Tuesday, March 8, 2016

Generating Ideas

Note that none of this is canon. None of this is required reading for running Traveller. I am not an engineer or scientist though I do roleplay them at times. I'm just throwing out some ideas for power consumption in Traveller ships.

Chris Vermeers started this by pointing out that in Traveller LBB '77 the maneuver drive is not unlimited but that:

"A fully fueled power plant will enable a starship an effectively unlimited number of accelerations (at least 288) if necessary to use the maneuver drive during the trip…" (emphasis by Chris)


Then I was perusing the Boom Table at Atomic Rockets where I unearthed this nugget of knowledge:

3.4 * 10^14 joules is the energy from fusing one kg Deuterium and Tritium.

That sounds like a lot of power to me! I began to wonder if maneuver drives might be analogous to a photon rocket. Direct enough energy out the back of your ship and you will move but it will take 3 * 10^8 joules to generate a lousy newton of thrust but still that's a lot of zeros for that kilo of frozen hydrogen. To continue the table of thrust vs. power for a photon rocket:
1 newton of thrust (1 kilo at one meter per second or .1 kg at one gee) ~3 * 10^8 joules
1 kg thrust ~ 3 * 10^9 j. (yes that's gigawatts squire)
1000 kg thrust ~ 3 * 10^12
1 ton of thrust ~ 3 * 10^15
A Scout masses about 1000 tons and thrusts at 2 gees for 2000 tons of thrust (I'm not talking displacement tons (volume) here, I'm talking metric tons (mass))

Therefore with a photon drive propelling a Scout generates 2 * 10^3 * 3 * 10^12 = 6 * 10^15 j.

Therefore full thrust with a Scout's engines requires 6 * 10^15/ 3.4 * 10^14 = 17 kgs of fuel per second. If you go with LBB 2 a Scout's in system drive had 20 tons of fuel. So it can thrust for 1176 seconds or just about one combat turn. Woof. That sucks.

Let's work it another way. The original LBB 2 said a load of fuel powered a ship for unlimited (at least 288 thrusts.)
288 * 10^3 seconds (a combat turn, I guess that's what they meant by maneuvers) yields 2.88 * 10^5 seconds.
20000 kg of fuel / 2.88 * 10 ^5 = .069 kg per second.

.069 * 3.4 * 10^14 = 2.4 * 10^13 j or 24 terawatts per second

If we go with the High Guard values the ship only needs 2 tons of fuel to do all this and produces 2 terawatts per second.

This is the equivalent of 500 tons of tnt. Don't get close to a Scout with a malfunctioning fusion plant. It can go off with the force of half a kiloton. Good to know

A 100 displacement ton ship(1000 tons mass) requires one terawatt to accelerate at 1 gee. That's a kilowatt per ton.

There's more fiddly science bits here for you. If the maneuver drive is 50% efficient then one half  terawatt per second has to be radiated as heat. That's a quarter kiloton or the annihilation of 5 milligrams of matter and antimatter. There is no stealth in space. I will leave that alone for the moment.

Compared to the costs of maneuvering and artificial gravity life support is really trivial. You can have ships running low berths for years and decades adrift in space or limping along at a few hundred kilometers per second. As an adventure hook a planet around TL 5-6 desperate for power might hire a couple of tramp freighters to stay a few weeks and help them by generating power while they take their generators offline and modernize their power grid. Earth in 2004 at TL 7 uses 15 terawatts per second. So 2 terawatts added to a backwater colony is a lot! Starships arriving after a disaster might make a killing selling power as well as blankets, first aid kits, and food. Or pirates seizing a ship (you thought I'd forget my pirates?) might discard everything but the fusion plant to sell to planets for energy generation.

Say a maneuver drive is similar to the gravitics powering the air/raft. A 6 ton air/raft takes up 13.5 x 6 = 81 cubic meters. If it is about the density of a modern commercial aircraft then it masses about 20 tons. That means its batteries supply about 20 kilowatts per second. If its batteries let it fly for a week solid then the batteries hold about 12 gigawatt seconds! That's the equivalent of 3 tons of tnt (don't go near malfunctioning air/rafts either.) To put an adventure hook spin on it the characters are stuck on a backwater wilderness when a malfunction drains their air/raft's batteries and they rig a lightning rod as a storm approaches to draw a lightning bolt and recharge the air/raft's batteries! Really go look at the Boom Table. Winchell Chung did us all a great service with that.

Let's look at the famed antimatter battery that those messy Ancients left lying around. Say a battery has a kg of antimatter held in stasis by immortal pixies or whatever. One milligram of matter and antimatter combined generates 1.8 * 10^11 j. A Scout draws 3 * 10^12 j so it will need 8 milligrams of antimatter per second (and also matter which it can get from dust particles the pixies round up.) A kilo of antimatter will power that Scout about 40 maneuver turns or 11 hours which isn't that great. More importantly that magical battery will not have anything near the power needed to make a jump and firing the lasers might be dicey as well.

This of course leads to many other questions like how much power does a turreted laser draw? What is the conversion between High Guard energy points and megawatts? I leave that to the engineer types. I'm sure some one could do a better job with this topic than me. I just got to it first.

As with all my pondering you may have a different idea how your tech works and what kind of power fusion generators put out. But if you take your assumptions and start extrapolating from there you may be amazed where they take you.