Does the NASA SRB chuff?

It's made of APCP, so I would assume it chuffs... but it doesn't! Or at least I've never seen it chuff. I would assume chuffing could ruin the space flight. How do they prevent it?

They don't use copperheads.

They use a complex ignition system that gets the motor up to operating pressure almost instantly, as well as being a lot more reliable than anything we use.

In space flight, a chuff could well be fatal. There is no holding the shuttle down while the motors come up to pressure. The SRBs can and will rip the hold-down bolts right out of the pad.

Simply put, they use massive amounts of engineering and fluid dynamics to make igniters that have the motor fully lit and up to pressure in a couple hundred milliseconds. If we spent as much money and time engineering some igniters as they did for the SRB, we could have 100% reliable instant ignition too.

Their igniter "system" has igniters lighting igniters that light the motors. The final igniter is a monster that apparently fires flames pretty well down the length of the SRB core...kinda like using an E motor to light an M...
...when it positively, absolutely has to light the first time...
edit... https://spaceflight.nasa.gov/shuttle/reference/shutref/srb/ignition.html

There have been a number of "stud hangups" where the massive holddown bolt(s) fail to rebound down into the catch buckets after the nuts are blown. Apparently, the departing SRB gets it's bolt hole "reamed" by the bolt...but it doesn't stop the liftoff to be sure.
Then there are some pics of chunks of pad concrete literally imbedded in the perimeter chain link fence hundreds of yards distant...now THAT's a motor!!!
Man, I do love a Shuttle launch!

As cjl said NASA does the engineering to make sure the SRBs light nearly instantly and reliably.

The SRB uses a series of cascaded ignitors with the last one being essentially a large rocket motor itself.

It shoots a flame down the entire length of the core, gauranteeing that the entire core is lit in a fraction of a second. As I remember that last "ignitor" is ~5 feet long and contains >100 lbs of propellant...about the same amount of propellant in a P or Q motor! Now *that's* an ignitor.


Kevin.

You guys don't need to put alot of engineering into your rocket motors in order to prevent chuffing, I think most of NASA's engineering is geared toward simultaneous ignition of the boosters moreso than the prevention of chuffing. If you run the correct grain geometry for a given propellant, the burn will be smooth and reliable. Using an ignitor that is robust and of the correct size will also prevent chuffing along with proper core preparation. If your core has grease, oxidation or that glassy smooth, just pulled off the mandral finish you might have ignition problems. By taking a few careful steps you can have pretty reliable ignition, though nothing like NASA

If you watch this video we were able to reliable cluster 3 7600Ns M motors pretty easily.

https://www.mdra-archive.org/photos/ESL107/BobUtley/Full/th-littlejohn.wmv

Also, the propellant was pretty fast, so that made it a little easier too.

The large amount of engineering isn't just to prevent chuffing. It's to ensure that the motors are ALWAYS lit within 300 milliseconds of the ignition signal, and that they ALWAYS come up to pressure consistently. You definitely don't need that much time and money just to prevent chuffs.

Yep - in other words, I was agreeing with you

OK, so..... here's a noob question......................... what's a chuff?

Originally posted by krypton21
OK, so..... here's a noob question......................... what's a chuff?

Click to expand...

Great glossary from our friends at EMRR

OK. Question answered! Thanks, DaveCombs.

Anytime. Others have done the same for me; you don't just get an answer, you get a whole new resource.

Someone on here posted a video of a rocket just sitting on the pad, chuffing happily but never going anywhere, until it popped the chute while still on the pad. It was really sad.

Geez.... sounds like it was similar to watching a dog with a bad limp. Makes you frown & feel bad for it.

Found it. It's from Jadebox's "Rockets Gone Wild" video - look for the yellow and orange rocket, about 2/3 of the way through the video.

Actually the SRBs do chuff but not in the way we think about it in our sport. The SRBs chuff during their re-entry as the remaining propellant is burned.

Originally posted by DaveCombs
Found it. It's from Jadebox's "Rockets Gone Wild" video - look for the yellow and orange rocket, about 2/3 of the way through the video.

Click to expand...

I've actually seen that vid before. I didn't know that was the video your were referring to.

And yeah, I laughed at that poor little rocket. Well, if laughter is contagious, then the guy laughing in the vid is to blame... not me. LOL

The SRBs do make a popping sound, which might be confused with chuffing. The popping sound is caused by a variation in the burn rate of the SRBs.

I was in Florida last summer, and I saw the July 4th shuttle launch. It was truly amazing. I watched it from the Astronaut Hall of Fame, which is about 10 or 11 miles from the launch pad. Even from that distance we could clearly hear the roar of the engines and the popping sound.

Here's a picture from the launch.


Click on the following link for the full-res version.
https://farm1.static.flickr.com/203/472539398_af484a4d00_o.jpg

Dave

So...Time for a nerd question...how many N-Sec. (or if you have to N-millisec.) is ONE SRB motor and what would be the designation of that motor (like a,b,c, etc)?

