Author Topic: DIRECT v2.0 - Thread 2  (Read 1356822 times)

Offline mrbliss

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Re: DIRECT v2.0 - Thread 2
« Reply #4460 on: 01/13/2009 02:51 pm »
Fifth is the fact that the SRB's were never designed to be utilized in this fashion with hundreds of tons of stage and payload on top.   They just weren't designed for these loads.

Why are these loads a big issue for the SRB, but not for Jupiter's ET-based core stage?  Is it because the core (being mostly tanks holding the liquids) can be redesigned to handle the loads, but the SRB can't be modified similarly?

Steve

Offline zapkitty

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Re: DIRECT v2.0 - Thread 2
« Reply #4461 on: 01/13/2009 03:27 pm »
Quote from: kraisee
Fifth is the fact that the SRB's were never designed to be utilized in this fashion with hundreds of tons of stage and payload on top.   They just weren't designed for these loads.
Why are these loads a big issue for the SRB, but not for Jupiter's ET-based core stage?  Is it because the core (being mostly tanks holding the liquids) can be redesigned to handle the loads, but the SRB can't be modified similarly?

Mostly because the ET-to-core stage conversion has been a longstanding concept at NASA with a lot of study already done towards it...

... If you want a reasonably detailed description of the sorts of changes required, I refer you to this public document:-
http://hdl.handle.net/2060/19930007493
The first 600 pages or so detail all the changes which are required to make each part of an ET into an NLS Core Stage.
But from page 611 onwards there is a really *great* description of how NLS was planning to modify the existing tooling -- and that gives you a glimpse into what's really involved in what they do day-to-day at Michoud...
Ross.

... as for previous studies towards an SRB-to-core stage conversion? Not so much...

Offline JIS

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Re: DIRECT v2.0 - Thread 2
« Reply #4462 on: 01/13/2009 03:35 pm »
Those wikipedia numbers represent the gross performance numbers without margin, and to the sub-orbital -11x100 "injection" point, not to the final orbit.

If you work it out that way (which is a plain stupid way I might add) Ares-I is supposedly able to lift 23,151kg for ISS missions and 25,573kg for Lunar -- but only to "injection", and without accounting for any performance margins at all.

Once you apply industry-standard margins and deduct the propellant used by the SM to achieve full orbit, you aren't delivering anything like that amount of actual payload to a useful orbit (220nmi circular, 51.6deg for ISS and 130nmi circular, 29.0deg for Lunar).

The 23mT and 25mT are really just meaningless "sales speak" figures.   Yeah, your car might be rated by the manufacturer at "125mph maximum", but if you need five miles of dead-straight downhill road to ever actually achieve it is that really an accurate statement?

The Ares-I will never, ever, ever be able to lift that amount of mass to stable orbit in practice.   No way, no how.

Every other rocket in the world quotes its final delivered performance to stable orbit, and states it after the routine margins have been accounted for.


This is demagogy. Stable or unstable - doesn't mater. It should be useful orbit for it's payload. -11x100nm is useful orbit for Orion. It's not so useful for some commercial payload. Ares would need to use some third stage to achieve higher orbit as Ares US is too big (many times bigger than common upper stages) to be left on orbit and it doesn't have any means to be safely deorbited.

Ares 1 payload capability would be very likely more for commercial payload as it doesn't need LAS and Ares can fly lofted (low Q) trajectory.

Quote
But Ares-I keeps on deliberately conning everyone because they hope nobody understands what they're actually looking at.   They refuse to reveal the apples-to-apples comparisons and instead persists in this practice of only ever publishing the "theoretical maximum" which they know the system will never actually be able to achieve in the real world.


Why is that?


Think again. Once Ares goes commercial you'll definitelly get your number.
Look at numbers for Ares V. Payload capability refers to injection orbit which is required for its payload (LSAM) only.

Quote
Because once you knock the industry-standard 10% margin off those figures and once you account for the propellant which the Orion needs to burn in order to achieve its final orbit, the final delivery performance is no better than the Delta-IV Heavy.

