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Solids, Q&A
by
tu8ca
on 03 Jan, 2011 21:50
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Why aren't solids used more for orbital launches?
I understand the fuel has less energy, so a larger rocket is needed. But why are liquid stages worth all the added complexity, cost and infrastructure?
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#1
by
butters
on 04 Jan, 2011 05:19
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Many, many reasons. One understated issue with large solid rockets is that they're very heavy preloaded with propellant and therefore difficult to transport.
Shuttle could not be moved from the VAB to LC-39 without the massive crawler-transporters to distribute the extreme load of the SRBs, which are obviously assembled from segments because of transportation issues.
Ariane 5 faces a similar fixed cost penalty because of its large SRBs, which have to be manufactured on-site at the Guiana Space Center and moved with a special locomotive equipped with a 32-speed transmission.
Add that to the numerous other reasons, including low specific impulse, low mass ratio (because the entire propellant tank is subject to combustion pressure), poor ground crew safety, poor shutdown capability, no restart capability, higher vibrations during flight, hydrochloric acid emissions, etc...
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#2
by
Space Invaders
on 04 Jan, 2011 06:33
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Poor ground crew safety? When was the last time a solid rocket killed a ground crew member? SRBs need very high temperatures to ignite, you can't just extinguish your cigarette on one to light it.
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#3
by
cd-slam
on 04 Jan, 2011 08:16
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#4
by
Nomadd
on 04 Jan, 2011 11:31
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Poor ground crew safety? When was the last time a solid rocket killed a ground crew member? SRBs need very high temperatures to ignite, you can't just extinguish your cigarette on one to light it.
How many times have you seen liquid engines cut off right after ignition because something wasn't right? Kinda hard to do with solids. Even harder to offload fuel to pull back into the hangar to fix something.
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#5
by
Space Invaders
on 04 Jan, 2011 13:33
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http://en.wikipedia.org/wiki/2003_Alc%C3%A2ntara_VLS_accident
Irrelevant of the fuel type. If it had been a liquid rocket that ignited suddenly in the same circumstances, the people standing on the launch pad would have died as well. They were far too close to survive any type of ignition.
How many times have you seen liquid engines cut off right after ignition because something wasn't right? Kinda hard to do with solids. Even harder to offload fuel to pull back into the hangar to fix something.
You don't need to cut solid engines right after ignition because they are much simpler and therefore problems are much less likely. The Challenger disaster was due to a design flaw and redesigned SRBs are safe.
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#6
by
ugordan
on 04 Jan, 2011 13:45
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http://en.wikipedia.org/wiki/2003_Alc%C3%A2ntara_VLS_accident
Irrelevant of the fuel type. If it had been a liquid rocket that ignited suddenly in the same circumstances, the people standing on the launch pad would have died as well. They were far too close to survive any type of ignition.
Not correct. That's kind of why the standard safety procedure is to have very few to no people around the liquid fueled vehicle when it's fueled. In other words, there wouldn't
be 20 technicians and engineers just standing around a fully fueled liquid vehicle. Also the fact the propellants are physically separated so you would literally have to blow up the vehicle first before it would provide an major explosion/fire hazard.
Now tell me you can have an
unfueled solid vehicle at the pad during checkouts...
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#7
by
ugordan
on 04 Jan, 2011 13:59
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You don't need to cut solid engines right after ignition because they are much simpler and therefore problems are much less likely. The Challenger disaster was due to a design flaw and redesigned SRBs are safe.
Design flaw/production flaw, what difference does it make? A failure is a failure.
Titan 34D, Delta II, Challenger, Titan IV failures were recent solid motor failures. Out of those 4, 3 were
explosive failures. How many U.S.
explosive liquid engine failures are you aware of in recent history?
Also, cocky statements like "redesigned SRBs are safe" are what gets people killed.
