When will we reach the Moon, Mars, Jupiter, another star and another galaxy...

Inquisitor said:
This isn't correct! The whole idea behind relativity is that velocity is a relative quantity, so it's impossible to determine one's velocity without an external reference point. Consequently they won't notice their own clocks running slowly; if they did, then they'd be able to determine their own velocity without such a reference point, which is in violation of relativity.
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That doesn't make sense... So not sure if one of use has misunderstood something. So half way along their journy there's a clock. As they pass it the clock has moved on by two years, but their onboard clock hasn't... So they therefore can determine their velocity and time differential? Not sure if we're talking about the same thing here or not :)
 
Fusion said:
You're wrong again. I've no idea where you're pulling this twenty years figure from. We measure the time to be 4.3 years in Earth's reference frame, taken to be stationary relative to the ship's movement. Moving clocks run slower, so they time the journey to be less than this. That's all there is to it.

Look at the example of Muon decay. A muon moving at 0.99c will have it's half-life measured by a stationary observer to be 15.6 microseconds. In our reference frame, the Muon will have travelled 4630m in this time. In the Muon's reference frame, this time is 2.20 microseconds.

So wait; speed = distance/time, speed = (4630m/2.2 x 10^(-6)s) = 2.1 x 10^9 m/s? That's seven times faster than light. But in the Muon's frame of reference, it thinks it has only travelled 653m, meaning that it's speed is still 0.99c and the laws of relativity remain intact.

At 0.999c, gamma is 22.366 so it would indeed seem to those on the ship that they had only been travelling for a few months.
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Yeah, see the edit, i got myself confused. I forgot about length contraction.
i got the 20 years from t=(gamma)t', with t'=4.3 years. gamma is about 0.015 at 0.99c, so t is about 20-25 years i think, with a lot of rounding (4/0.02). i got it backwards, it should actually be t=(gamma)t', with t=4.3 years, rather than t'. So yeah, a month or so passes on the ship.
In my original post, the ship would travel 20 or so light years in 4 years. I got the reference frames the wrong way around.
Hope this clears up my mistake.
 
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KNiVES said:
To the moon landing naysayers; you know with current tech it's practically a joke to pull off now. If we can keep the ISS in orbit and operational with constant spacewalks and maintenance, landing on the moon isn't far behind in terms of scale either.
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I'm not sure it's akin to "a joke", but it's certainly as achievable as it was when they took Apollo 8 around the Moon for Christmas '68.

One of the biggest problems is getting all the kit up into Earth orbit in the first place, and then getting the speed up enough to head to the Moon. Hence the development of the Saturn V, because the previous rockets were going to be next to useless without going the multiple launch route*. The Russians never did get a competitor to the Saturn V to work - Korolev's N1 never launched successfully in 4 attempts. Landing and getting back off the surface is a piece of duff after you've done that. Re-entry is slightly tricky given the narrow entry corridor that you have to hit, but they've had plenty of practice at it now and even 13's slightly compromised entry attitude only meant that they spent an extra minute or so under communications blackout.

I've noted on here before that there seems to be this attitude amongst the Hoax Believers that they are oh-so smart and NASA's legion of scientists and engineers are oh-so dumb. These of course are the same Hoax Believers who can't grasp reasonably simple concepts like parallax and camera exposure times, who won't spend five minutes reading the independent sources that tear apart the conspiracy theories, and who treat utter morons like Bart Sibrel and the late Bill Kaysing as if they knew anything. Kaysing was a particularly nasty piece of work, claiming that the Apollo 1 fire and the Challenger disaster were deliberate attempts by NASA to murder the astronauts because they were going to tell The Truth™. I wouldn't like to say that the world is a better place without him, but it's certainly a smarter one.

* - something that I think NASA is revisiting with Orion, isn't it? Orion gets launched on one rocket, the Altair lander and the Earth Departure Stage on another, then the two combine and head for the Moon.
 
JRS said:
I'm not sure it's akin to "a joke", but it's certainly as achievable as it was when they took Apollo 8 around the Moon for Christmas '68.

One of the biggest problems is getting all the kit up into Earth orbit in the first place, and then getting the speed up enough to head to the Moon. Hence the development of the Saturn V, because the previous rockets were going to be next to useless without going the multiple launch route*. The Russians never did get a competitor to the Saturn V to work - Korolev's N1 never launched successfully in 4 attempts. Landing and getting back off the surface is a piece of duff after you've done that. Re-entry is slightly tricky given the narrow entry corridor that you have to hit, but they've had plenty of practice at it now and even 13's slightly compromised entry attitude only meant that they spent an extra minute or so under communications blackout.

