Tuesday, November 22, 2016

M-Drives Made Accountable

"C'mon in back yer honor. I'll fix you a cup a' joe," Prigo said rubbing the mayor's shoulder. The Automat was closed for the night.

"Awful decent of ya, Steen," Louie said relighting his cigar and entering.

"No problem. Jorge was a good guy.  He will be missed. How's Miss Ranna doin'?" Prigo asked heading into the pantry for fixings.

"Miss Ranna is on tranquilizers and antipsychotics. She laid the beat down on two squires wanting to stop her from shooting up the offworlder bank. About middling. Louie inspected his cigar and reached for the light switch as he entered the kitchen.

The lights in the kitchen snapped on. A man with a crewcut in Tech Knight regalia stood there regarding Louie from behind a monocle. He held a plate with a slice of berry pie and a mug of tea.

"Come in your honor. We have much to discuss," the man said gesturing to a couple of stools by a counter. Louie frowned a little and took a drag as he sat. Prigo came through the door a moment later, dragged by the seat of his pants by a lumbering heavy.

"Dr. Elevator," Prigo gasped. That worthy removed his monocle and bowed. "Please join us sir ... and it is Professor Elevator!"

"Ya never got your doctorate? A bigtime supervillain?" Prigo asked. Behind him the heavy swore silently and winced slightly.

" ... what the hell is wrong with a Masters? I had to leave my final year ... familial issues! Do you have a Masters? Did you shut down the starport for a week? You cut rate hash slinger! Mort," Prof. Elevator snapped.

Mort administered a half-hearted dopeslap to Prigo who wisely shut up and remained rocking slightly from the buffet.

"If I'm to hear a monologue, I'll need that cup of coffee," Louie said.

"You will find I am prepared for your tricks Mayor Burns. I brewed a pot already!" Elevator indicated a sealed steel pot and Prigo began pouring out some cups by reflex for the Mayor and Mort. Prigo noted in passing that Professor Elevator had left a credit for the pie and coffee by the pot and pocketed it. No tip.

Mayor Burns took a sip and gave the mastermind his full attention. Elevator finished his tea.

"I'm hurt," Elevator said, waiting to see the effects of his words. He added a sugar cube to his tea.

"You're ... we're talking feelings here?"

"Of course! Mad scientists can't have feelings?!" Elevator gave Mort a stern look heading off a dopeslap aimed at the Mayor.

"You're the guy built the twenty foot diesel 'bot that tore up the Knight Day celebration? The one who masterminded the daring zeppelin bank heist, fixed the South Bend Stadium ballgames?"

"That last one was Doctor Switchboard. I'd never make the South Bend Razorbeaks lose!"

"Go Razorbeaks!" Prigo said. Slap!

"Awright. Sorry. I have trouble keeping you guys straight. The cops are kind of baffled by you," the Mayor said.

"I'm a cut above the rest. I have a mission, Mayor Burns. I WAS a Tech Knight ... until I realized they are a bunch of handymen turned tyrants repressing progress for their own means and enrichment."

"I can see your point. Hey could I get a piece of pie while we talk?"

Elevator uncovered a platter of various slices of pie. He took planning ahead seriously. The Mayor had to give him that. He grabbed a slice of berry pie and after a look at a glaring Prigo left a coin on the counter.

"Mayor Burns, Miss Morrigen and Mr. Guttman began a grand enterprise to spur this backwater rock into some semblance of progress. A home brewed space craft! Mr. Guttman's ... loss has left you bereft of technical genius. I wish to volunteer my services," Elevator monologued.

"You wish ... you're a crook ... sorry, a super criminal."

"So what? You guys are already hiring smugglers to move cargo and stay in the black! Don't deny it. I use those same guys! They're criminals! You're discriminating against me because I'm only local?" Elevator slid his tea mug a safe distance away and pounded the table for effect. then slid the mug back in easy reach.

"If I'm getting you, you're a crook ... super crook but a patriot!"

"Sure. I want you to inform the Tech Knights of my offer. I was going to cut in on radio broadcasts tomorrow but there's a ballgame on. Appearing in person would probably lead to massed gunfire before I got a word out."

"Flamethrowers too."

"Then you agree to send this message?"

