DIRECT v3.0 - Thread 2

[kraisee]

Starting a new thread here now, to help ensure that the server doesn't get too overloaded

Please continue discussions here.

Ross.

[spacecase]

Ross,

Why are you setting your thrust offset on your LAS simulation towards the horizontal. You get much better results if you thrust *up* to get above the falling debris field. Try it with a -10 degree offset instead of a +10 degree offset.

[kraisee]

Okay, I just posted the "Brute Force" solution to the LAS problem for Jupiter over on the other thread (http://forum.nasaspaceflight.com/index.php?topic=17295.msg451503#msg451503), and to go along with that I've also drawn up a 'quick n dirty' image of the new arrangement based on a chat with one of our team.

The outer-mold-line changes anyway compared to Ares, due to the tapering of the Ogive into the conical section of the PLF, so this doesn't actually affect the need to do the aerodynamic analysis afresh anyway.

But this unit would be more than twice as powerful as the current LAS and is more than capable enough of getting the Orion CM away from any SRB debris.

Ross.

[cgrunska]

these Direct threads are reaching 250 pages pretty fast now days...

[kraisee]

Ross,

Why are you setting your thrust offset on your LAS simulation towards the horizontal. You get much better results if you thrust *up* to get above the falling debris field. Try it with a -10 degree offset instead of a +10 degree offset.

I thought that was a fix too, but it isn't

Unfortunately you only get good results that way if you assume that the SRB's continue to thrust in the normal direction of travel, heading further down-range and heading away from the Orion's abort trajectory.

But what happens if the accident is occurring because the SRB has had a problem and it is now flying in a different direction (like in the case of a hard-over TVC fault for example).   An SRB could easily be thrusting into a completely different direction at the time of the destruct -- and it might now be heading towards the new Orion abort trajectory!   You have got to account for such problems if you want to be sure you'll get the crew back every time.

Try re-running the spreadsheet with a value like "135" in the box for "Angle Thrust of Booster" and you'll see the problem for yourself.


Another recommendation:   Always use the worst case values:   4g for SRB accel before destruct, 3s destruct time and 3.0ft for max debris size.   Also assume a heavier 20,500lb Lunar CM, not an ISS one.   And don't forget the corrected 8.2ft diameter for the Orion too!   Simple rule:   If it's designed to survive the worst case, it can survive the rest.

Ross.

[robertross]

these Direct threads are reaching 250 pages pretty fast now days...

Tell me about it!

It also means we sometimes hash things out over again...oh well.

So Ross, you and the team/bunch have fun yesterday???

I heard from one they thought your head could have exploded it was so great! 

I really wish I could attend one of these sessions. I'd love to stand up and make one heck of a presentation!

I'm glad you made it there. Sometimes I wonder how you make a living, with you involved in this as much as you are.

[kraisee]

Robert,
Some of the things the committee members said were pretty stunning IMHO.

The fact that they are seriously looking at alternative architectures in detail, that they're looking at architectures which are focused on Mars, but which can be tested at the Moon first, that they are seriously examining Propellant Depot's (!) and clearly understand just how radically they change the entire dynamic of space missions and the fact that Jeff Greason is coming around to the need for something a bit larger than the EELV-class of vehicles all put my jaw firmly on the floor.

Its all stuff we've been saying for three years in some fashion or another, yet they seem to have managed to come to these conclusions for themselves, having pursued their own paths to gain the understanding about how these can be implemented -- and I think that's a really great thing, because it means a separate group of experts have managed to come up with something similar, yet they've done so completely independently.

I think that's the best vindication of what we've been trying to do for the last few years.


One thing which I was somewhat concerned about, was the "Flexible Path" option.   I spoke to a couple of the committee members after the meeting was concluded and just raised the question that "while Flexible Path is probably the lowest cost option, if there are no human landings on any major bodies, how does the pure Flexible Path option intend to sustain the public and political interest in the program?".

When we talked a little about that, it was clearthat the FP option seems to be very "complimentary" to either (or better still both) of the Lunar and Mars landing architectures and would work *really* well if interleaved with them.


Another thought I hope the committee will consider is that with their Mars approach, which would attempt a "touch and go" test at the moon, there is a logical follow-up there...   If you've got one design of lander which can land at Mars, but which has already proven it can also land on the Moon -- WHY NOT USE IT FOR BOTH ??

