Space Shuttle SRB's - Fuel Burn Rate?

[AzoMittle]

 

The composition of the SRB's fuel is well documented. The burn rate is not - the reality is that this is not an actual requirement for my testing!! - I just thought that it was an easier question to ask, and may have been known by a few members of this forum. I could/should have titled this thread "APCP - Approx. Burn Rate - Any Ideas?"

 

I can see how anyone mentioning "scale-up theory" and APCP could be viewed in a negative light. From what I've read, the scaling of solid fuel rocket motors is a point of interest and not a known quantity even to professionals - "Real" Rocket Scientists.

 

I'm certainly not saying that I'm going to solve "Scale-up-theory" but it has always been of interest to me since I first ground up some bought gun powder and rammed it into a tube (some 30+ yrs back).

 

Cheers.

 

 

 

Quite frankly, that information flat out doesn't exist. The burn rate is variable, I can give you some rough ranges and such but you're not going to find an exact number, it will be different for every single flight every single rocket.

 

"Burning rate is a function of the propellant composition. For composite propellants it can be increased by changing the the propellant characteristics:

1. Add a burning rate catalyst, often called burning rate modifier (0.1 to 3.0% of propellant) or increase percentage of existing catalyst.
2. Decrease the oxidizer particle size.
3. Increase oxidizer percentage.
4. Increase the heat of combustion of the binder and/or the plasticizer.
5. Imbed wires or metal staples in the propellant.

Aside from the propellant formulation and propellant manufacturing process, burning rate in a full-scale motor can be increased by the following:

1. Combustion chamber pressure.
2. Initial temperature of the solid propellant prior to start.
3. Combustion gas temperature.
4. Velocity of the gas flow parallel to the burning surface.
5. Motor motion (acceleration and spin-induced grain stress)."

--Sutton's Rocket Propulsion Elements pg.440-441

 

The First-Stage Minuteman Missile Motor had a burning rate (in./sec @ 1000 psia) of 0.349 with burn rate exponent of 0.21 using a composition of 70% AP, 16% Al, and 14% binders/additives; meanwhile, the Orbus-6 Inertial Upper-Stage Motor had a burn rate (in./sec @ 1000 psia) of 0.276 with an exponent of 0.3-0.45 and a composition of 68% AP, 18% Al, and 14% binders/additives. But you have to realize that all changes based on other factors, for example the Minuteman used a six-pointed star grain where the Orbus-6 used a central perforation, they each have different loading densities, nozzle designs, flame temperatures, etc etc

 

Basically I don't think you'll be able to use this data the way you want to (for scaling?). You're better off doing some tests of your own, if you can get access to a strand burner via a local university/lab you should get comparable data.

 

I'm still not clear on why you want this data... Are you starting your own space program?

 

Anyways, here's some data for specifically for various compositions, I think this is the data you were really after (call me lazy but I'm not typing up another chart): mirror or see attached.

[Richtee]

Kid,

"TI3xIIS"?? I've never heard of that model, mine is the TI-30X IIS... just like the one you show in the link.

 

 

 

Kid? Here’s mine. LOL https://en.wikipedia.org/wiki/TI-59_/_TI-58

[stix]

Quite frankly, that information flat out doesn't exist. The burn rate is variable, I can give you some rough ranges and such but you're not going to find an exact number, it will be different for every single flight every single rocket.

 

The First-Stage Minuteman Missile Motor had a burning rate (in./sec @ 1000 psia) of 0.349 with burn rate exponent of 0.21 using a composition of 70% AP, 16% Al, and 14% binders/additives; meanwhile, the Orbus-6 Inertial Upper-Stage Motor had a burn rate (in./sec @ 1000 psia) of 0.276 with an exponent of 0.3-0.45 and a composition of 68% AP, 18% Al, and 14% binders/additives. But you have to realize that all changes based on other factors, for example the Minuteman used a six-pointed star grain where the Orbus-6 used a central perforation, they each have different loading densities, nozzle designs, flame temperatures, etc etc

 

Basically I don't think you'll be able to use this data the way you want to (for scaling?). You're better off doing some tests of your own, if you can get access to a strand burner via a local university/lab you should get comparable data.

 

I'm still not clear on why you want this data... Are you starting your own space program?

 

Anyways, here's some data for specifically for various compositions, I think this is the data you were really after (call me lazy but I'm not typing up another chart): mirror or see attached.

 

Thanks Azo for your hard work posting all that text - much appreciated. The chart you posted was indeed what I was after.

 

PBAN/AP/AI from the chart looks like a similar fuel to the SRB's. After doing some calculations including other data I've come accross as well, the average burn rate of the space shuttle srb's is around one 1/2 inch per second. Surprisingly slower than I thought.

