket/rocket3l.html#laserpistol

 

Your questions:

 

Power needed: approximately one kilojoule per shot.

 

Proposing to government: See Frank Herbert's "The Committee of the Whole." The inventors mail copies of the plans to everybody they know, in all the nations they know. Then they go to testify before Congress. Otherwise they'd be locked up in a top secret military lab for the rest of their lives.

 

Laser or Particle beam?: It could be either, but lasers are a more mature technology.

 

Nuclear powered: No need. A lead-acid battery could manage in a pinch.

 

Thank you for the entertaining link.I loved some of those old guns, esp the original BSG laser pistols.

[Nyrath]

Re: Random SF Science Questions

 

http://www.projectrho.com/rocket/rocket3l.html#laserpistol

 

Thank you for the entertaining link.I loved some of those old guns, esp the original BSG laser pistols.

I'm glad you liked it. It took me a long time to find some of those images.

[Pogo]

Re: Random SF Science Questions

 

That turns out not to be the case. The good doctor did address the problem of steam.

 

from http://www.projectrho.com/rocket/rocket3l.html

 

Originally Posted by Dr. Schilling

The plasma clears away easily in that time frame; debris is the real issue, and the driving force between the 5 microsecond pulse rate. That allows roughly 90% of the debris to clear the beam path, assuming a 1mm beam and instantaneous 1J pulses. 1 joule every 5 microseconds is optimal against soft tissue, other materials will want different pulse trains.

 

 

Darn, missed that. Oops. Thanks for pointing it out for me. I'd like to see his reasoning for the debris clearance time though. I think he may be overestimating the speed with which stuff moves, but it's nearly a decade since I worked with laser vaporization, so my memory is probably playing tricks on me (that and I was aiming at something not very flesh-like).

 

A potentially nasty problem with laser weapons is if you know the frequency and there is a commonly available gas which absorbs there, your opponents with the slug-throwers have a one way shield, so choose your frequency carefully. To take a silly example, no one will build a deadly fluorine excimer weapon lasing at 157 nm for use on earth. Both water vapor and oxygen absorb strongly at these wavelengths, so the range would be very, very limited.

[Curufea]

Re: Random SF Science Questions

 

Hmm' date=' I don't think this is correct. Conventional wisdom says that after you pass some point above a planet you are in space. The accepted limit for Earth is about 115 miles above the surface. From that point on, it's all hard vacuum. [/quote']

 

There is no "hard vacuum" and there is no transition line where you say "this is atmosphere" and "this is space" it's a completely subjective decision. The area with the least amount of particles you will find in the universe is between galaxies. There is a "halo" around a galaxy of particles.

[Thia Halmades]

Re: Random SF Science Questions

 

New question.

 

How feasible are giant robots? I'm surprised we haven't built them yet, even out of normal human curiosity. We like to build things in our images; why haven't we built Power Armor? Is it not yet cost efficient? Is there an element of the technology beyond our scope?

[Curufea]

Re: Random SF Science Questions

 

We don't have the materials science to create joints able to withstand the weights and torque required.

[oberon]

Re: Random SF Science Questions

 

Exoskeletons, however, are already being worked on. DARPA is developing an exoskeletal frame designed to boost the strength/endurance of its operator (http://www.darpa.mil/dso/thrust/matdev/ehpa.htm). The drawback is that it needs too much power to operate. The weight of a self-contained power source large enough makes it infeasible at the moment. Of course, with a really long extension lead

Also, check out http://www.plyojump.com/exoskeletons.html

 

oberon

[gojira]

Re: Random SF Science Questions

 

More or less what the above two posts said.

 

Structural strength increases as the square of the dimenesions of a material. It's cross sectional area. Take a metal I beam that's standing upright. The structural strength is equal to how thick it is, ie, it's depth times it's width. How tall it is doesn't really matter.

 

Structural weight increases as the *cube* of the dimensions of a material. Weight is proportional to volume, ie depth times width times height. The implications for giant robots (or any large structure) should be obvious. As the size of a structure grows, the cross sectonal area (or thickness) of it's support members must increase faster than it's height in order to support the weight.

 

A human 60' tall would need incredibly thick bones to support his weight. You can't just scale up a person and get a working, practical bigger person.

 

Tall buildings have a different type of skeletal structure than humans for a very good reason. You have to build them differently or they just plain couldn't stand up.

 

 

* * *

 

Humans and all animals are very effcient when using energy. Much better than any machine. Evolution has seen to that; wasteful species don't survive. Trying to make something much stronger and tougher than a human, but essentially human-like (eg a power suit) is a very very tough order.

 

OTOH, we do have powersuits now for people. They just don't look like people, because an effciently designed machine works on different principles. They're called Abrams tanks.

[Basil]

Re: Random SF Science Questions

 

New question.

 

How feasible are giant robots?

Very feasible, and existant. They're in many large manufactories, especially assembly lines.

 

Now, if you mean giant human-shaped robots: impractical for the reasons given regarding the square-cube law. Another problem has turned out to be balance; all those working on human-shaped robots have found it difficult to build a bipedal structure that can keep its balance, especially while moving. Turns out nature has given bipedal creatures a remarkably advanced balance/feedback mechanism.

[Nyrath]

Re: Random SF Science Questions

 

And even not-so-giant humans in man-amplifier rigs will have trouble engaging in combat inside building. Most floors cannot take the weight concentration of such rigs. Sigorny Weaver's cargo loader from Aliens II would cave in the floor with each step.

[Guest Schwarzwald]

Re: Random SF Science Questions

 

And even not-so-giant humans in man-amplifier rigs will have trouble engaging in combat inside building. Most floors cannot take the weight concentration of such rigs. Sigorny Weaver's cargo loader from Aliens II would cave in the floor with each step.

 

In a house, sure. Not in an environment made to handle the weight of heavy gear.