Here's an interesting variation on the shuttle design. Has some interesting advantages to it. It would make for a cool "alternate shuttle" model.

Basically, they connect the two SRB's together using an aft thrust beam, and have the ET slide down between them on T-rails... the LOX tank and LH2 tank flip positions, putting the MUCH heavier LOX on bottom, and the much lighter LH2 on top, negating the need for a heavy thrust beam in the intertank to take the thrust loads of the SRB's in flight, and transfer that thrust into the heavy LO2 tank above. It allows the more dense LOX tank to be made smaller diameter and longer, thus moving the SRB's and the orbiter and its SSME's closer to the centerline of the vehicle, improving performance, and placing the larger LH2 tank on top and forward, putting the SRB's and orbiter in the aerodynamic shadow of the forward tank, reducing air drag on ascent. At SRB burnout, the aft thrust structure is separated from the aft end of the ET via explosive bolts, and the pair of SRB's then slides rearward down the T-rails until they fall clear of the ET. No jettison motors for the SRB's are needed, but they can be used firing full forward (instead of laterally at an angle as the SRB separation motors did on the actual shuttle) to increase the speed of the jettison. No mention is made of how the SRB's would be recovered-- I'll go out on a limb and say that probably the SRB's would have to jettison the thrust beam via explosive bolts shortly after clearing the shuttle, to separate them and allow them to tumble freely (which they'd have to have a small tumble motor to fire and put them tumbling, which was essential to reduce their speed at reentry into the lower atmosphere, and spread the aerodynamic heating of reentry) and then allow them to separately deploy their parachutes... I would think that trying to land as a pair with the thrust beam still connecting them would be very difficult to achieve without warping or bending the casings from the water impact and parachute deployment sequence...

At any rate, it's an interesting design and would make a neat rocket...

Later! OL JR

Attached Files

STUDY SUMMARY-Patent-Shuttle with Rail System and Aft Thrust Structure Securing SRBs to ET.txt (7.0 KB, 102 views)

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Enjoy! OL JR

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So why not make a HPR version of it large enough to test the rail system and see the SRB's deploy and a large shuttle glide down?

Do it... I don't do HPR...

I'd love to see it! OL JR

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Wow, you don't think that LH2 tank above the orbiter would make the debris problem any worse, do you?

I wouldn't worry about it taking out a window because they are pretty tough, but that carbon-carbon nose is the same brittle stuff as the leading edge that got taken out on the Columbia.

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It depends...

Most of the debris problems were from the bipod ice frost ramps (which took out Columbia's leading edge RCC panel and caused the shuttle to burn/break up on reentry). These would be well behind the conical intertank with this proposal, and thus is a much more "protected" area from the supersonic slipstream...

