Asteroid Day 2018: Planetary Defense Progress Report

Earlier this month, the White House released a report detailing the current status of planetary defense efforts in the United States. The report discusses the ways that US government agencies would respond to an anticipated or unanticipated impact event, and outlines the steps that they should take to mitigate the danger. Unfortunately, this is just a report—any policy changes or future missions will require further action from the President and Congress.

This was a heartening but also concerning admission ahead of Asteroid Day. I’m encouraged that America is taking planetary defense seriously. Protecting against asteroid and comet impacts is arguably the single most important thing that we can be doing in space right now. However, it has not been the primary or even secondary focus of any major space agency. Much of the work has been limited to university researchers and private-sector organizations.

On this day, the 100th anniversary of the Tunguska Event, I would like to discuss our progress in planetary defense. While NASA and other organizations have done an excellent job tracking near-Earth asteroids and assessing their threat to humanity, we are not dramatically closer to impact prevention capabilities. Nevertheless, there is reason to be cautiously optimistic. Let’s discuss the major ongoing and future missions to explore and detect asteroids that could potentially threaten Earth.

To begin: just this week, the Japanese Hayabusa2 spacecraft arrived at the asteroid 162173 Ryugu. For the next eighteen months, Hayabusa2 will orbit the 900-meter-wide space rock. In addition to orbital observations, Hayabusa2 will release several surface probes and retrieve samples for return to Earth in late 2020. These samples will include material taken from the interior of the asteroid, extracted by detonating a small explosive device on the asteroid’s surface.


Hayabusa2 performs surface sample extraction at Ryugu.

Source: JAXA

Hayabusa2 is primarily focusing on planetary science, with consideration for eventual resource extraction. However, understanding the structure and dynamics of near-Earth asteroids is essential for predicting their impact odds and planning redirection maneuvers if need be.


Asteroid 162173 Ryugu as imaged on June 26.

Source: JAXA

Planetary defense is a major motivation of the OSIRIS-REx mission, which is continuing on its way towards asteroid 101955 Bennu. Astronomers estimate that there is a small chance that Bennu may impact Earth in about 200 years, so studying the asteroid up-close will considerably refine their calculations.

(Before someone asks: OSIRIS-REx Principal Investigator Dante Lauretta wrote a blog post specifically outlining the damage that Bennu would cause if it were to impact Earth. Note that all recent estimates place the impact odds far, far below one percent.)

OSIRIS-REx launched in 2016 and will arrive at Bennu in August of this year. The spacecraft performed a burn last January to put it on a trajectory for an Earth flyby, which occurred on September 22, 2017. This maneuver put the spacecraft on an appropriate orbit to rendezvous with the small asteroid.

Like Hayabusa2, OSIRIS-REx is also a sample return mission. Allowing scientists to study asteroidial material in laboratories on the ground massively increases the information we can glean from them, because many of the most interesting measurements and experiments are simply too heavy, bulky, or complex to cram within an interplanetary spacecraft.


OSIRIS-REx performs surface sample extraction at Bennu.

Source: NASA

Sample return is just one aspect of the OSIRIS-REx mission. In addition to the standard planetary science objectives, OSIRIS-REx will study the impact of non-gravitational forces on the orbit of a celestial body. Many of these forces are well-understood for conventional satellites, but the data for asteroids and comets is hazy when it exists. Characterizing these effects for objects like Bennu will go a long way towards predicting their orbits and thus the impact odds long-term.

Once we understand these risks, though, we need the capability to deflect any objects we find headed towards Earth. Here the progress has been less inspiring.

First, a mission is currently under development called the Double Asteroid Redirection Test, or DART. Planned to launch in December of 2020 or early 2021, DART will rendezvous with the asteroid 65803 Didymos in October of 2022. Didymos is actually a double asteroid, and DART with collide with the smaller moon when the asteroid is near its closest approach to Earth. Ground-based observers will measure the effect that the collision has on the moonlet, giving researchers some hard data on just how well the kinetic impact technique would work for asteroid deflection.

This is an interesting mission, both for its planetary defense implications and for its technology. DART is expected to be the first spacecraft to test the NASA Evolutionary Xenon Thruster (NEXT), and will sport the Roll-Out Solar Array (ROSA) design tested on the International Space Station in 2017. Unfortunately, there has been some uncertainty over whether this mission would actually fly. Though required by law, it was not included in the 2018 NASA Budget. The John Hopkins University Applied Physics Laboratory, however, has continued working on the project and as of April was discussing final design and fabrication later this year.

On a related note, the Asteroid Redirect Mission (ARM), which the mainstream science media so eloquently described as “giving the Moon a moon”, was recently cancelled in favor of pursuing manned Lunar missions. This is a questionable decision. ARM was a logical development conduit for key technologies in robotics, propulsion, and astrodynamics. All of these would have contributed greatly to manned exploration of the Solar System. Thankfully, much of this technological investment will be preserved, and may eventually pay dividends in planetary science and defense.


ARM grapples an asteroidial boulder to return to the Earth-Luna system.

Source: NASA

Nevertheless, having a six-ton asteroid in Lunar orbit would have provided a compelling intermediate target for human spaceflight. (The Deep Space Gateway would naturally fill the role of an intermediate target, but I’ll save the discussion of its advantages and disadvantages for another day.) Landing is a much bigger challenge than just returning to cislunar space, and the scientific knowledge from returned samples would also have been tremendous.

Another important project has also faltered: the Sentinel Space Telescope. This mission was designed by the B612 Foundation to detect asteroids that Earth-based telescopes miss by putting a dedicated spacecraft in solar orbit near Venus. Sentinel would have launched on a Falcon 9 rocket in 2018 or 2019 and cost $450 million to develop.

This proved way too expensive for a niche non-profit. NASA provided some funding, but this ended in late 2015, and B612 was unable to raise the remainder. Retired astronaut Ed Lu confirmed that the project was dead last year.


Rendering of the Sentinel Space Telescope on-orbit.

Source: B612 Foundation

B612 is instead focusing on telescopes mounted to significantly smaller satellites. They will use a new technique called synthetic tracking to spot smaller asteroids than previously possible. Few and fewer potential “killer” asteroids remain to be discovered as better and better telescopes come online, so the overall emphasis is turning towards the smaller rocks. These can still be deadly: the Chelyabinsk meteor was only about 20 meters across but caused thousands of injuries and millions of dollars in damages.

If mounting space telescopes on small satellites sounds ambitious, consider that the Canadian Space Agency launched a comparable spacecraft called NEOSSat with similar goals in 2013. Small satellites are much more affordable for non-governmental organizations, in part because launch vehicle cost can be distributed over multiple missions—NEOSSat rode to orbit with six other spacecraft. An audit in 2013 estimated the program was significantly over-budget. Total cost: CDN$25 million.

NASA and the Jet Propulsion Laboratory are also pursuing a Near Earth Object Camera, which would join the fleet at the Earth-Sun L1 point. NEOCam was passed over for the latest Discovery Mission opening, though was still under development as of April under the aegis of NASA’s Planetary Defense office. Without a clear funding commitment, though, mission planners are severely limited in developing the program.

