Problems with man-rating SRBs

[Danny Dot]

I have been a busy rocket scientist and made a tool to graphically show what it is like to abort off of an SRB.  It is not easy.  OK, building the model was fairly easy -- surviving the abort is the hard part. 

The Direct and side mount dynamic pressures don't solve the problem.  I jacked the abort system up to 22,500 pound mass, and there are still problems.

I broke the video into 2 parts so I could put it on youtube. 

Part 1:


Part 2:


PM me and I will send you the source code.

Danny Deger

Edit: I attached a copy of the source code.  It is a zipped Excel Spreadsheet with the numerical integration done in VBA.

Second edit: Fixed typo in Orion mass header.

[edkyle99]

I have been a busy rocket scientist and made a tool to graphically show what it is like to abort off of an SRB. 

Good stuff.  Great stuff!  I'm not sure about the underlying assumptions, etc., but this provides an excellent in-motion visual that helps to explain the problem.  Anyone interested in this issue should watch these simulations.  It gives a "feel" for what is involved.

 - Ed Kyle

[TrueBlueWitt]

Is there any differentiation between 4-Seg and 5-seg in terms of SRB acceleration after separation? 

Some people have suggested blowing the tops off the SRB(s) right after separation to reduce forward momentum.

Another thought.. is there a window between the prop tank(Direct), AUS(Ares) debris and the SRB destruct debris where you could have the LAS diverting Orion toward vertical, and let the SRB(s) go by before you blow them?

[butters]

Nice work.  Not that it will impress Jeff Hanley.  He's got supercomputers that tell him whatever he wants to hear.

[Lab Lemming]

Do you have a 3 minute version to present to the committee?

[mmeijeri]

I couldn't follow what precise scenarios you were analysing in the second video. In the first scenario you're talking about a liquid first stage. Does this include solid strap-ons or is it all liquid? You say the debris would be small and not burning, but at the same time you are talking about SRB propellant. If it's SRB debris why would it not be burning?

Another question: why do small chunks decelerate more quickly than large ones?

[Lab Lemming]

small chunk have higher cross-section to mass ratio- air drag.

Danny, why the long delays before destruct?  You'd think that anything over 0.2 sec would only happen if it was specifically programmed to give the LAS time to pull away.  Programming an 8 second delay into the avionics seems silly.

I couldn't follow what precise scenarios you were analysing in the second video. In the first scenario you're talking about a liquid first stage. Does this include solid strap-ons or is it all liquid? You say the debris would be small and not burning, but at the same time you are talking about SRB propellant. If it's SRB debris why would it not be burning?

Another question: why do small chunks decelerate more quickly than large ones?

[yinzer]

Good stuff.  Looks like a tradeoff between waiting long enough before blowing the SRB to let the capsule escape the blast wave, but not so long as to let the booster catch up.  Agreed on 8 seconds seeming silly - surely  an abort would trigger the SRB destruction, possibly via a delay fuze and/or ISDS.

That transonic base drag is a killer.  Base bleed?

[Danny Dot]

Nice work.  Not that it will impress Jeff Hanley.  He's got supercomputers that tell him whatever he wants to hear.

I used to beat the pants off of people with a very old PC running Quick Basic when they had great big main frames.  The trick is in the programmer, not the computer. 

Excel/VBA and a modern PC is like a Cray to me.  I was surprised it handles the Orion plus 100 pieces of debris as well as it does.  I had to add a loop doing a cosine a few thousand times to have it not run too fast.

Check my original post for the source code/spreadsheet.

Danny Deger

[Danny Dot]

small chunk have higher cross-section to mass ratio- air drag.

Danny, why the long delays before destruct?  You'd think that anything over 0.2 sec would only happen if it was specifically programmed to give the LAS time to pull away.  Programming an 8 second delay into the avionics seems silly.

I couldn't follow what precise scenarios you were analysing in the second video. In the first scenario you're talking about a liquid first stage. Does this include solid strap-ons or is it all liquid? You say the debris would be small and not burning, but at the same time you are talking about SRB propellant. If it's SRB debris why would it not be burning?

Another question: why do small chunks decelerate more quickly than large ones?

I don't think there is a plan for an auto destruct at all.  If there was, it would need to be something like 2 to 3 seconds.  Even then, keep in mind the reason you are aborting is because the booster has failed.  Perhaps the failure has taken down the auto destruct system.  The 8 seconds is modeling the time it might take the range safety guy on the ground to push the button.

Danny Deger

[mmeijeri]

The Orion mass is listed as 21000 pounds force. Shouldn't that be 21000 kg? I couldn't try out what difference this makes, because I have Open Office and the API is not quite compatible with Excel. If you want I can try to make in run on OO later today.

According to this link the thrust of the LAS is a "million pounds". It looks as if the numbers in your spreadsheet might both be in metric units after all. The code is working in imperial units however.

