Ok, of course we want a good story, and Steel, you can go to that website and start posting. Anyone else who wants to be part of this book, and seriously, part of this book, as in contributing as much as possible, should go there in the next couple of days. If you don't the password will have changed and you will have to email me at email@example.com for me to tell you the password to the forum. Have a nice day, for as of now, we will no longer be posting on this topic. OSC and all your family that posts on this site, thank you so much for being the grounds of a possible book. I will definitely tell you all if anything interesting happens. Don't worry, I'll still stick around Hatrack
Morpheus: You're right, my mistake. For some reason i thought Bernard's Star was closer while Alpha Centari was farther.
quote: How about writing a good novel with all of the science as accurate as possible? To make it a popular story, it has to be filled with sex, violence, and government conspiracy. The novel could be written on this forum as if it were a role playing game.
Wow WildZBill, thats sounds so familiar. Maybe we can get Mr. Robinson to help us.
The biggest challenge to any exploration right now is building fast enough engines. We need to be able to get at least 10% light speed before any trip outside the solar system is worth it. We need to get .1% light speed before common interplanet travel is reasonable. At that speed it would take 66 hours to reach Mars from Earth. It would take between 6 & 17 days for a trip to the Astriod belt, depending on what point you want to go to. This all depends on the fact that the Earth is the closest it can be before you launch.
.1% speed of light is ~671,000 mph; the space shuttle travels at ~17,500 mph. So you can see why we need faster engines.
This is an argument I found on another forum with it's author listed as "unknown". It seems to be a way to scientifically validate prophecy.
quote:An Argument in Favor of Precognitive Dreams
We must first accept that the space-time continuom has already been established for all eternity. All past and future events can be placed on a theoretical "map" of space and time.
Second, we must accept that energy is capable of traveling throughout the universe. Before matter, energy was, because without energy, matter could not have been created. Because energy has no form of its own, it moves through particles as heat, motion and (perhaps) thought.
Third, we must accept that "time" as we know it is a man-made contrivance. The theory of relativity states that there is no such thing as universal time, instead, time is affected by factors such as speed and even gravity. We think of "time" as a foward-moving process because our lives are a foward-moving process, but we have no proof that non matter bound forces, such as energy, cannot move backwards in time.
Because every "event" that happens MUST involve a tranference of energy, it is safe to assume that every event releases energy. Likewise, it is a safe assumption that the greater the event, the greater the amount of energy released. An event of immense importance would, perhaps, release energy both fowards and backwards in time!
The Brittish physicist James Clark Maxwell's theory predicts that energy moves away from its point of origin in waves like ripples in a pool. Therefore, the energy signiture of an event can be represented as two cones with their points touching. The bottom cone is the ripples of energy flowing backwards in time, and the upper cone is energy flowing fowards.
In traditional physics, this graph represents all points in time which could have affected the event (found in the lower cone) and all events that could be affected by the event (the upper cone). The point where the two cones intersect is, of course, the event itself.
Lets for a minute consider this instead a graph of all points in time that the energy from this event can be "sensed". It is obvious that any person affected by the event after it has transpired will, on some level, also be affected by the energy residue from the event. But could a person be affected by the energy residue before the event even takes place?
Though we do not like to admit it, human beings are, in fact, animals. We may have rationing abilities which make it easier for us to ignore those instincts which we deem to be "animalistic"; but it is the very same organ which can do this that eventually does us in. We may have developed higher cognitive capabilites, but we still have parts of our brains that are especially formed to respond to taste, touch, and especially to smell. Do you ever feel the need to sleep all day when it rain outside? Animals do that. If you're female - do you feel more "in the mood" at certain times of the month than others? Chances are that you are ovulating.
Because we ignore and repress our instincts, our subconscious is often the only part of us that pays attention to these things; but it does not mean that we are not aware. Instead, we dream, for that is how our subconscious likes to communicate with us.
And sometimes, when we are especially lucky, we dream about the future.
Wow, thanks Steel. That's a lot of important stuff there. I like the dream part. Heh...I'll have to read it over and think about it before I come up with some strong opinion on it.
Doug J: Your gonna hate me for this, but I think that someone mentioned that we can go 10% of the speed of light. The speed of light is 300,000 km a second, which converts into roughly 186400 mph, not 671,000. Sorry to have to change your info a little bit again. So I believe we almost go at 10% the speed of light. But thanks for those websites!
it seems i joined this forum a little late for the science of this post but I'm a good writer and would love to help in a novel if you'll have me.
