Solid rockets are not very performing in term of ISP or speed of the ejected gases.

So an all solid rocket will need 3 or 4 stages when an all liquid rocket need only 2 or 3.

But solid rocket can be made very powerful , with a big thrust and it is very useful at the beginning of the flight , to go through the low atmosphere and to accelerate the faster as possible.Because if you accelerate very slowly you waste your thrust just doing a little more than compensating for gravity.

These are the reasons they are used as strapon or as the first stage.

Also even if they are less performing they are cheaper and simpler to operate.

After 50 years of LV development - it's quiet clear that Solids have their place - thrust augmentation for 60-120s early in flight or the launch of small payloads via Vega, Pegasus, or Taurus.

Samkent clearly has an agenda which he is not being entirely clear about - and is, sadly, misrepresenting the facts to push this agenda.

Solids are pretty reliable but when they do fail, they fail spectacularly. So much so, the Air Force has assessed that if Ares I failed early in the flight, the crew will be killed. They based this study on the failure of a Titan IV SRB back in 1998. The analysis result is that the Orion launch escape system wouldn't be able to get the crew clear of the raining debris. Nylon parachutes don't like raining debris. Here's a video of a Delta II failure caused by an solid that exploded. Such failures are rare but they do happen from time to time.

Several things can cause a large solid rocket motor to fail. Two of the more common failure causes are insulation separation and propellant cracks. Insulation separation allows the hot combustion gases to come in contact with the casing wall. This can cause more propellant to ignite prematurely. Propellant cracks cause more propellant surface area than intended to be exposed for combustion, resulting in higher pressure inside the casing. In either case, the resulting explosion is usually spectacular.

The debris field from that Delta II explosion is pretty extensive with large, flaming chunks flying long distances.

Bob Clark

It's true the study said the Orion capsule wouldn't survive a launch abort attempt from T+30 to T+60 sec.

However, the study apparently assumed intentional self-destruct of the SRB, and escape system firing roughly coincident with that.

In the real world, that's not how it would work.

For a manned launcher, the SRB would be heavily instrumented with vital parameters tied into the escape system. An incipient catastrophic failure would trigger the launch escape system before that failure actually happened. This was done on each manned launcher before the shuttle.

You don't wait until something blows up to eject. Humans are too slow. Certain critical parameters will instantly trigger an abort, before the failure cascade destroys the vehicle.

In the Titan IV failure, there were several seconds BETWEEN the vehicle anomaly and BEFORE the destruct charges were fired. In a manned launcher those seconds would be used to get the crew to safety via the launch escape system.

Would a motor case failure (as occurred with a Titan IV motor during a 1991 static test, a Titan IV launch in 1993, and the 1997 Delta II launch that Larry Jacks linked to) give sufficient warning to trigger the LES beforehand? Unlike "burn-through" failures, case ruptures are usually sudden.

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“There’s nothing that spells progress in large, friendly letters like trying to combine two totally incompatible technologies.” – David Szondy, Tales of Future Past.

Would this not apply to any configuration using large RSRMs as well? (i.e. Direct)?
Note that the Titan was destroyed by the RSO, who hit the button and blew the (non-man rated) solids as well as the core. The Titan solids also have significantly thinner walls than the RSRMs.
I don't know what studies have been done on the various potential RSRM failure modes, but STS51L showed one, and the SRB survived that accident until blown by the RSO. Barring a major undetected structural flaw, it would "seem" the thick walled RSRMs are much less likely to present situations where the case "ruptures" (as in the Delta SRM failure, and the RSO destruct of the Titan).
I'm of the Story Musgrave thought on the big solids...they scare me. But they do have an amazing history of reliability, with the one major Shuttle exception. This case would not, it appears, be an automatic "100% fratricide" situation in an Aires 1 application.
BTW, how have all the seals been performing since the major post-51L redesign?
Just some thoughts at this end...

In the early ATK brochures, there was some sort of engineering analysis diagrams of SRB failures, and they "obviously" pointed towards a "sufficient warning" story...whether this was accurate, or just marketing, I couldn't guess.
I'm curious as to how far, in various flight regimes, the LES would carry Orion from the failing booster before drogue chute deployment?

