APCP what is it?

[shockwaveriderz]

Ok, this post ins't about the NAR/TRA -BATFE Lawsuit.

What exactly is the definition of APCP.

Is APCP defined as AP + a binder like HTPB/PBAN + Aluminum?
or is it simply AP + a binder?

Is AP + ANY Binder/elastomer considered APCP?
Is AP + Butyl Rubber (polyisobutylene) considered APCP?

I'm confused.

terry dean

 

[n5wd]

...What exactly is the definition of APCP.

"APCP is a composite propellant, meaning that it has both fuel and oxidizer mixed with a rubbery binder, all combined into a homogeneous mixture. The propellant is composed of Ammonium perchlorate, an elastomer binder such as Hydroxyl-terminated polybutadiene (HTPB) or Polybutadiene Acrylic Acid Acrylonitrile Prepolymer (PBAN), small amounts of powdered aluminum, and various burn-rate catalysts."

from Wikipedia

 

[powderburner]

If you are asking about the government definition:

As far as our ATF friends are concerned, it is my understanding that they consider ammonium perchlorate with *any* binder or with *any* additives to be included in their category of "APCP" and also consider it explosive, whether or not a specific mixture can even be made to detonate

(That is about as factual as I can state it without sounding like I agree or don't, or whatever I think of the ATF, or any other political statements)

APCP used in mid-power and high-power rocket motors is an entirely different critter than the APCP used in the shuttle boosters. It certainly doesn't help to call these two formulations by the same name.

 

[rstaff3]

I tend to agree with powder that the ATF's definition is AP mixed with anything.

To use the term 'composite' properly, the mixture must have "two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure." This would minimally imply AP and a binder.

And no, you don't need aluminum or any similar additive to make APCP.

 

[quickburst]

I'd give a hundred dollars to read the ATF's definition of APCP in print on their own letterhead.

I personally guarantee you, it doesn't exist.

Ask 50 agents/inspectors this question.

65% of them will say Huh?

25% of them will say "I'll get back to you."

The last 10% will lie.

 

[ben]

I'd give a hundred dollars to read the ATF's definition of APCP in print on their own letterhead.

I personally guarantee you, it doesn't exist.

Ask 50 agents/inspectors this question.

65% of them will say Huh?

25% of them will say "I'll get back to you."

The last 10% will lie.

I would too. And not what the dictionary says. What they have in their own documents that makes it regulated at OUR level.

Ben

P.S. I wonder how NASA got a magazine big enough to log their grains.

 

[shockwaveriderz]

I think this shows just how silly the list of explosives is:
AP by itself isn't an explosive but AP + ANYthing is an explosive.

sad

terry dean

 

[heada]

I thought AP in sub 15 micron was considered a high-explosive. Also, AP heated to it's critical temp is also a high explosive (see PEPCON explosion)

AP that we use in normally 200 micron or larger.

-Aaron

 

[2muchstuff]

...APCP used in mid-power and high-power rocket motors is an entirely different critter than the APCP used in the shuttle boosters. It certainly doesn't help to call these two formulations by the same name.

Whoops, you've got that wrong. It's essentially the exact same stuff. Here's the formula for the Shuttle motors:

NOTE: THIS IS NOT AN EX FORMULA. THIS IS USED FOR THE SPACE SHUTTLE BOOSTERS.

"The propellant mixture in each SRB motor consists of ammonium perchlorate (oxidizer, 69.6% by weight), aluminum (fuel, 16%), iron oxide (a catalyst, 0.4%), a polymer (such as PBAN or HTPB, a binder that holds the mixture together, also acting as secondary fuel, 12.04%), and an epoxy curing agent (1.96%). This propellant is commonly referred to as Ammonium Perchlorate Composite Propellant, or simply APCP. This mixture develops a specific impulse of 242 seconds at sea level or 268 seconds in a vacuum."

From: https://www.nationmaster.com/encyclopedia/Space-Shuttle-Solid-Rocket-Booster

I know the rules here prohibit posting EX formulas, so I won't. But talk to any commercial motor maker and they'll tell you that the above formula is pretty much the same as what's used in a basic hobby motor. Obviously, some hobby formulas use other ingredients for color or to modify the burn rate, but what we fly, and what the shuttle flys, is pretty much the same stuff.

