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Thread: My opinion (only my opinion, now) is that the 5-segments SRB can't work >>>

  1. #1
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    Arrow My opinion (only my opinion, now) is that the 5-segments SRB can't work >>>

    .

    I think that the new 5-segments SRB planned for the Ares-I and Ares-V can't work because it can't give more burning time nor more thrust (or a little more than a 4-segments version) but only more internal pressure and up to 140 mT of extra dry mass!

    I explain in detail the reasons of my opinion in this article: www.gaetanomarano.it/articles/011srb5.html

    Not "the better" but the ONLY choice for the Ares-I and Ares-V is the (standard) 4-segments SRB with (also) the great advantage that it is ready available NOW!

    .

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    I tried to read your website but your excessive use of BOLD RED made it a painful experience. I quit less than halfway though it. Really, what you're doing is a distraction and a hindrance to communication. Please give it a rest.

    I believe you're fundamentally mistaken about the 5 segment SRB because you're assuming that they're simply going to add another segment without changing anything else. It all comes down to the propellant geometry and the amount of exposed surface area during the burn. If you simply add another segment without changing the propellant geometry, then at the moment of ignition, you'll be exposing 25% more propellant face to combustion. This additional burn area will result in higher internal pressure (perhaps to the point of explosion if the casing can't withstand the pressure) but also higher thrust. However, if you modify the propellant geometry, you can get any number of thrust profiles. For example, if you leave out the hole for the 5th segment, you'll get a lower thrust for a longer time. Or, instead of a star geometry, you can go with a simple circle through all 5 segments. This would result in a high initial thrust with increasing thrust through the burn as more surface area is exposed.

    Solid rocket motor design isn't new. Engineers know how to tailor the geometry to get the desired thrust profile for the mission.

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    Quote Originally Posted by Larry Jacks
    I tried to read your website but your excessive use of BOLD RED made it a painful experience. I quit less than halfway though it. Really, what you're doing is a distraction and a hindrance to communication. Please give it a rest.
    you can see, it's the (bad or good) "style" of the entire website, not only of the articles

    however, for those don't like colors there is a simple way to de-tag the html texts: select all > copy > paste in the windows notepad

    I believe you're fundamentally mistaken about the 5 segment SRB because you're assuming that they're simply going to add another segment without changing anything else. It all comes down to the propellant geometry and the amount of exposed surface area during the burn. If you simply add another segment without changing the propellant geometry, then at the moment of ignition, you'll be exposing 25% more propellant face to combustion. This additional burn area will result in higher internal pressure (perhaps to the point of explosion if the casing can't withstand the pressure) but also higher thrust. However, if you modify the propellant geometry, you can get any number of thrust profiles. For example, if you leave out the hole for the 5th segment, you'll get a lower thrust for a longer time. Or, instead of a star geometry, you can go with a simple circle through all 5 segments. This would result in a high initial thrust with increasing thrust through the burn as more surface area is exposed. Solid rocket motor design isn't new. Engineers know how to tailor the geometry to get the desired thrust profile for the mission.
    I know all the points you quote and there are some pages on internet with the thrust profile of solid rockets with different propellent's shapes

    but THIS is (exactly) the point of my article... the 5-segments SRB needs too much changes, too much development time, too much money, to much tests and re-certification, redesign, etc. etc. etc.

    also, its real test to know if it's safe for manned launches will be... with manned missions... since the 5sSRB can't have the same (good and known) story of the 4-segments version!

    the first 20/30 Ares-I/CEV astronauts will be the "experiment's mouses" used to test the 5sSRB safety!

    you can read only the last words of my article: "the 4sSRB don't need a DAY nor a CENT of R&D and are ready available NOW... NOT in 2009 or 2011 or 2013 or 2015... NOW!"

    .