It would depend on where the event happened, altitude and velocity -- all of which impact airflow over the ejected material.

There are various SRB failure modes, all of which more likely than a case burst: loss of thrust vector control, burn-through of O-ring, igniter failure, etc.

Out of about 250 SRBs flown in the shuttle program, there has never been a case burst. The O-ring failure on Challenger was a progressive event that a launch escape system could have detected.

In general I believe ATK analysis pessimistically assumes an Ares I case burst would not be suvivable. However this category of failure represents only a small subset of all possible SRB and vehicle failure modes.

In reality there are probably survivable case burst events, depending on the exact circumstances, e.g, location on booster, size, altitude, velocity, launch escape performance, etc.

The SRBs on unmanned boosters are manufactured and tested to lower standards than the shuttle SRBs. Each shuttle SRB is X-rayed and ultrasonically tested hundreds of times. Also each shuttle SRB is designed and manufacturered with a 200% structural safety margin, far more than unmanned vehicles.

Thanks; more for me to look at.
But; besides my lack of fluency in boosters, I am trying to get across the idea that quantity of one or the other is not an indicator that it is better or worse.
There may be some correlation, but the design of the entire flight parameters seems to be a larger consideration.


(re: new design)
Yes; absolutely. I have no clue where to draw the line myself, but there are some that are much more obvious than others.

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Numbers are not case sensitive. (me)

yes.... that would be control.

Yeah, I was just being pedantic. I'm sure someone could devote an entire book to the engineering trade-offs involved in deciding between liquid and solid engines; neither is clearly superior.

I thought about going through formulaterp's list of launchers and marking them as "new" or "derived", but I realized that the dividing line would be arbitrary and I'd need a paragraph of text to explain each one.


While reading about large solids, I found something unexpected. A 1965 NASA study looked at replacing the first stage of the Saturn IB with a monster 260 inch (6.6m) diameter monolithic solid motor. Aerojet got as far as test-firing three motors before the funding ran out—another victim of end-of-Apollo cutbacks. So, the arrangement of a solid first stage and cryogenic second stage to put a capsule into LEO isn't so new after all.

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“There’s nothing that spells progress in large, friendly letters like trying to combine two totally incompatible technologies.” – David Szondy, Tales of Future Past.

Aside from the fact that the fuel costs are still quite tiny in comparison to the overall launch costs, meaning there isn't much to save by optimizing that portion of the costs...not all liquid rockets are equal. The Shuttle uses liquid hydrogen. Aside from being notoriously prone to leaking given the slightest excuse, the low density thus requires a huge tank with a large surface area, and liquid hydrogen is both deeply cryogenic and has a low heat of vaporization, boiling at 20K with only 0.9 kJ/mol compared to the 90K and and 6.8 kJ/mol of liquid oxygen. This adds up to large losses of the relatively expensive LH2.

A LOX/RP1 engine doesn't have this problem. RP1 doesn't boil away in the tank, and LOX is very cheap, the costs of dealing with it are mostly in the equipment and preparation. The LOX/RP1 combination is better suited for higher thrust first stages than LOX/LH2, making solid boosters unnecessary, and though it has lower specific impulse, it is far better in that respect than solids. The higher density also means a far smaller fuel tank, reducing the size of the first stage. The higher Isp of hydrogen is of more benefit on higher stages, which coincidentally also tend to be far smaller, reducing the boiloff problem...or hydrogen can be eliminated completely.

We went to the moon taking this approach, and the Saturn V still seems like a far better balanced vehicle than many of the vehicles which followed it, which seemed to have a confused obsession with both high performance and difficult to use LH2 and dangerous and low performance solid rockets.
http://commons.wikimedia.org/wiki/Fi..._schematic.jpg

But again...fuel costs are a tiny portion of the total costs. It's a few million dollars in this case, yes, but it's only a few million. There's far, far more money to be saved by looking elsewhere.

