The LM maneuvres pre docking

[ka9q]

I just gave it to you as it appears in the NASA News Reference.

Oh, I know. I marvel that we were ever able to reach the moon using English units. How come the hoaxers don't pick up on this? I mean, it's a bigger handicap than 100 kHz computers with 30 kB of ROM.

[VQ]

Well, there's experimental evidence to show that it is not pyrophoric with N₂O...

Provided the mixture is not shocked, heated, agitated, moved, catalyzed, or acknowledged.

[ka9q]

After I posted that, I realized that cyanogen would probably not be a good rocket fuel despite its extremely high flame temperature in oxygen. It contains no hydrogen. HCN would probably be better, and it's probably safer than hydrazine...

[Bob B.]

Bob, what kind of performance could one get from SiH4 and the usual oxidizer suspects?

I can't do that one.  The computer program I use doesn't currently contain any silicon compounds.  If I had a real need I could build the data tables, but that's too much work for a simple 'what if' experiment.

Hey, while you're at it, why not try cyanogen and hydrogen cyanide?

With what oxidizer?

[VQ]

I can't do that one.  The computer program I use doesn't currently contain any silicon compounds.  If I had a real need I could build the data tables, but that's too much work for a simple 'what if' experiment.

If you wanted to PM me a link to a dropbox with the data table format, I might take a crack at it if I get the spare time and inclination (no promises) - the NASA-mentioned possibility of it being a possible in situ Mars fuel is intriguing (are there any other in situ hypergols)?

[Bob B.]

After I posted that, I realized that cyanogen would probably not be a good rocket fuel despite its extremely high flame temperature in oxygen. It contains no hydrogen. HCN would probably be better, and it's probably safer than hydrazine...

HCN would be better in terms of molecular weight, but temperature is just as big a factor.  Exhaust gas velocity is proportional to (T/M)^1/2 so the higher the temperature and the lower the molecular mass, the better the propellant.  Of course specific heat ratio is also a big factor.

I determine the best mixture ratio by experimentation, but a good starting place is to include enough oxygen to oxidize the carbon to CO and the hydrogen to H₂O.  For cyanogen and HCN that's,

C₂N₂ + O₂  -->  2 CO + N₂

2 HCN + 1.5 O₂  -->  2 CO + H₂O + N₂

That's an average molecular weight of 28 for cyanogen and 25.5 for HCN.  Neither is great but HCN is better.

[Bob B.]

If you wanted to PM me a link to a dropbox with the data table format, I might take a crack at it if I get the spare time and inclination (no promises) - the NASA-mentioned possibility of it being a possible in situ Mars fuel is intriguing (are there any other in situ hypergols)?

If you go to http://www.braeunig.us/space/thermo.htm you'll see the required format at the bottom of the page under a section titled "STANJAN".  However, I've done some searching and it looks like there are very few compounds to even consider.  It looks like SiO₂ and maybe SiO are it.  With only two tables to create, I can manage that myself.

(ETA)  I've already found all the data I need.  I just need to get it into the right format.

[ka9q]

Hey, while you're at it, why not try cyanogen and hydrogen cyanide?

With what oxidizer?

N₂O, of course. We're trying to find safer alternatives to the hydrazines plus N₂O₄, remember? 

[cjameshuff]

They didn't. They use gaseous nitrous oxide, and don't get much performance from it. SS1 only had to hop up above 100 km altitude, and it appears SS2 can't even do that. There's rumors that they're looking at all-liquid systems now.

Really? How could you get anywhere near enough gaseous N₂O on board to burn the fuel? The fuel grain usually requires a liquid N₂O tank of roughly the same size to burn it

I've seen several references to them using gaseous nitrous oxide, and I remember someone specifically stating it was gas for some reason or other, though they may have been misinformed or misquoted. The diagrams I've seen have a tank with considerably greater volume than the burned fuel. The reported temperature and pressure from the Mojave accident were impossible for a tank containing liquid (70 F/21 C and 360 psi/25 bar). Some Scaled materials refer to liquid N2O and things like slosh baffles, though.

[cjameshuff]

Hey, while you're at it, why not try cyanogen and hydrogen cyanide?

With what oxidizer?

N₂O, of course. We're trying to find safer alternatives to the hydrazines plus N₂O₄, remember? 

Have you considered liquid oxygen?

[Bob B.]

Hey, while you're at it, why not try cyanogen and hydrogen cyanide?

With what oxidizer?

N₂O, of course. We're trying to find safer alternatives to the hydrazines plus N₂O₄, remember? 

To be consistent with previous calculations, I used a chamber pressure of 7 atm and a 50:1 expansion ratio.

N₂O + HCN  --->  299.1 s (vacuum)

N₂O + C₂N₂  --->  311.8 s (vacuum)

C₂N₂ is far better than I expected but that's because it burns incredibly hot, probably too hot.  While everything else burns at about 3000-3400 K, N₂O and C₂N₂ burns at about 4200 K.  Of course we could run oxidizer-rich and bring the temperature down to a more manageable level, but that will lower the specific impulse and defeat the purpose.  We'd be better off using acetylene.

(ETA) These calculations assume gaseous reactants.

[BazBear]

Hey, while you're at it, why not try cyanogen and hydrogen cyanide?

With what oxidizer?

N₂O, of course. We're trying to find safer alternatives to the hydrazines plus N₂O₄, remember? 

Have you considered liquid oxygen?

I think they want a storable oxidizer.

[Bob B.]

Have you considered liquid oxygen?

I think they want a storable oxidizer.

I believe that was the initial premise, but to be honest, I've lost track.

[JayUtah]

Who cares?  This is a great discussion.  Makes me wish I'd paid more attention in Chemistry.

[Luke Pemberton]

I've arrived home to find that this thread is now examining the use of HCN as a fuel. I don't know whether to laugh or feel alarmed at this deviation.