Conference 7.286::space

    On the news this morning it was stated that the test was successful
    and that the good results puts the schedual in a better light. 
    This tells me that the results from the test were needed and that
    it wasn't a wasted test on old hardware.
    
    jim
    

    It was a horizontal test FWIW.  Are vertical

    I gotta get more caffeine in me :-|  The end of the last reply is...
    
    Aren't vertical tests planned/called for?
    
    						Mike

    No.  It would "cost too much" to build a vertical test stand, and
    anyway, Morton Thiokol says they can get all the information they
    need from a horizontal firing.
    
    (Although I guess the vertical test planned for occurs sometime
    in June of 1988 when the first shuttle launch is planned.)
    

    	Oh, I'd really trust a statement from Morton Thioklol on SRBs!
                                   
    	(Note - the sarcasm is to MT, not you)
    
    	Larry
    

    RE: -.1
    
    Agreed.  It's getting so I don't trust anyone anymore when money
    is involved.  Some people would sell thier mother to increase corporate
    profits or make the corporation look good.  In my book MT falls
    in this category.
    
    Rich

    Shortly after the accident, it was determined that a Vertical test
    would be required before the next shuttle flight.  I have not heard
    that this has been cancelled.  All agree that it would be very
    expensive and the Rogers commision said test it anyway.
    
    jim
    

    My recollection is that NASA decided not to go with the vertical
    test.  If they had gone with it, they would not be scheduling the
    shuttle launch for as soon as a year from now.
    
    Burns
    

    I think .8 is correct. Oddly enough, the Titan boosters are test
    fired vertically, using an old F-1 test stand. Since the Titan-4
    boosters, at 10 by 122 feet, are not much smaller than the SRBs
    at 12 by 146 feet I wonder why there is so much reluctance to test
    the SRBs vertically. The F-1 stand was fairly recently modified
    to test the Titan boosters.
    
    gary

    re .9:  Just out of curiosity, why is an F-1 test stand so big?
    Did they have the whole Saturn sitting out there on top of them
    for tankage?
    
    Burns
    

    re .10
    
    Don't know. I assume they had one lying around that did not belong
    to a contractor (in which case it would have been destroyed in
    accordance with their contracts) and since it could withstand at
    least 1.5 million pound-weight of thrust it could cope with the
    Titan solids. I think it is at Ames.
    
    gary

        What is the validity of a single SRB test anyway? 49 of the last
        50 worked. A single test, at non-freezing temperature doesn't tell
        NASA anything that wasn't previously known. If they want to prove
        that the joint has been fixed, it will take repetitive tests, and
        tests at the 'edge of the operating envelope', i.e. below
        freezing. The only other practical way to test the SRBs is to use
        them on non-manned non-critical payloads. 

    re .12
    
    Not only was the test not in a cold environment, it had joint heaters
    in place and operating on of the field joints, graphite overwraps
    on two of the field joints and changes to the exhaust nozzle inlet
    ring to reduce corrosion. The purpose of the firing was to gather
    baseline data on the old SRB design. I can't help but wonder that
    they made too many 'minor changes' to invalidate that.
    
    On thinking further about vertical vs horizontal testing, I think
    it is probably not important. The stresses on the motor case would
    not vary greatly in either position, i.e. the gravity components
    would be fairly small compared to stresses produced by the motor
    firing.
    
    It would be far more interesting to simulate the flexing that occurs
    between main engine start and SRB start and immediately after SRB
    start.
    
    gary

    further re .12
    
    Can the shuttle fly unmanned??
    
    gary

    re .14
    
    NO, it cant't. Not without very extensive changes...

    re.14
    that is an interesting idea, the shuttle can not fly unmannded
    but the MLV or what every you want to call it could.  I think
    at one time I actually saw a drawing of an unmaned version.
    
    It still would require a lot of tooling, testing etc, but it
    could possible give us an unmanned MLV in a few years instead
    of 7 to 10.  Given the right codition of temperature, rain and
    lighting storms the MLV would be a very relable unit, the
    shuttle has had a very good record for successful launches
    and the unmaned version could fill the space gap untill a true
    HLV.  Not every lauch of the Shuttle needs to be manned, when
    you are simple sending put building supplies for a space station
    
    as for the test, I though it was strage that they tested all
    the heaters etc in a warm temp, but I am sure they did not have
    a enviromental chamber big enought.  Did they do any thermal
    stressing of the joint before launch, ie spray them with
    'cold spray' or did they freeze the boster before testing
    I dont think so , at least it was not mention, but someting
    like that would sure give me a better feeling about the
    safty of the unit.
    
    john
    
    

    Well, they could just run the test ou{doors in a Utah winter. Thats
    cold enough for most people.
    