Wouldn't be better to look at Delta-IV numbers for Orion like mission? Look into ESAS Table 6-4.
Hint: for 30x160nm 51.6deg it's 22.5mt.
Ares 1 like launcher (5seg HTBP SRB, 1xJ-2S with ISP of 451.5s) had 27.0 mt.

Quote

And CxP daren't risk anyone noticing that they're spending $14 billion of your tax dollars on a rocket which can't actually match our existing capability!


Existing? Human rated Delta doesn't exist yet as far as I know.

Quote


So lets actually work it out and see what the truth REALLY is...

***

The result is that the maximum *REAL WORLD* mass delivered by the Ares-I/Orion system is no more than 19,628kg to 220x220nmi, 51.6deg.

If I wanted to use Ares 1 for LEO commercial mission then I would use Ares 1 combined with some dedicated US. I wouldn't bother with Orion/LAS.


Quote
Delta-IV Heavy can directly insert the Orion spacecraft straight into that 220nmi circular orbit without Orion having to perform any of those extra burns.   And DIVH can actually deliver a little over 21,000kg to that exact same orbit in its Crew-launch configuration *after* it has successfully accounted for all its margins too.   That's the real apples-to-apples comparison 19.6mT for Ares vs. 21.0mT for Delta.

Any reference for your Delta numbers or is it from ESAS?

Quote
But Ares keeps on claiming "23 metric tons" or "25 metric tons".   They are successfully pulling the wool over many people's eyes with that claim because nobody understands the rocket science sufficiently well enough to disprove the claim.

Fortunately, you do.

Quote
They can try all they like to make it appear that Ares-I is more capable than the existing Delta system.   But the physics don't lie.   It is clearly not the truth.

Based on those ESAS numbers?
Wow.
BTW the original ESAS Lunar CEV CM (5.5m diameter) was 9.5mt. To what number it has been mutilated now (5m diameter)? To 8.7mt? Too bad.




'Old age and treachery will overcome youth and skill' - Old Greek experience

Offline clongton

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Re: DIRECT v2.0 - Thread 2
« Reply #4463 on: 01/13/2009 03:55 pm »
JIS:
1. Negative 11 nm x 100 nm is not an orbit - it's a crash and it's not useful for anything. It takes you 11 nautical miles beneath the surface of the earth.
2. There is no such thing as a commercial Ares-I. US law prohibits it. Even if there were, an EELV flight would be less expensive and more dependable.
3. A non-existant commercial Ares-I has nothing to do with DIRECT. This is a DIRECT thread. Stay on topic.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline sandrot

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Re: DIRECT v2.0 - Thread 2
« Reply #4464 on: 01/13/2009 05:01 pm »
1. Negative 11 nm x 100 nm is not an orbit - it's a crash and it's not useful for anything. It takes you 11 nautical miles beneath the surface of the earth.

That "orbit" is a trajectory that safely disposes of the US just as Shuttle does with ET. If you bring with you the US to a stable orbit, then you need to deorbit your US (some solids and pyrotechnics involved... again impacting LOC/LOM). But now since the US is insulated in foam, you can't deorbit the popcorns...
« Last Edit: 01/13/2009 05:02 pm by sandrot »
"Paper planes do fly much better than paper spacecrafts."

Offline jarmumd

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Re: DIRECT v2.0 - Thread 2
« Reply #4465 on: 01/13/2009 05:08 pm »
Fifth is the fact that the SRB's were never designed to be utilized in this fashion with hundreds of tons of stage and payload on top.   They just weren't designed for these loads.

Why are these loads a big issue for the SRB, but not for Jupiter's ET-based core stage?  Is it because the core (being mostly tanks holding the liquids) can be redesigned to handle the loads, but the SRB can't be modified similarly?

Steve

The SRB has no problem holding up the loads of the Ares upper stage, since two of them have to jointly hold up the entire fueled ET and Shuttle with payload in bending.  Ares US is ~400,000 lbs fueled, nothing close to the 1.6 million+ lbs of fueled ET alone.  And in flight, they can only apply a force in similar magnitude to the force they are creating. 