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    Quote Originally Posted by gaetanomarano
    I think that the new 5-segments SRB planned for the Ares-I and Ares-V can't work because it can't give more burning time nor more thrust (or a little more than a 4-segments version) but only more internal pressure and up to 140 mT of extra dry mass!
    Sure they can work, however it may require a reformulation of the propellant to alter the burn rate. There are several ways to control burn rate. We can change the percentage of oxidizer, change the particle size, or use burn rate catalysts and/or suppressants. The current 4-segment Shuttle SRBs include a catalyst to speed up the burn rate, so it should be pretty easy to slow the rate back down to get a longer burn time out of the 5-segment version.

    And by the way, more internal pressure will give more thrust. A higher chamber pressure increases the exhaust gas velocity, which increases the thrust for a given mass of propellant.

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    Quote Originally Posted by gaetanomarano
    but THIS is (exactly) the point of my article... the 5-segments SRB needs too much changes, too much development time, too much money, to much tests and re-certification, redesign, etc. etc. etc.
    If your point is that the 5-segment SRBs will take too long and cost too much to develop, then why did name this thread "My opinion (only my opinion, now) is that the 5-segments SRB can't work" and make an opening post posing an argument that the 5-segment SRBs won't work? Every indication is that your point was most definitely not about time and cost, but rather about functionality. Please stick to your original argument and not try to change it every time someone points out the flaws in your logic.

    Are you ready to concede you were wrong when you claimed the 5-segment SRBs "can't work"? If not, then please try to defend that argument and not some other argument about time and cost.

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    Quote Originally Posted by Bob B.
    Sure they can work, however it may require a reformulation of the propellant to alter the burn rate. There are several ways to control burn rate. We can change the percentage of oxidizer, change the particle size, or use burn rate catalysts and/or suppressants. The current 4-segment Shuttle SRBs include a catalyst to speed up the burn rate, so it should be pretty easy to slow the rate back down to get a longer burn time out of the 5-segment version. And by the way, more internal pressure will give more thrust. A higher chamber pressure increases the exhaust gas velocity, which increases the thrust for a given mass of propellant.
    spending sufficient time and money we can transform a ship in an airplane...

    I agree that with "deep changes" (oxidizer, shape, chamber, catalyst, etc.) a 5-segment version CAN work (as I've already written in my article) but, if we change near ALL of the SRB, it will be a COMPLETELY DIFFERENT rocket!

    the ESAS plan suggests the "simple and cheap way" to build a new boosters adding a 5th segment to the Shuttles' SRB, but this is NOT true, it's not simple, not easy, not cheap, not the same thing

    the 5-segments (a 4 seg. +1) CAN'T WORK while the "completely different" rocket we call (by mistake) "SRB" will work because it will be ANOTHER thing

    it's like call the Ares-V "a SaturnV with a few, easy, low cost upgrades"...
    .
    Last edited by gaetanomarano; 2006-Jul-30 at 08:03 PM.

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    Quote Originally Posted by Bob B.
    If your point is that the 5-segment SRBs will take too long and cost too much to develop, then why did name this thread "My opinion (only my opinion, now) is that the 5-segments SRB can't work" and make an opening post posing an argument that the 5-segment SRBs won't work? Every indication is that your point was most definitely not about time and cost, but rather about functionality. Please stick to your original argument and not try to change it every time someone points out the flaws in your logic.

    Are you ready to concede you were wrong when you claimed the 5-segment SRBs "can't work"? If not, then please try to defend that argument and not some other argument about time and cost.
    I don't agree

    the time and costs to build a new booster is only a (bad) consequence of the fact that a 5-segments SRB can't works in the simple way NASA and ATK suggest ("safe, simple, soon"...)

    the booster that CAN work is NOT an SRB+1seg... it is ANOTHER rocket build from (only) part of the "SRB knowlendge" about propellent, shape, etc. that needs changes, changes, changes, tests, tests, tests... and the hope that it will be safe and reliable like the Shuttle booster for manned launches...

    I don't need to change nothing in the title of this thread...

    however, I (or you) can open a new thread like... "the completely different booster NASA will build for Ares (that now we call "SRB" while waiting for a good name)"

    maybe... "ADB" = Ares Dedicated Booster

    .
    Last edited by gaetanomarano; 2006-Jul-30 at 08:04 PM.