Seems pretty logical that not only have you created your Mars architecture, but you also have a workable -- and proven -- Lunar architecture for free, no?


Generally I get a feeling that the committee is on the right path and I had a great day because of it.

The get-together in the evening was wonderful too.   A dozen of us discussing everything from rockets to cats.   It was a real pleasure to meet some 'voices' I've only ever previously talked to on the phone, to say hi to some familiar people and to meet a whole group of new people.   I think everyone had as much fun as I did and I really hope we can do it again soon.

I promised everyone that if we get any sort of Jupiter actually chosen, there's gonna be one helluva party down here!!!

Ross.

[phantomdj]

Simple rule:   If it's designed to survive the worst case, it can survive the rest.

Ross.

What is the worst case?  MaxQ? Range Safety presses destruct 10 sec, 20 sec late?

The reason I ask is this:  I test the Range Safety system on the SRB’s.  I was there during the Challenger accident and saw the video that stayed with the SRB’s until the Range Safety Officer blew the linear shape charge.  He waited at least 24 seconds until after the SRB’s were outside of the flight path.  Also, when the LSC blew there was little debris that went very far probably because most of the fuel was already burnt (about 50 seconds left) and pressure was down.

It’s just human nature that the RSO will not press the destruct button quickly and it is not automatic.  Are there thoughts of making it automatic if the escape rockets are fired?  If not, then it’s not reasonable to assume the SRB’s will be destroyed quickly after tank break-up.

[robertross]

Robert,
Some of the things the committee members said were pretty stunning IMHO.

The fact that they are seriously looking at alternative architectures in detail, seriously examining Propellant Depot's and clearly understanding how radically they change the entire dynamic of space missions and the fact that Jeff Greason is coming around to the need for something a bit larger than the EELV-class of vehicles all put my jaw firmly on the floor.

Its all stuff we've been saying for three years in some fashion or another, yet they seem to have managed to come to these conclusions for themselves, having pursued their own paths to gain the understanding about how these can be implemented -- and I think that's a really great thing, because it means a separate group of experts can come up with something similar, yet independently.

I think that's a pretty good vindication of what we've been trying to do for a while.
...
Generally I get a feeling that the committee is on the right path and I had a great day because of it.

The get-together in the evening was wonderful too.   A dozen of us discussing everything from rockets to cats.   It was a real pleasure to meet some 'voices' I've only ever previously talked to on the phone, to say hi to some familiar people and to meet a whole group of new people.   I think everyone had as much fun as I did and I really hope we can do it again soon.

I promised everyone that if we get any sort of Jupiter actually chosen, there's gonna be one helluva party down here!!!

Ross.

I'm glad you had a great time. For all the efforts you and the team went through, it must have been great to sit back and take it all in for once, as a bystander.

I know I was stunned at some of it too, just being able to follow along with the posts (for the most part) until the Q&A at the end. The whole panel is such a refreshing change for once. If we ever need to look to leadership, and people with vision & thoughtful decision making, we have our team.

Propellant Depots by far being a great bonus...it really is the way forward. The worries of raditation, the rocket classes that 'fit the bill'. Truly a better review than the one the previous day, and I don't want to even bother thinking about it (even though I will have to sit and watch it to know what was said and shown).

I still haven't even reviewed the Flexible Concept (that's for when I have time to digest it all in one reading). By the sounds of it, it's borderline, but I need to understand it first.

Thanks for sharing the outer details.

[kevin-rf]

A bit off topic here, but since blowing the nozzle on the SRB reduces the thrust reducing how fast it can chase Orion. What does blowing the nozzle do to a still thrusting SRB? As the nozzle separates does it create any temporary blockage that can spike the internal SRB pressure enough to cause a case rupture?

I am asking since it sounds like blowing the nozzle when the LAS fires gives the Orion extra margin to safely make an escape.

Of course I agree with Ross that you have to model worse case, meaning modeling with a nozzle does not blow.

[phantomdj]

What does blowing the nozzle do to a still thrusting SRB? As the nozzle separates does it create any temporary blockage that can spike the internal SRB pressure enough to cause a case rupture?

I am asking since it sounds like blowing the nozzle when the LAS fires gives the Orion extra margin to safely make an escape.