Foam shedding on the shuttle was just one of those things they never really satisfactorily solved... A lot of it was caused by entrapped air in any air bubbles or voids in the foam application-- the air would liquefy when chilled by the cryogenic propellants (especially the hydrogen which is colder than the liquefying point of all the atmospheric gases present in air) The liquid air is, of course, MUCH smaller in volume than its gaseous form, so as it liquefies it creates a vacuum in the void, and the 14.7 PSI atmospheric pressure then pushes inward on the surrounding foam, attempting to "implode" the void, which of course can crack the surrounding foam and weaken it. In addition, gases can make their way through the pore spaces of the foam to "relieve the vacuum" and end up with even MORE entrapped gases liquefying inside the void than was there before. As the vehicle lifts off and ascends, the foam starts to heat up from atmospheric friction, at the same time the liquid level of cryogenic propellants drops in the tank, eventually going below the void in the foam. As the liquid air in the void warms up, it soon begins to boil back into vapor, and expand to refill the void... if the void has partially collapsed from surface air pressure, the vapor would be boiling off to fill a void that had been crushed down smaller while sitting on the pad... and thus would exert more pressure on the smaller void, at the same time that the ambient external pressure had fallen off considerably toward a vacuum. If more gases had seeped into the void, coupled with the boiling off vapors of the trapped liquid air, it would create a high pressure bubble of air inside the void pushing outward from inside the foam, again, with the outside air pressure constantly dropping as the vehicle ascends. This basically sets up the situation where the bubble of trapped air pops the foam, causing a piece to blow off the tank. Analysis proved that the most critical time for foam shedding was after liftoff, about a minute or so into the flight where the vehicle has accelerated to a high velocity, but is still in fairly dense air-- any foam that is shed earlier in the flight, the vehicle is flying fairly slowly (relatively speaking) and the foam hits at a relatively slow speed and thus there is low risk of damage. The problem is, the foam has a high surface area and a low density/mass, so it decelerates very rapidly due to air drag, especially as the vehicle accelerates to higher velocities (drag squares as speed doubles) and so once the vehicle accelerates to a high speed, but it still in dense enough air to create high drag, shed foam from the tank RAPIDLY decelerates as the stack continues to accelerate and essentially "flies into" the shed foam, and since impact force for a given mass squares as the relative velocity doubles, (the old "a faster bullet imparts much more impact force than a heavier bullet travelling slower" axiom), the risks of damage from a foam impact at this point in the flight is much higher. As the rocket continues to accelerate, it's also ascending into thinner and thinner air, so that at 20 miles altitude it's above 99% of Earth's atmosphere... at that point, despite the hypersonic velocities, any shed foam has little/no air to create drag, and thus doesn't rapidly decelerate and impact the vehicle-- it decelerates much more slowly and simply "falls behind" the vehicle, lowering the risk of impact damage again...

It's all pretty interesting... I read a lot about the problem after Columbia...

Later! OL JR

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I wonder if--either at the beginning of the program or after Columbia's loss--NASA or the contractors looked into installing the insulation *inside* the tanks, as Douglas did on the Saturn S-IVB (and S-IV, IIRC) stages? That would have eliminated the foam break-away problem, although at the trouble of having to make absolutely certain that the internal insulation was all properly-bonded, to ensure that no bits of it would get sucked into the SSME propellant lines.

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Not seriously... the internal insulation was HORRIFICALLY expensive and difficult to do... that's why they got away from it...

Spray on insulation was SO much cheaper to apply and totally eliminated risks of insulation breaking off inside the tank and blocking propellant lines or being sucked into turbopumps and destroying them (they spin so fast that basically ANY foreign matter would cause them to explode (disintegrate) when it entered the impellers), in addition to any small bits of material that might make it through the turbopump and then plug the cooling jacket of the nozzle or combustion chamber, or barring that, plug up one/multiple injector orifices inside the engine itself, any of these which could potentially cause the engine to catastrophically fail (burn through of the nozzle or combustion chamber from localized hot spot caused by plugged cooling tube(s), combustion instability from a plugged injector orifice, etc.)

The main issues with all the things which caused the shuttle losses weren't the materials themselves, though that contributed, or even the design, which also contributed... it was the reaction of management toward "normalizing" or accepting excessive risks over time, failure to recognize the warning signs of a potentially catastrophic situation, and take the appropriate but costly and time consuming steps to minimize or mitigate the problems despite their impact on operations... Poor communication, too many "operational and programmatic" concerns (GO fever, Agency politics), and Byzantine bureaucracy making it difficult/impossible for the left hand to know what the right hand was doing, in addition to just plain failing to listen to their own engineers were the main factors in both shuttle disasters. It was WELL known and understood that the O-rings were a problem prior to the loss of Challenger, and in fact the "fix" for the O-ring problem was in the pipeline to replace the troublesome joints when Challenger was lost... The engineers understood the low temperature/increased leakage relationship that doomed Challenger, but the management was slow to accept it and integrate it into the operational rules, and they poorly understood it, and waved off concerns as "we've never had a problem before" (which was untrue-- several previous flights showed various levels of O-ring leakage and burned rings that varied directly with temperature at liftoff, including one leak that was so severe it ruined the SRB segment flange and had it been any worse would probably have destroyed the vehicle-- fortunately it was late enough in the flight that by the time the leak got severe enough to seriously damage the SRB, it was "tailing off" and soon jettisoned... ) The problem was to be addressed "in the future" and waved off for the time being (no harm, no foul) since it hadn't caused any serious problems, mostly due to operational concerns (the shuttle program was desperately trying at the time to "prove" that the shuttle paradigm worked, that it could be an "airliner to space" and would save money via high flight rates and quick turnaround times, despite the fact that all the experience of the program was telling them the exact opposite... but politically shuttle had to "prove it's worth" and the program managers and administrators were striving to 'hit their stride'... Shuttles flew 9 times in 1985 just before the accident, which is why the three prior scrubs of Challenger was SO troubling programmatically-- it was going to slow the entire program down and throw the entire schedule off for the rest of 1986... which played a big part in the decision to launch despite the rotten conditions...