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    Quote Originally Posted by gaetanomarano
    I agree that with "deep changes" (oxidizer, shape, chamber, catalyst, etc.) a 5-segment version CAN work (as I've already written in my article) but, if we change near ALL of the SRB, it will be a COMPLETELY DIFFERENT rocket!
    Yes, a 5-segment SRB is not a 4-segment SRB.

    Quote Originally Posted by gaetanomarano
    the ESAS plan suggests the "simple and cheap way" to build a new boosters adding a 5th segment to the Shuttles' SRB, but this is NOT true, it's not simple, not easy, not cheap, note the same thing
    The ESAS plan does not call for adding a 5th segment to the Shuttle SRB, it calls for developing a 5-segment SRB derived from the existing 4-segment SRB. I agree there is a distinction.

    Quote Originally Posted by gaetanomarano
    the 5-segments (a 4 seg. +1) CAN'T WORK while the "completely different" rocket we call (by mistake) "SRB" will work because it will be ANOTHER thing
    No one ever claimed, that I’ve seen, that they are just adding a fifth segment to the existing motor. The new 5-segment motor will require reengineering the existing technology; this issue is not in dispute.

    By the way, SRB means “solid rocket booster”, which is an appropriate term for the 5-segment version.

    I still fail to see why you named this thread as you did and opened with the post that you did. If you recognized the new 5-segment SRB was going to require reengineering, then what was the point of claiming something NASA is not doing can’t work? If your opening post is not an honest mistake based on ignorance of the engineering involved, then it is entirely pointless. Why didn’t you just open with what you wanted to say, i.e. that the time and expense of developing a 5-segment SRB is, in your opinion, not worthwhile?

    Furthermore, the explanation you gave in your opening post about why the 5-segment SRB wouldn’t work is incorrect. And although it is not applicable, it is not definitively established that simply added a fifth segment to the existing motor wouldn’t work. Increasing the burn surface will increase the gas production rate, which will drive up the chamber pressure. This will force a greater volume of gas out the nozzle at higher velocity, which in turn increases the thrust and specific impulse of the motor. The primary issue is whether the existing motor casing can handle the higher pressure.

    Do you wish to address the scientific and engineering points made in your opening post?

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    Quote Originally Posted by Bob B.
    By the way, SRB means “solid rocket booster”, which is an appropriate term for the 5-segment version.
    right ...if Ford, GM, BMW, etc. will call ALL new vehicles "CAR" (instead of Civic, Mustang, Twingo, etc.)

    call the (completely different) Ares booster "5-segments SRB" is like call a Mercedes "a 5-segments Honda Civic"

    I still fail to see why you named this thread as you did and opened with the post that you did... it is not definitively established that simply added a fifth segment to the existing motor wouldn’t work. Increasing the burn surface will increase the gas production rate, which will drive up the chamber pressure. This will force a greater volume of gas out the nozzle at higher velocity, which in turn increases the thrust and specific impulse of the motor. The primary issue is whether the existing motor casing can handle the higher pressure.
    my article and my thread are completely correct since I say (like you say) that a 5-segments SRB (a 4-seg.+1) can't work, while a completely modified SRB can... what you say is exactly what I write in my article

    however, an engine that "may explode" due to its higher internal pressure ALREADY IS an engine that "can't work" (NASA don't build firecrackers...)

    but there is another reason why a 4+1 engine can't work

    we can't forget that we talk of an engine built to lift "something" not only of a "burn test"

    I've already said that part of the higher internal pressure may give an extra 10% of thrust... but it is NOT sufficient to lift the 140 mT extra mass of the 5th segment... then, if the extra thrust is a full +25% the 5sSRB can work... if it will be around +20% the Ares-I can fly only without its payload... under 20% the extra thrust will be not sufficient to lift the 5th segment extra mass and the Ares-I remains on the launch pad or falls on itself

    then, my statement (in my article and here) is correct... a "5-segments can't work" (since it can explode or, simply, can't fly) while a "completely different booster" CAN

    probably you've not seen that, but we say the same thing

    the problem is that NASA have suggested to all peoples and politics (to have the funds...) the (completely uncorrect) idea that the ESAS plan can be made with (reliable, simple, safe, low cost and ready available) "shuttle-derived" hardware, while the reality is completely different

    my article about the 5-segments SRB is "the reality" about this part (not a simple change but a completely different design) and I can write similar articles about other parts of the ESAS plan changed these months or that will be changed until 2020...

    the final suggestion of my article is to don't build the (not simple) "5-segments SRB" but use the REAL "shuttle-derived" hardware like claimed by NASA last year... then, use the standard SRB, not a new rocket!