Just wanted to set the record straight.


tms

 

[uncle_vanya]

Whoops, you've got that wrong. It's essentially the exact same stuff. Here's the formula for the Shuttle motors:

But talk to any commercial motor maker and they'll tell you that the above formula is pretty much the same as what's used in a basic hobby motor. Obviously, some hobby formulas use other ingredients for color or to modify the burn rate, but what we fly, and what the shuttle flys, is pretty much the same stuff.

Just wanted to set the record straight.

Actually my understanding is that the Shuttle fuel is too rich in aluminum to be used in hobby motors. The aluminum in the boosters is able to be burned before exiting the nozzle due to the size of the motor - hobby motors don't scale down well from this and would not develop nearly the same ISP using the exact formula - at least this is what several motor guru's have said that I have talked with.

So it might be true that the Shuttle booster formula is similar but some might feel it is not "pretty much the same stuff" in the sense that it has a very high ISP and a higher amount of Aluminum than is typical. Personally I would think of it as nearly identical - that delta in ISP doesn't make it a different animal in my view.

 

[2muchstuff]

Actually my understanding is that the Shuttle fuel is too rich in aluminum to be used in hobby motors. .... So it might be true that the Shuttle booster formula is similar but some might feel it is not "pretty much the same stuff" in the sense that it has a very high ISP and a higher amount of Aluminum than is typical. Personally I would think of it as nearly identical - that delta in ISP doesn't make it a different animal in my view.

The ability to burn aluminum is dependent on many factors, case length being one of them. While the SRB formula may not work well in short motor cases, it would work fine in longer ones. There are many EX formulas that have at least that much metal.

The real point I was making is that the SRB fuel is essentially the same as what we put in our motors. The ISP is higher, but that's due to the efficiencies of big motors. You could mix up a batch of SRB fuel, put it in a larger EX motor case, and it would fly just fine. Powderburner's assertion that somehow the SRB fuel is not the same "critter" is just not true.

I think it's very helpful that it's the same stuff. Everyone remembers that when the Challenger fuel tank exploded, the SRB's flew out of that huge fireball and had to be destroyed by a ground command. It shows how stable and 'non-explosive' APCP really is.

I'd like to hear why Powderburner thinks comparing the two propellants is bad.


tms

 

[Micromeister]

Totally agree with To0 much Stuff on this one:
been using the same formula for several Hobby model related uses for years. not just for motors. APCP can be litterily any conbination of AP and a binder even polyurethane, or plain old epoxy. Metal content and type can vary widely. but APCP is APCP regardless.

 

[MarkM]

The real point I was making is that the SRB fuel is essentially the same as what we put in our motors. The ISP is higher, but that's due to the efficiencies of big motors. You could mix up a batch of SRB fuel, put it in a larger EX motor case, and it would fly just fine. Powderburner's assertion that somehow the SRB fuel is not the same "critter" is just not true.

Agreed. True, our hobby motor formulas may use less metal (as well as a different metal other than aluminum in some cases), use "coloring agents" and may have lower ISP than the shuttles's SRBs, but that doesn't mean they aren't comparable. They are chemically very much similar. I, too, would like to know how Powerburner can claim these two formulas are so different. And how is associating our APCP with the shuttle's "different critter" APCP bad? It just doesn't make sense to me.

 

[BayouRat]

The everyday field agent would not know the difference between an APCP slug and a pencil eraser. Not to say that they are stupid or anything like that. They just don't know anything about rocket fuel.

I have a high alum. percentage formula that I run in long motors. It kicks but. It produces a very cool blue and purple flame about 4 feet long. It leaves a good bit of slag on the nozzle. But I love all the smoke, fire and noise that this motor makes.

 

[powderburner]

I'd like to hear why Powderburner thinks comparing the two propellants is bad.

I was under the impression (can't remember right now where I read it) that the SRBs used some exotic additives, some sort of "altered" form of AP (a different micron size?), and a significantly different content of metal. The net effect supposedly made the SRB mixture behave differently than the APCP used in our hobby.

I am not a chemist by profession so I can't speak in detail to the different formulas but I had been told that "our" stuff would not work very efficiently in the big SRB-size motors. Some of you guys are now indicating that they would work about the same, that the different performance is size-related and not due to chemistry. Interesting. If that is true (ours is the same as theirs) it would seem that they could save a whole lotta bucks using our (cheaper) version?

