So, who wants to win 1 million Euro?

[Bob B.]

I used +9.16 kJ/mol, which I got from the Wikipedia page. Whether it's liquid or vapor is not specified, but the temperature is given as 298K. That's just above its nominal boiling point at standard pressure, so I assume it's for the gas, not the liquid, and that could account for the difference.

Yep, it looks like you were using the gas phase heat of formation.  According to my source, the heat of formation of N₂O₄ is H^o_f (gas) = 9.08 kJ/mol and H^o_f (liquid) = -19.56 kJ/mol.

[ka9q]

So we're consistent, then.

Actually, if you really want to get precise, another variable just occurred to me. The oxidizer probably wasn't pure N₂O₄ but rather MON - Mixed Oxides of Nitrogen, which is mostly N₂O₄ with dissolved NO, a gas with an enthalpy of formation of +90.29 kJ/mol. According to the Wikipedia page, NASA generally uses 3% NO. The primary reason is to reduce corrosion; there's an Apollo report about stress corrosion cracking of titanium that was solved by adding 0.78% NO. I seem to remember reading that the corrosion problems occurred only with some lots of N₂O₄ and not others, and the purer grades caused more problems. An analysis showed NO as an impurity in the lots that corroded less, so the discovery was serendipitous.

It also reduces oxidizer activity so I presume they use as little as possible.

And of course the N₂O₄ has substantial amounts of NO₂. Its standard enthalpy of formation is +34 kJ/mol at 298 K (presumably also a gas).

[gillianren]

Just curious, did any of us here actually say we _wanted_ the alleged million??

Not that I recall.

Since no one yet has said they believe it exists, wanting it or not is a bit irrelevant.  I mean, I'd love to get a million Euros from someone, but I no more believe that Heiwa has it to give than that my cat does.  My cat also appears to have a better understanding of orbital mechanics.

And Noldi, you win the coveted "I Made Graham Laugh" award!  He knows a bit of the context, because I've been attempting to amuse him with highlights (or possibly lowlights) from this thread the whole time, but I'm not sure he cared.

[LunarOrbit]

Just curious, did any of us here actually say we _wanted_ the alleged million??

Oh, if someone seriously offered me 1 million Euro I would gladly take it. But I put Heiwa's "contest" in the same category as those "Nigerian prince" scams.

First of all, if it sounds too good to be true it probably is. Secondly, I've been reading posts by people like Jay, Bob, ka9q, sts60, etc. for long enough to recognize the real experts. Heiwa is trying to bluff his way through a discussion with people who know a lot more than he does, and it's obvious to everyone but him.

[Bob B.]

Actually, if you really want to get precise, another variable just occurred to me. The oxidizer probably wasn't pure N₂O₄ but rather MON - Mixed Oxides of Nitrogen, which is mostly N₂O₄ with dissolved NO, a gas with an enthalpy of formation of +90.29 kJ/mol. According to the Wikipedia page, NASA generally uses 3% NO.

That's something I've wondered about for quite some time.  I've never been able to find a source that confirms whether or not MON was used and, if so, what percentage NO.  All the sources I've seen simply say nitrogen tetroxide, but I've suspected it might have really been some form of MON.

The primary reason is to reduce corrosion

I've never heard that before.  The reason for using MON that I've heard is to reduce the freezing point.  Pure N₂O₄ has a freezing point of just -9.3 C, which isn't very good in applications where cold temperatures are expected.  The more NO added, the lower the freezing point of the mixture.  MON-3 has a freezing point of -15 C, while MON-25 reduces the freezing point all the way down to -55 C.

One of the main reasons for the development and use of IRFNA is because it has a much better freezing point than N₂O₄.  IRFNA is/was often used in tactical missiles because of the possibility those missiles might have to be deployed on a freezing battlefield.  Examples are the American Lance and the Soviet Scud.  I don't remember the freezing point of IRFNA, but pure nitric acid is -41.6 C.

[ka9q]

For those who aren't chemists, some notes on the discussion Bob and I have been having that might make it a little more understandable.

The enthalpy of formation of a substance (formerly known as the heat of formation, but I guess that was too obvious to mere mortals) is the energy it takes to form the substance from its elements under standard pressure and temperature. By definition, the elements in their standard, stable states (e.g., N₂, not N) all have zero enthalpies of formation.

