Effectiveness of Ares I abort system called into doubt by USAF

[JIS]

Back to the key issue. How far will Orion get once the abort signal is sent to LAS and Ares 1 FS flight is terminated by FTS?
The worst case in the flight profile might be max Q.
The worst abort scenario will probably be the grain delamination, pressure increase inside the chamber and casing burst.
Samewhat better case could be an abort initiated by Ares/Orion systems.

I would expect that with FTS initiation the FS thrust is terminated and cloud of shrapnels created decelarating quickly in the lateral direction.
Orion continues under very high Q flight for several more seconds folowed by 10-20s of unpowered flight, folowed by 180deg turn, LAS jettisoning and drogue extraction. 

The question is how far will Orion get during the abort. I don't think that the mentioned USAF study was precise enough in the Orion flight profile.

Cx certainly study this stuff so there might be some document around.
I think that during the Gemini LAS trials the max Q was somewhere around 1500 psf. Orion LAS might achive even higher Q. Could be close to 2000psf? Twice as much as nominal Ares 1 flight?

[Jim]

The worst abort scenario will probably be the grain delamination, pressure increase inside the chamber and casing burst.

worst case is an FTS initiated by something other than a SRM failure, where a perfectly good SRM is burst by the FTS.

[Jim]

I would expect that with FTS initiation the FS thrust is terminated and cloud of shrapnels created decelarating quickly in the lateral direction.

It would react the same as the USAF study

[mmeijeri]

I would expect that with FTS initiation the FS thrust is terminated and cloud of shrapnels created decelarating quickly in the lateral direction.

Lateral isn't necessarily good if the Ares I is flying at an angle. Vertical gives you the 'Moses' scenario, horizontal gives you 'Sodom and Gomorrah'.

[sbt]

* If the results were similar, "Why was this risk deemed tolerable?"

70% LOC for an abort at this stage, which is what the Ares I risk spreadsheet give, is quite high - whether you believe that this effect was factored into that number or not.

The only way to regard that level of risk as tolerable is:

a) If you believe that you can modify things to bring the number down. i.e. That the number is an artefact of the current design rather than the result of an inherent property of the basic approach.

b) If you believe that the chance of an abort being needed during these 30 seconds of flight is low enough, or can be made low enough, that the overall risk is one or both of:

Acceptable in its own right.

Small compared to the risks of other stages of flight, such that improvements in the overall chance of crew survival during the relevant phase of First Stage have negligible effect on the overall chance of the crew surviving a mission.

Rick

[Antares]

Assuming that the range safety requirements don't say "must reduce the booster to tiny shards" (what about a liquid booster's engines, in that case?), the obvious next choice would be to cut the Ares booster circumferentially at or near one or more of the field joints.  Thrust would drop immediately to zero in all but the top segment (and would be greatly reduced there without a nozzle).  What's more, the un-split motor segments would be much more likely to retain their structural integrity, eliminating the issue of flaming shrapnel, since motor pressure would be released from the segment ends and not through a split in the casing.

It's not the casing of the SRB that's flaming shrapnel.  It's the propellant itself.  That's why a liquid engine doesn't have to be fragged.  It's not burning.  The propellant going through it is; and even then, liquids don't burn until there's a fuel and an oxidizer together with an ignition source.  Solids have both already mixed.

[Antares]

But if the RSO made a mistake (or if rules have since changed, circumstances were different, etc) it is not a counter example.

The rules have changed.  Free-flying SRBs are an extremely remote possibility now.  The ISDS (Inadvertent Separation Destruct System) sets off destruct systems if solids come off in an uncommanded fashion.

[joema]

...worst case is an FTS initiated by something other than a SRM failure, where a perfectly good SRM is burst by the FTS.

That's an excellent point. The issue isn't just SRB reliability. Ares would still be vulnerable to this problem, even with an infinitely reliable SRB.

There are numerous non-SRB failures which could trigger an abort. E.g, 2nd stage structural failure, guidance failure, etc. The abort would initiate FTS, which in turn causes the "fratricide" problem -- even though the SRB was running perfectly.

[renclod]

Could this be a possible thrust termination/limitation system for the 5+ psi Q launch abort situation ?

[Jim]

Could this be a possible thrust termination/limitation system for the 5+ psi Q launch abort situation ?

No, because what is circled is new because that portion of the LSC does not exist on a 4 segment SRB

[Danny Dot]

I am firming up a real time graphic program showing how to separate from an SRB debris field.  I need to know the burn rate in meter/sec (ft/sec or inches/sec?) of the propellant in the SRBs after they are exposed to air.

Please post answer here and send me an email.

Danny Deger

[rdale]

There have been recent reports containing a leaked preliminary internal Air Force assessment document regarding potential abort scenarios for the Ares I rocket and the effect on an Orion crew exploration vehicle.  The assessment, as preliminary, addressed a certain class of abort scenarios.  This class of aborts involves destruction of the first stage because of either a case over-pressure or because of a range safety initiated destruct command.  The majority of aborts do not fall into this category because of the abort criteria and flight rules the program is implementing.  The analysis is not an official Air Force position, but a starting point for working specific issues associated with the complexities of aborts.

