Ares vs. Jupiter Rocket Designs

[lumos]

lumos, look at the GPS 2R launch.

All it takes is a crack in the fuel element.

Do you have a link to the investigation? I can't find anything useful on Google other than video and short comments.

It looks to me that while the failure may have been "triggered" by an SRB structural failure, the explosion is from the liquid fuel, including nitrogen tetroxide/hydrazine.

Structural failure is bad for any mechanism.

 

[jadebox]

Wait... you turn off a solid fuel rocket by destroying the integrity of the fuel column enough that it can no longer generate thrust?

No, not at all. You just release the pressure in the casing and the propellant stops burning. The pressure release causes the temperature to drop low enough that the APCP no longer burns.

The rocket motors I use have enclosures at each end that are designed to fail if the pressure in the motor gets too high. This is intended to prevent the motor casing from rupturing if, for example, the rocket's nozzle gets clogged. I've witnessed a couple of cases where the rocket motor has failed like this during ignition. The most dramatic was about a month ago when a motor failed in my "Akavish" spider-themed rocket (see video). Apparently there was a crack in the propellant core which caused the motor to over-pressurize. The aft enclosure failed, causing the motor to shoot up through the motor mount, taking off the top of the rocket. When I went to recover the pieces, I found the propellant core intact. It looked like it hadn't been used since at all it stopped burning as soon as the enclosure failed.

Problems like the one I experienced are, fortunately, rare. I suspect that the propellant core I used had been damaged during handling before I bought it. It was bought second-hand (which I will avoid in the future!).

NASA x-rays the propellant cores used in the Shuttle to detect any cracks or bubbles that might cause a problem. That's a bit beyond my budget.

-- Roger

 

[neutrino_cannon]

Yeah, you got it. Isp isn't that big a deal though for 1st stage, it's massive mass ejection that counts - speed is low to some machs on 1st stage - nozzle is thus inefficient ...

It is possible to optimize the nozzle for the low-altitude pressure and high-mass low velocity throughput. Not sure how much you would gain from higher Isp at launch though; they did can the variable-geometry nozzle on the shuttle, after all.

Look for more simple hybrids on private ventures, that's where the action will be.

I liked the cut of theSpace X Falcon 1 rocket, even though it was liquid-propelled. I agree that we'll be seeing more simple, private rockets.

The rocket motors I use have enclosures at each end that are designed to fail if the pressure in the motor gets too high. This is intended to prevent the motor casing from rupturing if, for example, the rocket's nozzle gets clogged. I've witnessed a couple of cases where the rocket motor has failed like this during ignition. The most dramatic was about a month ago when a motor failed in my "Akavish" spider-themed rocket (see video). Apparently there was a crack in the propellant core which caused the motor to over-pressurize. The aft enclosure failed, causing the motor to shoot up through the motor mount, taking off the top of the rocket. When I went to recover the pieces, I found the propellant core intact. It looked like it hadn't been used since at all it stopped burning as soon as the enclosure failed.

Cool video, thanks.

Do you think that the pressure-relief valve concept would scale well?

 

[DrRocket]

You're right. The propellant in the SRBs is not an explosive and no solid boosters have exploded.

In point of fact all solid propellants are explosives. The most common space launcher propoellants are class 1.3 explosives, which the propellants used in some high performance ICBM stages are class 1.1 explosives. There have been a couple of accidents that might be called explosions. C4 rockets experiences such a failure. And there was a Delta II that ruptured the case shortly after launch, although that failure was attributed to damage to the case.

Several times a month, I fly rockets that use solid propellant motors made with basically the same propellant (APCP) as in the SRBs. APCP actually burns slower than typing paper. It's how quickly it produces a large volume of gas while burning - not how fast it burns - that makes it an effective rocket propellant.

The propellant used in the shuttle SRBs is called a PBAN propellant, named for the binder. It is a mix of PBAN, aluminum, ammonium perchlorate and a few other minor ingredients, including some iron oxide to catalyze burning. The burn rate is considerably faster than most paper. Space booster propellant burn rates, at 1000 psi are typically on the ordre of 0.35 in/sec radially outward from the surface which is largely the centerbore.

A problem with solid propellants is that, once lit, there's little direct control over the thrust during the flight. But, Ares, like the Shuttle, is using solid propellant for just the first stage. The second stage can be throttled to compensate for any variations in the perfomance of the solid booster.

