variable specific impulse magnetoplasma rocket interstellar capabilities?

[cantab]

We're all looking at physics and engineering here, but there is another route to the stars: biology and medicine. If humanity can cure aging and allow individual people to live for millenia, suddenly a 500-year trip becomes not so long.

[noobsrtoast]

my mind stayed intact upon reading that statement, seeing as i have seen what kind of fuel requirements a chemical rocket would need to get to lightspeed....

[noobsrtoast]

thats what i was saying too, if you can find a way to get over our biological flaws, suddenly interstellar travel becomes not so impossible

[noobsrtoast]

i feel like we should be taking more a fusion engine approach, seeing as we get more bang for our buck, but i think what people have neglected to mention in this post is the effects of traveling at interstellar velocities on the human body, as well as the risk of crashing into something as simple as a hydrogen atom. i think the biggest reason were holding back on interstellar travel is because we have to find a way around these issues. also there's that annoying twin paradox thing we have to get over, not to mention the various time dilation effects. im thinking magnetic fields might help a little bit with some of the situations, but not all, we still have to worry about what happens to us once we reach those velocities.

[noobsrtoast]

we need not to focus on the cost of such missions, or how much we will gain, we need to do it because of human curiosity, because of our desire to explore the universe around us. sure it will be costly but the reward is that our civilization gets to survive for longer, discover more, evolve further, advance our technologies even more, think of how much were going to learn in the process of constructing such a craft. the 2 gifts you gain from creating such a mission are: the gift of knowledge which is not something that should be taken for granted, and the reward of knowing we did that, we were able to ensure our races survival for billions of years more than we could have ever if we stayed inside our system. plus think of the sights you would see when you get there.

[cantab]

The twin paradox - the actual paradox where it seems that each twin should be younger than the other, not the non-paradox of one twin aging more - is perfectly well understood. The fact that one twin accelerates and the other doesn't is what makes the situation not symmetric and thus the accelerating twin younger.

[noobsrtoast]

The twin paradox - the actual paradox where it seems that each twin should be younger than the other, not the non-paradox of one twin aging more - is perfectly well understood. The fact that one twin accelerates and the other doesn't is what makes the situation not symmetric and thus the accelerating twin younger.

which would in turn mean that when the light speed vessel slows down and checks the date, they should find that they are at least 200+ years older than anyone on earth and likely either they have been forgotten or something better than their vessel has been developed, which is another challenge of interstellar flight in itself.

[Northstar1989]

@noobsrtoast Please stop triple-posting the thread with poorly-formatted (you're not even making use of capitalization) run-on posts. It's it bad form.

@Streetwind

I think you're beholden to some misconceptions- the bombs used in Orion *already are* a type of fusion propulsion- they are small thermonuclear warheads, which means the majority of their explosive power actually comes from the fusion component of the explosion.

The fusion proportion also goes up with larger bombs (the quantity of fissile materials necessary to initiate fusion remains relatively unchanged as you scale up the bombs- meaning you can pack in a larger percentage of fusion components), which is one reason the ISP of Orion actually *increases* the larger you scale-up the system...

Oh, and since the fusion components don't generate significant fallout, only the fissile materials do- a 25 km diameter Orion generates roughly the same fallout as a 250 meter version...

Thus *any* size of Orion comes in at about 1-2 total deaths caused by radiation per launch, and as the smaller (*less* cost-effective) designs are already at a lower cost than a Saturn V (one of the *major* breakthroughs Project Orion scientists made was in figuring out how to mass-produce small thermonuclear warheads- for obvious reasons those parts of the document are still HIGHLY classified...), you could *easily* use the money saved vs. a Saturn V (or SLS) sized conventional rocket to save dozens of lives in the developing world by providing people access to clean water, food, vaccines, condoms, education, etc...

Regards,

Northstar

P.S. I have never been one of those "we have too many issues to deal with here" type people when it comes to space exploration, as I *strongly* believe looking to the stars and pushing human limitations inspires people to peace and innovation back on Earth; BUT I believe it is a *MORAL IMPERATIVE* to meet our space-exploration goals as cheaply and efficiently as possible, so we have more money left over to deal with problems here. In other words, explore space, but don't be wasteful about how you do it...

Edited November 21, 2014 by Northstar1989

[NERVAfan]

Thus *any* size of Orion comes in at about 1-2 total deaths caused by radiation per launch,

There's no evidence that you can accurately extrapolate risk to that extreme of low dose/high population. Yes, the linear-no-threshold model of radiation risk produces that number, but that doesn't mean it reflects reality; that's extrapolating so tremendously far beyond the data the model was based on. It's pretty likely (IMO - this is hotly debated) that there would be no deaths.

