rwessel
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More Woe For Ares I

Wed Jul 22, 2009 4:56 am

According to a USAF study, based on an analysis of a Titan IV* explosion shortly after liftoff in 1998, the resultant extremely large fireball from the solids, punctuated by chunks of burning solid rocket fuel, would make the Orion escape system fail if used during the first minute of flight. As the Orion would still be inside the fireball when it deployed its parachutes (and would remain so until it impacted the ocean if it delayed deploying it chutes), the parachutes would be fatally damaged.

A significant part of the problem is the very high initial acceleration of Ares I, which causes very high dynamic loads early in the flight, which significantly reduces the escape system's rockets ability to pull (or push) the Orion away from the booster. The other significant part is that the SRB, being solid, cannot practically be shut down before burnout. A significantly more powerful escape rocket would solve the problem, but at the obvious costs in weight for the rocket and added structure. It's also unclear that the escape system's acceleration could be increased significantly, due to limits of human G tolerance, which makes the size increase worse.

Ares I / Orion is already having severe weight problems.

Some are calling this issue fatal for Ares I (obviously premature, but anything that adds more weight growth to the stack at this point is very troubling), and NASA states that its analysis is that this is not an issue, but they will be looking at the USAF's study.


http://www.newscientist.com/blogs/sh...eath-knell-for-nasas-ares-roc.html

http://www.orlandosentinel.com/news/...o-nasa-ares-071809,0,3051613.story



*The Titan IV has a pair of large SRBs – each roughly half the size of the Shuttle/Ares SRBs
 
connies4ever
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RE: More Woe For Ares I

Wed Jul 22, 2009 9:38 am

All the more reason to take another look at DIRECT. It may well have a shorter timeline than Ares I - or no worse - and possibly eliminate some of the existing weight/performance issues with Ares I.
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michlis
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RE: More Woe For Ares I

Wed Jul 22, 2009 10:47 am



Quoting Rwessel (Thread starter):
Some are calling this issue fatal for Ares I (obviously premature, but anything that adds more weight growth to the stack at this point is very troubling), and NASA states that its analysis is that this is not an issue, but they will be looking at the USAF's study.

I remember hearing that there were concerns about the effectiveness of the escape system for the Saturn V/Apollo configuration as well.
If you know the enemy and know yourself, you need not fear the outcome of a hundred battles.
 
rwessel
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RE: More Woe For Ares I

Wed Jul 22, 2009 9:59 pm



Quoting Michlis (Reply 2):
I remember hearing that there were concerns about the effectiveness of the escape system for the Saturn V/Apollo configuration as well.

While I don't know the specific concerns for Apollo, this is a different issue than would have been faced by the very slowly accelerating S-IB/S-V in the early part of the flight. Not to mention that the Saturns would have been at zero thrust as soon as the escape system activated. Those would have made the escape system's task of pulling the Apollo CM well clear of the booster much easier.

Nor would an exploding Saturn have generated a huge spray of burning and impossible to extinguish solid rocket fuel. Exploding liquid boosters will generate a very impressive fireball, but will inherently not spray burning fuel as far. Just the ballistics of a spray of liquid ensure that, and the liquids will either burn fairly quickly, or be dispersed, and then *not* burn, since they'll be away from an ignition source. The solid will basically all be burning (remember that and booster like that burns along the entire length, from the core out), and the remains will be likely tossed around in good sized chucks that have a much better (compared to a liquid) ballistic coefficient, and that will burn for a considerable time.

As I mentioned, the issue is whether the escape system can pull the Orion far enough away from the fireball, and if not how much of a weight increase it will take to upgrade it to perform satisfactorily.
 
PC12Fan
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RE: More Woe For Ares I

Mon Aug 03, 2009 9:18 pm



Quoting Connies4ever (Reply 1):
All the more reason to take another look at DIRECT.

Amen. More capable platform IMO. With DIRECT, it seems there are more mission types that could be achieved. For example, look at the configuration next to the shuttle.

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That could be an ISS mission or even a hubble type mission. Very limited to what Ares I could do. I'd say (easy for me) to still develop Ares V for those "super" payloads, along side a full DIRECT program.
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nomadd22
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RE: More Woe For Ares I

Tue Aug 04, 2009 12:08 am

The failure scenario that has so many undies in so many bunches isn't very likely. The two likely ways for a solid to fail are case failure or the stack veering off course.
A Challenger type failure would be a gradual push off course that would give the LAS plenty of time to act and launch in the opposite direction. It's not very steerable, but it is steerable. A more serious rupture would kill acceleration almost instantly by releasing the internal pressure.
Burning pieces of solid fuel aren't going to be shooting around like rockets.
There's almost no SRB failure scenario serious enough to kill An Ares that wouldn't have also doomed a shuttle. And there are a whole lot of them where the LAS would save the crew with Ares that the shuttle couldn't have survived.
No doubt this won't sway any of the folks who will proclaim Ares an impossible to build deathtrap every time they need to work through any of the thousand other issues and concerns that are part of any launcher program.
Anon
 
rwessel
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RE: More Woe For Ares I

Tue Aug 04, 2009 2:38 am



Quoting Nomadd22 (Reply 5):
There's almost no SRB failure scenario serious enough to kill An Ares that wouldn't have also doomed a shuttle. And there are a whole lot of them where the LAS would save the crew with Ares that the shuttle couldn't have survived.

That's not the problem. NASA's official safety standards for the new manned launch vehicle require the LAS to work in those situations.

Quoting Nomadd22 (Reply 5):
Burning pieces of solid fuel aren't going to be shooting around like rockets.

The Titan IV accident showed that there can be.
 
TheSonntag
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RE: More Woe For Ares I

Tue Aug 04, 2009 8:12 pm



Quoting Rwessel (Reply 3):
Nor would an exploding Saturn have generated a huge spray of burning and impossible to extinguish solid rocket fuel. Exploding liquid boosters will generate a very impressive fireball, but will inherently not spray burning fuel as far.

However, given the sheer amount of propellant in the Saturn-V, it would certainly have been substantial.

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