Ares VII

gaetanomarano · 2007-01-30 19:35:18

Is it the higher thrust but not longer burn time for the 5 segment being used?

yes, this is the main problem of the Ares-I and, second, the J-2x that has half the SSME power ...an half-thrust 2nd stage engine can work fine only if it starts burning at an higher altitude and speed than SSME ...but the new 5-seg.SRB doesn't add more burning time (to reach that higher altitude and speed) but only more thrust ...to be exact, the new 1st stage CAN reach an higher altitude and speed, but with too much "G" ...since (both) altitude and speed reached with the 5-seg.SRB are similar to the old 4-seg.SRB Ares design, the 2nd stage STILL needs an SSME (or similar power engine) and not an half-power J-2x ...the 5-seg.SRB is a good choice only if they want to lift more payload (but it needs a better 2nd stage)
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GCNRevenger · 2007-01-30 21:57:24

Nonsense!

Anonymous rumor mongers are not credible! They obviously seek to derail Ares-I for some reason, there is no chance they are right. If they are even NASA engineers. If they even know what they are talking about. And if they aren't lying. All these factors ruin their credibility; this is not a 50/50 "maybe so, maybe not" situation, they are WRONG.

you contradict yourself

Idiot, learn to read English. I said that NASA thought about a backup plan, but didn't seriously consider it since Apollo would almost definitely work.

And Griffin never did say any anything that implied Shuttle/ISS were failures, mistakes, etc. You are lying.

And you don't know anything about upper stages, Ares-I doesn't need an SSME-class engine, which is quite overkill. First of all the information you are basing this bogus assertion on is outdated and no longer applicable to begin with.

Second why are G-loadings too high? Aren't you complaining about Orion being heavy? Extra weight reduces G-loading!

If the five-segment SRB really does have the same burn-out time, altitude, and speed then that means the upper stage is heavier than the older "four-segment + SSME" version of Ares-I. And if its heavier, that means more fuel, so the upper stage could burn longer. Just like Ares-V, trading expensive engines for cheap fuel tank.

And the old comparison with SSME versus J-2 in the early days of Ares-I design planning was the J-2S type, which had not only less thrust but less specific impulse than the new planned J-2X model.

Don't try and weasel and moan about "oh its so simple logic," no no, your word is against NASA's here. Show, show why they are wrong or lying. Prove it.

SpaceNut · 2007-01-30 22:13:39

If indeed the SRB 5 segment burn time is the issue then looking at the Ares IV which is basically the Ares I with the first stage acting like an SRB. I have to believe that ATK and Nasa know how to do a solid booster design by now.

Now the question is does the Ares IV really require a new first stage tank or is using what would have been used on the Ares V for reduced costs the right avenue while reducing fuel loading of the tank the right approach to make an all liquid Ares I. Maybe some little strapons just to give it a kick start to get it off the pad but other wise is this a solution for Ares I even thou we need the 5 segments for Ares V.

Michael Bloxham · 2007-01-31 02:35:10

IMHO, the only reason Ares V uses 5-segs is because they're needed for The Stick anyway.

If the 5-seg SRB is too underpowered for the heavier Orion, then we need a bigger and more powerful SRB! (And if its not underpowered, then 6-segment SRB's will still be fun...)

A 6-segment SRB with the same thrust might give more burn time, and with the extra weight, decrease g-loading at the same time?

gaetanomarano · 2007-01-31 04:53:51

...Griffin never did say any anything that implied Shuttle/ISS were mistakes...

read this

...Ares-I doesn't need an SSME-class engine...

just wait a few months and see

...G-loadings...

read again my post, I talk about an hypothesis ...also, the major "underpower" of Ares-I seems come from its 2nd stage/engine

...the five-segment SRB really does have the same burn-out time...

from ATK test and NASA claims we know that the 5-seg. burn time is only 5 seconds more than a standard SRB

...your word is against NASA's here...

if you really want to read "word against NASA" and post tons of your core-business' product ("insults") go to the cospiracy theories' forums
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gaetanomarano · 2007-01-31 04:59:29

...6-segment SRB with the same thrust might give more burn time...

since the SRB propellent burns from center towards side, a 6-seg.SRB (with an enlarged nozzle) may give more thrust but not so much burning time (just a few seconds more)
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Michael Bloxham · 2007-01-31 05:41:53

