Honest-to-god propulsion systems at high interstellar speeds are too much of a headache. We're better off hacking away at building some kind of warp drive.
Well all it takes is the official Pinewood Derby kit and a piece stolen from the Hadron Collider.
TubularLuggage on
0
Options
KageraImitating the worst people. Since 2004Registered Userregular
Honest-to-god propulsion systems at high interstellar speeds are too much of a headache. We're better off hacking away at building some kind of warp drive.
Well all it takes is the official Pinewood Derby kit and a piece stolen from the Hadron Collider.
You don't wanna be doing that shit when Baby Farks McGeezax is around.
Honest-to-god propulsion systems at high interstellar speeds are too much of a headache. We're better off hacking away at building some kind of warp drive.
Yes, we are better off magically getting there instantly. But until we can do that, it probably does help to think of other ways.
I mean, yeah it blows chunks that it's so ridiculously far, but saying we should wait for warp is like looking at a canoe and saying we should wait for the Concord.
Edit: Or actually, like looking at a canoe and saying we should wait for a warp drive.
Actually its like looking a canoe and praying to the gods to carry us across a lake. If faster than light is possible, then its implementation is literally nothing to do with any form of current scientific understanding. The only thing which might be possible using current thinking is if we can somehow do the same thing photons and (possibly) neutrinos do (ie, get to the speed of light immediately without acceleration)
Travel in space just takes so blasted long, and each successive increase in speed is increasingly harder than the last one. Going from 10 km/s to 50 km/s, hard. Going from 50 km/s to 100 km/s far harder. Going from 100 to 150, incredibly harder. Its why an anitmatter ship only gets us to the planet 3 times faster despite being 50 times as good as a nuclear bomb powered ship.
Honest-to-god propulsion systems at high interstellar speeds are too much of a headache. We're better off hacking away at building some kind of warp drive.
Yes, we are better off magically getting there instantly. But until we can do that, it probably does help to think of other ways.
I mean, yeah it blows chunks that it's so ridiculously far, but saying we should wait for warp is like looking at a canoe and saying we should wait for the Concord.
Edit: Or actually, like looking at a canoe and saying we should wait for a warp drive.
Actually its like looking a canoe and praying to the gods to carry us across a lake. If faster than light is possible, then its implementation is literally nothing to do with any form of current scientific understanding. The only thing which might be possible using current thinking is if we can somehow do the same thing photons and (possibly) neutrinos do (ie, get to the speed of light immediately without acceleration)
Travel in space just takes so blasted long, and each successive increase in speed is increasingly harder than the last one. Going from 10 km/s to 50 km/s, hard. Going from 50 km/s to 100 km/s far harder. Going from 100 to 150, incredibly harder. Its why an anitmatter ship only gets us to the planet 3 times faster despite being 50 times as good as a nuclear bomb powered ship.
If that's true, wouldn't you start slowing down if you turned the engines off?
The rest of you, I fucking hate you for the fact that I now have a blue dot on this god awful thread.
0
Options
Gabriel_Pitt(effective against Russian warships)Registered Userregular
edited April 2009
Why?
Gabriel_Pitt on
0
Options
Gabriel_Pitt(effective against Russian warships)Registered Userregular
edited April 2009
Damn it, where's an edit button when you need one?
The rest of that post was supposed to be, 'If you turn off the engines you just coast along at the same speed until you encounter a significant gravity well.'
Yeah, you don't tend to get much in the way of friction in vacuum. Getting to a speed is hard, maintaining that speed is basically effortless. And the average super-long spaceflight would be half acceleration, half deceleration. There's no real "cruising" speed.
If that's true, wouldn't you start slowing down if you turned the engines off?
Eh?
As I understand it, no. Unless the ship had next to no mass and/or a massive surface area, collisions with tiny specs in space shouldn't alter its momentum (?) significantly unless we're talking some kind of catastrophic impact.
Forar on
First they came for the Muslims, and we said NOT TODAY, MOTHERFUCKER!
Yeah, you don't tend to get much in the way of friction in vacuum. Getting to a speed is hard, maintaining that speed is basically effortless. And the average super-long spaceflight would be half acceleration, half deceleration. There's no real "cruising" speed.
Not true actually, thats only with our incredibly slow low acceleration engines. If you had a nuclear engine, or antimatter engine then you would deploy your maximum possible acceleration and burn 50% of your fuel as fast as you possibly could. An antimatter drive ship espescially would simply blow up fuel as fast as it could radiate the heat. If your fuel use per time isn't limited you want to get to maximum speed ASAP. Maximum speed is controlled by mass/energy efficiency of the ship (ie, how much of it is directly converted to useful kinetic energy), average speed is controlled by how fast you get to that speed.
Cruising speed is the speed you get once 50% of your fuel is gone. Go any faster and you won't be able to stop.
