Cheap Space Launch: Place Your Bets!

[spacefire]

the obvious reason for sending explosives up to to the launcher rather than the launcher carrying fuel in it doesn't have anything to do with ISP...it's just that it's cheaper to run an installation on the ground (cannons, laser) which can deliver immense amounts of fuel to burn, rather than store a limited amount of fuel inside the craft itself. flight hardware is always going to be more expensive than ground hardware. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[bwhite]

JP Aerospace is way cool and thus far I have not read anything to persuade me it not possible. But until they do it . . .<br /><br />= = =<br /><br />An idea I have had before is to look at plastic SRBs.<br /><br />The Thiokol RSRM has an 85/15 fuel to dry mass ratio and a 4 segment has 192,000 pounds of structure (that's the 15%). A 5 segment would have 240,000 pounds of structure and this is all with 1970s metallurgy.<br /><br />Keep the fuel cores identical. No changes whatsoever. But re-design the casing to use carbon fiber, Kevlar, ceramic coatings, whatever 21st century composite materials we can think up. Not everywhere, but everywhere that is feasible to reduce dry mass. <br /><br />Reduce the mass of the structure by 1/3rd (92.5 / 7.5) and you can add 80,000 pounds to your 2nd stage payload, for a 5 segment booster. <br /><br />Reduce the dry structural mass by 50% and you can add 120,000 pounds to your 2nd stage payload, again for a 5 segment.<br /><br />For a cargo only "stick" you might top 100,000 pounds net to LEO - - add these savings to the current payload of the proposed stick. Not a bad HLLV for a single stick.<br /><br />NASA has been paying $35M for 4 segment RSRM. $75M for a 5 segment plus how much for a seven (7) RL-10 second stage? $1000 per pound? Its a Proton killer if nothing else. <br /><br />= = =<br /><br />PS - Obviously, its not re-useable. ;-)<br /><br />Use aluminum to fashion a rigid superstructure or skeleton framework and stretch composites to hold the pressure in.

 

[henryhallam]

<font color="yellow"><br />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.</font><br /><br />I haven't taken my thermofluids module yet but I thought that the point of a rocket nozzle was to transform essentially all of the thermal, pressure and undirected kinetic energy in the combusted gas into uniformly directed kinetic energy, i.e. they convert all the energy available into motion.<br /><br />So the gases released by a detonated explosive might have higher initial velocity than those from a deflagration, but they are in all directions so wouldn't only a certain component of them act in a useful direction to produce thrust?<br /><br />Are you saying that detonation releases more <b>overall</b> energy than "ordinary" combustion? Or just that the energy is released in a more useful form?

 

[najab]

I'm not saying it can't be done, but they tried this already - the fillament-wound SRB case was being developed to give the Shuttle enough performance to allow KH-12 deployment missions from VAFB.<br /><br />Many expected them to explode on the first launch.

 

[bwhite]

Thanks for the suggested google words (filament wound)<br /><br />Italy has recently test fired a composite SRB with a 91% - 9% fuel to dry mass ratio.<br /><br />http://www.spacedaily.com/news/Successful_First_Test_For_Vega_Zefiro_9_Engine.html<br /><br />= = =<br /><br />The alt-space RLV mantra has been RLV space-planes, RLV space-planes, RLV space-planes. But for slogging fuel to LEO, a mass produced plastic disposable solid rocket with very high fuel to dry mass ratios should lower costs as well.<br /><br />If there was a sufficiently high flight rate to churn them out on an assembly line and amortize tooling costs over a high volume of units produced.<br /><br />I read somewhere that an RL-10 is no more complicated (or finely engineered) than a gas turbine helo engine but because gas turbine engines are made in the thousands they cost $100,000 each while RL-10s are in the millions of dollars per unit. Slog fuel on a plastic solid with an RL-10 upper stage and make thousands of them and costs should fall through the floor.<br /><br />= = =<br /><br />If true, then the secret to low cost to LEO is more DEMAND, not break through engineering.