    .

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    gaetanomarano,

    Your arguments are based on obsolete information. Many of the details of the CEV and CLV design proposals in the ESAS have been superceeded already. You should consider reading the CLV threads on http://forum.nasaspaceflight.com/

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    Quote Originally Posted by gaetanomarano
    my article and my thread are completely correct since I say (like you say) that a 5-segments SRB (a 4-seg.+1) can't work
    I didn’t say a Shuttle SRB + 1 additional segment won’t work. I don’t know if it will work or not because I lack sufficient information to make that determination. It’s a moot point however because that is not what NASA is doing.

    Quote Originally Posted by gaetanomarano
    while a completely modified SRB can... what you say is exactly what I write in my article
    I agree a modified 5-segment SRB will work, but I won’t go so far as to say it will be “completely modified”. For instance, by increasing the nozzle size the motor can be made to handle the greater gas production rate while operating at the same chamber pressure as the original 4-segment Shuttle SRB. This should allow the existing casing and segment joint design to be reused. It seems to me the items requiring redesign are the propellant formula and geometry, the nozzle, and the recovery system (larger booster may need bigger parachutes).

    Quote Originally Posted by gaetanomarano
    I've already said that part of the higher internal pressure may give an extra 10% of thrust...
    You’re only guessing. The thrust can be calculated; there is no need to guess.

    Quote Originally Posted by gaetanomarano
    but it is NOT sufficient to lift the 140 mT extra mass of the 5th segment...
    Only if your guess is right.

    Quote Originally Posted by gaetanomarano
    then, if the extra thrust is a full +25% the 5sSRB can work... if it will be around +20% the Ares-I can fly only without its payload... under 20% the extra thrust will be not sufficient to lift the 5th segment extra mass and the Ares-I remains on the launch pad or falls on itself
    I’m not sure where you’re getting your numbers but I don't agree. Your hypothetical 5-segment SRB (4-seg + 1) will at least have the thrust of the 4-segment version. The 4-segment Shuttle SRB has a liftoff thrust of 2,900,000 lbf (sea level) and the RS-68 engines have a thrust of 650,000 lbf each (SL). This gives a total liftoff thrust of at least,

    2,900,000 x 2 + 650,000 x 5 = 9,050,000 lbf (SL)

    I don’t know what the new weight of the Area V is, but the original weight based on the SSME design was about 6,400,000 lbm. I estimate the new weight based on the RS-68 design to be perhaps as much as 7,500,000 lbm. 9 million pounds of thrust will certainly get 7.5 million pounds of mass off the ground.

    Quote Originally Posted by gaetanomarano
    then, my statement (in my article and here) is correct... a "5-segments can't work" (since it can explode or, simply, can't fly) while a "completely different booster" CAN
    NASA is not proposing adding a fifth segment without reengineering the booster, so who really cares what this hypothetical scenario can or can’t do?

    Quote Originally Posted by gaetanomarano
    the problem is that NASA have suggested to all peoples and politics (to have the funds...) the (completely uncorrect) idea that the ESAS plan can be made with (reliable, simple, safe, low cost and ready available) "shuttle-derived" hardware, while the reality is completely different
    I agree to a point. Even with all the changes that have taken place since the original ESAS report, there is still some Space Shuttle hardware we can derive from. This should result in some savings, but not nearly as much as originally indicated. I tend to like the way the Ares vehicles have evolved even though they’ve moved further away from existing Space Shuttle technology. I’m willing to except a larger price tag for a better vehicle.