An ongoing exchange of information and analysis is part of the formal process for the 45th Space Wing to evaluate a new vehicle’s request to use the Eastern Range and establish an operations agreement. NASA and the Air Force work together through routine technical interchange meetings to share data and analysis on launch vehicles and payloads. This is typical of how the two organizations have worked together in the past to evaluate Apollo, space shuttle, and nuclear payload missions such as New Horizons as they were in development. A joint team, comprised of experts from both NASA and the Air Force, meets routinely to collaborate on issues related to range safety, and works to provide answers to all outstanding questions and concerns.

The program will continue to work closely with the 45th Space Wing to mature the analyses as the development of the vehicle continues, with the top priority being the ability to protect the crew and public. ‪Ares/Orion were conceived and are being designed as the safest launch vehicles in history. The findings in this preliminary Air Force analysis have provided insight into the abort environment, and each issue and concern will be answered as NASA shares more in-depth studies and analysis with the Air Force and continues to refine its models and data. Constellation is a developing program and NASA will continue to work with the Air Force as the two agencies collaborate to assure both crew and public safety.‪

http://wiki.nasa.gov/cm/blog/Constellation/posts/post_1248719332967.html

[kyle_baron]

An excellent analysis, without the emotional or critical content.  Thank you.

[Danny Dot]

Lowering the dynamic pressure doesn't help a lot in aborting off of an SRB.  Even a LAS that weighs 22,600 pounds still has problems. 

I started a new thread, because this problem effects Direct, side mount, and EELVs.  Take a look at my data there.

http://forum.nasaspaceflight.com/index.php?topic=18071.0

Danny Deger

[Ben the Space Brit]

Okay, I've come up with a brainwave.  Stop me if someone else has thought of this or it can't work for some reason.  I'd be surprised if a real rocket scientist hadn't thought of this, but we'll see.

Right now, all LAS abort scenarios that I've seen assume a single powerful burn at the moment of abort to push the LAS/spacecraft as far away from the LV as possible before the destruct is executed.  The question that I want to ask is: Is there any reason why this has to be the only powered element of the abort?

I'll expand: In the specific case of a SRB destruct, the key issue appears to be getting the Orion outside of the 'hot zone' where the local air temperatures are inimicable to the parachute materials.  Right now, everyone seems to be focussing on the amount of impulse the LAS can impart to the Orion at the moment of detach from the stack.  My idea is that, instead of relying just on this one burn, have a twin-stage abort motor.  The first stage supplies the impulse to get the spacecraft away from the stack.  The second stage is a sustainer, whose only purpose is to keep the Orion airborne and moving away from the stack. 

The second stage (and this is something of a misomner, it would actually just be another set of slower-burning solid propellent motors inside the LAS motor casing) would burn for as long as it is feasable to build.  It would not impart much in the way of mean acceleration.  Rather, it would mostly be intended to lengthen the ballistic arc of the flight away from the LV so that, when the unpowered parachute descent starts, it is much further away from the 'hot zone'.

Now, I know that there would be a mass penalty to pay for such a scheme.  However, the non-Stick SDLVs have a significant mass surplus to play with.  In any case, I can't see an extra SRM or two weighing more than a couple of tonnes.

So, how about it, you experts? Am I onto something, or do I not know what I'm talking about?

[mmeijeri]

I'm definitely not an expert, but Danny's analysis does include a sustainer motor.

[Ben the Space Brit]

I'm definitely not an expert, but Danny's analysis does include a sustainer motor.

So the duration of the burn of the sustainer is the issue rather than the existance thereof.

[EDIT - removed irrelevant stream-of-consciousness chatter]

[Antares]

You'd rather tailor the burn rate to make it a continuous burn even if the mid part of that is very low impulse.  One would not want an additional ignition event that has to happen.

[Danny Dot]

I posted my latest data on this thread.  I think Ares is in really, really big trouble with this issue.   

I made a new thread because I thought Direct and side mount aborting off of an SRB didn't belong here.   You can download the model and play with sustainers all you want.  It looks like a reasonable sustainer is going to add about 10,000 pounds to the LAS.  You can see their effectiveness on my youtube uplinks you can find on this thread.

http://forum.nasaspaceflight.com/index.php?topic=18071.msg448163#msg448163

Danny Deger

[Danny Dot]

Back to the key issue. How far will Orion get once the abort signal is sent to LAS and Ares 1 FS flight is terminated by FTS?
The worst case in the flight profile might be max Q.
The worst abort scenario will probably be the grain delamination, pressure increase inside the chamber and casing burst.
Samewhat better case could be an abort initiated by Ares/Orion systems.

I would expect that with FTS initiation the FS thrust is terminated and cloud of shrapnels created decelarating quickly in the lateral direction.
Orion continues under very high Q flight for several more seconds folowed by 10-20s of unpowered flight, folowed by 180deg turn, LAS jettisoning and drogue extraction. 

The question is how far will Orion get during the abort. I don't think that the mentioned USAF study was precise enough in the Orion flight profile.

Cx certainly study this stuff so there might be some document around.
I think that during the Gemini LAS trials the max Q was somewhere around 1500 psf. Orion LAS might achive even higher Q. Could be close to 2000psf? Twice as much as nominal Ares 1 flight?

These are EXACTLY the questions my model is made to answer.  Do you have Excel?  Get a copy and have a great time looking all these issues.  And let us know what you find out. Someone is working on getting the model to run on Open Office for those that can't afford Office.

On making the range package sever the nozzle off, it would take the thrust to near zero.  We tried this on the AGM-130 and it worked in killing the thrust of the solid.  But, the 45th Space Wing might not like this.  They might want to turn the SRB into smaller pieces.

Danny Deger