james@bigtex.uucp (James Van Artsdalen) (05/10/88)
IN article <48048@ti-csl.CSNET>, kas@hp-pcd.hp.com (Ken Scofield) wrote: > Why > not just jettison the entire shuttle craft from the tank/booster assembly? > [...] Two arguments I've heard against > this are: The shuttle would break up due to aerodynamic forces, and/or it > would be burned up in the departing booster's firetail. Neither of these set > well with me, because (a) the shuttle is designed to re-enter the atmosphere > in excess of Mach 25, and (b) do so with skin temperatures of several thousand > degrees. So, what's the big problem? You may post this one, too, if desired. Shuttle is designed to re-enter at certain angles, with stress & temperature in certain places. Will not take large aerodynamic forces in wrong places, and will NOT take heat in wrong places. Heat shielding is by no means uniform even along the front/bottom of orbiter. Seems unlikely that (1) "aerodynamic" pressure within SRB exhaust is same as re-entry aerodynamic pressure (momentum of SRB is likely much greater than that of gases striking orbiter on re-entry) and (2) that shuttle could safely maintain exact attitude in that exhaust. If orbiter rotated or translated just a little bit, surfaces exposed to exhaust would change. Lastly, I'm not sure what if any provisions exist for steering SRB and external tank away from orbiter after separation. Center of mass moves significantly, so SRB/tank may want to change course. I don't believe SRB nozzles can be gimbled. -- James R. Van Artsdalen ...!ut-sally!utastro!bigtex!james "Live Free or Die" Home: 512-346-2444 Work: 328-0282; 110 Wild Basin Rd. Ste #230, Austin TX 78746
henry@utzoo.uucp (Henry Spencer) (05/12/88)
> Lastly, I'm not sure what if any provisions exist for steering SRB and > external tank away from orbiter after separation... I don't believe > SRB nozzles can be gimbled. The SRB nozzles are gimbaled -- they have to be, there isn't enough control authority in the SSMEs when the SRBs are firing. However, I believe all the smarts are aboard the orbiter, so they effectively run wild when you break that connection. Separating the orbiter from the tank/SRB assembly while the SRBs are firing is difficult. There are high loads on the connecting links, and the separation must be immediate and complete. The current links definitely are not designed for a safe separation under power; the rear link wouldn't separate cleanly and the orbiter would pitch up belly-on to the slipstream. This would destroy it: it's moderately heat-resistant but not terribly strong, and not even jet fighters can survive that kind of treatment at high speed. Redesigning the links for clean separation just might be possible, but it wouldn't be easy. Assuming we have clean separation, we then have to worry about what happens aerodynamically. It is *not* trivial to make sure that two large objects in close formation move away from each other in an orderly manner. Fighters and the like are carefully tested for proper "stores separation", and gravity often isn't enough: missiles "dropped" from fighters usually are blown or thrown clear, not just dropped. For the shuttle, we don't even have gravity pointing in the right direction to help, and it's impractical to fly full-scale tests. And *then* we have to worry about the shuttle being hit by the SRB exhausts, which are hot, dense, and abrasive. The shuttle re-enters in a carefully controlled way in hot but very thin air; it's not built to survive a large rocket exhaust at close range. In short, it's not quite impossible, but it's a lot harder than it looks. -- NASA is to spaceflight as | Henry Spencer @ U of Toronto Zoology the Post Office is to mail. | {ihnp4,decvax,uunet!mnetor}!utzoo!henry
dsmith@hplabsb.UUCP (David Smith) (05/14/88)
I'm not trying to say that orbiter separation during SRB firing could be survivable, but I wonder about some of of the reasons advanced as to why not. In article <1988May11.185145.592@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > Separating the orbiter from the tank/SRB assembly while the SRBs are > firing is difficult. There are high loads on the connecting links, > and the separation must be immediate and complete. True, but since the orbiter is pushing forward on the tank, and not vice-versa, might it be feasible to throttle down the SSME's to the point that the loads are manageable? > And *then* we have to worry about the shuttle being hit by the SRB exhausts, > which are hot, dense, and abrasive. The shuttle re-enters in a carefully > controlled way in hot but very thin air; it's not built to survive a large > rocket exhaust at close range. But Challenger wasn't much damaged by the SRB exhaust plume, aside from the local scorching it took from the failing joint prior to breakup. David Smith
CaptainDave@cup.portal.com (05/14/88)
Just a quick question. On launch, are the flight controls active or
stored in a neutral position. I realize that they are useless above 150K-200K
altitude, but would they be usefull in a Shuttle/SRB-ET seperation?
