Nearly all these fuels present some difficulty. Liquid fluorine, for example, is nasty stuff. It’s highly reactive with nearly any other element, which is a good thing for a rocket fuel to be. But it is also highly reactive with nearly any other element, which means it is amazingly difficult to store because it will react with its container. Hydrazine and tetrafluorohydrazine, both fluorine-based, are also extremely toxic and difficult to store. Kerosene and methane are easier to handle, but they’re not as powerful, and kerosene requires either a source of raw petroleum or a pretty elaborate chemical plant. And beryllium infusion requires a constant supply of beryllium—not impossible to manage, but why bother? Beryllium is an uncommon element.
It turns out that the best all-around rocket fuel, in terms of ease of supply, ease of storage, and specific impulse, is also the simplest: liquid hydrogen and liquid oxygen. Since hydrogen and oxygen are the components of water, if you’ve got a source of water and a way to split the water molecules, you’ve got a source of rocket fuel.
Unfortunately, liquid oxygen and liquid hydrogen are among the most bulky kind of fuel a spacecraft can use. Galactica needs a much more efficient type of propellant. It’s time to look past liquid fuels to more exotic forms of space propulsion.
Propulsion Type Specific Impulse Duration
APCP Solid propellant ~250 Seconds to minutes
Kerosene—liquid oxygen ~350 Seconds to minutes
Methane—liquid oxygen ~360 Seconds to minutes
Hydrazine—tetrafluorohydrazine ~380 Seconds to minutes
Liquid hydrogen(LH2)—liquid oxygen(LOX) ~450 Seconds to minutes
Liquid hydrogen(LH2)—liquid fluorine(LF2) ~460 Seconds to minutes
Liquid hydrogen/beryllium—liquid oxygen ~530 Seconds to minutes
At this point it is important to recall that thrust and specific impulse should not be confused with each other. Thrust is a measure of the instantaneous force generated by a system; specific impulse is a time-independent measure of integrated thrust per unit of propellant that is expended. Propulsion systems with very low thrust can have very high specific impulses. In fact, in many cases, for most of the propulsion systems listed the two values seem inversely proportional.
Nuclear thermal engines, though included in the “exotic” list, have actually been built here on Earth. In fact, they were going to be the keystone of NASA’s plan to land humans on Mars by 1980. They’re remarkably simple in design: a nuclear reactor heats hydrogen gas to enormously high temperatures, then shoots the hot gas out the back of the rocket. In reality, building such a rocket that didn’t blow up or contaminate the environment was next to impossible. NASA’s nuclear thermal development project was shut down in 1972 when it became obvious that we weren’t going to Mars by the end of the decade.
Arcjet rocket engines run a stream of propellant (such as hydrazine or ammonia) past an open electrical discharge (sort of like a continuous electric spark). This energizes the propellant and makes it exit the rocket engine more quickly. The down side to this design is that it requires additional equipment to generate the electricity necessary to produce the continuous spark, for only a fourfold increase in specific impulse over conventional liquid propellants.
A pulsed inductive thruster is a form of ion propulsion that uses perpendicular electrical and magnetic fields to propel ionized gas into space. Like regular ion thrusters, it produces very low thrust that can be kept up for a very long time. Unlike regular ion thrusters, PITs can be scaled up relatively easily by increasing the number of pulses per second (which means increasing the energy available to the electrical and magnetic fields). To propel something the size of Galactica might require the electrical power used by a city.
Ion engines were first proposed by Robert Goddard back in 1906, and they have been a stalwart in science fiction for over 50 years. Electrostatic ion thrusters work like an old-fashioned television set. Neutral propellant gas, usually xenon, is injected into a discharge chamber (imagine the picture tube of an old TV). A cathode ray tube (the cylindrical hump at the back of the picture tube) sprays electrons into the chamber, turning the neutral xenon into positively charged xenon ions. Electric or magnetic fields then accelerate a beam of these ions out the back of the spacecraft, generating thrust. In this sense, an ion engine can be considered a mini-linear accelerator. Before they leave the spacecraft completely, the ions pass negatively charged electrical grids that reattach electrons to the ions. This prevents the spacecraft from becoming electrically charged. Like all ion engines, this design trades low thrust—less than the weight of a sheet of paper here on Earth—for a very long operating life. For this reason, they are used primarily for station-keeping on Earth-orbiting satellites. Because they can run for weeks or months, ion engines have very high SI. They have recently been used as the main propulsion system for NASA’s Deep Space 1 and Dawn spacecraft, as well as the European Space Agency’s lunar-orbiting SMART-1.
