Discussion in 'Astronomy, Exobiology, & Cosmology' started by Mind Over Matter, Jan 12, 2012.
We should send Newt "major of the Moon" Gingrich up there with all his future wives...
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Enough with the unsupported words. - Time for a reality check.
(1) What is this speed (as it leaves the end of the rail gun)?
(2) What is the velocity direction as it leaves the rail gun? (Degrees from zero, the Earth radial direction or "straight up")?
(3) What is the length of the rail gun? (This and terminal speed fixes the required acceleration, a. Then the mass of the vehicle, m, fixes the force, F, (F=ma) that must be steadily applied to vehicle on the rails, presumably by many adjacent, large, high ampere-turn coils that do not tear each other from their mounts on the rail gun sides.)
(4) What is the weight of the iron in the vehicle that this magnetic force acts on, Or do you envision a massive copper plate and eddy current interaction force F achieved in it? Note iron or copper are much heavier elements than the hydrogen fuel a more convention vehicle has to get up to speed.)
(5) How far from the center of the Earth is the terminal end of the rail gun? (This determines the "gravitational hill" the vehicle must climb with reduction of its rail gun terminal velocity.
(6) What is the atmosphere density and resulting friction force, ff, on vehicle as it leaves the end of rail gun? (It surely is super sonic, so is producing a shock wave. That is an energy drain, E per meter of travel. So there is also a force retarding the vehicle to do that work / create the shock wave energy of fsD (force times distance but as E is for one meter, D =1 and fs=E. Thus the total retarding force Fr = ff + fs, but it decreases as vehicle gets further form the center of the earth (less dense air).
As a quick guess, these considerations very likely make it impossible to put even very small weight vehicles (say 100 pounds) into even low earth orbit, much less to climb out of earth´s gravity to point close to the moon where moon´s gravity is equally strong. Fact that no one even tries, is proof enough for most reasonable people. Rail guns are not even attractive for less than low earth orbit trajectories, such as Iran throwing explosives at nearby Israel etc.
SUMMARY Reality comes only from quantative analysis after these questions are answered, not from a bunch of hand waving words. Do you not suppose that rail guns have been considered, REALISTICALLY, (quantatively) by many well qualified rocket scientists, and rejected as they are less attractive for making vehicles leave the Earth than liquid fuels, especially light-weight, high-specific-impulse, hydrogen?
Now to answer the thread´s question:
US suffered a great psychological blow when the USSR put Sputnik into orbit. Going to the moon was done to restore self confidence (and as minor consideration, develop some required technology and do some scientific exploration - not nearly as useful or cheap as deep ocean research would have been, but the "science" was low priority compared to showing world US was still the most advanced country.)
Currently the US is again under stress, in danger of having lost its status of the world´s only reserve currency and the petrodollar convention with oil exporters - that allows the US to import nearly everything it needs and pay for these imports with printed green paper. As the large and growing debt with annual deficits of about 1.5 trillion dollars is the foundation of these global doubts about the fiscal soundness of the dollar, spending on a new manned trip to the moon would not help with the US´s current financial credit problems. It might even make SDRs, the increasing gobally used RMB, gold or some mix of these the "least ugly" currency (main reason dollar has not already collapsed is the lack of more attractive alternatives)
Railguns could be used to put raw materials in orbit, but the linear accelerator in an evacuated tube going up the slope of a tall mountain would be more effective and utilize much lower accelerations. Put a laser pumped ramjet on the back of the capsule and no propellant at all would be required for LEO and acceleration would be man friendly(2-3 G max).
Going to the moon for anything but research or raw materials is a huge waste. We should put robots at the poles to mine and lauch(Linear accelerators are nearly perfectly efficient in vacuum)water and other minerals to the Lagrange points and stay in freefall to build our habitats and vessels. Mars should be a one way destination for older scientists until infrastructure has been built for permanent settlement, then build a Beanstalk.
Gravity Wells suck!
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Looks like the deep ocean explorers are are starting see "bang for the buck",
and it's not on the ocean floor nor the moon surface (as many , even as myself, have been contemplating for years--nice to see things on a sensible track):
"...to add trillions of dollars to the global GDP" and "help ensure humanity's prosperity."..."
It ties nicely into NASA directives and already-achieved technical advancements.