CaptainDave@cup.portal.comeder@ssc-vax.UUCP (Dani Eder) (05/18/88)
In article <4706@hplabsb.UUCP>, dsmith@hplabsb.UUCP (David Smith) writes: > True, but since the orbiter is pushing forward on the tank, and not > vice-versa, might it be feasible to throttle down the SSME's to the > point that the loads are manageable? > I believe you are misinterpreting what is pushing on whom in the Shuttle stack. The majority of the mass of the Shuttle core, which is the Orbiter plus External Tank, is the oxygen in the ET. This comprises about 1.4 million pounds of the total 1.8 million pounds in the core at liftoff. There is a connection between the forward end of the Solid Rocket Boosters and the middle of the 'intertank' in the ET. This is a ball-and socket joint, with an aft-facing socket on the ET, and a forward pushing ball on the SRB. The socket is part of a large forging which spreads the push from an SRB over the intertank. The intertank is the corrugated region about one third of the way back on the ET. The intertank, in turn, spreads the push of the SRBs evenly along the rim of the Oxygen tank. The push from the SSMEs represents about 15% of the total thrust of the Shuttle early in the flight. The push from the SSMEs is transferred into the skin of the hydrogen tank through the connecting struts in the aft portion of the Orbiter. With the present design of the ball and socket joint, there is no way to separate the SRBs as long as they are firing, they simply apply too much force (3 million pounds each) to separate the joint. -- Dani Eder / Boeing / Space Station Program / uw-beaver!ssc-vax!eder (205)461-2606(w) (205)461-7801(h) 1075 Dockside Drive #905 Huntsville, AL 35824 34 40 N latitude 86 40 W longitude +280 ft altitude, Earth
dsmith@hplabsb.UUCP (David Smith) (05/19/88)
In article <1934@ssc-vax.UUCP>, eder@ssc-vax.UUCP (Dani Eder) writes: > In article <4706@hplabsb.UUCP>, dsmith@hplabsb.UUCP (David Smith) writes: > > True, but since the orbiter is pushing forward on the tank, and not > > vice-versa, might it be feasible to throttle down the SSME's to the > > point that the loads are manageable? > > > > I believe you are misinterpreting what is pushing on whom in the > Shuttle stack. The majority of the mass of the Shuttle core, > which is the Orbiter plus External Tank, is the oxygen in the ET. > This comprises about 1.4 million pounds of the total 1.8 million > pounds in the core at liftoff. > > ((description of SRB-ET connection omitted)) > The push > from the SSMEs represents about 15% of the total thrust of the > Shuttle early in the flight. I'm not impressed. See below. > The push from the SSMEs is transferred > into the skin of the hydrogen tank through the connecting > struts in the aft portion of the Orbiter. > > With the present design of the ball and socket joint, there is > no way to separate the SRBs as long as they are firing, they > simply apply too much force (3 million pounds each) to separate > the joint. You apparently gathered that I was talking about separating SRBs from ET. By referring to "the orbiter ... pushing forward on the tank", I was addressing the detachment of the orbiter from the ET/SRB combination with the SRB's still firing. Thank you for the weight of the core (orbiter+ET). Now let's look at weights of the SRB's. According to AW&ST, each SRB weighs 1.82 million pounds empty, and is loaded with 1.11 million pounds of propellant (note 1). Each SRB produces 3.3 million pounds of thrust at liftoff, "throttles" down to 2.4 million for max-Q, and back up to 2.7 million afterward (note 2). That's a thrust/weight ratio of 1.13 for the SRBs at liftoff, or 1.48 near burnout, vs. 5.22 for the orbiter (if I wildly guess its weight at 250,000 pounds). Clearly, the orbiter is pushing forward on the tank. At liftoff, each SRB's excess of thrust over weight comes to 370,000 pounds, or 740,000 pounds for the pair. The orbiter's excess of thrust over weight is 1,050,000 pounds using the 250,000 pound weight estimate. Acceleration of SRB's and orbiter reduce the amount of this available to accelerate the ET, so as to more heavily penalize the SRB's. Therefore, I conclude, >>>the SSMEs apply more thrust to the ET than do the SRBs,<<< notwithstanding the fact that they produce only around 15% of the total thrust. Notes: 1. That is a truly lousy mass ratio compared with liquid propellant systems. 2. Add the quoted component weights up, and you get 7.66 million pounds. Add the thrusts, you get 7.905 million. The resulting thrust/weight of 1.03 sounds small: perhaps due to rounding somewhere, or relieved by the propellant burned in the mains before liftoff. David Smith HP Labs
rjnoe@uniq.UUCP (Roger J. Noe) (05/26/88)
