Question about space elevators:

Originally posted by sonhouse
AC is only about 4 light years away. So taking 40,000 years puts the velocity at 1/10,000 c. That is about 32 kilometers per second. I would say we can reach at least 0.1c which puts AC 'only' 40 years journey. 0.2c, 20 years.
0.4c, 10 years and so forth. I don't think it will be a huge engineering problem to reach 1/10th c. For this century maybe but even ...[text shortened]... inherently more efficient in terms of what can be achieved with any kind of rocket, even fusion.

Here is a back-of-an-envelope calculation. The gamma factor associated with a relative speed of 0.1c is 1.005(04). Suppose our spaceship has the same mass as the USS Enterprise - that's CVN-65 not NCC-1701 - the big E had a displacement of 93,284 long tons or 94,777 tonnes.

E = gamma*mc²
T = (gamma - 1)*mc² =4.29(7) * 10^22 joules

A kilowatt hour is 3.6 mega joules and a GigaWatt hour 3.6*10^12 Joules. So the minimum energy needed to get to that speed is 1.19*10^10 giga Watt hours. For comparison the Tsar Bomba, the largest nuclear device ever tested, had an energy output of around 200 petajoules (= 2*10^17 Joules). So we need around five orders of magnitude more energy than the largest atom bomb ever built delivered.

Somehow I don't think this is feasible without dilithium crystals and matter anti-matter converters.

Originally posted by DeepThought
You do realise that the estimated time to reach Alpha Centauri is of the order of 40,000 years? Unless the speed of light turns out not to be the great barrier we currently think it is the prospects of colonising planets around other stars are about nil.

Besides, if the planets are habitable then the chances are they'll already be occupied and if they aren't then terraforming isn't a trivial exercise.

You do realise that the estimated time to reach Alpha Centauri is of the order of 40,000 years?

Using what? Rocket power? It will take about 44 years going 0.1c.
It is just a matter of time before the right kind of fusion nuclear power driven space propulsion, or, alternatively, using antimatter once a way is found of harvest it in sufficient quantities from that which is trapped around ionospheres so to allow a ship to go that fast.

Besides, if the planets are habitable then the chances are they'll already be occupied and if they aren't then terraforming isn't a trivial exercise.

it can be done by sending AI robots along with the equipment to seed new industry to the planet. They could use solar/wind power to power their industry and initially concentrate on making more robots to make more factories to make more robots and so on. When they cover the whole land surface with industry, they can then start processing the atmosphere. Then when the atmosphere and conditions are inhabitable for humans complete with infrastructure, technology and everything humans need to survive there, humans can colonize.

Originally posted by DeepThought
Here is a back-of-an-envelope calculation. The gamma factor associated with a relative speed of 0.1c is 1.005(04). Suppose our spaceship has the same mass as the USS Enterprise - that's CVN-65 not NCC-1701 - the big E had a displacement of 93,284 long tons or 94,777 tonnes.

E = gamma*mc²
T = (gamma - 1)*mc² =4.29(7) * 10^22 joules

A kilowatt hou ...[text shortened]... how I don't think this is feasible without dilithium crystals and matter anti-matter converters.

So we need around five orders of magnitude more energy than the largest atom bomb ever built delivered.

Somehow I don't think this is feasible without dilithium crystals and matter anti-matter converters.

No dilithium crystals or matter anti-matter converters required!
It is just a matter of time before technology catches up and can harvest sufficient quantities of antimatter from that which is trapped around ionospheres. It has been calculated to be feasible with sufficient antimatter. In addition, it is just a matter of time before technology catches up and uses fusion power. It has been calculated that 0.1c can be achieved if most of the mass of the spaceship is the nuclear fuel and there is no reason why it can't be.

Originally posted by humy

So we need around five orders of magnitude more energy than the largest atom bomb ever built delivered.

Somehow I don't think this is feasible without dilithium crystals and matter anti-matter converters.

No dilithium crystals or matter anti-matter converters required!
It is just a matter of time before technology catches up and ca ...[text shortened]... if most of the mass of the spaceship is the nuclear fuel and there is no reason why it can't be.

Since Tsar Bomba was a hydrogen bomb I don't think nuclear fusion will help. I'm sorry, but this is unfeasible with almost any imaginable technology.

This is to say nothing of the difficulties involved in making a ship capable of sustaining the lives of a minimum of 100 colonists for the trip. Alongside the risk that what they find at the other end simply cannot be made habitable, Alpha Centauri Ab is disputed - there may not be a planet at all, never mind one capable of sustaining or being made to sustain human life.

Originally posted by DeepThought
Since Tsar Bomba was a hydrogen bomb I don't think nuclear fusion will help. I'm sorry, but this is unfeasible with almost any imaginable technology.

This is to say nothing of the difficulties involved in making a ship capable of sustaining the lives of a minimum of 100 colonists for the trip. Alongside the risk that what they find at the other end ...[text shortened]... ot be a planet at all, never mind one capable of sustaining or being made to sustain human life.