A variable specific impulse magnetoplasma rocket (VASIMR) works much like the previously mentioned ion engines, with one huge difference: it can vary its output to provide low thrust/long life propulsion, or high thrust/short life propulsion. Theoretically, a VASIMR could be throttled up to take off from the surface of an airless moon, then throttle back to provide slow, long-term acceleration in outer space. While these might not be the engines Galactica uses, a version that somehow works in an atmosphere would be perfect for Vipers and Raptors.
External pulsed plasma propulsion used to go by the older name of “nuclear-pulsed propulsion.” It was a plan to explode small nuclear bombs behind (or even within) a spacecraft. The radiation from the explosion would vaporize a portion of a large “pusher plate” mounted on the back of the spacecraft. The vaporized material that shot off in one direction would propel the spacecraft in the opposite direction. By exploding a bomb every few seconds, a massive spaceship (early designs were the size of a battleship) could putt-putt its way to Mars in a few weeks, as opposed to the more typical 6 to 12 months, leaving a trail of deadly ionizing radiation behind it.
Recall that our battlestars and Vipers require a propulsion system with a combination of high thrust and high SI. Of the methods we’ve discussed so far, VASIMR or a variant is the only candidate for that, and not a particularly good one. Matter-antimatter engines are an old Star Trek standby that can probably be ruled out. The ability to produce and contain antimatter seems to be beyond the technology of the Colonial Fleet.
Enter tyllium.
For decades, science fiction writers and authors have invented new and exotic materials to power their spacecraft, or to endow their spacecraft /armor with the desired combinations of weight, strength, and other material properties. Borrowed from real-life engineers, a name has even been coined for fictitious substances that have such improbable combinations of material properties: unobtanium.dg
Unobtanium in the Star Trek universe is dilithium; in Battlestar Galactica it is tyllium. Tyllium was the fuel source for Galactica and her Vipers (and presumably Raptors as well) in both the original series and the reimagined series, with a minor difference in pronunciation. (In the original series tyllium was pronounced TIE-lee-um; more recently it has become TILL-ee-um.)
FINDING MATERIALS TO MAKE THE BLACKBIRD
When the writers David Weddle and Bradley Thompson wrote “Flight of the Phoenix,” the executive producer Ron Moore insisted that the materials used to make this craft shouldn’t simply appear out of nowhere, as might be the case on other television dramas. The Blackbird, he said, should be made from materials the viewer can expect to exist within the Fleet.
In a Fleet depleted of resources, it is amazing what one can come up with when looking hard enough. After the uprising and subsequent pardon of the prisoners on the Astral Queen, it’s reasonable that there might be a lot of iron—in the form of jail bars—available for an airframe. Battle damage might have created some usable rubbish—in particular, sheet metal that could be used on the aircraft. We know that th
e engines were spares taking up space on the flight deck of Baah Pakal.
Chief Galen Tyrol in “Flight of the Phoenix.”
Where on Caprica did the carbon composites come from for the airframe? Recall that the huge luxury liner Cloud Nine had a lake (before Cloud Nine was destroyed by the explosion of a nuclear warhead in “Lay Down Your Burdens, Part II.”) The resin used to repair paddle boats provided the outer skin for the Blackbird!‹
We have no way to perform a direct comparison of the thrust generated by a tyllium-powered propulsion system to that of modern-day solid, chemical, or even exotic propulsion systems. We also do not have a way to compare relative values of specific impulse. What we do know, however, is the enthalpy of tyllium.
Propellant Enthalpy (joules per kilogram)
APCP 3.1 × 107
LH2/LOX 1.3 × 107
Methane/LOX 1.1 × 108
In thermodynamics, the enthalpy of a chemical reaction is a measure of its thermodynamic potential—how much energy is locked up within a given mass of chemical reactants. While the total enthalpy is a difficult quantity to measure, the enthalpy change of a chemical reaction is useful and easier to measure, since it is a measure of the potential work that the reactants can perform. For example the APCP in the space shuttle yields 31 million joules of energy for every kilogram burned, or 3.1 × 107 J/kg.