> In article <1934@ssc-vax.UUCP>, eder@ssc-vax.UUCP (Dani Eder) writes: > > I believe you are misinterpreting what is pushing on whom in the > > Shuttle stack. The majority of the mass of the Shuttle core, > > which is the Orbiter plus External Tank, is the oxygen in the ET. > > This comprises about 1.4 million pounds of the total 1.8 million > > pounds in the core at liftoff. So far this looks pretty accurate. At launch the OV is something like 165000 lbs. with no cargo. The LO2 in the ET is about 1.33e6 lbs., the LH2 is 220000 lbs. and the ET itself is another 78000 lbs. for a total of 1.63e6 lbs. in the full ET. That does bring the ET+OV weight to about 1.8e6 lbs. at liftoff. > > The push > > from the SSMEs represents about 15% of the total thrust of the > > Shuttle early in the flight. I think comparing the sea-level thrust values (11.88e6 N per SRB, and a nominal 1.668e6 N per SSME) and assuming the SSMEs are running at 104% of nominal, you get more like 18% of the total thrust shortly after liftoff as being due to the three SSMEs, with the remainder due to the two SRBs. Good enough for government work. (For those of you who haven't yet learned metric, those thrust values are 2.67e6 lbs. per SRB and nominal 375000 lbs. per SSME, at sea level.) > > The push from the SSMEs is transferred > > into the skin of the hydrogen tank through the connecting > > struts in the aft portion of the Orbiter. > > > > With the present design of the ball and socket joint, there is > > no way to separate the SRBs as long as they are firing, they > > simply apply too much force (3 million pounds each) to separate > > the joint. This sounds right. Since the gross weight of an SRB at launch is 1.287e6 lbs. and the whole stack is accelerating at about 0.48g as the stack clears the tower, each SRB exerts a force of about 767000 lbs. (3.4e6 N) on the ET. The OV, with about half the allowable cargo, weighs almost 200000 lbs. and exerts a force of around 877000 lbs. (3.9e6 N) on the ET given the 0.48g upward acceleration value. Until the SRB thrust decreases greatly (and the SSME thrust increases; vacuum thrust per SSME is almost 100000 lbs. greater than their sea-level thrust) the ET and SRBs are inseparable, barring an accident. In article <4712@hplabsb.UUCP>, dsmith@hplabsb.UUCP (David Smith) writes: > You apparently gathered that I was talking about separating SRBs from ET. > By referring to "the orbiter ... pushing forward on the tank", I was > addressing the detachment of the orbiter from the ET/SRB combination > with the SRB's still firing. I feel that a certain Monty Python/Holy Grail quote about swallows and coconuts is about to become relevant. :-) > Thank you for the weight of the core (orbiter+ET). Now let's look at > weights of the SRB's. According to AW&ST, each SRB weighs 1.82 million > pounds empty, and is loaded with 1.11 million pounds of propellant (note 1). > Each SRB produces 3.3 million pounds of thrust at liftoff, "throttles" down AW&ST said this? My figures (which I admit are somewhat old, but at least they're ballpark correct) are 181000 lbs. for an inert SRB. The amount of reactant looks about right; I show a gross liftoff weight of 1.287e6 lbs. But can that thrust be right? I've got 2.67e6 lbs. sea-level thrust per SRB. > to 2.4 million for max-Q, and back up to 2.7 million afterward (note 2). > That's a thrust/weight ratio of 1.13 for the SRBs at liftoff, or 1.48 near > burnout, vs. 5.22 for the orbiter (if I wildly guess its weight at 250,000 > pounds). Clearly, the orbiter is pushing forward on the tank. I get more like 2.08 thrust/weight per SRB at launch and 5.85 for the OV. No matter; all three propulsive components are exerting forces on the ET. > At liftoff, each SRB's excess of thrust over weight comes to 370,000 > pounds, or 740,000 pounds for the pair. The orbiter's excess of thrust > over weight is 1,050,000 pounds using the 250,000 pound weight estimate. > Acceleration of SRB's and orbiter reduce the amount of this available > to accelerate the ET, so as to more heavily penalize the SRB's. Therefore, > I conclude, >>>the SSMEs apply more thrust to the ET than do the SRBs,<<< > notwithstanding the fact that they produce only around 15% of the total > thrust. This is the danger of believing your numbers when your intuition tells you otherwise. The excess of thrust over weight is more like 1.38e6 lbs. per SRB, 975000 lbs. for the OV with some cargo and 104% SSMEs, at liftoff. Yes, the OV does exert a greater force on the ET than does either of the SRBs, but *not* more than both of the SRBs! It has to be almost equally shared. My figures show about 36% of the net force on the ET coming from the OV with 32% from each of the SRBs. Of course, it's a dynamic relationship and I'm certain it changes considerably as the stack gains altitude. > Notes: > 1. That is a truly lousy mass ratio compared with liquid propellant systems. > > 2. Add the quoted component weights up, and you get 7.66 million pounds. > Add the thrusts, you get 7.905 million. The resulting thrust/weight > of 1.03 sounds small: perhaps due to rounding somewhere, or relieved > by the propellant burned in the mains before liftoff. The total