Thrust
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S-IC Stage Vs. SRBs Question

Sat Mar 24, 2012 5:00 pm

First off, these are things I've read that I'm not 100% sure ring true. I am posting this to get answers from more informed people.

Basically, apart from the S-IC not being able to be reused, I was wondering what the advantages of each were over each other. I know that the SRBs were more a penalty in terms of dry weight, and I don't know how good their performance was past max Q...specific impulse I think was a bit higher than the S-IC in the lower atmosphere, but I've read certain claims of the S-IC getting a specific impulse of something like 304 in the later phases of the launch.

The last advantage, which I'm not sure of or not, appears to be that the SRBs fully fueled had a higher thrust-to-weight ratio than the S-IC, which used almost 5,000,000 pounds of fuel and had to burn longer to get the Saturn V to the same altitude, although it could get the Saturn V up to 6,000 mph vs. the SRBs, which could only get the shuttle to about 3700 mph prior to separation.

One guy I know with some knowledge in rocket science claims that the S-IC was much less efficent than the SRB because it was a low thrust-to-weight ratio that ended up wasting a lot of fuel, although I would think that should be taken with a grain of salt since the S-IC used RP-1 and LOX, which I was told costs less per pound than aluminum percholorate, although I thought SRB was better for storing purposes.

I guess my final thought was which was more suited for heavy payloads? Could the SRBs have acted as replacements for the S-IC had the Saturn V been kept in production? I mean, they were almost as powerful.
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kc135topboom
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RE: S-IC Stage Vs. SRBs Question

Mon Mar 26, 2012 2:07 pm

The Saturn V was the biggest and most powerful rocket ever built and became opertional. The Saturn V also never had a payload launch failure.

The S-1C first stage was essential in getting heavy payloads into orbit. It had 5 F-1 engines, each producing over 1,522,000 of thrust, for a total thrust of 7,610,000 lbs. With this first stage the Saturn V rocket could lift a 262,000 lb payload into LEO. In contrast the SRB/Shuttle combination can lift a 53,600 lb payload to LEO. So the Saturn V can lift some 4.8 times what the shuttle can lift to LEO. The 'burn time' for the S-1C was some 150 seconds.

The SRBs each had some 2,800,000 lbs of thrust for a total of 5,600,000 lbs. Add to that initial thrust was the 3 SSMEs which each had about 418,000 lbs of thrust (1,254,000 lbs thrust from the SSMEs) making a total combined vehicle initial thrust of 6,854,000 lbs of thrust, some 756,000 lbs less initial thrust when compared to the S-1C alone. The 'burn time' for the SRBs is some 124 seconds.

Remember, the Space Shuttle and SRB combination was essentially a single stage to orbit, and could only achieve a max weight of 8,390 lbs to a GTO. In contrast the Saturn V 3 stage rocket could lift a payload as high as a Moon orbit.

But none of the Saturn V launch system was reusable, thus making it a very expensive one shot vehicle. At least one of the SRBs was used 43 times during the space shuttle program.

So which was better? That really depended on what you wanted to do and what you wanted to put into space.
 
KFLLCFII
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RE: S-IC Stage Vs. SRBs Question

Mon Mar 26, 2012 8:44 pm

Quoting KC135TopBoom (Reply 1):
In contrast the Saturn V 3 stage rocket could lift a payload as high as a Moon orbit.

Question...In theory, wasn't the Saturn V designed to get a payload as high as Mars? Or would the launch vehicle itself have required (extensive) modifications to do so?
"About the only way to look at it, just a pity you are not POTUS KFLLCFII, seems as if we would all be better off."
 
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kc135topboom
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RE: S-IC Stage Vs. SRBs Question

Mon Mar 26, 2012 11:29 pm

No, the Saturn V was to small to be able to lift enough mass for a Mars mission. In fact, the manned lunar missions were at about the extent of the S-V's capabilities. There were studies for a follow on rocket like the Saturn-C-VIII and the NOVA programs. In fact IIRC the NOVA-8C or the NOVA-8L were considered for the Mars mission. The Nova rocket could have had 8 F-1 engines.
 