I wanted to point out a few things. The first one being if serious space exploration is going to happen then ships will need a shield to protect them from micrometeors it will have to be an energy field, a metal shield that could withstand more than one micrometeor impact would be far too heavy to move with most propellants.
An FTL drive would probably involve this shield as well as some sort of pandimensional aspect, i mean this practically in the way that photons have been shown to react together (Michael Crichton's timeline)it suggests that there are particles which we cannot detect because they are only partially in our dimmension.
And if we wanted or could move mars why couldn't we move it to earth's exact orbit on the opposite side of the sun. Then mercantile ships could travel in the opposite rotation around the sun, keeping distance down and constant, only problem is that if your speed relative to the earth slows enough dont you fall into the sun because your velocity no longer defeat's the sun's gravity? logistical problems.
Maybe my boys can stop 'em, yeah... And maybe I'm a chinese jet pilot. ~brock
Posts: 46 | Registered: May 2003
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I think that it is more practical to beleive that faster than light travel is impossible.
I think that if interplanetary travel ever happens, it will happen in, essentailly, space stations. Moving at, perhaps, high speeds, but nowhere near the speed of light.
Posts: 497 | Registered: Apr 2002
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Ah, your turn to prove me wrong. I was thinking you were saying it was 671,040 miles per second for some reason. Ok, thanks.
And Brock, we'd love your help, goto this website: www.geocities.com/morpheus2god/index.html Click on the link that says "Click to Enter the Forum", then enter the password, "spaceexp" before 9:30 tonight, or post your email address here, and I'll send you the new password, because I am changing the password at around 9:30 tonight. Thanks! I'll be glad to see your posts there.
Why is it more practical to say well never go faster then light speed. Cavemen would have said it would be impossiable to just go into space but we do that fairly easly. Whos to say what will happen in the future. I prefure to belive that anything is possble untill you can prove with out a doubt that it is impossable.
Posts: 397 | Registered: Apr 2003
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It is hard for us to get .01% speed of light; I think we should work on these barriers first. Theoretically it is possible for us to go up to the speed of light, but to go faster than that is all guess work right now. We should keep researching the possibility but focus on the slower than light engines.
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More specifically than slower than light engines, we need to focus on slower than light transport, i.e., the actual practicality of travelling between the stars on a non-FTL ship. If we're heading for the Asteriod Belt, than of course the problem is simplified. However, if we're going interstellar, new problems arise. Obviously, the trip is long. How do you get people from here to there in one peice? Problems include supplies: food and water, and more pressingly, air. To support a mild-sized human population for any duration, you would need a massive amount of carbon dioxide converters (plants), and these take up space.
This may be a tie in to our asteroid concept. Supposing that we can move asteroids into orbit, why couldn't we move them onto a course to another star? This solves problems of living space as well as food, air, and water, assuming that we outfit the asteroid specially. In all likelyhood, we bore into it as well.
This is, of course, assuming that no breakthrough is made which allows for FTL travel, or for suspended animation. Therefore it is the least fictional of the concepts and, to me, the most original.
Posts: 497 | Registered: Apr 2002
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I've no doubt that faster than light "travel" is possible in some form, maybe even within the next 100 years. It is, however, currently an extremely far out idea with little or no scientific backing. Consequently, if we wanted to write a sci-fi novel about "space exploration and colonization" that was more sci than fi, I don't think it should involve FTL.
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Im not sayin we shold use FTL travel i was just talking about when Steel said "I think it is practical to belive FTL travle is impossable." if he menat in the short term then i mis-understood. The way I understood it he ment that it would never happen in any number of years.
Posts: 397 | Registered: Apr 2003
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it should be the spaceexp one still we decded to leave it since this is the only site to get it and anyone who goes over oughta be willing to help since everyone here is nice and will respect our wishs for you stay out if you arn't gona help.
Posts: 397 | Registered: Apr 2003
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My email or one of them is firstname.lastname@example.org Sorry i didn't see your post earlier, i just stepped into the forum long enough to post against Plemet and left, so please send the URL and password to me.
In the land of Mordor, where the Shadows lie.Posts: 46 | Registered: May 2003
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And I'd like to help with the book though I'm a late "forumer". I'm a pretty good writer and could help with the government conspiracy part. I know alot about government stuff, and could hep with that.
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Ok. I send you the website address and the password in an email Brock.
