[Ludi]

But oh well, I guess our Republican president is right in his view that everything's best left to the private sector.

I guess he's just trying to be "fiscally responsible."

[hillsidedigger]

At 25,000 miles per hour, the fastest people have ever flown, it would take 550,000 years to get there and consume more energy even for a small spacecraft carrying a couple of breeding pairs (inbreeding?) than mankind has yet consumed on Earth.

[Sixstrings]

At 25,000 miles per hour, the fastest people have ever flown, it would take 550,000 years to get there and consume more energy even for a small spacecraft carrying a couple of breeding pairs (inbreeding?) than mankind has yet consumed on Earth.

Once you're moving in space, you don't stop because there's nothing to stop you. So it's not like you have to burn fuel the whole way.. it's a matter of getting up to speed and coasting.

[dissident]

As noted above even at half the speed of light the amount energy required is immense.

E=gamma*m*c^2, gamma=1/(sqrt(1-(v/c)^2))

dE=E(v)-E(0) so for v=c/2 and a 100,000 ton space ship (a colony ship may have to be much heavier) we have

(1.155-1)*m*c^2=0.155*1e8*(299,792,458)^2=1.39e24 J

The 2008 world energy consumption was 4.74e20 J. Dividing this into dE we get 2939 years.
But, of course, the world was not consuming at 2008 levels throughout its history.

Instead of dreaming about moving our locust culture to destroy another world we are going to have to adapt or die out.

[EnergyUnlimited]

As noted above even at half the speed of light the amount energy required is immense.

E=gamma*m*c^2, gamma=1/(sqrt(1-(v/c)^2))

dE=E(v)-E(0) so for v=c/2 and a 100,000 ton space ship (a colony ship may have to be much heavier) we have

(1.155-1)*m*c^2=0.155*1e8*(299,792,458)^2=1.39e24 J

The 2008 world energy consumption was 4.74e20 J. Dividing this into dE we get 2939 years.
But, of course, the world was not consuming at 2008 levels throughout its history.

Instead of dreaming about moving our locust culture to destroy another world we are going to have to adapt or die out.

If you also take into account that the craft would have to carry its fuel used for acceleration and deceleration, and also consider specific impulse in your calculations, then you may rest reassured that we are not traveling anywhere.

Scotty must stay at home... Sorry...

[Sixstrings]

Instead of dreaming about moving our locust culture to destroy another world we are going to have to adapt or die out.

If you also take into account that the craft would have to carry its fuel used for acceleration and deceleration, and also consider specific impulse in your calculations, then you may rest reassured that we are not traveling anywhere.

Scotty must stay at home... Sorry...

Then again.. we actually don't know for sure what happens once you leave the solar system into deep space. It's possible there could be something unexpected regarding our understanding of physics.

We can't say anything for certain because we haven't gone that far out yet.. isn't the Voyager probe just now getting to the outer reaches of our solar system?

[Ludi]

"Voyager 1 is currently more than 17 billion kilometers from the Sun."

http://voyager.jpl.nasa.gov/

[EnergyUnlimited]

Instead of dreaming about moving our locust culture to destroy another world we are going to have to adapt or die out.

If you also take into account that the craft would have to carry its fuel used for acceleration and deceleration, and also consider specific impulse in your calculations, then you may rest reassured that we are not traveling anywhere.

Scotty must stay at home... Sorry...

Then again.. we actually don't know for sure what happens once you leave the solar system into deep space. It's possible there could be something unexpected regarding our understanding of physics.

Laws of physics are the same at least across visible Universe.
Nothing unexpected would happen to laws of physics once we have left Solar System or even Galaxy.
We have impeccable record based on astronomical observations to prove that.

[Sixstrings]

Laws of physics are the same at least across visible Universe.
Nothing unexpected would happen to laws of physics once we have left Solar System or even Galaxy.
We have impeccable record based on astronomical observations to prove that.

Well, it's just interesting. By definition, space is nothingness. And yet, to get to the this star we're talking about would take 25,000 whatever years. The fact that it takes so long to cross the "nothingness" of space implies that it's not "nothing" but rather "something." And yet it's not something, deep interstellar space is a total vacuum with no source of gravity for lightyears all around, no radiation even, just nothing. But how can nothing take so long to travel through?

But then I guess space isn't really "nothing" but is in fact full of "dark matter?" Which we barely know anything about at all, it's only theoretically inferred.. so lots to learn still.

[EnergyUnlimited]

Laws of physics are the same at least across visible Universe.
Nothing unexpected would happen to laws of physics once we have left Solar System or even Galaxy.
We have impeccable record based on astronomical observations to prove that.

Well, it's just interesting. By definition, space is nothingness. And yet, to get to the this star we're talking about would take 25,000 whatever years. The fact that it takes so long to cross the "nothingness" of space implies that it's not "nothing" but rather "something." And yet it's not something, deep interstellar space is a total vacuum with no source of gravity for lightyears all around, no radiation even, just nothing. But how can nothing take so long to travel through?

But then I guess space isn't really "nothing" but is in fact full of "dark matter?" Which we barely know anything about at all, it's only theoretically inferred.. so lots to learn still.

Of course space is not "nothing", it is something, even in absence of dark matter or other "fillers".
It would still take a time to travel though space even in absence of these "fillers".

