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How fast can a man-made object travel through space without negative consequences?

Posted on 2013-12-18
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The Milky Way is traveling through space at approximately 343 mi/sec, relative to the cosmic background at rest. What would happen to a man-made object traveling at 18,600 mi/sec through the Milky Way?

Also at 1G acceleration, how long would it take for an object to reach that speed?

Thanks,
John
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Question by:gabrielPennyback
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ID: 39727753
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d-glitch earned 71 total points
ID: 39727761
18,600 miles/sec * (1609.34 meters/mile) ==>  29,993,724 meters/sec

Divide by 9.8 to get 3,058,059 seconds  ==>  50975 min ==> 849 hr ==> 35 days
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Expert Comment

ID: 39727773
Nothing, until it bumps into something.
In the objects frame of reference, 18600mi/s * 1609.34m/mi / 9.80665m/s^2 = 3052390.36776s
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Expert Comment

ID: 39727780
What would happen?

The speed you selected is c/10, so there would be a host of relativistic effects.
But as long as it doesn't hit anything it should be fine.

How you could apply 1g acceleration for that time is problematic.
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abbright earned 71 total points
ID: 39728009
Speed is a relative thing. As long as things "near" the object travel with same speed no Problem occurs. Only objects that travel with a speed that differs a lot show relativistic effects.
To be more exact there is no such thing as a cosmic background at rest as there is no point zero. There is only the relative speed betwern two objects.
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Author Comment

ID: 39728140
Thanks for all the input.  What I'm trying to determine in my mind whether or not human interstellar travel is a real possibility. I'm obviously a total neophyte but I read somewhere that there's a speed  - depending on proximity to gravitational fields, I assumed - at which some kind of cosmic radiation or something would either destroy the spaceship or kill off the occupants. Is there any truth to that?

I know I'm all over the map here but other than the effects that would be apparent to the observer, what would prevent an object accelerating at 1G, from reaching the speed of light (relative to some very, very distant object)? Why would I as a passenger feel anything at all? If theoretically I wouldn't, then would I feel something if I were close to other massive objects?

Thanks,
John
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aburr earned 71 total points
ID: 39728141
the 35.5 days is correct
You can consider the cosmic background to be at rest if you want to.
Empty space is not empty but contains something like one hydrogen atom per cc.
The hydrogen is in the form of one proton so you object will be bombarded by a proton beam going at you  18600 mi/sec.
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ozo earned 215 total points
ID: 39728159
What prevents an object from reaching the speed of light is that velocities add via the Lorentz transform, not the Galilean transform.  See http://en.wikipedia.org/wiki/Special_relativity

Yes radiation in space is dangerous to humans.
The Earth has a large magnetic field protecting us.
It has been suggested that passenger ship might be protected in a similar way.
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Expert Comment

ID: 39728235
> In the objects frame of reference
In a reference frame moving with the objects initial velocity, it would be about 5 hours more,
in the proper time of the object, it would be about 3.5 hours more.
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tliotta earned 72 total points
ID: 39728549
...some kind of cosmic radiation or something would either destroy the spaceship or kill off the occupants. Is there any truth to that?

Yes.

The "Doppler effect" applies to electromagnetic radiation. There is no plausible location in space where some radiation will not be encountered. If you are traveling towards a radiation source, the wavelength of the radiation effectively becomes shortened. As your velocity increases in that direction, the radiation wavelength becomes shorter and shorter.

For example, when traveling towards the Sun, plain visible violet light can effectively become ultraviolet radiation. And when traveling away from the Sun, the opposite happens so that simple visible red light becomes infrared.

At more extreme velocities, visible radiation can effectively shift to become X-rays or gamma rays in one direction and microwaves in the other. Radiation that was initially emitted as X-rays can shift to gamma rays much easier than visible light can.

The Doppler shift of radiation is real.

Tom
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Author Comment

ID: 39728564
This is great stuff. RE: "The hydrogen is in the form of one proton so you object will be bombarded by a proton beam going at you 18600 mi/sec."   What kind of damage would that cause? And how many simultaneous such bombardmets would it to take to cause life-threatening damage?
RE: "It has been suggested that passenger ship might be protected in a similar way." 1) Is space radiation lethally dangerous? 2) Is it conceivable that a spaceship could produce a sufficient magnetic field?
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ozo earned 215 total points
ID: 39728598
I'd estimate that around 0.999999555c the cosmic microwave background would look about as hot as the sun,
but aberration would confine it to directly ahead, so that wouldn't be enough to threatening.
But going that fast toward the sun anywhere with the orbit of Neptune would be enough to cook you.
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ozo earned 215 total points
ID: 39728606
> Is space radiation lethally dangerous?
It can be, though short term exposure in milder places and times can still be within the range people have been willing to endure.

>  Is it conceivable that a spaceship could produce a sufficient magnetic field?
A spaceship as big as the Earth could do it, and people have conceived of far larger spaceships.
Other more practical configurations have been suggested, but they remain unproven.
http://en.wikipedia.org/wiki/Health_threat_from_cosmic_rays#Shielding
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Author Closing Comment

ID: 39730819
I hope I didn't leave anyone without any points. I'm sure I'll have more similar questions coming.

Thanks,
John
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Author Comment

ID: 39730855
OOC, how and where could we build a spaceship as large as the Earth? If we built it anywhere near Earth, wouldn't that possibly disrupt our orbit, leading to our extinction?

Thanks,
John
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Expert Comment

ID: 39731010
That wasn't meant as an example of what is practical, but an example of what is conceivable,
given that we know how well the Earth's magnetic field protects us.

But if you were to try to build one, you might want to try doing it at one of the Earth-Sun Lagrangian points.
The technology to assemble stuff there might not be enough to disrupt our orbit, but it would be enough to send stuff hurtling to Earth instead of to the L-point, which could lead to our extinction.
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