PITingres
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RE: S-IC Stage Vs. SRBs Question

Tue Mar 27, 2012 3:29 pm

Probably the big advantage of a liquid fueled stage is that it's throttlable and can be shut down on demand. The best you can do with a solid is fool with the central passage shape, and that doesn't give you much in the way of controllability (plus it's built in and can't adjust for conditions). Once you light off a solid, you are committed.

Solids are a bit easier to build, although the casting problems for really large solids like the SRB's can be tricky. Liquids need a crap-load of piping, cryogenic tankage (although LOX isn't really hard), and some fancy stuff in the engine itself.

I'd have to dig around in my references to say anything about thrust/weight or Isp for the F-1 vs the SRB. I do have a notion that part of the S-1C's problem wasn't that it was inefficient per se, but that it was underpowered. Gravity losses for the first 15 seconds or so were pretty bad.

As for reusability, yes, the SRB cases were reclaimed. I don't know whether that really made a material difference in overall system cost, when you factor in the cost of picking them up and cleaning them out.
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HaveBlue
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RE: S-IC Stage Vs. SRBs Question

Tue Mar 27, 2012 6:53 pm

Quoting PITingres (Reply 4):
As for reusability, yes, the SRB cases were reclaimed. I don't know whether that really made a material difference in overall system cost, when you factor in the cost of picking them up and cleaning them out.

That's what I have always wondered... when you have to clear vast areas for the drop, have ships with crews to pick them up, bring them in and clean them out.. just didn't seem like just making a bunch of them (they don't seem overly complex) would be way more expensive.
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Areopagus
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RE: S-IC Stage Vs. SRBs Question

Tue Mar 27, 2012 9:26 pm

Quoting KFLLCFII (Reply 2):
Question...In theory, wasn't the Saturn V designed to get a payload as high as Mars? Or would the launch vehicle itself have required (extensive) modifications to do so?

TopBoom's answer is correct if the gist of the question is about sending an Apollo-class payload to Mars. But Saturn V could have sent smaller payloads Marswards. NASA publicity materials at the time listed some pretty impressive payloads that Saturn V could have launched on interplanetary missions.
 
Thrust
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RE: S-IC Stage Vs. SRBs Question

Thu Mar 29, 2012 3:37 pm

I read that one of the reason the S-IC fell out of favor for the shuttle was not only expenses and lack of reusability, but also for wet weight savings.
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Thrust
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RE: S-IC Stage Vs. SRBs Question

Thu Mar 29, 2012 4:21 pm

Quoting PITingres (Reply 4):

It seems to me like the S-IC's disadvantages apart from non-reu

Quoting PITingres (Reply 4):

I'm not sure how much I agree with it being underpowered..especially after max Q, the Saturn V if anything was overpowered..total thrust increased to over 9 million pounds and one of the engines had to be shut down almost half a minute before separation because acceleration would get too high.
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KFLLCFII
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RE: S-IC Stage Vs. SRBs Question

Fri Mar 30, 2012 12:59 am

Quoting KC135TopBoom (Reply 3):
Quoting Areopagus (Reply 6):

Very good guys, thanks for the information.   
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Thrust
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RE: S-IC Stage Vs. SRBs Question

Fri Mar 30, 2012 5:27 pm

Quoting KC135TopBoom (Reply 1):

Didn't the SRBs have 3.3 million pounds of thrust each max? NASA claims the shuttle stack had a total of 7.8 million pounds of thrust with the SSME's and SRBs combined? The other thing I'm wondering is the behavior of the SRBs in a vacuum? Did their thrust increase, or were they throttled down after maximum dynamic pressure?...I guess I'm trying to gauge how they behaved in a vacuum compared to the F-1 engines...I've never been able to find a measurement for the SRB's max thrust in a vacuum...for the Saturn V, at least for the J missions, the total thrust increased to 9.2 million pounds in a vacuum...each F-1 engine's performance and efficiency improved dramatically.

The other thing I'm wondering about was the choice to use aluminium perchlorate and liquid hydrogen/LOX on launch vs. just a single stage with liquid kerosene and liquid oxygen. I'm curious as to what the advantages/disadvantages were of each, and if the SRBs strapped on to a much larger S-II stage could have done the same job as the S-IC. I'm just curious as to the performance of both types of propellants.