Glaucon, yeah, there's a bit of public involvment.I'm trying to keep the novel writing only open to people who have seen it here from Hatrack. Pretty much everyone here writes well, and is repectful, so we don't get any random people on our boards spamming. For anyone else who's just looking at this thread, and would like to join to help write this novel, we'd be happy to have you. Goto: www.geocities.com/morpheus2god/index.html Click on "Click to Enter the Forum", then type the password, "spaceexp". Your in! Feel free to start posting, and remember that this is a book that we need to be committed to. Don't go overboard and make sure you read all the posts before you start posting your own so you know what we already have. Remember to have some fun though
[ June 03, 2003, 02:12 AM: Message edited by: Morpheus God ]
Posts: 30 | Registered: May 2003
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Is it just me or is anyone else haveing trouble geting in when I click on the main link it takes me to the list of topics then when I click on a topic I have to put in the pass. and it won't work. Was it changed or if the forum screwed ? Whats the deal?
Posts: 397 | Registered: Apr 2003
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This thread has sort of wandered, and some of the stuff I've included has been bandied about, but here's my two cents on the original thread. I've also posted this at www.bryanerickson.com/intospace -
1. A trip to Mars using the lowest energy direct path, called a Hohmann transfer orbit, takes about nine months. You can expend a little extra energy to shorten the trip time down to seven or six months. The energy required to shorten the trip at all beyond that balloons, and is effectively impossible using traditional chemical rockets, and would instead require new propulsion technology, the logical candidate being nuclear rockets.
You'll notice that almost all space probes sent to Mars historically have had a trip time between nine and seven months. The major exception is the first Japanese Mars probe, Nozomi, which was sent on a trajectory that added years to the trip time at a ridiculously small savings in energy, by having the probe loop through space back to get a gravity boost from Earth.
2. The longest anyone has spent in space continuously is fourteen and a half months. That record was set by Valeri Polyakov, who launched on Soyuz TM-18 on January 10, 1994, stayed on board Mir, and touched down on Earth again on Soyuz TM-20 on March 22, 1995. The longest anyone has been in space cumulatively is over two years (747 days). That record is held by Sergei Avdeyev over three separate trips to Mir. A round trip to Mars and back, assuming you stay from one launch window to the next, would keep you off Earth for about the same amount of time, just over two years. Since half this time would be spent with the gravity and radiation shielding available on the Martian surface, this would be less of a health concern than staying in space for the same length of time.
3. Just how much energy would it take to move Mars into an orbit closer to the Sun? Say we just want to move it 10% closer to Earth than it is right now: from an average orbital radius of 228 million kilometers to 220 million kilometers. This would require about 6.8 * 10^30 joules, if done with perfect energy efficiency. The current power output of all the power plants on Earth is about 2.2 million megawatts. At that rate, we would generate that amount of energy in one hundred billion years of operation.
The present orbits of the planets are a delicate balance in the midst of potential orbital chaos, worked out in the violent early days of the Solar System. Even if we did move Mars any significant distance, it would almost certainly interact chaotically with Earth's orbit resulting in either a collision between the two or throwing the Earth into a much more elliptical orbit taking it either much closer to or farther from the Sun than it presently goes, setting the stage for further chaotic interaction with Jupiter or Venus. The final result for the Earth would almost certainly be collision with another planet, falling into the Sun, or being cast out of the Solar System.
4. If you want to build large-scale habitats in orbit around Earth, a far cheaper and safer alternative exists to redirecting entire asteroids. It is to mine raw materials from either near-Earth asteroids or the Moon and send the raw materials into Earth orbit in particulate form so even a mistaken trajectory would only cause a pretty meteor shower instead of a catastrophic collision. To get material off the Moon you have to overcome its 1.6 m/s^2 gravity, while putting asteroidal material in Earth orbit requires overcoming its momentum, with speeds up to 60 kilometers per second relative to Earth. With the materials in Earth orbit, you can use them to build your habitats. You wouldn't want to put them in low-Earth orbit, where the Space Shuttles and International Space Station orbit, because even in what we think of as the vacuum of space, there's enough matter to exert a slow, steady friction that degrades the object's orbit enough to plop it down onto the Earth after several years. That's what happened to NASA's Skylab station after NASA decided to use its last Saturn V rocket, the only vehicle available to raise the Skylab's orbit, for the Apollo-Soyuz Test Project in 1975 instead of boosting Skylab once more until the Space Shuttle would become available to take over station-keeping. Instead of low-Earth orbit, you can put habitats in what are called the Lagrange L4 and L5 positions with respect to the Earth and Moon. These are just the two positions (one on either side) that form equilateral triangles with Earth and Moon, where objects have long-term orbital stability.