This is a bit concerning, because NASA has a Congressional mandate to detect 90% of near-Earth objects 140-meters and larger by 2020. Much of this work was completed by the Wide-field Infrared Survey Explorer during its extended mission. WISE discovered over 3000 asteroids and comets, including 262 near-Earth asteroids. 47 of these are considered potentially hazardous. Detecting the remainder will probably require new hardware, so I’m doubtful that NASA will meet the Congressional mandate. If current legislators are serious abut this mission, they need to allocate funds—and quickly.


Artistic rendering of the WISE spacecraft.

Source: NASA

The probability that an undetected asteroid will hit Earth before that objective is met—on time or not—is low, but every day that passes risks another Chelyabinsk. Only once we know the threats can we take actions to mitigate them. Having the necessary technology ready-to-go would vastly improve our odds.

On the whole, I’m glad to see that the United States is taking planetary defense seriously, but there’s a lot of work left to do. Check back again next Asteroid Day to review the advances we make in the coming months.


Book Review: Elements of Spacecraft Design

Most aerospace engineers are familiar with the AIAA Education book series, which provides instruction on topics ranging from structural design to hypersonic propulsion. Charles D. Brown was an aerospace engineer who worked at Lockheed Martin and taught at UC Boulder. Brown wrote several books for the AIAA Education Series in addition to his work on various space projects, most notably Magellan.1 Elements of Spacecraft Design is his attempt at a space vehicle design textbook.

Like most aerospace design books, it breaks out the final product into the various subsystems and discusses each of these in turn. There’s no universally agreed-upon list of aircraft or spacecraft systems, but Brown addresses most of the major ones. He begins with an introduction to spacecraft generally, a brief exploration of spacecraft systems engineering, and then proceeds into the elements of design.

These are not exclusively subsystems. Usually, aerospace design decisions are dominated by the intended flight profile. Aircraft designers estimate the requirements to complete the assorted mission phases. Spacecraft designers break things down using orbital mechanics. Only once the various maneuvers are established can we begin the process of selecting and sizing the propulsion system.

Of course, it may not be possible to complete a particular mission with the propulsion systems which are available (remember that pretty much anything short of an Apollo-level mad-dash will be budget-constrained). In that case, revise the trajectory. Design is an iterative process.

Note, too, that the propulsion systems on spacecraft frequently do double-duty as the attitude control system. These two chapters immediately follow orbital mechanics, and bring us about halfway through the book. It might feel like these are a mini-book of their own, and sort of are, since Brown also wrote a primer on spacecraft propulsion covering much of the same ground.

The non-spacecraft engineers in the audience may be wondering what else is left to discuss. Quite a lot, actually! Power systems lead us off, which for Brown’s purposes are almost exclusively solar panels and batteries. Radioisotope thermoelectric generators get one (1) page of attention, and nuclear reactors get none, which caused some consternation for my senior capstone class. It is an older book, granted, but the former warrants a few sizing equations at least.

Closely related to power (at least if we’re doing solar panels) is thermal control. Both are heavily affected by the orbital regime of the spacecraft and, potentially, the vehicle configuration. The chapter mostly focuses on preliminary spherical satellite analysis, though it also introduces the tools for more detailed studies. Properly modelling the heat flow through a spacecraft can be a pretty serious challenge, though, with entire books dedicated to the subject.

Finally, our attention turns towards the reason we launched the mission in the first place: obtaining or relaying important information. Remember, we’re not just doing this because it’s cool. There’s valuable scientific or commercial data which we want to process and return to Earth. Moreover, we have to maintain control of the spacecraft if we want to get it. Brown gives us a general introduction to the problems of command & data handling and telecommunications.

These chapters are somewhat weak. A good deal of the information is presented too briefly, and not always in the most logical order. It took the entire class several days to figure out that we needed a figure from the previous chapter to finish one of the telecommunication problems. It was hard to believe that we would be excited to start in on structures—but we were!

Of course, the structures chapter only briefly addresses sophomore-level material mechanics, and then segues into acoustics, which is a graduate class where I went to school (though the actual equations presented in the book seem inadequate for any serious analysis). For the most part, it addresses qualitatively the major factors which affect spacecraft configuration and material selection, with examples of the common solutions.

This is where the systems engineering aspect comes back in—quite often, different subsystems impose competing requirements on the spacecraft configuration. The designer has to figure out the optimal approach for the particular mission in question. Brown addresses this in a few exercises through the text, but there’s ultimately only so much a student can learn without feedback from an instructor (or with prototypes through trial-and-error).

Overall, I found Elements of Spacecraft Design to be an informative and pleasurable read. It’s a good book for learning about spacecraft hardware, but I would not recommend treating it as a full-fledged spacecraft design book. It includes many of the elements of spacecraft design, yes, but hardly constitutes a full periodic table.

Consider this exciting image, which some AIAA editor thought would make ideal cover art:


Wouldn’t a rendering of Magellan be more appropriate?

Ignoring the fact that block diagrams don’t need to be painfully asymmetric, the astute reader will note that Elements of Spacecraft Design only covers the areas under the “spacecraft” header. Each of the headers could have similar subheading trees, but those aren’t the focus of Brown’s text. He addresses the interface between the spacecraft and other project elements, but not in any great detail.

If you need that information, one could consult some of Brown’s references, or just pick up a more detailed textbook like SMAD. Brown entirely omits some important areas such as cost estimation and manufacturing considerations, so any serious designer will need to turn to other books regardless. For this reason, I have to recommend using SMAD or its sequel, Space Mission Engineering, as a primary design book. Space Vehicle Design by Michael D. Griffin2 and James R. French also addresses some aspects, such as atmospheric entry and reliability engineering, but still skips ground segment design.

Brown covers some things which these other books gloss over, however. Perhaps the most important is providing clearer algorithms for mass and power requirements of the spacecraft. These include equations to estimate the cabling and launch vehicle adaptor masses, which are easy to overlook and a frequent location of cost and weight overruns. The data and resultant equations are old, mind you, but most other books suffer from much the same problem.

Still, an updated edition is overdue. Brown and his coauthors made a lot of mistakes and unstated assumptions which the copy-editors didn’t catch, and cause all sorts of headaches when trying to solve the problems and follow the examples. Many of the equations also conflate weight and mass when switching between the customary and metric versions. The book should really pick one as the default and then use a common substitution algorithm to derive the other on-need. It wouldn’t be a hard problem to tackle, but it’s unlikely that anyone will until AIAA offers a paycheck for it.

As long as you’re mindful of these issues, however, Brown provides a solid introduction to the problem of spacecraft subsystem design. Elements of Spacecraft Design covers most of the major areas—and a number of the minor ones—in a generally accessible and clear manner. This is one of the few textbooks I found myself enjoying, as opposed to merely slogging through to extract the relevant information. Brown is an engaging writer (though note that some of the chapters written by other authors are considerably drier), and I’ll probably read some of his other books in the near future. I doubt that they will fully educate me on the subjects, but just like Elements of Spacecraft Design, should provide a valuable framework for absorbing later, more detailed texts.


1Most of the planetary examples in the book use either Venus generally or Magellan in particular. It became a bit of a running gag in the class.

2Space Vehicle Design is partially based on Griffin’s experience with the JHU Applied Physics Laboratory, which designed many famous spacecraft, including New Horizons, MESSENGER, and the Parker Solar Probe. Griffin later went on to be NASA Administrator from 2005 to 2009 and is currently Under Secretary of Defense for Research and Engineering.


