Science Rapid Interstellar spaceflight, exploration and,colonization thread
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Trust me, it will when you have a whole ship meshed out and you find out it's all wrong. :dry:
Actually when you get up to the maximum exhaust velocity you can get out of a fusion reaction, you'll pretty much be using the fusion fuel as propellant (as I understand it). Atomic Rockets has an interesting table detailing the exhaust velocities possible with several different fusion reactions.
Proton-Proton fusion has the highest exhaust velocity of the lot- 11.7% of c, but fusing four protons together is nigh impossible. He3-D is a good option, but there will still be neutron-emitting side reactions. He3-He3 is entirely aneutronic (though I think I might have heard that it spits out a gamma ray once in a while), but requires more He3 and is harder to achieve than He3-D fusion (at least, it's harder to do than He3-D fusion, I don't know if it approaches p-B11 fusion in difficulty).
The kind of fusion drives I've desperately been trying to understand over the last few months are ones that inject hydrogen propellant into the plasma resulting from fusion or somehow otherwise use a fusion reaction to heat propellant. This increases thrust at the expense of exhaust velocity, and decreases efficiency, but also (unless I'm horribly, horribly incorrect here) decreases the amount of expensive fusion fuel needed.
Here you will need to use fusion fuel as propellant- you will need thousands of tons of fusion fuel. But interstellar spaceflight is not cheap. At least this fusion propellant is cheaper than antimatter.
In addition, since we want high thrust (the higher the thrust, the shorter the transit time), we're probably gonna have to go with something like Daedalus; inertial confinement fusion (my limited understanding tells me that ICF gets a higher thrust/mass due to not requiring the heavy magnets of a tokamak, or something like that).
Daedalus is the only concept that comes anywhere close to having a high thrust/mass ratio. This article describes some of the aspects of the Daedalus propulsion system.
This page also contains some interesting information pertaining to fusion propulsion. Just to highlight the power/mass and thrust/mass problems; with a spheromak with a specific power of 10.5 kW/kg, you would still need an engine massing 3800 tons for only a 40 gigawatt engine; clearly impractical.
I've even read that it might even be possible- using extremely powerful capacitors to initiate fusion- to build an IC drive with a T/W of over 1. But ICF propulsion still has problems; for example, pellet design, pellet storage, pellet transport to the engines, laser/particle beam emitter design, throttling, pulse rate, and dealing with the effects of vibration on the vehicle and its occupants.
But that fusion fuel will likely still need to be kept at cryogenic temperatures.
If you're using an antimatter beam-core drive, your matter fuel will likely be in the form of LH2. The antimatter, however, is an entirely different story. And if you're using something like Orion, your pulse units will not be stored in tanks at all, but rather in gigantic propellant magazines, feeding pulse units to the detonation point in a manner at least vaguely similar to a rifle feeding rounds into the chamber for firing.
Of course, the optimal drive here would be something that gets 0.25 c, 0.3 c exhaust velocity, is capable of high acceleration, requires minimal fuel, and does not require large amounts of antimatter. I don't know what that would be. Even a proton-proton drive, with a mass ratio of 20, could only get up to 35% of c (not counting relativistic effects), enough to get to Alpha Centauri in roughly 12 years, only enough to get to Gliese 581 in roughly 50 years ship-time.
Handwavion-catalyzed fusion, maybe? :facepalm:
Actually when you get up to the maximum exhaust velocity you can get out of a fusion reaction, you'll pretty much be using the fusion fuel as propellant (as I understand it). Atomic Rockets has an interesting table detailing the exhaust velocities possible with several different fusion reactions.
Proton-Proton fusion has the highest exhaust velocity of the lot- 11.7% of c, but fusing four protons together is nigh impossible. He3-D is a good option, but there will still be neutron-emitting side reactions. He3-He3 is entirely aneutronic (though I think I might have heard that it spits out a gamma ray once in a while), but requires more He3 and is harder to achieve than He3-D fusion (at least, it's harder to do than He3-D fusion, I don't know if it approaches p-B11 fusion in difficulty).
The kind of fusion drives I've desperately been trying to understand over the last few months are ones that inject hydrogen propellant into the plasma resulting from fusion or somehow otherwise use a fusion reaction to heat propellant. This increases thrust at the expense of exhaust velocity, and decreases efficiency, but also (unless I'm horribly, horribly incorrect here) decreases the amount of expensive fusion fuel needed.
Here you will need to use fusion fuel as propellant- you will need thousands of tons of fusion fuel. But interstellar spaceflight is not cheap. At least this fusion propellant is cheaper than antimatter.
