Here's an interesting study from June 1986 (shortly after the Challenger disaster that occurred at the end of January of that year) about the various ideas proposed for the shuttle and how technology (or lack of it) played into the decisions that were made. It's a pretty long summary, because there was very little in the 121 pages of the study that weren't particularly applicable and relevant. So, the best I could do is paraphrase and get rid of the all the extra verbiage and flowery engineer-speak and try to thin the herd enough to make it readable...

The thing is CHOCK FULL of GREAT info on the shuttle, and really brings to light WHY the shuttle ended up like it did, and WHY it never really had a chance to meet the expectations set for it from the day it was approved... expectations based on overly optimistic assumptions about flight rates, refurbishment, turnaround time between launches, program costs and component (like External Tank) costs, etc... some of the assumptions weren't just overly optimistic, they were completely ludicrous. Things like "the shuttle concepts using a disposable external tank can be competitive costwise with totally reusable shuttle concepts if External Tank costs can be reduced from $75 a pound to $20 a pound." The REAL costs for the External Tank-- $321 a pound in 1982 dollars... (and they've inflated a LOT since then!!!) This is but one example... the entire shuttle program is RIFE with such examples...

Then there are facets of shuttle operations and such that I for one had never considered before. Things that really impact the utility and flexibility of reusable shuttle type systems, and why they simply aren't suited for some missions (like the exploration missions that NASA is apparently set its course towards for the future). The shuttle, retaining the weight of its engines, wings, landing gear, massive heat shield to protect it all, systems used only on ascent, or only on reentry, or only on glide and landing, throughout the whole mission, but which contribute NOTHING to those phases of the mission... and which are MUCH heavier than simpler systems (like parachutes instead of wings and control systems and landing gear, etc.) People denigrated the "return to stupid capsules" for exploration in the post-shuttle era, but this report really makes the case that, from a technological and goal achievement point of view, the shuttle was a dead end off the road toward more capable and hopefully more affordable space exploration vehicles. It also points out the rightful role of shuttle type vehicles-- crew transport to LEO. This should demonstrate the lessons learned when inevitably at some point in the future, another glide-landing reusable spacecraft is proposed, funded, and designed. The factors, sensitivities, and realities are the same and equally valid today as they were forty years ago when shuttle systems were the preferred choice for the future. Now we have the demonstrated weaknesses and limitations of such systems, which is a valuable contribution in itself that the shuttle has provided.

Enjoy the read... Later! OL JR

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NASA STUDY SUMMARY- Tech Influence on Shuttle Development.txt (79.0 KB, 50 views)

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The full chart showing shuttle evolution through the concept phase...

Shuttle program objective... in a nutshell...

Shuttle cost comparisons... various concepts...

Shuttle turnaround comparison... 1972 baseline versus 1986 reality... shuttle was predicated and the whole idea justified on the basis that MASSIVE savings were possible with a fully reusable spacecraft, flying VERY often (up to 100 flights per year by some early estimates-- 60 flights per year was a basic goal (if unattainable), and having rapid turnaround time with little maintenance requirements. Of course a slip or mistaken assumption of ANY of these factors could RAPIDLY reduce any savings to the point that a reusable shuttle was no more efficient or cost-effective than the existing expendable systems it replaced, perhaps even less, and CERTAINLY less than simplified systems designed for low cost, simplicity, and realistic flight rates. Shuttle missed the mark on ALL these factors, and in fact as the design progressed through the concept phase, it strayed further and further from the very idea it was predicated upon. So it's no wonder the shuttle ended up SO very costly, even costlier than Saturn V and Apollo was on some metrics...

One interesting proposal, that would have made a LOT more sense and was actually supported in some quarters (but unfortunately not where it counted) was the reusable spacecraft atop a simplified, low-cost design expendable booster. At the flight rates the shuttle ultimately proved itself actually capable of (rather than TOTALLY unrealistic projections when it was designed) this approach was actually much better. That's why the idea has come around again-- the Dreamchaser reusable runway-landing spacecraft launched atop a "low cost" disposable Atlas V launch vehicle... (well, lower cost than shuttle anyway!) The vehicle itself in this picture bears a striking resemblance to the Dr. Zooch Lifting Body...