Scott Alexander once noted that, since he was twelve, his life could be divided into four-year periods. I’m a decade younger than him but can still do one better: my entire life so far can be divided into six-year periods.

The first five years of my life were spent in day care. Kindergarten sorta messes with this model, but not dramatically, because in my district it was a mere three hours per day. I spent the mornings playing at my grandmother’s house and the afternoons watching TV at home. It wasn’t until first grade that I came to despise school.

The next six years were varying shades of dreary as I developed a pre-rational mind. Then there were six years of secondary school. And then, concluding this last month, were six years of college.

I face the future with a certain degree of trepidation. Will this pattern continue? It would be very easy to spend a solid six years pursuing a doctoral degree, or working for a particular company, or living in a particular industrial center.

Whether any particular outcome would be good or bad depends on a number of factors not intrinsically linked to the overall category of the outcome itself. What graduate program, for instance, or what company, or which industrial center? Even within those, there is a great deal of flexibility and customization that could ultimately make or break my experience.

Or the pattern could break. I suspect that this is the more probable possibility. All of these increments have been defined by my education, and the educational system works in very coarse increments. The real world is not exactly like that. Industry does not run on the semester system and I am not entirely prepared for continuous living. This is one of my (many) major complaints with the educational system and something that probably contributes significantly to the difficulties that young people have establishing a sustainable independent existence.

Today I turned twenty-four. The fourth period is over, and what lies ahead remains to be seen. My time horizon is shorter than it has been since those painful days in 2014. This time, however, the ultimate meaning of that uncertainty is freedom of action. When new opportunities arise, the obligations which once interfered will no longer constrain me.

What happens next?

Wait and see.

Book Review: To the End of the Solar System

James Dewar set out to the write the story of the nuclear rocket, and that’s exactly what he succeeded in doing. To the End of the Solar System is a nearly complete history of nuclear-thermal propulsion research from the discovery of radioactivity in the 1890s through the cancellation of the American research & development program in 1973. He discusses the work done in subsequent years, though through the book’s publication in 2004 that research was largely theoretical.1 Dewar consequently directs his attention to the period when nuclear propulsion was a near-term possibility.

It is not, primarily, a technical tale. The majority of the book focuses on the political, managerial, and bureaucratic aspects of the program. There is a good deal of technical detail, but ultimately the engineering challenges are not the biggest hurdle for those supporting nuclear propulsion. Securing long-term support and funding from industry and Congress will be much more difficult.

The book also necessarily focused on the American nuclear program, though addresses briefly Soviet work. Unfortunately, our knowledge of their program comes from only a handful of sources, sometimes contradicting one another. How much useful information we can glean from them is uncertain.

The Cold War played a major role in the development of the nuclear rocket, but the story begins well before the Russian Revolution. A number of early rocketry theorists, including Robert Goddard, Konstantin Tsiolkovsky, and Hermann Oberth speculated on using the energy released from radioactive decay to propel spacecraft, but both the quantity available and isotopic energy output was minute. Discussion remained entirely abstract and largely an aside in the development of rocket propulsion until after the Second World War.

The ultimate motivation was military. As atomic bombs grew larger and larger, existing aircraft and missile designs struggled to keep up. A handful of scientists floated nuclear options to deliver these weapons, either in aircraft, missile, or pulse-propulsion form. The Pentagon developed a nuclear airplane program as a joint venture between the Air Force and Atomic Energy Commission with the express goal of developing an aircraft capable of delivering a hydrogen bomb inside the Iron Curtain.

Oak Ridge National Laboratory hired a young physicist named Robert Bussard2 to work on the nuclear airplane project. Brussard did excellent work but insisted on studying nuclear rockets alongside his official duties. Through months of feverish lucubration, he developed some of the first viable nuclear rocket concepts. His classified publications attracted the interest of several prominent physicists. Teams formed at Los Alamos and Livermore National Laboratories to develop Bussard’s concepts. Los Alamos eventually came to favor nuclear turbojets, while Livermore concluded that nuclear rockets were more viable.

When Congress got involved a few years later, the need for nuclear aircraft or missiles was waning as bomb mass fell and chemical launcher capability grew. However, Washington was beginning to think about spaceflight, and decided to continue funding both programs. Ironically, the AEC assigned Los Alamos to study rockets and Livermore to study nuclear jet engines. These became Projects Rover and Pluto, respectively.

Los Alamos began constructing facilities at the Nevada Test Site to put their series of reactor designs through the paces. Each reactor was a hard-won concession from Congress, which was worried about just how many tests and iterations would be necessary to develop a viable system. Throughout the program, many in Washington opposed Project Rover or believed that it should be transferred to the civilian space program. NASA was very skeptical of the program, however, and so a small clique of Senators fought to keep it under AEC aegis. Ultimately NASA and the AEC found a reasonable compromise, forming a joint Space Nuclear Propulsion Office.

The early Space Race initially helped Rover’s prospects, as the Soviet Union sped ahead in missions and technological firsts. Nuclear propulsion would enable much more impressive projects, such as manned planetary landings, massive probes to the outer Solar System, space stations, and Lunar bases.

In Nevada, reactors were steadily improving. Their thrust and successful burn-time grew, though several failures occurred, including one which required an expensive clean-up effort. Through a series of redesigns, however, the test articles began to closely match the existing aerothermodynamic models. Better designs were coming, but a large question mark hovered over the program: when would Rover get a reactor in-flight test?

RIFT was well-named, as it became a political hot-button issue. Early concepts involved dumping the used reactor into the ocean or using it to perform orbital insertion as a Saturn upper stage. Both of these concepts were eventually abandoned on safety grounds, but did nothing to advance the issue in Congress.

Ultimately, nuclear rockets became a chicken-and-egg problem. Congress and NASA leadership did not want to approve a program that required nuclear propulsion until the technology was ready, but also hesitated to develop nuclear technology until a mission required it.

Much of the opposition stemmed from budgetary concerns. NASA was a rapidly-growing slice of the federal budget, competing with the Vietnam War and Great Society for a shrinking set of tax dollars. Recall that fiscal conservatism was once common in both political parties, rather than a fringe movement within one of them. Few wanted to commit to the large, expensive missions which nuclear propulsion would enable (such missions being prohibitively expensive—in the extreme—with chemical propulsion).

The concept of preeminence rapidly fell out of favor. Washington decided that Apollo would be the extent of trying to upshow the Soviet with big flashy projects. After Skylab, the Space Race would be abandoned in favor of developing the “economical” space transportation system. Los Alamos was still developing reactors, including the most powerful reactor ever run, but the tide was shifting towards smaller reactors to complete technology validation. Stacking small reactors, it was thought, would provide adequate thrust and cut down burn durations.

Even the space transportation system came under attack as tax revenue continued to shrink in the Nixon years. The original plan included nuclear orbital tugs, the chemical shuttle, and a space station. Ultimately, only the shuttle was funded, with the design of its cargo bay becoming a proxy battle over the future of nuclear propulsion. Small nuclear engines could be carried to orbit in the shuttle cargo bay, after which they would be attached to larger spacecraft and activated once astronauts had left the vicinity.


The Space Transportation System concept in 1970.