In addition, since we want high thrust (the higher the thrust, the shorter the transit time), we're probably gonna have to go with something like Daedalus; inertial confinement fusion (my limited understanding tells me that ICF gets a higher thrust/mass due to not requiring the heavy magnets of a tokamak, or something like that).
Daedalus is the only concept that comes anywhere close to having a high thrust/mass ratio. This article describes some of the aspects of the Daedalus propulsion system.
This page also contains some interesting information pertaining to fusion propulsion. Just to highlight the power/mass and thrust/mass problems; with a spheromak with a specific power of 10.5 kW/kg, you would still need an engine massing 3800 tons for only a 40 gigawatt engine; clearly impractical.
I've even read that it might even be possible- using extremely powerful capacitors to initiate fusion- to build an IC drive with a T/W of over 1. But ICF propulsion still has problems; for example, pellet design, pellet storage, pellet transport to the engines, laser/particle beam emitter design, throttling, pulse rate, and dealing with the effects of vibration on the vehicle and its occupants.
But that fusion fuel will likely still need to be kept at cryogenic temperatures.
If you're using an antimatter beam-core drive, your matter fuel will likely be in the form of LH2. The antimatter, however, is an entirely different story. And if you're using something like Orion, your pulse units will not be stored in tanks at all, but rather in gigantic propellant magazines, feeding pulse units to the detonation point in a manner at least vaguely similar to a rifle feeding rounds into the chamber for firing.
Of course, the optimal drive here would be something that gets 0.25 c, 0.3 c exhaust velocity, is capable of high acceleration, requires minimal fuel, and does not require large amounts of antimatter. I don't know what that would be. Even a proton-proton drive, with a mass ratio of 20, could only get up to 35% of c (not counting relativistic effects), enough to get to Alpha Centauri in roughly 12 years, only enough to get to Gliese 581 in roughly 50 years ship-time.
Handwavion-catalyzed fusion, maybe? :facepalm:
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Eagle1Division
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What if you used stages? The Saturn V would've never worked as an SSTO, but it achieved a Delta-Vee many, many, many times greater than it's mass ratio by staging. (3 times for the booster, again for the command module, again for the LM, and again for the LM ascent stage. You could count it as 6 stages, in a way...)
Neat part about a space-only vehicle is you can just stage the fuel tanks, without throwing away expensive engines or other systems.
Neat part about a space-only vehicle is you can just stage the fuel tanks, without throwing away expensive engines or other systems.
Well, the Saturn V staged a lot of its parts simply because it didn't need to take them further (The S-IVB didn't need to be inserted into lunar orbit, the ascent stage didn't need to be brought along for TEI, etc).
The parallel between this and interstellar spaceflight is that if you have an acceleration and deceleration stage, dump the acceleration stage before you decelerate, because you don't need the deceleration stage (unless... I dunno... maybe you want to use it for raw materials at the destination, put then the decision of jettison or not jettison, depends on how valuable the stage would be at the destination). One might also consider a self-destruct mechanism on the stage, to prevent it from turning into an inadvertant RKKV.
Of course, the problem of jettisoning propellant tanks only arises when you have a huge mass ratio. Then you'll most likely start out with a big engine, and throughout acceleration you'll need to throttle that big engine down and down and down to keep acceleration steady. Eventually you'll exhaust so much propellant that the engine will be totally overkill, and a whole lot of parasitic mass. At that point, it makes sense to jettison the big, heavy, expensive engine, and use another, smaller, big, heavy, expensive engine...
The parallel between this and interstellar spaceflight is that if you have an acceleration and deceleration stage, dump the acceleration stage before you decelerate, because you don't need the deceleration stage (unless... I dunno... maybe you want to use it for raw materials at the destination, put then the decision of jettison or not jettison, depends on how valuable the stage would be at the destination). One might also consider a self-destruct mechanism on the stage, to prevent it from turning into an inadvertant RKKV.
Of course, the problem of jettisoning propellant tanks only arises when you have a huge mass ratio. Then you'll most likely start out with a big engine, and throughout acceleration you'll need to throttle that big engine down and down and down to keep acceleration steady. Eventually you'll exhaust so much propellant that the engine will be totally overkill, and a whole lot of parasitic mass. At that point, it makes sense to jettison the big, heavy, expensive engine, and use another, smaller, big, heavy, expensive engine...
Eagle1Division
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RKKV: ? Kinetic Kill Vehicle?
Just blowing it up wouldn't do much good, it'd just become a widely-dispersed (and thus much harder to miss) cloud of debris waiting to impact the ship. A better idea would be to use some small solid motors on a side to give it just a few mm/s of lateral velocity (depending on how long you want to wait before igniting the second stage engine), so it's not in the trajectory of the decceleration phase of the flight. Once you pass it, it's gone forever, more or less. (it'll just swing by your destination and make it's way towards the stars...)
