theltemes

Re: All Books In Warehouse: APG, Both 6th Ed

Yay! Just placed my pdf+book order for Vol 1/2, Basic and APG!

Re: Reminiscing About Star Fleet Battles

Yeah, the combination of Starmada and VBAM make for some really fun wargaming.

Re: Reminiscing About Star Fleet Battles

Pffftt...

There is no other version than the Doomsday™ edition. I like my ship combat rules to barely fit into a 3" 3-ring binder.

Re: Airlocks are for losers

Sublimation works in a vacuum. Evaporation' date=' too. Simple physical disconnection, as well.[/quote']

 

Yep. That's why you'll eventually end up as freeze-dried jerky if you spend too much time in an evacuated environment.

Re: Hard Science Help

basically, for those not understanding the whole "in the past" thing, relativity states that time moves differently depending on velocity. in particular, time moves more slowly for a body the closer to the speed of light it gets (the larger the ratio to c is). this is called time dilation, and has been expirienced by human researchers (though only in very small quantities).

It's all relative, baby.

The person moving near c experiences no sensation of time being different - he/she observes that the rest of the universe's time has sped up. Likewise, an observer of the really fast moving person would say that their time is moving at the "normal" rate, and that the person moving near c has almost no change in time. It still takes a person moving near c a little over a year to travel one light year to the outside observer, but to the person in the craft the journey is nearly instantaneous because of the relativistic length contraction of space.

Re: Hard Science Help

You have a good point there' date=' judge. I stand corrected.[/quote']

 

You could estimate the relativistic effects by choosing a small time interval, say an hour, and

 

1. Find the average velocity over that hour.

2. Calculate the relativistic time dialation over that hour.

3. Add up differentials over the acceleration period.

 

I bet an excel spreadsheet could handle this quite well. It's not as exactly what's going on, but from an engineer's perspective you get a "close enough" answer. It should provide some insight as to what's going on during the acceleration phases of the trip.

Re: Tac-nukes vs. Nuclear Warheads

why does it have to be a sphere when a cone or cylinder is the shape of most bullets

 

also an nuke going off as a skin to skin will do a good job unless you need a deep penatration

A sphere minimizes the surface area of the mass, resulting in decreased number of escaping neutrons, hence minimizing the critical mass needed.

A classic problem in nuclear engineering - determining the required mass for criticality:

Geometric Buckling = Material Buckling

Re: Astrophysics question

Traveling through a medium, the group velocity changes while the phase velocity remains at the speed of light in a vacuum.

Re: Modelling Explosives : TNT

I guess today is a good day for picking nits. I changed my post from STR 10 to 8 so you can sleep tonight.

Re: Modelling Explosives : TNT

As far as lifting mass goes, the FAA Human Factor Design Standard (HFDS) gives numbers for a 5th and 95th percentile lifting of weight to a height of 100cm. For males the values were 444.4 N and 931.0 N (average) and for females the values were 185.0 N and 443.0 N. If we assume the 50th percentile lies midway between the two extremes, the 100cm lifting strength for a STR 8 character is 687.7 N (male) or 314 N (female). Since the game mechanics don't differentiate between genders, let's go with the value of 687.7 N or 154.6 lb. So the work would be 688 N-m (70 kg-m) or 507 ft-lb.

The 4184 J per gram of TNT is a defined unit. Although you found it on Wikipedia, it is indeed correct.

The true destructive power of TNT is indeed its power (J/sec or Watts). TNT actually has a relatively low energy content per kilogram (4.184 MJ/kg). For comparison, the combustion of air-dried wood yields 15.5 MJ/kg, anthracite coal 31.4 MJ/kg, propane 50.3 MJ/kg. The advantage of TNT is that it doesn't need air to combust and the combustion rate is much higher.

Re: Another advanced and weird material

Meh. I've never though "Ion" this or that were any good as weapons or drives. Give me fusion torches for both

Preach it, Curufea!

Re: Future Tech Links

Check out the rest of the above site by using this link.

 

http://www.oz.net/~coilgun/home.htm

 

Another project that was listed on that site was the Coilgun. To me and the limited (and therefore Dangerous ) amount of knowledge that I have it seems that this is could develop into a personal sized railgun.