More to come! OL JR

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The 1 1/2 stage concept... a shuttle lifting itself and its propellant, partially or wholly stored in external drop tank(s). It required about 3X or more the main propulsion system as boosted designs, while still having the (underestimated) expense of a disposable tank(s)...

Fully reusable concepts, which were of course the lowest cost (by virtue of not throwing anything away but fuel). The Triamese was designed around the idea of three virtually identical vehicles, joined together in parallel, with the other two acting as "boosters" to the orbiter, providing its engines with propellant and carrying only fuel for the booster engines and orbiter engines as payload, while the orbiter itself carried the payload and crew to orbit. In effect, these were 'flyback boosters' designed identically to the orbiter airframe themselves to the extent possible. The "parallel/parallel" design reduced this arrangement to a single larger booster vehicle, carrying fuel for itself and the orbiter's engines, with the orbiter acting as a second stage, which lowered booster vehicle count, but meant there was little in common between the two vehicles. The "parallel/sequential" was a modification of this idea-- the booster acting as a first stage, lifting the whole stack to the staging point, at which point the orbiter engines would ignite and the orbiter continue on into space with the booster returning to the runway. "MSC" is the design favored by the Manned Spacecraft Center, the so-called "Faget shuttle" design with straight wings and a regular airplane type appearance. The last concept was the Langley Research Center design, using a nested arrangement...

Various concepts for a "shuttle" were proposed, with varying levels of simplicity or complexity, expendable parts or reusable parts, series burn or parallel burn, and various shapes and designs. The simplist was a large expendable SRM first stage lifting an expendable low-cost design high energy second stage to inject a reusable spaceplane in orbit-- what we call today "Dreamchaser" or in a previous iteration, "Orbital Space Plane (OSP)" More sophisticated designs moved up through the self-launching orbiter supported fueled by drop tanks, to the biamese and triamese concepts which were the most complicated...

The operational modes of various concepts from the previous pic...

The flight rates or "traffic" as they called it here (another colloquialism meant to blur the obvious distinctions between airliners flying common routes and spacecraft flying orbital missions). Note the rediculous projections and unrealistically high flight rates. It's a little like saying I can win the Indy 500 in a fully loaded semi "if only A, B, and C" or saying I can build the Keystone pipeline with only a used Yugo "if only X, Y, and Z". Another proof figures don't lie, but liars figure...

More coming! OL JR

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Mission requirements and characteristics for shuttle systems...

Technical risks and technology requirements of various proposals...

Cost projections in 1969 dollars for various concepts... development and operations costs...

Recurring (per flight) cost comparisons...

Recurring costs per launch of various concepts...

More later! OL JR

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Some Phase B shuttl design size comparisons (which could make interesting models!)...

Orbiter comparisons- internal versus external tank designs. Internal tanks went away for a couple reasons. First and foremost, nobody was sure how to build tanks that were certain to hold up under the repeated stresses of powered launch with the weight of the propellants, zero gee, reentry, and the forces and vibrations of landing, as well as handle the constant thermal cycling of holding propellants ranging from about minus 300 degrees or more to absorbing considerable heat from the surrounding structures heated by reentry, and be guaranteed not to leak or fail. The complexities of constructing an odd-shaped pressure vessel to fit within the airframe was another concern, and have it withstand the repeated pressurization for launch without getting stress fatigue, and have it still be light enough to actually make a shuttle feasible (IE not eat up all the payload capability with overweight tanks). The other issue was insulation, in that the tanks had to be EXTREMELY well insulated to prevent the formation of ice within the structure of the orbiter and protect the tanks and external surfaces of the orbiter itself, as well as other structural parts, from ice in the case of LOX and from liquified air itself (which is highly flammable) in the case of the much colder liquid hydrogen tank. Another big issue that was unsolved was "how to inspect such tanks to ensure they weren't developing cracks, deformities, or other issues that might cause them to fail?" Tanks are typically overpressure-tested or subjected to intense scrutiny mechanically or by various means... how to do this with tanks buried deep in a fuselage (which overpressure testing would likely destroy the orbiter in event of a tank failure during testing) without removing the tanks or insulation (a very time consuming and therefore expensive process) was never really solved. Hence the switch to the expendable External Tank...