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    Quote Originally Posted by selden
    Many of the details of the CEV and CLV design proposals in the ESAS have been superceeded already. You should consider reading the CLV threads on http://forum.nasaspaceflight.com/
    the site you quote has the same news of dozens other sites

    but, if you like so much that site, you may ask the to give an OFFICIAL source/link of the "stumpy" we are waiting fron days to know...

    .

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    Just to point out that this sort of upgrade to a large segmented solid motor has been done in the past. The solid boosters for the Titan 3C had five segments, but for the Titan 4 this was increased to seven segments.

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    Quote Originally Posted by Bob B.
    ...I don’t know if it will work or not because I lack sufficient information to make that determination...
    since you admit that an SRB with an higher pressure and the same case/nozzle "my explode" then it can't work... NASA can't launch nothing with a rocket that "may explode" (by design)

    I agree a modified 5-segment SRB will work, but I won’t go so far as to say it will be “completely modified”. For instance, by increasing the nozzle size the motor can be made to handle the greater gas production rate while operating at the same chamber pressure as the original 4-segment Shuttle SRB. This should allow the existing casing and segment joint design to be reused. It seems to me the items requiring redesign are the propellant formula and geometry, the nozzle, and the recovery system (larger booster may need bigger parachutes).
    the time and costs of the new boosters don't suggest it will be so simple and easy

    You’re only guessing. The thrust can be calculated; there is no need to guess.
    that is clearly true from my article... but it's unnecessary to know the exact % of extra thrust, since the SRB must lift "itself" before lift "something" and that can happen only with a full +25% increase of thrust

    I’m not sure where you’re getting your numbers but I don't agree.
    the article refers to the Ares-I not the Ares-V

    however, in the article I've made a mistake (I will correct soon) because I forget the Ares-V has two SRB with two 5th segment and twice the extra mass: 280 mT (not 140)

    then, also the Ares-V can't fly if the extra thrust of the 4+1 SRB (that "may explode"...) will be under 60% of the necessary 5sSRB +25% extra thrust

    NASA is not proposing adding a fifth segment without reengineering the booster, so who really cares what this hypothetical scenario can or can’t do?
    "words" are NOT the only way to "talk"... also images and diagrams (that NASA uses in its plans) ARE "words" ...and BETTER words, since "one image worth 1000 words"...

    well, "talking by images" NASA have said for montths to million peoples (and US politics) that its ESAS plan is fast, cheap and easy because...

    they use the image of the ET with the same shape, foam and color... but now we know it will have a completely new design/dimensions

    they use the image of a big CEV/SM to say it needs a new launcher... but now we know it will be lighter

    they use the image of the ready available SSME in both rockets... but now we know they will never use the SSME

    and, about the SRB, in last 12 months NASA have released dozens images of the "stick" and the CaLV with a 5th segment (simply) added on the top... so, millions peoples (and US politics) still believe it may need only a "simple change" to work... and (so far) only a few experts know that it's not true!

    NASA talks with images to millions peoples... and "by images" they talk wrong!

    .

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    Quote Originally Posted by gwiz
    Just to point out that this sort of upgrade to a large segmented solid motor has been done in the past. The solid boosters for the Titan 3C had five segments, but for the Titan 4 this was increased to seven segments.
    but the Titan 4 is not used to launch humans... also, we must know the changes made INSIDE the 7-segments boosters (propellent shape and mixture, nozzle dimensions, etc.)

    .

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    Not sure about the internals, but certainly a new larger nozzle.

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    Quote Originally Posted by gwiz
    Not sure about the internals, but certainly a new larger nozzle.
    that means the same must be made to the new SRB

    .

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    Quote Originally Posted by gaetanomarano
    since you admit that an SRB with an higher pressure and the same case/nozzle "my explode" then it can't work... NASA can't launch nothing with a rocket that "may explode" (by design)
    “May exploded” is a possibility only until it is determined whether or not the casing and joints can handle the higher pressure. At which time it will be known whether it “will explode” or it “won’t explode”, and whether it “will work” or it “won’t work”. Until such determination is made, we simply don’t know. And besides, it’s a moot point so can we stop talking about it.

