Chain of Command – Snippet 06
“Cha-cha has gone active with a drone!” Delacroix reported from the Tactical Three seat beside him, and Sam saw it on his own screen as well. USS Oaxaca, the command vessel for their four-boat destroyer division, nicknamed Cha-cha, had just launched a sensor drone and turned on its active radar.
“Multiple radar echoes,” Delacroix continued, “small projectiles incoming, bearing zero degrees relative. Range nine thousand kilometers and closing fast. Very fast.”
The projectiles were coming on the exact opposite heading. All the captain’s burn had accomplished was to add about two hundred meters per second to their collision velocity. Sam checked the calculated closing rate: 97,000 kilometers per hour. Jesus Christ, that was twenty-seven kilometers a second! They’d better get out of the way quick. He set a course intersect timer.
“Three hundred thirty seconds to impact,” he said.
Ensign Lee at Maneuvering One began working the current and projected courses. “Best evasion track is ninety degrees relative and flat. Permission to align the boat for burn.”
“Negative! It’s the captain’s call,” Huhn answered.
Ensign Lee, the only reservist line officer other than Sam, turned and looked at Huhn and then at Sam, her eyes questioning. Her face was round and fine-featured, chin recessed, mouth small, eyes always open wide, and her nose was incongruously large and wedge-shaped, which gave her the look of a slightly startled bird, even more so just then. She was right, though.Â Sam was sitting TAC One. It was his job to speak up.
“Sir, you’re in command until we’ve got comms to the bridge. We need to get the hell out of that cloud’s way.”
“Kramer, get me the division commander,” Huhn said. That would be Captain Bonaventure aboard USS Oaxaca.
“Incoming text from Cha-Cha now, sir,” Kramer answered from the Comm Station “Message reads: All red stingers, evade. Seventy-eight degrees relative, angle on the bow ninety, forty-second MPD full burn. Expedite. Signed Red Stinger Six Actual. End message.”
“Aligning the boat,” Ensign Lee said immediately, punching the acceleration warning klaxon. Huhn visibly started in his command station as it sounded. Sam saw him open his mouth to speak but then hesitate and close it again. For just a moment Sam was sure he had been about to order Lee to belay the alignment. Then Sam felt the side-ways acceleration as Lee turned the boat’s orientation with the attitude control thrusters. After a dozen or more seconds he felt the acceleration switch direction, begin slowing them to the new orientation. Sam played with the range adjustment and resolution on his tactical display just to keep his hands busy, waiting for the boat to finally settle on its new track, feeling the precious seconds bleed away.
“Boat aligned,” Lee finally announced. “Full burn.”
Again Sam noticed she didn’t ask for permission. He felt himself pushed back into his acceleration rig from the first thruster pair, then rapidly climbing to a half gee once all six thrusters kicked in, roaring out 8,500 tons of thrust for forty seconds.
“Two hundred five seconds to impact,” Sam said when the thrusters fell silent and they were weightless again. A plot of the course change due to the burn showed they’d have displaced forty kilometers laterally from their former position by the time the cloud got to them. Forty kilometers wasn’t much in deep space, where they usually measured distance in light seconds, each of which was about three hundred thousand kilometers.
If the intel briefing had been right, the pellets in the cloud were small, maybe not much bigger than sand, and the search radar couldn’t track individual particles that size, just the collective reflection of a whole bunch of them. That made it hard to tell how wide the cloud was and exactly how far they were from its leading edge. The shipboard tactical system had made some assumptions about likely dispersion and had predicted they’d avoid the likely danger zone, but assumptions weren’t facts.
How had a cloud that small, relatively speaking–actually three of them in succession–happened to hit them in all this big black vacuum, and on an exact reciprocal course? Whoever lived through this had better give that some hard thought.
“One hundred sixty seconds to impact.”
They sat in silence, feeling the burden of time’s glacial passage, waiting to empirically discover their fates. As they did so, Chief Petty Officer Abhay Patel glided through the hatch and wordlessly strapped into the Tactical Two chair. Sam nodded to him.
Maybe they should have burned longer, but for Puebla that would have meant emptying their energy storage system. They’d have had to use the direct fusion thruster to get back on course. Everyone in the star system would see that. Maybe everyone already knew where they were. Maybe they all should have just used the direct fusion thrusters and poured on two gees of acceleration for the full two minutes they had until impact. Maybe.
One thing occurred to Sam: if the pellet cloud hit them now, it would hit them broadside, and that would do a lot more damage. Huhn didn’t look as if he was thinking things through very well, and it was Sam’s job as Tac One to remind him.
“Commander Huhn, I recommend we re-orient the boat nose-on to the angle of attack. The forward micro-meteor shield will give us some protection.”
Huhn jerked a bit in his acceleration rig and looked at Sam, eyes wide.
“Sir, shall I order Ensign Lee to reorient the boat?” Sam asked.
Huhn stared at him blankly. His eyes blinked.
“Yes, sir,” Sam said. “Ensign Lee, reorient the boat to our previous heading.”
“Aye, aye, sir,” she said and sounded the boat-wide acceleration klaxon.
“One hundred to impact,” Sam said as he felt the Puebla begin to turn.
Why wasn’t Jules or anyone else on the bridge answering their commlinks?