Makes enough sense about the engine, though. Unless you do want to decelerate very quickly. As you said, more acceleration means less transit time. And not staging means more acceleration, in this case. (or, rather, a longer time spent accelerating because deceleration is much quicker. Overall still a much shorter flight time.)
Just blowing it up wouldn't do much good, it'd just become a widely-dispersed (and thus much harder to miss) cloud of debris waiting to impact the ship. A better idea would be to use some small solid motors on a side to give it just a few mm/s of lateral velocity (depending on how long you want to wait before igniting the second stage engine), so it's not in the trajectory of the decceleration phase of the flight. Once you pass it, it's gone forever, more or less. (it'll just swing by your destination and make it's way towards the stars...)
Makes enough sense about the engine, though. Unless you do want to decelerate very quickly. As you said, more acceleration means less transit time. And not staging means more acceleration, in this case. (or, rather, a longer time spent accelerating because deceleration is much quicker. Overall still a much shorter flight time.)
Avoiding the jettisoned stage should be easy enough; the problem is sending that high velocity object at full speed to fly through another star system. There could be stuff in that system that you don't want to damage. Stuff that can't avoid relativistic rocket stages. It might even be a matter of political courtesy; I certainly wouldn't like to see relativistic objects travelling through my system, even if they were AUs away from me.
Dispersing the object is good because it spreads the kinetic energy over a wider area, and thus it would reduce its potential to do damage. A spacecraft- especially a light propellant tank- could be disrupted over a wide area by such a "range safety" charge. Over light years, the fragments could disperse by quite a great distance.
Of course, breaking the object up into smaller pieces also increases the probability that they would impact with something, even though the results of that impact would be less severe.
The ideal "range safety system" in this case might be a low yield nuclear device, designed to vaporise the object to the greatest extent possible. This would likely pose the lowest threat, though of course there are several issues with having nuclear devices aboard spacecraft...
But planetary systems contain far more empty space than they do interesting/important stuff. It'd probably be more of a nice gesture than anything else.
Dispersing the object is good because it spreads the kinetic energy over a wider area, and thus it would reduce its potential to do damage. A spacecraft- especially a light propellant tank- could be disrupted over a wide area by such a "range safety" charge. Over light years, the fragments could disperse by quite a great distance.
Of course, breaking the object up into smaller pieces also increases the probability that they would impact with something, even though the results of that impact would be less severe.
The ideal "range safety system" in this case might be a low yield nuclear device, designed to vaporise the object to the greatest extent possible. This would likely pose the lowest threat, though of course there are several issues with having nuclear devices aboard spacecraft...
But planetary systems contain far more empty space than they do interesting/important stuff. It'd probably be more of a nice gesture than anything else.
Eagle1Division
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Ok, I thought you meant for the second stage to avoid hitting the first stage. I was also envisioning a pioneering spacecraft to colonize a new star system. And I don't think that the first stage would have a course anywhere near a nearby different solar system, given that entire solar systems are just specks separated by vast distances. It's not a matter of AU's, it's a matter of LY's away.
Fsci123, you're going to need to find more information on that on your own. We can't design an entire propulsion system right here right now because someone asked... :blink:
Read Atomic Rocket/Project Rho. It will solve all of those problems...
Specifically the Engine Table will serve you greatly.
It's also a good idea to be educated in basic, advanced and realistic designs.
Fsci123, you're going to need to find more information on that on your own. We can't design an entire propulsion system right here right now because someone asked... :blink:
Read Atomic Rocket/Project Rho. It will solve all of those problems...
Specifically the Engine Table will serve you greatly.
It's also a good idea to be educated in basic, advanced and realistic designs.
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fsci123
Future Dubstar and Rocketkid
Well I never ask for anybody to design an entire spacecraft... I am a relatively busy kid... And my 13 year old mind can't fit realistic rocket design into my average schedule because it is taken up by money/women with a mix of hip-hop...
jedidia
shoemaker without legs
13? Well, that explains a lot... in your favour. At that age you don't know too much advanced chemistry yet, let alone the math involved in the problems posed here.
You'll be better off in the future by asking for more detailed explanations under the assumption that you don't know yet how things work. It's no shame at that age, you know (hell, at that age I still tried to get my head around why a binomial works the way it works...) You're at a prime age for learning, if you use it right you will be able to profit a lot from it :thumbup:
Maybe we should introduce age tags, so the older board members can go a bit easier on the younger ones than we sometimes do. Apologies for some of my behaviour earlier on, I would have put a lot of things differently if I'd known your age!
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Y'know, that shouldn't really be an issue. Nobody ever bothered to teach me any of this stuff; I have to learn it myself (which is partially the reason for the dubious accuracy of anything I say).
