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Saturday, October 17, 2009

Reading List: The Nuclear Rocket

Dewar, James with Robert Bussard. The Nuclear Rocket. Burlington, Canada: Apogee Books, 2009. ISBN 978-1-894959-99-5.
Let me begin with a few comments about the author attribution of this book. I have cited it as given on the copyright page, but as James Dewar notes in his preface, the main text of the book is entirely his creation. He says of Robert Bussard, “I am deeply indebted to Bob's contributions and consequently list his name in the credit to this book”. Bussard himself contributes a five-page introduction in which he uses, inter alia, the adjectives “amazing”, “strange”, “remarkable”, “wonderful”, “visionary”, and “most odd” to describe the work, which he makes clear is entirely Dewar's. Consequently, I shall subsequently use “the author” to denote Dewar alone. Bussard died in 2007, two years before the publication of this book, so his introduction must have been based upon a manuscript. I leave to the reader to judge the propriety of posthumously naming as co-author a prominent individual who did not write a single word of the main text.

Unlike the author's earlier To the End of the Solar System (June 2008), which was a nuts and bolts history of the U.S. nuclear rocket program, this book, titled The Nuclear Rocket, quoting from Bussard's introduction, “…is not really about nuclear rocket propulsion or its applications to space flight…”. Indeed, although some of the nitty-gritty of nuclear rocket engines are discussed, the bulk of the book is an argument for a highly-specific long term plan to transform human access to space from an elitist government run program to a market-driven expansive program with the ultimate goal of providing access to space to all and opening the solar system to human expansion and eventual dominion. This is indeed ambitious and visionary, but of all of Bussard's adjectives, the one that sticks with me is “most odd”.

Dewar argues that the NERVA B-4 nuclear thermal rocket core, developed between 1960 and 1972, and successfully tested on several occasions, has the capability, once the “taboo” against using nuclear engines in the boost to low Earth orbit (LEO) is discarded, of revolutionising space transportation and so drastically reducing the cost per unit mass to orbit that it would effectively democratise access to space. In particular, he proposes a “Re-core” engine which, integrated with a liquid hydrogen tank and solid rocket boosters, would be air-launched from a large cargo aircraft such as a C-5, with the solid rockets boosting the nuclear engine to around 30 km where they would separate for recovery and the nuclear engine engaged. The nuclear rocket would continue to boost the payload to orbital insertion. Since the nuclear stage would not go critical until having reached the upper atmosphere, there would be no radioactivity risk to those handling the stage on the ground prior to launch or to the crew of the plane which deployed the rocket.

After reaching orbit, the payload and hydrogen tank would be separated, and the nuclear engine enclosed in a cocoon (much like an ICBM reentry vehicle) which would de-orbit and eventually land at sea in a region far from inhabited land. The cocoon, which would float after landing, would be recovered by a ship, placed in a radiation-proof cask, and returned to a reprocessing centre where the highly radioactive nuclear fuel core would be removed for reprocessing (the entire launch to orbit would consume only about 1% of the highly enriched uranium in the core, so recovering the remaining uranium and reusing it is essential to the economic viability of the scheme). Meanwhile, another never critical core would be inserted in the engine which, after inspection of the non-nuclear components, would be ready for another flight. If each engine were reused 100 times, and efficient fuel reprocessing were able to produce new cores economically, the cost for each 17,000 pound payload to LEO would be around US$108 per pound.

Payloads which reached LEO and needed to go beyond (for example, to geostationary orbit, the Moon, or the planets) would rendezvous with a different variant of the NERVA-derived engine, dubbed the “Re-use” stage, which is much like Von Braun's nuclear shuttle concept. This engine, like the original NERVA, would be designed for multiple missions, needing only inspection and refuelling with liquid hydrogen. A single Re-use stage might complete 30 round-trip missions before being disposed of in deep space (offering “free launches” for planetary science missions on its final trip into the darkness).

There is little doubt that something like this is technically feasible. After all, the nuclear rocket engine was extensively tested in the years prior to its cancellation in 1972, and NASA's massive resources of the epoch examined mission profiles (under the constraint that nuclear engines could be used only for departure from LEO, however, and without return to Earth) and found no show stoppers. Indeed, there is evidence that the nuclear engine was cancelled, in part, because it was performing so well that policy makers feared it would enable additional costly NASA missions post-Apollo. There are some technological issues: for example, the author implies that the recovered Re-core, once its hot core is extracted and a new pure uranium core installed, will not be radioactive and hence safe to handle without special precautions. But what about neutron activation of other components of the engine? An operating nuclear rocket creates one of the most extreme neutronic environments outside the detonation of a nuclear weapon. Would it be possible to choose materials for the non-core components of the engine which would be immune to this and, if not, how serious would the induced radioactivity be, especially if the engine were reused up to a hundred times? The book is silent on this and a number of other questions.