 

That info is just a point of reference, To what end, I'll try to post a reasonable explanation in the next day or so.

 

---

 

Are you starting your own space program?

 

Cape York Peninsula, approx. 12deg south of the equator with vast expanses of un-populated land would seem like an exceptional and ideal location for a Space Port. The idea was put foward in 1988 but through lack of vision, money and no consent from the original owners, the dream perished.

 

Unfortunately most governments cannot see beyond the 4yr electoral cycle.

 

It's approx. 720kms (450 miles accross) at the base - Karumba to Innisfail.

 

Edited May 17, 2016 by stix

[AzoMittle]

 

Thanks Azo for your hard work posting all that text - much appreciated. The chart you posted was indeed what I was after.

 

PBAN/AP/AI from the chart looks like a similar fuel to the SRB's. After doing some calculations including other data I've come accross as well, the average burn rate of the space shuttle srb's is around one 1/2 inch per second. Surprisingly slower than I thought.

 

That info is just a point of reference, To what end, I'll try to post a reasonable explanation in the next day or so.

 

---

 

 

Cape York Peninsula, approx. 12deg south of the equator with vast expanses of un-populated land would seem like an exceptional and ideal location for a Space Port. The idea was put foward in 1988 but through lack of vision, money and no consent from the original owners, the dream perished.

 

Unfortunately most governments cannot see beyond the 4yr electoral cycle.

 

It's approx. 720kms (450 miles accross) at the base - Karumba to Innisfail.

 

You are welcome! Glad it helps, somehow.

 

I was joking about the space program but to be real I foresee that being a large commercial industry soon. The US has been privatizing space deliveries, construction, and resupply for a while now; NASA is doing their own thing, doing science stuff, while people like SpaceX and Boeing are making money sending food rations to the ISS. Over the past decade or so, I've also seen a few movements for things like small, personal satellite delivery companies, and space tourism or zero-g vomit comet trips. Anyways, I'm excited to see where we will be in another 10 years.

[stix]

. . . I was joking about the space program . . .

 

Well I wasn't!!!

 

Fun to think about those things though. Australia could/should have such facilities. Large expanses of land etc...

 

Getting back to my question about the burn rate of the shuttle boosters - seems like around 1/2 inch per second, but happy to have better info, but not nesser.

 

The point of my original posted question is about "scaling". Not necessarily "scaling up" but let's invert it, and consider "scaling down".

 

What would happen if you were given a chunk of the space shuttle fuel and shaped it to suit a small motor. Like 3/4" (19mm ID) x about 8 inch high or so. From my observations you would have a wall thickness of around 1/4" (6mm) which would result in a total burn time of .25 seconds - and likely to CATO.

 

Think about it.

 

Please be aware that this is not the same scenario for BP.

[kramrocket]

Hi stix,

 

The issue regarding how motors may perform when scaling up or down with a given solid fuel, has been a subject of interest for me for many years.

 

The analogy you gave using a fuel sample of the SRB's used for the space shuttle is a good one.

 

It seems certain to me that if one produced a 100th scale version of the booster, it would cato for sure !!!

 

The burn rate would simply be too high with a scaled down model... thoughts ???

[kramrocket]

The same theory can be applied to using a 'scaled-up' version of a well made suger/potassium nitrate fuel for an SRB for the shuttle ... it will not have the burn rate or the energy required to provide the SRB nozzle exit area with enough gas to do the job... simple

[AzoMittle]

Yes, if there was one thing I learned from this book I keep quoting it is that every rocket has to be designed for its particular purpose. Actually I'm going to just straight up plug this book, it's worth the $65 for anyone that's as interested as you guys are: http://smile.amazon.com/Rocket-Propulsion-Elements-George-Sutton/dp/0470080248?ie=UTF8&me=&ref_=mt_hardcover

[stix]

Hi stix,

 

The issue regarding how motors may perform when scaling up or down with a given solid fuel, has been a subject of interest for me for many years.

 

The analogy you gave using a fuel sample of the SRB's used for the space shuttle is a good one.

 

It seems certain to me that if one produced a 100th scale version of the booster, it would cato for sure !!!

 

The burn rate would simply be too high with a scaled down model... thoughts ???

 

Thanks Kram - good to see that you've finally signed up to this forum.

 

After many years of us both discussing "scaling theory" perhaps this forum will finally give a reasonable answer. That answer may well be provided on the "Rocketry Forum" http://www.rocketryforum.com/ but as pointed out, that avenue of learning has been cut off due to the restrictions regarding "home made fuels, freedom of information, geography and laws".

 

Also when I think about it, discussing such things on this forum may well be clamped down on - similar to the "High Explosives" section on this forum that is vetted by Mumbles. I agree with that one.