In comparison, the exotic propulsion system that best optimizes thrust and specific impulse is VASIMR, which can generate 4.3 × 1011 joules per kilogram of propellant.
In the episode “The Hand of God,” Dr. Baltar says that the enthalpy of tyllium is “half a million gigajoules per kilogram,” or 5 × 1014J/kg. If 1 kg of tyllium is converted directly into energy by E = mc2, that would release 9 × 1016J/kg. If Dr. Baltar is correct, the energy locked away within tyllium is slightly over half a percent of the yield of a direct conversion of mass to energy (which is equal to the output of a matter-antimatter reaction). Put differently, there is several million times more energy locked away in tyllium than within the most powerful chemical rocket fuels known today. Tyllium even has thousands of times more potential energy than the most promising exotic propulsion technologies on the near-term horizon. Consider the places humankind might have ventured today with access to tyllium-based propulsion!
THE BLACKBIRD’S DDG-62 ENGINES
If an author wishes to write convincingly on a topic, he or she has to do a boatload of research. The willingness to do so can be the difference between a good writer and a not-so-good one.
My friendship with Brad Smith dates back to seventh grade. During the first two years of the run of Battlestar Galactica—until his career took him to bigger and better things—Brad, known by his crew as Captain Smith, was the commanding officer of the Arleigh Burke class guided missile destroyer USS Fitzgerald (DDG-62).
Each type of ship in the U.S. Navy has a given designation. An aircraft carrier is a CV, a cruiser is a CG, and a destroyer is a DD. If the destroyer has the capability to launch guided missiles, then it is referred to as a DDG. The hull number of Fitzgerald is 62, hence the proper designation of USS Fitzgerald is DDG-62.
Before moving to Japan, the “Fightin’ Fitz” had a Tiger Cruise just off the coast of San Diego. In Navy-speak a Tiger is any relative or friend of a ship’s crew member, so a Tiger Cruise is essentially “Friends and Family Day.” The ship put to sea for a few hours, and the visitors got to see first-hand what life is like aboard a U.S. Navy warship.
Since much of Battlestar Galactica is, in fact, about life aboard a warship—albeit one in space—I figured that this presented a great opportunity for our writers. With the captain’s permission, I invited the entire writing staff of Galactica to join us on Fitzgerald that day. Many were interested, some had previous commitments, a couple more had to cancel at the last minute. Ultimately only Bradley Thompson and his significant other, Peggy Sue, were able to attend.
While on Fitzgerald Bradley saw and experienced as much as possible, and made the most of his time aboard. To him this was research, so he took copious notes during his day-long visit. Although it might be a stretch to say they had a direct influence, those notes and that experience subsequently impacted the writing of the first two episodes of season two, “Scattered” and “Valley of Darkness.” Bradley’s experience had a very small, but more easily observable, influence on two other episodes, “Flight of the Phoenix” and “Pegasus.”
Recall that in the episode “Flight of the Phoenix,” Chief Tyrol made the decision to build the Blackbird stealth craft. It looked like construction would come to an end, sadly, because there were no engines available. Commander Adama supported the construction of the Blackbird, but insisted that no parts be used that could have value in operational Vipers or Raptors. A solution came from the most unlikely of places: Colonel Tigh. Claiming that he owed the XO of the Baah Pakal a favor, Tigh said that there was a pair of “old DDG-62 engines taking up space in their cargo hold.” The Blackbird was the recipient. In the next episode, “Pegasus,” aeronautical engineer Peter Laird took note of the DDG-62 engines while inspecting the Blackbird, and commented to Tyrol that he had designed them.
The DDG-62 reference was a thank you to the captain and crew of USS Fitzgerald for their hospitality.‹
From appearances, the blue exhaust from Galactica’s engines looks similar to the exhaust of ion or magnetoplasma engines, so that’s probably how they travel within the Twelve Colonies. Perhaps tyllium, then, is used to generate electrical power, which, in turn, powers a more exotic type of engine.
