Why not construct an Earth-based mass driver in order to throw stuff into orbit?<br /><br />The basic construction would be a cylindrical tube, several kilometers long. The tube would be level for much of the way, but would angle upwards and into the core of a mountain (say kilomanjaro, as it's close to the equator, although other sites would work as well). The exit point for the tube is located at/near the summit. The tube would be pumped to (near) vacum and lined with magnetic motors (much like monorails). Cars could then be accelerated to great speeds and launched upwards. To provide secondary thrust, the car could be equipped with a rocet motor itself, or an ice pack could be strapped to the rear of the car, to be vaporized by lasers emplaced at the summit near the tube exit point. The acceleration in such a system could also allow passenger cars to use it, assuming the tube was long enough to accomodate the slower acceleration.
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When there's a maglev line linking Baltimore and Washington DC, or SF and LA, <i>then</i> we'll talk about building one up the side of a mountain. I'm not holding my breath. <img src="/images/icons/wink.gif" /><br /><br />Massdrivers, cannons, and the like have been discussed as a good, cheap way to orbit bulk consumables for space stations (water, food, air, propellants), and maybe even raw materials for on-orbit construction. You use that to create the infrastructure required to go back to the Moon, build a massdriver there to send up materials there, turn the Moon into a prison colony, watch rednecks flock TO the places where the revolting colonists say they're going to land massdriver-thrown chunks of rock...
Does anyone have a reasonable cost estimate for such a system? It's a pretty large engineering undertaking, but is there anything in it that we couldn't do today? I really don't see any reason why this wouldn't be feasible. Thoughts?
Yes, I've read this book too, quite a good read. <br /><br />The laser system would be nice, but I don't see why a conventional propulsion system couldn't be integrated into the car instead. As for the exit point, if the car was given a sufficiently aerodynamic shape, why couldn't a simple airlock be used? Granted, the doors of the lock would have to be spaced quite a distance apart so as to give them enough time to open when the car is traveling at speed. After a launch, the section between the doors can be depressurized again without having to mess with the bulk of the tube. I'm not an engineer, just an enthusiast, so please point out any obvious errors on my part. I just see a construction like this as being enormously profitable.
"A few kilometers" was clearly a gross underestimation on my part. I should have done some math first, my bad. Still, all we'd need to do would be to extend the starting point of the tube, nothing that requires a technological quantum leap. Perhaps a constant 3Gs?
While I have no question that a concept like this is no way impossible to implement, there are several elements that may also need to be considered:<br /><br />1. There would probably have to be sequential airlocks throughout the 'tube' to efficiently maintain a vacuum and structural integrity of the chamber, a potential safety risk if one fails!<br /><br />2. If it were to be accelerated to a velocity where it would be capable of reaching orbit, then this would have to be significantly higher than just orbital velocity to compensate for the loss due to air pressure. <br /><br />3. The large g-force experienced during acceleration, would also be reversed and amplified on exit of the tube due to the now exposure to air pressure, posing a significant risk of damage to the space craft and cargo, whether that be equipment, supplies or people.<br /><br />This is where a chemical rocket may be of an advantage compensating for this deceleration on the exit, the vehicle structure though would have to be immensly strong to withstand these intense compression forces.<br /><br />Maglev, while a very effective technology, it is not very efficient, something along the lines of a rail gun may be more appropriate, it would be significantly simpler and easier to maintain (if you have a couple of hundred km of track to check everytime you launch.) due to the simplicstic nature of the system.<br /><br />But considering this, it may be a more practical solution to single stage to orbit.<br /><br /> <div class="Discussion_UserSignature"> </div>
Mach 25 at 30000 feet is going to tax your TPS. You will also dissipate velocity up to roughly 400000 feet and it will either need to be made up with an upper stage (which implies boosting more mass) or an even higher speed at the termination of the acceleration device.<br /><br />Probably would like like to see small refueling modules shot to space station first as a proof of concept technology demonstrator. Work out the kinks with cheap payloads, then upgrade system to launch items more complex than fuel bladders. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
<font color="yellow">"Mach 25 at 30000 feet is going to tax your TPS"</font><br /><br />Drag force is directly proportional to air density and square of speed. Columbia did Mach 18 at 207000ft when it went kaput. Density at that altitude is, according to 1976 standard atmosphere calculator, 0.0002kg/m<sup>3</sup>. 30000ft gives 0.4583kg/m<sup>3</sup>. So unless there are several orders of magnitude errors in that atmospheric model, the TPS taxing will be over in milliseconds and then rest of the craft is 'taxed' as well...
Hmm, the drag was the part of the whole concept that seemed to me to be the hardest to overcome. Are there any ideas? Would, perhaps, a sufficiently "needle-like" car shape solve the problem? Also, it would seem to be a good idea to have some form of booster on the car to correct for loss of velocity due to drag and to provide the delta-V to put the car into an orbit.<br /><br />I like seeing the idea bounced around like this, it's exactly what I was hoping would happen, let's keep at it. Who knows, maybe we'll come up with something really gold, lol.