Since Tsar Bomba was a hydrogen bomb I don't think nuclear fusion will help

sorry, misspelling; that should have been “fusion” (specifically using hydrogen ) ; and that WILL help!
0.1c using fusion has been calculated.

Originally posted by DeepThought
Since Tsar Bomba was a hydrogen bomb I don't think nuclear fusion will help. I'm sorry, but this is unfeasible with almost any imaginable technology.

This is to say nothing of the difficulties involved in making a ship capable of sustaining the lives of a minimum of 100 colonists for the trip. Alongside the risk that what they find at the other end ...[text shortened]... ot be a planet at all, never mind one capable of sustaining or being made to sustain human life.

This is to say nothing of the difficulties involved in making a ship capable of sustaining the lives of a minimum of 100 colonists for the trip.

It wouldn't have to sustain life. It is just a matter of time before technology catches up and allows people's cells to be safely generically modified and then genetically modified to, like the wood frog, tolerate being frozen solid and then revived. Then the humans can travel in frozen hibernation with no energy expenditure for life support during the voyage. In fact, they can be frozen both when they go on the spaceship and when they are taken off (by the AIs and then be revived on the planet's surface ) thus no need for any life support on the spaceship.

Alongside the risk that what they find at the other end simply cannot be made habitable,

Not if they send AI robots first to check first and then do any of the required transforming before the humans arrive -see my other post.
If it isn't possible to terraform, the AIs would send a message back saying so so that humans don't go there and only go to where planets have already been confirmed to be terraformed (by the AIs. No need for humans to do the terraform themselves )

Originally posted by humy

Since Tsar Bomba was a hydrogen bomb I don't think nuclear fusion will help

sorry, misspelling; that should have been “fusion” (specifically using hydrogen ) ; and that WILL help!
0.1c using fusion has been calculated.

Got a reference, preferably online, for that calculation?

Originally posted by DeepThought
Got a reference, preferably online, for that calculation?

I tried but couldn't find any link giving specific calculations for this but I got that "0.1c" figure from where it says "10%" below:

http://en.wikipedia.org/wiki/Interstellar_travel

"...

Project Orion team member, Freeman Dyson, proposed in 1968 an interstellar spacecraft using nuclear pulse propulsion that used pure deuterium fusion detonations with a very high fuel-burnup fraction. He computed an exhaust velocity of 15,000 km/s and a 100,000-tonne space vehicle able to achieve a 20,000 km/s delta-v allowing a flight-time to Alpha Centauri of 130 years.[35]
Later studies indicate that the top cruise velocity that can theoretically be achieved by a Teller-Ulam thermonuclear unit powered Orion starship, assuming no fuel is saved for slowing back down, is about 8% to 10% of the speed of light (0.08-0.1c).[36]
An atomic (fission) Orion can achieve perhaps 3%-5% of the speed of light.

A nuclear pulse drive starship powered by Fusion-antimatter catalyzed nuclear pulse propulsion units would be similarly in the 10% range and pure Matter-antimatter annihilation rockets would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light. In each case saving fuel for slowing down halves the max. speed. The concept of using a magnetic sail to decelerate the spacecraft as it approaches its destination has been discussed as an alternative to using propellant, this would allow the ship to travel near the maximum theoretical velocity..."

note the impressive theoretical possible "80%" of c above if use antimatter.

However, there is a BIG catch though that I forgot about until just now; on such a long interstellar journey, there is bound to be some collisions of space dust against the fast moving spaceship. Even the tiniest bit of space dust colliding with the spaceship at a relative velocity of ~0.1c would be something like a one-ton bomb striking it! (at lower speeds of course ) . How can the spaceship be prevented from being blown apart from that? The obvious way of just putting a shield in front of it may require the shield to be so massive that its mass would lower the top speed of the spaceship by something like ~100 fold less making it utterly pointless!

I thought of various schemes to work around this problem which I would discuss on request but so far each schemes I have come up with has its own big problems.
Perhaps there really is no practical way around this? if so, then the biggest barrier by far to fast interstellar travel is, perhaps surprisingly, simply dust!
Or perhaps there is a partial solution but we would be forces to compromise and just stick to a speed limit of ~1% of c?

Originally posted by humy
I tried but couldn't find any link giving specific calculations for this but I got that "0.1c" figure from where it says "10%" below:

http://en.wikipedia.org/wiki/Interstellar_travel

"...

Project Orion team member, Freeman Dyson, proposed in 1968 an interstellar spacecraft using nuclear pulse propulsion that used pure deuterium fusion detonations with ...[text shortened]... rtial solution but we would be forces to compromise and just stick to a speed limit of ~1% of c?

Wouldn't an antimatter shield annihilate regular matter? However, there must surely be more energy consumption associated with anti matter shield ( probably rendering the proposal a mute point). I must say this type of physics is all way out of my realm of understanding, so please be gentle if I say something ridiculous.

