Propulsion Technology

[Larspeart]

Okay, I am conviced that the ONLY way humankind is going to make any kind of progress in the future in regards to space is in a breakthrough in propulsion technology. Besides Ion Drives (which are still kind of primitive), we haven't developed anything of note in 30-40 years, right?

What kinds of work is being done on this right now, and what do you all forsee as the solution? Or, should we even bother to explore/colonize space?

[garys_2k]

Still bound by action-reaction for the time being. I don't think any of the reactionless propulsion systems that NASA checked out have gone anywhere (:D ).

[Crossbow]

Our part of the galaxy is sparlesly populated and as such there are vast distances to be overcome in order to explore even the nearby stars.

Even if one could make a drive that could propel a ship to a bit less than the speed of light (the speed limit for anything with mass), then it would still take years to travel from one star to another. So unless there is a away to travel much faster than the speed of light, it looks like we are pretty much stuck here.

[Larspeart]

That is pretty much what I thought as well. Kind of depressing, but hey, it is what it is, right? :)

Forget colonizing other star systems (unlikely, unless we are talking, 'the Earth is about to die, and we ALL have to leave and go elsewhere as there won't BE an Earth' type scenario), and lets just focus on 'Our Neighborhood', i.e. the Solar System. Mars is the 1st, obvious, and frankly only immediate place to go, with the moon possibly having some uses as well. We don't need to advance 'too' much in terms of propulsion to reach them in efficient time frames. To go beyond them, say to Europa, Titan, Or any of the outer planets and their moons, we would need something faster to make the trip doable in reasonable time frames (days/weeks instead of months/years)

Or, are we locked not only out of the rest of the galaxy, but in fact destined to spend out time on this particular rock?

[arcticpenguin]

The latest issue of Discover magazine (Augsut 2003?) has an article on propulsion systems with interstellar potential; things like fission, fusion, hydrogen ramjet. None of them look too affordable or near-term feasible.

[Crossbow]

It is hard to say if we are really stuck here or not.

After all, there have been some great changes in science just when people have thought that everything was pretty well set. I think the year was 1872 when the person in charge of the US Patent Office suggested closing it down since everything worthwhile had already been invented.

And the next year, X-Rays were discovered which in turn lead to Atomic Studies and a whole new way of looking at the world that was so unexpected that not even fiction writers touched upon the subject.

So who knows if we are really stuck here or not for all time?

[Larspeart]

Got a link to that issue of Discover? I'd be interested in seeing that.

As far as leaps and bounds in advancements, I am a big believer in them. Going faster then light though seems tricky (to say the least). I have heard that we have actually seen evidence that things can move faster then light (strictly sub-atomic level so far) but that is aa far as I have seen/heard on it.

Of course, there is always the old 'Wrinkle in Time' cliche; Instead of going to two points in space, bring the 2 points together. . .



:roll:

[arcticpenguin]

Originally posted by Crossbow
I think the year was 1872 when the person in charge of the US Patent Office suggested closing it down since everything worthwhile had already been invented.

You might want to check that one out on Snopes or elesewhere.



Originally posted by Larspeart
Got a link to that issue of Discover? I'd be interested in seeing that.

No, I get my copy in the mail well before they roll over their web site. (For which I am grateful). If I remember in a week or two I'll come back and give a link.

[rockoon]

Originally posted by Crossbow
Our part of the galaxy is sparlesly populated and as such there are vast distances to be overcome in order to explore even the nearby stars.

Even if one could make a drive that could propel a ship to a bit less than the speed of light (the speed limit for anything with mass), then it would still take years to travel from one star to another. So unless there is a away to travel much faster than the speed of light, it looks like we are pretty much stuck here.

Also note that there is a limit to the amount of acceleration the human body can survive. I think we will end up being very practical and stick with an acceleration of 10 meters/sec or there abouts. This acceleration will simulate earth gravity nicely. It will only take a year or so to get near the speed of light.

[Jethro]

Keep in mind that as far as space exploration goes, even if it takes a near luminal ship several decades to reach another star, this is only as measured in the earth's frame of reference. In the ship's frame of reference (and therefore the crew's frame of reference) it will take less time.

[Sundog]

Originally posted by Jethro
Keep in mind that as far as space exploration goes, even if it takes a near luminal ship several decades to reach another star, this is only as measured in the earth's frame of reference. In the ship's frame of reference (and therefore the crew's frame of reference) it will take less time.