5. As for it taking centuries to colonize Mars: ridiculous. An effort of similar magnitude to Apollo could put long-term colonies on Mars in ten to twenty years. See Robert Zubrin, "The Case for Mars" and "Entering Space: Creating a Spacefaring Civilization." NASA Johnson Space Center used Zubrin's mission architecture as the basis for its mission design reference for a human mission to Mars. Now, *terraforming* Mars would take hundreds of years with foreseeable technology, but we could (relatively) easily live within local structures. Many current astronauts, who are top experts in mission design and engineering, believe that political will and financing are the only real obstacles keeping us from putting people on Mars during their careers. I've heard three of them say so in person: Robert Cabana (Jan. 1999), Scott Horowitz (Aug. 2000), and Eileen Collins (Aug. 2001), all three of whom are shuttle commanders.
This would be by far the cheapest and easiest way to start humans living permanently off of Earth. The main limiting factor for humans living away from Earth is availability of resources. As long as all our resources have to be lifted out of Earth's gravity, living away from Earth will be enormously expensive and will continue to cost at least millions of dollars per person for even the shortest trips. Becoming able to go somewhere away from Earth and use local resources is the key to breaking out of this need. The surface of Mars has plentiful oxygen, carbon, and nitrogen, and hydrogen, all in easily usable forms to make breathable air, water, food, rocket fuel, and all the other necessities of life. The Moon has plenty of oxygen but locked up in minerals requiring tremendous energy and complicated engineering to get into usable form; it also has little to no hydrogen, carbon, or nitrogen. The polar craters, and a few near-Earth asteroids, may have some water ice, making them more attractive; a few asteroids have carbon; and of course metals are found in all of the above; but only Mars has everything, and in convenient form. The Moon also has two weeks of sunlight alternating with two weeks of darkness, making it more difficult to grow crops; Mars has a day-night cycle only 37 minutes longer than the 24 hour Earth day-night cycle, so growing crops in greenhouses there is a relative cinch. Mars also has 38% Earth gravity, another big bonus over the Moon and asteroids.
6. To correct a few points by several posters: We know the mass of Mars extremely precisely by measuring its influence on many space probes on flyby and orbit. Altering a planet's magnetic field would have no measurable effect on its orbit around the Sun, and anyway, several of them, including Mars and Venus, have no significant magnetic field. The entire arsenal of Earth's nuclear weapons exploded on Mars would not significantly alter its orbit. The "theoretical stages" of faster-than-light travel, as considered by those with and without NASA grants, remain for now, and perhaps for good, in the realm of extreme physics speculation - there is no guarantee that any conceivable progress in physics will reveal a method for faster-than-light travel; general relativity doesn't constrain the Universe to be of finite size today, because spacetime itself expanded during the inflationary period of the early Universe at a speed that was many orders of magnitude faster than the speed of light; the new variable speed of light (VSL) theory, as established by Andreas Albrecht and Joao Magueijo, is now considered by many experts as a serious alternative or supplement to superstring theory, which itself has continued to struggle to make any testable predictions, let alone any successful predictions. The original paper by Albrecht and Magueijo is available online at http://www.arxiv.org/PS_cache/astro-ph/pdf/9811/9811018.pdf Besides that, recent theoretical indications indicate there may be other universes in causal connection with our own, including a progenitor universe responsible for our big bang, so the possible infiniteness of existence may have to include more than our own universe per se. The million-solar-mass black hole at the core of our galaxy has been eating matter and spewing hard radiation for 13 billion years; that hasn't caused us to need to escape the galaxy yet, nor will it, since we are a cozy 30,000 light-years away.
As for "Problem with solar sail-on-asteroid idea:
1) The solar wind moves uniformly out from the sun 2) The asteroid belt is further away from the sun than earth.
Result: Solar wind will only push asteroid further from earth."
This is not true, because you can angle the solar sail to reflect the sunlight into your direction of motion and use it to lose speed and therefore drop into a lower orbit; this is precisely analagous to tacking into the wind with a normal sailboat, which is why sailboats aren't limited just to going in whatever direction the wind is blowing.
