In reality, I think the higher max-Q numbers are due to the fact that the SRM cannot be throttled back while the vehicle is moving through the regime with the greatest aerodynamic loading. Currently the SSMEs provide this capability for the Space Shuttle. Hence the “go with throttle up” command heard on every shuttle launch.

I can think of a plausible reason a higher max-q may be acceptable for an SRM based rocket, which is simply that they have a more rigid construction than the large fuel tanks that make up the early stages on smaller rockets.

Much of the max-q is applied to the nose end of the rocket, whereas there is a large amount of thrust coming from the tail end. The result is that the tank walls have to bear very large loads during the ascent in order to stop the rocket from buckling in the middle.

In a flying-fuel tank design, the tanks are pressurised to provide rigidity, but there are limits on how much you can do this before you have to make the walls thicker to bear the weight. In an SRM-based booster, the walls have to be much thicker in order to contain the combustion pressure. On the other hand, the SRM motor is longer and thinner, and so may resist buckling less well. The bottom line is that you have to do the sums to work out when each design would be likely to fail.

Why not write to them and see if you get a response? Or perhaps I’ve been in academia for too long.

I guess I really don’t see that as being a legitimate interpretation of what they were saying. I really think it’s pretty clear that they were saying that the Stick was given a higher max-q limit than the other vehicles. Any other answer is kind of silly.

Having said this, let me add that firing engineers who dare to dissent with those management decisions is no way of leadership I sympathize with.

That we can agree on.

~Jon

You wrote: “Um…are you saying that you think they meant that GR&A to mean they would start with those max-q numbers as a guess for their analyses? That’s not how I read it at all. Remember, these are *Ground Rules* and assumptions.”

You read them as “Ground Rules”, but to me it would make some sense to interpret them as “Assumptions” for analysis instead, like Dart says.

I see no reason to rule out the possibility that Griffin and his team did this analysis with best intentions. I agree with those who say that the resulting Ares program is not very much of a vision. But since after Apollo all visionary programs of NASA didn’t go far, so a traditional and down-to-earth approach might have been a sensible management decision. Other political aspects sure did influence the decisions. Us engineers don’t like it, but it’s the way a bureaucracy like NASA works (and has to work to keep itself alive).

Having said this, let me add that firing engineers who dare to dissent with those management decisions is no way of leadership I sympathize with.

OK–let’s assume they made mistakes–after the study why did not NASA publish them? We all know why? They knew what a bad and hacket job they did on the EELV’s.

let’s move to COTS!! Guess what COTS vircheals that were not selected?? Any company that descided to use an EELV.

Many of the other things you point out are pretty discouraging, particluarly managers who use only what they want to hear. But I think the analytical team did their best with what they had available.

I don’t think so. Higher max-q doesn’t actually give you any benefits as far as I understand. It drives up structural mass, decreases safety, makes the GN&C harder, and in general doesn’t help. But why do you ask? How would the question of “whether or not other stages would benefit from the exception” make the way they did that exception any less dishonest looking?

Or could it be that these max-q number are meant to be assumptions instead of rules or limits?

Seriously, do you think for half a second that if the EELVs failed one of the GR&As that they wouldn’t have been tossed out in a heartbeat? Do you think that they would’ve been given a special exception, or that they would have been treated as mere guidelines?

If this is so, it seems only fair to assume higher max-q for those concepts that have only SRM as first stage.

Um…are you saying that you think they meant that GR&A to mean they would start with those max-q numbers as a guess for their analyses? That’s not how I read it at all. Remember, these are *Ground Rules* and assumptions. It’s pretty clear that this was meant as a number that vehicles were not supposed to be allowed to exceed (much like the 4G ascent limit), not that the analysis should assume those max-q numbers.

And as a consequence the mass penalties you were talking about should then have been included in the LVA analysis automatically.

If you look at the data shown for the various launch vehicles, it pretty clearly shows that they all used the same LES/LAS mass, regardless of what the max-q for that booster is.

Am I understanding your questions/statements right? You phrased things in a way that didn’t make a lot of sense to me.

~Jon

~Jon

Page 26 explains: “Based upon [...] Ground Rules and Assumptions (GR&A) established, a preliminary concept is sized using the Mass Estimating Relationships (MERs) in the INTegrated ROcket Sizing Program (INTROS). An initial trajectory is flown of this vehicle in the Program to Optimize Simulated Trajectories (POST) [...] and then the initial vehicle weights and trajectory outputs are sent for more detailed structural sizing with Launch Vehicle Analysis (LVA). Loads, forces, material properties, and design techniques are all considered within the LVA analysis[...]”

If this is so, it seems only fair to assume higher max-q for those concepts that have only SRM as first stage. And as a consequence the mass penalties you were talking about should then have been included in the LVA analysis automatically.