    The shuttle, manned or unmanned, is above what I would consider
    a medium launch vehicle (MLV) in launch capability. Various shuttle
    derived vehicles have been proposed for the new Advanced Launch
    System (aka Heavy Launch Vehicle).
    
    If it is true that the shuttle absolutely requires a human in the
    control loop that means it would be impossible to bring it down
    after say a fatal depressurisation. I find this a little hard to
    beleive, but not impossible given the event of the last year and
    a half.
    
    I'm not suggesting that launching an unmanned shuttle would be useful
    any kind of production launch (Titan 4/Centaur G-Prime can fly almost
    anything a shuttle can) although it could be a viable test. If I were
    an astronaut, I'd feel a lot better if I knew it had worked once
    before.
    
    gary 

    Sence I happen to work in the field of reliability testing, (Though
    skewed toward electronic and statistical rather than mechanical or
    one shot probabilities.) I have a real problem with this sort of
    testing in the first place.  I happen to feel there was a combined
    effect present that this test totally ignores, as well as the obvious
    "tinkered" configuration (horizontal, hardware changes, temp at
    the joints, load suspention.)  I have un resolved questions in my
    mind concerning SRB mounting at the incident temp and the flex of
    the propellent and configuration.  Unless I am wrong, the SRB is
    mounted via just 2 connect rings.  This leaves a verrry long 
    un supported section of two motor segments (3 joints total I believe)
    to be independent of vehicle dynamics.  If at warm temps the solid
    fuel compound is very much more elastic than at cold, pressure in
    the vessel is uniformly distributed adding support to the structure.
    In the shuttle failure event, we see two observations of joint 
    venting one at launch for a few sec, and again just before the 
    final collapse of the structure.  Remember the fuel is the primary
    reason the SRB does not normally blow up.  It acts as insulation
    to keep combustion temps from heating the case and as a structural
    member by transmutation of internal pressure to the case.  (Ie:
    Take a full unopened coke in a can and stand on it. Try to dent
    the side.  You cannot unless you rupture the can.  The liquid
    distributes the dynamic load.  Take an empty undented coke can.
     The average person can stand on one! top to bottom.  However if
    the side is dented, the thing collapses.)
    
    I feel the dynamics of the fuel in pressure distribution have been
    ignored.  Once again the symptom is being treated because that was
    the most visable (if not spectacular in a depressing sense :-().
    The "basic" question I ask is why did the fuel fail in its mission
    in a two fold manner, that is in both pressure distribution *and*
    thermal insulation.  Sorry, but a slightly leaky joint does not
    fit the following model.  Ignition smoke from joint (fuel failure
    to transmit heat and pressure from case) "fixes itself" thru dynamics
    to MAX Q.  After MAX Q, dynamics change fissure reappears - venting,
    death.  Fuel fails mission again.  This model fits the observed
    facts.  A hole in a pressure vessel such as the SRB is always a
    hole unless fuel or residue can perform a sort of dam.  If the internal
    dynamics for this dam remain constant, great.  But since the
    foundations of the dam are constantly being eroded, how can they
    remain constant.  Changes around the dam such as joint flex, after
    MAX Q would certainly hasten this demise.  The SRB had better than
    30% of its "life" left at failure and therefore should have had
    an equal amount to heat and pressure capability left, it had just
    been throttled up bringing pressure to a max and again change the
    dynamics to the dam.
    
    The test in question is actually a mote point.  The "FIX VERIFY" test
    is one such has been suggested:  launch, or static firing at cold temps
    with the capability of flexing the joints via the two SRB suspention
    points.  Otherwise I feel we not only will have pasted another
    bandaid to our national space banner, but we risk a future shuttle
    launch to the "empty coke can symptom". 
    
    	{Insert NO BANDAID sysmbol here}
    
    Les
    
    PS:  You can remove one or more spokes from a wheel and still have
    a wheel.  The squeaky one still gets the grease whether the wheel
    needs spokes or not.

    re .18:  The fuel is not designed to be part of what keeps a joint
    from leaking.  I don't know about whether it is intended to be
    structural, but I doubt it.
    
    My reason for saying this is that the fuel in some segments is
    designed to burn simultaneously from the center out and from the
    bottom up.  This means that the joint at the bottom of these segments
    is exposed directly to the full combustion pressure almost immediately.
    
    They do this by not coating the fuel with inhibitor at the bottom of
    the segment which they wish to burn this way. Thus, the flame invades
    the joint between fuel segments and starts burning up the uninhibited
    section, but not down the inhibited segment. This is part of how they
    make the thrust profile change.  I would guess that when the thrust
    reduces at MAX Q, this is because one of those segments (which has been
    burning on two fronts) has burned out. 
    