Ross, I'm sure this will upset you, but I think you need to take it down a notch.  Passion is good, but in all honesty your post above with the bold text and italicizing, and comments of the "truth" all remind me of a certain Italian that needs to stay off the internet.

Marc

Offline sandrot

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Re: DIRECT v2.0 - Thread 2
« Reply #4466 on: 01/13/2009 05:17 pm »
[...] all remind me of a certain Italian that needs to stay off the internet.

Not me, I hope!  ;D
"Paper planes do fly much better than paper spacecrafts."

Offline Lobo

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Re: DIRECT v2.0 - Thread 2
« Reply #4467 on: 01/13/2009 05:33 pm »
  The SSMT was never designed to carry payload on it's nose, or have rocket engines under it, with all the avionics that entails.  Modifying to to do that could be as expensive and problematic as building a new chasis from scratch that -is- designed for it.


Not true.

The ET (not MT)  to Direct core is not the same as F-15 to stealth fighter.

It is more like F-15 C/D to F-15E.

The same assembly jigs and tooling can be used for both.  Skin thicknesses are the basic differences.  New domes on the LO2 and LH2 tanks are basically the same as the remaining ones on the tank.  The thrust structure and forward adapter are not hard items to build. 
Avionics has no bearing, new avionics is being designed for Ares I which would be adapted

Good points.
It was just an analagy.  But the my point is still converting an exsting vehicle to do something it was never intended to do, -can- be much more involved than one thinks it might be, and in the end, you can end up with basically a morphidite in a role it was never intended for and a purpose built-vehicle would have been a better option.
The SST was never intended to carry nose payload, or have thrust directly under it, or go beyond LEO.
This is part of the issues with those thinking about using the EELV's for man missions.  Not to say it won't work.  Not to say it wouldn't work well.  Each case is it's own animal.  But working in the pneumatic indusdury, I've seen what happens when people try to modify existing equipment to perform new rolls it wasn't designed for.  Often, it never works as well as buying new, proper equipment.  And often ends up costing a lot more on the back and so all of your front end savings are gone in the long haul.

Obviously I'm speaking in generalities here, from my experience. 
Doesn't necessarily mean this will be the case with DIRECT.  Sometimes modifying existing equipemnt for a new use works swimmingly.

But to stick to the F15 analgy, The F15-E was more economcal than the Air Force developing a purpose-built light bomber, but will never be as good as a dedicated bomber in it's side.  It's basic air frame was designed for high-G maneuvers and Air Superiority, not for coming in low and quiet and hauling and dropping massive ordinance and/or internal bay ordinance on the target. 
It was deemed it would do a "good enough" job that the cost saving were more attractive.  The same with using an F/A-18 to replace the F-14's and A6's on a carrier.

So, is DIRECT, "good enough"?  Or is it the best vehicle?
Sometimes you can't afford the best vehicle, and have to make do with "good enough".  No shame in that.  But I'd like to know which is legitimately the better system. 

Offline Pheogh

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Re: DIRECT v2.0 - Thread 2
« Reply #4468 on: 01/13/2009 05:35 pm »
Fifth is the fact that the SRB's were never designed to be utilized in this fashion with hundreds of tons of stage and payload on top.   They just weren't designed for these loads.

Why are these loads a big issue for the SRB, but not for Jupiter's ET-based core stage?  Is it because the core (being mostly tanks holding the liquids) can be redesigned to handle the loads, but the SRB can't be modified similarly?

Steve
, and comments of the "truth" all remind me of a certain Italian that needs to stay off the internet.

Marc

That's quite a stretch

Offline Lobo

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Re: DIRECT v2.0 - Thread 2
« Reply #4469 on: 01/13/2009 05:55 pm »
Those wikipedia numbers represent the gross performance numbers without margin, and to the sub-orbital -11x100 "injection" point, not to the final orbit.

If you work it out that way (which is a plain stupid way I might add) Ares-I is supposedly able to lift 23,151kg for ISS missions and 25,573kg for Lunar -- but only to "injection", and without accounting for any performance margins at all.

Once you apply industry-standard margins and deduct the propellant used by the SM to achieve full orbit, you aren't delivering anything like that amount of actual payload to a useful orbit (220nmi circular, 51.6deg for ISS and 130nmi circular, 29.0deg for Lunar).