    Quote Originally Posted by gaetanomarano
    the time and costs of the new boosters don't suggest it will be so simple and easy
    Why must it be simple and easy? Why must it be fast and cheap?

    Quote Originally Posted by gaetanomarano
    that is clearly true from my article... but it's unnecessary to know the exact % of extra thrust, since the SRB must lift "itself" before lift "something" and that can happen only with a full +25% increase of thrust

    the article refers to the Ares-I not the Ares-V
    Don’t forget that the Ares I was originally designed to be lifted by a 4-segment SRB. I don’t know the current mass figure for the Ares I, but back in November 2005 the liftoff mass was listed as about 1,775,000 lbm. It’s possible there could have been some mass growth since then, but surely not significantly. Why do you claim a 2,900,000+ lbf booster can’t lift this?

    Quote Originally Posted by gaetanomarano
    well, "talking by images" NASA have said for montths to million peoples (and US politics) that its ESAS plan is fast, cheap and easy because...
    I’ve heard comments that using Shuttle derived technology can save time and money, which it can, but I haven’t heard anyone at NASA claim it will be fast, cheap, and easy. Shuttle derived doesn’t mean off the shelf Shuttle components.

    Quote Originally Posted by gaetanomarano
    and, about the SRB, in last 12 months NASA have released dozens images of the "stick" and the CaLV with a 5th segment (simply) added on the top... so, millions peoples (and US politics) still believe it may need only a "simple change" to work... and (so far) only a few experts know that it's not true!
    I think there are two major groups of people: (1) enthusiasts who are following what is going on and understand what NASA is doing, and (2) those that haven’t a clue and couldn’t care less. If a person wants to know what is going on they have to take the initiative to educate themselves. NASA has provided plenty of information to whoever wants it and their budget is public knowledge. If someone has a problem with NASA's plans and budget they can complain to their congressman, but I’ve seen no deceit on NASA's part.

    EDIT: I think most people either support manned space exploration and are delighted about returning to the Moon and are not overly concerned with the cost, or they do not support manned space exploration and think any money spent is too much. I don’t think there are too many people out there who support a manned moon program but only if it can be done on the cheap. I think we should either build the rockets we need to get the job done most effectively or we don’t do it at all. I don’t think we should cobble together something less just to save a few bucks or a couple years. I believe that will cost more in the long run due to lesser capability.
    Last edited by Bob B.; 2006-Jul-31 at 02:07 PM.

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    Post Comparison between 4-segments and 5-segments SRB

    .

    now that (I think) all misunderstanding about the first part of the article/thread is solved I talk here of the second part about the time/money saving of the 4-segments SRB choice

    to better explain that I've made a comparison chart of the two boosters:


    _________________standard SRB________5-segments SRB____


    available_____________NOW!______________2009+

    CEV/Ares launch______~2011______________2014+

    1st moon landing______~2016______________2020+

    R&D costs_____________$0______________$3+ billion!

    unit cost_____________$40M_______________$60M+

    shared R&D costs_______$0________________$100M+

    already man-rated______yes__________________no

    manned launches_______115__________________0

    successful launches_____114__________________0

    launch pad changes_____little_________________big

    safety______________very good____________unknown

    reliability____________very good____________unknown

    reusable_______________yes_______________unknown

    shuttle-derived_________100%_____________a little bit

    the 4-segments SRB is clearly the better choice (no matter if NASA will build one or two rockets)

    the comparison chart is valid also for the 3-segments SRB excluding only the unit price that may be close to the standard version

    .

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    Quote Originally Posted by Bob B.
    “May exploded” is a possibility only until it is determined whether or not the casing and joints can handle the higher pressure.
    +25% internal pressure (without the right case and nozzle) may be sufficient to give "problems" (flame leak or explosion) then, the 4+1 is not safe

    Why must it be simple and easy? Why must it be fast and cheap?
    it's not my claim... it's an ATK claim ("safe, simple, soon") that NASA accepted without any critics

    ...there could have been some mass growth since then, but surely not significantly...
    probably the less powered J-2x needs more fuel, a bigger tank and more burning time

    ...Shuttle derived doesn’t mean off the shelf Shuttle components...
    true, but, unfortunately, great part of the drawing, concepts, specs and info given in the early days suggest exactly the opposite

    ...and (2) those that haven’t a clue and couldn’t care less...
    but 99% of them are in the 2nd group

    ...and are not overly concerned with the cost...
    also if that cost will grow to $230B+ like an US federal office claims these days?

