Starship Design Example

[atpollard]

I was reading the

MT Starship Design Example

and was suprised at the comments on the required fuel. Am I alone in finding it excessive to provide fuel to allow 30 days of continous operation of the spinal mount, bay weapons and turret weapons. Would any starship survive even 24 hours (144 turns) of continuous combat? Rather than gut the ship of Jump Drives and Maneuver Drives, just reduce the operational time of the energy weapons.

I was just interested in hearing other thoughts.

[jtgibson]

Sadly, one of the (debatable) shortcomings of the MegaTraveller system is that it assumes that all screens, guns, drives, and other devices are running "hot" at all times. This helps balance out the fact that ships which have powerful weapons and drives actually need to mount tons of fuel and power plant output to be able to use them, but is a major handwave in terms of realism.

In the case of an aircraft, the engines have to run at nearly full power at all times -- an idling aircraft engine uses almost as much fuel as an engine at full power. In the case of a ground vehicle, the engine runs at minimal power when idling. The idea of how much power a spaceship uses when idling is a matter of debate, but one would assume that most of the weapons and screens would be completely unpowered, or running at only a capacitance-level setting.

I've been considering this in order to write a house rule, but haven't gotten to finishing it.

[aramis]

One of the things where MT differed from CT is allowing multiple PP's on at once. So for pirates, starmercs, and Naval Ships, I often put only a week for the combat plant, and 28 days (an imperial month) for the Base Ops Plant.

Also, in MT, you can run a plant down to (IIRC) 30% with a parallel lowering of fuel used; thus 7 days in Jspace is gonna count 3 days fuel for a typical single plant ship.

[GypsyComet]

In fact, the "multiple short duration" powerplant epiphany, which happened more than three years into the MT era, was what finally made CT designs workable below TL15.

In design terms this doesn't change the size of the "powerplant" itself, since anything you're going to install on a starship will be above the top threshold for volume efficiency, but it impacts the fuel needs hugely. If you wanted to get really picky and somewhat risky, you could designate 30 days duration for the LS/controls/etc *only*, reduce drives to about 20 days, and weapons/screens to 1-2 days. Given that drives and weapons are generally 90% of your power needs, a 60-70% reduction in non-Jump fuel needs is certainly possible.

The additional color isn't a bad thing either. "We've got multiple intercept bogeys. Engineering, bring Reactors Three and Four online and rig for battle."

[DonM]

But unfortunately, the Example was written to design thought when MT was published, and I'd want to do a completely different ship for the "PP Epiphany". (I've never heard it called that before, but that is certainly what happened).

[Whipsnade]

Originally Posted by GypsyComet

... the "multiple short duration" powerplant epiphany...

GC,

I remember first reading about the epiphany in a DGP Q&A column.

My first reaction was "Phew, my house rule isn't too far off..."

My second reaction was "Why the #*&&#$@@ didn't they tell us this in the beginning?"


Have fun,
Bill

[DonM]

I first saw it in an online discussion on GEnie just before I resigned as a Quadrant Editor for HIWG.

[GypsyComet]

Originally Posted by Whipsnade

GC,

I remember first reading about the epiphany in a DGP Q&A column.

My first reaction was "Phew, my house rule isn't too far off..."

My second reaction was "Why the #*&&#$@@ didn't they tell us this in the beginning?"

Based on the DGP construction example referenced above, the DGP folks hadn't yet had the epiphany. In fact, it was one of the more prolific ship designers who apparently started it. The MOST prolific designer, Rob Dean, was just one step away from giving us the epiphany years earlier, as his solution for lower TL designs was to simply reduce the duration across the board. This was already a pretty radical step, by the way. It took another designer to hit on the final solution.

It was apparent that DGP recognized the problem early on, however, as the MT design system was where Jump fuel requirements changed. Looking at the whole picture, this step was obviously the attempted fix to the runaway powerplant fuel problem (which derived from using Striker assumptions for much larger vehicles than Striker was meant for). In retrospect, DGP should have introduced another step in fusion plant scale efficiency instead, but what's done is done.

Of course, the other problem is a "reality check" issue, and is what led the TNE revision to reduce all power numbers by an order of magnitude or more. The reality check comes from the simple triple beam laser turret, which is a modest one displacement ton structure that is being asked to channel 750 MW in one side, feed that much raw power into three laser emitters, and fire the resulting beams out the other side. All without melting the whole thing (or the conduits running from engineering to the turret) into slag (or boiling the metals off as vapor, for that matter). Repeatedly. 750 MW is a LOT of juice.

[zonk]

So what, exactly, does the PP epiphany require in the way of changes? I, vaguely, understand that multiple powerplants are required because of fuel limits.

[GypsyComet]

Here is the section summary from the MT Ship Design Example, trimmed to show just the power:

Hull Section Total 0
Locomotion Total -892,500.02
Communication Total -0.200
Sensors Total -1,011.70
Weapons Total -563,580
Screens Total -106,125
Environ Total -73,903.74
Fuel Purification -1,265.63

The total powerplant volume will be the same whether we make the default single plant assumption or a multiple plant assumption, because we still want, in this case, to be able to generate all that power at once. However, instead of using the total, let's break it up into sections. Spreading the 27,287 KL/day fuel requirement around proportionately, we get:

Hull Section Total 0
Locomotion Total 14865 Kl/day
Communication Total 0.033 Kl/day
Sensors Total 16.85 Kl/day
Weapons Total 9386 Kl/day
Screens Total 1767 Kl/day
Environ Total 1231 Kl/day
Fuel Purification 21 Kl/day

Now, instead of multiplying the total by 30, you pick and choose.

Hull, Commo, Sensors, Environ, and Fuel Purification are all on the full 30 day ride for 1269 x 30 = 38070 Kl of fuel

Locomotion for a warship is a complex issue, and one that calls for a closer look at the intended mission of the ship. For now, let's assume that 5 days at full juice will be enough. 14865 x 5 = 74325 Kl of fuel.

Finally, Weapons and Screens. If a naval battle lasts longer than a day or two, you're pretty much hosed anyway, so lets provide enough endurance to run these systems for two days. 11153 x 2 = 22306 Kl of fuel.

So these plus the total power plants volume of 181910 Kl, adds up to 316611, which is below the 323699 Kl that was available. Bump our maneuver powering fuel endurance up to 5.4 days adds 5946 Kl to the fuel for a total of 322557. We can simply add that last 1142 Kl (about 81 dtons) to fuel as a "last gasp" or to cargo as more ration carrying space. A bowling alley is also a possibility...

That help any?