# Re: [humanism-174] Space travel according to Victor Stenger

 From: Linas K M. Sent on: Friday, April 26, 2013 3:32 PM
That won't be cheap!  Not with the cost of gas these days!

On Fri, Apr 26, 2013 at 3:29 PM, Tim Campbell <[address removed]> wrote:
I agree. The problem of course is maintaining that acceleration!  This would require in effect 2400 years of fuel: enough to accelerate, and then enough to brake in both directions!

Tim

In a message dated 4/26/2013 2:36:15 P.M. Eastern Daylight Time, [address removed] writes:

It's the acceleration.  He's saying that the force of the acceleration would make "down" the direction of the engines as a consequence of the whole equal and opposite reaction business.
You accelerate at 32 feet per second squared (1g) until you hit the halfway point.  Then you have to spend the rest of the trip slowing back down.  So, you turn the ship around and decelerate at 32' per sec sq, and it will continue to feel like 1 gravity.
The only time you're weightless is at the turn around because that's the only point when your velocity is constant.  Easy.

In a message dated 4/26/2013 1:27:44 P.M. Eastern Daylight Time, [address removed] writes:
I'll jump on someone's shoulders to see ya Tim! ha

Again, my head is spinning without layman terms, but what does this mean:

Of course, the ship can't continue to accelerate, since it needs to be moving at the same speed as the planet when it arrives. When it reaches the halfway mark at 600 light-years from Earth, the crew turns the ship around so it then decelerates at one g for the remainder of the trip. Those onboard notice no change. They continue to experience the equivalent of gravity on Earth.

I don't get it....

To be honest, I am not certain what he is talking about here either!  "One g" is basically the gravitational force that we feel here on Earth.  We use our "g" as the reference point for gravity anywhere else in the universe! If you weigh 100 pounds on earth, then on a planet with a gravity of 2g you would weigh 200 pounds, and so on.

But g forces have nothing to do with speed or acceleration once you are in space.  Once you have escaped earth's gravitational force, you would be essentially weightless unless your ship did something to give you an artificial gravity.  We see science fiction concepts of space stations being wheels for this reason. It is guessed that the wheel shape would be spun so that the centrifugal force would create a kind of gravity for the inhabitants.

I understand that he is positng a speed high enough to utilize the relativistic effects on time, but in order for a 2400 year trip to take 14 years in astronaut time, the ship must be coming very close to the speed of light.

The orientation of the ship would have nothing to do with the acceleration or deceleration or on-board gravity. however, if the speed is changing, then that change WILL have an effect on the relativistic effect as well.

Until a speed of appr 670 MILLION MILES PER HOUR is technically feasible, any journey to another solar system will involve either multiple generations or some form of suspended animation/hybernation for the crew.

Of course, I will be discussing this in detail in July!

Tim

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