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Eleniar
2007-Oct-03, 01:03 AM
Greetings and Felicitations,

I am looking for reference materials for a personal project. I need a resource that has current and/or projected speeds for different methods of propulsion. I already have the speed of the current fastest probe but need more information for a thesis on the possible range of exploration based on current and projected future scenarios. For example, how far we could get before the sun expands into a red giant if we started at the current time.

Any help would be most appreciated.

In Peace,
Eleniar

danscope
2007-Oct-03, 01:39 AM
Hi, For clarification: Do you mean 'How far mankind could travel ,assuming that we could enjoy some remarkable suspended animation system such that we could traverse the gulf between the stars and survive long enough to find a new home world? "
Once you have left the solar system, there is litterally nothing to stop you from reaching your destination. Whether you get there intact or in little pieces
or simply perforated , fried or frozen is open to question.
But...provided that the subsystems of your hypothetical ship survive intact
and have an eternal power supply which cannot deteriorate (I'm thinking
Krell technology here ...you know....the good stuff..) time then becomes meaningless. But you have to consider the potentiality of incurring gamma burst radiation enroute, and sustained radiation from any other source and the interception of cosmic debris at super velocity. And just who or what is steering this ship? What method of course correction? What method of propulsive breaking will be available or even work at the other end?
If, at the other end of your planned voyage, you find yourself waking up in the viscinity of a potentialy non-hostile solar system with the holy grail of life
present...a planet with water and a non-poisonous atmosphere
and with sufficient minerals and an atmosphere which protects one from the
damaging radiation of the local star, and has a low rate of volcanism and potentially stable geology .....and oxygen and some co2 ...n0t too much ...
and.....not so many hostile micro organisms that want to kill you off immediately...(the little things..)

and all of your systems survived such that you can live and operate within your ship and make a safe descent to said planet....
well,......that's the trick, in it !
Imagine if we arrived on earth and crash landed in the ocean near Georgia.
Your ship has sunk. You blow ashore with a life raft and a few 'things' and your hides. And even that would be a most collosal achievement of all time.
It's a house of cards in a wind storm...sort of.
But...hey....we are humans. We can dream.
Best regards, Dan

Kaptain K
2007-Oct-03, 02:36 AM
danscope,
Not to take anything away from your post (well done), but:
All of this has been covered in depth in Sci-fi from "the golden age" of science fiction!

danscope
2007-Oct-03, 02:46 AM
Hi,
Ah yes,......the great 'Golden Age'. You know, Captain James T. Kirk
Never ever spilled his coffee when they changed course at warp factor 5!
And he went from one star system to another in a few days. :):)
But...I degress.
Best regards all,
Dan

danscope
2007-Oct-03, 02:51 AM
Hi Elleniar, Your question was taken seriously. I have been accused of making fun of Captain Kirk from time to time. But....I loved the series.
Best regards, Dan

Jens
2007-Oct-03, 03:55 AM
For example, how far we could get before the sun expands into a red giant if we started at the current time.


I think that in any case, the answer here would be "a long, long ways." Far enough that you'd never notice it had expanded into a red giant. The pioneer probes are moving out of the solar system, and in a couple of billion years, they'll be really far away.

I think, but am not absolutely certain, that the major propulsion systems used today, i.e. rockets and ion engines, will both easily get you out of the solar system using gravity assists from planets. Because there's so much energy available from the momentum of the planets. So if we seriously decided to try to get out of the solar system before the sun becomes a red giant, it would be quite easy even with current propulsion. The problem is what you do once you get out there.

Kaptain K
2007-Oct-03, 04:03 AM
danscope ,

As much as I love Star Trek, the golden age was over by then.
The 30s, 40s and 50s. That was the golden age!

danscope
2007-Oct-03, 04:43 AM
Yes, I was fond of the series.."Flash Gordon".
Anything black and white was classic. Remember "Things to come"?
Dan

danscope
2007-Oct-03, 04:46 AM
Greetings and Felicitations,

I am looking for reference materials for a personal project. I need a resource that has current and/or projected speeds for different methods of propulsion. I already have the speed of the current fastest probe but need more information for a thesis on the possible range of exploration based on current and projected future scenarios. For example, how far we could get before the sun expands into a red giant if we started at the current time.

Any help would be most appreciated.