If a substance has a positive enthalpy of formation, that means it takes energy to make out of its elements and it is quite likely unstable -- it wants to fall back apart into those elements (or to other less energetic materials). An example is hydrazine, N₂H₄, with an enthalpy of formation of +50.63 kJ/mol. (A "mol" is a specific number of molecules, currently defined as 6.02214179 x 10²³, otherwise known as Avogadro's Number.)

A substance with a negative enthalpy of formation, on the other hand, is more stable. It's hard to tear apart. Common examples are water (-285.8 kJ/mol as a gas) and carbon dioxide (-393.5 kJ/mol). If there are other substances with the same elements having even more negative enthalpies of formation it could still spontaneously decompose to form them.  An example is hydrogen peroxide (-187.8 kJ/mol), which spontaneously decomposes into water and oxygen. But there are no other compounds of hydrogen and oxygen or carbon and oxygen with more negative enthalpies of formation than water or carbon dioxide respectively, so those two substances are very stable by themselves.

Because hydrazine has a positive enthalpy of formation, the nitrogen and hydrogen in it would be much happier in their elemental forms, and in fact it can be decomposed with a catalyst as in most monopropellant rocket engines. Because other compounds of nitrogen and hydrogen have negative enthalpies of formation, most notably ammonia (-46 kJ/mol), decomposing hydrazine generally produces a lot of ammonia and nitrogen as opposed to just hydrogen and nitrogen.

To find the energy available from a chemical reaction you just add up the enthalpies of formation for the reactants and subtract the enthalpies of formation for the reaction products. If the result is positive, the reaction is exothermic and will tend to go by itself (and produce a lot of heat). If the result is negative, the reaction is endothermic and requires an external source of energy. Needless to say, the reaction of rocket propellants is highly exothermic, producing lots of energy per mol (and per unit mass).

[sts60]

ka9q wins the Educator of the Thread prize ("threaducator"?).  Very lucid explanation.

[ka9q]

The primary reason is to reduce corrosion

I've never heard that before.  The reason for using MON that I've heard is to reduce the freezing point.

Thanks, I had forgotten that. So there are two good reasons to use MON as an oxidizer.

Freezing point depression is also a reason to use Aerozine-50 vs straight hydrazine. Straight hydrazine freezes at +2C (even worse than N₂O₄ at -11.2C) while UDMH freezes at -57C. (I don't know offhand if they form a eutectic that freezes at a temperature below either pure compound.)

Straight hydrazine also cannot be used in regeneratively cooled rocket engines (i.e, most bipropellant engines) because it would decompose.

UDMH cannot be used in monopropellant rockets, so I guess the high freezing point of straight hydrazine is one reason to switch to a more complicated bipropellant engine. On the other hand, some spacecraft with large bipropellant engines use hydrazine-fueled monopropellant thrusters for attitude control so at least one set of tanks still has to be kept warm.

So why not just use straight UDMH in bipropellant engines? Some rockets do (or did), notably the original Ariane 1 design. Its second launch failed due to a combustion instability, an event I remember very well because my group had a payload on it. One of the design modifications was to switch to UH-25, 75% UDMH + 25% hydrazine. I'm not sure why it helped.

Another reason to add hydrazine to UDMH is to increase its average density. Hydrazine is 1.021 g/cc while UDMH is only 0.79 g/cc.
 

[ka9q]

Very lucid explanation.

Thank you. One group I really wish could understand this enthalpy stuff are the cranks who think they can make hydrogen from water for free. Many say they just need the right catalyst and the water molecule will just fall apart. They just don't understand that to catalyze a reaction, it must already be thermodynamically favorable; the catalyst just helps get it going.

I know that water will spontaneously decompose if it's hot enough, and that's the basis of several hydrogen production schemes based on solar and nuclear heat. I don't know the details of the thermodynamics, and the processes aren't as simple as merely heating water, but I'm guessing that water's enthalpy of formation under those conditions actually goes positive, meaning it's more stable as hydrogen and oxygen. Anybody know?

[Heiwa]

2. One of your main claims - that the Apollo spacecraft could not carry enough fuel to, say, enter lunar orbit - is based on a complete misunderstanding of how such quantities are calculated.  Your attempt at an energy balance is fundamentally broken because you simply neglect a major component of the system in its final configuration - the expelled reaction mass. ...

I am a practicing space systems engineer with over two decades in this line of work, and I will be happy to assist you in learning about space flight as best I can - but can only do so if you actually want to learn something.  Do you?