She and Sam had hit it off almost as soon as he came on board. They were officers and both understood their responsibilities–she probably better than he–so they hadn’t crossed any lines, hadn’t broken any rules. Maybe they should have.
The radar image of the pellet cloud disappeared when it crossed the 1700 kilometer range band and snuffed out ChaCha’s drone and its active radar.Â Sam’s screen went back to displaying just the passive thermal images of the nearby friendlies.
“Sixty seconds to impact.”
It was funny. His taste in women usually tended toward the buxom, but Jules was thin, wiry even. But people aren’t just types, are they? You think you know what you want, where your life is going, and then someone comes out of nowhere and just surprises the hell out of you. She had this amazing smile.
“Twenty seconds to impact.”
“Damage control party has reached the bridge,” Karlstein reported, her voice strained. “Multiple casualties.”
Sam breathed in slowly.
“Impact in five, four, three …”
As I said, there was an obvious possible reason why no one on the bridge was talking to them.
I wonder what kind of electric thrust the author has decreed that they use to get 8500 tons of thrust. Usually electric thrust gives very high ISP but very low actual thrust. Even for a ship with a fusion power plant, this seems wrong. Electric thrust works by throwing very light particles out the back very fast. The high speed is why it has high efficiency, but the “very light” part is why it has low actual thrust.
Oh wait, I see he specified “MPD”. That is one of the higher-thrust electric engines. Hard to imagine how they would get it to be as high thrust as he is describing here, but maybe with enough power….
Wikipedia puts the upper end of current MPD efficiency at 60%, while NASA only reports on a Russian one at 45%. For simplicity, let’s call it 50% efficiency.
Approximating a ton of thrust at 1MN (this is basically using metric tons), we’re looking at 8.5GN of thrust, with an acceleration of 4.9m/s^2 (half a gee). Because I’m doing envelope math, let’s say that means the first second moves us 2.5 meters along the new course, using 21.25GJ. Double that for our 50% efficiency, and you probably need around 50GW to power that.
A modern terrestrial fission reactor put out upwards of 500MW, with some as much as 1GW. You’d need about 50 of those just to drive the thrusters, so I hope your fusion power plant is efficient. Eh; I can live with that.
Actually, let’s go back and get the mass from that 8.5GN of thrust. To get 4.9m/s^2 from that thrust, the mass of the ship would have to be about 1.7Gg, or about 1700 tons. That’s … about the displacement of the average destroyer launched in the 1930s.
The other thing that bothered me was the implication that the MPD had no signature, or at least a smaller signature than using the alternative (some sort of fusion torch drive). The thing is, 50% efficiency means that the same amount of power goes to waste heat as goes to the drive. So let’s say that the drive took 21GW like you estimated. Then they would also have to dump 21GW of heat out as well. Their radiators must show up like beacons.
The ISS radiators can dump out 70 kW of heat. So we’re talking radiators that radiate about 300X more energy than the ISS.
(Well, also the drive exhaust itself carries away waste heat. But really hot exhaust is really detectable exhaust….)
Anyway, the point is only exaggerated when you get the correct order of magnitude. The waste heat alone from a MPD drive that could provide that much thrust would be immense.
My guess as to how the enemy got their position: Their space drive contains tracking technology at the least, a whole Trojan hacking AI.
The other obvious explanation would be that the fleet used a predictable flight profile. Maybe they didn’t feel a need for as much paranoia or those Cottohaz rules involve space traffic control guidelines.
And good luck on the “optimal” evasion path…
I’m assuming they put themselves into an orbital path, given that they weren’t under thrust at the start, and someone tossed their sand into the predicted orbital path.
They are on their way to reach an orbit, yes. There would be a mathematically optimal flight profile of acceleration and deceleration, yes.
However, they can be thousands of kilometers off that optimal flight path at the cost of only a few minutes or hours of flight time, and do that in a completely random manner. And that would be a very smart idea in military terms.
“Then they would also have to dump 21GW of heat out as well. Their radiators must show up like beacons. The ISS radiators can dump out 70 kW of heat. So weâ€™re talking radiators that radiate about 300X more energy than the ISS.”
Um, 21GW = 21*10^9. 70 kW = 70*10^3. That’s 0.3*10^6 = 300,000 times the power radiated by the ISS. It’s also about equal to the power wasted in out door lights (mostly light pointing up) in the entire United States.
An interesting constraint is provided by the Stefan-Boltzmann law, which gives the power per unit area radiated by a black body as a function of temperature. Most of you have seen this in operation in an incandescent light bulb. In order to radiate that much power, the radiator must be rather warm, in which case it functions like a light bulb. A bright light bulb. No, you clearly need totally efficient quantum energy transmission here.
The destroyers did not have an alien space drive on board, so there was some other way to track them.
Oh, yeah. I was thinking MW. So I was only three orders of magnitude off.
Fun fact: I did all the math with three zeroes slipped and determined that the destroyer weighed less than a light truck before going back and checking my numbers. (I had figured a ton as 1000g instead of 1000kg, as it turned out.)
Huhn — Star Honor Graduate, Pavel Young School of Command Leadership.
As I was told in command school, even a sub optimal decision in time to make a difference is better than no decision.
So did the emissions of the radar drone eventually scatter back from something interesting?