Look at it this way, if I burn the same amount of fuel in 10 seconds at the start and end of a ten year trip, I achieve an average speed ~100% of my max speed, if I do the same total burn over 5 years acceleration and deceleration my average speed is 50% of my max.
Yeah, you don't tend to get much in the way of friction in vacuum. Getting to a speed is hard, maintaining that speed is basically effortless. And the average super-long spaceflight would be half acceleration, half deceleration. There's no real "cruising" speed.
Not true actually, thats only with our incredibly slow low acceleration engines. If you had a nuclear engine, or antimatter engine then you would deploy your maximum possible acceleration and burn 50% of your fuel as fast as you possibly could. An antimatter drive ship espescially would simply blow up fuel as fast as it could radiate the heat out the front. If your fuel use per time isn't limited you want to get to maximum speed ASAP. Maximum speed is controlled by mass/energy efficiency of the ship (ie, how much of it is directly converted to useful kinetic energy), average speed is controlled by how fast you get to that speed.
Cruising speed is the speed you get once 50% of your fuel is gone. Go any faster and you won't be able to stop.
Look at it this way, if I burn the same amount of fuel in 10 seconds at the start and end of a ten year trip, I achieve an average speed ~100% of my max speed, if I do the same total burn over 5 years acceleration and deceleration my average speed is 50% of my max.
Either way, it's not like the engine is what keeps you at that speed, it's only what gets you up to it.
Yeah, you don't tend to get much in the way of friction in vacuum. Getting to a speed is hard, maintaining that speed is basically effortless. And the average super-long spaceflight would be half acceleration, half deceleration. There's no real "cruising" speed.
Not true actually, thats only with our incredibly slow low acceleration engines. If you had a nuclear engine, or antimatter engine then you would deploy your maximum possible acceleration and burn 50% of your fuel as fast as you possibly could. An antimatter drive ship espescially would simply blow up fuel as fast as it could radiate the heat out the front. If your fuel use per time isn't limited you want to get to maximum speed ASAP. Maximum speed is controlled by mass/energy efficiency of the ship (ie, how much of it is directly converted to useful kinetic energy), average speed is controlled by how fast you get to that speed.
Cruising speed is the speed you get once 50% of your fuel is gone. Go any faster and you won't be able to stop.
Look at it this way, if I burn the same amount of fuel in 10 seconds at the start and end of a ten year trip, I achieve an average speed ~100% of my max speed, if I do the same total burn over 5 years acceleration and deceleration my average speed is 50% of my max.
Either way, it's not like the engine is what keeps you at that speed, it's only what gets you up to it.
Yes, you need a little bit of thrust due to the enormous volume swept out and the enormous momentum of the particles striking you (momentum transfer/(m^2 s) of a ship in interstellar void is about a billionth of a plane travelling at mach 1 on on earth, so its not zero for trips like this) Still, this force is tiny compared to the amount of thrust required to get you to that speed.
So I was under the impression that when you hit relativistic speeds, the effects of hitting stray dust particles were pretty damned serious. Is this the case, or not? Even in near-vacuum, wouldn't it amount to hitting thousands of massive particles at, say, 0.5c, per second?
ElJeffe on
I submitted an entry to Lego Ideas, and if 10,000 people support me, it'll be turned into an actual Lego set!If you'd like to see and support my submission, follow this link.
So I was under the impression that when you hit relativistic speeds, the effects of hitting stray dust particles were pretty damned serious. Is this the case, or not? Even in near-vacuum, wouldn't it amount to hitting thousands of massive particles at, say, 0.5c, per second?
Serious in terms of sheer impact force, but not in terms of actually slowing you down that much. Remember that the amount of energy expended to reach this speed is enormous. Fortunately most of them are effectively protons (hydrogen atoms will be ionized and stripped by the initial collision). The damage to exposed systems would be enormous, but the ship would need to be so well shielded against the radiation damage from the engines that the impacting particles would just be a question of changing design rather than new technology. IE, you'd put a cone on the front of your ship made of the same material as your pusher plate.
I mean, if you ran into 10 g dust grain or something you might get seriously screwed. Considerations for this would probably take a few % c off your max speed, since you might need to invest 10% mass in impact shielding or something. However stuff with any actual mass is so rare in interstellar space that its not a gamebreaker.
Gotcha. I was pretty sure that something like an Apollo lander traveling at 0.5c would be fucked sideways, but I'd forgotten that something the could even handle the forces required to hit that speed could be made pretty sturdy.
ElJeffe on
I submitted an entry to Lego Ideas, and if 10,000 people support me, it'll be turned into an actual Lego set!If you'd like to see and support my submission, follow this link.
Gotcha. I was pretty sure that something like an Apollo lander traveling at 0.5c would be fucked sideways, but I'd forgotten that something the could even handle the forces required to hit that speed could be made pretty sturdy.
Its effectively what places the 'minimum' size on any such ship. Your front shielding and pusher plate have to be of a size defined by your maximum speed and thrust intensity. Effectively it means that a properly fueled bigger ship will go faster, since more of it can be fuel by mass.