Source: Marshall Space Flight Center

Quite suddenly, though, all funding was terminated in 1973. Congressional funding was falling but still there, and researchers thought they were approaching flight test readiness. The change was ultimately a decision made by bureaucrats in the executive branch, which reprogrammed the funds without the consent of Congress or the President.

Believe it or not, this was technically a legal move. Several Senators were enraged by it, including Barry Goldwater—not exactly a friend of large, expensive federal programs. Within a few years, laws were introduced which required the Executive Branch to spend funds on the programs which Congress had allocated them for.

The defunding took the Soviets by surprise, to the point that they suspected it was a false-flag move to classify the work. Unfortunately, this does not appear to be the case. In fact, some of the officials involved in cancelling Rover were involved in the later Air Force Project Timberwind, which again attempted to develop nuclear propulsion. This too was cancelled after the end of the Cold War, without producing any real results.

All of this was really fascinating history, which I think should be discussed more widely in the spaceflight community. Nuclear propulsion, despite some extreme challenges, came very close to practicality. In the end, it was cancelled by politicians who failed to see the opportunities it provided rather than for the technological difficulties it faced.

It is quite arguable that Project Rover was well-worth the cost, and could have been justified on technology-development grounds alone. The program created entirely new industries, such as commercially-affordable cryogenics, and demonstrated all kinds of new material sciences. One would expect spaceflight advocates to mention this more often.

To the End of the Solar System does discuss the technical details, but is ultimately a political history. The style is somewhat confusing in this regard, routinely switching between Washington and Nevada—and not necessarily in chronological order. I would like to reread it to see if contextualization improves the narrative, but sadly it goes back to the school library tomorrow. Maybe one day I’ll buy a personal copy.

However, the appendices are worth reading. They provide a decent introduction to the major aspects of nuclear propulsion, without drowning the reader in technical minutiae. The discussion of radiation safety, for instance, was extremely informative and should allay many fears about the dangers of nuclear rocket testing. Dewar also dedicates a section to the Russian nuclear propulsion program. These are a good introduction to the subject, though hardly an expert make. I’ll be diving into dedicated nucleonics and advanced propulsion resources Soon™.

On the whole, To the End of the Solar System: The Story of the Nuclear Rocket is a rich resource for those studying the history of nuclear propulsion, whether for technical or non-technical reasons. Understanding the story of advanced propulsion is essential for those of us who wish to see humanity spread out into the Solar System, and James Dewar has written an excellent introduction. The book does not appear to be particularly common in print3, but if you get the chance to read it, you definitely should.

Image result for to the end of the solar system dewar

1Dewar mentions Project Prometheus to explain that it was too early in the program life-cycle to discuss. As it turns out, Project Prometheus went nowhere. In 2017, NASA issued new hardware contracts for exploring the manufacturing and testing requirements for making nuclear propulsion viable, but it is too early to say whether these will yield results, either.

2Bussard is better known for his later work on advanced propulsion, proposing a fusion ramjet fueled by the interstellar medium.

3I believe that it has had only two printings: initially from the University of Kentucky Press in 2004, and a second run from Apogee Books later in the decade. New hardbacks are hundreds of dollars on Amazon. There might be a PDF version floating around, but if there is, I haven’t come across it. Libraries are probably the best bet.

Astronomer Discovers New Way to Measure the Distance to Other Galaxies

A research astronomer at Mount Wilson Observatory has discovered a new way to measure the distances to other galaxies.

E. P. Hubble is a former college athlete and US Army Officer who somehow ended up in the stargazing business. Shortly after his discharge, he was hired by Mount Wilson and soon developed his innovative trick.

Hubble’s technique builds on the work of previous scientists, and uses a special type of variable star. Early on, astronomers recognized the bright star Delta Cephei changes brightness about every five and a half days. Over time, quite a few similar stars have been discovered, with different periods and of different brightnesses.


The brightness of Delta Cephei varies regularly over several days.

Source: ThomasK Vbg

For a long time, it wasn’t clear if brightness related to period, because how bright a star looks from Earth (known as its apparent magnitude) depends both on the star’s intrinsic luminosity (or true magnitude) and how far away it is. Since scientists couldn’t measure the distance to any of these stars, called Cepheid variables after the nearest specimen, the relationship between their brightness and period was a mystery.

That is, until an assistant astronomer named Henrietta Leavitt started studying them.

Leavitt focused on stars in the Small Magellanic Cloud, an irregular region near the edge of the Milky Way. The Cloud is so far away that its size is negligible compared to its distance from the solar system. Leavitt reasoned that brighter Cepheid variables in the Small Magellanic Cloud would be be more luminous not just in appearance but in fact, so she could determine whether that had anything to do with the period.

As it turns out, brighter Cepheid variables have a longer period, while smaller ones have a shorter period. With a little math, astronomers can work out the true brightness of a Cepheid variable from how long it takes to complete a full cycle.

Leavitt’s supervisor at Harvard College Observatory, Harlow Shapley, realized that this relationship could determine true distances in space. Shapley used a statistical analysis of Cepheid variables to determine their true distance in space, as indicated by the Doppler shift of their spectral lines.

Hubble was the first astronomer to apply this tool to measuring galactic distances. He made a dedicated search for Cepheid variables in other galaxies, the Andromeda Galaxy in particular.

The results were shocking. All the galaxies where Hubble found Cepheids turned out to be much further away than scientists had previously thought. Several other teams have already confirmed the findings, but it will probably take astronomers and physicists a years to figure out all the implications.

Happy Amazing Breakthrough Day!

Some Things That Affect Spacecraft Orbits

The derelict Chinese space station Tiangong-1 is expected to re-enter this weekend. The precise time and location aren’t easy to predict, and this has caused some concern among various members of the public. A space station is much bigger than a normal satellite, and it’s conceivable that larger pieces could cause major property damage or even injuries on impact. So why don’t we know where it will hit?

The answer is actually pretty complicated, because there many, many things which affect the paths of even simple, Earth-orbiting satellites. Some are immediately obvious, like drag from the upper atmosphere and Lunar perturbations. A lot are more subtle, like interference from Earth’s magnetic field. In this post I’d like to briefly explain all the significant factors, without going into too much math. Hopefully this will emphasize to specialists and laymen alike the value of responsible debris mitigation and the importance of safely disposing old spacecraft before ground controllers lose contact.

Atmospheric drag is, of course, the largest force affecting satellite orbits, and the reason Tiangong-1 is re-entering. As I explained in my last post about orbital mechanics, there is no clear upper edge to the atmosphere. Below about 500 kilometers, the atmosphere is still sufficiently thick to de-orbit most debris. Satellites above this altitude can remain in space for decades without any maintenance, and geosynchronous orbiters will last centuries or even millennia.

Low Earth Orbit is the natural regime to place crewed spacecraft, since the debris risk is dramatically lower. (The radiation hazards are also significantly higher in the medium orbits, and our current manned capsules can’t easily punch through the Van Allen belts.) This is fine as long as the spacecraft is operational and performing orbital maintenance maneuvers. The International Space Station has to perform these regularly.


ISS altitude over the last year. Discontinuities between decay regions represent maneuvers to raise the orbital height.