Coil guns (propelling an object through a solenoid) and a rail gun (propelling an object along a pair of conducting rails) are two drastically different technologies.

Re: Future Tech Links

Princeton Plasma Physics Lab fusion website.

Re: Interplanetary colonies

Does that estimate factor into account the capability to manufacture water and oxygen from the lunar regolith, or are they assuming that all consumables would have to be transported from Earth?

Re: That's no moon, that's a space station!

Proving once again that life indeed imitates art.

Re: Fusion transmutation.

Agreed' date=' and there are those who have their doubts about p-B11.[/quote']

 

p-B11 and 3He-3He would be under the "rubber tech" classification.

Re: Fusion transmutation.

Now I'm just a fusion power reactor engineer, so take what I say with a grain of salt

Once you get out of the realm of these reactions:

• D-T
  
• D-D
  
• D-He3
  
• He-3He3
  
• p-B11
  

You are definitely in the realm of "magic tech" if you are thinking about generating elements using fusion that we can sustain with any conceivable technology based on real-world physics.

Also, you would only generate very small amounts of matter on a scale of thermal waste that we know how to deal with. For example, a 3000MWth DT inertial confinement fusion reactor (the same output as a modern fission reactor) will use up 30mg of DT per second producing a bit less than 10mg per second He4. I mention inertial confinement here because a tokomak really won't work for nucleosynthesis - a major problem that we have now is how to get the fusion products out of the reactor while keeping the fuel inside (the products tend to poison the reaction in a tokomak plasma).

Re: Fusion transmutation.

One side effect of fusion is that only .7% of the mass converts to energy, the rest fusions up the periodic table to a higher element.

 

So, for instance, since traveller setting fusion technology uses hydrogen, plain ordinary hydrogen, it would likely end up as helium.

 

Now, if you put some more energy into the fusion process, you can fuse helium into the next element and get energy out of the process, and so on up to iron, where the amount of energy released by the fusion woudl equal the amount put into fusing it.

 

Puting more energy into it would allow you to fuse iron to higher elements, even gold, lead, uranium, etc. But it would end up costing you energy to do that and likely take a hell of a lot more equipment that 'simply' fusing hydrogen for energy and getting helium would release.

 

Still, a lot of useful elements could likely be produced by low level fusion. A few runs thru a fusion reactor could turn hydrogen into oxygen, generally a useful thing to have on a spacecraft with a human crew, for example. Mix oxygen and hydrogen and get water, again a useful thing to have when humans are around.

 

Lithium is a useful metal that's fairly low on the periodic table, and can be used to make fusion reactor linings if I recall my science correctly.

 

So why not discuss the possibilities opened by practical fusion power in terms of building up higher elements from basic hydrogen? I believe the process is called 'nucleosysthesis" if I recall correctly.

Wouldn't be a whole lot easier to just collect the materials you wanted from the planets and asteroids in whatever star system you happen to be in?

Re: Advanced energy sources: Some thought and pretty big numbers.

On the other hand' date=' fusion power right now also depends on neutron-rich species (so it also is going to have the neutrons poisoning/hot waste problem that fission reactors have), so relief from the waste problem is not apparent. And the cynical part of me notes that fusion power has been just a decade or two away since I first heard of it when I was 11 or 12. Bluntly, I have reached the point where I don't think it's going to happen in my lifetime.[/quote']

 

You can mitigate some of the neutron problems by using a relatively neutron-poor reaction like D-He3. As a fusion power source, DT power reactors may be built sometime toward the end of this century. DT reactors are not really viable for a worldwide power source as tritium is too scarce to support a worldwide consumption need. What will likely happen is that we will end up relying on DD or DHe3 power reactors, which are a technology which won't see practicality until at least the middle of the next century.

 

Radioactive waste from fusion plants have a greatly reduced half-life (on the order of a century), but the volume of waste will be greater as the activated materials are structural materials as opposed to relatively dense fission waste.

Re: BSG Hero Update

You may want to consider lightening the sidebar graphics. The dark gray graphic makes the text a little hard to read in the areas where they overlap.

Re: Mars Colony by 2025?