Regarding the recent USAF study, there's a major point I didn't see made here.
When a LAS on Ares I is triggered and before SRB destruct at the time point this study talks about (IIRC between 30 s and 60 s into the flight), the dynamic pressure on the Orion/LAS stack is immense. This is an inherent "feature" of the Ares I design (one that actually drived the already oversized LAS for Ares I) and other shuttle-derived approaches don't suffer as much.

The end effect of it is that even though the LAS motor is firing, it's not actually putting much distance between Orion and the failing booster - the dynamic pressure drag just negates all that escape rocket impulse. At the other end you've got this high thrust booster thing potentially chasing you. You need it to terminate thrust and stop chasing you ASAP.

There is talk here about how SRBs are safe and fail very rarely, but the point is it doesn't have to be an explosive SRB failure to result in this scenario at all. It can be any other reason for abort during that time period - a guidance failure (like the Titan IV, Ariane V), SRB thrust vector control failure, upper stage structural collapse due to loss of pressurization, etc. Even though these aren't immediately catastrophic SRB failure modes, the way the SRB termination system works effectively makes no difference. The SRB blows up raining a hail of flaming chunks, regardless of whether the casing ruptured by itself or was ripped apart deliberately.

Also bear in mind the range safety requirement is that a failing booster needs to be destroyed as early as possible in order to prevent the possibility of FTS getting disabled by ongoing booster breakup/failure, resulting in no way of disposing of a tumbling booster which can potentially harm the innocent public. All the more since the timeline we're talking here is still early flight, SRB close to the pad and still loaded with propellant.

Just to throw something else in the mix, Fraser just posted today an article on a biofueled LOX rocket test.

Company Flies Biofuel Rocket (Video)

Along with the whole "green" aspect, the article claims that the JP-8 mix outperformed a similar RP-1 rocket, and ran cleaner.

The costs of delaying a shuttle launch do not show the advantages of solids, but the disadvantage of cryogenic liquid fuels. If you were to find the costs to delaying, say, a Proton launch - they would be a lot less, even taking into account the smaller payload.

Cryogenics are a major pain in the arse to use; but they have a clear advantage over solids and other liquid fuels in terms of Isp. It is popular to pretend the Shuttle is just a big pile of rubbish engineering decisions, but using liquid hydrogen is not one of them. The combination of high thrust/low Isp solids for boosters and lower thrust/high Isp for the main stage is a sound method for building rockets, which is why the European Ariane 5 uses the same approach despite being designed independently.

In any case, solids have a big set of problems that any liquids do not have:

1. Not practically throttlable.
2. As mentioned by myself and others, not great Isp
3. Worse vibration problems that liquid engines, which has caused difficulties with Ares I

And there are problem more I can't of right now. Rocket scientists are not fools; if solids were so universally better nobody would bother spending the huge amounts of money required to develop and fly liquid engines.

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"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995

Those are good points. Any major failure in any system during powered SRB ascent will generally necessitate firing the FTS charges on the SRB. Even if the SRB itself was infinitely reliable, there would still be valid scenarios where other systems fail and the SRB must be destroyed.

The disagreement is between the USAF and NASA models for that case. Namely, NASA says there would be adequate separation between the capsule and the detonated SRB, where the Air Force says no.

Also it's not totally clear to me the FTS must be fired immediately after LAS activation. In the Challenger situation, the RSO waited 37 sec before firing the FTS on the SRBs. Admittedly that was somewhat further downrange and SRB propellant was mostly expended, so potential risk to public was less.

However the Challenger situation would seem to indicate the FTS system is robust and reliable.

Consider that it could be a no-win situation either way.

* If the SRB is destroyed immediately after abort, you don't have to worry about the booster chasing you, but you have a bunch of flaming propellant fragments engulfing you after you deploy parachutes. IIUC, the assumption in the study is the propellant fragments have a similar drag coefficient as Orion so they will feel similar aerodynamic effects. End result: because of high dynamic pressure you didn't get far away from the debris.