The 23mT and 25mT are really just meaningless "sales speak" figures.   Yeah, your car might be rated by the manufacturer at "125mph maximum", but if you need five miles of dead-straight downhill road to ever actually achieve it is that really an accurate statement?

The Ares-I will never, ever, ever be able to lift that amount of mass to stable orbit in practice.   No way, no how.

Every other rocket in the world quotes its final delivered performance to stable orbit, and states it after the routine margins have been accounted for.


But Ares-I keeps on deliberately conning everyone because they hope nobody understands what they're actually looking at.   They refuse to reveal the apples-to-apples comparisons and instead persists in this practice of only ever publishing the "theoretical maximum" which they know the system will never actually be able to achieve in the real world.


Why is that?

Because once you knock the industry-standard 10% margin off those figures and once you account for the propellant which the Orion needs to burn in order to achieve its final orbit, the final delivery performance is no better than the Delta-IV Heavy.

And CxP daren't risk anyone noticing that they're spending $14 billion of your tax dollars on a rocket which can't actually match our existing capability!



So lets actually work it out and see what the truth REALLY is...


ISS:-
23,151kg is Ares-I's maximum theoretical performance.   So start by knocking this down to 90% to cover regular 10% margins:   20,836kg is therefore the actual *practical* maximum payload mass which the system can insert to -11x100nmi, 51.6deg.

Orion must then circularize to 100x100nmi or it will be heading straight back to Earth.   Using a Hohmann Transfer, that requires a 62.241m/s burn, assuming Orion masses the full 20,836kg at the start and that its engine is 326.0s vac Isp, and ignoring any wasted propellant used during the engine start sequence, Orion will use 402kg of propellant to perform Burn #1.   Total mass now drops to 20,434kg to 100x100nmi, 51.6deg stable initial orbit.

Now the Orion needs to boost its orbit ready for a rendezvous with the ISS which usually has a nominal orbital altitude of 220nmi circular.   Another two Hohmann burns are therefore required.   Burn #2 is 64.603m/s and uses another 409kg of propellant leaving 20,025kg total Orion mass.   Burn #3 is then a 64.068m/s burn using another 397kg of propellant.


The result is that the maximum *REAL WORLD* mass delivered by the Ares-I/Orion system is no more than 19,628kg to 220x220nmi, 51.6deg.


Not quite as impressive as the 23 metric tons they keep telling us, is it?   In fact the true apples-to-apples comparable performance of the system is actually only 85% of the figure which they keep telling us.   I think deliberately and continually over-quoting things by 15% is rather deceitful myself.

There are laws in most industries clearly saying that if you market a product as one thing, say a bar of Milk Chocolate clearly marked as 1kg in weight, and the customer takes it home and finds there's only 850 grams of chocolate inside they have a legal claim to get their money back.   I consider this a very similar situation, albeit at a much more expensive level.


Delta-IV Heavy can directly insert the Orion spacecraft straight into that 220nmi circular orbit without Orion having to perform any of those extra burns.   And DIVH can actually deliver a little over 21,000kg to that exact same orbit in its Crew-launch configuration *after* it has successfully accounted for all its margins too.   That's the real apples-to-apples comparison 19.6mT for Ares vs. 21.0mT for Delta.


But Ares keeps on claiming "23 metric tons" or "25 metric tons".   They are successfully pulling the wool over many people's eyes with that claim because nobody understands the rocket science sufficiently well enough to disprove the claim.

They can try all they like to make it appear that Ares-I is more capable than the existing Delta system.   But the physics don't lie.   It is clearly not the truth.


Anyway, I digress.   That was totally off-topic...

Ross.

Ross,

No, not off topic.  Very informative.  These are the things I am interested in knowing.  Like I said before, I have no real dog in the fight, just want the best dog to win.

If your numbers are correct, that's interesting indeed.