IMO only practical solution is to forget achieving near orbital speeds at the end of the accelerator. Even just 1000m/s initial speed would save a lot of fuel on the space craft, allowing making it more sturdy that it might be able to survive the mass driver. Is it worth the trouble and effort, billions in static infrastructure and fighting environmentalists/politics for the few possible locations on earth, that's another question. I'd go for XB-70 style 'White Knight' carrier aircraft if complex first stage is a must.
I think if you calculate the kwh requirements to accelerate 1 ton, 10 tons and 100 tons at 9g for 6 or 7 kilometers you will be astonished. I think the 100 ton number will be a significant fraction of total northern American installed generator capacity.<br /><br />Gonna need a heavy extension cord for this gadget. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
<font color="yellow">a single-stage to orbit rocket plane launched on a very long guide rail</font><br /><br />I'm no engineer either, but it sounds to me like a two-stage rocket, where the first stage is tied to the ground, contributing speed but no altitude, so when the second stage lights, it's still in the thick of the atmosphere. That hurts drag, it hurts engine performance because the nozzle isn't as specialized to a certain pressure...
<font color="yellow">Yes, but wouldn't the fact that the rocket plane would be given a tremendous momentum before it would have to use any of it's own fuel give it a performance advantage over a vehicle that had to carry ALL of it's fuel from a standstill?</font><br /><br />The second stage of a rocket gets a tremendous momentum before it has to use any of its own fuel. Or from the other side, the vehicle does carry all of its fuel from a standstill, it's just that a big chunk of that fuel is in the scramjet sled.<br /><br />I think the big advantage to a maglev style launcher is that the fuel source for the first stage is finally put somewhere that it doesn't have to move. If the power source to drive the maglev sled was inside the sled, it'd be useless, because it's still moving. By shifting the power source to the ground... a hydroelectric dam, a nuclear plant, whatever... it's not moving, you don't waste energy moving it, the only thing being moved is the fairly light sled and the thing you actually want to put in space.
Which, of course, is exactly what we're talking about with a mass driver. It can be scaled up or scaled down, but the concept is the same. And it's a good concept too.
No need for a 370Km track.<br />Accelerate most of the way in a circular tube with a large enough diameter that only a small fraction of the mass is pushing against the rail the outside (to reduce stractuale stressess to minimum).<br />You can bury the tube horizontally under ground like particles accelerator with only the nozzle coming out. This may help to keep the reduced atmosphere and to handle structural stresses a 10 mile track may be sufficient.<br /><br />The biggest problem is the out point. The friction with the air and the sonic shock waves may disintegrate everything. There should be some smart engineering involved.<br /><br />Best.
Everyone seems to be missing the main point. The limiting factor is Max Q. There is simply no way to push an object through the atmosphere at a high enough velocity to reach orbit, let alone orbital velocity at lower altitudes, and there are no mountains high enough to reach that altitude. I don’t recall what that altitude is, but that is the point at which the STS says “Go at Throttle Up”. They have to keep it throttled back until they reach that altitude.<br /><br />Having said that, a rail launch assist could be used to reduce the amount of fuel used at launch by providing the initial velocity, about Mach 1.5 IIRC. There would be an initial fuel savings plus the savings of the fuel needed to lift that fuel.<br /> <div class="Discussion_UserSignature"> <p style="margin-top:0in;margin-left:0in;margin-right:0in" class="MsoNormal"><font face="Times New Roman" size="2" color="#ff0000"><strong>Our Solar System must be passing through a Non Sequitur area of space.</strong></font></p> </div>
The other basic problem not explicitly mentioned here is that you cannot achieve orbit without a second stage or a guided flight path. An object tossed upwards will always return to the same altitude it was tossed from. You have to modify the ballistic path or your trajectory will intersect the planet's surface.<br /><br />Even on an airless world, even if you have orbital velocity at time of launch, the ellipse of your attempted orbit is bound to the center of that world, and it will have a perigee less than the launch altitude.<br /><br />IOW, lithocapture. 
The Big Crunch. The spacecraft is replaced by a crater, you get the idea.<br /><br />The only exception is if you actually exceed escape velocity at the time of launch. Actually it's not an exception because escaping the gravity field is still not achieving orbit.<br /><br />With atmosphere, Max Q is HUGE. Build it with unobtainium.<br /><br />Another big problem is the fact that a horizontal track forces you to change your velocity vector to go *upwards* - whether before or after release - and the g-forces are HUGE if you want a reasonable turn radius. Plus you either have to build on a mountain or have very strong (heavy) wings.<br /><br />Rail launch does hold out some hope for outsmarting the rocket equation. But I have yet to see an actual plan with valid calculations demonstrating the theoretical possibility, let alone dealing with the practicalities.<br /> <div class="Discussion_UserSignature"> </div>
The Big Crunch. The spacecraft is replaced by a crater, you get the idea.<br /><br />The only exception is if you actually exceed escape velocity at the time of launch. Actually it's not an exception because escaping the gravity field is still not achieving orbit.<br /><br />With atmosphere, Max Q is HUGE. Build it with unobtainium.<br /><br />Another big problem is the fact that a horizontal track forces you to change your velocity vector to go *upwards* - whether before or after release - and the g-forces are HUGE if you want a reasonable turn radius. Plus you either have to build on a mountain or have very strong (heavy) wings.<br /><br />Rail launch does hold out some hope for outsmarting the rocket equation. But I have yet to see an actual plan with valid calculations demonstrating the theoretical possibility, let alone dealing with the practicalities.<br /> <div class="Discussion_UserSignature"> </div>Suspend the rail gun or maglev launch rail from a high altititude ballon. That would get you out of the thickest part of the atmosphere.<br /><br />LOL<br /><br />And No I'm not being serious.