    ...just to save a few bucks or a couple years...
    the ESAS plan don't cost exactly "a few bucks"... also, if there is a ready available (and good!) alternative, why lose years and burn money?

    the time and money saved can be used to accomplish more moon missions!

    .

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    Can you give us some calculations, along with some insider information on the structural changes being made to accommodate the additional stresses of extended length,mass, thrust output, and burn time that demonstrate the flaws in a five segment booster design?

    And do so in plain text, in black on white?

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    Quote Originally Posted by Doodler
    Can you give us some calculations, along with some insider information on the structural changes being made to accommodate the additional stresses of extended length,mass, thrust output, and burn time that demonstrate the flaws in a five segment booster design?
    as claimed many times here, there are no problems with a re-designed 5-segments booster

    .

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    Quote Originally Posted by gaetanomarano
    +25% internal pressure (without the right case and nozzle) may be sufficient to give "problems" (flame leak or explosion) then, the 4+1 is not safe
    Irrelevant because no one is planning to build a hypothetical 4+1 SRB.

    Quote Originally Posted by gaetanomarano
    probably the less powered J-2x needs more fuel, a bigger tank and more burning time
    The J-2X has almost the exact same efficiency as the SSME -- specific impulse of 451.5 s for J-2X versus 452.1 s for SSME -- thus there should be little difference in the propellant requirements due to the change in engine.

    If anything, I see the second stage being smaller in the revised 5-segment design because the first stage has gotten bigger. The bigger first stage should provide more delta-v, thus the second will be required to provide less and can therefore be smaller. However, since the first stage uses less efficient solid propellant, the overall rocket size will need to increase.

    Roughing out some numbers, I estimate that to get the same delta-v with the same payload mass as the original 4-segment CLV design, a 5-segment design will have a total launch mass in the 2,000,000 lbm neighborhood. This is a more significant increase than I would have guessed without doing the math, but it is still small enough that a 2.9+ million lbf thrust booster could lift it off the pad without difficulty.

  24. #24
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    Quote Originally Posted by Bob B.
    ...J-2X has almost the exact same efficiency as the SSME...
    the figures I've read are around 290,000 lbf the J-2x and 408,500 the SSME

    ...the second stage being smaller in the revised 5-segment...
    true if the new SRB burns more time to reach an higher altitude and speed

    ...booster could lift it off the pad without difficulty.
    I've already agreed on that point (for the re-designed booster)

    .

  25. #25
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    Quote Originally Posted by gaetanomarano
    the figures I've read are around 290,000 lbf the J-2x and 408,500 the SSME
    Those are thrust figures, not efficiency (specific impulse). A lower thrust engine can, theoretically, provide the same delta-v as a higher thrust engine using the same amount of propellant provided they have the same specific impulse. The lower thrust engine just has to burn longer.

    Since the 5-segment first stage will impart more velocity than the smaller 4-segment stage would have, the J-2X will have to do less work than the SSME would have been required to do. The J-2X can manage despite its lower thrust and it will produce thrust at essentially the same efficiency as the SSME. Because the J-2X burns propellant and lower rate, it may have to burn a little longer even though it's providing less delta-v.

  26. #26
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    Quote Originally Posted by Bob B.
    ...lower thrust engine just has to burn longer...
    exactly the same thing I've said... more fuel and burning time

    ...will impart more velocity...
    this is unknow now... the new booster may have more thrust or more burning time or a mix of them... we must wait the final specs

    .

  27. #27
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    Quote Originally Posted by gaetanomarano
    exactly the same thing I've said... more fuel and burning time
    No, not more fuel. Burning 40% less propellant per second for 25% longer equals less total propellant burned.