Not to play Devil's advocate, but Ares still seems like it could perform the role of ISS supply and crew rotation, even if their numbers are inflated.  And could theoretically still deliver replacement components to the ISS, as [I believe] the largest single component delivered by the Shuttle was 17.6 tons, in the solar arrays and Kibo main lab.  (Per your data, Ares 1 can still lift 21.6 tons to the ISS)
That's assuming of course they can or would modify it to carry dedicated payloads.  I know that'd been part of the the original goals in the Ares design to launch cargos to the ISS, but haven't heard much about that idea lately.  Have they abandon using Ares 1 for anything but carrying Orion?

But, that's not to say it's the best design to do it.  Just that it could still do what it's supposed to, just not as well as NASA is claiming, if you are correct. 

Again, thanks for the info.  I'm always looking for more.

Offline Lobo

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Re: DIRECT v2.0 - Thread 2
« Reply #4470 on: 01/13/2009 06:06 pm »
There are actually over 160 other documents like that one publicly available on ntrs.nasa.gov dealing with similar Shuttle derived systems, be those NLS, ALS, Shuttle-C and whatever.

Not one of NASA's studies prior to 2004 ever mentioned a "Stick" configuration like Ares-I.   And none ever tried to propose a Shuttle-derived configuration as ridiculously large as Ares-V has become.

It is my opinion that a Shuttle-derived solution needs to at least retain the 4-seg SRB's and the 8.4m tank to qualify as "Shuttle Derived".   If there's less than 25% of the system actually with real heritage back to Shuttle, its not very honest to try to claim its Shuttle Derived any more.

If you bought a car from a dealer and later found that only 10% of it was actually the original car identified by the VIN plate, you'd have an open-and-shut case for getting your money back.

I believe we represent the evolution of the "horse we are riding" today -- which I will remind everyone is *Shuttle*, not Ares.

Ross.

Ross,

Out of curiosity.  Could Direct (or for that matter Ares V) use a 3rd or a 4th 4-stage SRB strapped to the core, as some of the EELV's strap on more SRB's depending on their payload?  Could Jupiter 232 actually be upgraded with an additional SRB and larger diameter fairing (to let's say 10 meters, the diameter of Ares V) and boost larger payloads than the 110 tons max the 232 is projected to do?

As you are obviously more intune to this than I, could even Ares use 3 or 4 standard 4 segment SRB's, rather than 2 longer ones?
I am assuming the longer SRB's give you longer burn times rathar than just more, but I'm not sure.  As I understand they burn from the inside out, top to bottom, so a reduced orafice will extend burn time?

Always wondered about that, but hadn't really found any place with good answers.

Offline Lobo

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Re: DIRECT v2.0 - Thread 2
« Reply #4471 on: 01/13/2009 06:08 pm »
  The SSMT was never designed to carry payload on it's nose, or have rocket engines under it, with all the avionics that entails.  Modifying to to do that could be as expensive and problematic as building a new chasis from scratch that -is- designed for it.


Not true.

The ET (not MT)  to Direct core is not the same as F-15 to stealth fighter.

It is more like F-15 C/D to F-15E.

The same assembly jigs and tooling can be used for both.  Skin thicknesses are the basic differences.  New domes on the LO2 and LH2 tanks are basically the same as the remaining ones on the tank.  The thrust structure and forward adapter are not hard items to build. 
Avionics has no bearing, new avionics is being designed for Ares I which would be adapted

If you want a reasonably detailed description of the sorts of changes required, I refer you to this public document:-

http://hdl.handle.net/2060/19930007493


The first 600 pages or so detail all the changes which are required to make each part of an ET into an NLS Core Stage.

But from page 611 onwards there is a really *great* description of how NLS was planning to modify the existing tooling -- and that gives you a glimpse into what's really involved in what they do day-to-day at Michoud.

It should be noted that NLS had the additional complication that they were planning to manufacture up to 14 NLS Cores at the same time as continuing production of up to 9 Shuttle ET's every year -- all occurring in parallel.   We don't have that same complication.

The details are a little out of date because this is all dealing with LWT structures, not SLWT.   Most of the general principles all still apply, as does quite a large portion of the same tooling actually, just not all.

I find it amazing that they believed they were able to do this in 1993, so much so that the program passed its PDR.   Yet 'some' people are trying to tell us its 'too hard' to do these days, all the while promoting an option which requires everything to be 100% replaced.   That argument holds no water for me.