 

[josh_simonson]

The energy density of high explosives is comparable to that of LOX/LH2 - and you truely would be on top of a 'flying bomb'. A launch failure would make a MOAB look tiny.<br /><br />The only mention I've found of high explosives used in rocketry was nitro-glycerine in ballistite, it was inhibited to burn slowly, but ISP wasn't all that great, only to the upper 200s.<br /><br />However, pulse detonation engines don't require high explosives - they can also detonate a mixture of O2/H2(or other fuel). The nozzle and valves of these engines need to be very robust, which is why they're still a work in progress at the moment. They don't offer much higher ISP either, rather they attempt to simplify rocket/jet engines mechanically and increase T/W ratio. <br /><br />Interestingly, by varying pulse frequency their DC thrust can be throttled from 0 to 100%. Being lighter and highly throttleable, pulse detonation engines should lend themselves to 'engine out' designs better than current engines.<br /><br />Here's the air breathing and rocket version descriptions:<br />http://www.grc.nasa.gov/WWW/AERO/base/pdet.htm<br />http://www.nasa.gov/centers/marshall/pdf/100369main_pulse_detonate.pdf

 

[mlorrey]

"I haven't taken my thermofluids module yet but I thought that the point of a rocket nozzle was to transform essentially all of the thermal, pressure and undirected kinetic energy in the combusted gas into uniformly directed kinetic energy, i.e. they convert all the energy available into motion. <br /><br />So the gases released by a detonated explosive might have higher initial velocity than those from a deflagration, but they are in all directions so wouldn't only a certain component of them act in a useful direction to produce thrust? <br /><br />Are you saying that detonation releases more overall energy than "ordinary" combustion? Or just that the energy is released in a more useful form? "<br /><br />I am not an explosives expert, but my understanding is that more of the fuel burns much faster in detonation, which is why you get the supersonic expansion wave, versus the subsonic effects of deflagration.<br /><br />One assumption you are making that is not quite accurate is to assume that a detonation will go in all directions with no nozzle-like structure. It was only in the Orion project that they proposed a simple pusher plate, primarily because the explosive energy of nukes is so high that normal materials can only take so much. More modern designs, like Daedelus, envision a hemispherical nozzle.<br /><br />Chemically powered Pulse Detonation Engines currently in development are generally straight tubes that are built to resonate the shock waves so that resonances from previous detonations ignite following detonations, as well as to direct all exhaust gasses rearward. <br /><br />A PDE does not require a converging/diverging nozzle like a rocket engine does for the same reason that a scramjet doesn't need one, but a ramjet does.

 

[henryhallam]

Okay, thanks for the explanation. This does sound interesting, I will have to read up on it more.

 

[soccerguy789]

Has anyone else read the book "The Space elevator" It discusses the ribbon model, and really makes it seem very possible. of course this would be the point of any book put out by Dr. Edwards, butthe numbers make sense, and it is not only easily expandable, but the more you have,m the cheaper they get to build. They discuss designs for up to several hundred tons at a time. They also have the ability to fling spacecraft from earth's orbit. That seems very nice.<br /><br />Scramjets, ejector ramjets, and other air-breathing rocket engines, on the other hand, seem more realistic, even after reading a book supporting elevators. such spaceplanes are extremely scaleable, and while they cannot fling cargo out of orbit, the design costs, whihc are the priomary cost for a fleet that could be very large, are similar to those of 1 space elevator.<br /><br />So what do you think, any even beter ideas. I think rail launchers may be used on scramjet vehicles, or could they take off and land like airplanes with little consiquence. lets hear it?!

 

[mlorrey]

I think that until we actually build a space elevator, we are going to need to use the best we can build for launchers.<br /><br />It seems to me that the best launcher plan is the following three stage system:<br /><br />a) launch rail/tube/tow/catapult: <br /> speed: 0 to ~M0.5<br /> altitude: 0 to 1,000-10,000 ft<br /> reusability: high, fixed infrastructure, highly reliable<br /> Isp: infinite<br /><br />b) ramjet (possibly using MIPCC, structural cooling, and other techniques to increase range of ramjet propulsion)<br /> speed: M0.5 to M8-10<br /> altitude: up to 160,000 ft<br /> reusability: high, no significant TPS to recover functional stage, potential self guided vertical landing.<br /> Isp: 1500-2400 secs<br /><br />c) nuclear upper stage, or possibly chemical PDE:<br /> speed: M8-10 to M25+<br /> altitude: 160,000 to infinity<br /> Isp: 600-800 (nuke), 1000-4000 (PDE)<br />Upper stage reusability: dependent on need. Could carry shell TPS in trade-off for payload capacity. TPS equipped vehicles could collect propulsion systems from other vehicles in orbit to return them to earth for servicing and re-use. Fuel tanks are not worth recovering, can be recycled as habitat space in orbit, on lunar or martian surfaces, or used as cargo pods or LunOX transport tanks.

 

[craig42]

Any technology that satisfies a demand for a high flight rate