In Peace,
Eleniar

As far as velocity, you may be looking at an upper limit of 75,000 MPH.
Hope you have brakes for the end stop.
Best regards, Dan

neilzero
2007-Oct-03, 05:17 AM
Danscope gave an excelent summary of the broad topic.
Jens made an accurate observation that I will expand. We can build a ship by 2020 (at enormous cost) that will take a million humans a billion kilometers from the sun, most of the people in the form of frozen sperm and embyos. At a billion plus kilometers the red giant stage will be interesting to observe, but not dangerous.
So we are about as far from the Sun as Saturn in 2040: Will anyone survive until 2041. Not likely unless we work smarter the next 13 years. A craft for 2 or a few humans is extreemly complex with billions of things that can go wrong. We have to sucessfully recycle the air and water and food for 21 years. We know how to do that for about 2 years at present, so 21 years is very optimistic.
Let's assume we do work much smarter the next 13 years, and two grand daughters of the first two are alive at 2120. They need a computer chip for the oxygen recyling system. They brought 8 spares, but none of them work as they failed because they are 100 years old. Think about the percentage of 100 year old machines that are still functional today. There are some, but not one in 8, if we are talking about something a tiny fraction as complex as a computer chip. Perhaps the two ladies can construct the replacement chip they need: Very improbable, and much less probable that they can construct the billion other parts the ship will need before the Sun becomes a red giant. Neil

Jens
2007-Oct-03, 06:21 AM
And just to add to my post, I got the following information about Voyager 1, which is currently traveling away from the sun.

It is moving at about 3.6 au / year
There are about 63,000 au in a light year
The sun is expected to become a red giant in 4.5 billion years.

So say Voyager 1 can go a light year in 20,000 years. That means that in 4.5 billion years, it will have gone something like 100,000 light years. That's like 1/20th the way to the Andromeda Galaxy.

My math may be totally wrong, but I think those are ballpark figures.

neilzero
2007-Oct-03, 06:37 AM
If speed was the only consideration, a ten kilogram payload could pass the orbit of Saturn in about one year with a specially built spacecraft, without the aid of any sling shot manuvers, before Saturn. We would start with the largest possible rocket with today's technology and it would be a 4 or 5 stage rocket. Saturn could perhaps add another 20% to the speed of the ten kilogram payload. So a billion kilometers per year is possible = 2,700,000 kilometers per day = 112,500 kilometers per hour, perhaps a bit more. If the ten kilogram payload was an ion engine, it might reach 200,000 kilometers per hour in another year. At present we would not expect the ion engine to operate more than a year, continously, but better ion engines (or equivelent) are likely soon. Predicting what a future major break thru might do is mostly guesswork. Neil

Urbane Guerrilla
2007-Oct-03, 07:38 AM
Captain James T. Kirk lived in a society that stepped readily from star to star -- and can't or doesn't have a remedy for male pattern baldness...

Jens
2007-Oct-03, 08:29 AM
Captain James T. Kirk lived in a society that stepped readily from star to star -- and can't or doesn't have a remedy for male pattern baldness...

It's funny, I was thinking something similar today. That the doctors at Hogsworth can mend bones in a moment, and do lots of magical things, but apparently can't fix myopia, or even conjure up contact lenses for that matter. :)

astromark
2007-Oct-03, 09:40 AM
Your post is interesting and I enjoy this type of thinking ( a fresh idea ) I do not have all the information you seek and doubt that any could be supplied as the future is a strange and unknown place. Just this week we celebrate the 50th anniversary of 'Sputnik' In that 50 years we have achieved much or very little depending on your view and expectations.
For me its been a disappointment that money or the lac of it has suppressed the momentum of humanities journey into space. Not that we have not achieved much, we have. To answer your questions is imposable as we do not know what as yet un thought of methods of propulsion could be in our future.
I agree with the previous posts in regards to the fact that even with our currant methods of propulsion we could be light years away from sol before she engulfs the inner planets. Humanities advanced scientific achievements are numerous and three to five billion years is a very long time.... mark.

Eleniar
2007-Oct-03, 10:18 AM
Greetings and Felicitations,


Hi, For clarification: Do you mean 'How far mankind could travel ,assuming that we could enjoy some remarkable suspended animation system such that we could traverse the gulf between the stars and survive long enough to find a new home world? "
Once you have left the solar system, there is litterally nothing to stop you from reaching your destination. Whether you get there intact or in little pieces
or simply perforated , fried or frozen is open to question.
But...provided that the subsystems of your hypothetical ship survive intact
and have an eternal power supply which cannot deteriorate (I'm thinking
Krell technology here ...you know....the good stuff..) time then becomes meaningless. But you have to consider the potentiality of incurring gamma burst radiation enroute, and sustained radiation from any other source and the interception of cosmic debris at super velocity. And just who or what is steering this ship? What method of course correction? What method of propulsive breaking will be available or even work at the other end?
If, at the other end of your planned voyage, you find yourself waking up in the viscinity of a potentialy non-hostile solar system with the holy grail of life
present...a planet with water and a non-poisonous atmosphere
and with sufficient minerals and an atmosphere which protects one from the
damaging radiation of the local star, and has a low rate of volcanism and potentially stable geology .....and oxygen and some co2 ...n0t too much ...
and.....not so many hostile micro organisms that want to kill you off immediately...(the little things..)

and all of your systems survived such that you can live and operate within your ship and make a safe descent to said planet....
well,......that's the trick, in it !
Imagine if we arrived on earth and crash landed in the ocean near Georgia.
Your ship has sunk. You blow ashore with a life raft and a few 'things' and your hides. And even that would be a most collosal achievement of all time.
It's a house of cards in a wind storm...sort of.
But...hey....we are humans. We can dream.
Best regards, Dan

I am looking at this from a purely propulsive angle. The basic idea is to delineate a bubble of exploration based on possible engine designs coupled with several different time frames. I will attempt to explain further.