Atmospheric drag on spacecraft is governed by a simple equation, which will be extremely familiar to even underclassmen aerospace engineers:

F_D = \frac{1}{2} m C_D \rho A V^2

In essence, this equation states that drag force F_D on the spacecraft is equal to half the product of the spacecraft mass m, cross-sectional area A, atmospheric density \rho and the square of the relative velocity V^2, all multiplied by a fudge factor C_D. We call the fudge factor the drag coefficient, and for satellites it tends to fall between 2.1 and 2.3, though higher values are common depending on the spacecraft configuration and materials used.

Density is the biggest unknown factor. It varies based on the altitude, time of day, time of the year, and how active the Sun has been lately. A number of these factors also affect relative velocity, because the atmosphere isn’t still. Upper atmospheric winds can be significant, often hundreds of meters per second.

Altitude plays a role, because different gases have different masses.  Mass is related to velocity via kinetic energy and the ideal gas law, which essentially states that the velocity of a particle, for a given internal energy, with be greater if the particle has a lower mass. Essentially, heavier gases like molecular oxygen and nitrogen will hug the planet, while lighter gases such as hydrogen and helium can easily climb into the thermosphere.

Additionally, the amount of solar and cosmic radiation is higher the further one rises. Collisions with energetic particles cause molecules to break into their components, so the frequency of atomic oxygen and nitrogen increases dramatically. This affects the effective density of the upper atmosphere and therefore the drag force. Since the amount of solar radiation is highly variable over the short term and changes with the eleven-year solar cycle, the numerical density of the upper atmosphere isn’t at all constant.

Solar radiation was ultimately responsible for the failure of a previous space station: Skylab. Initially NASA expected it to remain on-orbit till the early 1980s, when the space shuttle could have pushed it higher. The sun was particularly active during that era, however, and by the mid-1970s it was clear that the station would re-enter much earlier. A special mission would have saved it, but NASA never seriously planned one and Congress never allocated any funds. Skylab disintegrated over Australia on July 11, 1979. Despite widespread concerns, there was very little damage and no one was hurt, though one jurisdiction fined NASA $400 for littering.


Skylab photographed by the last departing crew in February 1974.

Source: NASA

Temperature changes over the course of the day and year also affect the upper atmospheric density. Warm gases move faster and rise higher, and which can be seen in aggregate as an increase in pressure. Warm air near the surface displaces upwards, effectively increasing the size of the atmosphere. This can significantly increase the drag which a satellite experiences.

Generally speaking, day is warmer than night. Summer is warmer than winter, though of course that depends on which part of Earth you’re considering. (Remember that seasons are caused by axial tilt, not the eccentricity of our path around the Sun.) Advanced density models take all of these factors into consideration—date, time of day, latitude, longitude, altitude, and multiple indices of solar activity.

Atmospheric density is the biggest effect that astrodynamicists have to consider, especially for satellites in low orbits, but there are several other major forces which can cause significant accelerations, particularly upon smaller objects. From Newton’s Second Law, the acceleration a force has on an object is directly related to the mass of the object in question. Space stations have high masses, so only large forces can affect them. Cubesats have much lower masses, and can see large perturbations from forces that space station controllers happily ignore.

One of the larger effects we have to worry about is Earth oblateness, usually abbreviated as J_2. This is a low-order model of Earth’s shape, which is actually really complicated. High-fidelity models often reach high two-digit orders, though these are only needed for the most precise of missions.

The effect of J_2 is to reduce the inclination of an orbit, while also causing the orbit to change its orientation around Earth. The essential mechanism is that, because Earth is not exactly a sphere, when the spacecraft is north of the equator, it will be experienced an unbalanced force pulling it south, which the reverse occurs when it passes below the equator again. Over time, the satellite trajectory will approach an equatorial orbit, precessing around the pole.

We can define a J_2 value for every planet, because their non-sphericity is caused by rotation. Other gravitational effects may also be present, though these can usually be neglected. Luna is a notable exception. The internal mass distribution of our moon is so irregular than only a handful of orbital inclinations are stable. We learned this the hard way when Apollo astronauts left hand-launched microsatellites in orbit. One lasted for over a year, while other crashed within weeks.

This alludes to another important point: anything the size and density of a planet is not going to be perfectly rigid. In addition to ocean tides, gravitational effects from the Sun and Luna also cause internal tides, as the solid material within the planet bends slightly. These are called solid Earth tides, and affect satellite orbits about an order of magnitude more than the ocean tides. Usually these can be neglected, but precision gravity models need to taken them into account.

Accelerations of about the same order of magnitude (\approx 10^{-12} \ \textrm{km}/\textrm{s}^2) arise from general relativity. Because the spacecraft is travelling around a deep planetary gravity well, there will actually be a small but measurable change in velocity over time due to the spacecraft’s velocity through space. Mathematically, this is stated as:

a_r = -3\frac{\mu}{r^2}\frac{v^2}{c^2}

where a_r is the relativistic acceleration, \mu is the standard gravitational parameter for the body in question, r is the distance of the spacecraft from the body, v is the instantaneous velocity of the spacecraft, and c is the speed of light. This acceleration will get smaller the further the spacecraft is from the primary body, and the slower it is moving (which, incidentally, spacecraft in higher orbits tend to do).

Generally, the position effects of relativity will be on the order of a centimeter, so orbit determination on larger scales can neglect that easily. Spacecraft in higher orbits probably won’t be affected, though spacecraft in very low orbits may see significant effects if they remain in space for a long time. The planet Mercury, orbiting so close to the massive Sun, experiences a dramatic relativistic acceleration. Astronomers once suspected that another planet lurked close to the Sun, perturbing Mercury’s orbit in a more typical way, until Einstein’s theory closely predicted the observed variations.

The Sun and Luna cause the greatest gravitational perturbations to Earth orbiting satellites, dragging the satellite slightly astray as it swings around our green planet. If we want to be really precise, though, we need to consider accelerations from other worlds, as well. Astrodynamicists rarely find a case where any besides Venus and Jupiter can be worth the trouble (and even those rarely). Venus is important because it is close to Earth, while faraway Jupiter is merely massive. Mars is nearly as close as Venus during much of its orbit, but is so much less massive that we neglect it entirely.

There’s one final type of force which affects orbits directly: radiation pressure. This can be somewhat counter-intuitive, because the majority of the radiation in question comes in the form of massless photons. F = ma would seem to break down. Massless though they be, photons carry momentum. The rigorous definition of Newton’s Second Law of Motion is really that force is the change in momentum, which is the product of mass and velocity. We simply assume that mass remains constant in most applications.

Since photons carry momentum, however, they can produce a force directly. It’s not much, but when you consider how many photons are streaming through space each second, it turns out to be significant. The radiation flux from the Sun is usually around 1376 \textrm{W}/\textrm{m}^2, while the reflected radiation from Earth is around 459 \textrm{W}/\textrm{m}^2. Dividing by the speed of light, we find the two radiation pressures.

The force F_s from this pressure P_s is a function of the cross-sectional area of the spacecraft and the angle \alpha between it and the incoming photons:

F_s = P_s\cos\alpha

The same equation can be used to calculate the effect of Earth radiation pressure, though the incidence angle will necessarily be different.