The showstopper problems with Orions are politics (anti-nuclear fear and nuclear proliferation concerns), EMP, and likely cost, not radiation.

[Streetwind]

I think you're beholden to some misconceptions (...)

I am not "beholden to misconceptions", I was making a comparison for people to help visualize the concept of the fusion pulse rocket in their head

Also, as NERVAfan said, the "x number of deaths per launch" metric is complete nonsense. It ignores things like effects on the ecosystem, loss of plant and animal life, localized fallout concentrations vs. global spread vs. population densities and the highly variable effects this brings with it, nonfatal radiation deseases, the entire spread of non-radiation-related effects of a rapid series of thermonuclear detonations... and last but not least, ethics. When is it ever acceptable to think of human lives as a currency? Regardless of whether there would be actual deaths or not, using that metric as an argument in favor of Project Orion is unacceptable, and just underlines how far removed from reality the concept really is.

[magnemoe]

@noobsrtoast Please stop triple-posting the thread with poorly-formatted (you're not even making use of capitalization) run-on posts. It's it bad form.

@Streetwind

I think you're beholden to some misconceptions- the bombs used in Orion *already are* a type of fusion propulsion- they are small thermonuclear warheads, which means the majority of their explosive power actually comes from the fusion component of the explosion.

The fusion proportion also goes up with larger bombs (the quantity of fissile materials necessary to initiate fusion remains relatively unchanged as you scale up the bombs- meaning you can pack in a larger percentage of fusion components), which is one reason the ISP of Orion actually *increases* the larger you scale-up the system...

Oh, and since the fusion components don't generate significant fallout, only the fissile materials do- a 25 km diameter Orion generates roughly the same fallout as a 250 meter version...

Thus *any* size of Orion comes in at about 1-2 total deaths caused by radiation per launch, and as the smaller (*less* cost-effective) designs are already at a lower cost than a Saturn V (one of the *major* breakthroughs Project Orion scientists made was in figuring out how to mass-produce small thermonuclear warheads- for obvious reasons those parts of the document are still HIGHLY classified...), you could *easily* use the money saved vs. a Saturn V (or SLS) sized conventional rocket to save dozens of lives in the developing world by providing people access to clean water, food, vaccines, condoms, education, etc...

Regards,

Northstar

P.S. I have never been one of those "we have too many issues to deal with here" type people when it comes to space exploration, as I *strongly* believe looking to the stars and pushing human limitations inspires people to peace and innovation back on Earth; BUT I believe it is a *MORAL IMPERATIVE* to meet our space-exploration goals as cheaply and efficiently as possible, so we have more money left over to deal with problems here. In other words, explore space, but don't be wasteful about how you do it...

However the orion bombs are not very efficient fusion, the fusionable material is just a small part of each bomb, structure, chemical explosives and fission parts take up a lot of the mass. Efficiency is also pretty limited.

Yes its more than good enough for interplanetary trips, enables you to send ship sized cargo everywhere.

However taking 50.000 ton to 0.1c sounds a bit optimistic.

It might be that they was thinking some more advanced pulsed fusion engine where you did not use bombs but triggered the materials externally, this way you could get fusion in far more of the fuel mass.

[cantab]

When is it ever acceptable to think of human lives as a currency?

We might not like it, but it's done all the time. It's not affordable, nor even desirable, to eliminate risk and preserve life as much as possible. An estimate of the statistical value of a human life is necessary to decide whether a particular safety improvement is worth the cost, whether a risky activity like spaceflight is worth doing at all, and even which treatments can and can't be provided by the state health service. For developed countries the average value is on the order of $10 million. For developing countries it's considerably less - again, something we might not like and something we might want to and certainly can work to change, but it's the current reality.

And then there's war, where lives are very much one of the currencies.

[rkman]

It is variable, but can go much higher than 5,000s

...15,000 seconds.

Goes to show how huge the challenge of interstellar travel is. A 300% improvement is somewhat extraordinary in terms of human scales, but insignificant compared to the many, many orders of magnitude improvement in effiency that we need. It is so far outside of current knowledge that it makes sense to look for travel methods that are Completely Different (warp drive etc) - even though we have even less of a clue about how to achieve those.

[SciMan]

I see plenty of talk about fusion power and explosive pulse propulsion.