weight of the STS at liftoff is more like 4.4e6 lbs. and the total thrust is around 6.5e6 lbs. for a ratio of 1.48, which gives the initial acceleration of +0.48g I mentioned earlier. This improves very substantially as the launch progresses; it's nearer to 2.5 thrust/weight (or better) as you get near SRB separation, and the OV+ET combination gets up to 4.0 as you near MECO. Now back to the original question: > > In article <4706@hplabsb.UUCP>, dsmith@hplabsb.UUCP (David Smith) writes: > > > True, but since the orbiter is pushing forward on the tank, and not > > > vice-versa, might it be feasible to throttle down the SSME's to the > > > point that the loads are manageable? The fact that the OV is exerting a net force on the ET is not the problem. Consider what would happen if you tried separating the orbiter vehicle from the rest of the system while everything's running. First you have to shut down the SSME's and disconnect the OV from the ET propellant lines. In that time, all the thrust is from the SRB's and both the ET and the OV are dead weight. If about one fourth the ET fuel is gone, the ET weighs a total of about 1.24e6 lbs. The OV still weighs about 200000 lbs. and the SRBs may be down to about 460000 lbs. each. So the total weight of the stack is down to about 2.36e6 lbs. with a thrust of around 6.2e6 lbs. for a thrust to weight ratio of about 2.63. Cutting off the SSMEs loses around 1.2e6 lbs. thrust for a ratio of 2.12, a loss of about 0.5g. If this cutoff takes 0.1 second, that's a change of 5g/sec. Now what happens when you detach the OV from the ET? The OV suddenly loses another 2.12g of acceleration! If this separation takes 0.1 second, that's 21g/sec! The ET+SRBs combination would gain about 0.19g in this same time from the dropped mass. I think we've already seen what happens when you subject the STS to such rates of change in acceleration while it's flying: the ET disintegrates, the SRBs fly off, and the OV becomes something you stuff down an abandoned missile silo. -- Roger Noe ihnp4!att!uniq!rjnoe Fox Valley Software ihnp4!nwuxf!rjnoe Uniq Digital Technologies +1 312 510 2105 Batavia, Illinois 60510 41:50:56 N. 88:18:35 W.
dsmith@hplabsb.UUCP (David Smith) (06/01/88)
In article <478@uniq.UUCP>, rjnoe@uniq.UUCP (Roger J. Noe) writes: > In article <4712@hplabsb.UUCP>, dsmith@hplabsb.UUCP (David Smith) writes: > > Thank you for the weight of the core (orbiter+ET). Now let's look at > > weights of the SRB's. According to AW&ST, each SRB weighs 1.82 million > > pounds empty, and is loaded with 1.11 million pounds of propellant (note 1). > > Each SRB produces 3.3 million pounds of thrust at liftoff, "throttles" down > > AW&ST said this? My figures (which I admit are somewhat old, but at least > they're ballpark correct) are 181000 lbs. for an inert SRB. The amount of > reactant looks about right; I show a gross liftoff weight of 1.287e6 lbs. > But can that thrust be right? I've got 2.67e6 lbs. sea-level thrust per > SRB. AW&ST said this in their coverage of Challenger's problem with the SRB, Feb. 10, 1986, p.55. If they messed up and slipped a decimal point on the weight, it wasn't in final printing, as they spelled out "million". Actually, I'd prefer to believe AW&ST made a mistake (it wouldn't be the first) than that the SRB is such a stupid design (ahh, well, ...) I'm less willing to believe they made a mistake on the thrust, since they made a point about performance improvements introduced on the 8th shuttle flight that raised liftoff thrust by 200,000 lb. from 3.1e6 to 3.3e6. > Now back to the original question: > > > In article <4706@hplabsb.UUCP>, dsmith@hplabsb.UUCP (David Smith) writes: > > > > True, but since the orbiter is pushing forward on the tank, and not > > > > vice-versa, might it be feasible to throttle down the SSME's to the > > > > point that the loads are manageable? > > The fact that the OV is exerting a net force on the ET is not the problem. > Consider what would happen if you tried separating the orbiter vehicle > from the rest of the system while everything's running. First you have to > shut down the SSME's and disconnect the OV from the ET propellant lines. > In that time, all the thrust is from the SRB's and both the ET and the OV > are dead weight. I had in mind chopping the attachments and fuel lines while the engines were still running: just let them shut down when the propellant in the pipes runs out in a few seconds. I have continued this topic as the devil's advocate, but will probably not say more. David Smith HP Labs
DMeyer@mips.csc.ti.com (Dane Meyer) (06/03/88)
While it may be true that SRB/ET - OV separation during liftoff
realisticly will never be developed due to one or more of; technical
complexity, expense, or politics, I find this discussion quite
informative and interesting. I've been forwarding your messages to
Ken Scofield who really asked the original question and sent me this
note regarding Roger's comments.
