Riding the Red Horse (14 page)

Fifteen minutes later Peter's radio squawked. He listened, hearing the commands over static and jamming. “Call the men together,” Peter ordered when he'd heard it out.

“It's this way,” he told them. “We still hold Zaragoza.

There's a narrow corridor into the town, and unless somebody gets down there to hold it open, we'll lose the village. If that goes, the whole position in the valley's lost.”

“Cap'n, you can't ask it!” The men were incredulous. “Go back down into there? You can't make us do that!”

“No. I can't make you. But remember Zaragoza? Remember how the people cheered us when we marched in? It's our town. Nobody else set those people free. We did. And there's nobody else who can go help keep them free, either. No other reinforcements. Will we let them down?”

“We can't,” Allan Roach said. “It needs doing. I'll come with you, Cap'n.”

One by one the others got to their feet. The ragged column marched down the side of the ridge, out of the cool heights where their water was assured, down into the valley of the river of sand.

They were half a kilometer from the town at dawn. Troops were streaming down the road toward them, others running through the olive groves on both sides.

“Tanks!” someone shouted. “Tanks are coming!”

It was too late. The enemy armor had passed around Zaragoza and was closing on them fast. Other troops followed behind. Peter felt a bitter taste and prepared to dig into the olive groves. It would be their last battle.

An hour later they were surrounded. Two hours passed as they fought to hold the useless olive groves. The tanks had long since passed their position and gone but the enemy was still all around them. The shooting stopped, and silence lay through the grove.

Peter crawled across the perimeter of his command: a hundred meters, no more. He had fewer than fifty men.

Allan Roach lay in a shallow hole at one edge. Ripe olives shaken from the trees fell into it with him, partially covering him, and when Peter came close, the sergeant laughed. “Makes you feel like a salad,” he said, brushing away more olives. “What do we do, Cap'n? Why you think they quit-shooting?”

“Wait and see.”

It didn't take long. “Will you surrender?” a voice called.

“To whom?” Peter demanded.

“Captain Hans Ort, Second Friedland Armored Infantry.”

“Mercenaries,” Peter hissed. “How did they get here? The CD was supposed to have a quarantine....”

“Your position is hopeless, and you are not helping your comrades by holding it,” the voice shouted.

“We're keeping you from entering the town!” Peter answered.

“For a while. We can go in any time, from the other side. Will you surrender?”

Peter looked helplessly at Roach. He could hear the silence among the men. They didn'tsay anything, and Peter was proud of them. But, he thought, I don't have any choice. “Yes,” he shouted.

The Friedlanders wore dark green uniforms, and looked very military compared to Peter's scarecrows. “Mercenaries?” Captain Ort asked.

Peter opened his mouth to answer defiance. A voice interrupted him. “Of course they're mercenaries.” Ace Barton limped up to them.

Ort looked at them suspiciously. “Very well. You wish to speak with them, Captain Barton?”

“Sure. I'll get some of 'em out of your hair,” Barton said. He waited until the Friedlander was gone. “Pete, you almost blew it. If you'd said you were volunteers, Ort would have turned you over to the Dons. This way, he keeps you. And believe me, you'd rather be with him.”

“What are you doing here?” Peter demanded.

“Captured up north,” Barton said. “By these guys. There's a recruiter for Falkenberg's outfit back in the rear area. I signed up, and they've got me out hunting good men for Falkenberg. You want to join, you can. We get off this planet next week; and of course you won't fight here.”

“I told you, I'm not a mercenary—”

“What are you?” Barton asked. “Nothing you can go back to. Best you can look forward to is being interned. Here, come on to town. You don't have to make up your mind just yet.” They walked through the olive groves toward the Zaragoza town wall. “You opted for CD service,” Barton said.

“Yes. Not to be one of Falkenberg's—”

“You think everything's going to be peaceful out here when the CoDominium fleet pulls out?”

“No. But I like to choose my wars.”

“You want a cause. So did I, once. Now I'll settle for what I've got. Two things to remember, Pete. In an outfit like Falkenberg's, you don't choose your enemies, but you'll never have to break your word. And just what will you do for a living now?”