At first this seems an insuperable obstacle. Who would accept the condition that you would be forever separated in time from Earth? But if we look at it closer, that's inevitable anyway. Communications would take many years each way. Civilizations on other stars will, of necessity, be completely independent of Earth and of each other, their only word of the mother planet coming from decades-old transmissions.

The good news is, a galactic empire is impossible. No empire can exist without communications. If mankind makes it to the stars, it will be as many completely independent societies that will even one day be different races because of lack of contact with each other.

[Larspeart]

I believe the same thing Sundog does. While it seems unlikely, or abhorrent, to think of 'leaving everything' it is really the only way LONG range travel/colonization can take place (as we understand physics and the universe today).

In terms of propulsion, if we look at the ion drive (viable for inter-solar system jaunts), it works on the principal of slow, but steady and consistent acceleration, right? What if it was to slowly, but CONSTANTLY accelerate? Give it a HUGE fuel supply, and in essense, let it burn. You get it into orbit, at orbital speed. If it takes one week to double that speed (or 4 weeks for that matter) so be it. After 3 months, it is going to be clipping along pretty darn fast, right? Lets say it doubles in speed every week, starting at orbital speed (forgive me, as that number illudes me at the moment). How long would it take to reach near-light speed? In this case, it isn't a matter of new propulsion, but almost strickly fuel concerns.

DEEP had a fairly small fuel tank compared to solid or liquid fuel systems, so it seems it is far more efficient, right?

[arcticpenguin]

Originally posted by Sundog

At first this seems an insuperable obstacle. Who would accept the condition that you would be forever separated in time from Earth?
Anyone coming off a really bad relationship.

I see a movie about this, starring Bruce Willis.

[Wile E. Coyote]

Travelling at these enormous speeds presents more barriers than just propulsion. The faster you go, the more you have to worry about unavoidable small objects in your path. At .5c, you are looking at complete anihilation from contact with a stray pebble.

The only way to go is slow (currently, and forseeably). Multigenerational, fully self-sufficient ships are the only chance for success. Of course, we need to build fully self-sufficient habitats in orbit of Earth, or the Sun, first. Propulsion is not the biggest problem.

[Larspeart]

True, but haven't studies been done on the likelyhood of hitting anything in space (being that is is so, well, BIG and empty) are darn near nil?

You plot a course to get you outside of the solar system, and from there until your destination system, you (should) not run into much of anything, right? Between star systems (where most matter in the universe is located) there really isn't much to hit.

[Sundog]

Originally posted by Wile E. Coyote
Travelling at these enormous speeds presents more barriers than just propulsion. The faster you go, the more you have to worry about unavoidable small objects in your path. At .5c, you are looking at complete anihilation from contact with a stray pebble.

The only way to go is slow (currently, and forseeably). Multigenerational, fully self-sufficient ships are the only chance for success. Of course, we need to build fully self-sufficient habitats in orbit of Earth, or the Sun, first. Propulsion is not the biggest problem.

Excellent point, barring some magical device to shove them aside.

In which case, ironically, to master space travel it is essential that we become expert in managing ecosystems on the hundreds- or thousands-of-years scale... and how better to learn than by rescuing our own Earth and learning how to live sustainably on it?

In other words, Earth is a test case. If we can't make THAT spaceship work, we have no chance of making the other ones work.

Success in space travel for mankind = success in rescuing the Earth from ecological disaster.

[Wile E. Coyote]

Originally posted by Larspeart
True, but haven't studies been done on the likelyhood of hitting anything in space (being that is is so, well, BIG and empty) are darn near nil?

You plot a course to get you outside of the solar system, and from there until your destination system, you (should) not run into much of anything, right? Between star systems (where most matter in the universe is located) there really isn't much to hit.

Although the distribution of matter is sparse, there are pockets of dust and random bits of debris floating about. It would be an awful waste to send a bunch of people on a long journey only to lose them to the "unlikely" space rock.

I also wonder about radiation effects from light being noticeably shifted to shorter wavelengths as the craft moves faster. I have not done the math, so I cannot say, but it seems like this might also offer some difficulties.

[Sundog]

Originally posted by Wile E. Coyote


Although the distribution of matter is sparse, there are pockets of dust and random bits of debris floating about. It would be an awful waste to send a bunch of people on a long journey only to lose them to the "unlikely" space rock.

I also wonder about radiation effects from light being noticeably shifted to shorter wavelengths as the craft moves faster. I have not done the math, so I cannot say, but it seems like this might also offer some difficulties.