"I'll give it a whirl. I better do it before Ranna comes down off her pills," the Mayor muttered.

I hate true reactionless drives for the following reasons:

1) They turn every ship into a weapon of mass destruction. Just speed it up as high as you want and slam it into the planet you hate. Endanger however many dinosaurs as you wish.

2) It breaks the laws of physics and that is a genie better left in the bottle except where you really need it (for FTL a/o psionics!)

3) It makes space travel too easy. Space should still be hard on some levels to keep a true space feel to a setting.

4) You don't need a really fast ship or torchship for that matter. If you have a jump drive you could use it within  a system easily enough in the 2d6 OGL or Cepheus Engine systems.

So, in my setting, M-drives send a stream of super hot plasma into a wormhole leading to jump space. In fact repulsion forces, heat exchange and m-drive systems all make use of jump space. It's a case of spin off tech. Like using lasers to scan barcodes when you only wanted something to cut an enemy in half.

An m-drive functions like a torchship. I cheerfully admit I used Phil Eklund's quotes (from his High Frontier game) on the Atomic Rocketsite to model my maneuver drive. I also admit I tried to leave established designs still workable for 2d6 system games.

Of these reactions, the fusion of deuterium and tritium (D-T), has the lowest ignition temperature (40 million degrees K, or 5.2 keV). However, 80% of its energy output is in highly energetic neutral particles (neutrons) that cannot be contained by magnetic fields or directed for thrust.
In contrast, the 3He-D fusion reaction (ignition temperature = 30 keV) generates 77% of its energy in charged particles, resulting in substantial reduction of shielding and radiator mass. However, troublesome neutrons comprise a small part of its energy (4% at ion temperatures = 50 keV, due to a D-D side reaction), and moreover the energy density is 10 times less then D-T. Another disadvantage is that 3He is so rare that 240,000 tonnes of regolith scavenging would be needed to obtain a kilogram of it. (Alternatively, helium 3 can be scooped from the atmospheres of Jupiter or Saturn.)
Deuterium, in contrast, is abundant and cheap. The fusion of deuterium to itself (D-D) occurs at too high a temperature (45 keV) and has too many neutrons (60%) to be of interest. However, the neutron energy output can be reduced to 40% by catalyzing this reaction to affect a 100% burn-up of its tritium and 3He by-products with D.
The fusion of 10% hydrogen to 90% boron (using 11B, the most common isotope of boron, obtained by processing seawater or borax) has an even higher ignition temperature (200 keV) than 3He-D, and the energy density is smaller. Its advantage is that is suffers no side reactions and emits no neutrons, and hence the reactor components do not become radioactive.
The 6Li-H reaction is similarly clean. However, both the H-B and 6Li-H reactions run hot, and thus ion-electron collisions in the plasma cause high bremsstrahllung x-ray losses to the reactor first wall.
For my purposes, unrefined fuel has trace amounts of tritium in it. This will react with the deuterium used normally in any sort of generator that can burn deuterium and Helium-3. This produces neutrons, power fluctuations, secondary reactions and in general is something you wish to avoid in temperamental unobtainium drives. You want to carefully remove the tritium from your fuel (but it has other uses on the bright side.) Neutrons will also transmute bits of your drive and cause maintenance hassles and inaccurate jumps.

Luke Campbell said
This puts your maximum exhaust velocity at 7,600,000 m/s, giving you a mass flow of propellant of 34.6 grams per second at 1 terawatt output, and a thrust of 263,000 Newtons per terawatt.

I confess I am guilty of rounding off on this next part but ... if we assume a standard ship masses 500 tons per 100 displacement tons (which really measure volume - 1 dton equals ~14 cubic meters. Five tons mass for 14 cubic meters is about .28 tons/cubic meter and in line with  modern aircraft and ships.

Anyway going with Luke Campbell's exhaust speed gives a specific impulse of 775,000. Wow. Plugging that into the equation for Delta-v:

Delta-v = Velocity (exhaust) * ln (R)

Where R is Mass of (fuel expended/mass of rocket) +1. For a Hawking Class Scout that masses 500 tons burning two tons of fuel will give a mass ration of (2/498 = .0004)

Delta-v = 7,600,000* ln (1.0004)
Delta-v = 7,600,000* (.0039)
Delta-v = 30339 meters per second or 30 kps or 3 one gee burns per 2% of displacement tons used as fuel.