Is there no way to slow the burn time?

gaetanomarano · 2007-01-31 05:53:33

Is there no way to slow the burn time?

a larger SRB/propellant (vs. the standard version) may increase the burning time (and the inverse) but a larger SRB needs very much R&D time, money and tests
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SpaceNut · 2007-01-31 08:39:50

GCNRevenger this has been the only comparison chart that I can find on the 4 versus 5 segment it does not indicate if the 5 segment is a different propellant.

http://www.bautforum.com/attachment.php … 1168091856

Burn time: 124 sec for the 4 segment

Burn time: 139 sec for the 5 segment

The test page back in 2003 of the 5 segment added pressure seal test:
http://www.nasaexplores.com/show2_5_8a. … essonlinks

Shuttle preformance to max Q time
RELATIVE
EVENT MET VELOCITY MACH ALTITUDE
(d:h:m:s) (fps) (ft)

Maximum Dynamic Press 00/00:01:04 1,548 1.61 41,635(Max Q)

SRB Separation 00/00:02:04 4,221 4.04 152,519

GCNRevenger · 2007-01-31 21:50:02

You really don't have a clue about how rockets actually work do you gaetano

If a rocket has the same burn time, burn out altitude as well as air speed but has more thrust than a similar rocket, that means whatever it carries is therefore heavier. It can be no other way, since the payload must be heavier to weigh the rocket down.

You whine about how the upper stage "doesn't have enough thrust," but compared to what? Compared to the SSME? Has it ever occurred to you that maybe the SSME-equipped upper stage had MORE thrust than it needed? Back when the SSME was proposed for Ares-I's upper stage, NASA had more political interest in the engine and thought modifications required would not be that difficult nor expensive.

Since it turned out that SSME was not going to be affordable, the political penalty for dropping the engine wasn't so bad, and the larger five-segment booster would work best for Ares-V then NASA didn't need SSME anymore. To help put things in perspective, look at the Delta-IV Heavy, which is the most similar rocket in performance: although the upper stage does less work with the Delta rocket compared to Ares-I, its engine has Twenty Times less thrust than SSME does.

I think its plainly obvious that a 500,000lbs thrust engine is overkill for Ares-I

Also, if the four-segment booster has similar burn out time/altitude/airspeed in the original "Four segment + SSME" Ares-I concept, and if lack of thrust were a problem with J-2X, then the heavier upper stage afforded by the five-segment booster permits more fuel to be carried. More fuel with a lower thrust engine means a nice long burn, which would largely make up for gravitational losses versus SSME anyway.

Bigger cheap fuel tanks and cheap simple engines are a good trade for expensive engines in expendable rockets.

Lastly, you don't seem to have any clue about how solid rockets like the Shuttle SRB are actually shaped: the "fuel grain" is not a solid cylinder, nor is it a hollow cylinder with a circular channel down the middle. No no, large solid rockets have star or cross-shaped channels down the middle, which means that the surface area remains approximately constant throughout the burn. Thus yielding approximately constant thrusts too.

But I digress, solid rockets must have this channel to develop useful amounts of thrust and have a uniform pressure inside, but the cross-sectional shape of this channel can be most any shape you want. By changing the shape of the channel, you can tailor the thrust to do whatever you like (over a reasonable range), plus change over the course of the burn.

cIclops · 2007-02-01 01:24:04

IMHO, the only reason Ares V uses 5-segs is because they're needed for The Stick anyway.

ESAS determined that a 5-Seg SRB was needed for Ares V back in 2005. At that time the 4-seg SRB (+ SSME US) was specified for Ares I. Later NASA decided to maximize synergy between the two vehicles by using the same 5-seg SRB and J-2X for both of them. This also had the advantage of reducing development costs and risks, even though it extended the development time for Ares I.

cIclops · 2007-02-01 01:40:28

...Griffin never did say any anything that implied Shuttle/ISS were mistakes...
read this

In that meeting with the USA TODAY editorial board a lot must have been said, such meetings usually last an hour or more. Note the tiny quote they managed to extract from him criticizing STS/ISS and that becomes the headline. As it says in the second paragraph, Griffin's comments were about the programs not the design of STS or ISS. This point, and he has made the same comment elsewhere, is that these programs took NASA in the wrong direction, namely only to LEO instead of continuing exploration at the Moon and beyond.

gaetanomarano · 2007-02-02 11:55:30

...has the same burn time, burn out altitude as well as air speed but has more thrust than a similar rocket, that means whatever it carries is therefore heavier...

don't post the obvious...
if the (real) SRB5 will match the (expected) specs it may lift an higher upperstage weigh... but the question is: "has the 2nd stage engine enough thrust to lift that extra-weight to orbit?"