I am using several different time frames. The first is the estimated life time of animal life on Earth as proposed by Donald Brownlee and Peter D. Ward in The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World (http://www.amazon.com/Life-Death-Planet-Earth-Astrobiology/dp/0805075127/ref=sr_1_1/103-3729379-2022215?ie=UTF8&s=books&qid=1191406169&sr=1-1). In addition, I am using the estimated time of solar expansion into a red giant and the final death of the sun.
In combination with this data I am using various current and projected engine speeds to calculate possible bubbles of expansion. What I am doing is basically creating a series of If...then equations. After I create this list I plan to reverse them in order to estimate the cost (in time and range) of delaying space exploration.

I hope this helps with the issue.

In Peace,
Eleniar

Eleniar
2007-Oct-03, 04:23 PM
Greetings and Felicitations,



I agree with the previous posts in regards to the fact that even with our currant methods of propulsion we could be light years away from sol before she engulfs the inner planets. Humanities advanced scientific achievements are numerous and three to five billion years is a very long time.... mark.

This is one of the disagreements I have with Brownlee and Ward's book. They have taken the pessimistic approach and decided that humanity will never escape the death of the sun because the distances are so far. I have no doubt that life will be spread into the universe from Earth. I just have been curious about the possible area that humanity could spread into even given our current technological limits.

In Peace,
Eleniar

danscope
2007-Oct-03, 05:18 PM
Greetings and Felicitations,



I am looking at this from a purely propulsive angle. The basic idea is to delineate a bubble of exploration based on possible engine designs coupled with several different time frames. I will attempt to explain further.

I am using several different time frames. The first is the estimated life time of animal life on Earth as proposed by Donald Brownlee and Peter D. Ward in The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World (http://www.amazon.com/Life-Death-Planet-Earth-Astrobiology/dp/0805075127/ref=sr_1_1/103-3729379-2022215?ie=UTF8&s=books&qid=1191406169&sr=1-1). In addition, I am using the estimated time of solar expansion into a red giant and the final death of the sun.
In combination with this data I am using various current and projected engine speeds to calculate possible bubbles of expansion. What I am doing is basically creating a series of If...then equations. After I create this list I plan to reverse them in order to estimate the cost (in time and range) of delaying space exploration.

I hope this helps with the issue.

In Peace,
Eleniar

Hi, We must look at one particular problem: Spare parts . How do you deal with the failure of complex systems ......in time . Solid state parts are better
but not imortal. And you cannot reduce the size of an electronics manufacturing facility into something you can take with you. So...you have to take everything you need plus spares . Increased weight.
But by far, the worst problem is your unknown destination.
Who says that the "Nearest star" (how convenient) has any potential for harboring a planet capable of supporting life.....our life?
And we are taking "Cabin fever" to a new level. After so much time,
the occupants may envy the dead.
As far as propulsion, for every action there is an equal and opposite reaction. So...to propel a ship forward, you need to expel something in the opposite direction. At some time, you run out of material to expel.
Rockets do this in a matter of a few short minutes. With great effort and expended treasure , we can assemble and fuel up a rocket in orbit so as to get some truly amazing velocity .....well beyond an earth launched ship.
But...you still have the problems of how to deal with propulsion requirements at the other end. People often overlook this. Kind of like going to Disneyland at 125 MPH in a car with no brakes on an icy lake.
"Well, ya can't get to heaven.....on a roller skate..
'cause you'll roll right past......those pearly gates . "
An old song from childhood.

We have some real and serious and propbably insurmountable problems
with star travel including the physical and mental health of the travelers.
The operational condition of the devices for the project and their repair.
The danger from radiation over time .
Our ability to slow down and manuver at the destination.
And the anticipated but unproven likelyhood of anything aproximating an habital world at the other end .
As a side note: you can boost fuel ahead to Mars ....held in orbit and employed in the return trip, and return the people and treasure (gravel)
to Earth by shuttle. That is an extraordinary exercise requiring extraordinary commitment in time and treasure . That's just Mars!
The stars ? ? ? ? ? ? ? ?? You have a better chance of inventing upsidaisium . And if you get to Mars, you may find Mr. Big . He was last seen clutching a piece of upsidaisium , floated up and away and was never seen again.
There is an interesting book entitled " Interstellar Travel " by
John W. Macvey pub. Stein and Day 1977 isbn o-8128-2278-1 .
May it serve you well.