The SSME's were another area where the development program was vastly underestimated given the goals that were set for it... The SSME, a large, high thrust, staged combustion, high pressure, 100 flight reusable with minimal maintenance, LO2/LH2 rocket engine, which was basically a quantum leap in propulsion technology from anything that's been attempted before or since (with the possible exception of F-1, though it's nowhere NEAR as sophisticated, but it WAS an ENORMOUS engine for its time and broke new ground in that regard, and had the requisite development problems of ANY grounbreaking technology when it's first attempted). Note the "resources" dedicated to F-1 and J-2 development, even RL-10 (the first hydrogen burning engine, which again was a groundbreaking achievement). Yet SSME, which was much a much more sophisticated design, was to be achieved on only a fraction of the resources dedicated to these earlier projects...

Comparisons of aerospike and bell engine installations. Aerospikes had been flirted with for a considerable part of the 60's as possible upgrades to Saturn V (see a number of the other NASA Study Summaries posted in this section of the forum) such as the HG-3 high-pressure engine (which in some respects was a forerunner to SSME. Aerospikes, while attractive in some regards, were generally heavier and also more problematical to install and service, which is why they were passed over for the more conventional bell nozzle arrangement... There were enough unknowns in the world of staged combustion high pressure SSME's without adding the complexities of aerospike or plug nozzles...

Another big question in shuttle concept development was whether to go with the series or parallel burns. Both had advantages and disadvantages. Ultimately the parallel burn model won out. Series burn made the vehicle taller and while it protected the orbiter from more debris, it also made a much heavier gross liftoff weight (GLOW). It's main advantage was that it made the vehicle much more decoupled, meaning that later upgrades to the booster stage(s), ET, or the orbiter design itself could be integrated much much easier. BUT, it required an airstart of the highly finicky SSME's which were being developed, a pretty big unknown. Parallel burn vehicles kept the vehicle more compact (shorter), though that also put the orbiter down into the area of greater risk from debris and such (which ultimately led to the loss of two orbiters when Challenger disintegrated after the SRB demolished the ET and Columbia was fatally struck by debris that pierced its TPS and caused it to break up on reentry). BUT, the parallel arrangement made the entire stack quite a bit lighter at liftoff, and also allowed for the start and checkout of the SSME's before the vehicle lifted off the pad...

More coming! OL JR

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The X-87B Cruise Basselope-- THE Ultimate Weapon in the arsenal of Homeland Security and only $52 million per round!

Flight vehicle evolution, Phase C/D, 1972 to 73. Notice the differences as the shuttle evolved, in how it was mated to the ET (also how the SRB's were mounted), the ET nose design changes (from conical to ogive), the deletion of the ET deorbit retro SRM on the nose, and the changes to the orbiter nose section itself and the OMS pods...

The orbiter TPS was another one of those areas of cutting edge development that could make or break the entire vehicle as far as its cost goals were concerned. The original design with internal tanks, straight wings and tailplane, (the Faget Shuttle) was sufficiently "fluffy" (surface area to weight ratio, returning with those empty tanks) that it could reenter with a simple metallic heatshield-- so called "hot structures" similar to SR-71 and X-15. When the larger external tank delta wing high-crossrange large payload bay (AF requirements) shuttle design took over, it was too heavy and too small for its weight to use this relatively simple system. Therefore a heatshield of some sort became mandatory. Refractory metal heatshields were rejected on the basis of weight and oxidation concerns, as well as mounting and maintenance. Eventually, silica tiles were chosen, though this was far from the panacea promised by the proponents of it... shuttle tiles were notoriously brittle and a maintenance nightmare, and the fragility of the TPS led to the fatal loss of one orbiter...

SRB's were chosen over LRB's (liquid rocket boosters) fairly early in the design process, simply due to economics. Shuttle was designed "on the cheap" because, of all the proposals they took to Nixon, he only approved the cheapest one (which incidentally had the highest recurring costs per flight, which is EXACTLY what we got, although to a degree NOBODY would have EVER expected in 1972-73). SRB's were another of those things that looked good on paper but turned out differently in real life. The safety benefits were farcical, as was demonstrated by the loss of Challenger in 1986, and they ultimately proved VERY expensive and limiting to the growth and flexibility of the system due to their "maxing out" the supporting infrastructure, and not sharing costs with any other system. LRB's could be shut down in flight in the event of emergency, but it came down to simple economics-- and boosters were where the design was 'cheapened up' to spend money on more pressing issues (like SSME development, structures, TPS, avionics, etc...) Here's the basic specs on the SRB's...