    Burns 

    re .18
    
    I may have missed something as I found it very hard to follow your
    points, but I won't let that stop me making some comments :-)
    
    The SRB does have only two attach points, one of which has been
    redesigned. The new attach ring was on ETM-1A (the motor just fired)
    but you can bet that the SRB is well strapped down during a static
    test and they probably do not use the flight attach points. SRBs
    exhibit a 'twanging' phenomenon during flight where they oscillate
    presumably as a result of ignition stresses (the twanging decreases
    with time).
    
    As for the propellant protecting the casing, that is true for simple
    single segment core burning engines but may not be true for the
    SRBs. There are segmented propellant configurations that rely upon
    the ends of the segments burning as well as the core. In that event
    you must design the casing to not rely upon temperature insulation
    from the propellant. The propellant provides little if any structural
    strength. If you consider a single segment progressive core engine
    (or even a neutral burning 'star' core) the time of maximum combustion
    pressure will be at burnout when the propellant is no longer one
    piece. So, the combustion chamber alone must be able to withstand
    the maximum chamber pressure.
    
    If we look at thermal protection, even if the propellant segment ends
    are inhibited from burning some of the hot gas in the chamber will leak
    through the interface between the segments. The combustion chamber at
    that point must be able to withstand the full flame temperature. In the
    SRB this means the joint area. The combustion pressure in the SRB will
    be high enough to force the segments together so that the amount of hot
    gas reaching the chamber wall will be very small, under most (but not
    all) circumstances. If the SRB flexes or twangs, obviously the segments
    could seperate briefly at various places. The propellant is case bonded
    and would be much more effective at thermal insulation away from the
    segment interfaces. 
    
    Polybutadiene propellants do not go brittle at the temperatures
    encountered, even with high solids loading used in these propellants.
    The segments may shrink however, which would increase the gap between
    segments slightly.
    
    I don't think the propellant failed in any way.
    
    My guess is that the joint area was never adequate but had been
    relatively protected by the propellant in previous flights and the
    degree of that protection was not understood. The combination of
    factors for the Challenger launch were such that the segment joints
    finally had to perform the job they were designed for and were not
    up to the task. In my opinion the major technical factors were low
    temperature causing joint components to malfunction, the same low
    temps could have caused some propellant shrink thus increasing the
    stress on the joints and the higher than usual wind shear leading
    to even more stress on the joints.
    
    There have been a few 'near misses' with the SRBs in the past but
    NASA managed to keep quiet about those.
    
    gary

    re .19
    
    Thanks, I didn't know if the SRB burned any segment ends, but the
    thrust-time curve sure looks like it. Grain geometries where a core
    and one or more segment ends burn are sometimes called bates cores.
    
    Also, the core shape and size varies throughout the engine. It is
    tapered cylindrical for most of the core, starting from the bottom.
    The top part is a wagon wheel design (almost a star). The top segment
    looks like it would burnout before the rest of the engine thus exposing
    that segment to exhaust gasses earlier in the burn.
    
    gary

    Just reread note 142 and some others as well as Gary's discussion
    in 292.20.  I did not get the impression that the joints were directly
    exposed to the actual flame of combustion until now.  I was under
    the impression that the stacking process had some how baffelled
    the actual joint area between each segment with inert material (putty
    In the AP articles).  The point I poorly made I guess is that the
    observable data of the disaster does not really fit the fix.  If
    I poke a hole in my pressureized "coke can" I must do something
    to stop the coke from spuing out, or I will keep seeing the stuff
    come out.  Certainly 5500 degree (AP again) flame within the SRB
    visable at launch would not just dissappear for more than a minute
    and then reappear just prior to breakup.  I am glad to see that
    someone agrees with me that laying one of these things on its side
    and clamping it down to keep it from getting away just does not
    fit the failure nor does it fit the mode of operation (twang).
    
    I do apologize to everone for the hasty writting of .18 but I could
    not contain my silence on the SRB reliability and wanted to vent
    some smoke concerning the whole SRB.  I am guilty of haste.  I am
    not guilty of silently sitting back.  If I had been asked if I would
    have maintained the grounding of the shuttle this long based on
    the currently public data, I would have to say no.  I would have
    resumed launches of military payloads long ago with existing hardware
    at anytime the launch site temp was 5 degrees warmer than that of
    the coolest successful launch.  Does the current research into the
    joint redesign fix the problem? no.  I am in 100% agreement with
    Gary.  Some little understood effect, present at more than the launch
    of 51L caused the disaster.  Strapping a SRB to the ground does
    my uninformed opinion prove nothing.  Causeing a joint to fail at
    will with a SRB strapped down or having a successful trial under
    the suspected conditions with fixes installed.  I would prefer
    replacation in this case as only 50% of the SRB's under the 
    suspected conditions failed and less than 1% have failed for all
    causes.  Given these type of stats, Making something fail on command
    should prove you knew what was wrong, had it in control, and then
    could prove the fix addressed the true cause via non distructive
    means.