Author Topic: Interstellar Propulsion Research: Realistic Possibilities and Idealistic Dreams  (Read 57243 times)

Offline rdale

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    Though physically possible, interstellar travel will be exceedingly difficult. Both the known laws of physics and the limits of our current understanding of engineering place extreme limits on what may actually be possible. Our remote ancestors looked at the night sky and assumed those tiny points of light were campfires around which other tribes were gathered -- and they dreamed of someday making the trip to visit them. In our modern era, we've grown accustomed to humans regularly traveling into space and our robots voyaging ever-deeper into the outer edges of our solar system. Traveling to those distant campfires (stars) has been made to look easy by the likes of Captains Kirk and Picard as well as Han Solo and Commander Adama. Our understanding of physics and engineering has not kept up with our imaginations and many are becoming frustrated with the current pace at which we are exploring the universe. Fortunately, there are ideas that may one day lead to new physical theories about how the universe works and thus potentially make rapid interstellar travel possible -- but many of these are just ideas and are not even close to being considered a scientific theory or hypothesis. Absent any scientific breakthroughs, we should not give up hope. Nature does allow for interstellar travel, albeit slowly and requiring an engineering capability far beyond what we now possess. Antimatter, fusion and photon sail propulsion are all candidates for relatively near-term interstellar missions. The plenary lecture will discuss the dreams and challenges of interstellar travel, our current understanding of what may be possible and some of the "out of the box" ideas that may allow us to become an interstellar species someday in the future.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090020444_2009016488.pdf

Offline GI-Thruster

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I for one don't believe interstellar travel will be practical until we have a working warp drive or traversable wormhole generator.  Both these are in the realm of possibility.  Especially given the data from Jim Woodward's latest experiments this last year demonstrating the ability to fluctuate mass based upon Mach's Principle and General Relativity, it seems especially likely to me we'll see designs for warp drives not too many years in the future.

Both these technologies, warp drives and wormhole generators; require negative mass.  Jim Woodward has shown the ability to temporarily fluctuate mass.  All that remains is to show it can be fluctuated beyond 100% such that even if temporarily, it will have negative inertial.  Given the ability to generate negative inertia, we can certainly build warp drives.

Gene Roddenbury didn't make this stuff up.  He was a student of the best physics of his day.  Back in the 50's there were explanations about warp drives.  We just didn't know how to fluctuate mass.  Now we do.

So, not worth holding out for ships that take many years to reach the next, closest star when we can build ships that without violating GR, can warp space and travel at any arbitrarily high speed, without generating a time dilation effect.  These are the kinds of real answers we need to hold out for, IMHO.

Offline Sith

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don't believe interstellar travel will be practical until we have a working warp drive or traversable wormhole generator
Or a Tachyon particle


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

Offline ANTIcarrot

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I for one don't believe interstellar travel will be practical until we have a working warp drive or traversable wormhole generator.

I disagree. I think slow interstellar travel (in the form of probes at +1% C) could be built within a hundred years or so. Whether fusion reactors can economically power cities remains to be seen, but I'm not sure anyone anymore questions that they can work at all.

You can argue about whether 0.01C is 'practical' or not, but it's better than nothing.

Offline Lampyridae

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I for one don't believe interstellar travel will be practical until we have a working warp drive or traversable wormhole generator.

I disagree. I think slow interstellar travel (in the form of probes at +1% C) could be built within a hundred years or so. Whether fusion reactors can economically power cities remains to be seen, but I'm not sure anyone anymore questions that they can work at all.

You can argue about whether 0.01C is 'practical' or not, but it's better than nothing.

0.01c is possible with an aluminium lightsail. Maybe a bit higher with a titanium lightsail.
0.1c is possible with a super-duper ORION with fusion pulse units.

In the real world, they'd take decades to develop and hundreds of billions (especially if NASA was in charge) but they are possible with today's technology as a starting point.
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Offline Lampyridae

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don't believe interstellar travel will be practical until we have a working warp drive or traversable wormhole generator
Or a Tachyon particle


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

Thanks but I'd not disinitegrate into incoherent Cherenkov radiation upon returning to STL speeds.
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Offline khallow

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Let us also keep in mind that we already have 5 interstellar vehicles. They might not travel as fast as we like or do much as interstellar driftwood, but it's a data point that indicates to me that interstellar travel need not be that hard once you get away from the flashy vehicles traveling at a significant fraction of the speed of light.
Karl Hallowell

Offline pierre

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Let us also keep in mind that we already have 5 interstellar vehicles. They might not travel as fast as we like or do much as interstellar driftwood, but it's a data point that indicates to me that interstellar travel need not be that hard once you get away from the flashy vehicles traveling at a significant fraction of the speed of light.