So I was under the impression that when you hit relativistic speeds, the effects of hitting stray dust particles were pretty damned serious. Is this the case, or not? Even in near-vacuum, wouldn't it amount to hitting thousands of massive particles at, say, 0.5c, per second?
Serious in terms of sheer impact force, but not in terms of actually slowing you down that much. Remember that the amount of energy expended to reach this speed is enormous. Fortunately most of them are effectively protons (hydrogen atoms will be ionized and stripped by the initial collision). The damage to exposed systems would be enormous, but the ship would need to be so well shielded against the radiation damage from the engines that the impacting particles would just be a question of changing design rather than new technology. IE, you'd put a cone on the front of your ship made of the same material as your pusher plate.
I mean, if you ran into 10 g dust grain or something you might get seriously screwed. Considerations for this would probably take a few % c off your max speed, since you might need to invest 10% mass in impact shielding or something. However stuff with any actual mass is so rare in interstellar space that its not a gamebreaker.
you'd also have to accelerate very slowly to avoid g forces capable of ripping your ship in half or turning everyone onboard into a pancake instantly
So I was under the impression that when you hit relativistic speeds, the effects of hitting stray dust particles were pretty damned serious. Is this the case, or not? Even in near-vacuum, wouldn't it amount to hitting thousands of massive particles at, say, 0.5c, per second?
Serious in terms of sheer impact force, but not in terms of actually slowing you down that much. Remember that the amount of energy expended to reach this speed is enormous. Fortunately most of them are effectively protons (hydrogen atoms will be ionized and stripped by the initial collision). The damage to exposed systems would be enormous, but the ship would need to be so well shielded against the radiation damage from the engines that the impacting particles would just be a question of changing design rather than new technology. IE, you'd put a cone on the front of your ship made of the same material as your pusher plate.
I mean, if you ran into 10 g dust grain or something you might get seriously screwed. Considerations for this would probably take a few % c off your max speed, since you might need to invest 10% mass in impact shielding or something. However stuff with any actual mass is so rare in interstellar space that its not a gamebreaker.
you'd also have to accelerate very slowly to avoid g forces capable of ripping your ship in half or turning everyone onboard into a pancake instantly
Not really, this is an 82 year trip. You'd accelerate for a year or two and then coast. Ignoring relativity you can get to 0.4 light speed in 0.4 years at 1 g. Acceleration here is not force limited, its limited by how much radiation the pusher plate can tolerate before it cracks.
In the sense of "having it not kill us", it wouldn't be super bad. In the sense of "where the hell are we going to go on a 78 Km deep ocean?" it would be tough. If we're lucky it turns out that it actually is tectonically active and we get a whole world of Hawaiis.
First, could everyone do me a favour and not say that mass increases as you approach the speed of light. "Relativistic mass", which is sort of a outmoded term anyway, increases, but invariant mass does not and inertia works off invariant mass. But I digress.
Second, the best engine for is something with a very high specific impulse. You want to be able to burn your engines ideally the entire way there so you are constantly accelerating. Right now, there's no good means of propulsion, but ion trusters or VASIMR engines are our best bet at the moment, but even they are less than ideal for the purpose.
Now, if we could get a Bussard ramjet going, that would be AWESOME.
How long do you want it to take? On the timescale of 10000 years or so, perfectly possible (by the standards of building an antimatter powered super ship to cross 20 light years). Bombard the planet with comets and genetically modified bacteria and fungi and watch it bloom. Move the orbit by crashing moons into it and very slow corrections using our anti-matter drive, its all not 'impossible'
With current tech I'd say that perhaps you could take a planet in the correct orbit with the right mass and no life and terraform it over a few tens of thousands of years.
The idea of making a place habitable in decades though is not possible, barring technology beyond anything we can imagine.
It depends on two things. How long are you willing for it to take and what kind of planet is it?
Terraforming Venus is definitely doable with some advances in genetic engineering and a long enough time scale. Mars is the same, but requires different advances in technology. Both suffer from the fact that they lack a magnetic field, which is a long-term problem.
As far as time scale, we're talking centuries if not millenia. It's definitely much more "cost" effective to find Earth-like planets rather than trying to make them. Or, you know, we could just adapt to living in space. Humans are great at building things to protect us from whatever obstacles the environment presents us, but we're not quite as good at changing the environment to suit us.
First, could everyone do me a favour and not say that mass increases as you approach the speed of light. "Relativistic mass", which is sort of a outmoded term anyway, increases, but invariant mass does not and inertia works off invariant mass. But I digress.
Second, the best engine for is something with a very high specific impulse. You want to be able to burn your engines ideally the entire way there so you are constantly accelerating. Right now, there's no good means of propulsion, but ion trusters or VASIMR engines are our best bet at the moment, but even they are less than ideal for the purpose.