At this point, let’s return to the question of Tiangong-1. We’ve seen a great many reasons why it is challenging to make long-term predictions about its orbit. However, there is another problem which affects derelict spacecraft in particular: we don’t know its orientation in space. Now a large spacecraft can be imaged by radar, which gives us some idea about its orientation, but that will not work for smaller satellites. To make matters worse, it turns out Tiangong-1 is rotating, so its orientation will be different depending on when we look.

“What causes this rotation?” you might be wondering. I’m glad you asked. There are four major disturbance torques that attitude control engineers have to consider, though several of the above forces can also cause smaller torques.

At low altitudes, the largest torque by far is aerodynamic torque T_a. Recall the drag force equation I introduced above. Any offset between the center of the cross-sectional area and the center of mass will produce a moment arm L, over which the the force can act to induce rotation:

T_a = F_D L

We again find ourselves facing the fact that we may not know the cross-sectional area. If the precise forces and and orientation are well-known when ground controllers lose contact, we can model its rotation forward for a time, but not long enough to predict the re-entry of Tiangong-1.

But that’s not the end of it. There’s also force from Earth’s magnetic field, which will align any magnetized object with it, including spacecraft. The magnetic torque T_m is a function of the residual magnetic dipole M on the spacecraft, the Earth’s magnetic field strength B, and the misalignment \theta between the two:

T_m = MB\sin\theta

The magnetic field strength is a function of altitude r and latitude l, as follows:

B = \frac{B_0 r_0^3}{r^3}\sqrt{3sin^2l + 1}

where B_0 is the magnetic field strength at sea level (3\times 10^{-5}\ \textrm{T}) and r_0 is the average radius of Earth (about 6,370\ \textrm{km}).

Finally, the spacecraft orientation leads to torques due to the small gravity gradient between its highest and lowest components. Measuring gravity gradient torque T_g requires very accurate information about the moment of inertia distribution, which is often difficult to determine without detailed blueprints. It is also a function of altitude above the planet, because gravitation force (and therefore torque) drops off with increasing distance, and the angle \theta off vertical”

T_g = \frac{3\mu}{r^3}\lvert I_z - I_y\rvert\theta

where I_y and I_z are the moments of inertia about the y– and z-axes, respectively.

As a general rule, the aerodynamic and magnetic torques dominate at lower altitudes, but may be significant for higher orbits or with special spacecraft configurations. These have to be determined on a case-by-case basis.

So that’s why we don’t know exactly when or where Tiangong-1 will re-enter. There’s a lot of variables involved, many of which are difficult to estimate, and often are strangely coupled at higher orders. There are many things which can be improved if we’re willing to spend enough money, such as building better atmospheric and gravitational models or tracking debris more regularly. Ultimately, though, there’s no substitute for responsible disposal at the end of a spacecraft’s mission, either into a stable graveyard orbit or by de-orbiting at a safe location.

…and all of this assumes that the spacecraft generates no thrust. Imagine how complex it gets when we consider outgassing!


  • Brown, C. D., Dukes, E. M., Elements of Spacecraft Design, edited by J. S. Przemieniecki, AIAA Education Series, AIAA, New York, 2003.
  • Knipp, D. J., Understanding Space Weather and the Physics Behind It, 1st ed., McGraw Hill, New York, 2011.
  • Moe, K., Moe, M. M., “Gas-surface interactions and satellite drag coefficients,” Planetary and Space Science, Vol. 53, No. 8, 2005, pp. 793–801
  • Montenbruck, O., Gill, E., Satellite Orbits: Models, Methods, and Applications, 1st ed., Springer-Verlag, Berlin, 2000.
  • Vallado, D. A., Fundamentals of Astrodynamics and Applications, 4th ed., Microcosm, Hawthorne CA, 2013.

Book Review: Artemis

Andy Weir made it big with The Martian, a survival story about an astronaut abandoned on Mars. The Martian is a very individualized book, focusing mostly on the exploits of a single person, with brief interludes to small teams at NASA and in space.

Artemis is a very different sort of story. Like The Martian, it is set at some unspecified point in the future, probably still the mid-to-late 21st Century. But instead of an astronaut alone on a planet, Artemis is the tale of a smuggler trying to pay off her debts in the first Lunarian city. It may only be about 2000 people, but they’re packed in tight. That itself is a very different sort of setting.

It’s also a different sort of conflict. Mark Watney was trapped on Mars essentially by accident. Jasmine Bashara is paying a much more dangerous game: industrial sabotage for one of the richest people on the Moon, who wants to steal a government contract from even richer people on the Moon. Well, what passes for a government contract. Artemis doesn’t really have a coherent political structure, or even a real currency. Transactions are conducted in soft-landed grams, or slugs, which are basically a credit with the megacorporation that set up the lunar colony in the first place.

That turns out to be a significant plot point. Slugs aren’t real currency, and aren’t monitored as such. Criminal organizations from Earth exploit this little fact to launder money on Luna, with marginally-profitable aluminum production as a front. They aren’t happy when Jasmine destroys several of their ore collectors. Barely making it back into the city, she’s suddenly on the run from—not the law, exactly, but definitely from the mob. Her employer is brutally murdered and she realizes her family is in danger. She goes into hiding and asks her estranged father to do the same.

As Jazz tries to figure out what’s going on, she realizing that money-laundering was just the beginning. That story could be told anywhere, but this is Artemis, the only city outside Earth’s gravity well. The real MacGuffin in a new technology, worth at least billions of dollars, that can’t be manufactured in a high-gravity environment. If the cartels get control of its production, then Luna will be in their pocket, forever.

She assembles an unusual team to finish the job of taking down Sanchez Aluminum. An ESA scientist, the chief of the EVA guild (which tried to prevent her from making it into the city), an ex-friend (who let her back in despite his better judgement), and her father, a career welder. With the tacit blessing of Artemis’ chief executive, they plot to shut down the Sanchez Aluminum facility directly.

It’s a relatively simple plan: scare the staff out of the smelting facility, breach the dome’s hull, trick the control system into thinking the smelter is undertemperature, and let it overheat trying to compensate. Once the facility is out of commission, Sanchez Aluminum will lose their power-for-oxygen contract, killing their profitability. Jazz’s erstwhile employer had a large reserve of oxygen and machinery built up, and his orphaned daughter will step in with the same offer to take over supplying the city in exchange for unlimited free power.

Okay, maybe it’s not a that simple of a plan. And, this being fiction, something has to go wrong. Most of the Sanchez Aluminum employees evacuate per plan, but one doesn’t. Loretta Sanchez, mastermind of the company, thinks she can resolve a little toxic gas alarm by herself. Jazz realizes that Sanchez has no idea what’s about to happen to her prized smelter, and barely manages to force her into the jerry-rigged airlock.

As they head back for the city, they realize there’s a problem. No one is answering the radio. Sanchez runs through the possible products of the smelter explosion and figures out that a massive amount of chloroform has entered the city’s air supply, incapacitating the entire population. Contrary to the movies, chloroform kills after about an hour of exposure. They’re on the clock.

The next thirty minutes are complication-tastic and I won’t try to summarize them. Long story short, Jazz has to head outside to open up the oxygen tanks, and can’t do it in the tourist pressure suit she donned in haste. (They’re called hamster balls for a reason.) She punctures the suit to get leverage, fully expecting to die in the process.