Space has precise, defined physical properties.
For example 2 notable physical properties of space are magnetic permeability (μ0) and electric permeability (ε0).

Now perhaps you would like to know from where speed of light c, an ultimate speed limit is coming?

Well, here you are:

c=1/sqrt(μ0*ε0)

As you can see speed of light is a consequence of well defined, intrinsic properties of space.

Space is "something" and it takes time to travel through it.

It is also mistaken view that deep space is devoid of gravity and radiation.

You know, you are yourself subjected to gravity of our galactic center (galactic year is about 250 000 000 years and it is a time of full rotation of Solar System around galactic center - massive compact object known as Segetarius A which is 28 000 light years away), gravity of Andromeda Galaxy and even gravity of distant quasars.

Deep space is also filled with radiation (microwave radiation, and energetic cosmic radiation from various sources comes to mind).

Turn on analogue TV with old fashion antenna and don't tune it to any channel.
These teeming dots, which you can see are actually a record of microwave radiation which fills entire space of Universe from Big Bang onwards....

[Tanada]

Odds are by the time we are ready to try such a journey we will have developed Bussard Ramjets to power our flights, which over such a range would allow us to reach a respectable percentage of light speed before turnover and deceleration back down to average interstellar speed of the target star on the end of the journey.

http://www.google.com/search?q=bussard+ ... =firefox-a

[Golgo13]

Then you hit a nickel-sized piece of space debris at ludicrous speeds and your entire ship and crew are gone.

[Ludi]

Why not just develop the Universal Will To Become drive ships?

[Sixstrings]

Then you hit a nickel-sized piece of space debris at ludicrous speeds and your entire ship and crew are gone.

In the vastness of space, is that really likely?

Edit: quoted the wrong person, corrected

[EnergyUnlimited]

Odds are by the time we are ready to try such a journey we will have developed Bussard Ramjets to power our flights, which over such a range would allow us to reach a respectable percentage of light speed before turnover and deceleration back down to average interstellar speed of the target star on the end of the journey.

http://www.google.com/search?q=bussard+ ... =firefox-a

There are some calculations done by dr Robert Zubrin showing that these ramjets would generate more drag than thrust.
I couldn't find proper reference to these calculations online, but here you can find some remarks about it:
http://www.wordiq.com/definition/Bussard_ramscoop
Essentially it suggests that this ramjet will remain to be fantasy for ever.

Another problem is that protons don't like to fuse too fast (that damn weak force, you know) and reaction rates available in some conceivable catalytic cycles (CNO or more advanced neon and sodium involving cycle) are nowhere near the rate which is needed to ensure proper working of the setup.

If only said drag don't exist and vacuum of space is filled with D + T mixture instead of protons... maybe in another Universe...

[Sixstrings]

There are some calculations done by dr Robert Zubrin showing that these ramjets would generate more drag than thrust.

How can you have drag in space?

[Tanada]

Interstellar dust and gas, on the order of one molecule per cubic meter, adds up too lots and lots of teeny tiny impact events that slow your craft down as you collide with them and ricochet off of them. The faster you go the more of them you run into during a set period of time and as you approach half light speed it becomes more like flying a plane than coasting through empty vacuum. The purpose of a Bussard ramjet is to use this interstellar gas as fuel and burn it to maintain your velocity.

[EnergyUnlimited]

There are some calculations done by dr Robert Zubrin showing that these ramjets would generate more drag than thrust.

How can you have drag in space?

In addition to what Tanada have said I must add that charged particles will react by repulsion against approaching funnel shaped magnetic field of the "scoop".

This effect alone will cancel out (as per dr Zubrin's calculations) any thrust generated by fusion reactors.

Again, space is not as empty as you think, however there is more matter on the way to Earth orbit than from there to the end of visible Universe.

[Tyler_JC]

My physics is a little rusty but I found a simple calculator online for the kinetic energy formula.

To move a one kilogram object at 10% the speed of light would require the energy equivalent of ~98,000 barrels of diesel. But, of course, you have to account for the weight of the fuel. Obviously we wouldn't use diesel fuel in space but it gives you a sense of how much energy we're talking about here.

The space shuttle, a craft FAR too small for anything even approaching interstellar travel, weighs more than 100,000kg.

A more realistic interstellar space craft might be 50 times heavier (after all, we have to take care of a crew of people for decades). That means we're talking about a five thousand metric ton craft that has a magic fuel source which weighs nothing.

Amount of energy required to move a 5,000,000kg object at 10% the speed of light?

2.25E+25 Joule

Amount of energy that hits the Earth every year from the sun?

5.5E+24 Joule

So our space ship would need to use 4 times more energy than hits the earth every year just to accelerate to 10% the speed of light. If we also wanted to slow our ship down to zero again (you know, rather than just collide with the planet and create a massive freaking crater), we would actually need 8 times as much energy as hits the Earth every year.

That is several orders of magnitude more energy than humanity has used during its entire existence.

We cannot and will not devote that much energy to interstellar space travel.

[Sixstrings]

I've been watching Star Trek: Enterprise on DVD lately. In one of the early episodes, they mention Earth finding a planet just 20 lightyears away and it being "too close not to colonize." So they sent a colony ship which took years to get there and then the colony was lost and the story went on from there.

Anyway, was just ironic about the perfect planet 20 lightyears away part, this show was produced before Gliese 581g was discovered.