...look at the Delta-IV Heavy, which is the most similar rocket in performance: although the upper stage does less work with the Delta rocket compared to Ares-I, its engine has Twenty Times less thrust than SSME does...

no, they are not "the most similar rocket in performance" ...the standard SRB has a 123 sec. burn time and (with the Shuttle) is jettisoned at 45 km. while the DeltaIV core stage has a 249 sec. burn time (twice+ the SRB) and (since it launch unmanned satellites) flies with an higher acceleration than the (3G max) Shuttle, so, it can reach a much higher altitude and speed than (both) the old and new SRB ...then, the 2nd stage has a "Twenty Times less thrust than SSME" engine because it NEEDS (only) a "Twenty Times less thrust than SSME" engine!

...the five-segment booster permits more fuel to be carried. More fuel with a lower thrust engine means a nice long burn...

that's true ONLY if the final J-2x will have (less than SSME but) SUFFICIENT thrust

...don't seem to have any clue about how solid rockets like the Shuttle SRB are actually shaped: the "fuel grain" is not a solid cylinder, nor is it a hollow cylinder with a circular channel down the middle. No no, large solid rockets have star or cross-shaped channels down the middle, which means that the surface area remains approximately constant throughout the burn...

...do you have learned that in my (august 2006) SRB's article?
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GCNRevenger · 2007-02-02 20:54:47

Woo the return of the "exciting" colored lettering!

You cannot really believe that the Ares-I upper stage requires twenty times the thrust of a rocket with similar payload. Thats just absurd. Yes the Delta-IV first stages do some more pushing, but not that much more!

Twenty!

And the two rockets do have similar performance overall, because they lift about the same payload. And because you missed it, the max G-loading of Ares-I is five G's, not three like Shuttle.

And who is to say what G-loading the Delta-IV Heavy has? Do you know? How do you know? Don't you know that the big D-IV-H first stages have a poor thrust/weight ratio? It takes a full 11sec just to clear the pad! That means lower G-forces, which translates into longer burns but not a far greater amount of "push" than the Ares-I first stage.

The note about the fuel grain shape was for Michael, not you.

gaetanomarano · 2007-02-03 07:50:43

...cannot really believe that the Ares-I upper stage requires twenty times the thrust of a rocket with similar payload...

1. the Delta IV Medium payload (without strap-ons) is 3,900 kg. ...less than 15% of the Ares-I payload+LAS mass at lift-off

2. the Delta IV 2nd stage engine (RL10B-2) thrust (24,720 lbf) is only 16.5 times the SSME thrust (408,568 lbf) ...NOT "twenty"

3. the (expected) J-2x thrust will be around 295,000 lbf ...25% less than an SSME and (not "twenty", but) TWELVE times the RL10B-2 ...then, a working Ares-I may NEED that 25% "extra-thrust"...

...the two rockets do have similar performance overall, because they lift about the same payload. And because you missed it, the max G-loading of Ares-I is five G's, not three like Shuttle...

as claimed in the Aug. 3, 2006 NASA press conference the "astronauts will experience an estimated maximum of 3.25-3.5 times the force of gravity during the Ares 1’s launch" ...NOT 5G ...the max G of a Shuttle launch remains under "3G" since the Shuttle throttles down its three SSMEs after lift-off to avoid too much G for the astronauts

...what G-loading the Delta-IV...

all unmanned rockets don't need to have a low G, so, assuming they are slow at lift-off, they can reach 4, 5, 6 G or more... however, the most important figure of Delta specs is the (twice+) 1st stage burning time (249 sec. vs. 123 sec. of the standard SRB) that allows the 2nd stage (small) engine to start burn at (about) twice the Ares-I 2nd stage burning altitude (maybe 80-100 km. vs. 55-60 km.)

