Problems with man-rating SRBs

[MP99]

Thanks for the inputs guys.  I beefed up the model a lot while watching the HSF meeting here in Houston.  I was told some "suits" at NASA don't like me right now.  Apparently my book on how we got stuck with Ares I is making the rounds and not popular with some.  I decided to stay at home and do some rocket science work instead of risking a confrontation at the meeting.

Danny Deger

I have to say I'm disappointed Danny. You have an opportunity, as obviously someone who is very well respected among the ranks there, to shed a sombering light to this whole mess.

Robert,

Danny doesn't yet seem to have come to a conclusion that he feels he can state definitively, and then stand behind.

That's an ideal time for someone to attempt to pre-empt / discredit him.

Danny doesn't sound like a guy that will avoid that meeting once he's confident of his facts, nor someone who would go into that meeting half-cocked.

cheers, Martin

[MP99]

Just to clarify for my own mind.

We are discussing two SRB failure modes:-

1) an unzip of the SRB in response to an abort (however triggered).

2) a blockage of the nozzle which causes the SRB to explode.


This is emulating (1) rather than (2). How different (if at all) is the debris field generated by the two types of fail?

cheers, Martin

I'm still not quite clear if the controlled "unzip" results in the same fragment velocities as a blocked-nozzle event.

NASA claims they have 5 seconds of warning time for a plugged nozzle.  This is complete nonsense.  This is how their got the Ares I crew survival numbers they needed to justify the project.

There is no warning time for a plugged nozzle and the crew will certain die if this happens.

I have attached a zero warning time video.  Orion is right in the middle of the debris field for the first couple of seconds. Keep in mind the upper stage/ET will certainly go off when the SRB comes apart and there will be blast.

What separation do you assume between SRB & Orion before events kick off? J-246 should have 35m+.

cheers, Martin

[rsp1202]

. . . So many things with Ares-I are wrong.

And things never seem to get better. Ares I is a black zone.

[Danny Dot]

The takeaway seems to be that the delay between abort and destruct dramatically affects the required LAS mass, perhaps more so than the dynamic pressure.

If the abort motor only burns for 2 or 3 seconds, then the SRB thrust has to be terminated quickly to maximize separation.  So what is the minimum delay that allows the CM to escape the initial explosion?

Why not have an automatic delay trigger (activated at SRB ignition) to unzip the SRB a certain number of milliseconds after an abort?  Are there concerns that this may trade public safety for crew survivability?

At 1200 psf, even 3 seconds is not enough for the close end problem.  Too much drag!!!

Let me run shuttle like q and see what happens.

Here is a link to a video of the situation.

1200 psf dynamic pressure with 3 second warning.  A close up.


Danny Deger

[MP99]

Danny,

you've made comments re 3g or more continuous SRB acceleration before destruct is issued.

Is there a possibility to push a rogue SRB's TVC over to maximum? For an 8 sec delay between separation & destruction, could this stop it from thrusting 8 secs at 3-4g in one consistent direction, and therefore stop it catching up to the capsule?

I'm well aware this suffers the same issues as destruct - how do you decide to heel over the TVC when you're not yet sure if things are bad enough to destruct the SRB? But if an SRB mistakenly heels itself over, could the vehicle compensate enough to allow a safe LAS firing, then vehicle destruct? If so, could this be built in automatically, ie SRB detects 3-4g acceleration (mistakenly or not), decides that it has detached, heels over TVC and sends (possibly redundent) LAS-trigger signal. This will likely result in ET failure and eventual SRB destruct, but maybe more benignly for Orion?

In the event of a genuine detach / rogue SRB event, the SRB will angle away from the vehicle & Orion, but expose ET to the full wash of motor exhaust.

In the event of a false detection of detach / rogue, thrust will vector which may allow a relatively graceful LAS abort & vehicle destruct.

cheers, Martin

[Danny Dot]

A hard over actuator would kill the effective thrust.  It should be considered.  I don't like it because it assumes a healthy booster, not a good assumption in my opinion.  If the booster was healthy, we wouldn't need to abort off of the darn thing in the first place 

But it looks like a 2 second delay to destruct might be OK for shuttle like profiles.  Here is a close-up view of the separation.  Keep in mind I do not model the base suction of being close to the booster.  But it looks like Orion is about 300 feet away at destruct.  This is also with the current Orion LAS thrust which is only 10 Gs.  Bumping up the Gs to 15 would help a lot.

http://www.youtube.com/user/dannydot863#play/all/uploads-all/1/oEvISWwImkw

But, even with a 2 second delay, shuttle profiles are in trouble.  My model shows Orion "slightly" inside the debris field when the drogue opens.  Certainly too close to call.  It looks like shuttle like will need a sustainer.  John Shannon thanked me for coming up with this idea.  I wonder if such a big change to Orion will increase the gap.   I think it must.