The Mars Rover has shown ample use of mineral identification technologies.
Robotics for major far-space grunt work.
Humans for aesthetics, self esteem, Earth-orbit manufacturing city-pod dressing, remote control of far-space robot machinery, repair/maintenance of far-space machinery**).
**The spaceman/woman with suspenders, a fedora, tuna sandwich stains on the overalls, and a toolbox.
Houston, we have a future....
So we answer the OP as, not yet, not until we're ready to make the moon a lucrative endeavor.
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Good to see you still up and about, mate!
Yes, that would be a better way to go if the cost of the long/extensive tunnel and associated infrastructure/land requirements and risk of sabotage to vacuum tunnel during takeoff can be managed OK.
All that you say is quite much better on both cargo and humans, and would also encourage international co-operation etc.
I agree with your take on all those aspects, mate.
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I am not personally attached to any particular launch system, merely musing on the possibilities, mate. As for the technical aspects you mentioned, I suppose I am musing on the possibilities of:
- siting the railgun infrastructure in any one of the many extremely deep mine shafts around the world, and extending the vertical run of the structure above grund to as convenient an altitude as possible with the steel and concrete girder/tube construction techniques available;
- providing for a cradle which would have all the actual electro-magnetic boost components which would interact with the rails, so that the vehicle itself just sits in the cradle and when the vehicle & cradle exit the 'muzzle', they would separate and the cradle (robust) would be recovered using integral parachutes and re-used;
- muzzle velocity is a function of the power and the rail-length used, which would be 'tuned' to the actual installation (I haven't any hard figures, as I am only musing on the possibilities);
- trans-atmosphere vertically reduces the in-atmosphere dwell-time consisiderably, so the drag is over a lesser time than in conventional rocket trajectories (conventional rockets also go supersonic very early in atmosphere and suffer from the greater surface area of the much greater bulk of stage one and two rockets motors and tanks etc);
- given high muzzle velocity, the dwell time for railgun-type launcher vehicles (much less bulky and heavy and fragile than the conventionally launched vehicles etc) is relatively short and the carbon-carbon nose protection is enough to cut through the atmosphere with least drag profile/area, and the rest of the vehicle can be made of relatively cheap steel because the dwell-time in the atmospheric heating regime is so short that the heat transfer between the shock 'stagnation' boundary layers to vehicle surfaces has little time to take place before the vehicle is in space and radiating.
As for why Iran et al are not using this way to hurl warheads at neighbours, I would imagine that SECRECY would be hard to ensure given the long run needed and the 'sitting duck' nature of the installation would make it child's play for the potential target nation to destroy such an installation before it became operational (and in the worst case where the first warhead has been sent, the destruction of the site would be pretty well assured not long thereafter). Also, the expense would be too high for just a ONE OFF 'weapon' application' since its destruction would remove any usefulness for further civilian and other return-on-investment applications in science/space programs.
Anyhow, mate, I am not in the field of railgun technology nor do I know of the very latest technical/military developments in the efficiencies/feasibilities for various railgun applications at various scales/power.
In any case, as Grumpy has pointed out, the linear accelerator in evacuated tube might be a better way to go....OR EVEN a HYBRID? of the two, with the linear accelerator providing some of the initial speed along a horizontal track and then this curves up a mountain where the last section of track is a railgun type for the final boost to high 'muzzle velocity' and vertical orientation?
I leave it to you and others to explore this area if you're interested. I have made my musings and suggestions on the topic and will lave it at that, mate!
If you or anyone comes up with any hard data/figures on the options/possibilities mentioned, I would be very interested to read same next time I'm surfing through here. Thanks.
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“…Two years after BAE Systems was awarded a US$21 million contract from the Office of Naval Research (ONR) to develop an advanced Electromagnetic (EM) Railgun for the U.S. Navy, the company has delivered the first industry-built prototype demonstrator to the Naval Surface Warfare Center (NSWC) Dahlgren. …
While the muzzle velocity of gunpowder-propelled projectiles is generally limited to around 4,000 ft per second (2,727 mph/4,389 km/h), the U.S. Navy says its railgun will be capable of launching projectiles at velocities of 4,500 to 5,600 mph (7,242 - 9,012 km/h). This kind of speed translates to greatly extended range. Navy planners are initially targeting a 50 to 100-nautical mile (57 to 115 mile/92 to 185 km) range, …”
From the very latest (7 Feb 2012) not yet tested most advanced rail gun. More at: http://www.gizmag.com/first-industry-railgun-prototype-launcher/21377/
They do not tell the projectile weight, but I think it is less than 100 pound and must be 100% conductive metal.
