Solar-pumped laser power transmission, a way to dramatically decrease launch costs?
in [Physics]
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From: William Mook on 11 Mar 2010 11:30 On Mar 10, 10:52 pm, Fred J. McCall <fjmcc...(a)gmail.com> wrote: > William Mook <mokmedi...(a)gmail.com> wrote: > > : > :Let's do an example calculation. > : > :Lets say we want to send payloads to the moon and back on a regular > :basis. This means we've got to carry our payloads through a delta vee > :of 18 km/sec. Let's say we do this with six stages. Lets also say > :structural fraction is 10% of total weight. > : > > Bad assumption. Structural fraction (dry weight) will vary by fuel > choice. > > : > :We have two systems > : > > For some value of two that approximates three... > > : > :A hypergolic system with a 3.0 km/sec exhaust speed > :A jetfuel lox system with a 3.5 km/sec exhaust speed > :A liquid hydrogen lox system with a 4.0 km/sec exhaust speed. > : > > The first two will have a structural fraction down around 8% (or > lower). The third will come in over 10%. > > : > :Six stages and 18 km/sec per stage, is 3 km/sec per stage. > : > > So 18 equals 3? Not at all. 6 into 18 is 3. That's because the delta vee required to get to the moon and back is 18 km/sec. To do that in six stages means each stage must impart 3 km/sec With a 10% structural fraction and 3.0 km/sec propellant (hypergolic)and 3.5 km/sec propellant (jet fuel and lox) and 4.0 km/ sec propellant (hydrogen and oxygen cryogens) we have the following payload fractions per stage; 1/exp(3.0/3.0) -.1 = 0.267879 1/exp(3.0/3.5) -.1 = 0.324373 1/exp(3.0/4.0) -.1 = 0.372367 Divide these figures into one to obtain stage ratios 1/0.267879 = 3.733 1/0.324373 = 3.083 1/0.372367 = 2.686 Since we have six stages, multiply each number by itself six times - this is called raising this figure to the sixth power. This gives you the ratio between the payload and the take off weight 3.733^6 = 2,706.2 3.083^6 = 858.5 2.686^6 = 375.1 Multiply this ratio by the payload you're taking to the moon and back. In this example, I used 60 tonnes, so take off weight is; 60 * 2,706.2 = 162,373.4 tonnes - hypergolic ship 60 * 858.5 = 51,509.1 tonnes - lox jet fuel ship 60 * 375.1 = 22,507.5 tonnes - lox liquid hydrogen ship Multiply this total by structural fraction to get total structure weight 0.1 * 162,373.4 = 16,237.3 tonnes structure for hypergolic ship 0.1 * 51,509.1 = 5,150.9 tonnes structure for lox jet fuel ship 0.1 * 22,507.5 = 2,250.8 tonnes structure for lox liquid hydrogen ship Multiply this total by the cost per tonne of building the hardware. At $10 million per ton for structural hardware these ships cost anywhere from $22.5 billion to $162.4 billion each. The launch infrastructure scales with the size of the ship you're handling, and they end up costing 2x the cost of a single ship. A fleet of five ships with launch center will cost around 7x the cost of a single ship. So, we're talking about a program costing somewhere between $150 billion to $1,000 billion for this fleet of reusable moonships capable of putting 60 tonnes on the moon and bringing it back to Earth. We can see that improved exhaust speeds decrease the amount of propellant used, and that decreases the size of the ships and ultimately, the cost of the program. If we wanted to build a nuclear pulse spaceship with an exhaust speed of 20 km/sec we can see that a single stage is possible, since 18 km/ sec is less than 20 km/sec. We could still elect to do multiple stages. Lets look at building two kinds of nuclear pulse ships. A one stage with 18 km/sec delta vee, and a two stage ship with each stage having a 9 km/sec delta vee, again with a 10% structural fraction. Stage Payload fractions for One Stage and Two Stage operations 1/exp(18/20) -0.1 = 0.306570 1/exp( 9/20) - 0.1 = 0.537628 Stage Ratios 1 / 0.306570 = 3.262 1/ 0.537628 = 1.860 Overall Ratios 3.262^1 = 3.262 - one stage 1.860^2 = 3.460 - two stage Multiply by the payload to get take off weight 60 * 3.262 = 195.7 tonnes 60 * 3.460 = 207.6 tonnes Multiply by structural fraction to obtain structure weight 0.1 * 195.7 = 19.6 0.1 * 207.6 = 20.8 Each of these ships will cost around $200 million each at $10 million per tonne - and a fleet of five and launch center will cost $1.4 billion. If we spent $10 billion to develop the nuclear pulse propulsion system we'd be way ahead of the