Originally, the External Tank was to be carried all the way into orbit along with the orbiter itself. This created a problem, as nobody wanted a 150 or so foot long 28.5 foot diameter house-sized tanks floating around up there until their orbit finally degraded and they reentered uncontrolled, over who knows where, and burned up/ broke up. SO, the ET was to be fitted with a "deorbit motor" on its nose, sort of like a backward facing escape rocket. Once the ET was jettisoned in orbit, a system installed in the ET would maintain a radio link with the orbiter, and monitor the ET's attitude and direction as it coasted around the Earth with the orbiter, slowly drifting apart. At the correct time, the deorbit motor would fire, slowing the ET down enough for it to reenter the atmosphere and burn/break up over the Indian or South Pacific Oceans. This system proved to be costly and another risk of failure, which potentially, depending on the nature of the failure, could risk the vehicle in the event of a malfunction. SO, a manager in the shuttle office proposed dumping the whole system, and going with simply shutting down the SSME's a BIT before reaching orbital velocity, at a point where the perigee of the orbit halfway around the world would still be well down into the atmosphere. The shuttle would jettison the tank, and then fire its OMS engines at apogee to raise the orbital perigee and attain orbit. The discarded tank would continue on the suborbital hyperbolic trajectory, entering the atmosphere above the Indian or South Pacific Ocean and burning/breaking up. This saved an estimated $62 million per flight...

There were a number of upgrades to the shuttle, some occurring before it ever flew, and these upgrades continued throughout the program, to greater or lesser degrees. One such upgrade was the concept of disposable filament wound SRB cases. These were proposed when the polar orbit shuttle performance had fallen below that needed by the Air Force for its California launched national security missions which were planned. After looking at concepts such as adding small SRM's to the SRB's (similar to Atlas or Delta) or even installing extra engines under the external tank from other rockets, Hercules proposed ditching the heavy reusable steel SRB casings and using much lighter weight disposable Filament Wound Casings, (FWC's). Since the filament wound casings, like their ballistic missile counterparts, were by necessity expendable, this would also mandate the deletion of the heavy recovery gear from the SRB's as well. The weight savings were sufficient to return the payload capacity lost for the lower-efficiency launches to polar orbits. Hercules and Morton Thiokol, the SRB manufacturer, were contracted to study the concept and come up with designs, which they did, even coming up with designs that would retain the well-known and understood field joints used at KSC to assemble the rocket segments together into functional SRB's, by using steel adapter rings on either end of the filament wound casing segments. These "Advanced SRB's" (ASRBs) were ultimately canceled-- their original Air Force mission had evaporated in the post-Challenger shakeup that saw the Air Force withdraw from shuttle and pursue expendable launch vehicles for their national security payloads, and while the ASRB's promised considerable payload increases for ISS construction missions, funding was ultimately cut and canceled. Some of the test casings for the ASRB's survived though-- they're on display as part of the shuttle mockup standing behind the US Space and Rocket Center in Huntsville, Alabama, standing in for the heavier (and still in use at the time) steel cased SRB's, flanking a test and development ET in their shuttle mockup.

They didn't even cover Shuttle/Centaur, which was being readied for flight at the time of the Challenger disaster and was canceled soon after as "too dangerous" to fly aboard shuttle, therefore leaving missions like Galileo in a lurch for several years until alternatives were developed. I guess that was just too fresh at the time this report was written. This report has a lot of lessons that are equally valid in most cases today as they were in 72 or 82 or 92 or 02... it appears to have been written in part of the "soul searching" NASA went through post-Challenger, when there were REAL doubts as to whether shuttle would (or SHOULD) continue or whether something else should be designed to take its place, which actually happened with the National Launch System, a 'shuttle derived' family of launch vehicles that used "off the shelf" shuttle propulsion elements as the basis for new booster designs, to loft a new manned expendable capsule with a launch escape system (which would theoretically prevent a Challenger type crew loss in the future).

Later! OL JR

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The X-87B Cruise Basselope-- THE Ultimate Weapon in the arsenal of Homeland Security and only $52 million per round!