Cheap Space Launch: Place Your Bets!

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soccerguy789

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Alright, Eventually, access to space needs to get cheaper, and eventually, it's going to happen. I'm talking major reductions, and a complete rithink of how it's done. I'm talking about changes far more dramatic than what they are talking about with the CXV or falcon projects. I'm talking Scramjets and Space elevators. So tell me, What do you think is going to come first, and what do you think will work best?
 
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mlorrey

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space elevators will not get the mass in orbit they need until launch costs come down considerably, to $1000/lb or less. This requires that all operating boosters must have some air breathing capacity below 150,000 ft, to raise average vehicle Isp without going to exotic fuels or nuclear. Serious consideration of nuclear propelled upper stages should also be given, also to raise average Isp. Using hydrogen for these upper stages will ensure that none of its radiation will fall back to the surface of Earth.<br /><br />SCRAMjet technology is not necessarily required, esp given the issues with current materials technology and hypersonic heating. Simple ramjet technology with rocket ejector modes would provide significant help.<br /><br />That being said, once nanotube technology gets good enough to build a tether, building entire airframes and TPS for a vehicle from the same material would also become possible, which would make RLV SSTO and SCRAMjet RBCC propulsion from ground to orbit completely feasible. <br /><br />It is likely you could build such a launcher in less time than it would take to build a GEO tether, so such launchers would likely be built to put such a tether in orbit.
 
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josh_simonson

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I like the single stage to tether option. It takes the easiest parts of the re-useable SSTO and the space elevator and puts them together. No climber, minimal TPS, high flight rate, a partial gravity LEO platform to work and live on. There's a lot of things going for it. <br /><br />Another thing that might be even cheaper for cargo (not people) would be an airship mounted mass driver.
 
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mlorrey

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absurd, Josh. Do you know how large a mass driver has to be? First I'd suggest (once again) you do your homework and read up on Gerald Bull's work with gun launching, then do some real calculations. You'd need a mass driver kilometers long to launch something to space from earth, even if you could have it at altitude, altitude is not the problem, velocity is, and you are not going to be able to lift a big enough mass driver with an airship. The best you can do is build one up the side of a mountain.
 
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josh_simonson

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Lab scale railguns fire at twice orbital velocity right now, just get the atmosphere out of the way and it's not a problem - hence the airship to get most of the atmosphere out of the way. Sure it might be big, but airships are cheap to build big. JPaerospace's high altitude missions inspired the idea.<br /><br />There's no reason to be condescending, poor sportsmanship is counterproductive. It's not like NASA's spending 10 billion on my airship-mass-driver that could be spent on your hyper-dart. It didn't even seem like you understood the gist of my post when you slammed it.
 
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najab

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Jerry Bull got 85% of the way to orbit with 2 18-inch Battleship guns mounted end-to-end and bored out to 19-inches.<br /><br />Total weight of the gun was ~140 tons, total length about 80 feet.
 
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tap_sa

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<font color="yellow">"Jerry Bull got 85% of the way to orbit"</font><br /><br />Measured how?
 
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najab

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Height and velocity - they could get up to height (I think the peak altitude reached was ~90 miles), and were working on an 'upper stage' that would get orbital velocity.
 
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tap_sa

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Do you have information what the projectile velocity was at apogee (or at the moment the upper stage would have ignited) ? Just curious about how much of the total orbital energy required the gun part would have contributed.
 
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najab

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I'm not sure...there isn't a great deal of detailed information out there. There's an EA article about the Martlett 2G, but I know this was only a crash effort when the project funds were drying up- Bull's real goal was to be able to put a few hundred kilos up at a time.
 
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tap_sa

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<font color="yellow">"There's an EA article about the Martlett 2G"</font><br /><br />1,900m/s muzzle velocity so there's still a lot of dv to do for the two stage half tonne projectile. Too bad Bull was so reckless about politics, it would have been interesting to see how this concept would have played out.<br /><br /><br />Jordin Kare promotes beam propulsion as CATS for small payloads. Here's a paper heavy with numbers and a presentation for easier digestability.
 
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mlorrey

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Josh, what is the payload size of the railguns that achieve 'twice orbital velocity'?<br /><br />Firstly, ANY use of such velocity in atmosphere dense enough to float an airship is going to incur massive aerodynamic losses from hypersonic shock effects.<br /><br />Secondly, the length, mass and power requirements of mass drivers scale with the payload size, so an 80' long mass driver that drives a 100 gram payload is going to be monstrous to drive a 100 kg payload.<br /><br />Thirdly, how are you going to power your airship mass driver? You going to run an extension cord to the surface? How are you going to accumulate the power for the shots? You are talking some significant mass for the capacitors. I happen to know quite a bit about mass drivers, I've built a few, so I know what requirements they have.<br /><br />If I "slam" your ideas Josh, it is because you've established a reputation on this forum of making unsupported assertions without backing them up with any numbers, calculations, or references. You don't do your homework. <br /><br />You shouldn't expect any better treatment from any other objective scientific forum intent on anything other than lip flapping.
 
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mlorrey

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NajaB,<br />Altitude means little with getting to space. Essentially, airlaunching at 50,000 at 600 mph gives you about 5% savings on your mass fraction.<br /><br />Reaching 90 mile altitudes, in a vertical trajectory, with no downrange velocity, means very little with 'getting into orbit' unless you are launching to a plaform suspended from a geosynchronous tether.
 