.

RedStreak · 2007-02-03 08:26:48

IMHO, the only reason Ares V uses 5-segs is because they're needed for The Stick anyway.
ESAS determined that a 5-Seg SRB was needed for Ares V back in 2005. At that time the 4-seg SRB (+ SSME US) was specified for Ares I. Later NASA decided to maximize synergy between the two vehicles by using the same 5-seg SRB and J-2X for both of them. This also had the advantage of reducing development costs and risks, even though it extended the development time for Ares I.

Just makes more sense using common elements as well.

GCNRevenger · 2007-02-03 10:18:00

I'm not talking about the Medium, I am referring to the triple-core Heavy version of Delta.

But I digress, it would really help your arguing skills if you would bother to actually read the documents you cite, that SSME produces >512klbs of thrust in vacuum ("vac"). Since the booster will bring SSME to a high altitude where the air is thin, it should be capable of attaining 500klbs.

Plus you again claim that the Ares-I needs 20X the thrust of rockets with comparable payloads (Delta-IV Heavy, Atlas 551), which is just crazy. It can't possibly need that much! The upper stage simply is not 20X heavier than the EELV upper stages. Remember, its not the thrust, its the thrust-to-weight ratio.

Ares-I will indeed have a maximum G-limit of 5G, which is the maximum amount allowed. If it doesn't accelerate at 5G, then thats because it doesn't need to. Since the thrust-to-weight controls the G-loading, then that means the planned rocket actually has extra thrust probably.

Remember, J-2X was originally conceived for the big Ares-V, which has far more payload and a bigger upper stage (~8m vs 5.5m), which despite igniting the stage at higher velocity probably requires as much or more thrust than Ares-I's upper stage.

Nonsense! You don't know anything, comparing two different rockets burn times but not their accelerations is meaningless! Remember, attaining orbit is about speed, altitude is meaningless. Witness how Shuttle, Apollo, and other rockets curve their path almost immediately after liftoff. A rocket with a longer burn time but less acceleration delivers no more push than a rocket with short burn time with higher acceleration you idiot.

Altitude is virtually meaningless, speed is everything!

And come, prove that unmanned rockets have higher acceleration, show us, prove it. Prove it prove it prove it! Don't come back and flap your gums about this until you can! Come, go and find the video of the first Delta-IV Heavy launch, watch as it lumbers with painful slowness to even clear the pad, then come back and tell us its acceleration is higher.

gaetanomarano · 2007-02-03 12:06:24

...triple-core...

since the Ares-I doesn't have a "triple-core" it can't be compared with the DIVH

...500klbs...

since the Ares-I is very much different from Delta rockets the ONLY correct comparison is: J-2x vs. SSME ...well, assuming the full 500 klbs. figure for the SSME thrust, the J-2x (300 klbs.) thrust is about 60% of an SSME, then, the "RIGHT" thrust an Ares-I's 2nd stage will NEED to lift the given payload may EQUALS the planned (J-2x) 300 klbs. or (as I think) must be HIGHER (maybe, it will need an SSME or two J-2x or something around 400-450 klbs. of thrust)

...upper stage simply is not 20X heavier than the EELV upper stages...

read again my posts... the similar (but not the same) payloads' EELV need a smaller 2nd stage engine because their 1st stage burns twice the time than Ares-I and the EELV's 2nd stage engines start burning at a MUCH HIGHER altitude and speed!

...Ares-I will indeed have a maximum G-limit of 5G, which is the maximum amount allowed...

I've given you a source of "my" 3.25-3.5G figure, then, please give me a source of "your" 5G figure ...however, the REAL FLIGHTS max G will be those claimed by NASA, of course...

...J-2X was originally conceived for the big Ares-V, which has far more payload and a bigger upper stage...

the AresV 2nd stage/EDS needs LESS thrust-per-payload than Ares-I since it works much close to a DeltaIV with a longer 1st stage core burn and a 2nd stage start at an higher altitude and speed

...short burn time with higher acceleration...

but the fact that Ares-I has a solid (ICBM-like) 1st stage doesn't allow it to have a "short burn time with higher acceleration" since it has humans atop, not nuclear heads, then, it must fly at (about) 3G (less than a sat/probe launch rocket)

...you idiot...