The amount of thrust decrease from nozzle jettison is insignificant compare to that of the linear shape charge splitting the SRB down the side.

[clongton]

What does blowing the nozzle do to a still thrusting SRB? As the nozzle separates does it create any temporary blockage that can spike the internal SRB pressure enough to cause a case rupture?

I am asking since it sounds like blowing the nozzle when the LAS fires gives the Orion extra margin to safely make an escape.

The amount of thrust decrease from nozzle jettison is insignificant compare to that of the linear shape charge splitting the SRB down the side.

The only way to terminate thrust prior to unzipping the cases is to blow both the nozzle *and* the nose so that the internal pressure is released, thus terminating thrust. I suppose that's possible but the timing would need to be impeccably perfect. But that does not stop the burning process, it just isn't thrusting anymore. While the RSO is understandably concerned with the survival of the crew he or she must also be aware of where the SRB is as unzipping it could also potentially drop burning debris into a populated area on the ground.

[phantomdj]

What does blowing the nozzle do to a still thrusting SRB? As the nozzle separates does it create any temporary blockage that can spike the internal SRB pressure enough to cause a case rupture?

I am asking since it sounds like blowing the nozzle when the LAS fires gives the Orion extra margin to safely make an escape.

The amount of thrust decrease from nozzle jettison is insignificant compare to that of the linear shape charge splitting the SRB down the side.

The only way to terminate thrust prior to unzipping the cases is to blow both the nozzle *and* the nose so that the internal pressure is released, thus terminating thrust. I suppose that's possible but the timing would need to be impeccably perfect. But that does not stop the burning process, it just isn't thrusting anymore. While the RSO is understandably concerned with the survival of the crew he or she must also be aware of where the SRB is as unzipping it could also potentially drop burning debris into a populated area on the ground.

This is why the SRB’s are designed the way they are.  The most efficient way to stop the SRB’s from thrusting in the direction of flight is split the case with the linear shape charge.  The thrust is then mostly sideways  from flight.

[cixelsyD]

I submitted this question earlier, but it may have gotten lost. I don't know much about risk analysis with the SRBs but doesn't one failing catastrophically cause the other to fail too? Ares has to escape 1 SRB, albeit a bigger one, and one that's closer, but Direct may have to escape 2. Is there a way to stop SRBs from interacting with each other in case of failure?

[gospacex]

A bit off topic here, but since blowing the nozzle on the SRB reduces the thrust reducing how fast it can chase Orion.

I think the most important part is that it reduces *the pressure*. When the case is unzipped milliseconds later, it will not blow up like a pressurized gas cylinder. Fragments will not fly as fast.

[Danny Dot]

A bit off topic here, but since blowing the nozzle on the SRB reduces the thrust reducing how fast it can chase Orion. What does blowing the nozzle do to a still thrusting SRB? As the nozzle separates does it create any temporary blockage that can spike the internal SRB pressure enough to cause a case rupture?

I am asking since it sounds like blowing the nozzle when the LAS fires gives the Orion extra margin to safely make an escape.

Of course I agree with Ross that you have to model worse case, meaning modeling with a nozzle does not blow.

It does look like 3 feet max size is about right.  1.5 was too small.  I have two data points.

First, 1.5 debris field radius is too small.  The 45th report said 7,900 feet radius.  3.0 gives about the right size debris field.

Second, this from the report, "many of which are several feet across and weighing hundreds or thousands of pounds -"

On blowing the nozzle.  This needs lots of work.  First the 45th may not agree to this.  They may not like the SRB to stay intact.  And blowing the nozzle might result in case fragmentation anyway.  The current method doesn't fragment the case, it opens it up with a line down the side.  Last, I worked on the AGM-130 air to ground missile that had a strap on solid.  We did a test to terminate thrust by blowing the nozzle.  In the long run thrust goes to basically zero, but there is a temporary 10 fold increase in thrust.  During the test, this thrust spike had enough impulse to rip the stapon off the bomb and it went something like 2,000 feet.  Maybe an SRB with a blown nozzle will do something like this and come after Orion in a big hurry.  Anyway, I don't think the 45th is going to like a range package that makes the SRB goes like a bat out of hell before the thrust goes down.  Consider an abort fairly close to the ground.  The thrust spike might throw the SRB to downtown Coco Beach.

