Closest non solar planet

[klr]

Agreed.
There was a Scientific American article about 10 years ago, written by a couple of NASA scientists, who predicted that, within 500 to 1000 years, humans could build a star ship capable of accelerating to between 0.1c and 0.2c. That would do it.

It would need the same amount of energy again to slow down the other end.
And hopefully, not hit anything on the way. At those speeds, even a grain of dust would create a collision like in the Hadron Collider.
Over that kind of a distance, even just normal cosmic rays would amount to a huge total, when you total up the distance you're travelled through.
It might destroy the shielding, long before you get there.
It's like travelling through light rain. You hardly notice it when you're stood still, but at 100mph it really stings.

Wise cosmic traveler you are. Those points was I going to make. Very thick shields we will need, and constant repair and replacement will needed be.

[Blind groper]

The thing about cosmic rays is that they are electrically charged. That means they can be diverted using an appropriate magnetic field. I have no doubt that, in 500 to 1000 years, using that technique to divert them away from the human part of a starship would not be difficult.

[mistermack]

The thing about cosmic rays is that they are electrically charged. That means they can be diverted using an appropriate magnetic field. I have no doubt that, in 500 to 1000 years, using that technique to divert them away from the human part of a starship would not be difficult.

It might be more difficult than here on Earth.
Cosmic rays would have the additional energy of a relative speed of 0.1c added to their actual energy.
And time would be running much slower on the Starship, so everything, including the manetic field generators, would be operating differently. What the effect of that would be is anyone's guess.

But at least the travellers wouldn't age as much. You might do the trip in a week of your life, even if it took five Earth years.

[Blind groper]

mistermack

It is unlikely that we will ever be able to accelerate to more than 0.2c (if we want to decelerate again), according to those NASA scientists I quoted, and so effects of aging will be almost unmeasurable. Also, the energy already in cosmic rays is so outrageous, that an added 0.1c to 0.2c is going to make little difference. We can already achieve magnetic deflection. With another 500 years plus technological development, I doubt that extra will be a problem.

[Xamonas Chegwé]

Cosmic "rays" are actually super-high energy matter particles - mainly unattached protons but also nuclei of various elements, electrons and several more exotic particles (such as muons and a tiny bit of anti-matter). They are already travelling so close to the speed of light (99.many many9s %) that the speed of a 0.2c spacecraft wouldn't make any significant difference to their velocity relative to the passengers on board!

Furthermore, once you leave the solar wind behind, any craft would be bathed in far more of the little buggers than we are in the solar system.

As for using magnetic deflection - the trouble with that is, not all of the particles are charged and those that are can be positive or negative.

[mistermack]

Luckily, I don't think there will ever be a desperate rush to reach the next star.

Our own Sun is good for another five billion years, or something in that region, anyway.
I don't think we're going to be desperate for another planet to colonise, even if there was one available.
I think that gigantic space stations with artificial gravity will be what most humans will live their whole lives on, within a few hundred years.
That might seem a bit outlandish, but look at what's happened in the last 100 years.

Energy-hungry projects like space travel will change for ever, once we learn how to maintain fusion reactions. I do have faith that it will be cracked within the next 100 years. And once you get to a certain point in space station construction, and space living, the price of energy on Earth will become irrelevant, with unlimited solar energy available in space.

We just need to reach that certain level, of making things in space, and obtaining materials from the moon etc. Once you get to that self-sustaining point, the rate of expansion will be exponential.

Especailly as manufacturing and computing will be automated beyond belief, in 100 years time.

[Blind groper]

As for using magnetic deflection - the trouble with that is, not all of the particles are charged and those that are can be positive or negative.

Actually, close on 100% of all cosmic ray particles are protons, alpha particles, or heavier nuclei - all positively charged. A few electrons are present, but the number is tiny by comparison.

[Blind groper]

That might seem a bit outlandish, but look at what's happened in the last 100 years.

I do not think it is outlandish. But I doubt it will happen in a few hundred years. A small number of people in a few hundred years, but the majority of humanity, no. A few thousand years, maybe.

Of course, if you have a large population inside a space city, spinning for gravity, and with some kind of shielding mechanism, then a trip to Alpha Centauri may not be such a problem. It is simply a case of having some large thrusters attached, and enough reaction mass carried. If we are looking forward that far in time, we can assume that the thrusters will of highly advanced design, and capable of acceleration to 0.1c, or at least, not much less. If, in addition, we assume that advanced medicine gives the inhabitants long life, the journey time of 50 to 60 years may not be that big a deal.

I think we can also assume that, well before that time, using advanced telescopes, humanity will have a detailed knowledge of what Alpha Centauri will have to offer. Possibly even the results of robotic probes. Our would-be cosmic travellers will know in advance what planets and other orbiting objects will be present.

[Xamonas Chegwé]

We can assume that the thrusters will of highly advanced design, and capable of acceleration to 0.1c, or at least, not much less.