Ross.

Thanks, I'll check it out.  :-)

Offline zinfab

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Re: DIRECT v2.0 - Thread 2
« Reply #4472 on: 01/13/2009 06:11 pm »
Lobo, it is technically conceivable to strap on more SRBs. Early on in the DIRECT conversation (first thread?), someone (maybe Antonio) mocked up a version as you describe-- but it was only done to amuse the geeks on the forum.

That said, it would lose all commonality with launch infrastructure (pads, MLPs, etc.).

As I understand DIRECT's goal, they want to keep the same launch footprint. If you increase the diameter of the ET, then you're starting to talk about ARES V territory. At that point, it probably makes more sense to pursue ARES V or a clean-sheet launch system.
« Last Edit: 01/13/2009 06:12 pm by zinfab »

Offline Matthew Raymond

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Re: DIRECT v2.0 - Thread 2
« Reply #4473 on: 01/13/2009 06:13 pm »
The SRB has no problem holding up the loads of the Ares upper stage, since two of them have to jointly hold up the entire fueled ET and Shuttle with payload in bending.  Ares US is ~400,000 lbs fueled, nothing close to the 1.6 million+ lbs of fueled ET alone.  And in flight, they can only apply a force in similar magnitude to the force they are creating. 

Forgive any mistakes in my math henceforth. I don't exactly have a PhD in aerospace...

Orbiter + Payload = Total Weight of Orbiter
68,585 + 25,061 = 93,646

SSME Thrust x 3 = 400,000 x 3 = 1,200,000

1,200,000 - 93,646 = 1,106,354

So 1,106,354 pounds of positive thrust from the orbiter.

1,600,000 - 1,106,354 = 493,646

493,646 / 2 = 246,823

So each 4 segment SRB would support 246,823 pounds of external fuel tank, not 400,000. Let's assume we get a 5/4 improvement in thrust with an additional segment:

246,823 x (5 / 4) = 308,529

That's still almost 100,000 pounds short. Granted, my reasoning is probably flawed, but I think I've sufficiently illustrated that the mass of the tank itself is not proof of an SRB's capacity to lift weight on its own.

Offline jarmumd

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Re: DIRECT v2.0 - Thread 2
« Reply #4474 on: 01/13/2009 06:32 pm »
The SRB has no problem holding up the loads of the Ares upper stage, since two of them have to jointly hold up the entire fueled ET and Shuttle with payload in bending.  Ares US is ~400,000 lbs fueled, nothing close to the 1.6 million+ lbs of fueled ET alone.  And in flight, they can only apply a force in similar magnitude to the force they are creating. 

Forgive any mistakes in my math henceforth. I don't exactly have a PhD in aerospace...

Orbiter + Payload = Total Weight of Orbiter
68,585 + 25,061 = 93,646

SSME Thrust x 3 = 400,000 x 3 = 1,200,000

1,200,000 - 93,646 = 1,106,354

So 1,106,354 pounds of positive thrust from the orbiter.

1,600,000 - 1,106,354 = 493,646

493,646 / 2 = 246,823

So each 4 segment SRB would support 246,823 pounds of external fuel tank, not 400,000. Let's assume we get a 5/4 improvement in thrust with an additional segment:

246,823 x (5 / 4) = 308,529

That's still almost 100,000 pounds short. Granted, my reasoning is probably flawed, but I think I've sufficiently illustrated that the mass of the tank itself is not proof of an SRB's capacity to lift weight on its own.

What about prelaunch when the tank is filled but the SSME's are not on?

What you have illustrated would be the loads on the stack after the SSME's have fired, but before the SRB's fire.  Btw, this is part of the reason for the "twang" before liftoff, when the nose of the ET rocks forward and then back a few feet (or so, can't remember exactly).