best conventional system. By the way, staging usually lowers overall weight, but increases it here. The reason is obvious. The exhaust speed is higher than the mission delta vee, so adding stages doesn't have the same effect as when exhaust speeds are lower than mission delta vee. Even so, a two stage ship is interesting and can save money even though heavier overall. That's because the first stage launches 111.6 tonnes into LEO and quickly returns to Earth. The second stage is then free to carry out extended missions to the moon and beyond. Several upper stages can then be built to operate lofted to orbit by only a few first stages, thus expanding lift capacity at lower cost than a single larger stage. Off world operations dealing with a smaller ship also have a lower cost infrastructure as well. > <remainder elided> > > -- > "Ignorance is preferable to error, and he is less remote from the > truth who believes nothing than he who believes what is wrong." > -- Thomas Jefferson
From: William Mook on 12 Mar 2010 11:51 Freddie is really grasping at straws - The facts remain very clear. The higher the exhaust speed of the rockets you use, the smaller and less costly the system you get for a given performance. This is why we are best served spending money improving engine performance before building the next generation of launch vehicle. On Mar 11, 8:14 pm, Fred J. McCall <fjmcc...(a)gmail.com> wrote: > William Mook <mokmedi...(a)gmail.com> wrote: > > :On Mar 10, 10:52 pm, Fred J. McCall <fjmcc...(a)gmail.com> wrote: > :> William Mook <mokmedi...(a)gmail.com> wrote: > :> > :> : > :> :Let's do an example calculation. > :> : > :> :Lets say we want to send payloads to the moon and back on a regular > :> :basis. This means we've got to carry our payloads through a delta vee > :> :of 18 km/sec. Let's say we do this with six stages. Lets also say > :> :structural fraction is 10% of total weight. > :> : > :> > :> Bad assumption. Structural fraction (dry weight) will vary by fuel > :> choice. > :> > :> : > :> :We have two systems > :> : > :> > :> For some value of two that approximates three... > :> > :> : > :> :A hypergolic system with a 3.0 km/sec exhaust speed > :> :A jetfuel lox system with a 3.5 km/sec exhaust speed > :> :A liquid hydrogen lox system with a 4.0 km/sec exhaust speed. > :> : > :> > :> The first two will have a structural fraction down around 8% (or > :> lower). The third will come in over 10%. > :> > :> : > :> :Six stages and 18 km/sec per stage, is 3 km/sec per stage. > :> : > :> > :> So 18 equals 3? > : > :Not at all. 6 into 18 is 3. That's because the delta vee required to > :get to the moon and back is 18 km/sec. To do that in six stages means > :each stage must impart 3 km/sec > : > > Go read what you wrote again. Why? Clearly 3x6=18 that's what I'm talking about. Only you would focus on a typographic error and ignore the rest of the article. > Let me add emphasis to the appropriate > parts - "Six stages and 18 km/sec PER STAGE, is 3 km/sec PER STAGE." I'm talking about six stage vehicle taking a payload through a total delta vee of 18 km/sec - each stage imparts 3 km/sec per stage - that's the basis of the entire calculation and what I'm discussing. So, you read all of that and focus only on the typographic errors (two instead of three, 'per stage' where it shouldn't be) and waste your time and everyone else's making idiotic statements based on those minor errors in typography? - haha - you truly are grasping at straws Freddie. > So we have you saying that 18 km/sec PER STAGE is 3 km/sec PER STAGE. > The only possible conclusion is that 18 is equal to 3. No, the only conclusion is that you're grasping really hard to try to find fault with what I'm saying and failing miserably. > : > :With a 10% structural fraction and 3.0 km/sec propellant > :(hypergolic)and 3.5 km/sec propellant (jet fuel and lox) and 4.0 km/ > :sec propellant (hydrogen and oxygen cryogens) > : > > Repeat your bad assumptions all you want. They're not bad assumptions at all - they're soundly based. They're simplifications to get at the root of the importance of exhaust speed in determining overall vehicle mass and from that overall costs. Which is the point of the post. In the context of the discussion about specific impulse the difference between 7% structural fraction for hypergolics and 12% structural fraction for cryogenic systems is secondary. Why do