She wakes up in the city medical center, with the sort of radiation and heat burns one would expect after being exposure to the vacuum of space and lunar surface. Her EVA partners managed to get her inside before hypoxia did permanent damage, and the city is more-or-less saved. No one died of chloroform poisoning, and the low gravity prevented any fatal injuries.

The mob may have been deactivated in Artemis, but Jazz is still on the hook for a variety of crimes. The head administrator intends to deport her to Earth, which wouldn’t quite be a death sentence, but not exactly a good outcome for our protagonist.

Jazz manages to strike a deal. She’s the dominant smuggler in Artemis, and always keeps careful control over what comes in. Without her, less scrupulous characters will step in to satisfy demand. In exchange, she gives the city a “‘Deport-Jazz for Free’ card”, a confession to her various offenses which they can use if she breaks an official rule again.

By this point, she’s paid off her debt: a new workshop for her father with the equipment and material stock destroyed in a fire Jazz started during her irresponsible teenage years. That costs about half the fee she’d earned for taking down Sanchez Aluminum. Artemis takes the rest, in the form of a “voluntary donation” since they don’t technically have fines. From an economic standpoint, she’s back to square one.

Socially, it’s a different story. A lot of Artemisians are unhappy with her, but she’s also earned a lot of trust back from her friends and family. It’s also strongly implied that she’s going to start dating her scientist friend, though that isn’t definite.

I’ve seen some criticism of Weir’s decision to write a female narrator. Some have even gone so far as asking whether he’s talked to a woman. According to the acknowledgements, he has, and I’m willing to give him the benefit of the doubt of this. Just because a particular male-written female character feels unnatural to you doesn’t mean she’s unbelievable. Personally, I find plenty of male-written male characters unrelatable.

There’s a lot of different ways to be a human. The space of possible minds is bigger than anyone can possibly imagine, and our experiences are not universal. It’s totally absurd to demand that someone raised in a totally different culture and community to duplicate my own mental architecture. Sure, there’s general principles to get right, but details? Impossible. It’s called speculative fiction for a reason, and seeing coherent mind-models different from my own is part of why I enjoy it.

Some may be tempted to compare Artemis to The Moon is a Harsh Mistress, but I would caution against that. Yes, they’re both stories about lunar communities coming into their own, but Artemis has dramatically less social and political theorizing. Displaying some trace of economic comprehension doesn’t automatically make it a libertarian novel, just a more satisfying one.

In the end, Weir managed to write a science fiction thriller without firing a single raygun, blaster, or bullet. Instead, he manages to tell a very human tale through very real science. I know some people find that tedious, but I enjoyed it. The worldbuilding is adequate, though of course I have a hundred questions about Artemis and society on Terra that will probably never be answered. But if Weir does decides to set another book there, I’m guaranteed to read it.


Book Review: Introduction to Objectivist Epistemology

Introduction to Objectivist Epistemology is what it says on the tin: an introduction. The original book was extremely short, barely 100 pages. An additional essay by Leonard Peikoff and extensive discussion transcripts are included in the second edition. The transcripts come from a series of workshops conducted between 1969 and 1971, discussing Objectivist epistemology with about a dozen (anonymous) professors.

I would advise against reading the appendices on a first pass through the book. It’s not that they’re bad, but they contain a lot of high-level material that takes a long time to process usefully. Fully comprehending the basic concepts put forth in the main text is higher priority. The appendices are included to help flesh out the information academically. Lay readers can probably skip them entirely.

The basic concept which Rand is trying to get across is measurement omission. By this, she means the process of noticing similarities between the essential aspect of concretes, and thus developing general categories that omit the non-essential characteristics of the concretes. This, Rand argues, is the crux of concept-formation.

Objectivist concept theory is very similar to the reductionist model. Unfortunately, I don’t think Rand spends enough time explicitly arguing against the idea of things having essences. A lot of Objectivists still get hung up on “but it is a X?” questions rather than one would naively expect. This is a metaphysical matter, but a relevant one. Rand is very clear in all her works that epistemology follows from metaphysics. Getting epistemology right is a lot easier you’re your metaphysics is right, though developing an accurate metaphysics requires a functional epistemology.

Spending more time on philosophical development would have been valuable. Instead, the details of concept formation—what concepts are valid, what concepts aren’t, how to tell the difference, and so on—are the bulk of the book. This is, possibly, more practical, and Objectivism is a philosophy for living on Earth.

Still, I’m not sure that practical philosophy can achieve wider acceptance without stating the case clearly, in language that serious lay readers can understand. The appendices cover a lot of important ground, but not in the most efficient manner. Writing summaries probably would have been more efficient, but ARI Objectivists tend to tread carefully when it comes to interpreting what Ayn Rand really meant. Naturally, they opted for edited transcripts over new material. This gives a better insight into the ensuing philosophical development, but makes untangling final conclusions slow and laborious work.

Nevertheless, I would recommend Introduction to Objectivism Epistemology. It covers a number of useful ideas for developing a personal theory of knowledge, and warns against several common pitfalls. The main body of the text is interesting and readable, but the appendices are a bit more challenging. Non-academics should probably just skim for material that looks interesting and avoid reading those sections in their entirety.


Annual Themes

The last few years have seemed to have a pattern for me.

Before 2014, I don’t think I was the same person as afterward. I was very young, and only beginning to develop some kind of adult wisdom when I arrived at college. Feeling the brain develop is a strange sensation from the inside, and the process didn’t really finish fast enough. I spent the latter half of 2014 struggling with the consequences.

New Year’s Eve of that year was one of the first halfway-decent mental health days that I’d had in many, many months. It wasn’t a grand victory or anything—I cleaned (one corner of) my room, and piled up a few books to read. But it was something. 2015 felt like I was, slowly, becoming myself again. Or maybe for the first time.

In 2016, I adjusted to that role, but it didn’t go particularly well. Academically, I did alright, but found myself struggling again. I tried to blog regularly and failed. I read more, though hardly enough. My relationship peaked and ended. Mom and Dad decided to move. By December it felt like my life had mostly fallen apart around me.

This year began with uncertainty. I didn’t know how I was going to do in school, and my personal life might as well’ve been nonexistent. Classes proved interesting, but my performance left a lot to be desired.

I disappointed some of my classmates, and only after getting some scathing peer evaluations did I really shape up. I pulled my first all-nighter since 2014 on May Day. This fall I put in a lot more effort and hopefully rebuilt some part of my reputation.

2017 was the year that I learned how to try. 2018 is the year I actually try.

Talking about your specific goals is generally a poor idea, so I won’t delve into the details of what I’ll be trying to do. I’m hesitant to even announce my intention to try, but since one of the major items is a group effort with people I respect, there will be some accountability for it. Even so, I’m already a bit behind. There were things I’d planned to do over winter break, and I haven’t completed as many of them as I’d wanted. I need to get to work, and talking about it won’t help. So stop “trying” and just try.

Book Review: A Canticle for Leibowitz

A Canticle for Leibowitz was one of the last science fiction books about nuclear war published while surviving such a conflict was relatively plausible. ICBMs weren’t really a thing yet, so most of the bombs would have to be delivered by submarines, intermediate-range missiles, and airplanes. The death toll probably would have been a lot lower than it would have been later.

