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View Full Version : NASA STUDY SUMMARY: "Design Considerations for Orbital Transportation System"


luke strawwalker
03-02-2012, 04:03 PM
Here's an interesting study from July of 1967, looking at the various approaches and their relative merits, advantages, and disadvantages, to creating a reusable space transportation system (space shuttle). It's a rather illuminating study because, being from the early days of the consideration and study of such things, its refreshingly candid about the various possibilities and the factors influencing the choices that can be made, and the various effects of the assumptions made about the use and flight rates of such vehicles on the ultimate program costs and recurring expenses of such vehicles compared to then-existing expendable launch vehicles. It's a shame so many of the conclusions were lost in the rush to "justify" building a space shuttle in the wake of the Apollo program, which fell into many of the pitfalls predicted in this very report.

It's interesting to note that this study ultimately suggests developing a reusable spacecraft first, launched by the Saturn IB, which would itself cut costs of missions by about 40%, since the expendable Apollo spacecraft was such a large part of the mission costs... while at the same time it would allow for the gaining of experience on reusability, turnaround, and refurbishment issues that would affect the cost/benefit analysis of reusable space systems. This information would then be reintegrated into the program to develop a reusable first stage (powered glide back to runway landing) and went on to note that the reusable second stage was the riskiest and most expensive part of such a reusable space system, with the most uncertain cost/benefit ratio and also the most sensitive part of the system to flight rates, development costs, and turnaround, refurbishment, and integration/checkout costs of the whole system... IOW, this goes a LONG way to explaining WHY the shuttle we ended up with from 1981-2011 never lived up to the expectations set for it... expectations based on faulty assumptions, tradeoffs and compromises during design and development that came back to bite the most sensitive parts of reusable vehicle development... the dependency on high flight rates to amortize costs, and the high sensitivity of cost estimates to ACTUAL refurbishment and turnaround times, as well as integration and checkout costs and how they all contribute to ongoing program recurring costs. In point of historical fact, the shuttle basically proved that you can either spend the same amount of money doing expensive refurbishment and turnaround and doing integration and checkout of an expensive, complicated reusable vehicle, or spend the same amount of money repeatedly buying and replacing expendable vehicles and doing integration and checkout on them and foregoing the expensive and time consuming refurbishment and turnaround of the reusable systems.

