Interstellar Travel

[cicatrix]

Breakthroughs are not happening spontaneously. What we call 'breakthoughs' in our history is a result of scientific experiments that had been conducted to test some theory. It goes like this (very simplified, actually, imagine the familiar tech tree instead)

(16-19th century):

Theory #1 -> N Experiments -> Proof (Breakthrough) -> --> Theory #2 -> N² experiments -> Breakthrough #2

(20th century):

--> Theory #3, #4, #5 -> N⁴ experiments (time, labor, money) -> Breakthrough #2.1 (and we need another 9 iterations to get to level 3)

(21th century):

--> Theory #5, #6, #7 -> N⁸ experiments (time, labor, money) -> Breakthrough # 2.1.1 (and we need another 9 iterations to get to level 2.2)

etc.

Now we have

Theory # N and we need N^over9000 experiments (and even larger amounts of labor, resources and money) to reach another level.

It's exponential. And even supercomputers, technology and huge budgets help little. Each new step costs us more by a whole magnitude. Scientists die out of old age without achieving their goals and we make a step backward. Seriously, the average human lifespan hinders the scientific progress now more than ever and it would only get worse. Progress is a complex thing, you can't get a breakthrough only in spacecraft propulsion without having similar successes in neighboring branches of science. This is why I don't expect any 'breakthoughs' in the near future.

[rtxoff]

I agree with that, we are hitting a wall in science progress.

[wasmic]

I don't agree at all. If you look at how technology has developed in the last decades or even centuries, you'll find that technology (if not scientific knowledge) is accelerating. I wouldn't be surprised if the next 20 years brought more technological progress than the last 50.

[Kibble]

I don't agree at all. If you look at how technology has developed in the last decades or even centuries, you'll find that technology (if not scientific knowledge) is accelerating. I wouldn't be surprised if the next 20 years brought more technological progress than the last 50.

The last few centuries are pretty unique in human history - we discovered industry, which brought unimaginable progress. Most of the time we're not in a technological revolution of this scale. The last time was when we discovered agriculture!

[KerikBalm]

If humanity would focus efforts on Fusion power (more than some side-show called ITER that is more often used for political purposes to show Fusion is not viable and we should continue to encourage oil and coal extraction), we could manage probes that could travel at significant portions of the speed of light...

Although I think such probes would be wasted going to just the Alpha-Beta/Proxima Centauri system - the acceleration would be soo poor, that you'd spend years accelerating... 10% of the speed of light to alpha Centauri would "only" be 50 years....

But if you spend 20 years accelerating.... its going to take a lot longer, especially if you don't want to just do a flyby (but then again... you could do a flyby and then have the probe go to a more distant location).

We could also get some pretty impressive speed with fission, and fission would be very practical for exploring our own system...

But there seems to be some taboo about loading nuclear reactors on top of massive disintegrating-totem-poles-of-boom.

Even though a reactor isn't so bad until its actually fired up for the first time...

A newly built and never run reactor should be an acceptible launch risk.

[Wesreidau]

Nuclear Salt Water Rocket. I don't see a need to go interstellar within the century, however. We've got enough Lebensraum in the heliosphere to last a millennium.

[crazyewok]

Possibly.

I wont say no and I wont say yes.

I can barely predict the technology we will have in 10 years let alone 90 years.

[xenomorph555]

I say possibly, either with the advent of new technology or they legalise nuclear engines and let them develop for a few decades.

[AngelLestat]

I vote yes (and I am sure of that), because interstellar travel for me count as the first probe mission launched to another star without taking into account the arrival date.

A solar sail interstellar probe that reach 5% to 7% of light speed is not so difficult to achieve, it can also brake using a similar maneuver in the star destination.

With all instruments printed in the same solar sail, in can be super light, plus the solar sail can act as parabolic mirror for comunication.

[Requia]

Going anything near the speed of light is basically like sitting in the beam of a particle accelerator. Space isn't truly empty, even between stars. At normal astronomical speeds it's irrelevant, but as you go faster the individual hydrogen atoms start to have higher and higher impact energies.

[SargeRho]

So you'll need a magnetic field, or some other way of deflecting the hydrogen, or at least a way to soften the impacts.