* If the SRB isn't destroyed immediately, because the SRB+US stack has so much more mass per surface area, it doesn't feel the aerodynamic drag as much of an issue, while your light Orion capsule struggles with its LAS to get away. So you could (depending on the breaks and how much the booster tumbles and in what direction) have the booster chase you quite closely. Then after a delayed destruct you again end up in a debris field.

This is just one of the side-effects of baselining a shuttle booster for something it was never intended to do - be the sole first stage of a launch vehicle. All its shortcomings have come up - the thrust oscillation problem, the controllability issue and now this. SRBs were logically designed to provide as much of a kick early in the flight for the shuttle and when you translate that to the Ares I design, it means higher maximum dynamic pressures than any other launch vehicle, liquid or SDLV. Which is a nightmare for LAS design.

They can be throttled, but I believe that's done by the packing of the solid propellent, which means that they can only fly a predetermined profile, not ones that can be controlled in flight.

Yes, of course, what I meant was you can't actively control the throttle. Its determined when the propellant is manufactured.

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"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995

Which is exactly like ALL liquid booster engines except the space shuttle SSME. With that one exception, liquid engines also cannot be throttled.

In fact, solids are relatively easy to manufacture with a fixed throttle schedule. E.g, the shuttle SRBs vary thrust by nearly 2:1 over the flight period. They throttle back during max Q, then throttle up afterwards. By contrast, most liquid engines have fixed thrust determined by design and manufacture.

That is very wrong.

As I understand, both EELV variants throttle, as do some other liquid fuelled LV's.

The RS-68 can also be throttled. As can the Soviet/Russian NK-33. And the RD-170. But don't let yourself be troubled by facts.

So, like I just said, SRBs can't be throttled actively. SSME's, as well as those engines I mentioned, and certainly more engines that I couldn't quickly confirm as throttlable - can be throttled actively.

Solids have no control over the thrust or duration of burn once they are lit. This means you can forget about engine-out capability, and you can also forget about accurate burns of any kind. Solids belong on the sides of a big liquid fueled rocket during the first couple of minutes of launch. You can't build an entire space program on them.

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"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995

True, but how often is that capability needed outside of the normal flight profile reasons for it?
On a single engine machine, I think you can forget about engine out capability completely anyway.
Why? And to what degree?

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Numbers are not case sensitive. (me)

Isn't that exactly what NASA is doing? Are you saying NASA with it's big computers and big budget is wrong and it won't work???

The LM DPS could be throttled.

Every flight profile would require a different solid fuel grain mix. If you tweaked the payload much, it's be a new requirement, a new thrust profile, a new grain mix and thus a new qualification program.

Make the booster only part of the thrust profile and you can compensate with the liquids and you have much more flexibility.


And yes, Samkent, imho, Ares 1 is wrong. Part of NASA has got this wrong. I believe Space X, LoMart, Boeing, Ariane, Starsem, Energia, the Direct team etc etc..... I don't believe the Constellation program has it right. I think they have it wrong. I'm not alone.

I can see your point, but I really don't see this happening with Ares I. It is a very specific use booster with a very specific payload.
I'm not sure what kind of load variances there would be, but I would think that if the variance was so much to change the burn profile, that they might rethink the payload.

I realize you are replying to Samkent, but I wanted to comment.
I personally am not sure that they got it right, but I do feel that they got it close enough to right that there might be factors that I don't understand that bring it into right.
I will wait and see, I will be satisfied with a performance on par with the Russians, but that's going to take some time. Otherwise, I really don't see an apples to apples comparison with cargo.

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Numbers are not case sensitive. (me)

The Orion will evolve. We have a 4 seat version for ISS. Hopefully they'll restore a 7 seat version for ISS. Then there's the Lunar version, or beyond E-M system missions. There are launches to ISS. There are launches for Earth-Orbit-Rendezvous. Something like the Shuttle must surely adjust its launch profile for different ISS missions, I'd wager Saturn V adjusted its thrust profile from Apollo 8 to Apollo 17.

Margin margin margin. That's what a chap is saying to the Aug. Comm. right now. Ares 1 doesn't have any.

No. NASA is not building an all-solid orbital launcher.

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"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995