you think they are primary? They're not. You would know this if you actually knew anything about the subject. > However, see above. The > choice of fuel will affect what percentage structure you need for > tankage, etc. For non-cryo fuels it is down around 8% or less. For > LH2 it is up over 10%. So all your jiggering with numbers breaks down > because you're too stupid to make reasonable assumptions. Not at all, I chose to ignore those minor differences to focus on the importance of exhaust speeds. > You are also ignoring things like drag losses getting out of the > atmosphere, I'm not ignoring them at all. Its included in the total delta vee requirement which applies to all of them. Jiggering with the details doesn't change the conclusions of the argument, and the importance of exhaust velocity to determining vehicle size and project costs. > which are going to be higher for the cryo-fueled rocket. Talk about meaningless numbers. haha - What Freddie is talking about is that liquid hydrogen and liquid oxygen propellant is less dense than liquid oxygen and jet fuel, and that's less dense than hydrazine and nitric acid. That means larger propellant volumes for the less dense stuff. This means larger tank volumes. This means larger cross section and higher drag for the less dense stuff. This adds SLIGHTLY - VERY SLIGHTLY to the delta vee requirements of the lower density stuff. So, the cryogen system will have an air drag loss of about 0.8 km/sec and the lox jet fuel system will have an air drag loss of about 0.6 km/ sec and the hypergolic system will have an air drag loss of 0.5 km/ sec. This is what Freddie is bellyaching about. A 0.3 km/sec difference to an 18 km/sec total delta vee. Its like Fred's bellyaching about me choosing 10% structural fraction throughout because current systems are 7% structural fraction for hypergolics and 10% for lox jet fuel and 12% for liquid hydrogen liquid oxygen. haha - or pointing out that I wrote two instead of three, or inadvertently typed per stage in a sentence. in short, he's attempting to lie to everyone about what I'm saying by mischaracterizing what I'm saying. Why is he taking the trouble to do this? Who knows? The facts remain very clear. The higher the exhaust speed of the rockets you use, the smaller and less costly the system you get for a given performance. This is why we are best served spending money improving engine performance before building the next generation of launch vehicle. > <snip meaningless numbers> > > : > :We can see that improved exhaust speeds decrease the amount of > :propellant used, and that decreases the size of the ships and > :ultimately, the cost of the program. > : > > If you make unrealistic assumptions about the way the world works. > Your cryo-fueled ships with the higher exhaust velocity will be LARGER > because of the lower density of the fuel. This is why the structural > percentage on such vehicles MUST be higher than is required for > non-cryo fueled vehicles. > > <more meaningless numbers zeroed out> > > : > :Each of these ships will cost around $200 million each at $10 million > :per tonne - and a fleet of five and launch center will cost $1.4 > :billion. If we spent $10 billion to develop the nuclear pulse > :propulsion system we'd be way ahead of the best conventional system. > : > > And if wishes were fishes we'd all cast nets in the sea. > > Hell, build a teleport. No mass for the ship means no cost, by your > figuring. > > -- > "Ordinarily he is insane. But he has lucid moments when he is > only stupid." > -- Heinrich Heine
From: William Mook on 12 Mar 2010 12:24 If we add in the details that Fred is bellyaching about here is what we get 17.7 km/sec and 7% structural fraction for hypergolic system 17.8 km/sec and 10% structural fraction for lox jet fuel system 18.0 km/sec and 12% structural fraction for lox liquid hydrogen system Six stages divided into each of these obtains a stage delta vee of 2.95 km/sec stage delta vee for hypergolic 2.97 km/sec stage delta vee for lox jet fuel 3.00 km/sec stage delta vee for lox liquid hydrogen system Exhaust speeds of each system 3.00 km/sec hypergolic 3.50 km/sec lox jet fuel 4.00 km/sec lox liquid hydrogen Which gives us this propellant fraction 1 - 1/exp(2.95/3.00) = 0.62594 1 - 1/exp(2.97/3.50) = 0.57157 1 - 1/exp(3.00/4.00) = 0.52763 Which gives us this payload fraction 1 - 0.62594 - 0.07 = 0.30406 1 - 