Here is the video of Orion on the edge of the debris field with a 2 second delay with 6 feet diameter debris.   

http://www.youtube.com/user/dannydot863#play/uploads

Ask me anything you wish and I will model it for you.  I am not too bad at this line of work.  Too bad NASA fired me for writing 31 personal emails in a 2 month period. 

Danny Deger

[robertross]

John Shannon thanked me for coming up with this idea.  I wonder is such a big change to Orion will increase the gap.   I think it must.

Danny Deger

I can't watch/see the videos, but I must say the Excel program and data so far is outstanding Danny. Thanks for sharing.

For a change is LAS, if (for arguement's sake) Ares-I goes ahead, then it only took them (what, 2-years?) to get the initial unit to this stage. Getting a replacement in time for Orion's IOC wouldn't seem too far out, except for the mass penalty which we all know Ares-I can't afford a hit on.

The same probably holds true for dropping the SRB nozzle with charges to reduce the chamber pressure. It could help, but the mass penalty for explosive bolts/charges may be excessive.

The problem with Ares-I, as you and most already know, is it can't grow any longer, whereas liquid-fuelled rockets can (to a certain degree) as needs arise.

[Danny Dot]

I can't watch/see the videos, but I must say the Excel program and data so far is outstanding Danny. Thanks for sharing.

For a change is LAS, if (for arguement's sake) Ares-I goes ahead, then it only took them (what, 2-years?) to get the initial unit to this stage. Getting a replacement in time for Orion's IOC wouldn't seem too far out, except for the mass penalty which we all know Ares-I can't afford a hit on.

The same probably holds true for dropping the SRB nozzle with charges to reduce the chamber pressure. It could help, but the mass penalty for explosive bolts/charges may be excessive.

The problem with Ares-I, as you and most already know, is it can't grow any longer, whereas liquid-fuelled rockets can (to a certain degree) as needs arise.

You can't watch youtube???

That's what you get for living in Canada

I would upload them here, but there is a 20Meg limit.

Moving the destruct package to remove the nozzle is probably not more weight -- assuming the charge to open the whole case is removed.   

I understand current LAS is in some trouble with its active control system.  Adding a sustainer requirement is not going to be trivial.  As a minimum, the outer mold line will change and all that wind tunnel data and CFD is going to need to be redone.  The sustainer is going be something like 10,000 pounds according to my analysis.  This is going to mean lots of rework on structure analysis and maybe changes to structure to carry this very large LAS.  Not to mention the flight software changes to operate the sustainer.  All in all, it stacks up to a lot of work.

A nice liquid booster is sounding very good at this time.  Does anyone have one operational to sell NASA??? 

Danny Deger

[jongoff]

I understand current LAS is in some trouble with its active control system.  Adding a sustainer requirement is not going to be trivial.  As a minimum, the outer mold line will change and all that wind tunnel data and CFD is going to need to be redone.  The sustainer is going be something like 10,000 pounds according to my analysis.  This is going to mean lots of rework on structure analysis and maybe changes to structure to carry this very large LAS.  Not to mention the flight software changes to operate the sustainer.  All in all, it stacks up to a lot of work.

A nice liquid booster is sounding very good at this time.  Does anyone have one operational to sell NASA??? 

Yeah.  Once your launch abort motor starts weighing more than the fully loaded crew capsule you have to start asking what you're doing wrong.  Sure, DIRECT has enough margin that they can bandaid over this, but I'm sure that you're adding more failure modes in and more complexity...EELVs (especially ones without solid boosters) are starting to look better and better.

~Jon

[Danny Dot]

snip
Yeah.  Once your launch abort motor starts weighing more than the fully loaded crew capsule you have to start asking what you're doing wrong.  Sure, DIRECT has enough margin that they can bandaid over this, but I'm sure that you're adding more failure modes in and more complexity...EELVs (especially ones without solid boosters) are starting to look better and better.