Just to give you some slight understanding of how nonsensical your suggestion of rail gun launch to moon etc. is, note that the escape velocity required to climb out of earth´s gravity field is 25,038.72 mph, falsely assuming that there is no friction with the air or energy loss producing the shock waves in the air. Actual terminal speed required off the end of the rail gun is much, much, higher and sort of a losing game as the higher the initial speed, the more energy is lost to the shock wave and air friction.
Thus this state of the art, rail gun falls short of speed needed at end of the rail gun by much more than 25,038.72 / 5,600 or at least by a factor of ten (or 100 times too weak in terms of energy).
This $21 million dollar gun does not even have enough range to let Iran throw even a copper slug at Israel, much less any HE. In fact it would very likely cause the HE to explode before it left the end of the rails – the heating of the “bullet” and the entire system is extreme. Read about that in the article.
Again, only hand waving words, with no quantative analysis, are self delusion in this case.
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Little time, mate. So briefly in answer....
1. Note the "Naval Warfare". So the kind/scale of would be compact for naval mounting platformetc, not in the 'long rail' versions I am speculating about. So your counter-arguments there are not that relevant.
2. The railgun launch system 'straight up' on shortest trans-atmosphere trajectory for orbit/moon would be appropriately designed with the necessary heat shielding/streamlining etc and would not be in the atmosphere long enough for the drag/heating to be a limiting factor. I covered this aspect before.
3. Any military shots/warheads are DESIGNED AS warheads, and not as space vehicles. So again, your arguments there are not that relevant. Apples and oranges. Because the space vehicles would have sustainer rockets for maintaining muzzle velocity and ensuring quick passage through the short vertical crossection of the atmosphere. Whereas the ground-to-ground weapons projectiles you speak of must be readily deployed and fired frequently and on a trajectory that would take them through the atmosphere for LONGER PERIOD in its upwards trajectory and its downwards trajectory, hence the drag/heating etc profiles to be allowed for would be entirely different.
I hope that clarifies the difference between what you are thinking of and what I am speculating about, mate! Please Register or Log in to view the hidden image!
My point is that words / speculation, etc with zero analysis is next to useless. In post 84 I asked you to answer 6 or 7 specific questions with numbers (and even told part of how these numbers would be used in evaluation of your ideas.) but that would just be a start - need especially to know how much energy goes into the shock wave - quite possilby more than in the fuel tank o a Saturn liquid fuel rocket
Yes a longer rail will make the required acceleration and forces lower, but you seem to want to accelerate both the vehicle and some sort of carrage that absorbes the magnetic force (Lot of iron or copper, most likely) and then separated with parachute recovery. That of course will greatly increase the total weight being accelerated, compared to the Navy´s bullet (just the copper or iron slug which is its projectile.
Answer the questions - I.e. specify exactly you are talking about, (length of rail gun, terminal speed, etc.) then do what you can to compute its feasibility. I will try to help you if you get stuck.
Parts of the problem are quite complex as the air drag varies with both vehicle speed, cross section and air density and other lesser things we can ignore like temperature and atomic mix. - I am sure there is information on how this drag force goes in the internet that would let you evaluated your sustaining rocket requirements. You could assume that the vehicle speed is always equal Earth escape velocity, which very slightly decrease with altitude.
One of the great advantages of the current high-specific-impulse liquid fuel systems which you seem to ignore, is that in the dense air the vehicle speed is low - not even a shock wave until in thin air. In contrast your peak speed is at the end of the rail gun, with huge rate of energy loss in shock wave generation in dense air. I would not be surprised if at earth escape velocity thru dense surface air up to 20 miles high that may be more energy than stored in the Saturn Rockets fuel main tank.