Now, if we could get a Bussard ramjet going, that would be AWESOME.
Not true, you want to accelerate as hard as you can as fast as you can and burn your acceleration fuel quickly. You get the same amount of kinetic energy whether you burn the fuel at the start, or all the way there, its just that the fast burning ship is going at maximum speed from the start.
Bussard ramjet is also not much use for us at these speeds even if we can gather all the material we need for perfect fusion bombs from the interstellar void. Fusion only gives about a 4% energy return compared to its total mass, and thus catching those particles at speeds more than 15% c would cause energy loss (if you give our fusion bomb ship the same deltaM to KE efficiency of 25% as our antimatter ship did), not energy return. (ie KE at 15% c is greater than energy released from fusion)
Bussard ramjets are nice if we dont want to go super fast, and we want a ship to cruise along at say 0.15 c and explore the galaxy then they might be a plan. They are totally useless faster than that. Even with 100% delta M to KE efficiency their speed tops out at 0.29 c
edit - even an antimatter ship tops out at 0.6 c, thats the point where making the fuel go that fast means you get no energy back from the fuel and you may as well not have brought it. Fission bomb ship tops out at 0.07 c. This is with the entire 'ship' being made of fuel, and the pusher plate 25% efficient
So I was under the impression that when you hit relativistic speeds, the effects of hitting stray dust particles were pretty damned serious. Is this the case, or not? Even in near-vacuum, wouldn't it amount to hitting thousands of massive particles at, say, 0.5c, per second?
Serious in terms of sheer impact force, but not in terms of actually slowing you down that much. Remember that the amount of energy expended to reach this speed is enormous. Fortunately most of them are effectively protons (hydrogen atoms will be ionized and stripped by the initial collision). The damage to exposed systems would be enormous, but the ship would need to be so well shielded against the radiation damage from the engines that the impacting particles would just be a question of changing design rather than new technology. IE, you'd put a cone on the front of your ship made of the same material as your pusher plate.
I mean, if you ran into 10 g dust grain or something you might get seriously screwed. Considerations for this would probably take a few % c off your max speed, since you might need to invest 10% mass in impact shielding or something. However stuff with any actual mass is so rare in interstellar space that its not a gamebreaker.
you'd also have to accelerate very slowly to avoid g forces capable of ripping your ship in half or turning everyone onboard into a pancake instantly
First, could everyone do me a favour and not say that mass increases as you approach the speed of light. "Relativistic mass", which is sort of a outmoded term anyway, increases, but invariant mass does not and inertia works off invariant mass. But I digress.
Second, the best engine for is something with a very high specific impulse. You want to be able to burn your engines ideally the entire way there so you are constantly accelerating. Right now, there's no good means of propulsion, but ion trusters or VASIMR engines are our best bet at the moment, but even they are less than ideal for the purpose.
Now, if we could get a Bussard ramjet going, that would be AWESOME.
Not true, you want to accelerate as hard as you can as fast as you can and burn your acceleration fuel quickly. You get the same amount of kinetic energy whether you burn the fuel at the start, or all the way there, its just that the fast burning ship is going at maximum speed from the start.
Bussard ramjet is also not much use for us at these speeds even if we can gather all the material we need for perfect fusion bombs from the interstellar void. Fusion only gives about a 4% energy return compared to its total mass, and thus catching those particles at speeds more than 15% c would cause energy loss (if you give our fusion bomb ship the same deltaM to KE efficiency of 25% as our antimatter ship did), not energy return. (ie KE at 15% c is greater than energy released from fusion)
Bussard ramjets are nice if we dont want to go super fast, and we want a ship to cruise along at say 0.15 c and explore the galaxy then they might be a plan. They are totally useless faster than that. Even with 100% delta M to KE efficiency their speed tops out at 0.29 c
edit - even an antimatter ship tops out at 0.6 c, thats the point where making the fuel go that fast means you get no energy back from the fuel and you may as well not have brought it. Fission bomb ship tops out at 0.07 c. This is with the entire 'ship' being made of fuel, and the pusher plate 25% efficient
Okay, somebody is going to have to explain this to me again. If you eventually plateau in speed when projecting a fixed amount of force, why don't you slow down from that speed when you eliminate said force?
Okay, somebody is going to have to explain this to me again. If you eventually plateau in speed when projecting a fixed amount of force, why don't you slow down from that speed when you eliminate said force?
That's only true if there's friction. There isn't in space, where a fixed amount of force will cause you to accelerate forever.
First, could everyone do me a favour and not say that mass increases as you approach the speed of light. "Relativistic mass", which is sort of a outmoded term anyway, increases, but invariant mass does not and inertia works off invariant mass. But I digress.
Second, the best engine for is something with a very high specific impulse. You want to be able to burn your engines ideally the entire way there so you are constantly accelerating. Right now, there's no good means of propulsion, but ion trusters or VASIMR engines are our best bet at the moment, but even they are less than ideal for the purpose.