Dane Meyer (Texas Instruments, Dallas)
ARPA/CSnet: dmeyer@csc.ti.com
UUCP: {convex!smu im4u texsun pollux ihnp4!infoswx rice}!ti-csl!dmeyer
----------------------------------------------------------------------------
In reply to Roger Noe:
>From: rjnoe@uniq.UUCP (Roger J. Noe)
>Subject: Re: Orbiter/SRB separation
>
> ... (much text on thrusts and weights deleted; I'll assume it's correct)
>
>The fact that the OV is exerting a net force on the ET is not the problem.
>Consider what would happen if you tried separating the orbiter vehicle
>from the rest of the system while everything's running. First you have to
>shut down the SSME's and disconnect the OV from the ET propellant lines.
>In that time, all the thrust is from the SRB's and both the ET and the OV
>are dead weight.
Why? The SSME's *are* throttlable, and there is some on-board fuel which
normally is used for final insertion into orbit, as well as the subsequent
de-orbit burn. So, the SSME's could be throttled down to some suitable
level, and be allowed to burn while the disconnect/separation is accomplished.
> If about one fourth the ET fuel is gone, the ET weighs a
>total of about 1.24e6 lbs. The OV still weighs about 200000 lbs. and the SRBs
>may be down to about 460000 lbs. each. So the total weight of the stack is
>down to about 2.36e6 lbs. with a thrust of around 6.2e6 lbs. for a thrust
>to weight ratio of about 2.63. Cutting off the SSMEs loses around 1.2e6 lbs.
>thrust for a ratio of 2.12, a loss of about 0.5g. If this cutoff takes 0.1
>second, that's a change of 5g/sec. Now what happens when you detach the OV
>from the ET? The OV suddenly loses another 2.12g of acceleration! If this
>separation takes 0.1 second, that's 21g/sec! The ET+SRBs combination would
>gain about 0.19g in this same time from the dropped mass.
So What? What you've described is the derivative of acceleration (known
as "jerk") which, in this context, I don't think particularly matters. As I
understand the Challenger situation, the thing that wiped it out were the
aerodynamic forces which were imposed on it by the sudden change in flight
path (i.e., it was thrown askew by the exploding ET). As long as the various
components separate cleanly, and don't make any extremely radical changes in
relation to flight path, I see no reason why the OV and ET/SRB (as separate
units) couldn't stay intact. Besides, if the SSME's were still burning, at
least at partial throttle as I suggested above, the "jerk" would be greatly
reduced (if it matters at all), and the OV could quickly accelerate away
from the impending ET/SRB fireball (or whatever). All the thrust-to-weight
ratios I've seen discussed indicate that the OV could easily "out-run" the
ET/SRB. And by the way, although the current connecting struts can't be
released while engines are burning, I can't imagine that it would be very
difficult to redesign them so that they could be released while under load.
*
/ \
|---/---\---| Ken Scofield C-9355
| Gone | Hewlett-Packard, ICO
| | 1020 NE Circle Blvd.
| Jumpin' | Corvallis, OR 97330
|-----------| Phone: (503)757-2000
{ucbvax!hplabs, harpo, ogcvax}!hp-pcd!kaslwall@devvax.UUCP (06/04/88)
In article <50665@ti-csl.CSNET> DMeyer@mips.csc.ti.com (Dane Meyer) writes:
: Why? The SSME's *are* throttlable, and there is some on-board fuel which
: normally is used for final insertion into orbit, as well as the subsequent
: de-orbit burn. So, the SSME's could be throttled down to some suitable
: level, and be allowed to burn while the disconnect/separation is accomplished.
No doubt there will be others who say this, but the on-board fuel is
hypergolic and is not fed to the SSME's. If you look carefully you'll see
a couple extra nozzles sticking out the back. The SSME's must be shut
down before separation or their various components will diverge when the first
bubble comes through and the turbos suddenly have nothing to slow them down.
