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Wednesday, June 11, 2008

Reading List: To the End of the Solar System

Dewar, James A. To the End of the Solar System. 2nd. ed. Burlington, Canada: Apogee Books, [2004] 2007. ISBN 978-1-894959-68-1.
If you're seeking evidence that entrusting technology development programs such as space travel to politicians and taxpayer-funded bureaucrats is a really bad idea, this is the book to read. Shortly after controlled nuclear fission was achieved, scientists involved with the Manhattan Project and the postwar atomic energy program realised that a rocket engine using nuclear fission instead of chemical combustion to heat a working fluid of hydrogen would have performance far beyond anything achievable with chemical rockets and could be the key to opening up the solar system to exploration and eventual human settlement. (The key figure of merit for rocket propulsion is “specific impulse”, expressed in seconds, which [for rockets] is simply an odd way of expressing the exhaust velocity. The best chemical rockets have specific impulses of around 450 seconds, while early estimates for solid core nuclear thermal rockets were between 800 and 900 seconds. Note that this does not mean that nuclear rockets were “twice as good” as chemical: because the rocket equation gives the mass ratio [mass of fuelled rocket versus empty mass] as exponential in the specific impulse, doubling that quantity makes an enormous difference in the missions which can be accomplished and drastically reduces the mass which must be lifted from the Earth to mount them.)

Starting in 1955, a project began, initially within the U.S. Air Force and the two main weapons laboratories, Los Alamos and Livermore, to explore near-term nuclear rocket propulsion, initially with the goal of an ICBM able to deliver the massive thermonuclear bombs of the epoch. The science was entirely straightforward: build a nuclear reactor able to operate at a high core temperature, pump liquid hydrogen through it at a large rate, expel the hot gaseous hydrogen through a nozzle, and there's your nuclear rocket. Figure out the temperature of exhaust and the weight of the entire nuclear engine, and you can work out the precise performance and mission capability of the system. The engineering was a another matter entirely. Consider: a modern civil nuclear reactor generates about a gigawatt, and is a massive structure enclosed in a huge containment building with thick radiation shielding. It operates at a temperature of around 300° C, heating pressurised water. The nuclear rocket engine, by comparison, might generate up to five gigawatts of thermal power, with a core operating around 2000° C (compared to the 1132° C melting point of its uranium fuel), in a volume comparable to a 55 gallon drum. In operation, massive quantities of liquid hydrogen (a substance whose bulk properties were little known at the time) would be pumped through the core by a turbopump, which would have to operate in an almost indescribable radiation environment which might flash the hydrogen into foam and would certainly reduce all known lubricants to sludge within seconds. And this was supposed to function for minutes, if not hours (later designs envisioned a 10 hour operating lifetime for the reactor, with 60 restarts after being refuelled for each mission).

But what if it worked? Well, that would throw open the door to the solar system. Instead of absurd, multi-hundred-billion dollar Mars programs that land a few civil servant spacemen for footprints, photos, and a few rocks returned, you'd end up, for an ongoing budget comparable to that of today's grotesque NASA jobs program, with colonies on the Moon and Mars working their way toward self-sufficiency, regular exploration of the outer planets and moons with mission durations of years, not decades, and the ability to permanently expand the human presence off this planet and simultaneously defend the planet and its biosphere against the kind of Really Bad Day that did in the dinosaurs (and a heck of a lot of other species nobody ever seems to mention).

Between 1955 and 1973, the United States funded a series of projects, usually designated as Rover and NERVA, with the potential of achieving all of this. This book is a thoroughly documented (65 pages of end notes) and comprehensive narrative of what went wrong. As is usually the case when government gets involved, almost none of the problems were technological. The battles, and the eventual defeat of the nuclear rocket were due to agencies fighting for turf, bureaucrats seeking to build their careers by backing or killing a project, politicians vying to bring home the bacon for their constituents or kill projects of their political opponents, and the struggle between the executive and legislative branches and the military for control over spending priorities.

What never happened among all of the struggles and ups and downs documented here is an actual public debate over the central rationale of the nuclear rocket: should there be, or should there not be, an expansive program (funded within available discretionary resources) to explore, exploit the resources, and settle the solar system? Because if no such program were contemplated, then a nuclear rocket would not be required and funds spent on it squandered. But if such a program were envisioned and deemed worthy of funding, a nuclear rocket, if feasible, would reduce the cost and increase the capability of the program to such an extent that the research and development cost of nuclear propulsion would be recouped shortly after the resulting technology were deployed.

But that debate was never held. Instead, the nuclear rocket program was a political football which bounced around for 18 years, consuming 1.4 billion (p. 207) then-year dollars (something like 5.3 billion in today's incredible shrinking greenbacks). Goals were redefined, milestones changed, management shaken up and reorganised, all at the behest of politicians, yet through it all virtually every single technical goal was achieved on time and often well ahead of schedule. Indeed, when the ball finally bounced out of bounds and the 8000 person staff was laid off, dispersing forever their knowledge of the “black art” of fuel element, thermal, and neutronic design constraints for such an extreme reactor, it was not because the project was judged infeasible, but the opposite. The green eyeshade brigade considered the project too likely to succeed, and feared the funding requests for the missions which this breakthrough technological capability would enable. And so ended the possibility of human migration into the solar system for my generation. So it goes. When the rock comes down, the few transient survivors off-planet will perhaps recall their names; they are documented here.

There are many things to criticise about this book. It is cheaply made: the text is set in painfully long lines in a small font with narrow margins, which require milliarcsecond-calibrated eye muscles to track from the end of a line to the start of the next. The printing lops off the descenders from the last line of many pages, leaving the reader to puzzle over words like “hvdrooen” and phrases such as “Whv not now?”. The cover seems to incorporate some proprietary substance made of kangaroo hair and discarded slinkies which makes it curl into a tube once you've opened it and read a few pages. Now, these are quibbles which do not detract from the content, but then this is a 300 page paperback without a single colour plate with a cover price of USD26.95. There are a number of factual errors in the text, but none which seriously distort the meaning for the knowledgeable reader; there are few, if any, typographical errors. The author is clearly an enthusiast for nuclear rocket technology, and this sometimes results in over-the-top hyperbole where a dispassionate recounting of the details should suffice. He is a big fan of New Mexico senator Clinton Anderson, a stalwart supporter of the nuclear rocket from its inception through its demise (which coincided with his retirement from the Senate due to health reasons), but only on p. 145 does the author address the detail that the programme was a multi-billion dollar (in an epoch when a billion dollars was real money) pork barrel project for Anderson's state.

Flawed—yes, but if you're interested in this little-known backstory of the space program of the last century, whose tawdry history and shameful demise largely explains the sorry state of the human presence in space today, this is the best source of which I'm aware to learn what happened and why. Given the cognitive collapse in the United States (Want to clear a room of Americans? Just say “nuclear!”), I can't share the author's technologically deterministic optimism, “The potential foretells a resurgence at Jackass Flats…” (p. 195), that the legacy of Rover/NERVA will be redeemed by the descendants of those who paid for it only to see it discarded. But those who use this largely forgotten and, in the demographically imploding West, forbidden knowledge to make the leap off our planet toward our destiny in the stars will find the experience summarised here, and the sources cited, an essential starting point for the technologies they'll require to get there.

 ‘Und I'm learning Chinese,’ says Wernher von Braun.

Posted at June 11, 2008 01:34