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#8
by
Jim
on 04 Jan, 2011 13:59
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Irrelevant of the fuel type. If it had been a liquid rocket that ignited suddenly in the same circumstances, the people standing on the launch pad would have died as well. They were far too close to survive any type of ignition.
You don't need to cut solid engines right after ignition because they are much simpler and therefore problems are much less likely. The Challenger disaster was due to a design flaw and redesigned SRBs are safe.
That is just plain wrong and shows a complete lack of understanding.
A liquid engine would not have ignited in the first place. The ignition danger is unique to solids.
Segmented solids are not "simpler". Solids have a higher failure rate.
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#9
by
Space Invaders
on 04 Jan, 2011 14:15
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Not correct. That's kind of why the standard safety procedure is to have very few to no people around the liquid fueled vehicle when it's fueled. In other words, there wouldn't be 20 technicians and engineers just standing around a fully fueled liquid vehicle. Also the fact the propellants are physically separated so you would literally have to blow up the vehicle first before it would provide an major explosion/fire hazard.
Now tell me you can have an unfueled solid vehicle at the pad during checkouts...
The R-16 of the Nedelin disaster was fueled
and surrounded by dozens of people. In other words, there could
be 120 technicians and engineers just standing around a fully fueled liquid vehicle. It just depends on how stupid they are.
And you don't need an explosion/fire to happen. If for some reason the liquid rocket fires prematurely and you're around, you die.
That is just plain wrong and shows a complete lack of understanding.
A liquid engine would not have ignited in the first place. The ignition danger is unique to solids.
Segmented solids are not "simpler". Solids have a higher failure rate.
Yet again, what about the Nedelin disaster? It was a liquid rocket and it ignited unexpectedly.
Design flaw/production flaw, what difference does it make? A failure is a failure.
Titan 34D, Delta II, Challenger, Titan IV failures were recent solid motor failures. Out of those 4, 3 were explosive failures. How many U.S. explosive liquid engine failures are you aware of in recent history?
Also, cocky statements like "redesigned SRBs are safe" are what gets people killed.
If you develop a liquid rocket with a flawed design, it will eventually explode too. If you develop a microwave oven with a flawed design, it will eventually catch fire or electrocute you too. Anything with a flawed design is dangerous. My point is that a flawed design has nothing to do with rocket type, rather it can affect any sort of rocket.
As for Titaan 34D, if you're talking about the 1985 accident, it happened after solid rocket booster separation.
Hey, it's not like I'm an ATK fan or something, but sometimes it seems solid rockets are the devil incarnate for some users here. Both liquid and solid systems have their roles and there's no point in preaching how wonderful and perfect liquids are and how horrible and flawed solids are.
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#10
by
Jim
on 04 Jan, 2011 14:43
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Yet again, what about the Nedelin disaster? It was a liquid rocket and it ignited unexpectedly.
If you develop a liquid rocket with a flawed design, it will eventually explode too. If you develop a microwave oven with a flawed design, it will eventually catch fire or electrocute you too. Anything with a flawed design is dangerous. My point is that a flawed design has nothing to do with rocket type, rather it can affect any sort of rocket.
As for Titan 34D, if you're talking about the 1985 accident, it happened after solid rocket booster separation.
Wrong again. The accidents are not the same. Alcāntara happened because of work directly on the rocket. This can happen anywhere and time with an SRM. See at EAFB and PSTF incidents. Nedlin happened because the control center sent commands and would have happen with or without a crew at the pad.
It has nothing to do with flawed design. SRM are sensitive to process flaws.
Do some research, there were two Titan 34D incidents.
Solid rockets
are the devil incarnate for manned missions
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#11
by
ugordan
on 04 Jan, 2011 16:38
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The R-16 of the Nedelin disaster was fueled and surrounded by dozens of people. In other words, there could be 120 technicians and engineers just standing around a fully fueled liquid vehicle. It just depends on how stupid they are.
You're grasping at straws now and are practically admitting it.