Now, if we could get a Bussard ramjet going, that would be AWESOME.
First, "relativistic mass" is the relevant mass here, because the effective inertia of a body (relative to some "stationary" observer, say, on Earth) depends on it and not on rest mass. Also, "invariant mass" does increase with velocity within a given system (which should include the reaction mass). It is a function of rest mass and particle energy, relative to the center of momentum of the system.
Second, specific impulse doesn't mean what you think it means. There's no particular reason you want to keep your engines operating the whole time; in fact that is undesirable as tbloxham points out. The only reason high specific impulse is associated with low thrust in reality is that we don't have any high specific impulse engines that are also high thrust. The way in which you increase specific impulse is to increase the exit velocity of your reaction mass, which has so far meant either using a fuel with higher enthalpy or dumping energy from some other source into the fuel (at which point fuel flow rate, and hence thrust, is limited by the available power). It isn't inherently useful to keep your engine on the whole time; we just can't supply enough power to use up all the propellant in a brief period of time at this point.
edit - even an antimatter ship tops out at 0.6 c, thats the point where making the fuel go that fast means you get no energy back from the fuel and you may as well not have brought it.
What?
CycloneRanger on
0
Options
HonkHonk is this poster.Registered User, __BANNED USERSregular
Okay, somebody is going to have to explain this to me again. If you eventually plateau in speed when projecting a fixed amount of force, why don't you slow down from that speed when you eliminate said force?
That's only true if there's friction. There isn't in space, where a fixed amount of force will cause you to accelerate forever.
There's some confusion here because on Earth - say, in a car - your top speed is drag-limited. Your car can put out a certain maximum force, and when that force equals the force of the air pushing back on you, you stop accelerating. Meanwhile, the weight of the fuel is so low compared to the weight of the car, you can pretty much ignore it.
In space, your top speed isn't drag-limited, but that doesn't mean there's no top speed. To burn your engine, you need fuel. To burn your engine a long time (or very hard for a short time), you need a whole fuckton of fuel. The problem is that the more fuel you carry, the slower you accelerate. So you get diminishing returns, depending on how fast you can shoot that crap out the back of your ship.
ElJeffe on
I submitted an entry to Lego Ideas, and if 10,000 people support me, it'll be turned into an actual Lego set!If you'd like to see and support my submission, follow this link.
edit - even an antimatter ship tops out at 0.6 c, thats the point where making the fuel go that fast means you get no energy back from the fuel and you may as well not have brought it.
What?
By 'anti-matter ship' I mean a ship fueled by antimatter. If you bring along a kilogram of antimatter and a kilogram of matter with you, and your ship is 25% efficient at turning reaction energy into kinetic energy by the time you get to 0.6 c you have spent more energy speeding up that antimatter than you are going to get back by blowing it up. Effectively you'd have gone faster without it.
Okay, somebody is going to have to explain this to me again. If you eventually plateau in speed when projecting a fixed amount of force, why don't you slow down from that speed when you eliminate said force?
That's only true if there's friction. There isn't in space, where a fixed amount of force will cause you to accelerate forever.
There's some confusion here because on Earth - say, in a car - your top speed is drag-limited. Your car can put out a certain maximum force, and when that force equals the force of the air pushing back on you, you stop accelerating. Meanwhile, the weight of the fuel is so low compared to the weight of the car, you can pretty much ignore it.
In space, your top speed isn't drag-limited, but that doesn't mean there's no top speed. To burn your engine, you need fuel. To burn your engine a long time (or very hard for a short time), you need a whole fuckton of fuel. The problem is that the more fuel you carry, the slower you accelerate. So you get diminishing returns, depending on how fast you can shoot that crap out the back of your ship.
Yup, and depending on how energy dense your fuel is if we assume we're going to be using things travelling at near light speed (gamma rays) to accelerate our ship.
edit - An interesting (but depressing fact) is that to deliver a 20 tonne ship to Gliese in around 45 years (I increased the acceleration levels), even using a technique which could produce antimatter from energy with 100% efficiency would require more energy for that single project than has been used by all human activities which have ever happened in history. IE, sending the ship costs more energy than all of humanity has ever used before.
Great so...how long would it take to get there at our highest attainable speeds right now?
A Valkyrie could at truly astronomical expense reach there in a little over 21 years. But even fueling such a probe would most likely be a 22nd century project. Just building the factorys to make the fuel would take decades and trillions with our current technology. Any larger manned craft would most like take 40 to 200 years to get there
Great so...how long would it take to get there at our highest attainable speeds right now?
A Valkyrie could at truly astronomical expense reach there in a little over 21 years. But even fueling such a probe would most likely be a 22nd century project. Just building the factorys to make the fuel would take decades and trillions with our current technology. Any larger manned craft would most like take 40 to 200 years to get there
Is a valkyrie something really tiny which isn't intended to stop and is powered by some kind of external giant laser array? No fueled vehicle can go faster than 0.8 c, and nothing using a realistic efficiency for energy conversion and required to stop can beat 0.44 c.
