Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!uwm.edu!uakari.primate.wisc.edu!ames!uhccux!goldader
From: goldader@uhccux.uhcc.hawaii.edu (Jeff Goldader)
Newsgroups: sci.space.shuttle
Subject: Re: SRB solutions
Keywords: Questions
Message-ID: <5149@uhccux.uhcc.hawaii.edu>
Date: 17 Oct 89 19:13:44 GMT
References: <5474@umd5.umd.edu>
Reply-To: goldader@uhccux.UUCP (Jeff Goldader)
Distribution: usa
Organization: University of Hawaii
Lines: 121

In article <5474@umd5.umd.edu> rossh@umd5.umd.edu (Hollis "NeXT-Dood" Ross) writes:
>What was the results of the Rogers Commision, ie what did 
>NASA change.  I seem to recall that just another O-Ring was 
>added. 

Well, it was more than that.  The SRBs are made in segments, as you know;
some of these segments are connected at the factory; in a fit of fancy,
they were named "factory joints;" some are put together in the field (i.e.
at KSC); they are called "field joints."  The old design used a "tang and
clevis" design, which was basically like this:

                 |
                 |
                 |	Upper segment
  Segment A      |
                 ^
	  	/ \
	       |   |
  Tang  --->   | | |
	       |o| |
	       |o| |
     Clevis ---> |
   Segment B	 |	Lower segment
		 |
		 |
		 |


where the two O-rings were on the inner side of the tang, shown here as two
small "o"s.  For various reasons, although the design was supposed to ensure
that at least one of the two O-rings always seated properly in its gap,
the design failed.  For Challenger, they failed to seat because they were
so cold that they had lost sufficient resiliency (springiness) that they
didn't deform correctly to fit the gap in the few milliseconds they had
to do so (before the pressure of combustion deformed the booster to such
an extent that proper seating was impossible).

The new design helps fix this.  It's called a "double tang" design:

                 |
                 |
                 |	Upper segment
                 |
                 ^
	  	/ \
	       |   |
  Tang  --->   | | | |
	       |o|o| |
	       |o| | |
		 |   | <--- Tang
		 |   |
		  \ /	Lower segment
		   v
		   |
		   |
		   |


The "double tang" design helps the new third O-ring seat, even of the inner two
fail to properly seat.  It's supposed to be tolerant ofinstallation error
and such.  The basic idea is that if the pressure is so great that the
joint is deformed to such an extent that the inner O-rings cannot seat, it will
be great enough to *force* the outer O-ring to seat.

I haven't heard of any O-ring problems since the resumption of flights;
such things were very common with the old design (it was called "blow-by,"
at term which meant that the O-rings had not seated correctly, and hot gas
was blowing by the rings)

>Someone mentioned (in this newsgroup) that he thought that 
>a segmented SRB is a very bad idea.  Is a non-segmented 
>SRB actually feasible without costing 1/2 of the current 
>defense budget? How much more expensive would it be to make 
>a Double wall SRB and would that be too heavy?.  

Well, you don't need a double wall.  What you need is the ability to cast
the solid fuel in a long motor.  The reason they were segmented in the
first place was that the technology didn't exist at the time to make
a consistent grain the size of an SRB (the fuel is poured in as a very
viscous fluid, and allowed to harden in the motor).

I remember Aerojet (or was it Hercules?) saying that they had the know-how
to cast the fuel into something the size of an SRB, but NASA didn't listen.
They are using another segmented design for the Advanced SRM, rather than
a single-section or (better yet) a liquid-fueled booster.

Of course, the idea of a non-segmented booster is that you can't have
Challenger-type joint failures....

As to expense, NASA is spending $$$ for the Advanced Solid Rocket Motor,
and I don't see how the no-joint version could cost much more.  I'd rather
spend the money making a safe booster than replacing the next lost shuttle.

>
>An off the wall question:  If enough fuel were available, 
>would it be possible for the shuttle to make a journey to 
>lunar orbit.  How long can the shuttle stay up, what are 
>the constraints for power, air, ect. 
>
Well, no.  I mean, *if* you had an infinitely large fuel tank, you could,
but the shuttle carries just about as much fuel as possible. 
No one has any good and reasonable ideas about how to get fuel into
orbit, and the shuttle engines are not restartable.

Currently, the limit for on-orbit time is about 10 days, with a few days
just in case.  I heard rumblings about modifying Columbia to have
solar panels or a tank of LH2/LOX in the cargo bay so it would have
power to saty in orbit for ~2-4 weeks, but I think NASA will kill
that idea (it would conflict with Freedom; can't replace the $40G
space station with a $300M retrofit to a 10-year-old shuttle, now,
can we?  :-(   )

Jeff Goldader                        University of Hawaii
uhifa.ifa.hawaii.edu                 Institute for Astronomy

"So, Lonestar, now you see that Evil will always win- because Good is stupid."
-The Dark Lord Dark Helmet, _SPACEBALLS_ 

Disclaimer: The opinions expressed herein are my responsibility alone.  
The University of Hawaii and the Institute for Astronomy neither support 
nor are in *any way* responsible for these opinions.