I don't know how much the shuttle and external tank weighed wet at the point of SRB separation, but it seems like both the S-IC and the shuttle weighed about the same at the points of the first separation.

I'm just curious as to why the S-IC had a much heavier mass of propellant than the solids...was it due to the propellants being in liquid form, or the F-1 engine's efficiency, and was it good or bad to have a 5,000,000 pound first stage booster. It just seems like in general that liquid kerosene and LOX has fallen out of favor as first stage propellants.

It does seem like the shuttle suffered more of a dry weight penalty than the Saturn V though. While the Saturn V was more massive, most of that mass came from propellant...dry weight I'm not sure if it was really any heavier than the shuttle. It certainly could launch bigger payloads.
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Thrust
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RE: S-IC Stage Vs. SRBs Question

Fri Mar 30, 2012 5:32 pm

Quoting KC135TopBoom (Reply 1):

If you include the shuttle as payload though, you actually end up getting pretty comparable statistics...I don't know if the external tank can be counted or not because I thought the shuttle didn't separate from it until after it reached orbital velocity...I'm not sure if it had reached orbit yet though...I thought it also fired burners after several minutes to boost it to its proper height.
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RE: S-IC Stage Vs. SRBs Question

Fri Mar 30, 2012 8:32 pm

Quoting KC135TopBoom (Reply 3):
was to small to be able to lift enough mass for a Mars mission

About 15 years ago, British Sci-Fi writer, Steven Baxter, wrote an alternative history novel, 'Voyage', featuring a manned NASA mission to Mars in 1985/86, via the technical, political and his character's personal challenges to make it happen.

He got a lot of collaboration from NASA insiders for researching it, basically a series of developed Saturn 'VB's, (an upgraded V with reusable SRB's attached to the first stage-doubling the weight deliverable to orbit), loft into LEO modified S-II and S-IVB booster, fuel and external tanks, the 'Mission Module' complete with the 1969/70 Space Task Group Mars Excursion Module proposal.
With the all of the launches and testing complete, assembled in LEO it leaves for Mars boosted by a Venus gravity assist swing by.

In this world, the Shuttle was never developed, but Saturn 5, Apollo CSM and Skylabs were continued and improved upon.
Those familiar with the NASA post Apollo projects in 1969/70 might ask 'what about the NERVA nuclear engine', a centrepiece of these ideas?
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kc135topboom
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RE: S-IC Stage Vs. SRBs Question

Sat Mar 31, 2012 11:55 pm

Quoting Thrust (Reply 11):
If you include the shuttle as payload though, you actually end up getting pretty comparable statistics...I don't know if the external tank can be counted or not because I thought the shuttle didn't separate from it until after it reached orbital velocity...

You are correct the shuttle/tank combo did not seperate until reaching orbit velocity, but not yet in orbit. It had to be that high and fast to assure the ET would burn up during reentry. I believe it seperated right after MECO.

The SRBs weighed in at 1,300,000 lbs each. The entire shuttle system had a launch weight of some 4,500,000 lbs, but, IIRC this was upgraded to about 5,000,000 lbs later, including payload. The S-1C first stage of the Saturn-V system weighed 5,000,000 lbs alone. The total Saturn-V system weighed in at over 7,500,000 lbs, including payload, which is 50% more than the shuttle system weighed.
 
Areopagus
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RE: S-IC Stage Vs. SRBs Question

Mon Apr 02, 2012 7:33 pm

After a little Googling I found a post that quotes the Saturn V Payload Planner's Guide as giving the following payloads.

100 nm orbit: 261,000 lbm, 118,390 kg
Earth escape: 98,000 lbm, 44,450 kg
Trans-Mars injection: 59,000 lbm, 26,760 kg

With Centaur 4th stage:
Earth escape: 107,000 lbm, 48,530 kg
Trans-Mars injection: 90,000 lbm, 40,820 kg

Wouldn't a 40,000 kg Mars mission have been fun!
 