0.57157 - 0.10 = 0.32743 1 - 0.52763 - 0.12 = 0.35267 Invert to get stage multiplier 1 / 0.30406 = 3.289 1 / 0.32743 = 3.045 1 / 0.35267 = 2.838 Raise to the sixth power (multiply by itself six times) to obtain payload to vehicle weight 3.289^6 = 1265.4 3.046^6 = 796.7 2.838^6 = 522.4 Multiply by 60 tonnes (our payload we're carrying around) to obtain take off mass 60 * 1265.4 = 75,923.7 60 * 796.7 = 47,804.0 60 * 522.4 = 31,346.1 Multiply by structural fraction to get empty vehicle weight 75,923.7 * 0.07 = 5,314.7 47,804.0 * 0.10 = 4,780.4 31,347.1 * 0.12 = 3,761.5 Which implies a vehicle cost of $5.3 billion to $3.7 billion each, and a program cost of $35 billion to $25 billion. Which replicates what I said earlier, but produces a narrower range due to the minor corrections Continuing as before, A nuclear pulse vehicle with 20 km/sec exhaust speed and a 20% structural fraction to account for the nature of the propulsion system, carrying 60 tonnes through a delta vee of 18 km/sec has a propellant fraction of; 1 - 1/exp(18/20) = 0.59343 and a payload fraction of 1 - 0.59343 - 0.20 = 0.20657 and a stage multiplier of 1 / 0.20657 = 4.841 and a take off weight (one stage!) of 60 * 4.841 = 290.5 tonnes and a structural weight of 290.5 * 0.20 = 58.1 tonnes So each vehicle costs $581 million and the total program costs $3.5 billion (not counting development costs for the engine). With an engine development cost of $3.5 billion - we have a savings of over $20 billion over any of the conventional programs above. So, the argument and conclusions are exactly the same, higher exhaust speeds reduce program costs. Significant increases provide significant improvements in cost. The numbers obviously are slightly different when these details are taken into account, as we might expect. Even so, since none of these numbers are written in stone, these numbers are no more accurate than the ones before. Reusable ships will have higher structural fractions than throw-away ships. Advanced materials reduce structural fractions over today's materials. Shape, staging and operational differences change air drag losses. All over the ranges indicated - which is why they were ignored in the discussion - the point remains regardless of Freddie's griping. Higher exhaust speeds mean lower access costs to space. Laser rockets and nuclear rockets both have the capacity to achieve higher exhaust speeds near term and radically lower program costs and operating costs near term.
From: William Mook on 13 Mar 2010 12:37 On Mar 12, 12:45 pm, Fred J. McCall <fjmcc...(a)gmail.com> wrote: > William Mook <mokmedi...(a)gmail.com> wrote: > > :Freddie is really grasping at straws - > : > :The facts remain very clear. The higher the exhaust speed of the > :rockets you use, the smaller and less costly the system you get for a > :given performance. > : > > If you use bad assumptions. So, what are you really saying Freddie? That higher exhaust speeds don't lead to smaller systems to achieve a given mission? How does that work Freddie? > > : > :This is why we are best served spending money > :improving engine performance before building the next generation of > :launch vehicle. > : > > Hogwash. Again, its hard to figure what Freddie is really saying since he says so little to support his views. Here he's saying that improving exhaust speed won't create smaller systems to achieve a given mission. Which isn't right. He's also saying smaller systems aren't less expensive than larger systems which again isn't right. > Go read up on the Mars Reference Mission, you dipwad. Which one? Here's one that is very low mass and low cost - because it has a high exhaust velocity for its primary mission http://www.youtube.com/watch#!v=E3Lxx2VAYi8 http://www.youtube.com/watch#!v=8rEa9ACC-TM It was first developed in the 1940s, and a program was instituted in the 1950s, and Freeman Dyson felt that we would have a fleet of interplanetary cruisers operational by 1970s. The film shown in the BBC special was classified by Eisenhower as was testimony by the experts. Why? He didn't want to excite the American people into creating a new space frontier, over spending on space while ignoring the very real challenges we had here on Earth. Some CGI work based on the studies http://www.youtube.com/watch?v=neLA_IuRLI8 http://www.youtube.com/watch#!v=qpFEJzD-U_o Work with micro-fission done at OSU and PSU and Phillips