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najab

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><i>Reaching 90 mile altitudes, in a vertical trajectory, with no downrange velocity, means very little with 'getting into orbit' unless you...</i><p>Or, the payload you get up to 90 miles then lights its engine and starts accelerating - above 99.9% of the atmosphere.</p>
 
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mlorrey

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Actually, 90 miles is above all of the conventionally measurable atmosphere (at least as far as airspeed indicators are concerned). However, you get 90% of the savings by simply airlaunching at 50,000 feet, which is above 90% of the mass in the air column. <br /><br />IMHO a proper gun launcher would launch a vehicle whose first stage is a scramjet, launched at a 45 degree angle and about mach 2.5. This would put your upper stage in a trajectory where the 2nd stage will light off at 60 miles altitude going mach 12 downrange. The 2nd stage will have a payload fraction of about 30%, depending on Isp.<br /><br />Gun launching is not easy, you can't just stick a normal rocket in it. The G forces it experiences are insanely high. The Martlett, for instance, demonstrated this by requiring a plug up through each rocket engine nozzle filling the entire chamber, otherwise the gun's G forces would have forced the fuel to settle in that space and the engine would not light.
 
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spacefire

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the future is somrthing like the Orion, only with converntional explosives. The trick is to fire pellets of fuel from a ring of cannons towards the rear of your ship and ignite them with a laser when they reach it. The second stage could be a fuel-less ramjet where air is heated explosively by the same laer. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>
 
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henryhallam

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<font color="yellow"><br /><br />the future is somrthing like the Orion, only with converntional explosives. The trick is to fire pellets of fuel from a ring of cannons towards the rear of your ship and ignite them with a laser when they reach it. The second stage could be a fuel-less ramjet where air is heated explosively by the same laer.<br /></font><br /><br />Why would the mostly undirected blast from a chemical explosive give better Isp than the carefully controlled combustion and expansion of hydrogen and oxygen? (the chemical reation that is the most exothermic possible for a given mass, apart from fluorine) Not to mention the extra mass of a pusher plate and shock absorbers. Orion is a terribly inefficient mechanism and only makes sense when you have the prodigious amount of energy that you get from nukes.<br /><br />Why use air as reaction mass in the SECOND stage? <br /><br />Where do you get the energy to run this mythical lightweight ~megawatt laser? Is it supposed to be ground-based?
 
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josh_simonson

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Airships can get above 99% of the atmosphere, certainly that makes gun launching from there easier. Mylar and helium are cheap, there's no reason you couldn't have a string of modular balloons supporting a huge gun - and if you want a high/cheap flight rate the one-off cost of the mylar and helium is alot cheaper than a complex engine on every payload. You could probably get by on a small booster to circularize the orbit enough to not re-enter.<br /><br />Though big, it's certainly less grand than a space elevator, and the power concerns are much simpler than some other power beaming concepts. <br /><br />It's undoubtedly cheaper and easier to do once you've got the high-altitude platform, so the only question is wether the balloons cost more than what they save at a given launch rate. There's certainly a point where this solution is better. It doesn't need to use a railgun either, a light gas gun or other system may prove better, since weight is an issue.
 
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mlorrey

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"Why would the mostly undirected blast from a chemical explosive give better Isp than the carefully controlled combustion and expansion of hydrogen and oxygen? "<br /><br />Good question, Henry. It is primarily because 'carefully controlled combustion' in a rocket engine is a deflagration-type combustion. Explosives combust through detonation, which is automatically much more efficient than deflagration.
 
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tap_sa

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<font color="yellow">"Explosives combust through detonation, which is automatically much more efficient than deflagration."</font><br /><br />In what way more efficient?
 
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henryhallam

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Faster, certainly, but why is it more efficient? I didn't know that was the case but I'd be interested to know the details.
 
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nacnud

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I think it is more effiecent, try looking up pulse detonation engines, you might find an explanation there (or maybe not, you might find a lot of dodgy Aurora sites <img src="/images/icons/crazy.gif" /> )
 
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spacelifejunkie

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Since we are in "hypothetical proposal land" what about this...<br /><br />1. A "White Knight 2" like vehicle raises a lifting body craft to 30,000 ft and a few hundred mph where it is dropped.<br />2. A pulsed detonation engine using O2 from the atmosphere raises altitude and speed to Mach 4+ and 100,000+ ft. <br />3. The PDE switches to LOX onboard to go the rest of the way to LEO.<br /><br /><br />My questions for the forum are these... <br />Has a PDE ever successfully been demonstrated using LOX in a vaccuum? <br />How much fuel would be saved compared to ramjets and rockets?<br /><br />It's not as sexy as SE's and Scramjets but it's completely resusable and there are no stages thrown away. Just a thought. If successful, refueling in space and going to the moon would be the next logical step.<br /><br /><br />SLJ
 
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gunsandrockets

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"I'm talking about changes far more dramatic than what they are talking about with the CXV or falcon projects. I'm talking Scramjets and Space elevators. So tell me, What do you think is going to come first, and what do you think will work best?"<br /><br />My favorite cadidate for exotic CATS is the JP Aerospace orbital airship. Wacky? true, but not as wacky as orbital towers which depend on presently non-existant materiel or beamed propulsion rockets which depend on presently non-existant beamers.<br /><br />On the other hand I am curious
 
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mlorrey

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Because it detonates, the combustion creates greater pressure, creates a shock wave from the supersonic combustion, and propells its waste gasses at higher velocities than would a deflagration combustion. Higher velocity for the same mass of waste products means greater thrust per pound of propellant, ergo higher Isp.
 
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