Re: how big?

I believe both of you are dancing the same dance, but not quite in step. Perhaps my take on it might help?

This is a somewhat longish post, sorry. You might just want to skip to the end if you know the basics. :)

Both of you seem to be correct in your basic terms:
speed = how fast you are going
velocity = how fast you are going, and in what direction
acceleration = how fast, and in what direction, your velocity is changing

Which brings up an interesting (and important for later) point: your velocity can change even though your speed doesn't. When you drive a car you can turn a corner at some constant speed -- you are accelerating into the turn while your speed remains constant.

In fact, that feeling of being "pulled out of your seat" when making a turn is another form of "artificial gravity", one that is mechanical in nature. This pull, falsely called "centrifugal force", results from your body's inertia wanting you to continue in a straight line. As you are (I hope) firmly buckled in, the car must exert force on you to accelerate you through the turn. According to your senses, you feel like you are being thrown away from the turn, when in fact you are being accelerated tthrough it.

Babylon 5's (and the Earth Alliance Omega Class Destroyer's) rotating sections are there for exactly that reason -- inducing this false constant gravity so the crew can function normally. Personally I'd hate serving in a Nova Dreadnought or a Hyperion Cruiser -- zero G most of the time would make life difficult. The only way they would feel the affect of artificial gravity would be when the ship was accelerating -- if the ship is thrusting forward, then the rearward bulkheads would (temporarily) become the floor. If the ship is rotating (yawing) left, folks flying loose in the front of the ship would find the right-hand walls coming up to meet them (potentially injuring them if they hit badly...).

Which brings me to my next point. The human body is used to the feeling of "weight". Weight does not really exist by itself -- it is the mass of your body being accelerated by the gravity of the planet you're sitting on. If you lose mass, you also lose "weight". If the planet you are on suddenly lost half its gravitational pull (rather destructive to the planet, as that means a proportional part of the its mass also disappeared) you would suddenly weigh half as much as you did the second before. This is the reason why an astronaut weighs so little on the moon compared to their weight here on Earth.

So, as I said, the human body is used to the feeling of weight caused by 1G. If the person is subjected to 4Gs, doing basic things like reaching for a light switch become difficult if not impossible. At 5Gs most people would black out unless they're wearing G suits. At 10Gs, survival is difficult. At 100Gs things go squish, and at 1000Gs -- well, let's just call it chunky salsa and leave it at that. :-P

What this means is unless you have a way to *cheat* the affects of acceleration, you must purposely design your ships to make sure that your maneuvers don't kill your crew. Fighter jets could be designed to turn much more tightly than they do, but what would be the point if the human controlling them isn't alive or conscious after the turn?

That is where the advanced technology of "gravatic drives" comes into play.

Please note the following is my interpretation of how gravatics would work. It is based on notes from AoG's B5Wars books (which were declared canonical by JMS).

Gravatic drives "mimic" gravity without the need of a handy planet-sized mass to induce it. This artificial gravity works internally (to induce the 1G condition inside the ship), and also *on* the entire ship and crew, to accelerate it in whatever way the navigator tells it to go. These separate "gravatational pulls" are cumulative, so both crew and ship are affected by them.

What this means is if the ship (with 1G in place for the crew) is also being accelerated with the force of 20Gs forward, all the crew feels is the 1G that makes the bulkhead they are standing on their floor.

Because they are being accelerated exactly the same as the ship, they have no way to sense the acceleration.

If this is confusing to you, think of the two guys up on the International Space Station right now. They (and the station) are being accelerated by gravity all the time, but because the station they are on is being accelerated exactly the same as they are, they have no sense of it and are thus in 0 net G.

So, the gravatic drive system can induce much higher accelerations than a conventional drive system without killing the crew. But no matter how fast that acceleration is, if you are starting from 0 velocity, it will take some time to get up to a speed that makes you somewhat better off than a sitting duck. :)

Hoped that rather long excursion into physics (real and sci-fi) helped.

D




Carl wrote:
"Mox Fulder" <alvaro@xxxxxxxxxxxxx> wrote in message 

Velocity (speed) and acceleration are different things.  Artificial
gravity can hide the acceleration but not the velocity.  Even at high
acceleration it still takes several minutes to get to a high speed.


Sorry, but that doesn't make any sense. Acceleration is nothing more and
nothing less than a change in speed.



Actually, it makes perfect sense.  If you were in space moving at a
constant velocity, you would be unable to detect that you were in motion.
If you were accelerating, you would feel pushed in the opposite direction
of motion.

If you had artificial gravity, it could counteract the push backwards, but
that would not affect the acceleration.



.

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