Research Lab in the 1980s which I was involved with, makes nuclear pulse cleaner, cheaper, safer than ever before. As I've said, the PI on that one is now working at USAF Phillips and no new papers have come out - despite ongoing work. We could spend $7 billion and have a small fleet of interplanetary cruisers that would allow us to explore and build outposts throughout the solar system using this technology. We could spend $70 billion and build a commercial fleet capable of capturing asteroids and orbiting significant industrial infrastructure to make life better on Earth. We could spend $700 billion and support small nation states throughout the solar system. We could spend $7 trillion and remove everyone to Earth orbit and beyond - living in city sized space homes and with this build a space faring culture leaving the Earth a vast nature preserve going back to its pre-human state. According to the Brookings Institute humanity spend $7 trillion in the last half of the 20th century wiring our world for nuclear annihilation. The same materials made into microfission triggers and operating nuclear pulse ships built on the same scale as ICBM and space defense networks, would have transformed our world engine poverty privation ignorance and made of humanity a space faring culture. > :On Mar 11, 8:14 pm, Fred J. McCall <fjmcc...(a)gmail.com> wrote: > :> William Mook <mokmedi...(a)gmail.com> wrote: > :> > :> :On Mar 10, 10:52 pm, Fred J. McCall <fjmcc...(a)gmail.com> wrote: > :> :> William Mook <mokmedi...(a)gmail.com> wrote: > :> :> > :> :> : > :> :> :Let's do an example calculation. > :> :> : > :> :> :Lets say we want to send payloads to the moon and back on a regular > :> :> :basis. This means we've got to carry our payloads through a delta vee > :> :> :of 18 km/sec. Let's say we do this with six stages. Lets also say > :> :> :structural fraction is 10% of total weight. > :> :> : > :> :> > :> :> Bad assumption. Structural fraction (dry weight) will vary by fuel > :> :> choice. > :> :> > :> :> : > :> :> :We have two systems > :> :> : > :> :> > :> :> For some value of two that approximates three... > :> :> > :> :> : > :> :> :A hypergolic system with a 3.0 km/sec exhaust speed > :> :> :A jetfuel lox system with a 3.5 km/sec exhaust speed > :> :> :A liquid hydrogen lox system with a 4.0 km/sec exhaust speed. > :> :> : > :> :> > :> :> The first two will have a structural fraction down around 8% (or > :> :> lower). The third will come in over 10%. > :> :> > :> :> : > :> :> :Six stages and 18 km/sec per stage, is 3 km/sec per stage. > :> :> : > :> :> > :> :> So 18 equals 3? > :> : > :> :Not at all. 6 into 18 is 3. That's because the delta vee required to > :> :get to the moon and back is 18 km/sec. To do that in six stages means > :> :each stage must impart 3 km/sec > :> : > :> > :> Go read what you wrote again. > : > :Why? Clearly 3x6=18 that's what I'm talking about. Only you would > :focus on a typographic error and ignore the rest of the article. > : > :> Let me add emphasis to the appropriate > :> parts - "Six stages and 18 km/sec PER STAGE, is 3 km/sec PER STAGE." > : > :I'm talking about six stage vehicle taking a payload through a total > :delta vee of 18 km/sec - each stage imparts 3 km/sec per stage - > :that's the basis of the entire calculation and what I'm discussing. > :So, you read all of that and focus only on the typographic errors (two > :instead of three, 'per stage' where it shouldn't be) and waste your > :time and everyone else's making idiotic statements based on those > :minor errors in typography? - haha - you truly are grasping at straws > :Freddie. > : > :> So we have you saying that 18 km/sec PER STAGE is 3 km/sec PER STAGE. > :> The only possible conclusion is that 18 is equal to 3. > : > :No, the only conclusion is that you're grasping really hard to try to > :find fault with what I'm saying and failing miserably. > : > :> : > :> :With a 10% structural fraction and 3.0 km/sec propellant > :> :(hypergolic)and 3.5 km/sec propellant (jet fuel and lox) and 4.0 km/ > :> :sec propellant (hydrogen and oxygen cryogens) > :> : > :> > :> Repeat your bad assumptions all you want. > : > :They're not bad assumptions at all - they're soundly based. They're > :simplifications to get at the root of the importance of exhaust speed > :in determining overall vehicle mass and from that overall costs. > :Which is the point of the post. In the