To travel between star systems, they use another form of propulsion entirely.
CHAPTER 22
Faster Than Light: Galactica’s Jump Drive
Most of space is empty and there aren’t a lot of strange things to bump into.
—Ronald D. Moore, Battlestar Galactica series bible
It is a fundamental mantra of the screen-writer: never wake the audience from your dream. A television concept can be the most poignant or beautiful work imaginable, but careless writing can instantly turn an “Oh wow!” moment into an “Oh please!” moment. Works of science/speculative fiction like Battlestar Galactica tend to attract a more technically literate fan base, which means that egregious technical gaffes are more readily spotted and denigrated (“Worst! Episode! Ever!”). There is an implied contract between those who create and those who enjoy science fiction: In defining the laws under which the artist’s fictional universe operates, the artist is allowed only a few “conceits”—ways in which the laws of the known universe may be bent or broken. If the artist subsequently remains faithful to the laws he or she has defined, we the audience will collectively and happily suspend our disbelief and allow ourselves to be taken on an adventure. But the elastic of the audience’s collective psyche will stretch only so far. It’s best if even the conceits have reasonable explanations.
Space is big. Really big. You just won’t believe how vastly hugely mind- bogglingly big it is.
—Douglas Adams, The Hitchhiker’s Guide to the Galaxy
Like artificial gravity, faster-than-light travel (aka FTL) has been one such conceit of science fiction since the inception of the genre, and for good reason. Although much of the appeal of Battlestar Galactica is the human drama, the political intrigue, and the never-ending specter that the next Cylon attack could be the final Cylon attack, it is beneficial if the Rag Tag Fleet actually has a chance of getting to Earth within the lifetimes of our central characters or, preferably, over the run of the series. That means that the Fleet has to cover the vast distances between stars in a short amount of time. The problem is the Second Law of The Science of Battlestar Galactica: “Space is mostly empty. That’s why it’s called ‘space.’”
A typical robotic Mars probe takes 6 months to a year to make its journey. It took the Cassini spacecraft 6 years and 8 months to reach Saturn. The most distant object ever built by humankind at present is the Voyager 1 spacecraft. In early 2010, Voyager 1 was slightly ov
er 112 astronomical units (AU) from the Sun, and it took more than thirty years to get there. Voyager 1 is currently traveling into interstellar space at 3.6 AU per year in the general direction of the constellation Ophiuchus. The spacecraft will eventually pass within 1.64 light-years of the small red dwarf star AC +79 3888, currently located in the constellation Ursa Minor, in approximately 40,000 years. So not only is the distance to even the nearest star, well, astronomical, but current technology has not yielded a propulsion system that can cover interstellar distances within a human lifetime.
Is interstellar travel even possible, when distances are measured in light-years as opposed to AU? As Admiral Adama once said, “Context matters.” Let’s put into context, then, the scale of how vast and empty our galaxy truly is. Let’s say that Sol, our Sun, was an orange sitting at the end of a basketball court in New York’s Central Park. In that scale, Earth would be the size of a grain of dust 70 feet away, about the distance from the baseline to the top of the opposing key. The nearest star to Sol is the trinary star system Alpha Centauri, 4.37 light years away, which would be represented by a slightly larger orange (Alpha Centauri A), in mutual orbit with a large plum (Alpha Centauri B), with a ball bearing in orbit about the pair (Proxima Centauri). At that scale, all three stars would be 3,663 miles (5,895 km) away, just east of Paris, France!
Laura Roslin and William Adama.
Saul Tigh and Laura Roslin.
Centaurus is a constellation in the southern sky, and since the bulk of Earth’s population is in the northern hemisphere, Alpha Centauri is below the horizon for most people. The closest star visible to nearly all of Earth’s population is also the brightest star in our sky: Sirius, 8.6 light years away. Relative to our orange in Central Park, Sirius would be a grapefruit resting outside of Karachi, Pakistan, 7,210 miles (11,604 km) away. If Voyager 1 were headed toward Alpha Centauri, it would take between 75,000 and 80,000 years to get there; if it were headed toward Sirius, it would take between 148,000 and 157,000 years.
The Science of Battlestar Galactica Page 17