~Jon

The current abort system comes in at 16000 pounds to take care of a 19250 pound capsule.  We are already close to a reasonable limit in my opinion.

Danny Deger

[Stephan]

These are videos of the screen, not me holding up my camcorder.  I am sure you will miss my enlightening commentary.

Hi Danny, you can record your commentary while running camstudio if you have a mike plugged in.

[mmeijeri]

A nice liquid booster is sounding very good at this time.  Does anyone have one operational to sell NASA??? 

Preferably a single-core one, though that will not be enough to launch Orion. Would kerolox be better than LOX/LH2? Can kerolox detonate?

[joema]

The current abort system comes in at 16000 pounds to take care of a 19250 pound capsule.  We are already close to a reasonable limit in my opinion. Danny Deger

It's bad -- LAS is already at 83% of vehicle weight. The Apollo LES was about 8,000 lbs, vs the CM roughly 13,000 lbs (62% of vehicle weight).

Ironically the heavier the LAS, the greater the incentive to jettison it early because of the mass penalty of carrying it uphill. That in turn drives consideration of LAS ascent assist modes, where you fire the LAS while still attached to get some benefit from that mass. Unfortunately that introduces yet more mass and/or complexity from structural reinforcement, additional LAS modes, etc.

[Antares]

Would kerolox be better than LOX/LH2? Can kerolox detonate?

From a detonation perspective, anything can.  The key is whether or not it mixes.  That determines detonability.  But, generally, kerosene is better for a first stage because it results in a smaller vehicle and doesn't require the purges or infrastructure that LH2 does.  However, since LH2 may make sense for upper stages, that means there are 3 ground propellant systems instead of just 2.  Yet, like Falcon 9, there may be a case for a kerolox upper stage too - on simplicity grounds.  It complicates the trajectory and decreases performance, though.

[butters]

A nice liquid booster is sounding very good at this time.  Does anyone have one operational to sell NASA??? 

Danny Deger

Largest operational all-liquid launch vehicle is Proton-M (21mT IMLEO) Delta IV Heavy (23-25mT IMLEO depending on source).

[Jim]

A nice liquid booster is sounding very good at this time.  Does anyone have one operational to sell NASA??? 

Danny Deger

Largest operational all-liquid launch vehicle is Proton-M (21mT IMLEO).

Delta-IV heavy is bigger

[mmeijeri]

Is Atlas the biggest single core all-liquid launcher?

[yinzer]

Proton is bigger and single-core.  But I'm not sure why "single-core" matters.

Either Atlas or Delta IV with a health monitoring system and LAS added would just as safe as anything else, down to the limit of our capability to tell.  They might have a slightly higher chance of random failure, but most launch failures aren't random.

[GraphGuy]

Quite sobering, fortunately Direct has the margin for a bigger LAS.

Danny any idea:
1. -When in the launch the CEV is deepest in the weeds if there is an abort?
2. -How much additional thrust is needed to get the CEV to safety assuming an abort at the worst possible moment?
3. -What the new max dynamic pressure would be with an upgraded LAS?


4. Why do I feel that NASA will see this and respond by eliminating the LAS from the CEV?

1. It looks like about 50 seconds

2. I ran an 80,000 pound force sustainer that burned for 15 seconds after the high thrust part of the abort.  I didn't look too much at just increasing the thrust

3. Just for you, I added a Max Q readout to the model.  The sustainer does not increase Max Q.  The current Orion off of the Ares I at 50 seconds is 1322 psf.  This is starting from 919 psf off of Ares I.  This may be low.  I have heard Ares actually goes to 1200 psf.

4. I don't think the astronaut office will allow this.

Danny Deger

P.S.  I am going to ask the moderators to merge this with the Ares I abort thread. 

Thanks for the quick answers, good to see that max Q is unchanged.

Here is another question that is much more difficult to model (please bear with me, I write graph algorithms, I am not a rocket scientist):

The CEV is traveling at supersonic speeds and some debris will be traveling in its wake when the CEV pulls away.  While the CEV experiences up to 1200 PSI of air pressure resistance the debris in its wake will experience much less resistance and so it will travel farther than debris outside the CEV's wake.  How much of a threat is any debris in the wake of the CEV?

[mmeijeri]

I was thinking of risk, but if that is no worse than single core as you say then cost is the only remaining issue. Three cores must be more expensive than just one, but likely a lot less than three times as much.