context of the discussion > :about specific impulse the difference between 7% structural fraction > :for hypergolics and 12% structural fraction for cryogenic systems is > :secondary. Why do you think they are primary? They're not. You > :would know this if you actually knew anything about the subject. > : > :> However, see above. The > :> choice of fuel will affect what percentage structure you need for > :> tankage, etc. For non-cryo fuels it is down around 8% or less. For > :> LH2 it is up over 10%. So all your jiggering with numbers breaks down > :> because you're too stupid to make reasonable assumptions. > : > :Not at all, I chose to ignore those minor differences to focus on the > :importance of exhaust speeds. > : > :> You are also ignoring things like drag losses getting out of the > :> atmosphere, > : > :I'm not ignoring them at all. Its included in the total delta vee > :requirement which applies to all of them. Jiggering with the details > :doesn't change the conclusions of the argument, and the importance of > :exhaust velocity to determining vehicle size and project costs. > : > :> which are going to be higher for the cryo-fueled rocket. > : > :Talk about meaningless numbers. haha - What Freddie is talking about > :is that liquid hydrogen and liquid oxygen propellant is less dense > :than liquid oxygen and jet fuel, and that's less dense than hydrazine > :and nitric acid. That means larger propellant volumes for the less > :dense stuff. This means larger tank volumes. This means larger cross > :section and higher drag for the less dense stuff. This adds SLIGHTLY > :- VERY SLIGHTLY to the delta vee requirements of the lower density > :stuff. > : > :So, the cryogen system will have an air drag loss of about 0.8 km/sec > :and the lox jet fuel system will have an air drag loss of about 0.6 km/ > :sec and the hypergolic system will have an air drag loss of 0.5 km/ > :sec. This is what Freddie is bellyaching about. A 0.3 km/sec > :difference to an 18 km/sec total delta vee. > : > :Its like Fred's bellyaching about me choosing 10% structural fraction > :throughout because current systems are 7% structural fraction for > :hypergolics and 10% for lox jet fuel and 12% for liquid hydrogen > :liquid oxygen. haha - or pointing out that I wrote two instead of > :three, or inadvertently typed per stage in a sentence. > : > :in short, he's attempting to lie to everyone about what I'm saying by > :mischaracterizing what I'm saying. > : > :Why is he taking the trouble to do this? > : > :Who knows? > : > :The facts remain very clear. The higher the exhaust speed of the > :rockets you use, the smaller and less costly the system you get for a > :given performance. This is why we are best served spending money > :improving engine performance before building the next generation of > :launch vehicle. > :> <snip meaningless numbers> > :> > :> : > :> :We can see that improved exhaust speeds decrease the amount of > :> :propellant used, and that decreases the size of the ships and > :> :ultimately, the cost of the program. > :> : > :> > :> If you make unrealistic assumptions about the way the world works. > :> Your cryo-fueled ships with the higher exhaust velocity will be LARGER > :> because of the lower density of the fuel. This is why the structural > :> percentage on such vehicles MUST be higher than is required for > :> non-cryo fueled vehicles. > :> > :> <more meaningless numbers zeroed out> > :> > :> : > :> :Each of these ships will cost around $200 million each at $10 million > :> :per tonne - and a fleet of five and launch center will cost $1.4 > :> :billion. If we spent $10 billion to develop the nuclear pulse > :> :propulsion system we'd be way ahead of the best conventional system. > :> : > :> > :> And if wishes were fishes we'd all cast nets in the sea. > :> > :> Hell, build a teleport. No mass for the ship means no cost, by your > :> figuring. > :> > :> -- > :> "Ordinarily he is insane. But he has lucid moments when he is > :> only stupid." > :> -- Heinrich Heine Freddie seems to care little for reality in his effort to bury the simple fact that highly energetic jets of material, made with laser or nuclear energy have the potential to vastly reduce the size of rocket systems and improve their performance to the point where rockets join jets to create a real space age, equivalent to the jet age - and create the world we deserve today.