Thrust
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RE: S-IC Stage Vs. SRBs Question

Fri Apr 06, 2012 5:14 pm

Quoting KC135TopBoom (Reply 13):

7.5 million pounds? Wikipedia says it weighed about 6.7 million pounds, and I've heard Jack King quote the mass of the Saturn V on countdown as being around 6.2 million pounds. Either way, considerably heavier than the shuttle. I also heard somebody say the shuttle's mass was increased to 5 million pounds...was this due to the super-lightweight tank? No launch I've ever seen has the shuttle weighing any heavier than 4 and a half million pounds at liftoff.
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Thrust
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RE: S-IC Stage Vs. SRBs Question

Fri Apr 06, 2012 5:22 pm

Quoting KC135TopBoom (Reply 13):

If the entire Saturn V weighed 7.5 million pounds, I doubt it would be able to lift off..that's nearly identical weight to the total F-1 engine thrust in pounds. your numbers are definitely off...4.5 million pounds was the gross liftoff weight for the shuttle, about 6.2-6.7 million pounds for the Saturn V.
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prebennorholm
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RE: S-IC Stage Vs. SRBs Question

Sun Apr 08, 2012 12:44 am

Quoting Areopagus (Reply 14):
With Centaur 4th stage:
Earth escape: 107,000 lbm, 48,530 kg
Trans-Mars injection: 90,000 lbm, 40,820 kg

Wouldn't a 40,000 kg Mars mission have been fun!

Sure! Probably even more fun than all those Mars missions which we have witnessed during the last fifty years.

But I have a feeling that you are dreaming about a manned mission. That wouldn't be so funny.

If we imagine a three men crew, then the food and oxygen needed to support them for the duration of a Mars mission, plus the fuel needed to handle that food and oxygen at Mars, that alone would exceed those 40,000 kg. Even if much of it would stay in Mars orbit for the duration of the crew landing.

And then we haven't counted one gram for the spacecraft.

When we start calculating the numbers involved, then a manned Mars mission looks more like a spacecraft being assembled in Earth orbit from a dozen Saturn V launches.

The major reason for the inflated numbers is not just the longer duration, but also the much higher escape velocity at Mars compared to the Moon.
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Areopagus
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RE: S-IC Stage Vs. SRBs Question

Mon Apr 09, 2012 7:06 pm

Quoting prebennorholm (Reply 17):

Sure! Probably even more fun than all those Mars missions which we have witnessed during the last fifty years.

But I have a feeling that you are dreaming about a manned mission. That wouldn't be so funny.

No, I wasn't dreaming of a manned mission. Note that I wrote earlier:

Quoting Areopagus (Reply 6):
TopBoom's answer is correct if the gist of the question is about sending an Apollo-class payload to Mars. But Saturn V could have sent smaller payloads Marswards.
 
Blackprojects
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RE: S-IC Stage Vs. SRBs Question

Fri Apr 13, 2012 4:05 pm

A development on the F-1 engine the F-1A was Made but never used it could Deliver 2,000,000Lbs Thrust per engine so the S-1C would have been able to Lift a lot more if it had been kept in Production!
 
rwessel
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RE: S-IC Stage Vs. SRBs Question

Fri Apr 13, 2012 6:37 pm

Quoting Blackprojects (Reply 19):
A development on the F-1 engine the F-1A was Made

That was a study - it was never built. Not saying it wouldn’t have worked - the F-1 is a fairly conservative* design, likely with considerable margin to absorb a significant upgrade.

And there were numerous studies about upgrading the S-IC (and the whole Saturn-V stack), including uprated engines, stretches solid and liquid strap-ons, not to mention exotic stuff like nuclear upper stages. If you're interested, there's a partial list at:

http://www.astronautix.com/fam/saturnv.htm

The leading (most practical) designs seemed to be a stretched S-IC with solid strap-ons (swiped from Titan), along the lines of:

http://www.astronautix.com/lvs/satvv4sa.htm

There were bigger designs, of course, such as the biggest versions of the Saturn V-D (720,000lbs to LEO):

http://www.astronautix.com/lvs/saturnvd.htm



*Except for that whole 1.5 million pounds of thrust bit
 
Blackprojects
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RE: S-IC Stage Vs. SRBs Question

Fri Apr 13, 2012 10:59 pm

Was it never Built Hmm then this is wrong then!