[Danny Dot]

The Orion mass is listed as 21000 pounds force. Shouldn't that be 21000 kg? I couldn't try out what difference this makes, because I have Open Office and the API is not quite compatible with Excel. If you want I can try to make in run on OO later today.

According to this link the thrust of the LAS is a "million pounds". It looks as if the numbers in your spreadsheet might both be in metric units after all. The code is working in imperial units however.

Thanks for catching the typo.  The mass for Orion is in pounds mass.  I got the thrust from figuring out the thrust needed to get 15 Gs on a 21,000 lbm Orion with a 9,000 lbm LAS.  A million pounds will over G the crew.  I might be wrong on any of this, but I think I am close enough to know Ares I can't survive the debris from its SRB destruction. 

The model is 100% imperial units.  I worked in imperial for all of my career and I think imperial.  I would have made VBA think in degrees instead of radians if I had that option. 

And please do see if you can make it run under Open Office.  It shouldn't be too hard.  I didn't do anything too weird.

Danny Deger

[mmeijeri]

This link says Orion dry mass is 14,045kg or 30,965lb with propellant mass 9,350kg or 20,613lb. This is a bit higher than I had been using in my own spreadsheet, maybe it includes the BPC? I believe maximum Orion mass through TLI of 21,500kg is set in stone, because of the total payload mass through TLI reserved for the AVUS.

All else being the same, I think this should make the problem worse.

[yinzer]

It'd be interesting to see what the range safety delay has historically been.  It was something like 30 seconds for Challenger, but that was because no one had considered that the SRBs might continue semi-controlled flight so the RSO had no way to tell what was going on.  The Titan IV with the wiring trouble self-destructed after a booster came off, and the RSO pushed the button 4.0 seconds later.

I don't see a reason that whatever initiates the abort can't also initiate a possibly delayed SRB destruct sequence.

[yinzer]

This link says Orion dry mass is 14,045kg or 30,965lb with propellant mass 9,350kg or 20,613lb. This is a bit higher than I had been using in my own spreadsheet, maybe it includes the BPC? I believe maximum Orion mass through TLI of 21,500kg is set in stone, because of the total payload mass through TLI reserved for the AVUS.

That's including the service module.  The LAS only has to lift the command module.

[mmeijeri]

Ah, of course. In my spreadsheet I have the following numbers for Orion 606E ISS version (taken from an L2 baseball card): CM dry mass is 9766kg or 21530.34lb, which is roughly what Danny is using. False alarm.

[JIS]

Good job. I haven't time to review equations so I have to believe you. Anyway, 3Gs SRB acceleration seems bit high. 3s LAS ignition delay is too big. There will be miliseconds between LAS ignition and SRB destruction - unless the range is happy to delay SRB destruction and in this case the Ares 1 is going to flip over or steer away before the destruction.
Adjusting the values you can get LAS/Orion escaping the debris field. That's probably the result Cook was talking about.

[Stephan]

Just a sidenote, if you want to record something from your screen, you should use Camstudio :

http://camstudio.org/
(free and open source)

[Ben the Space Brit]

Okay, I have come up with a possible solution.  Rather than cross-post it across the board, just follow THIS LINK to read it over on the Ares-I LAS thread.  Being an amateur, I have no clue whatsoever if it will work.  Maybe Danny or one of the other experts could find out.

[Lab Lemming]

There are more reasons to abort than a main booster fail.

The Titan used as a demo by the Air Force aborted because the guidance failed.  That either triggered an abort, or caused the TVC to pitch the rocket at max Q, inducing structural failure.

A Challenger type failure would result in a DIRECT abort, as would multiple SSME failures.

A sudden loss of cabin pressure or other life support issue could trigger an abort.

There are instrumentation failures that could trigger an abort due to false positive failure detection (which shuttle lost an SSME like this?).

small chunk have higher cross-section to mass ratio- air drag.

Danny, why the long delays before destruct?  You'd think that anything over 0.2 sec would only happen if it was specifically programmed to give the LAS time to pull away.  Programming an 8 second delay into the avionics seems silly.

I couldn't follow what precise scenarios you were analysing in the second video. In the first scenario you're talking about a liquid first stage. Does this include solid strap-ons or is it all liquid? You say the debris would be small and not burning, but at the same time you are talking about SRB propellant. If it's SRB debris why would it not be burning?

Another question: why do small chunks decelerate more quickly than large ones?

I don't think there is a plan for an auto destruct at all.  If there was, it would need to be something like 2 to 3 seconds.  Even then, keep in mind the reason you are aborting is because the booster has failed.  Perhaps the failure has taken down the auto destruct system.  The 8 seconds is modeling the time it might take the range safety guy on the ground to push the button.

Danny Deger