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Talk:Liquid rocket propellant: Difference between revisions

Revision as of 23:08, 16 August 2005

"Units have been converted to metric. "

All those units need to be specified, in all the tables. What's "pressure" in earlier table, for example. Gene Nygaard 17:08, 22 Dec 2004 (UTC)

Hmmm. "Pressure" is psia, which I'm sure you figured out from context. But this does bring up the point that psia is hardly metric. And 1000 psia is 6.894 MPa, which is hardly a nice round number. Iain McClatchie 19:38, 23 Dec 2004 (UTC)

You could just as easily use a nice round 10 MPa as the base pressure (the one multiplied by 1.00 in the first table, and the starting point in the second table), couldn't you? Or even if that is for some reason unsatisfactory, 7 MPa would certainly work just as well as 1000 lbf/in². Why use a halfway conversion, one still requiring reference to English units? Gene Nygaard 08:37, 27 Dec 2004 (UTC)

7 Mpa is not the same as 1000 lbf/in². The results of the program run are accurate enough that the difference between the two might matter. Iain McClatchie 18:32, 27 Dec 2004 (UTC)

Wolfkeeper,

You obviously know the subject, we're arguing over the meaning of words.

"believed" versus "noted".

• Nobody knows what someone once believed. That's definitely the wrong word.

The fact that they wrote stuff down supports this position that they believed it :-) Noted has connotations, for example you talk about 'noted researchers'. It sort of implies correctness/importance etc. which is not really true in this case. It's like I once refered to a serving lady as a 'wench', when she was giving me some lip. Whilst formally correct, the other connotations (which I didn't mean at all) could have got me into a lot of trouble :-) Connotations are important. WolfKeeper

• The correctness of hydrogen being "ideal": I agree, no propellant is ideal, so the problem word here is "ideal". How about "Many early rocket theorists noted that hydrogen would be a marvellous propellant, since it gives the highest specific impulse."

That would be ok.WolfKeeper

"whilst being very energy dense and lightweight"

• This is what high specific impulse means, so this phrase is redundant.

not precisely, they are not truly equivalent, but I don't feel strongly.WolfKeeper

"where a hydrogen stage's low fuel mass"

• I do not want to confuse Isp and mass. Helium cold-gas thrusters have low fuel mass too, but they have crummy Isp. Isp is what matters, not (directly) mass.

No, that's not correct. For a given stage's delta-v and for a given payload mass a hydrogen fuelled stage happens to weigh less than say, a kerosene one. That's mainly why they use it I believe, because the whole launch vehicle gets a lower GLOW, and hence ends up cheaper. But the fact that hydrogen gives a high Isp is significant, but not on its own enough. For example a theoretical fuel with an Isp 1 second less than hydrogen, but with several times higher density could easily give the same delta-v, but the stage would weigh less due to the better mass fraction.WolfKeeper

"in practice"

• Hydrogen is bulky in theory too. Even slush hydrogen is bulky in theory.

Without in any way trying to be evasive: it depends on the theory. A theory is just a model of reality; models always leave things out.WolfKeeper

• There are no other proposed hydrogen storage systems besides cryogenic storage. That makes it the only practical storage system. Would you quibble with the phrase "remotely practical"?

Yes. GOX for example has been used on Buran. There's no obvious reason why GH2 couldn't be used for similar purposes; it's much heavier that way, but that doesn't always matter, and gaseous propellants are easily space storable, liquid hydrogen is rather difficult.WolfKeeper

I'm leaving your edits up for now so we can talk about this and resolve it. But I don't agree with all of them.

Iain McClatchie 22:23, 16 August 2005 (UTC)[reply]