7. Barnard's Star, at 5.94 light-years' distance, is farther away than Alpha Centauri. Alpha Centauri is a triple star system, with the two bigger stars 4.4 light-years away, and the third a small, distant outlier at 4.22 light-years from us. At a cruising speed of 10% lightspeed, going to the more interesting central binary, with a little extra time for speeding up & slowing down, we could get there within 45 or so years. Relativistic time dilation would shorten the time as experienced by the travellers, but at that speed, only slightly, enough to take 9 months off their trip time, making them experience 44 years, 3 months. (t=to/sqrt(1-v^2/c^2)).
8. The discussion of precognitive sensing fundamentally misunderstands the science. Any information from an event is limited to transmission within the forward light-cone from the event, with the sole exception of transmission slightly outside due to quantum uncertainty, but only within a Heisenberg box, allowing for spacelike transmission that would be negligible for any human experience. Even quantum effects absolutely forbid reverse timelike transmission, which is what would be needed for any information to be transmitted from an event backward in time within the same region in space, i.e. any point in space from which light would have enough time to reach the point of the event before it occurs.
9. One poster said, "Why is it more practical to say well [sic] never go faster then [sic] light speed [sic]. Cavemen would have said it would be impossiable [sic] to just go [sic] into space but we do that fairly easly [sic]. Whos [sic] to say what will happen in the future. I prefure [sic] to belive [sic] that anything is possble [sic] untill [sic] you can prove with out [sic] a doubt that it is impossable [sic]." Cavemen also didn't understand why they couldn't go into space. We have a pretty good understanding of why we couldn't go faster than light. While our theory is incomplete, we have a theory with a vast wealth of experimental verification showing that it is impossible for any massive object to go faster than light, and no support from experiment or plausible theory showing how we might circumvent this. Even the new variable speed of light theory covers only an effect in the very early universe that would be impossible to duplicate today. On the other hand, since we do not have a final theory yet, we can't say what form it will take, so we can reserve hope that it will allow some sort of warp field propulsion or something to allow faster than light travel.
10. "Ok. Now that we have talked about it here, is there anything we can do about it to actually make a difference in the world?"
..... 1. Write frequently to your congressional representatives saying that you want a bigger and better NASA; that after 31 years going no further than 300 miles above Earth's surface, you want to see the astronauts go out and actually explore again (ideally on Mars!).
..... 2. There are societies out there that you can join whose reason for being is to advocate bolder exploration and activity in space. In descending order of size, the three major ones in the U.S. are the Planetary Society, the National Space Society, and the Mars Society. Get in touch with them at http://www.planetary.org , http://www.nss.org , and http://www.marssociety.org . Get involved. The oldest such society on Earth, co-founded by Arthur C. Clarke, is the British Interplanety Society, with a website at http://www.bis-spaceflight.com . They have published the Journal of the British Interplanetary Society for a long time, which has been the principal outlet for serious scientific studies of advanced possibilities for space exploration and colonization, and which a good library will have.
..... 3. Talk. Spread the idea. Volunteer to speak to teach high school groups, Boy Scout groups, or give a public presentation at the local bookstore. Become a NASA Solar System Ambassador at http://www.jpl.nasa.gov/ambassador ; they provide you with lots of materials and ideas for spreading the excitement of space exploration.
..... 4. Invest in innovative space exploration companies. I'm not going to get into specific companies; make your own investment decisions. But, that is probably the most direct way for any random person to contribute to the development of greater capacity for exploring space.
11. And as for "I'd like to put emphasis 'known'. As Douglas Adams points out in The Hitchhiker's Guide to the Galaxy: 'The universe is infinite, there are, therefore, infinite planets in the universe, which means, consequentially, that there is infinite chance of life on other planets.'"
As Richard Feynman said: We are either not the only intelligent species in the Universe, or we are; either possibility is astonishing.
Bryan, Thank you for your wonderful contribution to our knowledge. It is obvious that you are quite an expert on this subject.
I must admit that I posted the concept about moving Mars in jest. I have mentioned this idea a few times in the past to different groups, just as a way to make people think outside the box. While we do not have that kind of energy available at this time does not mean that we will never have that kind of energy. Actually I did not originate the idea, but rather read it somewhere. It was proposed as an intermediate step to building Nevin's Ringworld.
I will have to visit all of the sites that you linked to (Jeez, takes all the fun out of it ). But I do have several questions after reading your post.
In 2) you described the longest time spent in space so far. Were those cosmonauts able to walk on their own after the trip? If not, would creating artificial gravity by spinning the vehicle help?