Wiki says (and I've seen the same numbers elsewhere) 12.45MN (12,450,000 N) with a burn time of about 132 seconds giving about 94,000 Ns which seems somewhat low to me.

https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster

Very interesting section of ignition (seems somewhat on topic)

-Aaron

Aaron,

It looks like you divided by the burn time instead of multiplying. The Wikipedia entry shows a thrust curve for the SRB. I did a rough integration of the thrust curve and got 285 million pound-seconds, or about 1,270 Mega-Ns. The burn time is around 127 seconds, so the average thrust is 10 Mega-Newtons.

If a C motor has a total impulse of 10 Ns, then a Z motor would be 83,886,080 Ns. Therefore, one SRB is about 15 times a Z motor.

Since the total impulse of the SRB is so large it might be more convenient to represent it in other units, such as 39.6 ton-hours.

Dave

Very cool. Z*15-10000000-noneWhiteLightning!

...Thats only for ONE SRB!!!!!

Overkill?.....naaaaaaaaaaaaa:kill:

I need to hurry up and get my Aerospace degree and build me one of those suckers, and then.....build one BIGGER

How do the thrust curves compare between the 4 segmented SRB and the 5 segmented SRB, if anyone can find it for the 5?

The 5 has about 10% more peak thrust, about 27% more average, and about 24% more total impulse IIRC (with a slightly shorter burn time)

I know this is a tad off-topic, but I have... somewhere.... the original press release for the Shuttle (Orbiter, tank & SRB's) from February 1981. How cool is that?!

With that in mind, I'll see if I can dig it up & hand out free answers straight from the source.

First off let me apologize for this being a fairly lengthy post...But, read it to it's completion and you will see how it IS on topic for this discussion of the Space Shuttle:

Does the statement, "We have always done it that way" ring any bells?

The US standard railroad gauge (distance between the rails) is 4 feet 8.5 inches. That is an exceedingly odd number.

Why was that gauge used?

Because that is the way they built them in England, and English expatriates built the US Railroads.

Why did the English build them like that?

Because the same people built the first rail lines also built the pre-railroad tramways, and that is the gauge they used.

Why did they use that gauge then?

Because the people who built the tramways used the same jigs and tools that they used for building wagons, which used that wheel spacing.

Okay! Why did the wagons have that particular odd wheel spacing?

Well, if they tried to use any other spacing, the wagon wheels would break on some of the old, long distance roads in England, because that is the spacing of the wheel ruts.

So who built those old rutted roads?

Imperial Rome built the first long distance roads in Europe (and England) for their legions. The roads have been used ever since.

Now, about the ruts in the roads?

Roman war chariots formed the initial ruts, which everyone else had to match for fear of destroying their wagon wheels. Since the chariots were made for Imperial Rome, they were alike in the matter of wheel spacing.

The United States standard railroad gauge of 4 feet, 8.5 inches is derived from the original specifications for an Imperial Roman war chariot. Bureaucracies live forever.

Therefore, the next time you are handed a specification and wonder what horse's *** came up with it, you may be exactly right, because the Imperial Roman war chariots were made just wide enough to accommodate the back ends of two warhorses.

Now the twist to the story...

When you see a Space Shuttle sitting on its launch pad, there are two big booster rockets attached to the sides of the main fuel tank. These are solid rocket boosters, or SRBs.

Thiokol at their factory in Utah makes the SRBs. The engineers who designed the SRBs would have preferred to make them a bit fatter, but the SRBs had to be shipped by train from the factory to the launch site.

The railroad line from the factory happens to run through a tunnel in the mountains. The SRBs had to fit through that tunnel.

The tunnel is slightly wider than the railroad track, and the railroad track, as you now know, is about as wide as two horses' behinds.

So, a major Space Shuttle design feature of what is arguably the world's most advanced transportation system was determined over two thousand years ago by the width of a horse's ***.

.. and you thought being a HORSE'S A$$ was not important.

There ya go..If you always wondered..Originally the boosters were designed to be bigger, BUTT!

Pantherjon, pretty funny...

Originally posted by DaveHein
Aaron,

It looks like you divided by the burn time instead of multiplying. The Wikipedia entry shows a thrust curve for the SRB. I did a rough integration of the thrust curve and got 285 million pound-seconds, or about 1,270 Mega-Ns. The burn time is around 127 seconds, so the average thrust is 10 Mega-Newtons.

If a C motor has a total impulse of 10 Ns, then a Z motor would be 83,886,080 Ns. Therefore, one SRB is about 15 times a Z motor.

Since the total impulse of the SRB is so large it might be more convenient to represent it in other units, such as 39.6 ton-hours.

Dave

Click to expand...

Well, for calculations sake, let's call it 16 times a Z motor. If we get into double letters then (AA, then AB, etc), then a shuttle SRB would be an AD motor. Perhaps even an AD12-5? or would that be an AD8-3...?

I was just looking at the picture of the SRB parts.

https://en.wikipedia.org/wiki/Image:SpaceShuttleSolidRocketBooster.png

What do you suppose the forward and aft booster separation motors are rated at?