3 burns for 2% of your ship is not too shabby. At 30 kps gets you to jump limits in 11 hours. So you can say one day is spent in real space transit between most worlds. Note that you'd need another 2% to slow down. Your standard Scout (the Hawking is a lovable fuel hog) carries fuel for four weeks or 8%. That's a delta vee of about 300 kps. Traveling at half that (so you could slow down would let you travel an AU in 12 days. You could cut that further using more fuel/propellant. The upshot is traveling interplanetary distances in a timely manner will require a similar amount of fuel to a jump.

Refuelling at a gas giant is a familiar trope which I wrote a lot on. But we can still have this. Many, many systems seem to have gas giants a lot closer to the primary and prime real estate than our backwater system. In most red dwarf systems the gas giants and most of the planets are within a half au or less.

For planetary systems similar to Sol's you have infrastructure which means more ships, jobs for NPCs, and ship encounters. For example, a Sol type system would benefit from an outpost around Jupiter to service ships, a small fleet of corporate or independent tanker ships to refuel from Jupiter and truck the hydrogen to the jump limit for ships that are just passing through and do not want to visit, an outpost and fleet at Saturn to truck in 3He to the various planets. Ceres and other asteroids will get settled not because of their precious metals but because of the water they contain for refueling belters. All of these occupations are possible plot hooks and serve to flesh out your universe. There are many space travelers who may never leave their home system as there is money to be made there too.

So generally ships will jump to the mainworld and coast most of the way to it. Traveling between worlds in a system will take either months or a substantial amount of fuel (at least 10% for a micro jump) similar to FTL flight. A ship is only going to hit a gas giant for fuel if it requires less than a week's flight and less than 10% of its fuel. Good thing we're locating many hit Jupiters!

For that matter if you have a ship with any kind of mining apparatus it would probably be much easier to land at a moon like Europa and crack some ice or pump in some water than go mucking about in a gas giant's deadly atmosphere, especially for ships with less than three gee's acceleration.

Micro jumps also allow some stealth in space. People could tell you jumped but not where you are going. It's like the old shell game only with nuke armed ships.

Limited delta-vee also necessitates a new type of ship: a pursuit craft. Small vehicles with a huge load of propellant to chase down enemy or fugitive ships. Jumping to secure the jovian first as an escape route won't work the way it used to. You're going to blow at least 10% of your fuel and another week to get to to the real target from some gas giants.

A scout ship massing 500 tons will have to generate 40 terawatts of usable power to thrust at two gees. Most of that energy and the rocket exhaust is shunted into jump space (though there might be an exhaust for emergencies. Turning off the shunt will in general melt your ship so using your drive for a weapon is a one shot deal. If the Scout ship's power plant is 50% efficient (which is pretty darned good) we have a Scout ship putting out 80 terawatts just flying casual.

If you look on the Boom Table at Project Rho 80 terawatts is about 20 tons of dynamite. In case your players like going out in a blaze of glory. Most likely there are all manner of energy signals and radio alarms designed to tip off the curious that your space hobos are flying a small bomb. Not to mention safeguards designed to melt the ship or irradiate your dumb ass before the plant goes critical.

Generating 80 terawatts requires 34.6 grams of fuel per second. If you assume a month of operation this comes to about 9 tons of mass which is close enough to Cepheus Engine's 8 tons for a type A plant for me (so they get more than 50% efficiency, sue me.) So the fuel is also being used as propellant. Sort of like recycling.

My earlier post on fuel use and power generation did not take such inefficiencies into account (I also ignored the annoying little man in the front row asking me about radiators.) So if lifters draw a similar amount of energy to the m-drive, the lowly air raft (massing about 20 tons if it is similar in construction to modern aircraft) generates a little under a terawatt to zip along. If it cruises for a week its batteries would hold 600,000 terawatts (double this to account for waste energy) for a boom rating of ... .28 megatons.

I'll work some more on the lifter power scheme.

Sheesh. If I go with those numbers I could ignore starships safely but would have to worry about the air rafts!

No comments:

Post a Comment