This is basically true, althought the grain is shaped to provide a pre-planned pressure-time profile that is appropriate to the mission



There's also the problem that a solid propellant booster can't be easily shut down in case of a problem. During the Challenger accident, the Range Safety Officer fired explosives placed on the SRBs which broke open the cases. The drop in pressure caused the solid propellant to stop burning. But, you can't do something like that while the booster is still near the crew vehicle.

This is also true but not as important as you think. You can't shut down a liquid rocket either, at least as an abort mechanism. If you shut down the engine, then the rocket crashes back to the ground. No current rocket has an engine out capability, although Space X claime to be developing one.

In the case of the shuttle, abort procedures are rather limited. The shuttle has to be high enough to glide to an emergency landing. Even if the Challenger astronauts had recognized the problem, they probably would not have been high enough to make a safe abort.

The current shutele has no abort options once it has left the pad and until after SRM burnout and separation.

With the Ares, however, its much more likely the crew would survive a problem with the booster or second stage because the escape system could pull them quickly away from the rest of the rocket.

That is the plan. The escape propulsion is provided by solids with a very high burn rate.

 

[jadebox]

In point of fact all solid propellants are explosives.

No. APCP is definitely not an explosive. If APCP exploded, it would be useless as a rocket propellant.

APCP is listed as an explosive by the BATF, but that is currently being challenged in court. And, APCP is flammable, and, therefore, was once classified as "Class 1.3" for shipping by the DOT. They've changed their system of classification, but APCP, quite rightly, is still treated as a hazardous material for shipping.

But, APCP burns much too slow to be an explosive. The ATF's own testing showed that APCP in a rocket motor burned at about 5 mm per second. In testing by the ATF, bond paper burned about ten times faster. A true explosive would burn at a rate at least 200 times faster than that.

-- Roger

 

[jadebox]

Space booster propellant burn rates, at 1000 psi are typically on the order of 0.35 in/sec radially outward from the surface which is largely the centerbore.

According to the ATF's testing, paper burns at up to about two inches/second -- about five times the rate you quote for the solid propellant.

-- Roger

 

[jadebox]

There have been a couple of accidents that might be called explosions.

"Explosions" are not necessarily caused by explosives. If you blow up a balloon too much, it will "explode" but that doesn't make air an explosive.

If a solid rocket motor overpressurizes, the casing can explode from the pressure. But, that's not because the propellant is explosive. And, a nice thing about most solid propellants is that they only burn under pressure. If a motor casing fails, the propellant stops burning. That's not true of most liquid propellants.

No matter what kind of booster is under them, however, the astronauts in Ares will be much safer than in those the shuttle simply because there is a reliable launch abort system available.

-- Roger

 

[mhaze]

APCP is not an explosive.

 

[BenBurch]

Neither is steam;

 

[jadebox]

Neither is steam;

Sorry? Did anyone suggest that it is?

-- Roger

 

[neutrino_cannon]

I think the distinction can best be drawn between different classes of explosives; deflagrants, that being most propellants in all but the most exotic engines, which burn from a quickly-propogating flame front, and detonations, which burn from the pressure wave and have a much faster pressure spike.

 

[jadebox]

I think the distinction can best be drawn between different classes of explosives; deflagrants, that being most propellants in all but the most exotic engines, which burn from a quickly-propogating flame front, and detonations, which burn from the pressure wave and have a much faster pressure spike.

But, not everything that deflagrates is an explosive. In fact, most things that burn with a flame deflagrate, but aren't explosive.

In the case against the ATF, the Court of Appeals ruled that the ATF had not set standards for what separates a non-explosive which deflagrates from an explosive. The ATF replied that it is the rate at which the substance burns and attempted to show that APCP burns at a comparative rate to other substances on their explosives list.

When their own testing revealed how slowly APCP burns, they decided to compare it's burn rate to the "burn rate" of safety fuse. Safety fuse is, of course, designed to burn very slowly along its length. Nevertheless, the burn rate they calculated for the fuse is still faster than the rate at which APCP burns.

Of course, none of this has anything to do with the topic since both Ares and the Jupiter proposal use solid-propellant boosters.

-- Roger

 

[mhaze]

Excuse me, but we are not in this forum seriously going to discuss whether something is an explosive or not based on its inclusion or exclusion in a list of proscribed materials by a government regulatory agency of a certain country.