Larry Wall
lwall@jpl-devvax.jpl.nasa.govhenry@utzoo.uucp (Henry Spencer) (06/05/88)
> ... As long as the various > components separate cleanly, and don't make any extremely radical changes in > relation to flight path, I see no reason why the OV and ET/SRB (as separate > units) couldn't stay intact... As I've mentioned before, the aerodynamics of this sort of separation process are not trivial and should not be assumed to be trouble-free. Military aircraft are tested very carefully for proper separation of missiles, drop tanks, etc. > Besides, if the SSME's were still burning, at > least at partial throttle as I suggested above, the "jerk" would be greatly > reduced (if it matters at all), and the OV could quickly accelerate away > from the impending ET/SRB fireball (or whatever)... Uh, using what for fuel? The orbiter has no built-in tanks for the SSMEs, only for the low-thrust OMS. The SSMEs would have to be shut down either before or at the instant of separation. Once it separates, the orbiter is a glider; the ET/SRB combination will quickly accelerate away from it, potentially exposing it to the SRB exhaust. (Those who still think this is a trivial issue should consider that rocket engines have been used experimentally for drilling tunnels through hard rock; close-range exposure to the exhaust of a big rocket engine is likely to be fatal to something as flimsy as a shuttle orbiter). -- "For perfect safety... sit on a fence| Henry Spencer @ U of Toronto Zoology and watch the birds." --Wilbur Wright| {ihnp4,decvax,uunet!mnetor}!utzoo!henry
david@smythsun.JPL.NASA.GOV (David Smyth) (06/07/88)
In article <2170@devvax.JPL.NASA.GOV> lwall@devvax.JPL.NASA.GOV (Larry Wall) writes: >In article <50665@ti-csl.CSNET> DMeyer@mips.csc.ti.com (Dane Meyer) writes: >: Why? The SSME's *are* throttlable, and there is some on-board fuel which >: normally is used for final insertion into orbit, as well as the subsequent >: de-orbit burn. So, the SSME's could be throttled down to some suitable >: level, and be allowed to burn while the disconnect/separation is accomplished. > >No doubt there will be others who say this, but the on-board fuel is >hypergolic and is not fed to the SSME's. If you look carefully you'll see >a couple extra nozzles sticking out the back. The SSME's must be shut >down before separation or their various components will diverge when the first >bubble comes through and the turbos suddenly have nothing to slow them down. So what if the SSMEs disintegrate? We are talking about an emergency, where the current result would be the loss of the entire vehicle. As long as the airframe is not damaged by their disintegration, it may still be an acceptable abort procedure. It sounds like it would work to throttle back gradually, and when the SSMEs are pushing as hard as the SRBs on the ET, and therefore the loads on the connecting struts are minimized, that perhaps the connections could be blown. The SSMEs would then breakup, and the Orbiter could glide down, possibly with the crew parachuting out since ditching is not survivable.
david@smythsun.JPL.NASA.GOV (David Smyth) (06/07/88)
In article <1988Jun5.025213.23613@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >> [ Theory: reduce throttle on SSMEs, glide away from ET/SRB] > [ needs to be carefully investigated, aerodynamics are non-trivial, & > Orbiter will have no power except a little possible from OMS, > so could easily be fried by SRBs] OK: 1) Need to see if structural loads of ET/SRB separation could be kept safe by throttling back SSMEs and precise seperation, 2) Need to see if Orbiter can glide away from uncontrolled ET/SRB to avoid SRB exhaust. 3) If gliding won't work, how much thrust would it take? Remember Apollos, Geminis, and Mercurys needed an escape tower to do it, maybe the Orbiter needs a special thruster. Or, perhaps the RCS and OMS could do it (I doubt it) or be made more powerful to do it. Can anybody model this and see if its feasible?
lwall@devvax.JPL.NASA.GOV (Larry Wall) (06/07/88)
In article <2198@devvax.JPL.NASA.GOV> david@smythsun.JPL.NASA.GOV (David Smyth) writes:
: So what if the SSMEs disintegrate? We are talking about an emergency,
: where the current result would be the loss of the entire vehicle. As
: long as the airframe is not damaged by their disintegration, it may still
: be an acceptable abort procedure.
Maybe. But disintegrating turbos make lots of shrapnel. And there's a lot
of other things back there that are critical to controlled flight. Like
the control surfaces, the hydraulics to them, and particularly the APUs
to power the hydraulics. And some of the tanks of hypergolics that fuel
the APUs. If those go, you can probably kiss the whole back end goodbye.
If we're going to plan a disintegration, it seems to me that we've already
got a good idea how an orbiter breaks up. Revive the idea of hanging
a parachute on the cabin, but don't worry about the pyrotechnics to separate
it from the rest of the orbiter--they appear to be unnecessary, since
aerodynamical forces will do the job nicely for you. The parachute doesn't
even necessarily have to slow down the cabin enough for a survivable landing.
As long as the crew has sufficient oxygen to get to bail-out altitudes,
and a cabin stabilized by a small drogue chute, that should be sufficient.
There's another thing: it may not be possible for the orbiter to pull
away from the stack at all. In the Navy they discovered that they have to
be REAL careful about running two ships next to each other, because the
passage between the ships makes an excellent venturi, and sucks the two
ships together. It may be that the SRBs *must* be peeled off sideways first
(note that they have tractor rockets) in order to reduce the aerodynamic
cross-section of the stack, before the orbiter can separate. Also, the ET
is ordinarily dumped at a much higher altitude where the wind between the
orbiter and the stack will be considerably less.
On the other hand, I may be all wet.