I can assure you that, your knowledge of (so elementary and widely known) notions about rockets, doesn't transform you to a "genius"...

...speed is everything...

since all DeltaIV actually work well... that (clearly) means their 1st stages allow (both) the full altitude and SPEED they need...

...prove that unmanned rockets have higher acceleration...

I don't have the flight's profiles of all rockets, but, if a rocket has a BIG payload and a SMALL 2nd stage engine, its 1st stage MUST provide an higher (full flight) acceleration than Shuttle and Ares-I (since, without it, the 2nd stage falls in the ocean...)

...find the video of the first Delta-IV Heavy launch, watch as it lumbers with painful slowness to even clear the pad...

all liquid-engines big/heavy rockets are very slow at lift-off (look at the SaturnV launch) and reach the right speed at high altitude
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ftlwright · 2007-02-05 00:44:33

...prove that unmanned rockets have higher acceleration...
I don't have the flight's profiles of all rockets, but, if a rocket has a BIG payload and a SMALL 2nd stage engine, its 1st stage MUST provide an higher (full flight) acceleration than Shuttle and Ares-I (since, without it, the 2nd stage falls in the ocean...)
...find the video of the first Delta-IV Heavy launch, watch as it lumbers with painful slowness to even clear the pad...
all liquid-engines big/heavy rockets are very slow at lift-off (look at the SaturnV launch) and reach the right speed at high altitude.

Your breaking one of the cardinal rules of rocket design with this statement; the Payload-to-gross weight should be proportionate for each stage. It COULD be accomplished otherwise, but would not be very efficient system/stage-wise

gaetanomarano · 2007-02-05 07:02:10

...breaking one of the cardinal rules of rocket design...

it's just how liquid rockets works
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ftlwright · 2007-02-05 15:57:01

...breaking one of the cardinal rules of rocket design...
it's just how liquid rockets works
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This makes little sense. The first stage rocket is going to be tuned for operation at sea level, not for a large portion of the flight regime. If most of the propellant and lifting will be done by the first stage, you will suffer tremendously efficiency and parasitic loses for the bulk of you flight regime. Unless you are dealing this a aerospike engine and an extremely low structural coefficient (both extremely unlikely), the designer will match the stages as closely as possible (payload-to-initial stage weight).

Please take the time to review sp-125 or Rocket Propulsion Elements [Sutton] as these are fairly basic concepts. If you do not have either available, I may be able to provide and proof if you are still curious.

ftl

gaetanomarano · 2007-02-06 16:18:02

This makes little sense. The first stage rocket is going to be tuned for operation at sea level, not for a large portion of the flight regime.

probably there is some misunderstanding due to my (not good) english, but my description is how liquid rockets work (slow at lift-off and accelerate at higher altitude)
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GCNRevenger · 2007-02-08 23:16:27

Okay, now that the hard part of my week is over with, I can get back to this train wreck:

Can't compare Delta-IV Heavy with Ares-I? Bulls**t, they have the same payload, and thats what matters, not how many fuel tanks it has. One, three, ten, or fifty cores makes little difference.

thrust is about 60% of an SSME, then, the "RIGHT" thrust an Ares-I's 2nd stage will NEED to lift the given payload may EQUALS the planned (J-2x) 300 klbs. or (as I think) must be HIGHER (maybe, it will need an SSME or two J-2x or something around 400-450 klbs. of thrust)

Bulls**t, you don't know that! The SSME nor the J-2X was chosen for Ares-I because it needed the thrust, but rather because the same engines were going to be used on Ares-V. You don't know how much thrust is needed, but we can estimate, and no sane estimate is twenty times that of a rocket with similar or even somewhat larger payload. You. Don't. Know. Why do you "think" it will need even more? Where is your data? Where is your reasoning? You are just another anti-NASA liar.

the similar (but not the same) payloads' EELV need a smaller 2nd stage engine because their 1st stage burns twice the time than Ares-I and the EELV's 2nd stage engines start burning at a MUCH HIGHER altitude and speed!