The initial breakthrough in space propulsion from the first generation nuclear engines is projected to lead to rapid progress in optimising them, with four generations of successively improved engines within a decade or so. This would eventually lead to the development of a heavy lifter able to orbit around 150,000 pounds of payload per flight at a cost (after development costs are amortised or expensed) of about US$87 per pound. This lifter would allow the construction of large space stations and the transport of people to them in “buses” with up to thirty passengers per mission. Beyond that, a nuclear single stage to orbit vehicle is examined, but there are a multitude of technological and policy questions to be resolved before that could be contemplated.

All of this, however, is not what the book is about. The author is a passionate believer in the proposition that opening the space frontier to all the people of Earth, not just a few elite civil servants, is essential to preserving peace, restoring the optimism of our species, and protecting the thin biosphere of this big rock we inhabit. And so he proposes a detailed structure for accomplishing these goals, beginning with “Democratization of Space Act” to be adopted by the U.S. Congress, and the creation of a “Nuclear Rocket Development and Operations Corporation” (NucRocCorp), which would be a kind of private/public partnership in which individuals could invest. This company could create divisions (in some cases competing with one another) and charter development projects. It would entirely control space nuclear propulsion, with oversight by U.S. government regulatory agencies, which would retain strict control over the fissile reactor cores.

As the initial program migrated to the heavy lifter, this structure would morph into a multinational (admitting only “good” nations, however) structure of bewildering (to this engineer) bureaucratic complexity which makes the United Nations look like the student council of Weemawee High. The lines of responsibility and power here are diffuse in the extreme. Let me simply cite “The Stockholder's Declaration” from p. 161:

Whoever invests in the NucRocCorp and subsequent Space Charter Authority should be required to sign a declaration that commits him or her to respect the purpose of the new regime, and conduct their personal lives in a manner that recognizes the rights of their fellow man (What about woman?—JW). They must be made aware that failure to do so could result in forfeiture of their investment.

Property rights, anybody? Thought police? Apart from the manifest baroque complexity of the proposed scheme, it entirely ignores Jerry Pournelle's Iron Law of Bureaucracy: regardless of its original mission, any bureaucracy will eventually be predominately populated by those seeking to advance the interests of the bureaucracy itself, not the purpose for which it was created. The structure proposed here, even if enacted (implausible in the extreme) and even if it worked as intended (vanishingly improbable), would inevitably be captured by the Iron Law and become something like, well, NASA.

On pp. 36–37, the author likens attempts to stretch chemical rocket technology to its limits to gold plating a nail when what is needed is a bigger hammer (nuclear rockets). But this book brings to my mind another epigram: “When all you have is a hammer, everything looks like a nail.” Dewar passionately supports nuclear rocket technology and believes that it is the way to open the solar system to human settlement. I entirely concur. But when it comes to assuming that boosting people up to a space station (p. 111):

And looking down on the bright Earth and into the black heavens might create a new perspective among Protestant, Roman Catholic, and Orthodox theologians, and perhaps lead to the end of the schism plaguing Christianity. The same might be said of the division between the Sunnis and Shiites in Islam, and the religions of the Near and Far East might benefit from a new perspective.

Call me cynical, but I'll wager this particular swing of the hammer is more likely to land on a thumb than the intended nail. Those who cherish individual freedom have often dreamt of a future in which the opening of access to space would, in the words of L. Neil Smith, extend the human prospect to “freedom, immortality, and the stars”—works for me. What is proposed here, if adopted, looks more like, after more than a third of a century of dithering, the space frontier being finally opened to the brave pioneers ready to homestead there, and when they arrive, the tax man and the all-pervasive regulatory state are already there, up and running. The nuclear rocket can expand the human presence throughout the solar system. Let's just hope that when humanity (or some risk-taking subset of it) takes that long-deferred step, it does not propagate the soft tyranny of present day terrestrial governance to worlds beyond.

Posted at October 17, 2009 01:05