The matter is quite bad enough. Most sources I've found estimate the density at about one atom per ccm in interstellar space. I have no trouble believing that this alone would tear a ship to pieces that was traveling at any appreciable fraction of the speed of light.

We have people here who can actually perform calculations of this kind, hint, hint. ;)

[CurtC]

It refreshing to see the level-headed skepticism going on in this thread. The last time I saw a thread about the feasability of distant space travel, it was in reaction to the Straight Dope column, Why do we travel in space? (http://www.straightdope.com/columns/030307.html). The reaction is at http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=167867. Most of the people who responded said that Cecil lacked vision. I say he could see the plain truth perfectly well.

[Sundog]

The only time I ever object to ideas of space colonization is when it is clear that they are being voiced as answers to our problems here on Earth. As in, "Yes, Earth is overpopulated, but when we have cheap space travel all those problems will go away."

As I pointed out the other day, this is a pipe dream. Yes, we should colonize space. But no, it won't have the slightest effect on our home planet, except as an additional drain on resources.

[xouper]

Sundog: <span style="background-color: #ffc">The only time I ever object</span> to ideas of space colonization is when it is clear that they are being voiced as answers to our problems here on Earth. As in, "Yes, Earth is overpopulated, but when we have cheap space travel all those problems will go away."The only time? :) Even though I never made such a claim, you objected to my comment about space colonization anyway (in another thread (http://www.randi.org/vbulletin/showthread.php?s=&threadid=22579#post1869993605)). Or, if you think that's the claim I made, then I respectfully avow you are mistaken.

[daver]

Originally posted by Larspeart
I believe the same thing Sundog does. While it seems unlikely, or abhorrent, to think of 'leaving everything' it is really the only way LONG range travel/colonization can take place (as we understand physics and the universe today).

In terms of propulsion, if we look at the ion drive (viable for inter-solar system jaunts), it works on the principal of slow, but steady and consistent acceleration, right? What if it was to slowly, but CONSTANTLY accelerate? Give it a HUGE fuel supply, and in essense, let it burn. You get it into orbit, at orbital speed. If it takes one week to double that speed (or 4 weeks for that matter) so be it. After 3 months, it is going to be clipping along pretty darn fast, right? Lets say it doubles in speed every week, starting at orbital speed (forgive me, as that number illudes me at the moment). How long would it take to reach near-light speed? In this case, it isn't a matter of new propulsion, but almost strickly fuel concerns.

DEEP had a fairly small fuel tank compared to solid or liquid fuel systems, so it seems it is far more efficient, right?

Doubling your speed every week isn't the way acceleration works, even Newtonian acceleration. Given Newtonian acceleration, if it takes one week to gain 10 km/sec, it takes another week to gain another 10 km/sec.

Ion drives are more likely to be measured in milli-g's, or maybe km/sec/day. That's not too bad for interplanetary travel. You're still talking months to years to get anywhere. After three months of accelerating, you'd be going at about .5 au/week. So maybe nine months to Jupiter, two years to Pluto.

However, for interstellar drive, it sucks. 10%c at milli-g accelerations is going to take on the order of a century. Getting up to 87%c (where time dilation makes shiptime half of earthtime) takes an enormous amount of energy--if the energy could be supplied from outside the ship, it would require a mass equal to that of the ship to be completely converted into energy and applied to the ship. If the ship had to carry its fuel with it, it would require even more mass. I don't feel like rederiving the relativistic rocket equations; you might be able to get to 87%c with an anti-matter drive at a reasonable fuel fraction--i expect someone could google the answers if they wanted.

Fast interplanetary drives are going to require enormous amounts of energy--maybe a nuclear salt rocket, maybe some Orion variant, maybe fusion. Anti-matter would be great.

Anti-matter is about your only choice for interstellar drives that get to their destination within their crew's lifetimes.

[chance]

To me it seems likely that a drive capable of 10% c is not beyond the realms of science fiction, therefore the next problem is the human cargo. Hibernation would have to be achieved, or better grow your body (modified) once at the destination.

[rwald]

Or if you travel fast enough, time dialation will take care of it for you...

Personally, I like the idea of a ship accelerating at 1 g for the first half of the journey, and then in the middle turning around and decelerating at 1 g. I think that gets you to .999992c in 6 years and 3 weeks of ship's time.

