So the CEV concept is supposed to use a solid rocket booster. This is similar to the shuttle except for a couple of things: In the shuttle, the SME's do most of the steering and control, even though they do not provide most of the thrust for liftoff. Also there are two solid rockets.

But in the CEV there will be only one. This one rocket will have to be modified with a much more capable vector control system to keep the vehicle on course and flying correctly. The problem: These have been known to, from time to time, fail or jam.

Werner Von Braun always opposed use of solid fueled rockets for human space flight. The argument now is that technology has changed. Okay. So? Can you shut off an SRB now? No. Throttle it down? No. Throttle it up? No. change the thrust ratio of the engines? No, it only has one.

So what is nasa's plan for if this should happen:




Seems it might preclude the use of the launch escape system. Especially if it's headed toward the ground.

And a much more complicated weight distribution.
Does it? Do you have some reference to this? Since the center of gravity is now part of the stack, why wouldn't the current thrust vector control be sufficient?
But; just about all rocket technology has. What are the possibilities of this failure VS the other technologies, and what have we learned from each?
good
When, in the history of manned spaceflight has the thrust had to be adjusted outside of the planned throttle changes?

The plan is to use the escape system before the situation gets that bad.

It won't be headed for the ground when the problem is detected.

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IIRC, that corkscrewing missile was the first launch of a Trident SLBM back in the 1980s. Fortunately for the CEV and Ares I, this won't be the first launch of the SRM. Over 100 Shuttle missions (each using 2 SRBs) have flown with no control failures. That's a lot of experience in the space business.

Say what you will about the Ares I (and personally, I still favor using an EELV like the Delta IV Heavy or an Atlas V version), flight control of the SRM is one of the more proven elements of the design.

I was able to watch the last part of a segment of 'Daily Planet' the other night. They were taking about 'torque roll' on Orion/Ares. They said they wiil have thrusters on the service module to counteract torque roll.
You don't have to steer from the bottom of the stack.

I see nothing wrong with using SRM's for the initial phases of launch. At least they can be reused. Only the SM gets ditched in the end. It would seem to me to be a lot better for the enviroment in the long run. How much energy is used in the production of all that aluminum and titanium, just to get dumped in the Indian ocean.

When used within its design limits, the SRB has a 100% success rate after 200 launches. That is totally unprecedented. Using any launcher that has 200 "test" flights before using it is unprecedented. The SRB parts that already are the same now as they will be for Ares are quite likely to be very reliable, given their amazing track record.

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Concidering that SRMs have been used in 119 manned launches spanning 26 years, why the concern about them now? They seem to have a proven track record of reliability, don't you think? Also taking into account that Orion will have a launch abort system, Ares I certainly looks like a potentially safe launch system.

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The title question is a valid issue, but you're mistaken on several points:

The SSMEs do NOT provide most of the steering during stage 1. Rather the steerable SRB nozzles do. This is obvious from the relative thrust and gimbal angles. The SRB nozzles gimbal 8 degrees, the SSME nozzles 10 degrees, but the SRB motors together produce 5 times the thrust.

SRB nozzle steering simply must work, else the shuttle will go out of control. The SSMEs don't have sufficient steering authority to compensate for an SRB "hard over" steering failure. So there's nothing different about Ares I from this standpoint.

SRBs cannot be shut off, but neither can many other "criticality 1" pyros, which simply must work. All manned launch vehicles are covered in them. E.g, if the SRB pyros fail to release the vehicle at ignition, or fail to release the SRBs at separation, the vehicle will be destroyed. Think of the SRBs as simply large "criticality 1" pyros.

Neither shuttle, Ares I, nor solid boosters unique in simply having to work. If the Saturn V had a SINGLE F-1 engine failure early in the launch, the entire vehicle would fall to earth and be destroyed. Whether the F-1 engine could be shut down or not made no difference. All five had to work.

The SRBs are throttled up and down during each flight, according to a pre-planned schedule. The varying thrust comes from the internal construction. When the "throttle back", and "throttle up" calls are made, it is the SRBs NOT the SSMEs which are providing most of the varying thrust.

E.g, the SRBs are throttled back from a peak thrust of about 6.2 million lbf at T+20 sec, down to 4.2 million lbf at T+50 sec. IOW the SRB throttle range is greater than the entire combined SSME maximum thrust.

The SRBs throttle schedule is fixed at construction time and cannot be dynamically varied -- but the thrust does vary according to an intentional preplanned schedule. The SSME throttle range is best understood as a dynamic "fine tuning" of the SRB throttle range.

Re launch escape, the shuttle SRBs (at least before Challenger, don't know about now) are not highly instrumented. The reason was there's no launch escape system, what's the point.

