Re: Griffin Wants Inline SDLV and 5 Segment SRB/CEV

"Jorge R. Frank" <jrfrank@xxxxxxxxxxx> wrote in
news:Xns96899A96FA1AEjrfrank@xxxxxxxxxxxxxx:

> Reed Snellenberger <rsnellenberger@xxxxxxxxxxxxxxxxxxxxx> wrote in
> news:Xns96888704E26E7rsnellenbergerhousto@xxxxxxxxxxxx:
>
>> "Jorge R. Frank" <jrfrank@xxxxxxxxxxx> wrote in
>> news:Xns9687F1A3768B0jrfrank@xxxxxxxxxxxxxx:
>>
>>>
>>> However, that does not change Kim's basic point: without roll
>>> control, there is no way in hell that The Stick will be ready for
>>> qualification flights by late 2006. And honestly, I'd be pleasantly
>>> surprised if ATK was ready to demonstrate SRB roll control *in
>>> ground test*, let alone flight test, by the end of *2008*.
>>>
>>
>> Why do we care if the initial (test) flights of the booster roll? Is
>> there some booster hardware that cares (APUs, maybe)?
>
> Even a small roll acceleration (caused by propellant grain asymmetry,
> for example) can build up into an impressive roll rate in a few
> seconds if it is not actively controlled. The hardware that "cares"
> are the gyros in the control system and the gimbals on the pitch/yaw
> actuators. Once the roll rate exceeds the ability of either of these
> systems to handle, the vehicle will lose control completely, and will
> have to be range-safety destructed.
>

Got that from Pat's post ("what if the rocket rotates 180 degrees & heads
inland?"). right.


>> Otherwise, it's
>> a non-event, and early flights give us an excuse to accelerate
>> development of the pad infrastructure, etc.
>
> It won't accelerate anything, since it's not helping either of the
> "critical-path" development items (the upper stage and the control
> system). It will be a stunt, nothing more, and if it ends in a
> low-altitude range- safety destruct it could well do the program more
> harm than good.
>

Hardly a stunt -- given the need to develop a guidance system & roll
control motors, a few launches of the booster with just those systems
(and a dummy mass for the upper stage and CEV) would be useful to
qualifying them for manned flight. It would also be useful in
demonstrating and highlighting the transition from shuttle.

And if it results in a range-safety destruct, then you've learned
something that it was better to know without blowing up a perfectly good
upper stage and CEV. Call them "developmental/test launches" and
instrument the booster heavily so that there's little guess-work about
any problems -- then plan to launch the next one quickly with lessons
learned. Repeat as necessary...

>> Incremental development is what we should be working towards -- start
>> launching sticks as soon as you can get the pad ready, add the 2nd
>> stage when it's ready, and then you'll be ready for the CEV.
>
> The shuttle SRBs aren't suitable for incremental development. If
> incremental development is a priority for you, you should oppose an
> SRB- based stick.
>

Sorry -- I was talking about incremental development of the overall
system, not just the booster. Development of the upper stage and CEV are
obviously going to be the long-lead items, but a flight test program of
the SRM-based booster itself (including the roll-control motors &
guidance software) will need to be done as well, and I can't see why it
wouldn't be worthwhile to bring the booster online & testing (with a
dummy payload) as part of the kind of accelerated development program
that Griffin is proposing.

>> Is there any data (optically-derived, obviously) on the roll
>> characteristics of the Challenger boosters, post-breakup? I know
>> they flew solo for several seconds before range safety blew their
>> charges.
>
> Generalizing SRB performance from two data points is not smart. I
> think the 3-sigma roll torque characteristics of the SRBs over *all*
> their flights are more indicative of what the Stick roll control
> system should be designed to.
>

I didn't realize they gathered roll torque data for the SRBs as part of
the shuttle stack. An obviously good source for getting a statistical
handle on the thrust asymmetries you might get from motor, and (as you
suggest) how much control authority will be required.


--
I was punching a text message into my | Reed Snellenberger
phone yesterday and thought, "they need | GPG KeyID: 5A978843
to make a phone that you can just talk | rsnellenberger
into." Major Thomb | -at-houston.rr.com

.

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