I've only seen one mention of antimatter, and it was marked as "impractical". I respectfully disagree with that statement.

Antimatter-Catalyzed Fusion drives use very small* amounts of antimatter, but they use it very smartly. The antimatter is used to ignite fusion in a mass of fusion fuel, the reaction products from that can then either be directly used for thrust, or used to heat a larger mass of plain hydrogen which is then used for thrust. The high temperatures usually used to get high efficiencies demand the use of a magnetic field as an exhaust nozzle, but the fusion reaction itself can be confined inertially or magnetically.

Basically it's a pure-fusion Orion drive with the pusher plate replaced by a magnetic field. You can change the specific impulse by changing how much plain hydrogen is used to surround the fusion detonation in order to trade thrust for specific impulse. More hydrogen = more thrust, less specific impulse.

The closest thing I can think of that exists in KSP is the DT-VISTA engine from KSP Interstellar. That uses laser-initiated fusion, but the idea is basically the same.

* By "very small", I mean that it should be possible to make enough antimatter to send a fly-by probe on a mission to a nearby star in less than 10 years (I've heard 3 years, somewhere) using a particle accelerator no larger than anything we have already constructed, so long as that accelerator is fully dedicated to producing antimatter and down-times (maintenance, repairs) are minimized.

[-Velocity-]

Goes to show how huge the challenge of interstellar travel is. A 300% improvement is somewhat extraordinary in terms of human scales, but insignificant compared to the many, many orders of magnitude improvement in effiency that we need.

Yea... according to Wikipedia, Orion supposedly tops out at a theoretical maximum Isp of 1e5 s. Say your spacecraft carried 10X its final mass in fuel. That's only a delta-V of 1e5*9.81*ln(10) = 2.3e6 m/s. Your top speed is half that (since you'd like to stop and orbit Alpha Centauri), or 1.13e6 m/s (1130 km/s, 0.0038 c). Your spacecraft takes over 1100 years to reach Alpha Centauri.

Orion is great for puttering around in the solar system, but it's not going to get you to the stars. But... assuming we spread out into the solar system and invent intelligent machines, I still say that the stars appear to be within reach. 1100 years may not be such a formidable obstacle eventually, not to an intelligent, self-repairing machine. And the resources to build these kinds of things may be easy to come by, if we are eventually mining the asteroids and building stuff in giant space-based factories.

So as I said before, given the continued survival of civilization- a BIG assumption given all the many things that could destabilize us- I think that "we" WILL eventually go to the stars, because we already know of propulsive methods that should work within timescales that seem acceptable to the type of intelligent machines that seem inevitable to me. Humans, of an alternate form- uploaded minds- could even make the trip themselves, if we ever were to master that tech or something like it. Since they would not make the trip in physical form, you could even slow down the processing of their virtual brains so that the whole trip only seemed to take a few days. A sort of virtual time dilation (or time compression ). Maybe they could even have the option of teleoperating a physical robotic body in real time in case they wanted/needed to perform some physical activity on the ship themselves. Anyway, that's the only way I can see of "humans" really ever making an interstellar trip within their "lifetime".

[kStrout]

now remember, rockets aren't the only ways of getting something from point A to point B. Imagine this: far in the future, humans fire lasers at an asteroid in another solar system in just the right way to cause the atoms in the asteroid to fuse and combine in just the right configuration to make a teleporter which would receive signals from earth about the atomic makeup of what went into the teleporter on earth and create it out of atoms on the asteroid. Completely implausible? Yes. Rendered impossible by physics? No. Fully awesome? absolutely.

[How2FoldSoup]

now remember, rockets aren't the only ways of getting something from point A to point B. Imagine this: far in the future, humans fire lasers at an asteroid in another solar system in just the right way to cause the atoms in the asteroid to fuse and combine in just the right configuration to make a teleporter which would receive signals from earth about the atomic makeup of what went into the teleporter on earth and create it out of atoms on the asteroid. Completely implausible? Yes. Rendered impossible by physics? No. Fully awesome? absolutely.

Assuming you could do this, you're still limited to relatively nearby stars. The travel time to a star on the otherside of the galaxy is still 75,000 years while you wait for the laser beam to get there

[NERVAfan]

Yea... according to Wikipedia, Orion supposedly tops out at a theoretical maximum Isp of 1e5 s.