Larry Wall
lwall@jpl-devvax.jpl.nasa.govgreg@proxftl.UUCP (Gregory N. Hullender) (06/13/88)
In article <478@uniq.UUCP>, rjnoe@uniq.UUCP (Roger J. Noe) writes: > The fact that the OV is exerting a net force on the ET is not the problem. > Consider what would happen if you tried separating the orbiter vehicle > from the rest of the system while everything's running. First you have to > shut down the SSME's and disconnect the OV from the ET propellant lines. > In that time, all the thrust is from the SRB's and both the ET and the OV > are dead weight. If about one fourth the ET fuel is gone, the ET weighs a > total of about 1.24e6 lbs. The OV still weighs about 200000 lbs. and the SRBs > may be down to about 460000 lbs. each. So the total weight of the stack is > down to about 2.36e6 lbs. with a thrust of around 6.2e6 lbs. for a thrust > to weight ratio of about 2.63. Cutting off the SSMEs loses around 1.2e6 lbs. > thrust for a ratio of 2.12, a loss of about 0.5g. If this cutoff takes 0.1 > second, that's a change of 5g/sec. Now what happens when you detach the OV > from the ET? The OV suddenly loses another 2.12g of acceleration! If this > separation takes 0.1 second, that's 21g/sec! The ET+SRBs combination would > gain about 0.19g in this same time from the dropped mass. I think we've > already seen what happens when you subject the STS to such rates of change > in acceleration while it's flying: the ET disintegrates, the SRBs fly off, > and the OV becomes something you stuff down an abandoned missile silo. This article was great up to this point. Unfortunately, the comments about rate of change of acceleration are wrong; even if the system INSTANTLY stopped accelerating ALTOGETHER (experiencing an infinite rate of change in acceleration) that wouldn't stress the system. INCREASING acceleration can damage things, but it doesn't matter how fast or how slowly the increase happens, although how long it lasts could be important. What destroyed the Challenger wasn't change in acceleration; first one of the O-rings burned through (about 120 degrees of arc). Then strong high-altitude winds buffeted the vehicle and allowed a plume of hot gasses to leak out where the O-Ring had been. This plume touched off the ET, which detonated with the energy of a small nuclear weapon. The orbiter was then exposed to AERODYNAMIC forces of more than 20 g's, and it was those forces (not the explosion) that broke it into pieces. That problem with separating the orbiter during launch is still there, though; even if you used something like explosive bolts to accomplish the separation, how do you make the orbiter survive the aerodynamic forces? -- ------ My opinions are not necessarily those of my employer. Greg Hullender allegra!novavax!proxftl!greg
dep@cat.cmu.edu (David Pugh) (06/16/88)
In article <308@proxftl.UUCP> greg@proxftl.UUCP (Gregory N. Hullender) writes: >That problem with separating the orbiter during launch is still there, >though; even if you used something like explosive bolts to accomplish the >separation, how do you make the orbiter survive the aerodynamic forces? Has any consideration been given to using AMROC-type hybird boosters for the advanced SRBs? Being able to throttle the boosters would seem to provide numerous saftey advantages. Also, I seem to recall that the AMROC rockets had a higher Isp than the shuttle SRBs. -- DAVE BARRY'S 1987 IN REVIEW -- May 17th David Pugh The U.S. Navy frigate Stark is ....!seismo!cmucspt!cat!dep attacked by an Iraqi jet, which, under our extremely clear Mideast policy, causes us to prepare for violent confrontation with Iran.
mears@hpindda.HP.COM (David B. Mears) (06/18/88)
> . . . and allowed a plume of hot gasses > to leak out where the O-Ring had been. This plume touched off the ET, which > detonated with the energy of a small nuclear weapon. Wait a minute. I don't recall seeing anywhere anything published which said that the exhaust plume directly caused the explosion of the ET. Where did you this printed? It was always my understanding that the plume caused the lower strut to weaken and break, thus causing the SRB to pivot into the ET, causing the tanks to rupture, causing the H and O to combine and burn in the fireball seen on TV (though not exactly an explosion). Or are we saying the same thing only with more or less detail? > -- > ------ > My opinions are not necessarily those of my employer. > > Greg Hullender allegra!novavax!proxftl!greg > ---------- David B. Mears Hewlett-Packard Cupertino CA {hplabs, ihnp4!hpfcla}!hpda!mears
petej@phred.UUCP (Pete Jarvis) (06/20/88)
In article <3330005@hpindda.HP.COM> mears@hpindda.HP.COM (David B. Mears) writes: >Wait a minute. I don't recall seeing anywhere anything published which >said that the exhaust plume directly caused the explosion of the ET. Where >did you this printed? It was always my understanding that the plume caused >the lower strut to weaken and break, thus causing the SRB to pivot into the >ET, causing the tanks to rupture, causing the H and O to combine and burn in >the fireball seen on TV (though not exactly an explosion). Or are we saying >the same thing only with more or less detail? > David: The plume did cause the lower strut to weaken and break, but at the same time it also burned through the ET causing it to rupture and burn hydrogen rapidly out the bottom. This caused an instantaneous 20-G force ramming the top of the H tank into the bottom of the Oxygen tank. At the same time, the top of the SRB pivoted into the inter-tank area of the ET when the strut broke. I have the detailed and commented video tapes that discuss this when they were shown during the Rogers Commission proceedings. Peter Jarvis........Physio-Control, Redmond, Washington