Best regards,
Dan

eburacum45
2007-Oct-03, 06:46 PM
Take a look at Project Rho
http://www.projectrho.com/rocket/index.html
it may not give the answer you want, but it will show you just how difficult the question you are asking is.

Jens
2007-Oct-04, 02:00 AM
Again, just for my amusement, I made a calculation of what would happen if a person started walking out of the solar system, supposing there was a long sidewalk.

At a leisurely pace of 5 km/h, you would travel 43,800 km in a year. If you walked for 5 billion years, you would travel something like 219 trillion km. One light year is about 6 trillion km, so you would be nearly 100 light years away! It's an enormous distance. Though I suppose you'd get hungry along the way. :)

So I don't think the speed of the engine is really very critical at all. The real problems are those mentioned above, i.e. actually surviving a trip.

In addition, the sun's red phase is not the problem the we really face. The chances are very high that humanity will be wiped out long, long, long before that ever happens, by some horrible disease or a disaster of our own making or an asteroid impact or something like that.

In any case, I don't think that going to another planetary system would be the best possibility for survival. Building a space base on a place like Titan would probably make the most sense. You have an atmosphere to protect you from various rays, and resources to use for energy. I suppose you could dig a big cavern somewhere. It might seem like an enormous task but 5 billion years is a long time.

astromark
2007-Oct-04, 05:48 AM
http://www.projectrho.com/rocket/index.html ... a good link.
This is interesting but, I like Jens answer better. When I am prompted to use my imagination I can... If we could convert energy sufficient into a propulsion source that would enable us to accelerate for years at about 1G that would be effective as a method of slowing for the second half of the journey. I like the thought of not running away just modify what we know. Maybe a massive space base is the best option for us.. surviving our own foolishness is the primary goal.

eburacum45
2007-Oct-04, 10:05 AM
The closest star is Proxima Centauri; that star will never become a red giant, and will slowly grow brighter so that in a trillion years it will be the same brightness as our Sun is today.

All we need to do is get to that nearby star and build a rotating habitat (or several) which can be moved outwards as the star increases in luminosity, and our civilisation have the chance to persist for at least a trillion years.

That might be yet another solution to the Fermi Paradox; an advanced civilisation might see the danger of staying around a yellow dwarf which will leave the Main Sequence in a few billion years, and decide upon a single supreme effort to colonise a nearby red dwarf. Once they have achieved this they might just give up any dreams of interstellar colonisation, which as Danscope suggests, is very, very, very, very hard, but not (I would submit) inherently impossible.

eburacum45
2007-Oct-04, 10:17 AM
Surviving the redgiant phase in situ has been considered; see this link
Delayed Gratification Habitable Zone (http://www.astrobio.net/news/article912.html)
One problem is our star will change very dramatically quite rapidly over time, once it has left the main sequence, and not once but several times.
See this link
The Once and Future Sun (http://www.astronomy.ohio-state.edu/~pogge/Lectures/vistas97.html)
This will make it difficult for any ecology to be established on a fixed planetary surface.

Eleniar
2007-Oct-04, 01:23 PM
Greetings and Felicitations,

I think I am experiencing a miscommunication issue.

I do understand the difficulties of exploration. I am simply trying to create a limit-of-expansion scenario. There are many aspects to be worked out for the expansion of life into space. I don't simply consider this a human problem but a life problem. Until we have evidence to the contrary we have to accept that we may be the only life in the universe. I don't believe we are but we have no evidence to the contrary. If this turns out to be the truth then we have a great responsibility -- to insure that life does not fade from the universe with our homestars demise.
I am seeking to define a simple bubble of expansion without consideration of other difficulties. In other words, if we started sending probes out today and updated the program as other engine capabilities developed how far into space would those probes get before the following:
Possible inhospitability to animal life in approximately 100.000 years Expansion of sun into a red giant. Final explosion of the sun and termination of the solar system.


To do this I need projected and current engine speeds.

In Peace,
Eglaelin

Jens
2007-Oct-04, 02:02 PM
I am seeking to define a simple bubble of expansion without consideration of other difficulties. In other words, if we started sending probes out today and updated the program as other engine capabilities developed how far into space would those probes get before the following:
Possible inhospitability to animal life in approximately 100.000 years Expansion of sun into a red giant. Final explosion of the sun and termination of the solar system.


To do this I need projected and current engine speeds.


I don't see any miscommunication. Well, you didn't bring up point one about 100,000 years before. What does that come from?

But I think I gave you a good answer for number 2. If you're concerned about the expansion of the sun, then the engine speed doesn't matter. By the time the sun expands into a red giant, any probe with enough velocity to escape the solar system at all will be so far, far, far away that it will never notice that the sun became a red giant.

