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Question: why does Delta stagger SRB ignition?

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Morgoth

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Nov 13, 1996, 3:00:00 AM11/13/96
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For all you hard core model rocket and space fans..

On 11 Nov 1996, Andy Haber wrote:

> Date: 11 Nov 1996 15:21:57 GMT
> From: Andy Haber <an...@hcxio.hdw.csd.harris.com>
> To: sci-spa...@uunet.uu.net
> Newsgroups: sci.space.tech
> Subject: Re: Question: why does Delta stagger SRB ignition?
>
> In article <55t7ni$s...@phoenix.michsb.trw.com> d_pi...@vssi.trw.com (Dean C. Pilato) writes:
> >The Delta launch vehicle staggers the ignition of it's 9 solid rocket
> >boosters. Initially the Delta did not do this. Why now?
>
> It gives slightly better performance. The down side is that it makes
> operation slightly more complex. I once simulated a large model rocket
> that used a cluster of 7 solid rocket motors. If I lit all seven motors
> at launch, the simulator predicted 9000 feet of altitude and a maximum
> speed of about Mach 1.4 If I lit two motors, then slightly after burnout,
> two more motors, then again after burnout, two more motors, then after
> burnout, the seventh motor, the simulater predicted 17,000 feet of
> altitude. Clearly better performance from the same set of motors.
> McDonnel Douglas has now figured out this trick as well, and added the
> hardware needed to do it. Why didn't they do it before? It's more
> complex, and therefore entails some risk. They did have a strap-on
> fail to seperate one time and that made for a significant performance
> shortfall.
>
> >Also, why are some of the engine nozzles larger than others, as shown
> >in KSC net feeds?
>
> The strap-ons that are air started have nozzels that are optimized for
> operation higher in the atmosphere, which makes them a different size
> from the strap-ons that light at sea level.
> --
> Andy Haber (an...@mail.hcsc.com)
> Concurrent Computer Corporation, Ft Lauderdale, FL
>
>


From wie...@afit.af.mil Wed Nov 13 02:46:35 1996
Date: Tue, 12 Nov 1996 16:28:57 GMT
From: William Wiesel <wie...@afit.af.mil>
Newsgroups: sci.space.tech
Subject: Re: Question: why does Delta stagger SRB ignition?

In article <55t7ni$s...@phoenix.michsb.trw.com> d_pi...@vssi.trw.com (Dean C. Pilato) writes:
>From: d_pi...@vssi.trw.com (Dean C. Pilato)
>Subject: Question: why does Delta stagger SRB ignition?
>Date: 7 Nov 1996 17:53:54 GMT

>The Delta launch vehicle staggers the ignition of it's 9 solid rocket
>boosters. Initially the Delta did not do this. Why now?

The strapon solids tend to grow with time. You can simultaneously ignite
lots of Estes rocket strapons without exceeding the structural limits of the
booster. But with really big strapons you might want to burn some leaving the
pad, and some later in the trajectory.....

>Also, why are some of the engine nozzles larger than others, as shown
>in KSC net feeds?

Bigger nozzles (on the same solid engine) generally indicate that the
motor has been optimized for use in a near vacuum. Long nozzles extract more
of the energy of the exhaust gas in a near vacuum, but at sea level can lead
to separation of the exhaust from the engine bell, rough running, and possible
structural failure of the engine. So the strapons with the short engine bells
are for leaving the pad, while the ones with the long bells are for use at
high altitude.

These are my own personal opinions, and do not necessarily
represent those of the Air Force, Department of Defense, or U.S.
Government.

William E. Wiesel ph: 513-255-6565 ex 4312
Professor of Astronautical Engineering net: wie...@afit.af.mil
Department of Aeronautics & Astronautics fax: 513-476-7621
Air Force Institute of Technology
Wright-Patterson AFB, OH 45433-7765

SPC Mike Adams, AK ARNG
Fr. Morgoth, Cyberabbey of St. Cyril
LtCmdr Morgoth Gusiq, Chief Medical Officer USS Taliesin

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