 

kramrocket quoted:

The same theory can be applied to using a 'scaled-up' version of a well made suger/potassium nitrate fuel for an SRB for the shuttle ... it will not have the burn rate or the energy required to provide the SRB nozzle exit area with enough gas to do the job... simple

 

Agreed, Otherwise KNSU would be a much cheaper option to get into orbit. Perhaps there is little difference in scaling when we are talking about scaling up at smaller scales - if that makes sense.

 

To date, I've only done one scaling up test:

The SKINT-P1-AVE motor was scaled up "7 times" in volume, as one would scale up a 3D image in Autocad or Adobe Illustrator. It wasn't exact, as I was limited to the tooling at hand but I made sure the amount of fuel used was as close as possible.

The grey column is "based on" an average of 3 tests and used as basis. The yellow column shows extrapolated information with predictions. The green column show the final actual measured results. If read across the "rows of data" the results are close to the prediction.

The interesting and satisfying conclusion is that I used 7 times the amount of fuel and got 7 times the total impulse. Which is what you "should get". Which means to me that at least the fuel was burning efficiently with both tests. The other comparative data wasn't too far off either.

Edited May 22, 2016 by stix

[stix]

... The grey column is "based on" an average of 3 tests and used as basis. The yellow column shows extrapolated information with predictions. The green column show the final actual measured results. If read across the "rows of data" the results are close to the prediction ...

 

Well, this is bloody embarrassing!!. I was just informed that I didn't post the actual data table I was referring to - ie. the grey, yellow & green columns:

 

The burn time was lower than predicted, but that could be accounted for by the lower Kn Ratios? I have to admit that the fuel used for both tests was not exactly the same. The only difference being KNO3 milled in a coffee grinder (SKINT-P1-AVE) and ball milled (SKINT-20).

The comparisons between the predicted and actual are close but possibly a 'fluke'? In any case, more tests need to be done.

[EDIT] Also, to finalise the graphs and data posted, I should post a graph of the (SKINT-P1-AVE) which was derived from 3 tests. No such graph exists, but I could create one from the set of data. Not sure if it's necessary though because the details are already there in the table.

Edited May 29, 2016 by stix

[kramrocket]

I thought something was missing stix.

 

A look at the data tables does indeed appear to show why 'scaling up' isn't as simple as we would like it to be though.

 

If one is trying to prove a point about this subject, it is very important to use an exact same batch of fuel and Kn ratios for the small and larger motor.

 

Your tests did show a slower, therefore longer, burn time than expected for the scaled up version (yes, the Kn wasn't the same but given the fact that it was ball milled rather than coffee grinded, it should have at least been on par or quicker.

 

Without doing all the maths, I believe when scaling up a nice working motor, we need to consider the fuel burn rate too. It also needs to be scaled up so the pressure is kept up to please the nozzle exit area !!!

 

 

 

.

[taiwanluthiers]

Functionally the 83 and 84 are nearly identical. The 84 is basically the 83 with upgraded processing power and memory, some physical redesign, and more modern connectivity. Supposedly the 84 comes with more preloaded programs and functionality, and has some screen improvements. The 83/84 has been the standard for the last 20 years. This is good and bad. It's good to have a familiar and uniform platform, which has now been included into text books and can really be integrated into the curriculum. This comes with the downside that they basically have a monopoly now which allows them to still charge ca. $100 for a new calculator with no real technological improvements for two decades. Don't get me wrong, the functionality is great, but it's overpriced for technology that can be accomplished with a cell phone app now.

 

I have some friends who are math teachers, and there's been a growing movement to get away from the TI calculators. It prices out some lower income schools, they're commonly stolen, and like I said they're kind of ancient. There are programs and applications that mimic the interface and functionality available for free to very inexpensively.

 

TI-83 is still favored at my university (UT Austin) but I'm not wanting to get one because like you said, it's ancient technology and a laptop/tablet can do the same thing. It doesn't help for math classes because calculators are not allowed at UT for tests and exams so we still need to do things with paper and pencil. However some have told me that they have a TI83 for other classes such as physics where there's a lot of math component and that they would not allow tablets or phones for exams for obvious reason, but would allow them to use a TI-83 in those exams...

 

Not allowing calculators in tests meant professors had to have questions that gives nice whole number answers (or we leave answer as radicals or weird fractions) since there are limits on doing complex computations without using calculators... For example square root of 2.

[Nessalco]

A KNSU motor to orbit? Seriously?

 

Google "Sugar Shot to Space". Those guys have done a good job with the math, and are working on 'scaling up'. A whole lot more complicated than calculating a few burn rates - and they're only shooting for 100 kilometers.