Any engine is fine.

eburacum45
2007-Oct-04, 02:31 PM
The Sun doesn't really explode; I think you should read my link
The Once and Future Sun (http://www.astronomy.ohio-state.edu/~pogge/Lectures/vistas97.html) again, if you think it explodes (although the Helium Flash is pretty violent).

Additionally you should consider that speed is dependent on mass and power, so that if you have a powerful space drive you can use it to go very faster or to move a bigger load, but not both.

Do you want to move a very small package very fast and far away, or move a large package (perhaps holding a large number of refugees from the Solar System) at a slower speed?

Unless you define how big your payload will be, considerations of an 'expanding shell' are meaningless. The shell of expansion of a space program using very small probes is much larger than the shell of expansion of a program using large probes and the same technology.

And is there any significance to the 100,000 year figure?

Eleniar
2007-Oct-04, 05:05 PM
Greetings and Felicitations,


I don't see any miscommunication. Well, you didn't bring up point one about 100,000 years before. What does that come from?



And is there any significance to the 100,000 year figure?

The figure is from Donald Brownlee and Peter D. Ward in The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World. The book puts an approximate time frame on animal life on Earth at 100,000 years. They base this hypothesis on the projection of the fixation of carbon into the soil. According to them the only life that will probably be possible will be the large grasses. The major problem I had with their research was the absolutely pessimistic idea that space exploration was pointless because the distance frame made it unrealistic. This was the first motivation for my work on this subject.


Further into the future, the authors argue, the complex give and take between carbon trapped in rocks, water and oxygen in the sea, and carbon dioxide in the atmosphere-the latter playing the most important role in climatic change-will eventually turn earth into a barren sibling of Mars. While the authors don't make an airtight case for their claims about how our planet's climate and geology will begin to rewind, they do deftly bring together findings from many disparate areas of science in a book that science buffs will find hard to put down. The reference to the quote can be found in post number 16. I don't want to repost the URL because It causes my posts to be moderated.


In Peace,
Eleniar

PS. I will write more later. I have to get ready for work.

John Mendenhall
2007-Oct-04, 05:15 PM
Possible inhospitability to animal life in approximately 100.000 years



100,000 years? Much, much too short, unless you are proposing that we mess the planet up ourselves. In which case our efforts would be better directed to cleaning up the mess, rather than leaving it behind.

neilzero
2007-Oct-04, 06:33 PM
Hi Eleniar: How about we extrapolate the last 50 years top engine speed out to 4 billion years? That would be 18,000 miles per hour for Sputnick; about 36,000 miles per hour for New Horizons. If we double every 50 years: 72,000 in 2057, 144,000 in 2107, 288,000 mph = 80 miles per second in 2157....
In 1000 years, we are close to the speed of light and making relativistic adjustments. It appears your bubble has a radius of about 3,990,000,000 light years, after 4 billion years, or 4 billion light years after about 4.01 billion years of human expansion into space. That would include about 2.5% of the known Universe. As you can see a delay of 0.01 billion years = 100,000 years, hardly changes the 2.5% at all, but does mean billions? of cubic light years are not included in the bubble.
Where else but in astronomy could a few billion cubic light years, be close to negligible? I'm impressed. Neil

John Mendenhall
2007-Oct-04, 07:54 PM
Where else but in astronomy could a few billion cubic light years, be close to negligible? I'm impressed.



Asimov discusses this in one of his books, as I recall with respect to the fate of the universe. When he starts getting numbers like 10^146, he goes"Well, might be off by several orders of magnitude, but who cares?"

danscope
2007-Oct-05, 02:38 AM
Hi,

Concerning..."How about we extrapolate the last 50 years top engine speed out to 4 billion years? That would be 18,000 miles per hour for Sputnick; about 36,000 miles per hour for New Horizons. If we double every 50 years: 72,000 in 2057, 144,000 in 2107, 288,000 mph = 80 miles per second in 2157....
In 1000 years, we are close to the speed of light and making relativistic adjustments. "

The premise of speed doubling is somewhat invalid. You are assuming
that we run into some kind of super technology and can miraculously accelerate
a large mass at super velocity while violating the laws of physics.
We did very well with electronics and miniaturization. That is a triumph.
But you are talking about some basic science in propulsion.
Just how do you see future technology doing this?
Dan

neilzero
2007-Oct-05, 04:32 AM
I agree, we have little reason to think it might be a long term linear engine speed increase, but we are on track for 72 kilometers per second by 2057. A dozen engines that can accellerate continously for about a year are close to testing in space. An ion engine is one of them. We may be at 72 kps in just a few years, without the aid of a gravity assist manuver = sling shot manuver. Neil

eburacum45
2007-Oct-05, 11:01 AM
Ward and Brownlee are concerned that CO2 will fall too low to sustain plant life within 100,000 years, eh? There may be something in that.