Same thing with the foam issues... shuttles had been losing foam since the very first flight... some worse than others, but there had been foam loss nevertheless on virtually every flight. Some orbiters even came back with tile damage from foam strikes, and one even came back with a hole burned clean through the belly of the orbiter due to a tile knocked off by a foam strike and others nearby deeply gouged and cracked... fortunately the hole that burned through the felt underlayment to which the tiles are bonded and the aluminum skin to which the felt is bonded was located in an area where there were no critical systems, wiring, lines, etc. that were subsequently burned up by the hot gas impingement. So the problem was well understood, but simply "waved away" as "never having caused a serious issue before" (no harm, no foul) and the damage was considered "unfortunate but acceptable" and nobody stopped to say "but what if this happens to a CRITICAL area, like the wing leading edge or in an area of the belly with vehicle control wire looms just inside the skin, or hydraulic lines, etc. that would be burned through??" The question simply wasn't asked until the unthinkable happened...

Another problem that factored into both disasters was changes in materials... In the case of the O-rings on Challenger, the putty that was spread onto the abutting faces of the propellant on adjacent segments had its formulation changed-- the original spec putty contained ground up asbestos fibers in the putty carrier paste, but due to OSHA regs phasing out asbestos, the putty eventually became unavailable (even though the shuttle program had a waiver to the OSHA rules to continue procuring and using it for some time after the "ban")... It was replaced with a "substantially equivalent" putty that did not contain asbestos, but the new putty did not seal as well. The putty was only intended to provide a temporary seal in the first few milliseconds of the SRB ignition, to give the O-rings time to "blow into place" and seal from the pressure spike from the ignited SRB propellant. If the O-rings were a little too stiff (from cold, etc) or didn't get a perfect seal, they'd start to burn within a second or two due to hot gas erosion... if they sealed off, the trapped gases behind them cooled quickly and compressed, preventing hot gases from the burning propellant from flowing out and around the O-ring. The asbestos particles in the putty could also help seal because as the putty was burned away, the particles of asbestos could help "seal off the hole" by lodging in the gap and prevent excessive O-ring erosion, minimizing the damage and reducing the flow of hot gases through the leak. This wasn't the MAIN cause, but it was a contributory factor...

Similarly, the original spec spray-on foam used on the ET was different-- IIRC it used Freon as a carrier/propellant, and of course with the ban on Freon and restrictions on its use, shuttle operated under a waiver until the material became unavailable... then they switched to a more "green" foam application/material that was "substantially equivalent" but which was more prone to creating voids and holes in the foam in which liquid air could form, and also the foam did not have the same adhesion qualities or physical strength as the original foam did, leading to more shedding. Again, not the main cause, but contributory to it...

"Substantially equivalent" does not mean "exactly the same" and "no harm, no foul" is NOT a conducive to safety or an adequate safety program... and "Go Fever" is never a good idea... nor is allowing programmatic or political decisions, issues, or problems to overrule good common sense safety and engineering data, and previous experience pointing at potential problems...

Later! OL JR

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