From: William Mook on 13 Mar 2010 12:56
On Mar 12, 12:50 pm, Fred J. McCall <fjmcc...(a)gmail.com> wrote: > William Mook <mokmedi...(a)gmail.com> wrote: > > :If we add in the details that Fred is bellyaching about here is what > :we get > : > : 17.7 km/sec and 7% structural fraction for hypergolic system > : 17.8 km/sec and 10% structural fraction for lox jet fuel system > : > > Still too high. Stop trying to jigger the numbers and use realistic > ones. > > <arithmetic elided> > > If you have perfect rockets and jigger the numbers. What are you bellyaching about now Freddie? The fact that the results remain unchanged when you put in the details you were bellyaching about before?! Ha! What correction did you want to put in now? > Jesus, how did we EVER get to the Moon without six stage rockets? That's not the point Freddie. The point is that with a higher exhaust speed you use less propellant which reduces the size and complexity of the spacecraft with the higher exhaust speed. So, it makes sense to spend a little money to increase your exhaust speed and thereby reduce the size and complexity of the vehicles involved. An important detail is that we can get exhaust speeds in the 20 km/sec to 50 km/sec range - which gives us tremendous capabilities going forward, if we're smart enough to develop this capability. To your comment, we got to the moon and came back with six stages Freddie. The moon and back Freddie used six stages. Count 'em 1. SI - lift off 2. SII - ascent 3. S-IVB - orbit/TLI 4. Service Module - enter lunar orbit/exit lunar orbit 5. LEM-descent - descent to moon 6. LEM-ascent - ascent from moon I am proposing in my calculation for simplicity a direct ascent trajectory and six stages still. http://en.wikipedia.org/wiki/Direct_ascent You can see that the lunar module is replaced by a two stage deal, where one is used to descend, the other used to ascend. With four stages to get to the moon. 1. Lift off 2. Ascent 3. Orbit 4. Lunar Injection 5. Landing 6. Return Lunex used the same approach for the same reasons... ALL used six stages dude. http://en.wikipedia.org/wiki/Lunex_Project > It > MUST be impossible. Mookie says so. Never said anything of the sort. I would suggest you actually learn to count before making idiotic statements like this you lunatic. > : > :Continuing as before, > : > :A nuclear pulse vehicle with 20 km/sec exhaust speed and a 20% > :structural fraction to account for the nature of the propulsion > :system, carrying 60 tonnes through a delta vee of 18 km/sec has a > :propellant fraction of; > : > : 1 - 1/exp(18/20) = 0.59343 > : > :and a payload fraction of > : > : 1 - 0.59343 - 0.20 = 0.20657 > : > :and a stage multiplier of > : > : 1 / 0.20657 = 4.841 > : > :and a take off weight (one stage!) of > : > : 60 * 4.841 = 290.5 tonnes > : > :and a structural weight of > : > : 290.5 * 0.20 = 58.1 tonnes > : > :So each vehicle costs $581 million and the total program costs $3.5 > :billion (not counting development costs for the engine). > : > > Except you're now talking totally different systems and your WAG for > vehicle cost is out the window (among other things). > > : > :With an engine development cost of $3.5 billion - we have a savings of > :over $20 billion over any of the conventional programs above. > : > > Your claims for development costs are, as always, laughable. > > How much did it cost to develop the Saturn V, Mookie? Saturn V Development Cost $: 7,439.60 million According to government records. > Your present > claim is that developing a large nuclear pulse jet will be orders of > magnitude less expensive. Section 6 of "Nuclear Pulse Space Vehicle Study, Vol. 1 -- Summary" (1964) projected a development cost of about $2 Billion for the 10-meter version of the spacecraft. http://ntrs.nasa.gov/archive/nasa/ca...1965058729.pdf I suspect that using modern micro-fission I researched at OSU that cost could go down, but we'd elect to increase performance slightly, and today we'd build a superior version of this interplanetary cruiser - and spend only $3.5 billion to get all the detailed work done. > And that doesn't strike you as a > preposterous position? What's preposterous exactly? > -- > "Ordinarily he is insane. But he has lucid moments when he is > only stupid." > -- Heinrich Heine |