CO2 is getting incorporated into the crust over time, and has been slowly disappearing from our atmosphere since the Mesozoic. That is one of the reasons for the ice ages of the Pleistocene. I understand that by ten million years from now the CO2 level will be so low that permanent ice caps will form over most of the Earth's surface.

But ten million years is a lot further away than 100,000 years, and the rate of CO2 incorporation is too slow for such a drastic effect in that short period.

The rate of incorporation can be seen in this graph
http://www.clearlight.com/~mhieb/WVFossils/PageMill_Images/image277.gif
although CO2 has fallen steeply over the last 100 million years, it has tailed off recently- which suggests that we still have a few million years left before the biosphere really begins to suffer. In addition human intervention could create more CO2 from kerogen incorporated into rocks, once the fossil fuels have run out; the same anthropogenic global warming which today is feared as an environmental catastrophe may one day become the only thing keeping the biosphere alive.

IsaacKuo
2007-Oct-05, 11:51 AM
Concerning..."How about we extrapolate the last 50 years top engine speed out to 4 billion years? That would be 18,000 miles per hour for Sputnick; about 36,000 miles per hour for New Horizons. If we double every 50 years: 72,000 in 2057, 144,000 in 2107, 288,000 mph = 80 miles per second in 2157....
In 1000 years, we are close to the speed of light and making relativistic adjustments. "

The premise of speed doubling is somewhat invalid. You are assuming
that we run into some kind of super technology and can miraculously accelerate a large mass at super velocity while violating the laws of physics. We did very well with electronics and miniaturization. That is a triumph. But you are talking about some basic science in propulsion. Just how do you see future technology doing this?

I see it as the opposite problem. We already, today, have the physics and know methods to accelerate probes to high relativistic speeds. It's mostly just a matter of expense and need. For everything in system, there simply is no need for anything above 100km/s--going faster just means reducing payload and increasing cost for little benefit. For an interstellar mission, anything below 30,000km/s is pretty useless. So if we're going to do it at all, we're going to do it with a big "jump", not some slow doubling.

The only low risk technology we have for relativistic speeds is a laser sail--we know how the physics and technology of focusing and aiming lasers over extreme distances very well. This technology actually gets more energy efficient the faster it goes--approaching 100% efficiency as the sailship approaches c.

We know how to make powerful free electron lasers, and it's a technology which will scale up well in the vacuum of outer space. We know how to make the large 1+km diameter zone plates required to focus and easily aim those lasers over multi-light year distances (we know crude labor intensive brute force methods of doing it; there's vast room for improvement in reducing the costs). We know how to create the crude laser sails that would be adequate for acceleration by X-ray laser...and an X-ray laser has the extreme long range capability to reach high relativistic speeds even without extreme acceleration.

It's really mostly a matter of budget. With current launcher technology, the 200m long space laser would be outrageously expensive--and this space laser needs to be in solar orbit, rather than just Earth orbit. The 1km diameter zone plate would also be outrageously expensive to launch with today's launcher technology. It's simply a non-starter. And quite frankly, the lightweight probe we could afford to launch would lack the ability to stop and maneuver at the target star system. It would only be a flyby probe, and zooming past Alpha Centauri at 30%c would yield poor scientific results. You get a couple snapshots of each star, and then you kiss the system goodbye...

For a fraction of the budget of an interstellar probe mission, we could use similar technology to build an extremely high resolution fresnel telescope capable of directly imaging exoplanets. That would mean getting LOTS of high resolution pictures of ALL nearby systems, and without waiting years for the probe(s) to arrive and send back data.

We know how to accelerate a probe up to high relativistic speeds...at a stupendous cost. The questions are, what mission would be worth it, and when will launch costs be low enough that it's not better to just wait for the costs to go down?

eburacum45
2007-Oct-05, 12:45 PM
A number of technologies might allow some sort of interstellar travel; the first that springs to mind is the Daedalus Project
http://en.wikipedia.org/wiki/Project_Daedalus
which in theory would have used inertial-confinement fusion to take 500 tonnes at 12% of light speed to Barnard's Star (but without slowing down at the other end. To carry humans and to slow down at the far end you would probably need to scale the project up by ten times, and also probably be content with a somewhat slower speed. Remember that whatever speed you achieve on these missions will dictate how much deceleration fuel you carry.

Another type of craft that might allow interstellar journeys is the antimatter catalysed nuclear pulse motor
http://en.wikipedia.org/wiki/Antimatter_catalyzed_nuclear_pulse_propulsion
which is one which I like in particular, as it is the system which I have chosen for my own fictional interstellar ship. (http://thestarlark.blogspot.com/) The trouble is, the most detailed studies of this system yet carried out (AIMSTAR for instance) described a top speed of 0.003c, which is a little low for interstellar travel. Hopefully this method could be scaled up somewhat.