In 7) you describe a trip to Alpha Centauri at a speed of 10% of light. Is there any method of propulsion that can get us to that speed? Safely, without being destroyed by any debris in our way? I have become pessimistic about mankind ever leaving the Solar System.
In 10) you list a lot of ways to help this effort. I had hoped that the creation of a popular and truthful SciFi novel (or series of novels) would inspire more interest in this direction. I still believe that is possible, and I will study everything that I can (as time permits) and continue in that direction.
Thank you, again, for your post.
P.S. I tried to spell everything correctly, but please forgive me any errors, it's been a very long day.
Posts: 37 | Registered: May 2003
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1. The Russians have a tradition of being carried after landing from a long spaceflight. The American record holder for longest single spaceflight, Shannon Lucid, spent 188 consecutive days in space, and walked just fine immediately after landing. Rumor says the Russians were upset at her showing them up; other rumor says she did the prescribed 2 hours of working out every day while she was up and many Cosmonauts do not, which helped her do this. But at any rate, spinning a spacecraft for artificial gravity would be incredibly helpful for keeping the astronauts fit and strong, though you'd need at least a hundred meters or so of rotational radius to get significant artificial gravity without significant Coriolis force. That's not too hard, a tether with a counterweight would do fine.
2. You could protect the front of the spacecraft at such speeds by a combination of forward shielding, plus active sensors and lasers on the front that scan for any significant-sized debris and vaporize it before collision, or something like that; it's not a show-stopper.
Posts: 77 | Registered: Apr 2002
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Really. I always figured that hitting even a one pound object at 18,600 miles per second would release more energy than a nuclear weapon. It seems that it would be difficult (even for computers) to spot and shoot at something moving that fast. Consider that something the size of a baseball could destroy your craft, and if your laser can destroy it in one second, you have to be able to spot it (and start applying focused energy) when it is 20,000 miles away. Of course, the moon size objects would be easier to spot, harder to destroy.
Took me a while, I have been out of school for a long time. It looks like a 200 Kilo rock (about 450 pounds), which is smaller than some people that you see walking around, would create destruction similar to the Hiroshima bomb, when collided with at 10% the speed of light.
We will never visit another star system. You can not travel that fast, and if you could you would be destroyed by the things that you would collide with. Forget about destroying objects with lasers, if you had one powerful enough to destroy large rocks at 20,000 miles in one second, it would take more energy than your propulsion system. There is no such thing as survivable wormholes, and there is not even a clue of any way to make matter move faster than light.
This just means that we have to find a way to make this solar system as interesting as possible.
And we need to get some people off of this planet. Since we have potential mega-disasters such as comet collisions, super volcanoes, ice ages, tsunamis, technology runaways, etc., it would be wise to insure that someone survives.
Posts: 37 | Registered: May 2003
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Actually, it is my understanding that at 10% of light speed, even gas atoms pose a serious threat to equipment and soft squishy bodies. No way to detect and deflect something the size of a hydrogen atom.
Posts: 5383 | Registered: Dec 1999
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Along with Peter Ward and Donald Brownlee, you guys have given up too easily. First, a look at the numbers. The energy of any inelastic collision is just the kinetic energy, one half mass times speed squared. If you want to get more accurate and use the special relativity form of this equation, it will only make a difference of about 2% at only 10% the speed of light (0.1c). A hydrogen atom has a mass of 1.6 * 10^-27 kg, so if intercepted at 30 million meters/second, 10% the speed of light, would exert an energy on the collision site of 7 * 10^-13 joules. It's hard to describe how little energy this is; it's about the same amount of energy exerted on a surface from a single bacteria landing on it. With the density of gas in interstellar space, we would actually want to make a 0.1c spacecraft aerodynamic to reduce friction, but there is less risk of danger to the ship from hydrogen atom collisions than there is from spontaneous combustion of an onboard heavy metal drummer.
The hypothetical collision with a 200 kg rock is more serious, and actually much worse than you mentioned. At 10% c, this would unleash an energy of 9*10^16 joules, the same as a 22,000 kiloton explosion, or 1500 Hiroshima bombs, 1000 Nagasaki bombs, or about one large modern nuclear warhead. So if your ship were to collide with this size rock, that would obviously not be helpful to your mission. However, the questions to ask now are, what are the chances of encountering a rock of this size; what are the densities of other particles on a range of sizes from mission-critical down to insignificant; and what can we do about the particles that do pose a threat.