Being young isn't a disadvantage to attaining knowledge, it's a boon; as jedidia said, you're at a prime age for learning. Take advantage of that.
Too much of your schedule is dedicated to "money and women"? Really?
There is no such thing as "dedicating too much time" to learning. Stupidity is not lack of knowledge; stupidity is refusal to learn. And I'm sure that nobody truely wishes to be stupid. :thumbup:
Atomic Rockets is a very good starting point.
Being young isn't a disadvantage to attaining knowledge, it's a boon; as jedidia said, you're at a prime age for learning. Take advantage of that.
Too much of your schedule is dedicated to "money and women"? Really?
There is no such thing as "dedicating too much time" to learning. Stupidity is not lack of knowledge; stupidity is refusal to learn. And I'm sure that nobody truely wishes to be stupid. :thumbup:
Atomic Rockets is a very good starting point.
Eagle1Division
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:lol:
I'm not laughing at you, it's just that's so true for me, and for most people on forums in general.
Being young isn't a disadvantage to attaining knowledge, it's a boon; as jedidia said, you're at a prime age for learning. Take advantage of that.
Too much of your schedule is dedicated to "money and women"? Really?
There is no such thing as "dedicating too much time" to learning. Stupidity is not lack of knowledge; stupidity is refusal to learn. And I'm sure that nobody truely wishes to be stupid. :thumbup:
Atomic Rockets is a very good starting point.
Aye, that's a philosophy I've come to adopt independently. I think the difference in-between someone smart and someone dumb, is the smart person doesn't bother with things that don't matter and thinks about things that do. And spends time learning rather than entertaining, which eventually becomes quiet entertaining.
I'm 17 as of May 5th, and I think society's got things pretty mixed up. There's nothing wrong with being 13, I know the feeling of fighting for respect (which is why so far I haven't given my age), but don't be afraid to be 13, you don't have to rush into women, money, and hip-hop to be a man and earn respect. I've seen so many kids talking about things, saying things that nobody their age should be talking about and saying, and they do it to be "cool", and they just come off as perverted jerks. Don't get drawn into all that, I've seen what could've been good kids act like jerks because they're trying to be "cool".
I'm not saying that's you, or anything about you: just don't get drawn into all that; someone that's themselves is way more awesome than someone who does whatever they think is "cool", instead of what's right. There's a great power in standing out for what's right that doesn't come any other way.
---------- Post added at 09:20 PM ---------- Previous post was at 09:00 PM ----------
Unless there's anything really important to say... Let's not get the thread derailed too much, I still think more could come of it yet.
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fsci123
Future Dubstar and Rocketkid
Attention all my fans...
After days of calculation I have concluded that the laser sail design is the most logical interstellar spacecraft design achievable within 200 years... I will unveil the near complete models for the laser sail in a few days... I will form a group or webpage dedicated to the completion and publication of such design... I will be looking for people who can code vessels and animations...
After days of calculation I have concluded that the laser sail design is the most logical interstellar spacecraft design achievable within 200 years... I will unveil the near complete models for the laser sail in a few days... I will form a group or webpage dedicated to the completion and publication of such design... I will be looking for people who can code vessels and animations...
fsci123
Future Dubstar and Rocketkid
Number one: stop with the pessimism...
Number two: I came up with a slightly modified design...
Number three: you need a fuel tank 75 meters in radius filled with superfluid helium 3 inorder to reach a delta-v of 0.5c...
There is a big difference between pessimism and physics and engineering reality.
How did you bypass the physical constraints of such a system?
Superfluid? Why superfluid?
Why 75 meters in radius? For how massive a spacecraft? What is the mass ratio?
The Daedalus first stage had a dry mass of 1 690 tons and it carried 46000 tons of fuel. The first stage only took the second stage (wet mass of 4000-5000 tons) up to 0.071c...
fsci123
Future Dubstar and Rocketkid
Well I will be using multiple lasers so I presume that smaller lens could do the same job...
Well the helium was supercooled and it was pretty close to superfluid so I just made it superfluid...
Well I don't remember the exact weight as I am using my phone but it was relatively light...
Well my craft is suppose to travel at at peak speed of 0.5c so...
garyw
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.5c is very fast for an interstellar probe especially as that will give you just a few hours at the target system. If you want to brake then you need to start braking almost before you launch to the target system!
the only interstellar probe project thats being looked at today is Icarus which is a follow on to Daedalus and they are targeting .07c
the only interstellar probe project thats being looked at today is Icarus which is a follow on to Daedalus and they are targeting .07c
fsci123
Future Dubstar and Rocketkid
Well the problem is that it is a manned mission and is designed to stop and rendevous with the targe planet or moon... That's why I chose the laser sail...
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