Choice of fuel in a launch vehicle

[pmn1]

What determines the choice of fuel in a launch vehicle? <div class="Discussion_UserSignature"> </div>

 

[propforce]

Depending on launch vehicle's missions...<br /><br />Also depending on available exisiting components for cost & schedule reasons. <div class="Discussion_UserSignature"> </div>

 

[drwayne]

Mission/performance requirements, packaging requirements, cost requirements, schedule requirements.<br /><br />I know that sounds like a pat answer, but its pretty much true.<br /><br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[henryhallam]

Hydrogen (LH2) provides the most energy per unit mass, but is much bulkier (less dense) than other fuels so it requires a larger, heavier tank. Liquid hydrogen (which is the only practical way to store it) is extremely cold, colder than liquid oxygen (20K vs. 90K) so there are plenty of cryogenics issues assosciated with storing and pumping it.<br /><br />Kerosene (RP1) does not provide as much energy per unit mass but is a much friendlier substance to store and pump, requiring smaller tanks and less complicated support equipment.<br /><br />These characteristics generally tend to favour LH2 for upper stages and RP1 for first stages but as the guys above me (who really know what they're talking about because they actually WORK in the business <img src="/images/icons/wink.gif" />) have said what actually ends up being used depends on a number of features - what engines do you have available, how much funding do you have for ground support equipment and personnel, what reliability do you require, how quickly must the vehicle be ready for launch etc etc.<br /><br />A third choice is of course hypergolic propellants. These tend to be really nasty and toxic, and give performance comparable to or worse than LOX/RP1, but the equipment is quite simple AND the propellants can be stored in the vehicle for very rapid launch readiness. <br /><br />Ideal for missiles, ideal when it HAS to work (Apollo LM and SPS engines)... not necessarily the best choice for a commercial launch vehicle. Though as demonstrated by Titan it can be done - and perhaps this example shows that the choice is probably determined by what's available and known to work, more than a lot of other factors.

 

[mikejz]

Don't forget about solids (if that counts as a fuel)

 

[propforce]

Don't forget aluminum as fuel....<br /><br />... most of time, it was an unintentional consequences, but it still burns nevertheless in the presence of liquid oxygen <img src="/images/icons/cool.gif" /> <div class="Discussion_UserSignature"> </div>

 

[drwayne]

Minor pseudo-quibble:<br /><br />LH2 and LOX are hypergolic (as a set)<br /><br />For that matter, kerosene is hypergolic with FLOX (but then again most of creation is hypergolic with FLOX)<br /><br />Failing miserably to make a long story short:<br /><br />Your third choise *might* be better labeled "storable liquids" rather than hypergolic. Thats the way we talk about it around here anyway. (We avoid talking about FLOX of course whenever possible - somewhere, someone has some, and its listening)<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[drwayne]

Actually, did you know that the HTPB commonly used as a binder in solids is actually a quite good fuel in itself?<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[Swampcat]

<font color="yellow">"... HTPB commonly used as a binder in solids is actually a quite good fuel in itself?"</font><br /><br />Yes, let's not forget about hybrids. HTPB was the primary fuel component of Space Ship One's motor. The oxidizer being nitrous oxide. N2O is generally used as a hybrid oxidizer despite being relatively low in oxygen content, IIRC about 30%. LOX can also be used, but N2O is non-cryogenic and safer to handle. <div class="Discussion_UserSignature"> <font size="3" color="#ff9900"><p><font size="1" color="#993300"><strong><em>------------------------------------------------------------------- </em></strong></font></p><p><font size="1" color="#993300"><strong><em>"I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."</em></strong></font></p><p><font size="1" color="#993300"><strong>Thomas Jefferson</strong></font></p></font> </div>

 

[Swampcat]

It is rather amazing what can be used as fuel in a hybrid motor. Typically, things like polyethylene, PVC and ABS plastics are used, but I've heard of people using cardboard, parafin and sugar among other things. <div class="Discussion_UserSignature"> <font size="3" color="#ff9900"><p><font size="1" color="#993300"><strong><em>------------------------------------------------------------------- </em></strong></font></p><p><font size="1" color="#993300"><strong><em>"I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."</em></strong></font></p><p><font size="1" color="#993300"><strong>Thomas Jefferson</strong></font></p></font> </div>

 

[josh_simonson]

>It is rather amazing what can be used as fuel in a hybrid motor. Typically, things like polyethylene, PVC and ABS plastics are used , but I've heard of people using cardboard, parafin and sugar among other things. <br /><br />Yup, it's the steam engine of the rocket world.