Actually, I do think the colonization of other worlds is more or less economically unviable, and technologically extremely impractical with the human race as it stands. A post/trans-human race which can survive under harsher environmental standards is another kettle of fish entirely. The problem is for Mars, sans atmosphere and magnetic field, you've got a serious radiation problem down there. You'd have to set up a colony deep underground the planet's surface to keep radiation levels down to what human beings are used to.

 

The moon has similar issues to deal with. I can see a lunar outpost set up for scientific research purposes, but that's about it, at least until we get to a transhuman species that doesn't mind lunar conditions.

Reread my post about radiation conditions. You will need to live "underground" on Mars, but it only takes about 80cm of Martain regolith to protect you from SPE and GCR radiation. UV can be filtered pretty easily as well. The bigger environmental problem on both the Moon and Mars is actually dust, as others have posted.

As far as economic concerns go, it is a lot cheaper to launch spacecraft from either the Moon or Mars, as compared to the Earth. Both planets have an abundant supply of fuel, once it is processed out of the soil. In addition, the Moon and other airless bodies in the solar system, as well as Jupiter and Saturn, have abundant supplies of Helium-3. This is the stuff that will be used in commercial-grade fusion reactors (don't laugh, we are running a D-He3 experimental reactor in the basement where I work right now). In the future, recovery of He3 will be a very profitable economic factor. In fact, one space shuttle's cargo hold worth of He3 would be worth about 40 billion dollars in today's money.

For more information on the economic aspects of space, see the course notes from Resources from Space.

Re: Question: Launching Small Craft

Well, a mathematical way to guesstimate a launch rate:

(N x 2L)/v = Launch Time

N = number of craft that will fit through a hangar door simultaneously

L = Length of said craft (allow another craft length for a safety buffer)

v = the departure speed of the craft.

So if you are using meters for craft length and m/s for a departure speed, this will tell you the number of seconds between launches.

Re: Mars Colony by 2025?

Martian dust is a hazard as well. It is abrasive' date=' so it can cause failure in airlock gaskets. It might also cause silicosis if breathed in. What's worse, it can make dangerous electrostatic charges.[/quote']

 

Correct. So you would need a sufficient crew complenment that you could perform routine maintenance on exposed structures. For example, if you had a colony at Hellas Planatia, and a routine maintenance crew consisted of 2 people working a 12 hour shift each day (as I detailed in my post above) you would need a crew of at least six whose job consist only of maintaining the exterior facing components of the habitat. That doesn't account for illness or injury, so if you had a 50% crew reserve, that bumps you up to nine people just for repair work.

Re: Mars Colony by 2025?

Just a FYI for those planning on running adventures on Mars. Many people fail to consider the radiological environment on Mars. It has a very thin atmosphere, which means that human visitors/inhabitants on Mars will be exposed to a variety of radiation sources.

UV light will be a problem. Any habitats that have exposed windows will need to be UV protected, as will any people travelling on the surface in pressure suits. The UV radiation is significant enough that it would be advisable to have two different methods of UV protection for both the eyes and the skin. I would recommend UV coated helmets in addition to UV goggles. The UV radiation is intense enough that UV blocking sunscreen would not be sufficient. Martian workers would need UV absorbing materials in both their pressure suits as well as a second body glove, which is usually standard with a pressure suit (to regulate body temperature).

Cosmic rays and solar particle events will need to be shielded against as well. Approximately one meter of martian regolith will be required to protect habitats and roving vehicles from GCR and SPE radiation.

I have examined the radiation environment in three locations: Hellas Planatia, the Southern Highlands and Northern Lowlands. These locations were chosen as probable sites for an underground habitat. It turns out that for occupational radiation exposure (2.0 cSv/yr) that exterior crewed operations will be limited as follows:

Hellas Planatia: 19 12-hour days per every 50 day mission cycle

Southern Highlands: 8 12-hour days per every 50 day mission cycle

Northern Lowlands: 14 12-hour days per every 50 day mission cycle

So be prepared to have any martian inhabitants be spending a lot of time indoors.

Re: Earth's core

What annoyed me in Ocean's Eleven was the tech guy not dieing after letting off his experiment EMP.

Yeah, that was pretty funny too. I know some guys who work on Sandia's Z-Pinch project. That thing is housed in a room the size of a hockey rink. The experiment has to sit for several hours before the radiation decays enough for it to be safe enough for anyone to enter the room after the shot goes off.