http://www.thespacereview.com/article/588/1


If NASA wanted an F-1, it could hire Rocketdyne—now part of United Technologies Corporation—to build it. Actually, what Rocketdyne would build is the F-1A. The F-1 engine was designed to produce 6.7 million newtons of thrust. Rocketdyne uprated the engine and increased the thrust to 8 million newtons at sea level, or about 8.9 million newtons in vacuum. The design changes that increased the engine power were successfully demonstrated on two engines.
 
rwessel
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RE: S-IC Stage Vs. SRBs Question

Fri Apr 13, 2012 11:23 pm

Quoting Blackprojects (Reply 21):
The design changes that increased the engine power were successfully demonstrated on two engines.

AFAIK, those were tests of some upgraded (prototype) components, not complete F-1A engines. Certainly not flight-worthy engines.
 
Blackprojects
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RE: S-IC Stage Vs. SRBs Question

Thu Apr 19, 2012 5:16 pm

It looks like the F-1 Engines may be Revived!

http://www.spaceflightnow.com/news/n1204/18dynetics/
 
zanl188
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RE: S-IC Stage Vs. SRBs Question

Thu Apr 19, 2012 5:48 pm

Quoting rwessel (Reply 22):
AFAIK, those were tests of some upgraded (prototype) components, not complete F-1A engines. Certainly not flight-worthy engines.

Per the Springer/Praxis book on the F-1: two development F-1As were built and test fired. One of these engines demonstrated a throttling capability.
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SP90
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RE: S-IC Stage Vs. SRBs Question

Sat Apr 21, 2012 11:23 pm

Quoting Thrust (Reply 10):
The other thing I'm wondering is the behavior of the SRBs in a vacuum? Did their thrust increase, or were they throttled down after maximum dynamic pressure?

Aside from the thrust vectoring nozzle I don't know how else the SRBs could be controlled after ignition. The rocket motor burns from the inside out. Having a cylinder shape does expose enough of the propellent to generate sufficient thrust at liftoff. The cross section of the core is a star shape. After ignition as the rocket burns it becomes a cylinder shape. So the thrust does go down as time passes but not because of throttling in the traditional sense. I guess you could think of it as built in throttling.

The Wikipedia page for the SRB has a nice graph detailing the thrust levels over time but it's sea level thrust.

http://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster
 
Blackprojects
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RE: S-IC Stage Vs. SRBs Question

Mon Apr 23, 2012 4:21 pm

This gives an insight into the Saturn V S-1C for Apollo17

http://www.ehartwell.com/afj/index.p...light_evaluation/5_S-IC_Propulsion
 
rwessel
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RE: S-IC Stage Vs. SRBs Question

Tue Apr 24, 2012 4:56 am

Quoting Blackprojects (Reply 26):
This gives an insight into the Saturn V S-1C for Apollo17

http://www.ehartwell.com/afj/index.p...lsion

It really gives you a feel for the scale of the S-1C when the residual fuel at burnout totaled *32 tons*.
 
Thrust
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RE: S-IC Stage Vs. SRBs Question

Mon Apr 30, 2012 7:01 pm

Quoting Blackprojects (Reply 23):

I'm very excited about this if it's true!
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Thrust
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RE: S-IC Stage Vs. SRBs Question

Mon Apr 30, 2012 7:07 pm

Quoting Blackprojects (Reply 23):

My question is that two space shuttle SRBs would give significantly more thrust than the two F-1 engines...I'm confused as to why they would drop 3.3 million pounds of thrust for 1.8 million pounds of thrust...is it because of the better upper atmosphere performance? What kinds of g loads are expected for this rocket exactly? 4gs or 3?
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rwessel
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RE: S-IC Stage Vs. SRBs Question

Tue May 01, 2012 6:12 am

Quoting Thrust (Reply 29):
My question is that two space shuttle SRBs would give significantly more thrust than the two F-1 engines...I'm confused as to why they would drop 3.3 million pounds of thrust for 1.8 million pounds of thrust...is it because of the better upper atmosphere performance? What kinds of g loads are expected for this rocket exactly? 4gs or 3?

Each of the two Dynetics boosters (one replacing each SRB) would have *two* F-1s.

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