Also a complex problem to investigate is the shock wave inside your vertical mine shaft. I suspect that as the shockwave cannot expand away for the super sonic vehicle, as it normally does, it will effectively be a piston compressing the air immediately in front of the vehicle - perhaps to be the same as if you were trying to launch thru atmosphere several times denser than ground level air. You may need a significant fraction of the energy in the Saturn main fuel tank to get top the top of the mine shaft. - if true, you could melt your vehicle. Did you read how serious the heating problem is for the Navy´s new rail gun? At the very least you will need thick ceramic ablative ceramic coating for the vehicle as it is confined in its own red hot shock wave. Note that space craft returning to Earth frpom the moon are going slower than Earth escape velocity and slowing down as they enter the much thinner air, yet burn away part of their ceramic coatings.You will be going much faster in air at least 10 times denser. - A very serious thermal problem.
To some extent this happens when a big battleship gun fires - the air in front of the ~1 ton shell can not flow out of the open end of the barrel faster than the speed of sound, so there may be numerical studies of vehicle traveling into confined air it is compressing. Your problem is much worse as your speeds (approximately earth escape velocity) are at least 10 times greater than a battleship gun´s bullet and your distance of travel inside the confining walls of the mine shaft is many dozens of times longer.
Again, the easy argument against your ideas is fact there is nothing novel in them - they have been carefully considered at least two decades ago by experts and found not to be attractive, except possibly on the moon where there is no atmospheric shock wave stealing most of the energy the rail gun gives the projectile and the force of gravity is much less.
Your words, with no analysis, will not be interesting to anyone knowledgeable in the area. I am sure, as I read several articles a decade or more ago, on rail guns for launching materials extracted from the moon surface into low moon orbit has been extensively studied.* Read up on some of its quantative analysis, then try to find models of the shockwave and friction loses of a supersonic projectile traveling starigh up from near earth surface.
*Idea is to first build material processing base and rail gun on the moon to then build in low moon orbit a manned space craft for going to Mars, etc. Cost of taking materials needed from Earth is much greater.
A few notes here:
Believe it or not for a railgun launch you don't want to fire the thing vertically, you want to fire it horizontally. Conventional spacecraft launch vertically only because it's more convenient to launch them that way. They pitch over immediately because while they need only about 100 miles of altitude gain, which translates to a delta-V of about 4000mph. You need 18,000mph of horizontal delta-V to get into orbit.
So if you launch vertically you still need rockets to give you over 75% of your delta-V. Which means you still need (say) a Saturn V, just slightly smaller.
Your wording makes me think you have a slightly incorrect idea of what happens. At those speeds there is no "cutting." Air does not have time to get out of the way. The vehicle will burn up like a meteor. With careful selection of ablative materials you might be able to get part of your payload out of the atmosphere before it is completely destroyed, but you'll only achieve this by sacrificing much of the vehicle itself. There is no manner of careful aerodynamic design that allows you to cut through anything.
The amount of heat we are talking about will vaporize any material known to man. The trick is - will it vaporize slowly enough so that some of it survives?
And given the energies involved, every satellite on the planet (and even most ground based observers) will see the fireball heading from, say, Iran to Israel.
Google "space fountain" and "launch loop" for some hybrid designs.
You are correct in all you state except your first point is based on idea he is thinking of going into earth orbit (and he may be now that I told him how much speed he needs to escape from Earth); However if the vehicle, completely covered with thick ablating ceramic tiles, is to have any chance of surviving a worse than blast furnace heat load environment, it need to get out of the shock heated air ASAP.
I don´t think it possible to get even 1% of the vehicle mass to an altitude of 20 miles, but straight is probably best if it comes off the end of the railgun with escape velocity and then uses some "sustainer rocket" to keep escape velocity. (He is falsely thinking this sustainer rocket is small when it is probably nearly as large as the Saturn V.)
I made a wild guess at the energy an escape velocity vehicle would transfer to the air via shock wave while climbing straight up to 20 miles and is seems quite likely it is of the same order of magnitude as the Saturn V main fuel tank holds.
Certainly a fuel tank more than a dozen meters in diameter and say 100 meters long - quite a "vehicle" to accelerate to escape velocity on a rail gun! The "Gs" acting on that fuel would be very great even if the rail gun were a mile long. So the tank walls would need to be steel and it is likely to weigh more than the fully fueled Saturn V. Etc.