The hard part of "slow" interstellar travel is building complex machines that work for thousands of years without human intervention.

Not impossible and, IMHO, a perfectly reasonable way of doing it, but still hard.

Offline Star-Drive

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Or there may be a eaiser path that just uses Woodward's transient positive mass deltas to create a velocity boost factor for your interstellar vehicle.

See: http://www.springerlink.com/content/t52g457576w8m2x2/

A Discussion of Space-Time Metric Engineering
Journal General Relativity and Gravitation

Harold G. White1

(1)  Lockheed Martin Space Operations, 2400 NASA Road 1, C33, Houston, Texas, 77058

Abstract  The Alcubierre Warp Drive Metric, wherein a spacecraft can appear to vastly exceed the speed of light without locally ever doing so, derived in [1], is reconsidered. It is shown that the underlying driving physical mechanism (at least in a mathematical sense) is not the expansion/contraction of the space surrounding the spacecraft via the York Time T [2]. Rather, the driving mechanism is a boost that serves as a multiplier of the ship's initial velocity. This effect can in principle be likened to watching a movie in fast-forward. The expansion/contraction of space is merely a side effect of the warp drive's underlying mechanism - that can be viewed as sort of a Doppler effect, or stress/strain on space.

Boost - York time - metric engineering

« Last Edit: 06/02/2009 12:59 pm by Star-Drive »
Star-Drive

Offline ANTIcarrot

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0.1c is possible with a super-duper ORION with fusion pulse units.

In the real world, they'd take decades to develop and hundreds of billions (especially if NASA was in charge) but they are possible with today's technology as a starting point.

I'm not sure I agree about orion. Powerful and impressive as it was, it's exhaust velocity wasn't that good. According to Atomic Rocket, fusion orion has an exhaust velocity of just 73km/s. That would require a mass ratio in the 10^178 range to get up to 0.1C. Other fusion designs do better of course, but I think all versions of orion should stick to in-system work. :)

Development cost depend on your starting point. Building a new laptop today is easy. Making a machine of comparative power even ten years ago would be ruinously expensive. Starting from scratch today, yes, especially with the NASA trade union in charge. But if alt space and/or fusion power succeeds commercially, then R&D and/or launch costs could drop dramatically.

Offline khallow

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0.1c is possible with a super-duper ORION with fusion pulse units.

In the real world, they'd take decades to develop and hundreds of billions (especially if NASA was in charge) but they are possible with today's technology as a starting point.

I'm not sure I agree about orion. Powerful and impressive as it was, it's exhaust velocity wasn't that good. According to Atomic Rocket, fusion orion has an exhaust velocity of just 73km/s. That would require a mass ratio in the 10^178 range to get up to 0.1C. Other fusion designs do better of course, but I think all versions of orion should stick to in-system work. :)

Hence the need for the "super-duper" adjective.
Karl Hallowell

Offline kkattula

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Direct Fusion Product drives could have Isp from 100,000 up to possibly 1,000,000.

Low thrust, but these give mass ratio of 21 to get to 0.01 c & 0.1 c respectively.

Unfortunately, thrust would be so low it might take decades, if not centuries to reach maximum velocity. The reactor has to fuse at least 50 times it's own mass in fuel. Hard to conceive of one that could consume kgs of fuel a day yet mass less than a few tons.

Offline GI-Thruster

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And there are simpler ways to look at the issue.  Lets suppose one could get 0.1c velocity very quickly.  The closest interesting star system is probably 12 light years away so you're looking at 120 years to get there ignoring acceleration and deceleration time, or 240 years round trip.  No matter the time dilation, this is never going to be practical.

Who did we think would sign up for such a voyage and do we really want to place billions of dollars in hardware in the care of someone who has no real friends or family?  I don't think so.  Rockets for travel to other stars will never be practical.  Gene Roddenbury had this right and we need to stop taking his observations for granted just because he was a fiction writer.  He got his fiction from the facts.  To travel to other star systems, we need a warp drive.

Offline kevin-rf

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So you are saying we have two topics...

1. How do we build a ship that can go at a good fraction of C (say 0.1 C) for interstellar travel.

2. Is there anything that could get us over the 1.0 C barrier.

Should have two different threads, and anyone who crosses the T (thread) barrier should be modded ;)
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Offline GI-Thruster

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No, I'm saying we have one topic.  In order to do human interstellar travel, we have to have FTL travel.

Can you imagine the look on the Queen's face if Columbus had said they needed a ship capable of keeping its crew alive for 250 years?  STL travel to other stars is preposterous.  The "generational ships" we find in fiction are the place of fiction only.  No one would ever fund such an endeavor.