He had no answer to that. They walked on in silence.

“Somebody's got to keep order out here,” Barton said. “Think about it.”

They had reached the town. The Friedland mercenaries hadn't entered it; now a column of monarchist soldiers approached. Their boots were dusty and their uniforms torn, so that they looked little different from the remnants of Peter's command.

As the monarchists reached the town gates, the village people ran out of their houses. They lined both sides of the streets, and as the Carlists entered the public square, there was a loud cheer.

Science fiction tends to pride itself on anticipating and predicting technological advances and their implications. Heinlein’s Mobile Infantry from
Starship Troopers
, for example, come closer to reality every day. When those predicted advances fly in the face of the physically, intellectually, and morally possible, science fiction tends to fail. Conversely, when the impossible is shut out, science fiction can postulate other, more promising technologies and approaches.

Ken Burnside’s piece, “The Hot Equations: Thermodynamics and Military SF”, does some of that debunking the impossible through recourse to hard physics.

Ken has been a wargame designer since 1991 and run Ad Astra Games since founding it in 2001. Ken wrote the definitive space combat game for David Weber’s
Honorverse
, and is turning his attention to Marc Miller's
Travellerverse
as this goes to press. Ken’s also won an Origins Award for
Attack Vector: Tactical
, and been a hard science fact-checker for a number of mil-SF authors. He has contributed to the
Training & Simulations Journal
and reported for
Naval Technology
.

Ken now brings that expertise to bear to utterly smash any number of illusions and delusions commonly found in the science fiction world with regards to space travel and space combat. With those out of the way, maybe we can start writing about ideas that might actually work.

“Amateurs think about tactics, but professionals think about logistics.”

—General Robert H. Barrow, 27th Commandant of the Marine Corps, 1980

And futurists think about thermodynamics.

The maxim about tactics and logistics has been truth on the ground since Napoleon, and has been alluded to by writers going back to Sun-Tzu. As combat moves from the bosom of the Earth, and into orbital and interplanetary space, it will be limited by increasingly complex logistics and by thermodynamics.

Ignoring thermodynamics is one of the cardinal sins of science fiction authors writing military SF; the same authors who wouldn't dream of saying that a Colt 1911A fires a .40 caliber bullet will blithely walk into even more galling gaffes through simple ignorance and unquestioned assumptions.

Thermodynamics and You

For those who stopped shy of doing thermo classes in college, or who took the class and went on to do something less mind-bendingly insane with their lives, the basic role of thermodynamics is moving heat from where you have it to where you want it to be. Anyone who's fired a gun and had hot brass hit them in the chest or arm has experienced the first rule of thermodynamics: It never quite works the way you want it to. Hot brass is why caseless ammo never took off in the late '80s and early '90s; ejecting hot brass is a surprisingly effective way to manage the thermodynamics of a breech-loading gun. The rifles firing caseless ammo had a high jam rate because the heat normally rejected by throwing the case out the slide was retained in the feed mechanism, which would expand and evaporate lubricants. While the manufacturer solved the problem with a much more expensive feed mechanism, it raised the price of the gun, and NATO didn't adopt it.

The current problem child of the Pentagon, the F-35 Lightning II, is also running into thermodynamic constraints. The exhaust from the vectored thrust on the F-35C is hot enough to deform steel, and require the ships slated to carry it to move temperature sensitive stores from the spaces under the landing deck. There are currently engineering studies on new surfaces for those decks that can sustain the pressure and temperature combination, and the reports are an exercise in schadenfreude if your mind runs to an engineering bent.

While these examples illustrate the mundanity of thermodynamic limits on the earth, in space, thermodynamics is even more constraining. There are three ways to remove waste heat from a system: convection, conduction and radiation.

If you think of a pot of boiling water, you get to see all three of them in action: The interface where water converts to steam and heats up the air, causing the air to circulate is convection. It's the most efficient way to remove waste heat from a system—heat up the gas or liquid of the surrounding environment, let its expansion trigger circulation, and thermodynamics gets easier to manage—at least until you're melting the deck plates under your quarter-billion-dollar jets on takeoff.