Yes, it would be nice to call all mixtures "the same" and claim that ours won't detonate based on NASA tests, but even if that were true, our ATF friends don't seem willing to listen to facts like that.

 

[quickburst]

There's really not much difference between the SRB's propellant and a lot of hobby propellant.

The %Al is a little higher than what you normally see in hobby compositions.

From what I understand, and mind you I am not privy to inside information, the main difference between most hobby propellants and the SRB's propellant is the binder. Most hobby propellants use HTPB (Hydroxyl Terminated Poly Butadiene, say that five times fast).

The SRB's propellant uses PBAN as the binder. From what I have heard PBAN is a little more tolerant of moisture.

The book, "Experimental Composite Propellants" by Terry McCreary contains a lot of information on PBAN.

___________________________________________________________
From Wikipedia:
PBAN - Polybutadiene Acrylonitrile copolymer. Also noted as Polybutadiene — Acrylic acid — Acrylonitrile terpolymer.

This was the binder formulation widely used on the 1960-70's big boosters (e.g., Titan III and Space Shuttle SRBs). It is also sometimes used by amateurs due to simplicity, very low cost, and lower toxicity than the more common HTPB. HTPB uses isocyanates for curing, which have a relatively quick curing time; however, they are also generally toxic.

PBAN is normally cured with the addition of an epoxy resin, taking several days at elevated temperatures to cure.

PBAN will be used in future NASA missions, most notably the Constellation program, as this copolymer will be used in the first stage of the Ares I rocket in five segments.
___________________________________________________________


PBAN has to be cured at elevated temperatures (140 degree F +/-), while HTPB is cured at room temperatures, maybe this is why HTPB is preferred by hobbyists.

 

[bobkrech]

There's no secret about the Shuttle SRM propellant formulation. It is an APCP formulation containing: Aluminum Powder (16%) as fuel; Ammonium Perchlorate (69.93%) as oxidizer; Iron Oxidizer Powder (0.07%) as a burn rate catalyst; Polybutadiene Acrylic Acid Acrylonitrile (12.04%) as rubber-based binder and an Epoxy Curing Agent (1.96%)

The Shuttle SRM uses PBAN because PBAN formulations give a slightly higher specific impulse, density, and burn rate than equivalent formulations using HTPB, and PBAN requires an elevated curing temperature so it won't cure until you want it to which is a good thing when your propellant grain weighs nearly 300,000 pounds and it takes hours to mix and cast!

https://www.braeunig.us/space/propel.htm#solid

https://www.cs.tcd.ie/Stephen.Farrell/ipn/background/Braeunig/propel1.htm

Bob

 

[2muchstuff]

There's no secret about the Shuttle SRM propellant formulation. ...

Bob,
I think it's a bigger secret than you let on.

The formula you posted varies quite a bit from the one I posted earlier in the thread. (You may have missed it.) The formula I posted early in the thread matches the one at this NASA website:

https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/srb.html

However, the link at:

https://www.nasa.gov/returntoflight/system/system_SRB.html

lists a slightly different version.

The only reason this matters is the iron oxide. The two NASA sources I cite above list .2 and .4 percent iron oxide, while you list .07 percent. That's a pretty dramatic difference. My practical experience tells me .2 to .4 is closer to the truth than .07 percent. The sites you list are only compilations, and the author does not cite which specific source he used for his version of the SRB formula. Worse, the only NASA link he provided in the propellent section is a dead link. Do you have a NASA source that substantiates the version you provided? I'd like to know just how many 'official' versions of the formula are out there.

Thanks,


tms

(ps: and yes, all the formulas listed add to 100% total wt. Some of the formulas probably have the values rounded, and this may account for some of the difference.)

 

[Chrisn]

Maybe NASA doesn't stick to the same formula every launch? Or it has been changed?

 

[ben]

Maybe NASA doesn't stick to the same formula every launch? Or it has been changed?

They could have very well modified it. I believe the shuttle booster is 4 grain and they are making a new 5.5 grain for the Ares rockets(?) I wonder what kind of changes they will make for this.

Ben

 

[bobkrech]

Bob,
I think it's a bigger secret than you let on.

The formula you posted varies quite a bit from the one I posted earlier in the thread. (You may have missed it.) The formula I posted early in the thread matches the one at this NASA website:

https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/srb.html

However, the link at:

https://www.nasa.gov/returntoflight/system/system_SRB.html

lists a slightly different version.