Another method which may show promise is the beam-driven interstellar craft, as advocated by Isaac Kuo above; here the craft does not carry fuel for acceleration, but is accelerated using a beam of light or of particles, which is reflected by a sail (or in some concepts) actively heats propellant carried by the ship.
http://en.wikipedia.org/wiki/Beam-powered_propulsion
(I notice that the idea of sending microwave power to an on-board rectenna is mentioned- I had that idea way back when I was a teenager. I wonder how efficient it is...)
Beam powered craft can in theory be accelerated to quite a high percentage of the speed of light- the problem is decelerating them at the other end. Perhaps a slow, Daedalus or AIMSTAR mission might be required to get to the destination first, then build a deceleration beam station. But once a beam-powered system of transport was in place between stars, the 'expansion' of human civilisation could proceed at a steady pace.

IsaacKuo
2007-Oct-05, 12:58 PM
The problems with Daedalus and anti-matter catalyzed nuclear pulse are that they're essentially fusion rockets. Fusion fuel simply doesn't pack enough energy per gram of fuel to reach acceptable interstellar cruise speeds. The only internally carried rocket fuel with sufficient "punch" is anti-matter--which is mindbogglingly expensive, even with optimistic future technology.

The best alternative I've come up with so far is a kinetic impact powered rocket. This isn't powered by an on-board fuel, but rather kinetic impacts with near-c microsails. The energy of these impacts can be far better than what fusion is capable of, and can even be better than what you can get from an antimatter rocket. You get similar performance to an antimatter rocket, but with neither the stupendous costs of antimatter nor the technological challenge of an antimatter fuel tank.

Even though laser propulsion is only good for directly accelerating sails outward, those sails can power a rocket for deceleration, thanks to kinetic impacts.

eburacum45
2007-Oct-05, 01:45 PM
How so? I can only imagine microsails impacting the craft from behind; that seems likely to accelerate the vessel rather than decelerate it.

IsaacKuo
2007-Oct-05, 02:16 PM
How so? I can only imagine microsails impacting the craft from behind; that seems likely to accelerate the vessel rather than decelerate it.

The starship has shaped like a loop, with a large hole in the center. A near-c microsail passes through this hole, to impact a puff of inert propellant after passing through. That causes an explosion of plasma in all directions (assuming the rest mass of the inert propellant exceeds the rest mass of the microsail by a good amount). The starship includes a superconducting magnetic loop, so the plasma is deflected by the magnetic field--producing thrust.

This concept is similar to magsail-orion, except that kinetic impacts power the "bombs" instead of nuclear fission/fusion. The latter is limited to an average particle velocity of only a small percent of c, at best. The former can acheive an average particle velocity arbitrarily close to c (depending on exactly how close to c the near-c microsail impactors are). Overall efficiency plummets as you get near to c, though. For extremely long range journeys where you want a near-c cruise velocity, it's definitely worth using interstellar medium braking to slow down a bit first, before utilizing the kinetic impact powered rocket.

For extremely long range journeys (like intergalactic journeys), it probably doesn't make sense to send the microsails individually all the way from the source system. Instead, you'd send two starships. The first starship is the "main" starship. The second is an auxiliary starship which holds all the microsails. A few years before arrival, the auxiliary starship launches the microsails, while the main starship uses ISM braking to slow down a good fraction of c. This way, the microsails only need to perform stationkeeping for a few years.

eburacum45
2007-Oct-05, 02:45 PM
So you have to carry some on-board propellant, to get the full effect, eh?

I believe there is a magsail concept where fusion bombs are sent in front of the ship, and it magnetically gathers them up just before they explode. They could have some sort of proximity fuse to ensure they explode at the right distance. The deceleration not only relies on the explosive power of the bomb but also the relative difference of speed between the ship and the bomb. This method means you take less propellant on board the ship, but it does require many decades or centuries of forward planning, and equipment which functions reliably in interstellar space over a very long period.

IsaacKuo
2007-Oct-05, 03:39 PM
So you have to carry some on-baord propellant, to get the full effect, eh?

For the concept I described, a kinetic impact powered rocket, you do. By definition, a rocket carries its own propellant. Externally powered rockets might use an external source of power to actually cause the propellant to "go", but it's the fact that it carries propellant that makes it a "rocket".

There are other concepts which don't require carrying propellant, but I don't feel they are as practical.

For example, if you use visible light, it's conceivable to use a huge sacrifical mirror to reflect a laser to your starship for braking. The mirror flies off into the distance, while your starship decelerates into the destination. Unfortunately, visible light spreads much more than X-rays, so this requires an uber-huge sail, an uber-uber-huge sacrificial mirror (which btw has to be kept perfectly rigid within 1/4 wavelength), and an uber-uber-uber-huge home system laser.