[Crossbow]

Originally posted by Jethro
Keep in mind that as far as space exploration goes, even if it takes a near luminal ship several decades to reach another star, this is only as measured in the earth's frame of reference. In the ship's frame of reference (and therefore the crew's frame of reference) it will take less time.

Yes that is true, however that would mean that for anyone who went on such a trip by the time they came back to Earth, then everyone who was not on a similar voyage would be dead.

As such, I expect that it would be quite difficult to find people willing to sign up for such a mission.

[rwald]

Originally posted by Crossbow
Yes that is true, however that would mean that for anyone who went on such a trip by the time they came back to Earth, then everyone who was not on a similar voyage would be dead.

As such, I expect that it would be quite difficult to find people willing to sign up for such a mission.Originally posted by arcticpenguin
Anyone coming off a really bad relationship.

I see a movie about this, starring Bruce Willis.

[rockoon]

Originally posted by Crossbow


Yes that is true, however that would mean that for anyone who went on such a trip by the time they came back to Earth, then everyone who was not on a similar voyage would be dead.

As such, I expect that it would be quite difficult to find people willing to sign up for such a mission.

Where do I sign?

[Wile E. Coyote]

Originally posted by CurtC
It refreshing to see the level-headed skepticism going on in this thread. The last time I saw a thread about the feasability of distant space travel, it was in reaction to the Straight Dope column, Why do we travel in space? (http://www.straightdope.com/columns/030307.html). The reaction is at http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=167867. Most of the people who responded said that Cecil lacked vision. I say he could see the plain truth perfectly well.

I do not feel that space travel is a waste of time. I am just being realistic in that it will not be like Star Trek and that it will require the same kind of pioneering spirit that early settlers of the new world were known for.

Firstly, I truly believe that death is not inevitable. Science will eventually find a way to preserve human life forever, and then star travel that takes a thousand years will not seem so bad.

Secondly, I envision a "slow" ship that is extremely large, has a spin-induced artificial gravity, and is self sufficient. The ship would have a lot of satellites that would venture away from the ship to obtain resources, and the interior of the ship would be an enormous cylinder in which towns and forests and gardens would be available.

This also assumes that virtual reality comes to the point where it is indistinguishable from reality. Without this, I think a lot of people would become insane.

[Sundog]

Originally posted by xouper
The only time? :) Even though I never made such a claim, you objected to my comment about space colonization anyway (in another thread (http://www.randi.org/vbulletin/showthread.php?s=&threadid=22579#post1869993605)). Or, if you think that's the claim I made, then I respectfully avow you are mistaken.

I stand corrected!

I wasn't referring to you. The objection WAS related, though, as I felt you were making the same error (in my view) as others regarding availability of resources.

[Dr. Imago]

Originally posted by Larspeart
Or, should we even bother to explore/colonize space?

I think what's fascinating is that we, the current height of evolutionary achievement on the Earth, feel compelled to explore space and move to other planets as a long-term goal. We regularly visit this topic in our literature, and never cease to seem to be fascinated by the stars.

Yet, we are literally loaded with bacteria, latent viruses, and other microorganisms. So, it seems that if we accomplish this goal, it could possibly be argued that really the bacteria have simply figured out a quite ingenious way to get themselves to other places in the galaxy.

:D

-TT

[clusterm2]

Originally posted by rockoon


Also note that there is a limit to the amount of acceleration the human body can survive. I think we will end up being very practical and stick with an acceleration of 10 meters/sec or there abouts. This acceleration will simulate earth gravity nicely. It will only take a year or so to get near the speed of light.



Yes yes yes but when we have our inertia-less drives it won't be a problem. We just need to get the inertia bit out of the drives then Bobs your uncle, simple.

[sorgoth]

Yet, we are literally loaded with bacteria, latent viruses, and other microorganisms. So, it seems that if we accomplish this goal, it could possibly be argued that really the bacteria have simply figured out a quite ingenious way to get themselves to other places in the galaxy.



Heh. Maybe bacteria will become the true colonisers of space, remaining in places where all humans have long left...

Yes yes yes but when we have our inertia-less drives it won't be a problem. We just need to get the inertia bit out of the drives then Bobs your uncle, simple.

...Inertia-less drives? Yeah, right. Making an artificial wormhole would be easier than that.

[rwald]

But don't they have inertial dampeners in Star Trek? Why can't we make them in reality?

