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### Author Topic: How Long Would It Take To Decelerate From Near Light Speed ?  (Read 3902 times)

#### neilep

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##### How Long Would It Take To Decelerate From Near Light Speed ?
« on: 10/11/2007 23:17:07 »
Perhaps this should be in TECHNOLOGY or GENERAL SCIENCE !

ASSUMING MATERIAL INTEGRITY....say you had an ion propelled rocket that gets you to half the speed of light (or any other propulsion for that matter)....would it take equally as long to decelerate to a halt as it took to accelerate ?

#### lyner

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##### How Long Would It Take To Decelerate From Near Light Speed ?
« Reply #1 on: 11/11/2007 00:37:16 »
why should it not?

#### Soul Surfer

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##### How Long Would It Take To Decelerate From Near Light Speed ?
« Reply #2 on: 11/11/2007 00:48:35 »
Yes and it would take about half a year to do it at about 1g

#### neilep

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##### How Long Would It Take To Decelerate From Near Light Speed ?
« Reply #3 on: 11/11/2007 02:01:59 »
The reason why I ask (and THANK YOU for your comments thus far)....was that...say it was ION propelled.....could you not speed up the deceleration by using rockets instead ?

#### syhprum

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##### How Long Would It Take To Decelerate From Near Light Speed ?
« Reply #4 on: 11/11/2007 09:26:30 »
Ion propulsion is a much more efficient form of propulsion than rocket, with a rocket you can only use the chemical energy stored in the fuel but with Ion propusion you can obtain energy from Solar panels or on board nuclear power plants.
Present day Ion engines can only produce a modest thrust but they can keep it up for a very long time

#### Soul Surfer

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##### How Long Would It Take To Decelerate From Near Light Speed ?
« Reply #5 on: 11/11/2007 10:45:06 »
Ion engines are fundamentally no different from rockets. They both work by throwing stuff out the back as fast as possible its just that  ion engines throw things out faster.

In a theoretical situation like this you can decelerate as fast as you like but I was assuming that you wanted to survive and antyhing more than 1g will be very uncomfortable if not life threataning.

Another salutary calculation is the amount of stuff you need to throw out the back to achieve this acceleration and deceleration  even using a smallish payload of a few tons  remember as well as the stuff you throw out the back you have to generate the energy to accelerate it.  Its basically impractical unless you can design a matter antimatter anhillation drive  (this just puts the major energy consumption elsewhere because of the enrgy needed to create antimatter) even hydrogen helium fusion doesn't give you enough energy.

#### lightarrow

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##### How Long Would It Take To Decelerate From Near Light Speed ?
« Reply #6 on: 11/11/2007 18:14:31 »
The reason why I ask (and THANK YOU for your comments thus far)....was that...say it was ION propelled.....could you not speed up the deceleration by using rockets instead ?
With a starship you can decelerate as much as you can accelerate (it's not as with a car). So, if the best of the engines you could have pushes you at 100g of acceleration, then the best deceleration you can have is with the same engine, so 100g of deceleration. It only changes how you orientate your starship...
« Last Edit: 11/11/2007 18:18:07 by lightarrow »

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##### How Long Would It Take To Decelerate From Near Light Speed ?
« Reply #6 on: 11/11/2007 18:14:31 »