On the range safety guys waiting to hit the button.  It is horrible beyond the belief if this is the concept.  I think the destruct command must be automated to occur about 3 seconds after the abort.

And on the SRB changing attitudes.  It doesn't have to be a hard over.  For many failures the stack will not be in control.  It is inherently unstable and precise commands are needed to keep it pointed straight. 

Ross, can you post some video of your solution.  When we talked you were having problems.  It did turn out the -15 angle was bad for the sustainer LAS.  Did you fix it with a change to the thrust angle?

Danny Deger

[clongton]

The only way to terminate thrust prior to unzipping the cases is to blow both the nozzle *and* the nose so that the internal pressure is released, thus terminating thrust. I suppose that's possible but the timing would need to be impeccably perfect. But that does not stop the burning process, it just isn't thrusting anymore. While the RSO is understandably concerned with the survival of the crew he or she must also be aware of where the SRB is as unzipping it could also potentially drop burning debris into a populated area on the ground.

This is why the SRB’s are designed the way they are.  The most efficient way to stop the SRB’s from thrusting in the direction of flight is split the case with the linear shape charge.  The thrust is then mostly sideways  from flight.

Danny, does your spreadsheet properly vector the SRB to thrust sideways after being zippered?

[Danny Dot]

I submitted this question earlier, but it may have gotten lost. I don't know much about risk analysis with the SRBs but doesn't one failing catastrophically cause the other to fail too? Ares has to escape 1 SRB, albeit a bigger one, and one that's closer, but Direct may have to escape 2. Is there a way to stop SRBs from interacting with each other in case of failure?

We aren't talking about SRB failures really.  If the SRB fails while Orion is still on top, all is lost.  We are talking about all aborts.  The 45th will ALWAYS blow the SRB up for an abort of any type.  And this is both of them. 

Danny Deger

[gospacex]

A bit off topic here, but since blowing the nozzle on the SRB reduces the thrust reducing how fast it can chase Orion. What does blowing the nozzle do to a still thrusting SRB? As the nozzle separates does it create any temporary blockage that can spike the internal SRB pressure enough to cause a case rupture?

I am asking since it sounds like blowing the nozzle when the LAS fires gives the Orion extra margin to safely make an escape.

Of course I agree with Ross that you have to model worse case, meaning modeling with a nozzle does not blow.

It does look like 3 feet max size is about right.  1.5 was too small.  I have two data points.

First, 1.5 debris field radius is too small.  The 45th report said 7,900 feet radius.  3.0 gives about the right size debris field.

Second, this from the report, "many of which are several feet across and weighing hundreds or thousands of pounds -"

On blowing the nozzle.  This needs lots of work.  First the 45th may not agree to this.  They may not like the SRB to stay intact.  And blowing the nozzle might result in case fragmentation anyway.  The current method doesn't fragment the case, it opens it up with a line down the side.  Last, I worked on the AGM-130 air to ground missile that had a strap on solid.  We did a test to terminate thrust by blowing the nozzle.  In the long run thrust goes to basically zero, but there is a temporary 10 fold increase in thrust.  During the test, this thrust spike had enough impulse to rip the stapon off the bomb and it went something like 2,000 feet.

How about explosively opening holes in the sides of the SRB in order to vent the pressure without imparting any impulse? Say, two symmetrical holes in each segment on the opposite sides.

[Danny Dot]

The only way to terminate thrust prior to unzipping the cases is to blow both the nozzle *and* the nose so that the internal pressure is released, thus terminating thrust. I suppose that's possible but the timing would need to be impeccably perfect. But that does not stop the burning process, it just isn't thrusting anymore. While the RSO is understandably concerned with the survival of the crew he or she must also be aware of where the SRB is as unzipping it could also potentially drop burning debris into a populated area on the ground.

This is why the SRB’s are designed the way they are.  The most efficient way to stop the SRB’s from thrusting in the direction of flight is split the case with the linear shape charge.  The thrust is then mostly sideways  from flight.

Danny, does your spreadsheet properly vector the SRB to thrust sideways after being zippered?

The post zippered SRB is modeled on the 45th report that shows the SRB turning into many large chunks going in every direction.

Danny Deger