You STILL don't know anything, burn time DOES NOT control the lifting power of a given rocket stage, does not. If you had a hypothetical rocket that could accelerate a thousand times slower than the SRB but burned a thousand times as long, a full day of burning, they would reach exactly the same speed.

but the fact that Ares-I has a solid (ICBM-like) 1st stage doesn't allow it to have a "short burn time with higher acceleration" since it has humans atop, not nuclear heads, then, it must fly at (about) 3G (less than a sat/probe launch rocket)

It does compared to liquid fueled rockets! You said so yourself you babbling idiot! Right in the same post even! And they don't "must fly at 3G" you simpering moron, they did 5G or better in Apollo just fine on every shot! The 5G limit is around here in this very site if you look.

all liquid-engines big/heavy rockets are very slow at lift-off (look at the SaturnV launch) and reach the right speed at high altitude

Then that means the SRB, being different, must have higher acceleration. And with higher acceleration, that means a shorter burn probably. You can't even keep yourself straight in the same post.

And you didn't even look did you, some all-liquid launchers have nice fast accelerations like Saturn but most don't, especially not the big Delta-IV, which takes eleven seconds just to clear the launch pad. It takes Shuttle a lot less then that, and it sure carries people! Gently for a rocket too I might add.

You don't even know their accelerations, you don't know them but you are claiming that they are higher even though I just told you right here to your face the obvious factual proof, eleven is more that the few it takes Shuttle to lumber off the pad, which means its acceleration is less. Whether this changes at higher altitudes/speeds is irrelevant, since the comparison is with the SRB which only operates over the first minutes of flight, which has the highest G-loading in any case.

but, if a rocket has a BIG payload and a SMALL 2nd stage engine

It absolutely does not, this is very strongly influenced by the fuel efficiency, gravitational loss, and overall flight profile. Thrust and stage masses are only loosely coupled, there are other concerns besides just mass. The only reasons thrusts matters at all is to counter gravitational losses and air drag.
_______________________________________________
To wrap this up I want to point out why I think NASA picked J-2X and to challenge your stupid notion that Ares-I needs SSME-class thrusts with a very simple and obvious thought experiment:

Ares-V's upper stage may have to do less of the overall accelerating, but it has to push an even bigger upper stage (10m) with 5-6 times the payload. NASA also needed an engine for Ares-I a bit bigger than the best EELV engine (RL-60/ML-60), and happened to be building J-2X anyway, which would increase commonality between Ares rockets and reduce total costs. It was not necessarily selected primarily because of its thrust. NASA program statements that it was largely about money litter this board and the internet. Perhaps the J-2X even has excess thrust, but its wildly obvious that it doesn't need twenty times as much thrust, especially with the bigger SRB! But now for the obvious thing I promised:

How could it possibly need more thrust for the upper stage with a more powerful first stage? If the five-segment SRB has the same burn out time and speed, then that means the upper stage must be heavier than the one planned for the four-segment SRB + SSME. If this were not true, then the booster would have a higher burnout altitude/speed, since there would be more weight holding it down.

This being the case, if Ares-I needed 500klbs thrust for the old four-segment version, should it not need even more thrust for the new version??? There is no possible way J-2X can reach 500klbs, so it must not need to.

Thats as simple a reasoning as you can possibly get to show that you don't need an SSME class engine! You cannot possibly fail to understand that! It is an absolute certainty, there is no "oh but we don't know" crap about it, its simple and plain and obvious as can be.

gaetanomarano · 2007-02-09 06:09:56

...compare Delta-IV Heavy with Ares-I...they have the same payload...

no... because...

1. the max payload of a DIVH is 22.5 mT while the Ares-I is planned to lift over 27.5 mT (then, a +5 mT)
2. the DIVH has a small 2nd stage engine, then, it's 1st stage must fly to an higher altitude and speed than Ares-I SRB
3. the DIVH was build to launch satellites and probes, then, we don't know if its max-G is compatible for humans
4. the DIVH must be man-rated (if compatible for human launches) while the Ares-I will "born man-rated"

...twenty times...

you obsessive repeat of "twenty times" have nothing in common with reality... the Delta 2nd stage engine has 1/20th the power of a J-2x because it NEEDS only that power if it start burning at higher altitude and speed than an Ares-I's 2nd stage ...the Ares-I's 2nd stage (with the 5-seg.SRB) starts burning at 63 km. and less acceleration, then, it needs a J-2x ...also, since NASA claims that the upperstage mass must reduced of 1 mT, so, the 300 klbs. J-2x (working at its limits) is the MINIMUM requirement for the 2nd stage ...and the J-2x power is TWELVE times the Delta 2nd stage...