I don't know where they got that number. I'm pretty sure the Orion people were talking about velocities of several percent of the speed of light (for ultra-advanced versions), which would imply a much higher specific impulse.

the type of intelligent machines that seem inevitable to me. Humans, of an alternate form- uploaded minds- could even make the trip themselves, if we ever were to master that tech or something like it.

See, the thing is, nuclear pulse propulsion doesn't require any fundamental breakthroughs. This sort of thing involves quite a few, some of which may not even be possible (I'm not at all convinced you could put a human intelligence in a computer, at least not in any practical way -- brains are not electronic computers and do not work the same way).

And it doesn't really help solve the problem anyway, assuming any meaningful level of interstellar dust (and the Stardust probe apparently captured several grains), much less the possibility of hitting a head-sized chunk of Oort cloud object or something. You'll want a huge ship anyway to provide massive armor, so you might as well bring along a "worldship" while you're at it. 1100 years is probably quite workable for a generation ship on this scale.

Edited November 24, 2014 by NERVAfan
fixed quote tag

[NERVAfan]

Also, as NERVAfan said, the "x number of deaths per launch" metric is complete nonsense. It ignores things like effects on the ecosystem, loss of plant and animal life,

If it doesn't have noticeable effects on humans, it won't do so for other animals (and plants are quite resistant to radiation). The amount of radiation released, across the globe, is just not that much.

localized fallout concentrations vs. global spread vs. population densities

Airburst do not produce fallout, and you'd launch from a remote location to avoid this problem. I'd pick one of the unpopulated 'guano islands' of the Pacific that is already effectively a complete ecological dead zone due to most of the island being mined away.

nonfatal radiation deseases,

The point is that there's no good evidence (no evidence period, really) that this level of increase in radiation dose has any health effect. (And an effect on the level of 1 excess death in billions is in practice unmeasurable.)

the entire spread of non-radiation-related effects of a rapid series of thermonuclear detonations...

What non-radiation-related effects? EMP probably would be a major issue, but nothing else. We tend to think of nukes as overwhelmingly powerful - and they are, on a human scale - but to the Earth system, the energy release is nothing. Orion pulse units, especially for use in atmosphere, are very small anyway.

---

On a slightly related topic: radiation is not nearly the ecological problem people tend to assume it is, even when it is present in dangerous quantities. The Chernobyl Exclusion Zone is full of animals - there are some detectable effects, but on the whole it's pretty good. This is because for human health we care about individual outcomes, but for ecology we only care about populations, and there are already a lot of animal deaths - a few extra cancers just don't amount to anything ecologically. Short of an actual full-on nuclear war with groundbursts and fallout, radiation will not seriously mess up the ecology.

Edited November 24, 2014 by NERVAfan
fixed quote tag

[NERVAfan]

Anyway, as politics will prevent an Orion launch from Earth, the best way to do it is to mine thorium from the thorium-rich region of the Moon, turn it into U-233, and launch from the Moon.

[-Velocity-]

You'll want a huge ship anyway to provide massive armor, so you might as well bring along a "worldship" while you're at it. 1100 years is probably quite workable for a generation ship on this scale.

By the time we actually get to the point where we can spare the resources for a nuclear pulse propelled spacecraft to the stars- IF we ever reach that point- the idea of the generation ship is going to seem cute, quaint, and naive. We still have tremendous strides to make in biology and genetics, but our space technology is (comparatively) mature and advancing MUCH more slowly. I honestly see a near zero possibility that generation ships will ever take flight, unless its as a giant space colony that becomes self-sufficient enough to leave, and WANTS to leave. By the time we have the ability to build a generation ship, our advances in biology and genetics will make the whole idea obsolete. The seed of life can be spread via frozen embryos, artificial synthesis of biological components at the destination, etc- there's no need to transport actual living organisms. That would be massively inefficient, and so no one will do it. Why send one giant colony ship to colonize a single system, when for the same resource expenditure, you can send 50 seed ships to settle 50 different systems?

As far as the armor goes against dust- how much armor do you REALLY need if you're "just" going 0.01 c or less? If you're going that slow, the armor you need is significantly reduced. A dust grain 10 microns in diameter "only" packs like 10 J of energy. That's not all that much. A composite armor might be the way to go. You sandwich thin, dense barriers with thicker, lightweight ones. First, the dust hits a thin, dense barrier. It breaks up, and starts spreading out into the lightweight, thick material. Then the fragments- slowing down, less concentrated- strike the next thin, dense layer. And so on. Pretty soon the projectile fragments are spread out enough, and slow enough, to not penetrate the next thin dense layer.