[problemecium]

I think we have a decent chance... if another Cold War happens and we have to race Russia (or whoever) to the next star.

Interplanetary travel is of course a more viable and practical option to pursue first.

[theend3r]

No. I'm sure it's well within the scope of our abilities but so is inhabiting other planets which is far more important. United world government might speed things up (or slow down if it's full of hippies like the current EU) but it still doesn't make any sense.

There is the rule of interstellar travel that after you send a ship on a voyage you can build an even better ship that will arive there sooner. To send a ship to stars we need to be either very close to the physical limits of technology or in a dire need of doing so which won't happen for a while, certainly not within 100 years.

[PB666]

What if we are able to harness antimatter? Then 6 years to Alpha Centauri

Matter/antimatter drive?

Lets think about this. Assuming you have the technology to store antimatter (nope) using relativistic theory you would need approximately 10 times your payload to reach 0.1-0.2C to have enough energy to both accelerate and decelerate on arrival. 4 LY to AC means 20.5 years at 0.2C assuming you acceleration is no greater than 1g.

And BTW that is something like 10 exajoules of power magnitudes and more power than humans have ever produced. Its not realistically possible. And this power is going to be utilized in an ion drive, one of the slowest accelerating devices we have at our disposal.

Warp drive, worm holes and matter/anti-matter drives are something that Hollywood comes up because the reality of space flight is about 6 magnitudes to weak to have Shattner or Lorne Green zipping from planet to planet between tea servings. If we improved modern technology 100 fold, it would still take the entire time the human species has been on this planet to reach another potentially habitable world that would need to undergo eons of terraforming before humans could settle.

You want to get to the next star, make a long range probe, fill it with stable lyophilized microbes, put in some of the best engineered electronics and a really durable photocell and find a suitable target, 1,000,000 years later it arrives and does its job. You could do this for every goldilocks planet discovered. If the cannae drive works you can use the photocell to open solar panels and help guide the probe to its destination.

[K^2]

PB666, where are you getting these numbers from? For a matter-antimatter drive, effective Isp is 0.25 c/g in the worst efficiency case. That is 4:1 fuel to payload to get to .2c and back. So 2kg of antimatter to 1kg payload. This is the worst it could be. That factor 10 sounds entirely made up. Which brings to question your ability to gauge other factors as well.

For the record, realistically, we can get up to .5 c/g if we can get it to lase, perhaps higher with other trickery, and there are free braking alternatives, such as Bussard Ramjet. That brings fuel fraction down to 50%. And that is just tech we already have.

[Kibble]

For a matter-antimatter drive, effective Isp is 0.25 c/g

How can we know the effective Isp of a rocket engine that has never been flown, tested, or even built and which is powered by fuel for which we have only ever produced nine atoms, and only kept for 17 minutes? His point is still sound - fast interstellar travel is quite impossible, and will remain that way for a very, very long time.

[ZetaX]

How can we know the effective Isp of a rocket engine that has never been flown, tested, or even built and which is powered by fuel for which we have only ever produced nine atoms, and only kept for 17 minutes?

Because

a) he only gives a lower bound; in other words, if you can achieve that with current tech (and we can: put them into a huge dish to react, reflecting all energy backwards), then he is right;

it does not matter how exactly antimatter behaves; it's only relevant that it turns into pure energy when mixed with equal amounts of matter.

His point is still sound - fast interstellar travel is quite impossible, and will remain that way for a very, very long time.

No, a point is not sound because the conclusion is (probably) correct; "the sky is green, therefore cats are different from dogs" is not sound at all, for example. For an argument to be sound you need both the premises to be true (the sky is green / that factor 10) and the argument itself to be valid (the sky somehow having to do with those species / the calculations and the asserted usage of a slow ion drive being explained and them being correct). Neither of them is satisfied in my example nor in the post we are talking about.

Edited May 20, 2015 by ZetaX

[K^2]

Not even reflecting. That .25 factor corresponds to just combining matter and antimatter next to a led damper plate. Exactly 1/4 of available impulse will be absorbed. You literally cannot do worse. There are a bunch of ways to do better.