Basically, this study lays out the fact that CHEAPER and REUSABLE are NOT synonymous when it comes to spacecraft and spaceflight operations paradigms... and this at the VERY BEGINNING of serious contemplation of space shuttle design. The fact that the study recommends the development of a reusable runway-landing spacecraft as a first step, and then development of flyback first stages to further lower costs, shows the pragmatism of the engineers when looking at things how they actually are rather than how some wished them to be (and used such wishes to justify building a space shuttle, using faulty rosy assumptions that this study honestly warned were the most sensitive factors contributing to the economic savings or lack thereof, which was the entire reason upon which switching to a shuttle was predicated.) IOW, garbage in, garbage out! It also frankly discusses the design difficulties and performance tradeoffs involved in designing a reusable vehicle for both polar and low-inclination "eastward" equatorial orbits and how that negatively effects the design weight (and hence another of THE most sensitive aspects of reusable upper stages (IE orbiters) desing, construction, and economic efficiency) and capabilities of the vehicle, and therefore its affordability and efficiency. This too was a decision that would come to haunt the shuttle program, when it was conceived as a 'dual use' vehicle for the military and the civilian space program and therefore required to be designed for both military polar launches and mostly civilian space program equatorial low inclination orbit launches. In point of historical fact, the very decisions that encumbered the shuttle program and forced the design tradeoffs that in many ways ultimately contributed to the shuttle being the inefficient, low flight rate, uber-expensive vehicle it turned out to be, were in fact NEVER UTILIZED as the Challenger disaster and escalating costs ultimately demonstrated both the futility and narrow sightedness of relying on a complex and sophisticated MANNED vehicle for basic satellite launches and the benefits of using simpler, unmanned (even if expendable) vehicles for that role, which the military was learning through experience the preferability of unmanned satellites for the performance of their missions. Had these unfortunate design tradeoffs not been forced onto the space shuttle system to enable manned polar launches and other such 'dual use' considerations (which drove the requirement for the large payload bay, high crossrange requiring a large delta wing, etc.) then the entire shuttle program would likely have unfolded in a VERY different manner. Further, had the recommendations to proceed with a more incremental design concept been adopted, it's quite likely that the entire shuttle program would have evolved into something virtually unrecognizable from our modern historical viewpoint. It also just goes to show that "everything old is new again" as the lessons learned (forcibly via Challenger and Columbia as it turns out) come around again-- we currently have the Air Force flying a small, reusable UNMANNED spaceplane for certain missions (X-38B) following an incremental design concept by launching not from a fully reusable booster vehicle, but from existing expendable EELV launch vehicles (Atlas V). We also have one of the CCDev "independent commercial spaceflight companies" pursuing their "Dreamchaser" spaceplane, again to be launched atop an existing expendable booster (again, Atlas V) as an incremental development step perhaps to a more reusable system at some point in the future, as evidenced by the present Air Force studies into flyback booster replacements for the existing EELV rockets (Atlas V and Delta IV). This mirrors NASA's own thinking on the subject as shown in this report and evidenced by the Orbital Space Plane (OSP) project which was supposed to be a follow-on shuttle replacement for crew launch and limited cargo, again, a small reusable spacecraft launched atop existing expendable booster, again, a heavy variant of Atlas V or Delta IV heavy (OSP succumbed to the changes in priorities caused by the Columbia disaster which reoriented manned spaceflight over the long term from LEO operations back into something worthy of risking death, IE deep-space exploration, and was therefore canceled due to the superiority of CEV reusable capsule designs over reusable small spaceplane designs for missions beyond Earth orbit). Now, we are coming full circle as the reusable CEV designs in the beginning of the Constellation program, designed to replace shuttle, have had most of their reusability features designed out (land landings and such) in favor of expendable capsules. Of course given the infrequent flight rates of such missions, this is probably the most cost-effective way to do it anyway, since refurbishment costs are highly sensitive to flight rates as spelled out in this report.

It's a fascinating read and really shows the "why's" that led to many of the things that are now historical fact... and how a combination of bad decisions, bad tradeoffs, and willful self-delusion to justify design concepts is never a good idea.

Plus there are a few cool designs along the way that lend themselves to future/fantasy scale or just interesting sport rocket projects...

Enjoy! OL JR

luke strawwalker
03-02-2012, 04:05 PM
And here's the pics from the study...

Various rocket concepts studied, both series and parallel staged, vertical takeoff and horizontal takeoff, rocket and airbreather powered...

Reusable system characteristics...

A closeup of the Horizontal Take Off (HTO) design, using a rocket-powered sled to boost the vehicle up to takeoff speeds from the ground...

The Vertical Take Off (VTO) system, similar to the HTO in basic design (but with some important differences that proved beneficial) again powered completely by rockets and having both stages parallel staged and completely reusable...

The baseline rocket systems compared...

More later! OL JR

luke strawwalker
03-02-2012, 04:07 PM
The mission profile on ascent...

The mission profile on descent...

Typical "decoupled" landing modes, which were recommended to allow the development of the vehicles to be optimized for hypersonic flight and abort considerations, while allowing optimization for subsonic landing considerations later in the flight profile... but it adds a LOT of complexity, cost, and risk to the design for the additional performance and safety benefits...

The benefits of a detachable "slipper" mounted ablative heat shield for vehicle turnaround, inspection, and refurbishment time was obvious...

Incremental development approaches using existing rocket components and integrating reusable systems elements in various ways... reusable spacecraft first, or reusable first stage first with existing spacecraft, etc...

Later! OL JR

luke strawwalker
03-02-2012, 04:10 PM
Incremental design approaches compositions...

The composition of incremental design approaches...

Preliminary concept evaluations...

Total systems costs compared to various projected launch flightrates...

Development sequence evaluations for cost/benefit analysis of IDA (proposal) 5...

That's it for this one... Later! OL JR