propellant

[Peter the Dane]

would it be possibel to use explosives as fuel i a rocket?<br />eigther in launch or as in space propelant?<br /><br />

 

[najab]

If you mean as a means of propulsion - yes, but you'd have to deal with the fact that instead of a steady continuous thrust, there would be a series of violent explosions.

 

[vogon13]

I love talking about Orion!<br /><br />Orion propulsion concept is simply shoving a nuke out the butt end of a space ship every second or so and riding the explosions any where you want to go.<br /><br />All developed back in the fifties and sixties. Very well thought out, but never prototyped with nukes. Conventional explosives were tried once, and worked for 4 or 5 shots.<br /><br />Folks working on project felt Saturn (the planet) was achievable with a manned craft by 1970.<br /><br />Test ban treaty and some engineering questions stopped development in mid sixties.<br /><br />Big question about the technology was scaling it down enough to be useful (a small Orion spaceship weighs 4000 tons) and fireball engulfment of the vehicle during the first few detonations after launch. Cleaning up the radiological hazards of the nukes is also a problem, but boron in the radiation channel of the directed energy nuke design would have made quite a difference (IMO). Subcritical, boosted high yield nuclear cores probably can be made to burn fairly cleanly.<br /><br /> <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>

 

[scottb50]

Might be a rather wild ride! <div class="Discussion_UserSignature"> </div>

 

[tap_sa]

If you are thinking using ordinary explosives such as TNT then the answer is maybe, but definitely not worth the trouble. Good chemical propellant must contain a lot of energy per mass, ordinary explosives don't. For instance TNT contains only 4.2MJ/kg while ordinary gasoline 45MJ/kg and hydrogen 142MJ/kg. Here energy content means the amount of energy released when given mass is detonated or burned. In rockets we must account for the LOX need so actual MJ/kg figures for propellant will be lower, depending on mixture ratios. TNT requires no LOX so it would still be 4.2MJ/kg, hydrogen in common 6:1 ratio would result 142/7=20.3MJ/kg of propellant, still almost five times that of TNT.

 

[Peter the Dane]

yes I would like to use it as propulsion.<br /><br />I guess there will be some work to be done in rd to develop "engines" that can handel the forces. <br /><br />one solution meigth be having 10 or more engines that fire in pairs? <br /><br />

 

[Peter the Dane]

I read about development of new high energy explosives, containing more than usual of nitrogen. making them very energy rich.<br />later, at work ;-) , I were thinking in how to build the next generation of heavy launchers, what are needed to send 100+ metric tons in to orbit? energy. and lots of it.<br />as it is now the weigth of the energy supply are the troubel in it self.<br />using these very energy rich explosives will dramatically downscale the launcher. <br /><br />now the big question is, is it possibel to fire small "pellets" of explosives in an engine, and keep firing with very short intevals to deliver trust and speed? <br />

 

[najab]

It sounds like you are trying to build a pulse detonation engine. While these are fantastically efficient air-breathing engines, I don't think I've ever heard them proposed for spaceflight.

 

[tomnackid]

All chemical rockets are basically explosive devices. Hydrogen and oxygen is one of the most powerful chemical explosive combinations possible (substituting fluorine for oxygen can give you more power, but at the cost of having to handle an extremely corrosive and toxic substance). The reason more conventional explosives like TNT and nitroglycerine SEEM more powerful is that they react all at once. <br /><br />Using explosions for propulsion is usually not very efficient (pulse detonation engines are a special exception). The Orion concept only used a tiny fraction of an atomic bombs explosive power for propulsion. The concept works because nuclear energy is a million times more powerful than chemical energy so you can waste a LOT of power and still come out ahead.

 

[najab]

<blockquote><font class="small">In reply to:</font><hr /><p>All chemical rockets are basically explosive devices. Hydrogen and oxygen is one of the most powerful chemical explosive combinations possible...the reason more conventional explosives like TNT and nitroglycerine SEEM more powerful is that they react all at once.<p><hr /></p></p></blockquote>Hence the term 'explosive'. A hydrogen/oxygen mixture will almost always burn rather than explode, this is because the flame propagation speed is normally sub-sonic. It is only in special cases that you can get super-sonic propagation and an explosion proper.

 

[ve7rkt]

If you have ten engines firing in pairs, you're even worse off than one engine firing quickly. You haven't changed the fact that one pound of your explosive propellant gives less energy (less speed) to your ship than would one pound of hydrogen/oxygen propellant, and now you've got the added weight of nine extra engines.<br /><br />Interestingly, a model rocket motor is exactly the opposite of what you're talking about here. Low-end model rocket motors are black powder, a substance traditinally known for going boom, put together in such a way that it burns at a controlled speed instead.<br /><br />In addition to the Orion test with the conventional explosvies, you might want to read into the experiments done with laser propulsion. If I understand it right, you have a huge high powered laser on the ground firing up at the underside of a disc-shaped craft with little bits of ice on it. The laser bursts vaporize the ice, creating thrust.

 

[tap_sa]

<font color="yellow">"I read about development of new high energy explosives, containing more than usual of nitrogen. making them very energy rich. "</font><br /><br />Octanitrocubane?. 7.5MJ/kg, impressive for an explosive but wanting as a rocket propellant. I <i>think</i> it is impossible for chemical explosives to reach the energy content levels (MJ/kg) of chemical fuels. That's because desired properties of explosives (solid/plastic, insensitive to shock etc) require complex molecules which means a lot of energy is needed to break their bindings. If there's a chemist among readers, please verify or refute.