However -- the first four shuttle development flights (STS-1 through 4) had highly instrumenented SRBs. Given adequate instrumentation and a launch escape system, the Ares I booster could easily be instrumented to provide early automatic trigger of the LES. The Challenger SRB failure could easily have been detected early enough by instrumentation to trigger a LES.

So while using solids for human launches is a valid concern, various related assumptions are often incorrect.

Okay, your next two lines helped clarify your intent. The SRB's are preset to throttle down and throttle up at key times. Clarification, the throttle down and throttle up commands are given to affect the SSME's. Those commands would be pointless for the SRB's. But the majority of throttle change is occurring in the SRB's, as preset.

Heck, an LES could have triggered when the Challenger ET blew and still probably rescued the crew.

One thing that hasn't been mentioned on this thread is that the ammonium perchlorate used in SRM is highly toxic. Probably not a big deal as long as rocket launches are the rare events that they are today. However, perchlorates have already turned up in California milk. If we want space flight to become as routine as ordinary flight, some other fuel will have to be developed. It would be smarter to do it before the someone sues the EPA after billions and billions have been spent on an environmentally obsolete technology.

Indeed, the mere fact that NASA insists on sticking with perchlorate fuels tells me just how limited their ambitions are.

Well it's not simply an issue of throttle up/down. An SRB is lit and there ya go. It burns.. it burns till it's out of fuel. It's not something you could turn off, adjust or in any way control. You light it and aside from the vector nosels that's all you got.

You either wait for it to run out of fuel or perhaps try to stop it by blowing it up, which is a less than ideal solution.

The difference with a liquid booster: if there is a failure of the system, such as a loss of power to the turbo pumps, a major leak and so on, the engine is going to stop. The SRB keeps burning as long as it has fuel in it.

Your spacecraft could be tumpling, spinning, headed for the ground, with the vector control system completely out of control, the top part of the SRB coming apart, flames coming out of the joints and a giant flying clown head coming at you. And what can you do? Um... pretty much nothing.

In the following scenario where a liquid fuel rocket flies out of control and you shut down the engine(s), what happens when it hits the ground in the uncontrollable end point of its manic flight?

Indeed, KABOOOOOOOOOOM just like the SRB would do. Shutting down the engines doesn't make the rocket any less dangerous.

And besides, the point is quite moot since 200+ flights have shown the SRB is reliable. I don't know what safety you expect in spaceflight, but 100% after 200 flights is extraordinary.

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It would be nice if they'd develop something a bit more environmentally friendly indeed. Not like I demand carbon neutrality or anything from experimental rocket launches, but there must be something better than what the SRB burns. SS1 used a relatively harmless rubber fuel. Liquids often use H2/O2, which only is an environmental burden to make and cool, but totally not to burn. We've had (rather poor performing) kerosene rocket engines.

While the SRB's aren't exactly greenpeace's dream, there is some environmental concern at NASA, ESA and the russian program though. The most energetic fuel combination anyone has used upto now is H2/O2. There is one still more energetic, but it is extremely poisonous...luckily nobody thought "hey let's fly a rocket on that, never mind the environment!".

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\two words...range safety. The SRB has charges that literally unzip the case, extinguishing the motor. The motor runs on internal pressure, split the case and basically you have falling debris. See the pics of the recovered remains of the STS-25 SRBs...large amounts of unburned solid fuel, as the fire went out when the destruct signal was sent to the boosters after the vehicle breakup.

Of course, there are no perchlorates leaving the engine. The perchlorate is the oxidizer (ClO₄). When the motor burns, they completely decompose inside of the combustion chamber due to the intense heat and pressure. What's leaving the motor is Al₂O₃, HCl (gaseous, not in solution as hydrochloric acid), plus relatively small amounts of iron oxides and a few other chemicals.

That sounds less harmful. Though I don't know what HCl gas does to the environment.

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Good point, you can shut down an SRB if the vehicle is lost anyway, and it will likely give a smaller (or no) kaboom than a liquid rocket crashing. I didn't think about that in my previous post.

A disadvantage might be the fact that they're already loaded when toying around with the vehicle. Same thing goes for the shuttle of course, but there too they take safety precautions with the SRB's. Sure they can do similar things when dealing with Ares.

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one good thing about the SRB's that the general public learned this year is that if the fueled up sections fall off a railroad car, you don't have to worry about the fuel running into a river and killing a lot of fish or spontaneously blowing up.

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Indeed, upto the point it made me wonder why they were so cautious with the SRB's in the VAB. Well, in the context of SRB's accidentally igniting inside a building, you're better safe than sorry. And of course, individual segments cannot build up the required pressure, so a full stack is far more dangerous, even if it still needs some grenades to ignite. "No smoking" seems a very logical safety rule in the VAB to me.