My calculations are very simple - kinetic energy B of space craft Before and kinetic energy A of space craft After maneuver. It is a function of the variable Force applied to the space craft during distance travelled time used. The expelled reaction mass is also given, probably the difference in space craft mass Before/After maneuver.
As shown in my presentation they are not consistent at the various complicated maneuvers carried out, e.g. braking while changing direction while losing mass in a 3-D space with the pilots looking backwards doing something - steering (?) the space ship using the available systems. It seems nobody, incl. Willy at NASA, can explain what systems - manual and or automatic - were used to carry out maneuvers when 5-10 tons of fuel were used, etc, etc, and therefore I conclude that the whole trip was a hoax (purpose of the forum).
The final maneuver - the 6300 km/1080 seconds re-entry starting at 11 200 m/s velocity flying backwards up/down in Earth's atmosphere with a 5.5 ton capsule and then dropping down just in front of president Nixon - is so unlikely that I wonder how Willy could believe it or make it up. So it was a hoax IMO. 
So your clarifications are welcome so we can learn a little.

[ka9q]

And we tend to look toward LOX/LH2 as the "1.0" against which most other processes are normalized.

There are even better chemical propellants, but none have proved practical. They're either incredibly unstable or reactive (e.g., hypergolic with air), corrosive, produce incredibly toxic combustion products, gum up the works, or all of the above.

Although hydrazine and nitrogen tetroxide are incredibly toxic, at least their combustion products aren't so bad. Unlike, say, a rocket burning hydrogen + FLOX (liquid fluorine and oxygen), which would trail a plume of hydrofluoric acid on its way to space.

Another fuel occurred to me that might perform well if not for its nasty properties: acetylene. It has a positive enthalpy of formation, but will explode under even modest pressure. No problem for oxyacetylene torches where the acetylene is stored dissolved in acetone, but the weight of a solvent is not acceptable in a rocket. Then again, acetone is itself pretty flammable. Hmmm.

[nomuse]

My calculations are very simple - kinetic energy B of space craft Before and kinetic energy A of space craft After maneuver. It is a function of the variable Force applied to the space craft during distance travelled time used. The expelled reaction mass is also given, probably the difference in space craft mass Before/After maneuver.
As shown in my presentation they are not consistent at the various complicated maneuvers carried out, e.g. braking while changing direction while losing mass in a 3-D space with the pilots looking backwards doing something - steering (?) the space ship using the available systems. It seems nobody, incl. Willy at NASA, can explain what systems - manual and or automatic - were used to carry out maneuvers when 5-10 tons of fuel were used, etc, etc, and therefore I conclude that the whole trip was a hoax (purpose of the forum).
The final maneuver - the 6300 km/1080 seconds re-entry starting at 11 200 m/s velocity flying backwards up/down in Earth's atmosphere with a 5.5 ton capsule and then dropping down just in front of president Nixon - is so unlikely that I wonder how Willy could believe it or make it up. So it was a hoax IMO. 
So your clarifications are welcome so we can learn a little.

This is goobledegook.

I'm not one of the rocket scientists here -- that is, one of several people we have here who have performed actual engineering on satellites some of which are currently in operation.  But I am not flirting with Dunning-Kruger myself to say that I comfortably understand enough to see that what you said above is not physics, but word salad.

"Braking while changing direction?"  Only someone who was rooted in a pre-Newtonian, friction-dominated world could possibly describe anything in that way.  Braking IS changing direction.  Changing direction IS braking.  And neither is a very good way of putting it.  Spacecraft don't bank like airplanes.  They don't have rudders or keels.  They move, always, along a vector.

Pick your coordinate system.  Doesn't matter which.  Whatever it is, you can define a spacecraft's current motion in it, its future motion in it, and the difference between those two is arithmetic.  The orientation, the sign, of that change means damn-all, and the orientation -- the ATTITUDE -- of the spacecraft means less than that.

[Daggerstab]

2. One of your main claims - that the Apollo spacecraft could not carry enough fuel to, say, enter lunar orbit - is based on a complete misunderstanding of how such quantities are calculated.  Your attempt at an energy balance is fundamentally broken because you simply neglect a major component of the system in its final configuration - the expelled reaction mass. ...

I am a practicing space systems engineer with over two decades in this line of work, and I will be happy to assist you in learning about space flight as best I can - but can only do so if you actually want to learn something.  Do you?

My calculations are very simple - kinetic energy B of space craft Before and kinetic energy A of space craft After maneuver. It is a function of the variable Force applied to the space craft during distance travelled time used. The expelled reaction mass is also given, probably the difference in space craft mass Before/After maneuver.