 

What are you using to calculate fuel characteristics and burn rates? The shuttle fuel is fully characterized, and the info widely available. Plug in your motor geometry and you should have a good place to start.

 

Kevin

[stix]

... If one is trying to prove a point about this subject, it is very important to use an exact same batch of fuel and Kn ratios for the small and larger motor.

 

Your tests did show a slower, therefore longer, burn time than expected for the scaled up version (yes, the Kn wasn't the same but given the fact that it was ball milled rather than coffee grinded, it should have at least been on par or quicker ...

 

Yes agreed, there are two main issues. The fuel being inconsistent (although I reckon not far off - but can't be proven) and of course the Kn ratios. Unfortunately the Kn's were determined by the already made Nozzle forming tooling that I had to work with and the most likely reason for the slower burn rate.

 

This was only 'one test' so not following very scientific methods in that regard (at least three would be good). More tests will need to be done. Now that I have my own ball mill, I can grind the KNO3 consistently. Making new nozzle tooling will be the hard part.

 

 

A KNSU motor to orbit? Seriously?

 

Google "Sugar Shot to Space". Those guys have done a good job with the math, and are working on 'scaling up'. A whole lot more complicated than calculating a few burn rates - and they're only shooting for 100 kilometers.

 

What are you using to calculate fuel characteristics and burn rates? The shuttle fuel is fully characterized, and the info widely available. Plug in your motor geometry and you should have a good place to start.

 

Kevin

 

Nesscalo - surely you're not serious about me being serious about expecting Orbital performance from a Sugar Rocket! . Yes, I'm aware of the "Sugar Shot to Space" project. From what I remember, the 'technical' definition for reaching "space" is around 100kms, and that's what they are aiming to achieve. So, "Sugar Shot to Space" does not mean "Sugar Shot Into Orbit".

 

"What are you using to calculate fuel characteristics and burn rates?"

 

The calculated burn rate is pretty straightforward. The web thickness of the fuel (linear) is divided by the known burn rate - in this case the burn rate is 0.512 cms/sec. Therefore the web of the larger motor 1.25/0.512 = 2.44 seconds. This should work out close providing that the Kn ratios, which determine the chamber pressure are the same. They weren't for reasons described above, therefore the burn rate was slower.

 

The theoretical total impulse is a simple multiplication of the amount of fuel used. In the Alpha motor I used 31.45gm. The tubing and tooling I had available enabled me to use 7 times the amount of fuel in a reasonable scale up scenario. 7 x 31.45 = 220.5. Therefore 7 times the total impulse of the Alpha (3) was measured to be correct at (21) in the Beta.

 

The average and peak thrusts were derived working back from the total impulse.

[kramrocket]

Yes, if there was one thing I learned from this book I keep quoting it is that every rocket has to be designed for its particular purpose. Actually I'm going to just straight up plug this book, it's worth the $65 for anyone that's as interested as you guys are: http://smile.amazon.com/Rocket-Propulsion-Elements-George-Sutton/dp/0470080248?ie=UTF8&me=&ref_=mt_hardcover

 

I actually went to great trouble, time and expense 'photo copying' all of this book in my state library way back in the eighties !!! the version I have is by George P. Sutton and Donald M. Ross, 1976... I still have it. So much info in this book but WAY over my head then and still now !!!

 

I have argued for many many years with stix about why a simple physical 'scaling up' of motors with a standard solid fuel, wont give the expected results. eg: if the up-scaled version has say, twice the nozzle area, don't expect twice the thrust. (but you will get longer duration)

My reasoning is simply that all is NOT truly up-scaled... the fuel burn rate is not !

[dagabu]

"...twice the nozzle area, don't expect twice the thrust. (but you will get longer duration)..."

 

Do you mean core area? Either or, you will get less duration as the fuel will burn faster and with less thrust if the nozzle is bigger and with a longer (more) core area, you will get more thrust but for a shorter duration.

 

I think we may be speaking of Neutons and not thrust?

[kramrocket]

Dave,

 

This 'scale up' thing is really starting to piss me, it has gone on and on....

 

Lets just talk about thrust in kilos for a given small motor.

 

The small motor has a cored grain and a nozzle of 25 mm2.

 

KN ratios are say, 50 at start and 250 at the end of burn.

 

The results are 1 kilograms thrust at start and 5 kilograms at end.

 

Now if we used the same fuel in a 'scaled up' model, say four times the nozzle area and everything else scaled up in proportion ( for example taking a photo of the two with the bigger one further back but looks the same size) will we expect four times the thrust from start to finish ? I don't think so...

[kramrocket]

I really believe the more one 'scales up' with a given fuel, the less chance of cato...

 

The inverse is true too, if using a sample of SRB fuel in a smaller motor, cato is more likely...