:D

[xouper]

rwald: But don't they have inertial dampeners in Star Trek? Why can't we make them in reality?We can't? Heard on a recent commercial flight from Detroit to Tampa:

"This is your captain. We are now at a cruising altitude of 35,000 feet and there are reports of mildly turbulent air ahead, so we will be turning on the intertial dampers, and you will again be free to move about the cabin. Thank you for flying Enterprise™ Airlines."

:bgrin:

[daver]

Originally posted by rwald
Or if you travel fast enough, time dialation will take care of it for you...

Personally, I like the idea of a ship accelerating at 1 g for the first half of the journey, and then in the middle turning around and decelerating at 1 g. I think that gets you to .999992c in 6 years and 3 weeks of ship's time.

Well, Bussard rams have been discredited, so there's no longer any feasible mechanism for reaching that speed.

[rwald]

Remind me, what are Bussard rams?

[TexasBEAST]

Originally posted by rwald
Remind me, what are Bussard rams?
They call them Bussard "scoops" in Star Trek, right?

Ship-mounted collectors of space debris for use as fuel, theoretically allowing you not to have to carry everything onboard the ship from the very beginning.

Unfortunately, reality is there's just not enough particulate density out there to really be of much benefit. But still enough to blow a Columbia-esque hole in your hull.

---

Question: Antimatter anhilation is the greatest energy yield reaction yet known right?

Q: The greatest problem with action-reaction systems now is the mass of fuel required to be carried, right? The duration of the trip and time paradoxes and all that, those are uncomfortable to think about, but perfectly doable. Just the problem of how do you carry enough fuel?

Q: If a warp drive were built, would it really even be "propulsion" anymore? Or "drive"? Seems to me that it would be an environmental control device, rather than a ship propulsion device. Your nuclear reactor "impulse drive" would be "propulsion"; your "warp reactor" would not.

[rwald]

I'll try to answer your questions, TexasBEAST...

Q1: Well, with a matter-antimatter drive, you convert 100% of the mass of the fuel into energy. Therefore, I'm pretty sure that it's the greatest energy yield reaction. Of course, that doesn't account for the storage containment system, a system to ensure that all the energy goes into propulsion (instead of some of the gamma rays being absorbed by the ship), etc. But I suspect that you're already aware of this.

Q2: The other problem is just making enough fuel. Currently, antimatter is made one atom at a time, which isn't the most efficient way to create fuel. ;) So, these are the two main problems from a practical stand point.

Q3: I guess it would depend on your definition of "propulsion." If by "propulsion" you mean ejecting stuff out behind you so that you accelerate forwards, than no, a warp drive is not "propulsion." However, if you defined propulsion more loosely, than warp drive could be seen as propulsion. In the end, it doesn't really matter.

[Walter Wayne]

Originally posted by TexasBEAST
Q: The greatest problem with action-reaction systems now is the mass of fuel required to be carried, right? The duration of the trip and time paradoxes and all that, those are uncomfortable to think about, but perfectly doable. Just the problem of how do you carry enough fuel?This doesn't just apply to action-reaction systems. Assume 100% matter-energy conversion, at that all energy is turned to kinetic energy, and accelerating to any appreciable speed requires enormous amounts of fuel. So perhaps generational ships are much more reasonable than using time dilation to fix everything.

Walt

P.S. If my calcs are right (big if), to get to .999992c (as mentioned by rwald's in a post above) one requires the fuel to about 250 times the mass of the remaining ship and cargo.

[LucyR]

Originally posted by daver


Doubling your speed every week isn't the way acceleration works, even Newtonian acceleration.

I suggest that you take a few steps back and consider the difference between constant and non-constant acceleration.

Lucy.

[arcticpenguin]

The August issue of Discover Magazine is now linked at their web site. The article I was interested in doesn't seem to be on the web, but they do list some links here: http://www.discover.com/current_issue/index.html


Here's their link on Advanced propulsion concepts (http://www.islandone.org/APC/)

[daver]

Originally posted by LucyR


I suggest that you take a few steps back and consider the difference between constant and non-constant acceleration.

Lucy.

Why? Why would you want to accelerate at 1 milli-g the first week, 2 mg the second, 4 the third? If you can accelerate at higher g forces, why not do it all the time? A Bussard ram is the only drive proposal i'm aware of which would plausibly follow such a scenario, and as has been pointed out in previous posts, Bussard rams aren't feasible in this neck of the galaxy (the Sol system seems to be inside a particularly empty region of space).

[thaiboxerken]

Just accelerating would be difficult, but one would also have to start decelerating about half-way to the destination, eh?