I've noted on here before that there seems to be this attitude amongst the Hoax Believers that they are oh-so smart and NASA's legion of scientists and engineers are oh-so dumb. These of course are the same Hoax Believers who can't grasp reasonably simple concepts like parallax and camera exposure times, who won't spend five minutes reading the independent sources that tear apart the conspiracy theories, and who treat utter morons like Bart Sibrel and the late Bill Kaysing as if they knew anything. Kaysing was a particularly nasty piece of work, claiming that the Apollo 1 fire and the Challenger disaster were deliberate attempts by NASA to murder the astronauts because they were going to tell The Truth™. I wouldn't like to say that the world is a better place without him, but it's certainly a smarter one.

* - something that I think NASA is revisiting with Orion, isn't it? Orion gets launched on one rocket, the Altair lander and the Earth Departure Stage on another, then the two combine and head for the Moon.
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It has been revisited, see here:

http://www.tallgeorge.com/projectconstellation.php

and the animation here:

http://forums.overclockers.co.uk/showpost.php?p=14248666&postcount=105
 
lord filbuster said:
Yeah, see the edit, i got myself confused. I forgot about length contraction.
i got the 20 years from t=(gamma)t', with t'=4.3 years. gamma is about 0.015 at 0.99c, so t is about 20-25 years i think, with a lot of rounding. i think it should actaully be t=(gamma)t', with t=4.3 years, rather than t'. So yeah, a month or so passes on the ship.
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No worries, it's not an easy concept to get your head round, very non-intuitive.
 
- A human lands on the Moon again - sometime before 2020
- A human lands on Mars - 50 years
- A human reaches Jupiter (Arthur C Clarke said we'd already be there :)) - erm wouldn't like to hazard a guess
- A probe or human reaches another star - erm wouldn't like to hazard a guess
- A probe or human reaches another galaxy - exactly the same time to reach another star if you beleive that every star has its own planetary system
 
I was wondering this before, but no-one answered, If you got something to a really high speed to a different star sytem, how would it remain in place? surely even the most massive star could not keep an object travelling at close to the speed of light in orbit?
 
GreatAuk said:
I was wondering this before, but no-one answered, If you got something to a really high speed to a different star sytem, how would it remain in place? surely even the most massive star could not keep an object travelling at close to the speed of light in orbit?
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Not sure what you're asking, you would just switch on the brakes.
 
GreatAuk said:
I was wondering this before, but no-one answered, If you got something to a really high speed to a different star sytem, how would it remain in place? surely even the most massive star could not keep an object travelling at close to the speed of light in orbit?
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Slowing down is more difficult than accelerating (where you can use slingshots etc)... Would have to use fuel, or go through an atmostphere, some sort of exotic solar sail I guess...

But the most obvious method is accelerate for half the journey... Decelerate for the other half...
 
AcidHell2 said:
http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion
A shame this was shut down. could have been built in space. stick hundreds or thousands of nukes on board.

I hope they start this one back up at some point.
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It's interesting, it's a primitive and crude but effective way of achieving high speeds. Problem is, are you comfortable with us putting thousands of nuclear warheads up into our atmosphere using volatile chemical rockets? We'd have to use a space elevator which won't be around for some time.
 
Fusion said:
It's interesting, it's a primitive and crude but effective way of achieving high speeds. Problem is, are you comfortable with us putting thousands of nuclear warheads up into our atmosphere using volatile chemical rockets? .
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yes they can be safely transported. I'm sure they can build in a way to jettison them in case of an emergency. or just make hem fall to the floor in one bit. As long as they aren't pulverised then there is not a problem.
 
- A human lands on the Moon again - within 15 years
- A human lands on Mars - within 40 years
- A human reaches Jupiter (Arthur C Clarke said we'd already be there :)) - We wont go that far.
- A probe or human reaches another star - A probe very long time, humans never
- A probe or human reaches another galaxy Never the distances are too great without VTEC i mean without FTL travel, worm holes etc etc
 
Reaching another star would certainly be possible with even only nuclear propulsion.

Inquisitor said:
Besides, differences in the chemical behaviour of unstable isotopes of heavier elements are negligible. Not that it's possible to render them stable, of course.
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Well the astronaughts would probably not want the shuttle to be made of lighter radioactive isotopes. :p
 
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- A human lands on the Moon again - 15 years
- A human lands on Mars - 40 years
- A human reaches Jupiter - 80 years
- A probe or human reaches another star - probe 150 years, human 400 years
- A probe or human reaches another galaxy - probe 2700 years, human 3000 years.
 
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