Originally posted by joe shmo
Wouldn't an antimatter shield annihilate regular matter? However, there must surely be more energy consumption associated with anti matter shield ( probably rendering the proposal a mute point). I must say this type of physics is all way out of my realm of understanding, so please be gentle if I say something ridiculous.

Trust me, you wouldn't want to use an antimatter shield against collisions with matter even if that matter is only dust size! Just one collision would be like a small atomic explosion that would blow up the shield and anything (like a spaceship ) attached to it.

At relatively 'low' velocities, a Whipple shield would do just fine:
http://en.wikipedia.org/wiki/Whipple_shield
But, for this application, we need it for the much higher relativistic velocities and a Whipple shield won't work for that and, so far, I haven't work out a practical solution for these relativistic velocities.

I keep coming up with ideas though. One is to use gigantic magnetic fields so powerful that they would deflect even relatively non-magnetic dust from colliding with the spaceship. But I guess, even with the most effective superconductor coils, generating the necessary ridiculously strong and gigantic magnetic fields would be extremely difficult if not impossible. The coils would be likely to blow themselves apart will before enough electric current is pumped into them to generate that sort of magnetic field strength.
-Anyone else have an idea?

Originally posted by joe shmo
Wouldn't an antimatter shield annihilate regular matter? However, there must surely be more energy consumption associated with anti matter shield ( probably rendering the proposal a mute point). I must say this type of physics is all way out of my realm of understanding, so please be gentle if I say something ridiculous.

On the assumption you could produce enough antimatter to make into a shield how do you intend to manipulate it? The stuff annihilates with ordinary matter on contact so you'd have to use magnetic fields to hold it in place. If that goes wrong it would be pretty spectacular to watch from a safe distance.

Originally posted by DeepThought
On the assumption you could produce enough antimatter to make into a shield how do you intend to manipulate it? The stuff annihilates with ordinary matter on contact so you'd have to use magnetic fields to hold it in place. If that goes wrong it would be pretty spectacular to watch from a safe distance.

To be honest,...I didn't know the net effect of the matter/anti matter collision was exothermic or catastrophically explosive...For that matter, I wasn't even aware that it has actually been observed! So I guess using it as a shield would be pointless.

I guess I never really thought how one might use matter/anti-matter to propel a space ship. In this type of reactor, is the net fuel mass zero for the ship? In the reaction, do you obtain the rest mass energy of the matter reactant? Does it hold with : δU(universe) = 0

δU(universe) = -δT(universe)? Edit: this statement is nonsensical, sorry

Originally posted by humy
Trust me, you wouldn't want to use an antimatter shield against collisions with matter even if that matter is only dust size! Just one collision would be like a small atomic explosion that would blow up the shield and anything (like a spaceship ) attached to it.

At relatively 'low' velocities, a Whipple shield would do just fine:
http://en.wikipedia.org/wik ...[text shortened]... s pumped into them to generate that sort of magnetic field strength.
-Anyone else have an idea?

I don't think the magnetic field idea is a goer. However you'd need a pretty hefty magnetic field to protect the crew from cosmic rays, whether they're in deep freeze or awake.

For a grain of dust weighing a milligram a collision at a relative speed of a tenth of the speed of light would release about 450 megajoules of energy, or about 125 kWH. I don't think that's completely unmanageable. It's probably within the capabilities of a thick multi-layered Whipple shield. Anything bigger than that would be a problem.

Possibly the way forward would be a path clearer, you have several space ships, with the lead one designed solely to make sure any likely collisions were with it. Use lasers to make sure the trailing ships follow exactly in its path. If it hit anything big, say around a gram, the main ship would be going at a similar speed to the debris cloud so no danger accrues from the collision.

The pathfinder ships could be deployed on demand and wouldn't be required to be able to accelerate to that speed. During the constant velocity part of the trip this would probably work. During deceleration the engines will sort out any problems with space dust. The dicey part is the acceleration phase, where I think you'd just have to deploy pathfinders that accelerate with the ship and then recapture or discard them when they run out of fuel. Technologically it's no greater problem than getting to that speed in the first place, but economically it's horrible.

Originally posted by joe shmo
To be honest,...I didn't know the net effect of the matter/anti matter collision was exothermic or catastrophically explosive...For that matter, I wasn't even aware that it has actually been observed! So I guess using it as a shield would be pointless.

I guess I never really thought how one might use matter/anti-matter to propel a space ship. In this ty ...[text shortened]... matter reactant? Does it hold with : δU(universe) = 0 such that δU(universe) = -δT(universe) ?

A positron has the same mass as an electron - but the opposite charge and fermion number. So the total energy released is 2*mc², where m is the electron mass. The total energy of the universe doesn't change, assuming that that is what you meant by δU(universe) = 0.

Originally posted by DeepThought
A positron has the same mass as an electron - but the opposite charge and fermion number. So the total energy released is 2*mc², where m is the electron mass. The total energy of the universe doesn't change, assuming that that is what you meant by δU(universe) = 0.

Yeah that's what I meant,...Is the universes internal energy increased by the reaction? I'm thinking that it would have to since the universe lost mass.