Comparing:
a) an event from the very dawn of the space age, employing Soviet military procedures in a government regime which cared little about the value of human life
to
b) a civilian launch vehicle operation at the pad in the 1990's
...is disingenuous. Note I specifically stated it's a "standard safety procedure" to evacuate the pad while tanking/pressurizing tests because you would almost inevitably bring up Nedelin. The fact the Soviets didn't take adequate safety precautions to prevent that from happening does nothing to disprove the fact a solid booster is inherently more dangerous to work with because it is loaded
at all times.
And you don't need an explosion/fire to happen. If for some reason the liquid rocket fires prematurely and you're around, you die.
Once again that implies
1) that the vehicle is loaded with propellant
2) that you're stupid enough to be around at the time.
My point is that a flawed design has nothing to do with rocket type, rather it can affect any sort of rocket.
The point about the Challenger because of which you brought up that fact is that there is no health check at ignition because solids don't have that ability. The drop in Challenger SRB booster pressure could have been detected right at
liftoff ignition for all we care and it still wouldn't have mattered because once it ignites that's it. Design fault or no design fault. Both booster types are prone to failures happening at some point in flight. Liquids at least have the ability to prevent problems detectable right at ignition from dooming the flight later on. Not to mention that liquid engine failure modes are typically more benign than with solids, even if there are more of them relatively speaking (debatable).
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#12
by
tu8ca
on 04 Jan, 2011 17:18
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Many, many reasons. One understated issue with large solid rockets is that they're very heavy preloaded with propellant and therefore difficult to transport...
Come to think of it, most all-solid rockets are on the small end.
Does the cost of solid fuel come into play? I understand the cost of lox, h2 and kerosene
don't even show on the radar, compared to the rest of the launch cost. Solid fuel seems to be about 100x more expensive per pound (guestimating). Anyone have the numbers on this?
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#13
by
kevin-rf
on 04 Jan, 2011 17:35
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I believe that the cost of hypergolic's are also in the stratosphere. Cost does not seem to have kept them from being used. Though to be fair there is a desire to cut back on them from safety/accidental exposure side.
Anyone have a good list of costs?
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#14
by
tu8ca
on 04 Jan, 2011 17:49
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I believe that the cost of hypergolic's are also in the stratosphere. Cost does not seem to have kept them from being used. Though to be fair there is a desire to cut back on them from safety/accidental exposure side.
Anyone have a good list of costs?
I'm really interested in this. From the cost of rawmaterials, solid fuel seems to be below $5/lb (again, guestimating), but I've read that the SRB's fuel is around $20/lb after manufacturing.
JAXA is using a
thermoplastic binder instead of a thermoset. They say it reduces cost because they can manufacture ingots that are easy to store, ship and recycle, then cast the grain as needed from those ingots, thereby greatly reducing the size and cost of their solid fuel manufacturing facilities.
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#15
by
Comga
on 04 Jan, 2011 20:14
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#16
by
Proponent
on 11 Jan, 2011 02:34
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Thanks for the price list, Comga.
How does RP-2 differ from RP-1, and where's it used?
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#17
by
jbirdav8r
on 11 Jan, 2011 03:10
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RP-2 is similar to RP-1 with a lower sulfur content. I'm not aware it's being used at all...significantly more expensive to refine for a small benefit. Neither are solid fuels though...very high-grade kerosene.
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#18
by
Malderi
on 18 Jan, 2011 16:07
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Could someone talk a little bit about the tradeoffs among solid propellants, or point me to a source? Shuttle SRBs use PBAN, I think, but there's HTPB which has been talked about as an alternative. What are the tradeoffs between them (and potentially other solid fuels?)
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#19
by
baldusi
on 18 Jan, 2011 21:47
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Could someone talk a little bit about the tradeoffs among solid propellants, or point me to a source? Shuttle SRBs use PBAN, I think, but there's HTPB which has been talked about as an alternative. What are the tradeoffs between them (and potentially other solid fuels?)
There's also the China Lake Compound 20.