There is no limit on how close to c ANY thruster can get you - all you need is enough fuel! The 1st stage booster of a Saturn 5 could take it to 50%c in about 60 days - of course, it only had enough fuel for 167 seconds!

[Blind groper]

There is no limit on how close to c ANY thruster can get you - all you need is enough fuel! The 1st stage booster of a Saturn 5 could take it to 50%c in about 60 days - of course, it only had enough fuel for 167 seconds!

There are major practical limits based on the mass of the fuel you carry. If fuel is most of the ship's mass, then most of the fuel you burn is burned to accelerate and decelerate fuel, not payload. Less fuel means less velocity. You fire somewhat more than half of that fuel to accelerate, and somewhat less than half of the fuel to decelerate. The more fuel you carry, the slower the acceleration for a given thrust, while you need that extra fuel to achieve a higher peak velocity.

Even if all your fuel is fired out at a large fraction of light speed, you are not going to accelerate to more than a fraction of light speed, unless you decide not to decelerate at the other end.

I am not a rocket scientist, but the SciAm article, written by NASA scientists, suggested that 0.1 to 0.2c will be the practical limits.

[mistermack]

That might seem a bit outlandish, but look at what's happened in the last 100 years.

I do not think it is outlandish. But I doubt it will happen in a few hundred years. A small number of people in a few hundred years, but the majority of humanity, no. A few thousand years, maybe.

Not if a big comet hits the Earth.

Anyway, say a few means 300 or 400 years, that's enough time for a huge change.
Look what's happened to the size of the population of the Earth in the last 300 years. And look how many people fly in a plane every year now. If flying to a space station was easy, cheap and safe, people would do it just to get work.
And with room being limited on Earth, and unlimited up there, the space economy will eventually be way ahead of the Earth economy.
Zero gravity will at some point become an advantage, not a liability, so long as you have a living space that has artificial gravity.

All it needs to kick it off is a much cheaper way to get stuff up there. After that, the sky's the limit.
Ha !

[mistermack]

As far as acceleration goes, if you were to find a technique that could accelerate the propellant exhaust to near light speed, the ratio of fuel/weight would be not much of a problem.

That would mean that your ship would be producing high energy cosmic rays, in effect.
And funny enough, there are cosmic rays coming from all directions, and nobody knows what is producing the fastest ones.

Maybe someone out there has solved that problem a billion years before us, and is whizzing around at 0.5c all over the place.

And the cosmic rays that we're getting are just some of their exhaust trails.

[Blind groper]

Mistermack

We cannot know exactly what will happen in the next few hundred years. My statement was that I doubted most of humanity would be in space cities by then, and I stand by that. Certainly a very low probability event like an asteroid (not a comet, which would not do enough damage) hitting the Earth might kill off most of humanity. The last time such an event happened was 65 million years ago, so the probability of it happening again in the next few hundred years is very, very low.

We will, of course, have a cheaper way to get stuff into orbit. Either a space plane, or even a space elevator. But the majority of humanity is a hell of a lot of people to transport in a short time, even with such a technology.

On a propellant close to light speed.
We already have it, in the form of ions spat out of a linear accelerator. However, the thrust is pretty pathetic. Time may improve this technology. But such a drive will still not permit more than 0.1c to 0.2c maximum velocity, if we want to save fuel to decelerate to relative rest at the end of the voyage.

A linear accelerator, of course, still cannot spit out ions at cosmic ray energies - not by quite a few orders of magnitude. Maybe some time in the future, but I would not hold my breath.

[mistermack]

Mistermack

We cannot know exactly what will happen in the next few hundred years. My statement was that I doubted most of humanity would be in space cities by then, and I stand by that. Certainly a very low probability event like an asteroid (not a comet, which would not do enough damage) hitting the Earth might kill off most of humanity. The last time such an event happened was 65 million years ago, so the probability of it happening again in the next few hundred years is very, very low.

We will, of course, have a cheaper way to get stuff into orbit. Either a space plane, or even a space elevator. But the majority of humanity is a hell of a lot of people to transport in a short time, even with such a technology.

On a propellant close to light speed.
We already have it, in the form of ions spat out of a linear accelerator. However, the thrust is pretty pathetic. Time may improve this technology. But such a drive will still not permit more than 0.1c to 0.2c maximum velocity, if we want to save fuel to decelerate to relative rest at the end of the voyage.

A linear accelerator, of course, still cannot spit out ions at cosmic ray energies - not by quite a few orders of magnitude. Maybe some time in the future, but I would not hold my breath.

What about a fusion drive? Instead of harnessing heat, you direct the neutrons etc from the reaction out from the back of the ship. ( I'm making this up as I go along ).
So you get propulsion and heat at the same time, generating electricity, heat and and drive.

You would need plenty of traditional nuclear fuel, to provide power to the fusion reactor.
But maybe, with progress on fusion, you will be able to control a self-sustaining reaction, giving you thrust and surplus power.

[cronus]

It occurs to me that there may be non solar planets much closer but not attached to a star? perhaps just outside the solar system there a planet which was jettisoned from it's native solar system some time ago?