Now, I'm going to make some rough assumptions just to get a beginning idea of what we face. A real analysis would be a lot more rigorous than this, but this should get us into the ball park just to see what range of numbers we're dealing with.
With that said, assume there are 10^13 comets in orbit around our Sun (this is fairly well understood); the volume they occupy is (100,000 AU * 1.5*10^11 m/AU)^3 * 4/3 * pi = 10^50 m^3! Then assume a similar distribution around Alpha Centauri, and that the distribution is roughly similar along the entire path. (The Oort Cloud is understood to reach nearly halfway to Alpha Centuari). That makes the number density of comets in interstellar space about 10^13 comets / 10^50 m^3 = 1/10^37 m^3. Comets have a typical mass of 10^11 kg.
On the other hand, studies of interstellar dust show around 1 dust particle per 10^16 m^3 at an average mass of 10^-16 kg. What's not well understood is the density of particles in between.
Going from densities ranging from 1/10^37 m^3 to 1/10^20 m^3, 17 orders of magnitude in density, gets from 10^11 kg (comets) to 10^-6 kg (dust), 17 orders of magnitude in mass. From that, we can make a very rough assumption that for each order of magnitude we drop in mass, we can find particles of that mass in an order of magnitude greater number density. So, for instance, the density of 100 kg rocks, which would pack the punch of a modern nuclear warhead, with a mass 9 orders of magnitude (o.m.) less than a comet and 8 o.m. greater than a dust grain, has a density of 1 per 10^28 cubic meters, also 9 o.m. less than for comets and 8 o.m. greater than that for dust.
Now, what size of particle is big enough that we'd have to worry about it? What if we want to design the shielding in the front of our spacecraft just strong enough to be able to withstand the equivalent of a really bad auto collision. This is about 4*10^7 J, the equivalent of around 1% of 1 ton of TNT, or from a particle of 100 micrograms at 0.1c. I imagine a huge shield of tough material suspended by great shock absorbers in front of the ship would be able to handle an occasional collision of this magnitude without damaging the ship.
How many particles of each size class would the ship intersect going from Earth to the Alpha Centauri system at 0.1c? If the spacecraft is assumed to have the enormous radius of 1 kilometer, the volume swept out by the spacecraft over the journey, each way, is 270,000 AU * 1.5*10^11 m/AU * (1000 m)^2 * pi = 10^23 cubuc meters, so over the duration of the trip we will intercept about 10,000 particles of 100 micrograms (about every day and a half - these are the auto accident class impactors), 1000 particles of 1 milligram, 100 particles of 10 milligrams, 10 particles of 100 milligrams, 1 particle of 1 gram, a 10% chance of intercepting a particle of 10 grams, a 1% chance of intercepting a particle of 100 grams (capable of unleashing a Nagasaki sized explosion), a 1 in 1,000 chance of intercepting a particle of 1 kg, a 1 in 10,000 chance of a 10 kg rock, and a 1 in 100,000 chance of a 100 kg rock (capable of unleashing the yield of a modern nuclear warhead).
However, here are two things tending to reduce intercept frequency below what is shown above: first, threatening particles will tend not to be evenly distributed along our path, but mostly concentrated in the neighborhood of the two star systems at the beginning and end of our trip. These are also the regions where we are speeding up and slowing down, so going much slower than our cruising speed of 0.1c. So, there will be much less chance of intercepting threatening particles when they are going fast enough relative to us to be a threat.
And second, with an aerodynamic design for your collision shield, you can change the angle of these collisions, which will greatly reduce the energy of each collision. These two mitigating factors combined should make the shielding issue a lot easier than what I've shown above.
It's useful to compare these risks to risks we take every day, and to risks from other factors in the course of an interstellar mission. The risk that you will die in a car accident at some point in your life due to choosing to engage in automobile transportation in the United States is around 1 in 1,000. The risk of being killed from flying on a modern space shuttle, judging both from Richard Feynman's report and on the unfortunate track record, is around 1 in 50. The risk of dying prematurely from cancer from smoking is around 1 in 5. The risk of being killed in war by enlisting in the U.S. military in the last ten years is pretty close to the same figure as for driving, around 1 in 1,000. How much risk are the first interstellar travellers going to tolerate? Hopefully much less than that of smoking, at least, but they will probably have to accept more risk than that of Americans driving on the road or serving in the military. If we ask them to confront a risk similar to that faced by the astronauts of the past 25 years, and improve on it a little by designing for at most a 1 in 100 chance of failure, and assuming the accuracy of the figures above (which we would improve on a lot in a serious study), then we need to design the spacecraft to handle at least particles of 100 grams.