I submit a question of this sort should be answered by looking at the definitions of the words and the scientific processes involved.

Lawyers and or politicians do not define science and do not define explosive.

 

[jadebox]

Lawyers and or politicians do not define science and do not define explosive.

Although, there is a legal definition of an explosive (a substance "the primary or common purpose of which is to function by explosion"), I emphasized the scientific defintion (a substance which burns rapidly or undergoes detonation). I showed that solid rocket propellants do not meet that definition, because they don't burn rapidly or detonate.

Oh ... and I have tried, twice, to steer the conversation back on topic ......

-- Roger

 

[DrRocket]

Space booster propellant burn rates, at 1000 psi are typically on the order of 0.35 in/sec radially outward from the surface which is largely the centerbore.

According to the ATF's testing, paper burns at up to about two inches/second -- about five times the rate you quote for the solid propellant.

-- Roger

Ever to try to burn compacted rolled up paper at 2 inches per second.?

 

[DrRocket]

If by APCP you mean ammonium perchlorate composite explosive, then you are not even close to correct. It generally does not detonate, but it is a class 1.3 explosive. And I can assure you that the procedures for manufacturing it treat it as an explosive material. And I really don't care what the ATF says. I have been involved in the manufacture of literally millions of poinds of this stuff. The AP itself is actually detonable, though usually not considered sensitive. However the detonation of the Kerr McGhee plant that made AP ought to be enough of a demonstration.

The difference between rapid deflagration and full Chapman Jouguet detonation is well-known. But the difference would be lost on a nearby observer. Rapid deflagrations can create enough havoc and overpressure to satisfy almost anyone. I have seen enough results of both to not want to be very near either one.

APCP is not something that I would recommend be handled by amateurs. Particularly amateurs who think it is safe.

 

[mhaze]

Although, there is a legal definition of an explosive (a substance "the primary or common purpose of which is to function by explosion"), I emphasized the scientific defintion (a substance which burns rapidly or undergoes detonation). I showed that solid rocket propellants do not meet that definition, because they don't burn rapidly or detonate.

Oh ... and I have tried, twice, to steer the conversation back on topic ......

-- Roger

Yes, we are in agreement. The legal definition is quite irrelevant for the purposes of discussion of solid rocket propellants. Our solid rocket boosters are not going to blow up because of some lawyer's snakelike thoughts, or some regulatory agency idiot bureacrat typing some words into a list of "bad stuff".

Side comment back to OP: I think we could argue that highest reliability and safety in multistage manned rocket launch would be the product of rapid turn around schedules a la Soyuz - doing the same thing over and over for decades - not trying to innovate, keeping everything as simple as possible.

For these purposes, NASA is diametrically opposed to safety, reliability, and the other factors of interest - whatever product they push out to the pad.

 

[neutrino_cannon]

Hey, you should listen to the ATF; they have a lot of experience burning stuff.

Just how were these tests conducted anyhow? Was the burning paper under pressure?

And while we're at it; would there be any advantage to detonating rocket fuel? I'm thinking of something analogous to the air-breathing pulse detonation engines that there's so much interest in of late.

 

[DrRocket]

Although, there is a legal definition of an explosive (a substance "the primary or common purpose of which is to function by explosion"), I emphasized the scientific defintion (a substance which burns rapidly or undergoes detonation). I showed that solid rocket propellants do not meet that definition, because they don't burn rapidly or detonate.

Oh ... and I have tried, twice, to steer the conversation back on topic ......

-- Roger

You are utterly wrong. Class 1.1 solid rocket propellants do detonate and are actually high explosives. Such propellants are in use as we speak. In large rocket motors. Burn rates on such propellants are in the range of ).5 inches per second. Detonation velocities of the same propellants are thousands of meters per second. Burn rate has nothing to do with detonation rates or detonability.

Class 1.3 propellants generally are not considered to detonate -- which means that detonation waves tend to damp out, the propellants have a large critical diameter, or even that the hole in the witness plate was ragged rather than clean. They are explosives. APCP propellants quite obviously contain AP (ammonium perchlorate) AP is detonable.

People who think that APCP propellants are safe are themselves dangerous.

Accidents involving either the manufacture of APCP propellant or rocket case ruptures are quite impressive. And dangerous.

 

[BenBurch]

Sorry? Did anyone suggest that it is?

-- Roger

Point is a pressurized vessel can go kaboom even if what pressurizes it is not in any way an explosive.