It was repeatedly pointed out to you that your "simple" is wrong: for this comparison to work, you need to include the kinetic energy of the spent propellant.

As shown in my presentation they are not consistent at the various complicated maneuvers carried out, e.g. braking while changing direction while losing mass in a 3-D space with the pilots looking backwards doing something - steering (?) the space ship using the available systems. It seems nobody, incl. Willy at NASA, can explain what systems - manual and or automatic - were used to carry out maneuvers when 5-10 tons of fuel were used, etc, etc, and therefore I conclude that the whole trip was a hoax (purpose of the forum).

No, the only thing your presentation shows is that you don't know anything about spaceflight and orbital mechanics. Your newfound incredulity of "steering" also shows that you are ignorant of spacecraft guidance and unwilling to do any research until it's spoon-fed to you. Seriously, you can look up the answer on Wikipedia. (All the others, please don't give him any tips - let him flounder. )

Oh, and "ApolloHoax" is the title of the board, not its purpose. Apparently you have difficulties gasping such a difference.

The final maneuver - the 6300 km/1080 seconds re-entry starting at 11 200 m/s velocity flying backwards up/down in Earth's atmosphere with a 5.5 ton capsule and then dropping down just in front of president Nixon - is so unlikely that I wonder how Willy could believe it or make it up. So it was a hoax IMO. 
So your clarifications are welcome so we can learn a little.

So, you don't believe that anything can be returned from orbit? This is not a rhetorical question, so please answer it.

[nomuse]

Yeah, so....detente was a myth?  The Cuban Missile Crisis, the Missile Gap, all of that?  Because it is hard to see how an ICBM would be much of a threat if heat shields and terminal guidance were impossible fictions...

[Jason Thompson]

My calculations are very simple - kinetic energy B of space craft Before and kinetic energy A of space craft After maneuver.

And how many more times do you have to be told they are WRONG?

You cannot start with the energy of the spacecraft and fuel and end with the energy of the spacecraft. You MUST account for the mass of the fuel in your calculation and you do not. Ever. You can keep saying the same thing over and over and over again but you'll still be wrong.

The expelled reaction mass is also given,

Incorporating phrases you've never used before only after they've been used by those attempting to show you where you have made your errors without acknowledging it as a correction is hardly the act of an honest man who wants to be shown where he has made mistakes.

probably the difference in space craft mass Before/After maneuver.

'Probably'? I thought you were an expert...

braking while changing direction while losing mass in a 3-D space with the pilots looking backwards doing something - steering (?) the space ship using the available systems.

You think the astronauts looking backwards makes a jot of difference? Steering a spacecraft in space is not like sterring a car where you watch where you're going and adjust your heading according to what you can see out of the window. If you apply a force to the spacecraft it will change direction in accordance with normal laws of physics. You don't have to do anything except fire the engine and wait.

It seems nobody, incl. Willy at NASA, can explain what systems - manual and or automatic - were used to carry out maneuvers when 5-10 tons of fuel were used, etc, etc,

No, let's get this straight. The explanations ARE out there. They ARE published. They ARE very very detailed as to what systems were used. I have a number of books on my shelf including the information you say is not available. Your research skills are absurdly poor.

and therefore I conclude that the whole trip was a hoax

If you could demonstrate that your conclusion was based on any actual knowledge and understanding that would carry some weight. You can't. Your jargon salad explanations are pure crap. Still, I'm sure you feel better in your little delusional world where you and only you have the insight and knowledge to see what literally thousands of others with more knowledge and experience cannot. Must be fun living in your world.

The final maneuver - the 6300 km/1080 seconds re-entry starting at 11 200 m/s velocity flying backwards up/down in Earth's atmosphere with a 5.5 ton capsule and then dropping down just in front of president Nixon - is so unlikely

Ah, you don't understand it therefore it was impossible? Argument from incredulity. So atmospheric re-entry, that thing we've been doing for decades, is actually impossible? So all space flight that involves anything coming back to Earth is impossible?

So your clarifications are welcome so we can learn a little.

What absolute rot. You are not welcoming any clarifications. No matter what anyone here has said, no matter what numbers and calculations and sources you have been shown, you just repeat your same old tired and incorrect assertions as if they will suddenly be more true the more you say them. Sorry, reality fortunately doesn't give a damn about your inability to learn physics, or to comprehend that you even NEED to learn more physics to understand those systems you are presuming to dismiss as fake.