Miller speculates on what might come afterwards, and presents an all-too-plausible hypothesis. Once the dust settles and people start assembling a post-war society, the survivors decide to blame the engineers and scientists for the war, rather than the public’s elected officials. Technical types are killed en masse, to the point that “Simpleton” is the new comrade and mere literacy is a carefully-guarded secret.

A few professionals escape detection, often seeking refuge with the Catholic Church. The church apparatus survives and is now headquartered in North America, though it’s not clear from the text whether this is a relocation from Rome or a new establishment. The Church can’t protected everyone, but they take in many of the persecuted intellectuals and shield them from public wrath. This particular plot point seems implausible today, but strikes me as reasonable if World War III had happened in the early 1960s.

One of these professionals is Isaac Leibowitz, a Jewish electrical engineer who developed weapons systems for the military. He converts to Catholicism after the war, and with permission from New Rome, founds an Albertian Order in the southwest to hide and preserve ancient knowledge until such time as humanity wants it once again. Before the work is complete, however, he is captured and killed in the great Simplification. To the members of the abbey, Leibowitz a saint. Outside of it, no one knows his name.

The story begins in the 2500s, as Brother Francis of Utah performs his Lenten hermitage as an inductee to the Order. He is visited by a Wanderer, who frightens Francis, but who marks a rock that would make a good keystone for the stone structure which Francis is building to protect himself from wolves. After the wanderer leaves, Francis removes the stone, and causes an unexpected cave-in. That pile of rubble covered the opening to a fallout shelter. In the antechamber, Francis finds a human skeleton, and a toolbox that belonged to the Blessed Leibowitz himself. Francis’s amazement is doubled when the toolbox contains an actual blueprint, the first found in readable condition for centuries.

Unsurprisingly, this does not ease along Francis’s induction. Eventually, though, he is inducted, and the evidence satisfies New Rome that Leibowitz should be canonized. Investigators conclude that the skeleton belonged to Leibowitz’s wife. Proving that she died before he took the monastic vows was the last hurdle before his Sainthood.

As a monk of Saint Leibowitz, Francis becomes a scribe. His skill develops, and he soon begins to copy the writings he found in the cave, culminating in the blueprint. No one understands it, but it must be dutifully preserved regardless. Once the copy is made, Francis does research in the archives, and decides to produce a more dramatic, illuminated copy.

The Illuminated Blueprint is a success, and the Abbot decides to sent both the copy and original to New Rome. Francis is sent, travelling alone, and is robbed by mutants along the way. The mutants take the illuminated copy and hold it for a ransom that Francis could never pay. Discouraged, he continues with the original to New Rome.

Meeting the Pope, however, reassures him. The Pope points out that the mutants left the original holy relic, so the illuminated copy provided a great service. As Francis prepares to return to the abbey, the Pope further gifts Francis the gold necessary to pay the ransom. However, Francis is skilled as he approaches the robber’s lair. The Wanderer is watching, though, and denies the mutant murderer a meal. Eventually, the Wanderer returns Francis’s corpse to the abbey.

The second part of the book takes place six hundred years later, as humanity approaches a renaissance. The plot of this section is much less dramatic and memorable, focused on the scientist Thon Taddeo’s visit to the abbey from Texarkana. The monks barely beat Taddeo to the reinvention of the electric lightbulb, initiating a long dialogue on the conflict between science and religion.

War is brewing between the southern city-states. Taddeo gathers as much information as he can, and soon must depart. The abbey prepares to defend itself and take in refugees from the nearby town, on the condition that able-bodied men fight alongside the monks. We’re not told if the abbey even needs to defend itself in the coming wars. The section ends with a cynical Poet, tolerated by the long-suffering monks, dying in the sun after trying to save some harmless refugees from blood-thirsty cavalrymen.

The final part of the book picks up in 3781, as humanity prepares for atomic war once again. The first several pages break dramatically from the narrative style of the rest of the book, and the final part is punctuated with a few press conference transcripts from the Atlantic Confederacy’s Defense Minister. I think this is an artefact of the book’s history as a fix-up. More introduction was necessary when these final chapters stood by themselves, and that introduction was probably longer at the time.

In practice, we’re quickly shown a world with atomic spacecraft, interstellar colonies, and temperamental translation computers. Leibowitz is popular as the patron saint of electricians, and mostly forgotten for his work in booklegging.

The Atlantic Confederacy and Asian Coalition have, for undisclosed reasons, found themselves in a cold war. It builds slowly. An atomic accident—possibly a test—occurs in the Asian Coalition. The Atlantic Confederacy considers this violation of international law an act of war, and fires a warning shot over the Pacific.

Observers in the abbey watch the atmospheric radiation count rise and become worried. Realizing that the future likely holds nuclear war, they activate an old plan to “borrow” a starship from the government and carry the core teaching of the church to the extrasolar colonies.

Further bombings occur, destroying Texarkana and a number of Asian space stations. The World Court enforces a 10-day ceasefire, which both sides agree to. The Church mobilizes their survival plan, collecting the Leibowitzian monks with space experience to depart for Alpha Centauri.

At this point, Miller could have ended the book. Terra is about to erupt in nuclear flames once again, and the Church is prepared to survive. Honestly, I was feeling fairly sympathetic towards Catholicism after reading such believable, devoted characters. But Miller respects his readers too much for that. He pushes us.

During the ceasefire, millions of refugees leave the outskirts of Texarkana, suffering from radiation sickness. The Atlantic Confederacy’s government is still functional at this point (one wonders if ours would be, if Washington, D.C. (and just D.C.) were destroyed). The Green Star, their version of the Red Cross, sets up voluntary euthanasia camps to let those terminally afflicted die quickly without further suffering.

The abbot won’t stand for this. As a devout Catholic, he can’t assist in the matter, or even suffer it to continue. The majority of the population is Catholic, in the way that Americans are Christians, and the abbot tries to put the literal fear of God into them. The abbot desperately tries to stop a sick woman from taking her child to the camp, despite the fact that both are clearly terminal cases. He almost succeeds, before being stopped by the Green Star officials. Seeing the Church overwhelmed by worldly forces is enough to break the streak, or so the abbot thinks.

He doesn’t have much time to ponder the matter before war erupts again. A nuclear explosion destroys the rubble, trapping the abbot in rubble. As he lays dying, he’s visited a mutant woman he’s known for years, except something is different. Her second head, which everyone assumed was braindead, is awake, while her first head appears to be unconscious. The abbot had previously refused to baptize the second head, and desperately tries to rectify this error as his final act. Amazingly, she refuses, and instead gives communion to the abbot, implying that she is holier than him. She wanders off and the abbot slips into the final night. Meanwhile, the monks board their starships, ready to take the Church to the stars.

It’s an interesting book. Walter Miller was a Catholic convert, and clearly believed it very strongly. Still, I can’t imagine that a truly merciful God would care so much about self-destruction if a) you’re dying painfully of a hopeless disease and b) the entire world is about to be destroyed. Perform your own miracles, I guess. We’re conscious, I promise, but we aren’t omnipotent. A-bombs are a long way from the alpha and the omega.

Despite the depressive ending, it’s a book worth reading if you’re interested in moral theology or the material implications of nuclear war. The story is fast-paced and exciting, with a simmering suspense underneath it all. A Canticle for Leibowitz definitely earned its place in the canon of post-apocalyptic science fiction.