craig@think.COM (Craig Stanfill) (06/21/88)
>This article was great up to this point. Unfortunately, the comments about >rate of change of acceleration are wrong; even if the system INSTANTLY >stopped accelerating ALTOGETHER (experiencing an infinite rate of change in >acceleration) that wouldn't stress the system. INCREASING acceleration >can damage things, but it doesn't matter how fast or how slowly the >increase happens, although how long it lasts could be important. What you are saying here makes sense for static analysis, but you are completely ignoring system dynamics. The first thing to do is to straighten out the terminology in this discussion. The engines in a spacecraft do not apply an acceleration, they apply a force. When engines are turned on or off, the result is not an instantaneousl change in the acceleration of the structure, but an instantaneous change in the force applied to point in that structure. While the static equilibrium of the structure depends only on the magnitude of the force, the dynamics of the system very much depend on how quickly the force is applied. The problem is that the structure has massive components connected by elastic elements. All such systems are oscilators. When a force is applied, the entire system starts oscilating, with the suddenness of force application determining how energetic these oscilations are. If the force is applied suddenly enough, these oscilations may cause structural failure. A simple thought experiment should suffice to convince you of this. Suppose you have two bricks, each having a mass of 1 KG, and a spring that can withstand a tension of just slightly over 1 Newton. If we gradually apply a force of 2N to the front brick, the entire assembly will accelerate at a rate of 1 m/s/s. If, however, we suddenly apply a force of 2N to the front brick, then the first brick will accelerate at a rate of 2 m/s/s, while the rear brick is stationary. Until the spring can stretch to the point where it is under a tension of 1N, the first brick will be accelerating faster than the second. During this time, the first brick will acquire a considerably higher velocity than the second and, because it has momentum, will continue moving faster for some time. This will cause the spring to lengthen and, as a result, will increase the tension on the spring. The spring will then break. If you are uncomfortable with words, work out the differential equations; they are not terribly complex. - Craig Stanfill
john@frog.UUCP (John Woods) (06/24/88)
There has been a lot of discussion about this. Just to throw more LH on the fire, I thought I'd quote from the Report of the Presidential Commision on the Space Shuttle Challenger Accident, Volume 1, page 20-21: "The first visual indication that swirling flame from the right Solid Rocket Booster breached the External Tank was at 64.660 seconds when there was an abrupt change in the shape and color of the plume. This indicated that it was mixing with leaking hydrogen from the External Tank. Telemetered changes in the hydrogen tank pressurization confirmed the leak. Within 45 milliseconds of the breach of the External Tank, a bright sustained glow developed on the black-tiled underside of the Challenger between it and the External Tank. "Beginning at about 72 seconds, a series of events occurred extremely rapidly that terminated the flight. Telemetered data indicate a wide variety of flight system actions that support the visual evidence of the photos as the Shuttle struggled futilely against the forces that were destroying it. "At about 72.20 seconds the lower strut linking the Solid Rocket Booster and the External Tank was severed or pulled away from the weakened hydrogen tank permitting the right Solid Rocket Booster to rotate around the upper attachment strut. This rotation is indicated by divergent yaw and pitch rates between the left and right Solid Rocket Boosters. "At 73.124 seconds, a circumferential white vapor pattern was observed blooming from the side of the External Tank bottom dome. This was the beginning of the structural failure of the hydrogen tank that culminated in the entire aft dome dropping away. This released massive amounts of liquid hydrogen from the tank and created a sudden forward thrust of about 2.8 million pounds, pushing the hydrogen tank upward into the intertank structure. At about the same time, the rotating right Solid Rocket Booster impacted the intertank structure and the lower part of the liquid oxygen tank. These structures failed at 73.137 seconds as evidenced by the white vapors appearing in the intertank region. "Within milliseconds there was massive, almost explosive, burning of the hydrogen streaming from the failed tank bottom and the liquid oxygen breach in the area of the intertank. "At this point in its trajectory, while traveling at a Mach number of 1.92 at an altitude of 46,000 feet, the Challenger was totally enveloped in the explosive burn. The Challenger's reaction control system ruptured and a hypergolic burn of its propellants occurred as it exited the oxygen-hydrogen flames. The reddish brown colors of the hypergolic fuel burns are visible on the edge of the main fireball. The Orbiter, under severe aerodynamic loads, broke into several large sections which emerged from the fireball." Reading the telemetry report was kind of interesting. The Challenger control systems were indeed making a valiant effort to cope with the bizarre goings on, right up until the radio stopped... -- John Woods, Charles River Data Systems, Framingham MA, (617) 626-1101 ...!decvax!frog!john, john@frog.UUCP, ...!mit-eddie!jfw, jfw@eddie.mit.edu Guns don't kill people; I kill people.