Now, that doesn't mean we should stop there; if we can improve a lot on that without it being the limiting factor in feasability of performing this mission at all, then we can minimize collision risk to a negligible contribution to overall mission risk. Dealing with collisions by bigger and better shielding is likely to be more expensive and impractical the bigger the collision particle becomes, but on the other hand, ability to detect a particle ahead of time gets easier with increasing size. Ideally, we could have a complementary system where the active detecting & neutralizing technology is just sophisticated enough to handle anything too big for the passive shielding to handle, with a comfortable overlap between the two. Meanwhile, since the larger the body is, the further ahead of time we can spot it and destroy it, we can easily erase the odds of all the large impactors. The limiting factor in our technology will be the particles at the lower size limit of our detector's capability, which should then become the largest particles our shield will have to deal with.
How could we possibly detect and neutralize an oncoming particle at 0.1c though? It sounds like a daunting task with today's technology, but it's not theoretically impossible. We can separate all speculative technologies essentially into two categories:
1. technology that would only become possible by new physical theory that contradicts physics theory as understood today; 2. technology that is consistent with current, well-understood physics theory but would require engineering applications within that theory beyond current engineering sophistication.
Warp drive would fall into category 1. A system for scanning for oncoming particles at 0.1c and disintigrating them before they strike a spacecraft falls into category 2. For that matter, a propulsion system for accelerating a spacecraft to 0.1c, especially a craft large enough to support human astronauts for a round trip time of at least 90 years, also falls into category 2. The propulsion is at least as difficult as the collision neutralizer, but we accept that the propulsion is possible, and competent studies by expert engineers have shown the same thing.
The closest analogy for the scanning technology today is our current round of telescopes. Telescope systems using multiple scopes that use interferometry to make their effective diamater equal to the separation distance between the individual scopes have been in use for decades in radio wavelengths, where it's easiest, and are now being prepared in microwave and infrared. Continuing this progress to develop interferometric scopes in visible, ultraviolet, and x-rays is consistent with understood theory, and is just a matter of continuing engineering sophistication. Low infrared will be the ideal anyway for detecting potential colliders. The technology is within reach today, and making them way more enormous is just a matter of cost. Active detectors could also be based on magnetic sensors, since we have rich evidence that interstellar dust tends to be magnetized and aligned along galactic magnetic field lines. There is no reason in physics theory why a combination of freaking beefy interferometric infrared and magnetic detectors, based on sufficiently advanced engineering, would not be able to detect and characterize any threatening particle well in advance of collision. Vaporizing the particles is easier than detecting; once we know where they are, a nanosecond-long *BRAP* from an X-ray laser would be far more than enough to tear the dust particle into its constituent atoms and then some - probably, in overkill, to tear all the electrons off and cast all the particles well clear of the spacecraft's path. Based on the numbers above, this thing would have to flash once every two weeks on average to keep the spacecraft safe, and could fire more often to pick off little guys the shields would also be able to handle, just for the sake of overlap. If the factors of dust rarefecation in the cruising speed zone, and aerodynamic design, lowered the figures above another order of magnitude or two, the detector and laser would only have to work a few times a year.
The remaining issue is the critical distance of how far away they would have to detect a particle for the computer to process the information from the imaging system and issue a command to the laser. The smallest particle the detector can pick up at the critical distance would have to be able to be safely intercepted by the impact shield, with a comfortable overlap. You would also want lots of redundancy in your detectors, computers, and lasers, and have some ace engineers tending them, because there's no way to slow down for repairs if they go offline.
Incidentally, it's also possible to conceive of passive systems for vaporizing rock, to bypass entirely the need to detect them. For instance, imagine we've placed a set of electrically charged bodies way out in front of our vessel, suspended in front of our ship or flying in formation with us. Any dust approaching it would be electrically polarized by the presence of the charge, and a static shock would be delivered to it, disintigrating it. Or, since we have good evidence that interstellar dust is magnetized, we could have a magnetic shield in front of our ship that would automatically deflect the dust out of our path.
All of this doesn't mean these numbers are very accurate, or that these are the solutions that will eventually be chosen. But it is a proof of concept: there is no fundamental reason why we can't travel between the stars, the obstacles have difficult but foreseeable engineering solutions based on well-understood physics. We will journey to the stars someday, if we have the nerve.
Posts: 77 | Registered: Apr 2002
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