Human Spaceflight Myth-busting

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“Urban myth,” Wikipedia tells us, “is a form of modern folklore consisting of stories thought to be factual by those circulating them.” More often than not, any kernel of truth at the core of the stories is somewhat exaggerated in their modern retelling. As we recede from the 40th anniversary of the first steps taken by humans on another world, it has become clear that the intervening time has allowed for many myths to arise in the exploration folklore. And those myths have now led us down a dead-end, almost certainly unsustainable, path back to where we started.

One such myth is the idea that “bigger is better.” Since the dawn of the space age, the people who build rockets have almost continuously sought to make them bigger, enabling larger and larger payloads to be thrown intact into orbit. The behemoths are needed, we are told, for a number of reasons, mostly mythical as well: integrated testing of multi-module equipment on the ground is too complicated; assembly on orbit is risky; extravehicular activities (EVAs) are dangerous; high flight rates lead to logistics logjams; and multiplicative probabilities of failure in piece-wise assembled systems result in lower mission reliabilities.

Yet, somehow, the international space station (ISS) complex is on orbit. It has been incrementally assembled from smaller pieces of international origin. And while they may never become routine, the 253 EVAs to date were mostly regular non-events. As many as 19 flights from all partner countries are scheduled for lift-off to ISS next year and are being accommodated logistically. Lifetime projections for this modular assembly now run out to the vicinity of 2028. Pretty good numbers for such an “improbable” vehicle.

The space shuttle came into being on a multiuse premise, sharing now extinct requirements with the Department of Defense. Heavy-lift launch vehicles initially configured for human spaceflight cargo are once again being sold for their ability to loft larger, more complex science payloads as well. Of course, with an infrastructure- and operations-dominated budget, one has to ask just where the extra funds will come from to develop and build the multibillion-dollar telescopes that would justify the infrequent use of such lifting capability? We are told that human missions to Mars will require multiple launches in short periods of time to loft mass on the order of the size of the ISS. Yet, a heavy-lifter approach that puts a significant fraction of one-of-a-kind, high-value mission hardware on a single launcher, bets the program each time ignition occurs.

“Heritage is faster,” is another myth holding us back. We have now driven that into the heads of undergraduate engineers so hard that most have lost the ability to innovate and typically start with an existing design to claim cost advantages for the development of their senior design projects. Still, any advantages of starting with off-the-shelf hardware are immediately mitigated by the first swipe of the refining pencil.

Consider the history, still on paper, of the Ares 1 and 5. Four-segment solid-rocket boosters, common with the space shuttle have now mutated into brand new five-segment boosters, with different propellant grain, nozzles, stiffened structure and thrust oscillation characteristics. The shuttle external tank design has to be modified to handle the compression caused by five or six rocket engines pushing from below. These “heritage” designs require all of the structural and thermal loads analysis and testing that a clean sheet design would require along with band aids addressing the original design’s inefficiencies. Accordingly, preliminary design reviews and critical design reviews have gapped to the right from their original heritage-based streamlined prognostications.

Finally, consider the myth that the “time and expense to man-rate an Evolved Expendable Launch Vehicle (EELV) is prohibitive.” A cold-hearted analysis of the same launch vehicle that today carries billion-dollar satellites to orbit and are insured at market set rates reveal that they are reliable enough to carry humans with less actuarial value. If you are uncomfortable with that view, then the addition of an ultra-reliable launch abort system should be on your critical path. A stock Delta 4 or Atlas 5 could be flying humans the day after that abort system is available, albeit with the heightened initial possibility of a higher number of aborts pulling astronauts to safety. Over time, these rockets can be incrementally improved upon with redundancy and health management systems, but those improvements need not hold back a waiting Orion or Commercial Orbital Transportation Services program vehicle.

If we leave these and the other accumulated myths of the last 40 years behind, we could employ existing assets to assemble missions on orbit to the destinations of our choosing. Using the ISS as a transportation hub, we could spend our precious resources on developing the landers, habitation and surface systems we need to homestead in deep space without redesigning, yet again, the pieces we already have. Such an approach will reinvigorate and attract the innovation of graduating students desiring to work on something new instead of their grandfather’s retread. And, with international and commercial participation, we could start an expansive program of exploration the day after the venerable space shuttle retires.

I encourage the august group of men and women reviewing the options for human spaceflight, and the architectures to carry out these missions, to consider the reliability of these myths, which for so long have held back progress and stymied out-of-the-box thinking. Smaller packages, flown more frequently, benefit from mass production economics and improvements from multiuse reliability. Much as the steady moving tortoise overcame the gap with the swifter, mocking hare, so too will our exploration endeavors benefit from a re-reading of the fairy tales holding back the realization of our spacefaring dreams.

 


Michael F. Lembeck, Ph.D., was the requirements division director of NASA’s Exploration Systems Mission Directorate during the formation of the Vision for Space Exploration and is currently vice president for engineering at DCI Services and Consulting in
Houston
.