After the SRB's light, the force at the intertank attachment post is equal to the force of the SRB - the Mass of the SRB (very generally).  And as such, it's going to get larger as the thrust of the SRB stays relatively constant, but it's mass changes by almost a million lbs.  So imagine the force from the SRB before tailoff (FYI, for the Ares I, at ~ t=100, you get 2.7 million lbs of thrust, and a mass of 350,000 lbs or an applied force of 2.4 million lbs to the upper stage of Ares or shuttle or Jupiter).

If you make the claim that the segments are in tension, then all the applied force comes from the upper dome during flight, then our worst compressive loads come from when we have the most weight on the stack.  This is when the tank is fully fueled so 800,000 lbs on each SRB before SSME ignition (with almost 100,000 lbs hanging way off the side).  Almost double the weight of Ares on the SRB.

Marc

Edit: for the sake of being on topic, the SRB loads on Jupiter would certainly be less the shuttle.  You could argue that having the mass of the Orion on the nose could create some issues on rollout, but having that other SRB really helps out with that.
« Last Edit: 01/13/2009 06:37 pm by jarmumd »

Offline sandrot

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Re: DIRECT v2.0 - Thread 2
« Reply #4475 on: 01/13/2009 06:36 pm »
And it seems to me there is some mixup kg vs lb
"Paper planes do fly much better than paper spacecrafts."

Offline Lobo

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Re: DIRECT v2.0 - Thread 2
« Reply #4476 on: 01/13/2009 07:07 pm »
Lobo, it is technically conceivable to strap on more SRBs. Early on in the DIRECT conversation (first thread?), someone (maybe Antonio) mocked up a version as you describe-- but it was only done to amuse the geeks on the forum.

That said, it would lose all commonality with launch infrastructure (pads, MLPs, etc.).

As I understand DIRECT's goal, they want to keep the same launch footprint. If you increase the diameter of the ET, then you're starting to talk about ARES V territory. At that point, it probably makes more sense to pursue ARES V or a clean-sheet launch system.

Well, I'd thought to keep the ET/core the same diameter as with the proposed Jupiters, not widen them like Ares, except perhaps with a modification of allowing more external boosters to it (I have no idea if that'd be a fairly easy mod, or a complete redesign of the whole ET, which would of couse defeat the purpose.

So, 1) would the tank have to be drastically altered to withstand the force of a 3rd or 4th SRB?
2)  Would the launch pad need to be modified significantly to withstand the force of an extra SRB or two (how much different would that be from current design?  Maybe one pad could be modified, so it could launch either the 120/232 or the new heavy with 1 or 2 additional SRB's.  How much real cost is there in that? If not significant, that could be looked at as a growth path 10 years down the road.  The Ares V wouldn't be ready for another 10 years anyway.
3)  Once the 3 or 4 standard 4-segment SRB's are exhausted, is there enough fuel/thrust available in the core to insert the heavier payload into LEO?  Getting it off the ground is only part of the battle, it needs to still have enough juice to get into LEO.  That I don't know but am curious about.  Would the additional SRB's allow the RS-68 engines to be throttled down enough to conserve enough fuel so they could be kicked up to full thrust after SRB separation and have enough fuel and thrust to get a larger payload into LEO?

Really I bring this question up for these reasons.
As I understand, the SRB really give you one of the best fuel to weight ratio, as well as being simpler than liquid fuel as you don't have any cryo, or pumps, etc.  The drawback is more vibration, non throttleable, and a slow thrust speed, so they are good to get you going, but you need something with a faster exhaust velocity to boost you to the fast speeds.
Hence why they are used for 1st stages but not after that.

So could we use more, rather that new larger ones for Ares V?
Could we use more, to boost the weight of the Jupiter's?
I forget how the Jupiter nomenclature works, so I'll call it a Jupiter -232 Heavy for now.

If you can utilize the additional lift off thrust of extra SRB's, can the fuel in the ET be throttled back to conserve until SRB separation, and then have enough to still get how much payload into orbit?
Can it be fitted with a 10 meter fairing?