Not to throw cold water on this thread but….Balloon supported MD launch was proposed in the 80s. Others have argued that the initial mass movement is what takes most of the fuel for orbit so they propose to let gravity accelerate the mass first DOWN a slope to a horizontal (curved buried tracks cannot be supported at high velocities from a bearing or maglev design without great arcs considered too large for financial viability.. See costs for the Chunnel Project between UK and France) track for more acceleration, then up a steep incline where chemical rockets assist the climb to orbit. We actually do put things in orbit with chemical rockets already but the fuel and reduced payload mass make it very expensive. The former Soviet launch company initially marketed payloads to orbit at $600/lb. The US government however, lobbied by several defense contractors, forced them to raise their rates comparable to current US launchers and the Shuttle ($8K to $10K) to subsidize the space launch industry. The Russians maintain that they can launch payloads into orbit for less that $600/lbs. but the US Congress will outlaw export of any technology for launch of they do and several joint efforts and funding to Russia would be withdrawn. In all this thread, I have heard nobody discuss what the viability requirement would be concerning cost to orbit numbers. From this thread, it is known there is yet the technology to create a vacuum tube that can do the job or that energy efficiencies can power such a MD on a gravitational mass with atmosphere. Rail guns and MD were proposed for hard vacuum environments. So the closer you start to vacuum the better, i.e. balloon support rail launches in the upper thin atmosphere. Great if there were no air currents and no airspace violations, but realistically impractical as the MD from Earth. It is NOT important how to get to space, but how it is paid for. If an HLLV can do the job or a space elevator is viable, then so be it. But this i
Mach 1.5 might be good, but the prototype should be sub sonic. How about a 7 kilometer tube with vacuum in front and compressed air to accelerate the projectal? Maglev only the first kilometer. A 45 degree up slope for the first 3 or 4 kilometers, changing gradually to about 85 degrees, so as to get the projectal out of the atmosphere as quickly as possible. Some mountains in Equidor are about 26,000 feet. There is presently negigible infrastructure at the low end of tube, so a world class jet air port and a small city is needed at perhaps twice the altitude of Denver, Colorado. My guess is too costly for a 2nd stage with a tiny amount of delta V. Getting to the jet port is the first stage and a third stage is needed to get to Earth orbit or solar orbit. I understand payload is reduced drastically for a jet plane taking off from 10,000 feet, but landing is not a problem. Neil
It would be best to exit at a speed that would be ideal for operating a RAM/SCRAM jet. The biggest hurtle in a SCRAM jet stage intermitant to orbit is the need to accelerate the plane to a speed to operate it. (biggest hurtle besides the actual engine isn't yet fully proven) This could eliminate an engine/stage from the orbiter making it lighter and having a better initial mass fraction. <br /><br />Also I believe that the drag forces that would be expirenced after exiting would be a large shock to the plance/car. The airlock stage could be at partial atmospheric pressure to reduce this shock. The partial atmospheric pressure would also allow the SCRAM jet to automatically start before it exited the tunnel.
The only problem is a Ram/Sram jet would only work for a few minutes or less before it ran out of atmosphere.<br /><br />The only reason SCRAM Jets are being studied is to power Nuclear armed re-entry vehicles that can maneuver away from defensive weapons. They have no use at all for launch systems. <div class="Discussion_UserSignature"> </div>
Yes very true, furthermore is the fact that with the higher density of air near sea level, or even 30,000 ft is the much higher airframe heating. I haven't done the calculations, but it is probable that it would be more than could be removed through active cooling through cryogenic fuels.<br /><br />That being said the an intelligent design of a scramjet engine should also be able to function as a rocket motor. Any feasible design of a SCRAM jet I have seen will require regenerative cooling to not melt down. Same as most rocket motors. <br /><br />Could the back end of the Rocket/plane be used as a nozzle like inside the atmosphere. Would this function as half of an aerospike nozzle?
I don't know how efficient it would be using an aerospike nozzle but a fixed bell nozzle would be pretty inefficient. The problem still remains getting to a point a Scram-jet or even a Ram-Jet could be usable. <br /><br />Overall it seems kind of useless to field an air breathing engine that would be used for two or three minutes of a launch.<br /><br />Maybe a dual cycle engine would work. A large turbofan engine ducted into a combustion chamber where Hydrogen or even kerosene is added. as air density decreases LOX is fed in and the engine is shut down. The problem would still be the nozzle though. <div class="Discussion_UserSignature"> </div>
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