    (Percentages are approximate.)

    Quote Originally Posted by gaetanomarano
    this is unknow now... the new booster may have more thrust or more burning time or a mix of them... we must wait the final specs.
    We don't have final specs yet, but the math certainly indicates that the velocity at stage 1 burnout for the 5-segment design will be considerably higher than the velocity at stage 1 burnout for the 4-segment design.

  28. #28
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    Quote Originally Posted by Bob B.
    No, not more fuel. Burning 40% less propellant per second for 25% longer equals less total propellant burned.
    do you have the final specs of the J-2x before Rocketdyne?

    We don't have final specs yet, but the math certainly indicates that the velocity at stage 1 burnout for the 5-segment design will be considerably higher than the velocity at stage 1 burnout for the 4-segment design.
    we don't know the specs NASA and ATK will give to the new boosters

    if they need only to lift more upperstage mass the speed may be similar to a Shuttle SRB

    .

  29. #29
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    Here is a story from 2003 about a successful 5 segment SRB test. In this test, they choose to generate higher thrust for a slightly longer period than a standard 4 segment SRB.

    This test motor -- the third in a series of four to be tested -- ran five seconds longer than the motors fire when launching the Space Shuttle, produced 300,000 pounds of thrust over the motor's maximum limit of 3.3 million pounds, and included an additional fifth motor segment adding 25 percent more propellant. Of the test motor's total weight of 1.56 million pounds, propellant accounts for 1.37 million pounds.

    For the proposed Ares vehicles, they can tailor the particular thrust vs time parameters by adjusting the propellant geometry. If they use the same case segments, same propellant, and keep the pressures to the point where they can use the same nozzle and associated actuators, then there will be a great deal of reuse between the new 5 segment SRBs and today's Shuttle SRBs. It really isn't a serious issue despite all the RED BOLD scare statements.

  30. #30
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    Quote Originally Posted by Larry Jacks
    Here is a story from 2003 about a successful 5 segment SRB test. In this test, they choose to generate higher thrust for a slightly longer period than a standard 4 segment SRB.

    This test motor -- the third in a series of four to be tested -- ran five seconds longer than the motors fire when launching the Space Shuttle, produced 300,000 pounds of thrust over the motor's maximum limit of 3.3 million pounds, and included an additional fifth motor segment adding 25 percent more propellant. Of the test motor's total weight of 1.56 million pounds, propellant accounts for 1.37 million pounds.

    For the proposed Ares vehicles, they can tailor the particular thrust vs time parameters by adjusting the propellant geometry. If they use the same case segments, same propellant, and keep the pressures to the point where they can use the same nozzle and associated actuators, then there will be a great deal of reuse between the new 5 segment SRBs and today's Shuttle SRBs. It really isn't a serious issue despite all the RED BOLD scare statements.
    thank you very very very very very much for this post!!!

    the test confirms 100% my evaluations about a 4+1 segments SRB: no extra burning time (5 sec. are near zero) and +10% of thrust!!!

    that means I'm right 100%... the 4+1 SRB can't work since +10% of thrust is not sufficient to lift the 5th segment mass (140 mT) but only 55 mT ...with an extra 85 mT to lift... an extra "dead-weight" IMPOSSIBLE to lift for (both) the Ares-I and the Ares-V also WITHOUT any payload!

    also, the remain 15% of propellent will increase only the internal pressure, so, the 4+1 SRB may be very dangerous in a real flight!

    four tests are not sufficient to know if the booster is safe and reliable for a manned flight!

    don't forget that these tests was made ON EARTH with the higher atmospheric pressure!

    just imagine what may happen in a REAL flight when the 4+1 SRB reaches the max altitude of 150,000 feet (or before!) with a +15% of internal (unexausted) pressure and the external vacuum!!!

    it may explode 100% of times!

    to add a +25% of thrust, the booster must be re-designed spending $3B+ and 3+ years

    as explained in the comparison list, the 4-segments SRB has too many advantages to change it with the 5-segments booster!

    .

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