I guess I keep looking at it beyond just the ISS and moonshot.  The Ares V would give a lot of flexability for lifting large volume, heavy mass payloads into orbit for future space stations, satillites, telescopes, and Mars Mission Hardware.  Can the Jupiter architecture provide a reasonable groth path to that end?  Wouldn't necessarily even have to match the Ares V, but for basically just the additional cost of 1 or 2 more SRB's, you can get 150 or 170 tons into orbit, with a larger diameter, then you have some growth potential.
Future space telescopes are a primary beneficiary of payload width flexability.  Telescopes are all about mirror size, the larger the mirror, the farther you can see, period.  I've already been reading proposed project for new space telescopes based on the width and lifting capability of the Ares V.  Simply opens up entirely new avenues in astronomy if you can put up a 10 meter telescope.  Basically, that's the width of the Keck Telescopes on Mauna Kea (which I've visted many times while vacationing on the Big Island of HAwaii).  Hubble is like 1.6 meter diameter.  And with current Space Shuttle, EELV capability, Hubble is about all we can put up.  They have some new designes for fold out multiple mirror designs (similar to the Keck mirrors), but these are super, SUPER precise instruments, and adding the ability to fold out and deploy adds exponentially to the odds of something malfunctioning and having a 400 million dollar piece of space junk floating around.  Having the ability to prefab a 10 meter diameter mirror on the ground is obviously a huge advantage.

If the Jupiter could add to it's payload weight and diameter, than for guys like me who are thinking we'll be stuck with whichever design for several decades would feel more comfortable.  With Direct over the long term.

Offline jarmumd

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Re: DIRECT v2.0 - Thread 2
« Reply #4477 on: 01/13/2009 07:20 pm »
Sorry, feeling a bit post happy today...

FYI a 5 seg SRB weighs almost 1.6 million lbs ready to go.  Unlike a liquid engine, you have to carry all that mass to the pad (liquids fill at the pad).  They weigh almost an order of magnitude more than the empty tank / spacecraft.  Thus, adding two more doubles your weight and is much to heavy for the crawler - so upgrade crawler, and for the crawler way - so rebuild path.  It's just way too expensive when you could better design your spacecraft.

Offline HIP2BSQRE

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Re: DIRECT v2.0 - Thread 2
« Reply #4478 on: 01/13/2009 07:25 pm »
Fifth is the fact that the SRB's were never designed to be utilized in this fashion with hundreds of tons of stage and payload on top.   They just weren't designed for these loads.

Why are these loads a big issue for the SRB, but not for Jupiter's ET-based core stage?  Is it because the core (being mostly tanks holding the liquids) can be redesigned to handle the loads, but the SRB can't be modified similarly?

Steve

The SRB has no problem holding up the loads of the Ares upper stage, since two of them have to jointly hold up the entire fueled ET and Shuttle with payload in bending.  Ares US is ~400,000 lbs fueled, nothing close to the 1.6 million+ lbs of fueled ET alone.  And in flight, they can only apply a force in similar magnitude to the force they are creating. 

Ross, I'm sure this will upset you, but I think you need to take it down a notch.  Passion is good, but in all honesty your post above with the bold text and italicizing, and comments of the "truth" all remind me of a certain Italian that needs to stay off the internet.

Marc

This is what I said to the Direct Team yesterday under Marketing Plan:

•On blogs, forums etc stay professional.  Put the facts out, but change tone to look appear more professional.  No side remarks, etc.  Personal attacks such as saying a person does not know what he is doing look childish and have hurt Direct.

Offline Matthew Raymond

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Re: DIRECT v2.0 - Thread 2
« Reply #4479 on: 01/13/2009 07:38 pm »
And it seems to me there is some mixup kg vs lb

Oops, you're right. I'll rerun the numbers:

151,205 + 55,250 = 206,455

393,800 x 3 = 1,181,400

1,181,400 - 240,000 = 941,400

1,667,000 - 941,400 = 725,600

725,600 / 2 = 362,800

362,800 x (5 / 4) = 453,500

DOH!!!

Of course, this assumes a 5-segment SRB actually has x1.25 the thrust of a 4-segment SRB. It also doesn't account for the fact that the 400,000 lbs of mass for the Ares I is a second stage is static, while the weight of the external tank decreases over time due to fuel consumption. Then again, an Ares I might have less aerodynamic drag...

Moral of the story: Leave rocket science to the rocket scientists. ;)

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