Yeah, I just read the article about Valkyrie ships on the bbc. Its wrong. They've forgotten that their fuel has mass and that even antimatter just stops being useful at certain speeds. Just look up the kinetic energy at relativistic speeds article on wikipedia. Once you get to 0.8 c or so even a perfect ship (all fuel, 100% efficient) has expended as much energy accelerating the fuel as it will get back from it. A ship powered by some kind of external laser can beat this speed, but if you want it to stop as well the amount of energy needed becomes insane.
Yup, and depending on how energy dense your fuel is if we assume we're going to be using things travelling at near light speed (gamma rays) to accelerate our ship.
edit - An interesting (but depressing fact) is that to deliver a 20 tonne ship to Gliese in around 45 years (I increased the acceleration levels), even using a technique which could produce antimatter from energy with 100% efficiency would require more energy for that single project than has been used by all human activities which have ever happened in history. IE, sending the ship costs more energy than all of humanity has ever used before.
That just makes actually doing it so badass. Spaceship captains all "Want to use the entire energy output of humanity from birth to around the 22nd century to get a space-burrito?"
Generation ships are a bad idea. It is all but certain that we'll develop the technology necessary to put humans into suspended animation before we have the combination of industrial capacity and political will necessary to build a generation ship. Hell, we'll probably have defeated aging in general before we have generation ships.
There are two real ways to explore the wider galaxy—find some way to cheat, through whatever contrivance of engineering, and get there faster than would seem possible now, or live for a really, really long time.
Still requires you to get to around 99.99% of the speed of light before it's usable, which is beyond the capabilities of any known or projected propulsion system. I guess maybe a really insane battery of lasers near Sol pushing on a solar sail might work, but that'd take an engineering program of a truly enormous scale. It's also technically possible that you could achieve this with antimatter, I guess, but I wouldn't bet on it.
Not really. Maybe I did the math wrong, but in the example of 82 years going more or less 66% of c (unless I misunderstood tbloxham's post) it should shave it down to only 60 something years for the people on the ship. Which is still a long time, but 20 years is nothing to sneeze at.
Its not 66% of c unfortunately, its about 40% of c at maximum speed, where you will spend 33% of your time. The ship I described is also unfortunately not practical, it requires the mass production and safe storage of antimatter in ludicrous quantities. To get 100 kg of ship to this planet in 82 years would require 450 kg of anti matter, which even if we can do matter to energy conversion requires 4e19 joules of energy. This is the total energy produced by all earth sources (solar, tidal and geothermal) for 4 minutes. Which is quite a lot.
The problem is that although your true 'maximum' speed is C, you need to carry fuel to speed up, and by the standards of going really really fast even antimatter is pretty low energy density. Even without relativity think about it like this, each extra joule of energy you add speeds you up less than the one before did. To get close to C you need to not have to carry your fuel with you. Now, extrapolating from current tech we could perhaps build a giant space laser and use it to impel the ship remotely, but it would still need to be carrying 50% of the required antimatter to stop quickly.
(this is all aproximate, because mass of the ship changes continually as fuel is used, and that makes the equations hard to solve)
A possible ship design is an orion drive system which would be a TITANIC construction weighing millions of tonnes and carrying thousands upon thousands of nuclear bombs. It might be able to top out its speed at 0.1 c, since nuclear bombs are about 8% as good as antimatter explosions. So it would likely take more than 250 years or so to get there.
So? What is it is more power than our world uses now?
Build giant solar panels near mercury have them power antimatter factories. Big enough soler arrays and a large number of factories can give you a very large amount of anti matter.
Generation ships are a bad idea. It is all but certain that we'll develop the technology necessary to put humans into suspended animation before we have the combination of industrial capacity and political will necessary to build a generation ship. Hell, we'll probably have defeated aging in general before we have generation ships.
You know, if there was ever a country that might try such a thing, it's China. They've got it all:
Really powerful government that doesn't care much about human rights
A lot of people for said government to send away
Large and quickly growing industrial capacity
Growing space program
Likes to do big, grand gestures
Posts
Well all it takes is the official Pinewood Derby kit and a piece stolen from the Hadron Collider.
You don't wanna be doing that shit when Baby Farks McGeezax is around.
Actually its like looking a canoe and praying to the gods to carry us across a lake. If faster than light is possible, then its implementation is literally nothing to do with any form of current scientific understanding. The only thing which might be possible using current thinking is if we can somehow do the same thing photons and (possibly) neutrinos do (ie, get to the speed of light immediately without acceleration)
Travel in space just takes so blasted long, and each successive increase in speed is increasingly harder than the last one. Going from 10 km/s to 50 km/s, hard. Going from 50 km/s to 100 km/s far harder. Going from 100 to 150, incredibly harder. Its why an anitmatter ship only gets us to the planet 3 times faster despite being 50 times as good as a nuclear bomb powered ship.