The part of the handle on the pan that gets hot—and the reason why there's an insulated grip for you to hold on to—is conduction. Thermal conduction, like electrical conduction, varies with the material; metals are mediocre conductors of heat; surprisingly diamond and carbon nanotubes are the top dog in this area. Thermal conduction, by and large, is a problem.

The IR signature of your pot of boiling water is radiation; you can detect IR by moving your hand next to the pot and feeling the heat radiating off of it. Radiation is the least efficient way of disposing of waste heat…and the only one available in space.

Space as a Sensor Environment

When you look at the night sky, the first impression your brain makes is "Gosh, that's dark, you can't see anything." Space, at least from the context of sensors, is an amazingly friendly environment for two reasons.

The first is the lack of a horizon. At the time this was written, I can be reasonably certain you were born and raised on the surface of a planet; you automatically assume that there is a horizon. You are inclined to think that there's a distance beyond which something can't be seen, due to the curvature of the assumed planetary body.

In space, the horizon assumption is almost always wrong. The one exception is Low Earth Orbit (LEO), where the limb of the earth can temporarily obscure something for roughly an eighth of an orbital period; this is about a 15-minute window, tops. Detection range is never limited by terrain for militarily significant increments of time.

In modern sensor paradigms, there's detection range, identification range, and targeting range. In space, object detection is fundamentally one of time. Current consumer-grade hardware is capable of processing full sky searches for anomalies against the background in seconds. The number of Earth-crossing objects we identify doubles every six to seven months, and that's before putting a skywatch platform in the Earth-Sol L1 position to see them as they reflect sunlight back at the sun from a different angle.

Thermodynamic radiation is what defines the detection parameter in space. Conduction means that objects develop hot spots and reach radiative equilibrium over their surface. This radiative equilibrium is called the “black body” temperature. At Earth's orbital distance, that temperature is about 250 to 260 Kelvin (K) depending on the material and surface color. If you look at the sky with an IR sensor, you can identify dark objects by their black body temperature. The background of space has a temperature of about 2 to 5 K, and spotting something a few hundred degrees warmer is easy, provided you can take enough pictures, stitch them together and compare them to your last data processing pass.

How much time do you have? Consider that going from LEO to Lunar orbit is roughly a three-day trip. Going from Earth to Mars is a 9-month trip at an optimum conjunction with current technologies. Even with long duration drives, minimum travel times from Earth to Mars will still take six to eight weeks.

Detecting Spaceships

We're spotting asteroids via the temperature differential between 250 to 260 K and the 2 to 5 K background temperature of space. Water ice melts at 273.15 K. Room temperature is 20 to 25 degrees C, which is 293 to 298 K. Human crews need some part of the ship at room temperature, and that's 30-40 K warmer than blackbody re-radiation temperature at Earth's orbit. If everything else is turned off, your life support systems make your ship a dim, but visually distinct object.

Power generation, even by solar collection, only makes it worse. Terrestrial power plants dissipate waste heat by circulating a working fluid. On a nuclear submarine, they can use the thermal mass of the surrounding ocean as a heat sink and gain vastly in efficiency. On a spaceship, that's not an option. You only get rid of heat by radiation, and power plants run hotter than life support systems.

Useful work is done by the temperature differential between the hot and cold side of a power plant. Using the archetypal hot equation – the Stefan-Boltzmann black body radiation law, j=σT4, radiative efficiency (j) increases at the fourth power of the temperature of your radiator times the Boltzmann constant. The radiance (brightness) of your radiator per unit area also goes up with the fourth power of your radiator temperature—the more effective your radiator is at dissipating waste heat, the brighter it will be. Optimizing your radiator mass and efficiency along with your power source means you want the smallest, hottest running radiators you can manage with the widest delta between radiator temperature and reactor temperature. The place where those curves cross is radiators running at 75 percent of your reactor temperature, radiating 3.5 to 5 Watts per Watt of useful energy generated.