He is only blowing hot air ideas with zero understanding of the thermal problem and falsely supposing that no one considered rail gun launch decades ago. There is a good reason why rocket climb above most of the dense air before going many times supersonic. The concept of leaving end of the rail gun with escape velocity in near surface air is too ridicules to discuss - In post 84, I gently tried to get him to do a little analysis and let him discover that himself but now it is time to be more blunt.
I would think the answer is that manned moon missions do not substantially further scientific aims when compared to the relatively low-cost (but scientifically more significant) unmanned missions.
Couple that with the even more extreme cost differential of sending a manned mission to land on an extra-terrestrial body like the moon, where a large chunk of the funds used must be diverted to getting them off the surface of that other body and home again (unlike the usually one way robotic missions).
Other than the national prestige of having set foot on the Moon, there is not much reason to send humans there again right now. At some point we may find that it is feasible and cost effective to mine something on the moon, in which case commercial interests will take us back there. Until then, going back is just about ego.
The commercialization of space will take men back there...possibly sooner than we all might think. I can't post links yet, but Larry Page and James Cameron are exploring a potential commercial/exploratory space mission (feel free to Google it), details of which will be announced shortly. I think private space exploration and natural resource extraction sounds much better than getting the federal government involved.
It is amusing that two recent science fiction films both had plot elements involving aliens for why we haven't gone back to the Moon:
Transformers: Dark of the Moon.
However, the main reason is because of cost. The Constellation program that would have taken us back to the Moon had a projected cost of $100 billion, which led to it being cancelled.
But the recent push for a more commercial approach to spaceflight has shown that development costs can be cut by as much as 90%(!)
I believe this will lead to more affordable flights to LEO and BEO. In this post to my blog I show a manned lunar flight can be done using the upcoming Falcon Heavy for a cost of a few hundred million dollars:
SpaceX Dragon spacecraft for low cost trips to the Moon.
I know this is not a subject and moderators can delete my post if they want to, but I have one question, which I hope someone will answer regarding Moon landing-have scientists ever made and conference or something like that to disprove conspiracy theorists (who think that we have not been on the Moon)?
To be honest, I'm trying to find the source of anything like this to prove to my collegue that humans were on the Moon
You don't have to answer me here, you can send me private message, since this is not a subject of this thread and should be excluded.
Unfortunately I didn't know how and where to ask about this.
I should have contected moderators, I will fully understand if they delete my post-no hard feelings.
Well, I truly hope mderators will answer me what to do, because I really don't want to post this on conspiracy theories sub-forum, but here on science forums and read some answers from scientists and people with healthy mind.
Thanks to all posters and moderators here.
Actually, the film Moon did not have aliens as a plot element for why we didn't go back to the Moon, though it was probably the best of the recent science fiction films that had the Moon as a theme.
The other film I was thinking of with aliens as a plot element was actually Apollo 18:
Apollo 18 (film).
Note: these wiki articles on films always have severe spoilers.
Very probably not as there would be no point to it. Crack Pots would just say the photo of Earth rising over limb of the moon in foreground, etc. was done with photo shop & that there is nothing to prove that the moon rocks, etc. were from the moon, & astronauts are paid well to lie, etc. The whole scheme was just to divert billions of tax payer´s dollars into the pockets of the few who staged it all. How can you be so naive as to think man actually walked on the moon when movies show him doing so with credits to the "special effects" department?
Some people prefer to hold fast to their ignorant POVs. I think the flat earth society still has a few dozen firmly believing members.
Lunar boom: Why we'll soon be mining the moon
May 16, 2012
As history has repeatedly shown, where there are valuable minerals to be unearthed, adventurous humans will arrive in droves – even if it means battling extreme conditions and risking life and limb.
So what will happen when the next great “gold rush” in our history is quite literally out of this world? And what kind of technology would be needed for the mining? After many years of trying, I believe I have a workable answer to the second of these questions – but what about the first?
Business analysts may poke fun at the “impossibly” expensive cost of mining nearby celestial bodies such as asteroids, or even the moon, but these pursuits are not beyond the realm of possibility.
Returning to the moon for the purposes of mining will require new technologies and new ways of thinking, and this extends to the conventional business model. We cannot write these pursuits off based on high cost alone, especially given the hidden treasures to be found.
more at link.
Perhaps the future of space exploration lies in the hands of private enterprises rather than the U.S. government (or any government for that matter). Within this century, space will become commercialized. I have no doubt in my mind.
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