We are not scavenging entire planets for materials. No Harrier, that's a bad Harrier!
If that's true, wouldn't you start slowing down if you turned the engines off?
The rest of that post was supposed to be, 'If you turn off the engines you just coast along at the same speed until you encounter a significant gravity well.'
Eh?
As I understand it, no. Unless the ship had next to no mass and/or a massive surface area, collisions with tiny specs in space shouldn't alter its momentum (?) significantly unless we're talking some kind of catastrophic impact.
Not true actually, thats only with our incredibly slow low acceleration engines. If you had a nuclear engine, or antimatter engine then you would deploy your maximum possible acceleration and burn 50% of your fuel as fast as you possibly could. An antimatter drive ship espescially would simply blow up fuel as fast as it could radiate the heat. If your fuel use per time isn't limited you want to get to maximum speed ASAP. Maximum speed is controlled by mass/energy efficiency of the ship (ie, how much of it is directly converted to useful kinetic energy), average speed is controlled by how fast you get to that speed.
Cruising speed is the speed you get once 50% of your fuel is gone. Go any faster and you won't be able to stop.
Look at it this way, if I burn the same amount of fuel in 10 seconds at the start and end of a ten year trip, I achieve an average speed ~100% of my max speed, if I do the same total burn over 5 years acceleration and deceleration my average speed is 50% of my max.
Either way, it's not like the engine is what keeps you at that speed, it's only what gets you up to it.
Yes, you need a little bit of thrust due to the enormous volume swept out and the enormous momentum of the particles striking you (momentum transfer/(m^2 s) of a ship in interstellar void is about a billionth of a plane travelling at mach 1 on on earth, so its not zero for trips like this) Still, this force is tiny compared to the amount of thrust required to get you to that speed.
Which must, of course, be designed in such a way that they can be Macgyvered into just about anything the crew will need.
Serious in terms of sheer impact force, but not in terms of actually slowing you down that much. Remember that the amount of energy expended to reach this speed is enormous. Fortunately most of them are effectively protons (hydrogen atoms will be ionized and stripped by the initial collision). The damage to exposed systems would be enormous, but the ship would need to be so well shielded against the radiation damage from the engines that the impacting particles would just be a question of changing design rather than new technology. IE, you'd put a cone on the front of your ship made of the same material as your pusher plate.
I mean, if you ran into 10 g dust grain or something you might get seriously screwed. Considerations for this would probably take a few % c off your max speed, since you might need to invest 10% mass in impact shielding or something. However stuff with any actual mass is so rare in interstellar space that its not a gamebreaker.
Its effectively what places the 'minimum' size on any such ship. Your front shielding and pusher plate have to be of a size defined by your maximum speed and thrust intensity. Effectively it means that a properly fueled bigger ship will go faster, since more of it can be fuel by mass.
EDIT:
That is, seeing it from Earth, not taking off from Earth :P.
you'd also have to accelerate very slowly to avoid g forces capable of ripping your ship in half or turning everyone onboard into a pancake instantly
How realistic is the concept of terraforming?
Not really, this is an 82 year trip. You'd accelerate for a year or two and then coast. Ignoring relativity you can get to 0.4 light speed in 0.4 years at 1 g. Acceleration here is not force limited, its limited by how much radiation the pusher plate can tolerate before it cracks.
Second, the best engine for is something with a very high specific impulse. You want to be able to burn your engines ideally the entire way there so you are constantly accelerating. Right now, there's no good means of propulsion, but ion trusters or VASIMR engines are our best bet at the moment, but even they are less than ideal for the purpose.
Now, if we could get a Bussard ramjet going, that would be AWESOME.
How long do you want it to take? On the timescale of 10000 years or so, perfectly possible (by the standards of building an antimatter powered super ship to cross 20 light years). Bombard the planet with comets and genetically modified bacteria and fungi and watch it bloom. Move the orbit by crashing moons into it and very slow corrections using our anti-matter drive, its all not 'impossible'
With current tech I'd say that perhaps you could take a planet in the correct orbit with the right mass and no life and terraform it over a few tens of thousands of years.
The idea of making a place habitable in decades though is not possible, barring technology beyond anything we can imagine.
It depends on two things. How long are you willing for it to take and what kind of planet is it?
Terraforming Venus is definitely doable with some advances in genetic engineering and a long enough time scale. Mars is the same, but requires different advances in technology. Both suffer from the fact that they lack a magnetic field, which is a long-term problem.
As far as time scale, we're talking centuries if not millenia. It's definitely much more "cost" effective to find Earth-like planets rather than trying to make them. Or, you know, we could just adapt to living in space. Humans are great at building things to protect us from whatever obstacles the environment presents us, but we're not quite as good at changing the environment to suit us.