...SSME nor the J-2X was chosen for Ares-I because it needed the thrust, but rather because the same engines were going to be used on Ares-V...

that may be an additional reason for the early choice of the SSME, but the main reason is its power ...if the 5-seg.SRB Ares-I absolutely NEEDS a 300 klbs. J-2x engine (working at its limits) the less powerful 4-seg.SRB Ares-I (clearly) needs a bigger engine of the SSME-class

...burn time DOES NOT control the lifting power of a given rocket stage, does not...

true, but you must made a choice... to put in orbit a 22.5 mT payload with a 2nd stage 24 klb. engine, the DIVH 1st stage + boosters must burn more time OR have an higher acceleration, not both... the first option appears the most probable, while, the latter (if real) may add too much G for a manned launch

The 5G limit is around here in this very site if you look.

in the Aug. 3, 2006 press conference about Ares-I new details, NASA said that Orion's astronauts "will experience an estimated maximum of 3.25-3.5 times the force of gravity during the Ares 1’s launch" ...NOT 5G ...also, the Shuttle was designed to have a max 3G at launch since it was planned to have many common passengers (engineers, scientists, etc.) and not only Apollo-like military and test pilots

...that means a shorter burn probably...

infact the 5-seg.SRB will burn only 128 sec.

...which means its acceleration is less. Whether this changes at higher altitudes/speeds is irrelevant...

no, it IS relevant, since solid and liquid rockets have two different flights' profile (that's why a Delta needs a smaller 2nd stage engine)

...NASA picked J-2X...

because they NEEDS its power (and it works at its limits on the Ares-I)

...the J-2X even has excess thrust...

no, it has the MINIMUM power required for the Ares-I (infact, Orion must lose 1 mT of mass to match it)

...If the five-segment SRB has the same burn out time and speed, then that means the upper stage must be heavier than the one planned for the four-segment SRB + SSME...

that's exactly the NASA choice from a 123 sec. 4-seg.SRB + SSME Ares-I to a 128 sec. 5-seg.SRB + J-2x Ares-I and an heavier 2nd stage

...There is no possible way J-2X can reach 500klbs...

I doubt that a 300klbs engine can be upgraded to 500klbs ...the known NASA goal is "295 klbs" ...so, if the Ares-I 2nd stage will need more power, the choice is two J-2x or a better engine
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SpaceNut · 2007-02-09 07:46:34

Here is a Delta 4-Heavy rocket demo launch timeline note throttle back time, max Q, booster seperation ect...

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#101 2007-01-30 19:35:18

Re: Ares VII

#102 2007-01-30 21:57:24

Re: Ares VII

#103 2007-01-30 22:13:39

Re: Ares VII

#104 2007-01-31 02:35:10

Re: Ares VII

#105 2007-01-31 04:53:51

Re: Ares VII

#106 2007-01-31 04:59:29

Re: Ares VII

#107 2007-01-31 05:41:53

Re: Ares VII

#108 2007-01-31 05:53:33

Re: Ares VII

#109 2007-01-31 08:39:50

Re: Ares VII

#110 2007-01-31 21:50:02

Re: Ares VII

#111 2007-02-01 01:24:04

Re: Ares VII

#112 2007-02-01 01:40:28

Re: Ares VII

#113 2007-02-02 11:55:30

Re: Ares VII

#114 2007-02-02 20:54:47

Re: Ares VII

#115 2007-02-03 07:50:43

Re: Ares VII

#116 2007-02-03 08:26:48

Re: Ares VII

#117 2007-02-03 10:18:00

Re: Ares VII

#118 2007-02-03 12:06:24

Re: Ares VII

#119 2007-02-05 00:44:33

Re: Ares VII

#120 2007-02-05 07:02:10

Re: Ares VII

#121 2007-02-05 15:57:01

Re: Ares VII

#122 2007-02-06 16:18:02

Re: Ares VII

#123 2007-02-08 23:16:27

Re: Ares VII

#124 2007-02-09 06:09:56

Re: Ares VII

#125 2007-02-09 07:46:34

Re: Ares VII

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