Offline William Barton

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No, I'm saying we have one topic.  In order to do human interstellar travel, we have to have FTL travel.

Can you imagine the look on the Queen's face if Columbus had said they needed a ship capable of keeping its crew alive for 250 years?  STL travel to other stars is preposterous.  The "generational ships" we find in fiction are the place of fiction only.  No one would ever fund such an endeavor.

I don't think FTL is necessarily required for interstellar travel (unless you're writing a fantasy that pretends to be science fiction, which I do from time to time). Here are a couple of scenarios I've written about, both of which are far more plausible than FTL:

1. Interstellar space may be full of planetesimal bodies. We don't know right now how far the Oort Cloud extends, or what's beyond that, so it's possible the debris clouds of the stars blend together. It may be that objects the size of Ceres or Quaoar are only a few light hours apart, all the way to Alpha Centauri. A space faring civilization would naturally expand outward, and would eventually find itself approaching other stars, without ever having intentionally begun "interstellar travel."

2. What are the real limits on human (or, more likely, augmented post-human) lifespan? We don't know. Someone who expected to live 7,000 years would be a lot more sanguine about a ride on the slow boat to Delta Pavonis than someone who figured he'd be dead in 70 years or so.

And, of course, there's Asimov's original idea ("There's noplace like Spome") that if you were building space colonies and living in them, you wouldn't miss Earth if you left the solar system, colony and all.

Offline GI-Thruster

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William, you realize your first answer is to deny the question?  The question concerns interstellar travel so finding bits of rock between the stars doesn't come to the issue.

Extending human life is certainly possible.  Lets hope not to see it in our lifetimes as the consequences for us all are dire.  I did a thesis on this for philosophy of technology once upon a time.

Asimov was wrong.  Anyone who wouldn't miss the sight of the ocean, or the grandeur of Banff, or the sublime pleasure in a sunset with clouds and colors is already severely impaired and only partially human.

Honestly, you think this all more likely than FTL?  Have you been following in the field theory thread?  For warp drive all we need is negative mass with negative inertia and all the signs seem to say we are well on our way.  It's entirely likely Paul March generated negative mass in the lab back in 2002.  Have you been following that thread?

Offline rklaehn

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I think the most promising approach is to extend the lifetime of humans or posthumans to a few thousand years so that spending 100 years in a sub-light spacecraft won't be such a big issue. Hibernation is also quite promising.

But there is also the gradual approach: once you have mastered nuclear fusion, there is no particular advantage in being close to the sun. So interstellar travel might happen gradually by people moving into the main belt, the jupiter trojans, the oort cloud etc. At some point you will have people living on objects that are 0.5 lightyears away from the sun and only very weakly bound to the solar system. Sooner or later a settlement will decide to leave the solar system and arrive at the next star system.

Of course this would take several 100000 years, but compared to geological time spans that is still very short.

But it is not productive to worry about this now. Before you can cross the atlantic you need to be able to build a boat to cross a small river. And the solar system contains enough resources to keep us busy for at least a few thousand years.
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Offline Sith

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Asimov's original idea ("There's noplace like Spome") that if you were building space colonies and living in them, you wouldn't miss Earth if you left the solar system, colony and all.
Asimov was a writer, not a scientist, and his ideas are more than half century old.

Offline William Barton

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William, you realize your first answer is to deny the question?  The question concerns interstellar travel so finding bits of rock between the stars doesn't come to the issue.

Extending human life is certainly possible.  Lets hope not to see it in our lifetimes as the consequences for us all are dire.  I did a thesis on this for philosophy of technology once upon a time.

Asimov was wrong.  Anyone who wouldn't miss the sight of the ocean, or the grandeur of Banff, or the sublime pleasure in a sunset with clouds and colors is already severely impaired and only partially human.

Honestly, you think this all more likely than FTL?  Have you been following in the field theory thread?  For warp drive all we need is negative mass with negative inertia and all the signs seem to say we are well on our way.  It's entirely likely Paul March generated negative mass in the lab back in 2002.  Have you been following that thread?

Actually, no, I am not "denying the question," merely questioning the sense of it. And if your "Asimov was wrong" paragraph reflects your belief, then clearly you believe space exploration, other than an a form of stunt flying, is a waste of time.

I realize its fun to make that sort of nonsensical "have you been following the thread" commentary, but it accomplishes nothing. I've been following field theory. Have you been following developments in biochemistry? The problems you allude to as inherent in life extension are based on the theories of a writer who died around 200 years ago. He was wrong, and if he'd thought about it, he'd've known it then.

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