Not true, you want to accelerate as hard as you can as fast as you can and burn your acceleration fuel quickly. You get the same amount of kinetic energy whether you burn the fuel at the start, or all the way there, its just that the fast burning ship is going at maximum speed from the start.
Bussard ramjet is also not much use for us at these speeds even if we can gather all the material we need for perfect fusion bombs from the interstellar void. Fusion only gives about a 4% energy return compared to its total mass, and thus catching those particles at speeds more than 15% c would cause energy loss (if you give our fusion bomb ship the same deltaM to KE efficiency of 25% as our antimatter ship did), not energy return. (ie KE at 15% c is greater than energy released from fusion)
Bussard ramjets are nice if we dont want to go super fast, and we want a ship to cruise along at say 0.15 c and explore the galaxy then they might be a plan. They are totally useless faster than that. Even with 100% delta M to KE efficiency their speed tops out at 0.29 c
edit - even an antimatter ship tops out at 0.6 c, thats the point where making the fuel go that fast means you get no energy back from the fuel and you may as well not have brought it. Fission bomb ship tops out at 0.07 c. This is with the entire 'ship' being made of fuel, and the pusher plate 25% efficient
Okay, somebody is going to have to explain this to me again. If you eventually plateau in speed when projecting a fixed amount of force, why don't you slow down from that speed when you eliminate said force?
That's only true if there's friction. There isn't in space, where a fixed amount of force will cause you to accelerate forever.
Second, specific impulse doesn't mean what you think it means. There's no particular reason you want to keep your engines operating the whole time; in fact that is undesirable as tbloxham points out. The only reason high specific impulse is associated with low thrust in reality is that we don't have any high specific impulse engines that are also high thrust. The way in which you increase specific impulse is to increase the exit velocity of your reaction mass, which has so far meant either using a fuel with higher enthalpy or dumping energy from some other source into the fuel (at which point fuel flow rate, and hence thrust, is limited by the available power). It isn't inherently useful to keep your engine on the whole time; we just can't supply enough power to use up all the propellant in a brief period of time at this point.
What?
There's some confusion here because on Earth - say, in a car - your top speed is drag-limited. Your car can put out a certain maximum force, and when that force equals the force of the air pushing back on you, you stop accelerating. Meanwhile, the weight of the fuel is so low compared to the weight of the car, you can pretty much ignore it.
In space, your top speed isn't drag-limited, but that doesn't mean there's no top speed. To burn your engine, you need fuel. To burn your engine a long time (or very hard for a short time), you need a whole fuckton of fuel. The problem is that the more fuel you carry, the slower you accelerate. So you get diminishing returns, depending on how fast you can shoot that crap out the back of your ship.
By 'anti-matter ship' I mean a ship fueled by antimatter. If you bring along a kilogram of antimatter and a kilogram of matter with you, and your ship is 25% efficient at turning reaction energy into kinetic energy by the time you get to 0.6 c you have spent more energy speeding up that antimatter than you are going to get back by blowing it up. Effectively you'd have gone faster without it.
Yup, and depending on how energy dense your fuel is if we assume we're going to be using things travelling at near light speed (gamma rays) to accelerate our ship.
edit - An interesting (but depressing fact) is that to deliver a 20 tonne ship to Gliese in around 45 years (I increased the acceleration levels), even using a technique which could produce antimatter from energy with 100% efficiency would require more energy for that single project than has been used by all human activities which have ever happened in history. IE, sending the ship costs more energy than all of humanity has ever used before.
A Valkyrie could at truly astronomical expense reach there in a little over 21 years. But even fueling such a probe would most likely be a 22nd century project. Just building the factorys to make the fuel would take decades and trillions with our current technology. Any larger manned craft would most like take 40 to 200 years to get there
Is a valkyrie something really tiny which isn't intended to stop and is powered by some kind of external giant laser array? No fueled vehicle can go faster than 0.8 c, and nothing using a realistic efficiency for energy conversion and required to stop can beat 0.44 c.
Yeah, I just read the article about Valkyrie ships on the bbc. Its wrong. They've forgotten that their fuel has mass and that even antimatter just stops being useful at certain speeds. Just look up the kinetic energy at relativistic speeds article on wikipedia. Once you get to 0.8 c or so even a perfect ship (all fuel, 100% efficient) has expended as much energy accelerating the fuel as it will get back from it. A ship powered by some kind of external laser can beat this speed, but if you want it to stop as well the amount of energy needed becomes insane.
Or travel so fast that time slows to crawl
Build giant solar panels near mercury have them power antimatter factories. Big enough soler arrays and a large number of factories can give you a very large amount of anti matter.
You know, if there was ever a country that might try such a thing, it's China. They've got it all:
Really powerful government that doesn't care much about human rights
A lot of people for said government to send away
Large and quickly growing industrial capacity
Growing space program
Likes to do big, grand gestures