Slightly more practical is the idea of a sacrificial laser ship. Same basic idea, except instead of a sacrificial mirror you have an entire sacrifical laser system. The advantage? The sacrificial system only needs to be a relatively doable X-ray laser, and the starship sail doesn't need to be uber-huge. The disadvantage? The sacrifical system is really really heavy, and it needs to be launched in the first place.

Getting much more practical is some sort of "pellet track" system. Instead of carrying on board propellant, the home system launches a series of pellets after the starship. After the pellets are launched, the near-c microsails are launched. Things are timed and aimed perfectly, so that the pellets and microsails collide just in front of the starship (after passing through the large loop hole). This basically works the same as the rocket I described above, except the sacrifical propellant is in the form of pellets launched after the starship. The advantage? The starship is lighter, making it easier to launch in the first place and making it easier to decelerate because it doesn't need to decelerate a heavy propellant tank. The disadvantage? You've got to perfectly aim all those pellets and the microsails need to hit a little pellet rather than a big puff of gas.


I believe there is a magsail concept where fusion bombs are sent in front of the ship, and it magnetically gathers them up just before they explode. They could have some sort of proximity fuse to ensure they explode at the right distance. The deceleration not only relies on the explosive power of the bomb but also the relative difference of speed between the ship and the bomb. This method means you take less propellant on board the ship, but it does require many decades or centuries of forward planning, and equipment which functions reliably in interstellar space over a very long period.

The problem is the forward planning. If you look at the total mission time, you're limited by the maximum particle velocity of the fusion bombs. My early "bombtrack" concepts relied upon the idea that SOME particles from the fusion bombs travel at 20%c, even if the average particle velocity is much lower. Thus, you could launch a set of fusion bombs at 20%c and this "track" of bombs could be enough to decelerate the starship.

However, fusion bombs are expensive and politically touchy (do you really want to mass produce millions of fusion bombs, launch them into space, and hope none of your launchers fail and none of the bombs get into the wrong hands?). The bombtrack drive is also very inefficient, utilizing only a very small fraction of the bomb's energy. And ultimately, 20%c is a bit too slow, anyway.

So I looked at different concepts.

Actually, one idea that I have which might be workable (I'm really not sure), is a "torusail". This uses a torus shaped magnetic field generated by several magnetic loops in a "donut" formation. If you perfectly place the bombs along the centerline of the starship's path, and perfectly time the detonation by the exact time before the starship reaches it, the torus magnetic field will deflect the positively charged nuclei in just the right way to produce thrust even if the starship's relative speed is greater than the bomb product velocity. If it's workable, the potential efficiencies can be extreme.

It's essentially the magnetic version of what's known in sailing as "reaching". Reaching allows traveling even faster than the wind, by deflecting wind that's moving perpendicular to the direction of motion.

But it presents a daunting technical challenge. Millions of perfectly placed bombs? Could be done, but it's a challenge. Perfect timing of the detonations? Hmm...the timing is really touchy when the starship is passing by at .5c.

That's one reason why I favor the kinetic impact powered rocket. While the starship does need to be maybe three times heavier because of the propellant tank, the timing is just so much easier. When it puffs some inert propellant, it doesn't matter if the incoming microsail is a tenth of a second later than expected. The starship can just emit a constant stream of gas, and the incoming microsails will impact when they may.

eburacum45
2007-Oct-05, 07:50 PM
I am not sure we need to go quite that fast. Interstellar colonisation, if it ever happens, will probably be a very slow process. And, as I suggested in an earlier post in this thread, just getting to the nearest star (Proxima) and no further may extend the lifetime of our civilisation by a trillion years.

But I am very glad someone is considering practical ways of travelling faster than a comparative crawl.

IsaacKuo
2007-Oct-05, 09:04 PM
Oh, we certainly don't NEED to go that fast. But we'll probably do it someday anyway because we CAN. For early interstellar missions to our nearest neighbors, somewhere between 30%c and 50%c is a good "sweet spot". Going much slower than that runs into human lifetime problems and the problem that a mission launched decades later with better technology will actually overtake you. Going much faster than that only shaves a few years off the mission time but greatly reduces your payload (for a given budget).

But what happens after the first few forays to our nearest neighbors? Sooner or later, someone decides to do some serious expansion. That's when it starts looking good to send out long range high relativistic colonization missions. The gaps can be filled in later.

And there's also the possibility of exotic remote laser etching of Von Neuman colonizers. You just need to image a suitable rocky body, and you zap it with long range lasers to "colonize" it. This sort of colonization goes at the speed of light!

eburacum45
2007-Oct-06, 10:35 AM
That last is really only a remote possibility, in all senses of the word.