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Thank you.
I'm tired of hearing people freak over the ingredients of a chemical reaction rather than the emissions of one.

Anyway; for the level of effects of perchlorate being observed, I doubt that the space program has any noticible affect on the levels. Although; I don't have any numbers to back up my opinion.

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And those would be the Flourine mixes?

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The last time I felt a warm fuzzy feeling, I was informed by my doctor that it was just gas.

As previously explained, in many scenarios it makes little difference. If one F-1 engine on the Saturn V shut down before about T+60, the entire vehicle would be destroyed.

The mere ability to shut down an engine has it's own risks. It means the engine can be shut down by accident. This has already happened. On STS-51-F the entire vehicle and crew was nearly lost because of a spurious SSME shutdown. There was nothing wrong with the engine, it was a sensor problem. Likewise one Soviet N-1 vehicle was lost because of spurious engine shutdowns during stage 1.

Personally I think liquid engines are somewhat better, but it's not that black and white. The ability to shut down a liquid engine has its own risks.

If you lose either a large solid or large liquid engine early in flight, it's basically loss of vehicle. The astronauts must eject, if a LES is present. Whether the liquid engine shuts down, or the solid engine goes out of limits, the result is the same -- fire the LES. The fact you shut down the liquid engine and lost the vehicle is little consolation.

It's true there are narrow conditions later in flight where loss of a single liquid engine is sustainable, as was demonstrated on STS-51-F and Apollo 13. But you don't typically use solid engines in that flight regime anyway, so it's not an option.

Solid boosters don't just blow up instantly with no warning. Even with the limited instrumentation on Challenger STS-51-L, there was plenty of indication the right SRB was malfunctioning, and time to auto-trigger a LES (had it existed).

With the upcoming Ares I, I'm sure the solid booster will be highly instrumented to make this even more possible.

I'm sure these results aren't perfect, but I've run some calculations to determine the exhaust products of a Shuttle SRB. This is what I estimate at the nozzle exit:

by Mole
H2 ... 30.00%
CO ... 23.08%
HCl ... 15.52%
H2O ... 13.03%
N2 ... 8.26%
Al2O3 ... 7.77%
CO2 ... 1.97%
H ... 0.26%
Cl ... 0.10%
HO ... 0.01%
Other ... trace

by Mass
Al2O3 ... 30.23%
CO ... 24.65%
HCl ... 21.58%
H2O ... 8.95%
N2 ... 8.82%
CO2 ... 3.31%
H2 ... 2.31%
Cl ... 0.13%
H ... 0.01%
HO ... 0.01%
Other ... trace

The large amount of carbon comes mostly from the PBAN binder and, to a lesser extent, the epoxy curing agent (though I had to guess at the epoxy formulation). I didn't figure any iron in the reaction because the iron oxide catalyst makes up only 0.07% of the propellant mass, plus I don't have data tables for Fe products.

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Solid boosters don't just blow up instantly with no warning. Even with the limited instrumentation on Challenger STS-51-L, there was plenty of indication the right SRB was malfunctioning, and time to auto-trigger a LES (had it existed).

Actually, they can explode very quickly with virtually no warning. I know of a Titan 34D failure in 1986 and a Delta II failure in 1997 that happened within seconds of ignition. Both caused severe damage to the launch pad. These catastrophic explosions are usually caused by either a failure of the insulation between the propellant and casing (allowing more propellant to ignite, causing excessive pressure) or of a crack in the propellant grain (exposing more propellant surface to combustion, leading to excessive pressure). You can include pressure sensors inside of the casing but you'd have very little time to escape should either of those scenarios occur. Fortunately, the Shuttle SRBs have a proven track record of success.

Very good Bob! Your calculations are quite close to NASA's own figures!

Unfortunately, even assuming 100% combustion of perchlorate (which seems overly optimistic to me), the exhaust is still environmentally problematic. Specifically, HCl breaks down to Cl₂, which in turn causes ozone depletion.

Again, as I said in my earlier post, the amount of pollution from SRBs is probably neglible as long as SRB launches are embarrassingly exceptional events.

Those number are pretty close.

The exact equilibrium composition of the exhaust depends on the temperature and pressure. Since these conditions change as the gas expands through the nozzle and into the surrounding atmosphere, a wide variety of answers can be calculated depending on exactly where the measurement is being taken. The slight differences between my numbers and NASA's could very well be due to calculating for a different set of conditions.

I also see the linked page gives the PBAN content as 14%. I've generally seen the PBAN content given as 12.04% with 1.96% epoxy curing agent. I also left the 0.07% iron oxide out of my calculations. These differences in propellant formulation no doubt alters the results somewhat.

