Re: Semi-OT: A question on Power Ratios in Sci-fi
 

some SI prefixes:

<font class="small">Code:</font><hr /><pre>
Factor Name Symbol
10E24 yotta Y
10E21 zetta Z
10E18 exa E
10E15 peta P
10E12 tera T
10E9 giga G
10E6 mega M
10E3 kilo k
10E2 hecto h
10E1 deka da

10E-1 deci d
10E-2 centi c
10E-3 milli m
10E-6 micro µ
10E-9 nano n
10E-12 pico p
10E-15 femto f
10E-18 atto a
10E-21 zepto z
10E-24 yocto y
</pre><hr />

so to answer your question, a terawatt is 1000 gigawatts; or 1,000,000,000,000 watts (12 zeros).

edit: typo

Re: Semi-OT: A question on Power Ratios in Sci-fi
 

Many of your questions (and many more) are answered a tthe excellent http://www.projectrho.com/rocket/index.html - which basically looks at the physical limitations of engineering (as they are currently understood) and applies them to all the essential aspects of spacecraft design. It's an invaluable read for any aspiring scifi author who hopes to write with a degree of scientific credibility.

There is a section there headed "artificial gravity" that answers your latest question quote neatly, as well as frequent references to power requirements in the propulsion and weaponry sections.

Re: Semi-OT: A question on Power Ratios in Sci-fi
 

First, artificial gravity is only really useful for manned spacecraft, and the most important reason for sending people into space nowadays is so that they can perform experiments in zero g. Having the whole ship rotate would make those experiments possible only at the center of the ship, and having just a section of it rotate would cost extra. Also, and perhaps most important, the rotating section would have to be BIG in order to avoid seriously disorienting the astronauts. If you've ever been in a centrifuge and looked away from the center, you'll know what I mean. The human perception system does not handle that kind of rotation very well.

Nothing except artificial gravity can prevent muscles from atrophying and bones from weakening during extended stays in space. Even with highly rigorous exercise regimens, astronauts that stay in space for months, or maybe even weeks, aren't even able to stand up on their own when they return to Earth. The whole human maintenance cycle evolved around the assumption of gravity always being present, and the human body has a distinct tendency to deteriorate in long term weightlessness.

Re: Semi-OT: A question on Power Ratios in Sci-fi
 

Not entirely sure but here are some reasons I can imagine:

- the "zero g" environment is preferred for lots of things:
-- some experiments are specifically designed for zero g. Yes, you could place them at the exact center of the craft, but true zero g only exists at a point.
-- making the robotic arms and mechanical things requires much less power/strength. If there were centripital forces needed to be overcome, in practical terms, this means more weight=more money=less payload for other things.
-- reorienting the ship/craft takes less thrust. To overcome gyroscopic forces created by rotation requires more fuel =costlier, less payload, etc.

- the "gravity" will decrease to zero at the center; making it somewhat cumbersome to manage placement of things. (see 2001: Space Odessy for a pretty realistic portrayal)

- in order to simulate earthlike gravity, either the rotational speed or the radius must be increased. But in general the size of the ship/station would need to be larger to make "gravity" somewhat uniform; =costlier, etc.



Perhaps if humans were to undertake a long space journey there would be another solution to simulate artificial gravity. Picture this: A large spacecraft with a huge funnel "scoop" in the front. The scoop would catch residual hydrogen to use as fuel and accelerate at 1g toward the destination. This way the crew lives under 1g all the time. At the halfway point, the crew section and the engine (not the scoop) is rotated 180 degrees and the ship is decelerated at 1 g for the remaining half of the trip. The crew still sees 1g toward their feet during the second half of the trip. I just thought of this, so there are probably a million things that make this just as impractical. (edit: like exceeding the speed of light in a short time...)

Re: Semi-OT: A question on Power Ratios in Sci-fi
 

Constant acceleration at 1 g is the perfect solution - if you can find enough fuel. Trying this over any significant distance (astronomically speaking) would require a truly colossal amount of fuel if you carry it all with you, and your collection array would have to be incredibly large to gather enough on the way. Interstellar matter density is typically on the order of 1 atom per cubic meter IIRC.

Re: Semi-OT: A question on Power Ratios in Sci-fi
 

Not to worry, though.

Relativistic time dilation and length contraction will ensure you reach your destination (regardless of if it's a finite distance or not) before that happens.

Re: Semi-OT: A question on Power Ratios in Sci-fi
 

Crunched a few numbers:

At 1g, you could accelerate for 353.8 days and still not reach the speed of light (barely).

During that time, you would travel 2.85 E12 miles (yes, Starhawk, that's teramiles http://forum.shrapnelgames.com/images/smilies/happy.gif )

So if you would start decelerating at 1g at the halfway point, you could travel ~5.7 E12 miles (just under 1 light-year) in 2 years.

Re: Semi-OT: A question on Power Ratios in Sci-fi
 

Not bad at all.

Re: Semi-OT: A question on Power Ratios in Sci-fi
 

Hey thanks for that link I've always been a fan of space ships and the like (as you can probobly tell lol) so that web site will probobly keep me entertained for hours http://forum.shrapnelgames.com/images/smilies/happy.gif

One reason I've asked some of these questions is because the first book of the Icaran series (hopefully I can write a series http://forum.shrapnelgames.com/images/smilies/happy.gif I have a plan for 3 books) would cover their earliest days of space travel within the Sol system and I was considering ships with rotating sections toward the aft section of the ship for the sleeping quarters and the like while the duty stations were all in zero g.

I've also heard people saying that within my lifetime we'll probobly see the earliest stages of Space based colonization and therefore military expansion (early infantry security forces and primitive space warships) from the Super Powers, I don't know if this is at all true but it could be very interesting (and probobly somewhat scary) to see it come true.

Re: Semi-OT: A question on Power Ratios in Sci-fi
 

Slick writes: "At 1g, you could accelerate for 353.8 days and still not reach the speed of light (barely)."

In a Newtonian universe, yes. In our relativistic universe, however, the ship's speed can asymptotically approach c, the speed of light, but never reach it. Meanwhile the ship's mass increases, its length decreases, and time slows down for the ship and its crew. For an entertaining look at relativistic space travel I recommend Poul Anderson's 1970 novel "Tau Zero".