[SpaceXray]

The stars are like a tease to us. So many exoplanets to go to, yet so far. Painfully far. I wish I could live up until the moment reaching them is possible.

[NERVAfan]

By the time we actually get to the point where we can spare the resources for a nuclear pulse propelled spacecraft to the stars- IF we ever reach that point- the idea of the generation ship is going to seem cute, quaint, and naive. We still have tremendous strides to make in biology and genetics, but our space technology is (comparatively) mature and advancing MUCH more slowly.

That's because of lack of investment and (even more so) fear of nuclear stuff, not technological maturity.

I honestly see a near zero possibility that generation ships will ever take flight, unless its as a giant space colony that becomes self-sufficient enough to leave, and WANTS to leave.

That's essentially what I had in mind, though the space colony would probably build a new structure rather than convert their existing one - I doubt a pure O'Neill colony would be built to stand up to thrust, and it would likely be dependent on sunlight.

By the time we have the ability to build a generation ship, our advances in biology and genetics will make the whole idea obsolete. The seed of life can be spread via frozen embryos, artificial synthesis of biological components at the destination, etc- there's no need to transport actual living organisms.

That requires the existence of an AI/non-human system that can raise vaguely functional human beings. That is an extreme breakthrough if possible at all.

That would be massively inefficient, and so no one will do it. Why send one giant colony ship to colonize a single system, when for the same resource expenditure, you can send 50 seed ships to settle 50 different systems?

As far as the armor goes against dust- how much armor do you REALLY need if you're "just" going 0.01 c or less?

If you're going that slow, the armor you need is significantly reduced. A dust grain 10 microns in diameter "only" packs like 10 J of energy. That's not all that much.

Not really - but it's a long way to Alpha Centauri. If the stardust probe's dust collector was hit by seven dust grains, even a tiny interstellar ship would probably be hit by millions. It will be eroded away.

And one slightly-bigger dust grain or chip of Oort cloud ice and the spacecraft is destroyed.

A composite armor might be the way to go. You sandwich thin, dense barriers with thicker, lightweight ones. First, the dust hits a thin, dense barrier. It breaks up, and starts spreading out into the lightweight, thick material. Then the fragments- slowing down, less concentrated- strike the next thin, dense layer. And so on. Pretty soon the projectile fragments are spread out enough, and slow enough, to not penetrate the next thin dense layer.

Essentially, yes (and with vacuum layers too like a Whipple shield) - but I'm suggesting to make that composite armor layer, say, 100 meters thick or more. Enough to stand up to, say, a human-sized chunk of Oort cloud ice (100 kilotons TNT equivalent or so).

Edited November 25, 2014 by NERVAfan
quote tags

[-Velocity-]

That requires the existence of an AI/non-human system that can raise vaguely functional human beings. That is an extreme breakthrough if possible at all.

Tell will tell of course, but I think that sitting here today, in the midst of a continuing revolution in computer technology, in the midst of us seeing AI get ever stronger and stronger, you cannot reasonably believe that it is unlikely for us to ever achieve a truly intelligent machine. The march of technology is clear, and there is no known physics that prevents us. It's like observing the post-war tests of V2 missiles captured from Germany and believing that we'll never walk on the Moon- only worse, because every one of the seven billion human brains on this planet proves that synthetic, practical, truly intelligent thinking machines CAN exist. It's not like nuclear fusion, where we haven't observed a net power gain outside of the cores of stars or thermonuclear devices. A more reasonable question is whether creating such a machine is possible and practical with silicon microfabrication technology or its derivatives. If not, they would likely take a much longer time to be realized, or at least, miniaturized.

So while I don't feel that truly intelligent machines are certain to be developed, I just feel that given what we know, it is unreasonable to believe that they are unlikely to be developed, at least eventually.

But as we're trying to predict the future here in this thread, we should consider the ALL technologies that are most likely to be developed, not just one. You should NOT try to predict the future by only projecting forward progress in one field of technology, which is what the "generation ship" assumes- mostly it represents only progress in space utilization, really. Instead, when you look at the total SUM of technologies that are most likely to be developed, the idea of generation ships becomes silly and obsolete, because the VASTLY more efficient "seed ship" becomes possible with advanced machine intelligence and genetics/biology. In fact, the seed ship not only becomes possible it appears to become somewhat practical too, assuming we spread out into space and utilize the vast resources out there in the asteroids.

Edited November 25, 2014 by |Velocity|

[Kryten]

In that case, why bother with humans at all?