Edit: I lied. You can do slightly worse with a dumb pp' burner due to meson/lepton production. The ee' reaction is pure gamma, but bare positrons are hard to store. If you could keep positronium stable, that would be ultimate photon drive fuel. But wishing won't make it so. For existing tech, I'll do a proper check on worst case for anti-Hydrogen tomorrow. The fraction for heavy stuff won't be large, so it should not be a big deviation, but I feel like I owe you guys a number now.

Edited May 20, 2015 by K^2

[Xannari Ferrows]

1.68

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2374

000190.2374.5

[PB666]

Not even reflecting. That .25 factor corresponds to just combining matter and antimatter next to a led damper plate. Exactly 1/4 of available impulse will be absorbed. You literally cannot do worse. There are a bunch of ways to do better.

Edit: I lied. You can do slightly worse with a dumb pp' burner due to meson/lepton production. The ee' reaction is pure gamma, but bare positrons are hard to store. If you could keep positronium stable, that would be ultimate photon drive fuel. But wishing won't make it so. For existing tech, I'll do a proper check on worst case for anti-Hydrogen tomorrow. The fraction for heavy stuff won't be large, so it should not be a big deviation, but I feel like I owe you guys a number now.

The lead plate is not your payload, the 0.25 scenario is unrealistic considering that humans need space and food, and they don't do particularly well with high energy gamma rays plunging through their bodies. When you are using 10 fold or 100 fold more A/AM. The higher fuel to PL weight the better final velocity, but the more initial starting weight in matter antimatter which one cannot contain. I stand by my previous, even in the fantasy (that is what it is, nothing more than a fantasy) matter/antimatter never gets higher than about 0.2c.

The type of energy production on a lead plate (low melting point) is going to do what at the beginning of the burn when you have alot of fuel to accelerate at 1g? OK since this maybe to much we slow accleration to 0.1g, which means reaching 0.2C takes two years and slowing down takes a year. and the trip to AC takes 20.

Yeah and so, matter/antimatter doesn't really get you to the next star at warp 1.

[Thorenn]

The Technology exists...Orion

But:

1. No Money

2. No Interrest

3. Fear

[crazyewok]

The Technology exists...Orion

But:

1. No Money

2. No Interrest

3. Fear

Hush thats a dirty word round here.

Nuclear pulse propulsion is a taboo subject

Anyway its not any good for manned installer travel only unmanned.

Edited May 20, 2015 by crazyewok

[AngelLestat]

I am agree with K2, I read many methods already simulated with cern software which can achieve 0.6c isp, I read other papers how to achieve even 0.99c (pure photon rocket).

But the biggest problem of antimatter is not the engine.. never was..

The real problem is how to storage and produce big amounts of antimatter in the first place.

Those are the 2 main issues which are very very difficult to solve with our current technology and knowledge level.

And any practical craft using antimatter would not be made in this century from what we know so far, so it does not qualify for the topic..

Anyone who has a better idea than a solar sail probe at 0.07c + brake in destination, please tell me how to achieve it in this century.

Edited May 20, 2015 by AngelLestat

[ZetaX]

The lead plate is not your payload, the 0.25 scenario is unrealistic considering that humans need space and food, and they don't do particularly well with high energy gamma rays plunging through their bodies. When you are using 10 fold or 100 fold more A/AM.

That 0.25 is Isp. And as such it is probably correct. Isp does not care about your mass, payload or whatever. So no, it is very realistic (and probably simply factual). Now it is another question if it allows us to reach 0.25c, but K^2 didn't say that; he only claimed 0.2c at 4:1 ratio (which by the way is again just a calculation and has nothing to do with future tech). Read up what he claimed and what Isp has to do with this; you said nothing that contradicts what he wrote.

If you would go for a 16:1 ratio, you could go for ~0.4c (ignoring relativistic effects for simplicity). Therefore more than 0.2c is not fantasy. But maybe not worth it.

Humans needing space/shielding/food is also no concern. There is enough space out there, and enclosing (or shielding) something scales slower than volume (until you reach some other problems, but we probably won't). Food and other goods (each being a miniscule part of the total mass) can either be recycled or be used for the M/AM reaction; so no waste there.

[PB666]

I am agree with K2, I read many methods already simulated . . . .

Simulated is the key word. If lead is the blast plate, what happens to the lead over time. 0.6c/g and 0.99c/g is fiction, pure and simple, its a hype train used to keep supercollider and space research funding going.