The only reason this matters is the iron oxide. The two NASA sources I cite above list .2 and .4 percent iron oxide, while you list .07 percent. That's a pretty dramatic difference. My practical experience tells me .2 to .4 is closer to the truth than .07 percent. The sites you list are only compilations, and the author does not cite which specific source he used for his version of the SRB formula. Worse, the only NASA link he provided in the propellent section is a dead link. Do you have a NASA source that substantiates the version you provided? I'd like to know just how many 'official' versions of the formula are out there.

Thanks,


tms

(ps: and yes, all the formulas listed add to 100% total wt. Some of the formulas probably have the values rounded, and this may account for some of the difference.)

There really is no secret, just poor penmanship. There appears to have been transcription errors in the quoted formulations.

Many technical folks, myself included, use a crossed 7 to differentiate the value from a script 1. Additionally many technical folks, myself included, write too quickly and sometimes three handwritten numbers, a crossed 7, 2 and 4 can be confused. This would account for the discrepancy between the three values since the convention is to add up all the minor components and balance the equation with the AP percentage.

Thiokol, not NASA, makes the propellant and therefore set the specifications for the composition. I located an AIAA paper from 1975 that discusses the original Shuttle SRM in detail. According to Solid Rocket Motor for the Space Shuttle Booster, THIRKILL, J. (Thiokol Corp., Brigham City, Utah) AIAA-1975-1170, American Institute of Aeronautics and Astronautics and Society of Automotive Engineers, Propulsion Conference, 11th, Anaheim, Calif., Sept 29-Oct 1, 1975, AIAA 8 p. the proper formulation is:

Aluminum Powder (16%) as fuel;
Ammonium Perchlorate (69.6%) as oxidizer;
Iron Oxidizer Powder (0.4%) as a burn rate catalyst;
Polybutadiene Acrylic Acid Acrylonitrile (12.04%) as rubber-based binder; and
an Epoxy Curing Agent (1.96%).

This formulation was used by Thiokol before for DOD applications and that appears to be the reason why it was chosen.

"The specific formulation selected for lhe SRM is essentially identical to that employed in the Stage I Poseidon motor (Table XI). The propellant is a minor modification (0.4% iron oxide added) of the Stage I Minuteman propellant to achieve a slightly higher burning rate. The simplicity of the formulation. which contains only four major ingredients, assures reproducible propellant ballistic and mechanical properties. Availability, experience. cost. and performance are all criteria which are readily met with the selected PBAN formulation."

All good and logical reasons for the composition chosen.

Bob

 

[2muchstuff]

<snip>Thiokol, not NASA, makes the propellant and therefore set the specifications for the composition. I located an AIAA paper from 1975 that discusses the original Shuttle SRM in detail. According to Solid Rocket Motor for the Space Shuttle Booster, THIRKILL, J. (Thiokol Corp., Brigham City, Utah) AIAA-1975-1170, American Institute of Aeronautics and Astronautics and Society of Automotive Engineers, Propulsion Conference, 11th, Anaheim, Calif., Sept 29-Oct 1, 1975, AIAA 8 p. the proper formulation is:

Aluminum Powder (16%) as fuel;
Ammonium Perchlorate (69.6%) as oxidizer;
Iron Oxidizer Powder (0.4%) as a burn rate catalyst;
Polybutadiene Acrylic Acid Acrylonitrile (12.04%) as rubber-based binder; and
an Epoxy Curing Agent (1.96%).
<snip>

Bob,
I guess I figured everyone knew Thiokol made the propellent - who could forget after watching the Challenger hearings? However, you would think NASA would be a good source for the formula since it is made to their specification. You can see SRB tests done by Thiokol on Youtube, including a really cool night test.

I'm glad I got the formula right the first time - I liked your long winded explanation of how 'technical folks' sometimes just make mistakes. Seems to me 'technical folks' ought to be more careful with those numbers - after all, non-technical folks (like me) depend on those numbers being correct when it counts! I knew the .07 percent iron oxide did not make sense. I guess sometimes practical experience allows even a non-technical person to see past poor penmanship!

At least as interesting is the idea of a conference between AIAA and SAE. Checking the web I see we just missed the 44th annual meeting. I bet that would be a fun trade show to wander around. You can see a cool looking rocket model in the Aerojet exhibit from last years show:

https://www.aiaa.org/Content.cfm?pageid=714



tms