Ammonium perchlorate decomposes at a temperature of around 240 C. With a flame temperature of over 3,000 C, I think we can safely assume the perchlorate will be completely consumed.

I don't doubt that.

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True, an astronaut could not see a red annunciator, think about it and pull the eject lever. But the same is true for many failure modes on liquid-fueled boosters. The LES on both Mercury and Apollo was on an automatic hair trigger for certain failure types. Neither astronauts nor flight controllers could react fast enough, but automated fault detection logic can.

I think the fault detection system and LES on a man-rated solid booster would be designed to work fast enough for the most common failure modes. Just because the initial failure and propagation cascade happens fast ("within seconds") from a human standpoint doesn't mean automated fault detection logic isn't fast enough.

From external cameras, solid booster failures seem sudden, explosive. It gives the visual impression of no warning whatsoever. However the same is true for certain liquid booster failures.

The Ares I Launch Abort System is currently planned to boost at least 15 g for at least two seconds. IOW it will accelerate the capsule away from the stack at about 500 feet per sec per sec. The reason is to provide escape opportunity for an on-the-pad booster explosion. The fault detection logic that triggers this would have sufficient sample rate to make the overall endeavor worthwhile, else why do it.

But the question is valid about does this cover all possible Ares I solid booster failiure modes? Knowing that requires a lot more than looking at old footage of past solid/liquid booster failures. It would require detailed high resolution telemetry from those past failures, plus SRB tests, coupled with an engineering analysis of the Ares and shuttle SRBs.

Here's a clip of the 1997 Delta II failure on YouTube.

I've read that during Apollo the major concern regarding the LES (at low altitude) was getting the CM far enough from an exploding booster that the overpressure didn't destroy it. Would an exploding SRB produce the same overpressure as an exploding LOX/LH2 stage? From that video it doesn't look like it would, but I'm certainly no expert on explosives.

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It generally shouldn't, due to the method of explosion. With a liquid fuel, as soon as the tank is ruptured, the fuel's surface area increases dramatically, and the fuel is almost all consumed in seconds after the event. Most solid rocket explosions happen from larger than anticipated surface areas of propellant burning (from a cracked propellant grain) and/or a clogged nozzle. Either one of these will drastically increase the internal pressure of the SRB, likely causing failure. However, after the initial rupture/blast, the remaining fuel stays in chunks rather than turning into a flammable mist, vastly increasing the time that the remaining fuel will burn (and reducing the amount of gas generated by that fuel). The initial rupture could be disastrous, but the overpressure afterwards from burning fuel will be greatly reduced.

Oh - good info bob. I forgot to account for the carbon in the binder.

Alright... I'm only going to say this once.

Based on what I have been informed of here and the information it has pointed me to and references I have thus perused as well as the points made by those in this thread...

I've pretty much changed my mind about using a solid rocket booster being a dangerous and dumb idea in general. (Although I'm still not sold on other aspects of the Ares but eh..)

Seriously... if you know me at all, you should be shocked, because I'm not one to admit I'm wrong in general...

The safety of using a solid booster for Ares I is a valid issue, but we don't have enough data to conclude what plausible failure modes might exceed the detection and reaction time of an automated launch abort system.

From the Titan IV, Delta, and other solid booster explosions, it superficially appears to happen very fast -- with no visual warning. However an instrumentation and launch abort package designed specifically for that situation might be fast enough.

Some previous liquid booster failures also seemed to happen very fast. An early unmanned Mercury/Atlas launch suffered structural failure. It happened very fast -- to the eye instantly. Yet instruments detected the failure and the LES fired moments before this, pulling the capsule away. There is video of this, but I can't find it on line.

I'm sure designers of the Ares I abort system and contingency procedures are wrestling with this issue right now. There may be some SRB failure modes which happen so fast that even an automated detection and abort system cannot react in time. However we can't determine that reliably just from the visual appearance of past solid booster failures.

If I recollect from the CAIB hearings, the current shuttle SRB casings are overdesigned (from a structural strength standpoint) by a factor of 2. IOW their ultimate structural limit is 200% of the maximum worst-case scenario. So they are pretty rugged, but obviously a catastrophic failure would destroy the vehicle (shuttle or Ares I). I don't think unmanned solid boosters have such huge design margins.

Either way, the question is can an automated fault detection and launch abort system react fast enough for most Ares I SRB failure modes. Also can it do so with low probability of a false trigger (that was a concern during the Mercury program). Launch abort systems typically have an approx. 10% fatality rate from the system alone (extreme g force, parachute/pyros failure, etc), so you obviously don't want a false trigger.