 

[henryhallam]

<font color="yellow"><br />LH2 and LOX are hypergolic (as a set) <br /></font><br />Interesting, I didn't know that! But presumably once they reach the chamber they are gaseous and no longer hypergolic so you still need a torch igniter or something to start the engine off?

 

[tap_sa]

<font color="yellow">"Interesting, I didn't know that! "</font><br /><br />Ditto. Is it the thermal shock that would set them going or what?

 

[propforce]

Neither do I. That makes 3 of us <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> </div>

 

[drwayne]

If you take a small amount of liquid hydrogen, and a small amount of liquid oxygen, you get water, and a boom. They react upon contact - which is essentially the definition of hypergolic.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[drwayne]

One of those things that you have to do - once in a lifetime.<br /><br />From an engine point of view you are of course right, its not as clean, because you have phases going on.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vogon13]

When launching an Orion vehicle from earth's surface, stick with the smaller nukes till your upward velocity (and oncoming air flow) is sufficient to arrest fireball engulfment of the vehicle. <br /><br />Also, at low altitudes, the atmosphere helps couple bomb energy to the pusher plate, so smaller nukes are acceptible in this flight regime. Probably easier on the launch facility, too.<br /><br />Most vehicles launched will achieve satisfactory performance from small fission devices. Low yield fusion bomb performance is classified and the additional complexity of the staged detonation is not necessary for a presumably small (4000 ton) vehicle.<br /><br />Large interplanetary and interstellar vehicles ( < 25 million ton payload) will require large fusion devices by necessity as fission bombs max out around 500 kilotons.<br /><br />Recent posts here regarding the large Soviet era nuke, Tsar bomba, with an apparent yield exceeding 50 megatons, may be useful if pusher plates can be made to utilize them. These may be very desirable 'fuel' for a very large Orion craft due to their high efficiency.<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>

 

[propforce]

<font color="yellow">f you take a small amount of liquid hydrogen, and a small amount of liquid oxygen, you get water, and a boom. They react upon contact - which is essentially the definition of hypergolic. </font><br /><br />Really? Wayne, did you do this in your lab? <img src="/images/icons/smile.gif" /><br /><br /> <div class="Discussion_UserSignature"> </div>

 

[CalliArcale]

I kinda thought you needed a spark -- that it wasn't a truly hypergolic mixture. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[drwayne]

There is certainly a difference between an engine and behind a block wall...<br /><br /><img src="/images/icons/wink.gif" /><br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[drwayne]

This is an interesting article:<br /><br />http://www.inspacepropulsion.com/tech/pubs/2004_3494.pdf<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vogon13]

My chemistry is rather weak after all these years, but my recollecttion is that as liquid hydrogen and liquid oxygen diffuse into each other, energy is available to initiate combustion.<br /><br />Keep in mind, this mixture is so volatile, that you literally only have to spark a few molecules of each to set it off. Agitation from diffusion may be sufficient.<br /><br />Wish I could remember that stuff better.<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]

You still need an ignition source. H2/O2 is not hypergolic. <div class="Discussion_UserSignature"> </div>

 

[propforce]

<font color="yellow">There is certainly a difference between an engine and behind a block wall... </font><br /><br />Ahhhh.... perhpas you're refering <i>auto-ingition</i> of gaseoius H2 and gaseous oxygen (GOX/GH2) at "elevated temperature" (aka hot gases) with adequate mixture ratio <img src="/images/icons/smile.gif" /> <br /><br />If you drop a cup of liquid hydrogen (LH2) into a bucket of liquid oxygen (LO2), what will happen? Nothing, except a very violent boiling of LH2 that quickly vaporize and rise up in air. <br /> <div class="Discussion_UserSignature"> </div>

 

[drwayne]

It made a pretty good little boom.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>