Green Ronin Publishing

With my new Spaceship Zero campaign heading for its third episode and the crew looking like they are going to be spending a lot of time in space, I thought I would need to come up with a few more spacecraft for the game. The only problem is (being an engineer) that I needed to work out some of the technological basis. Using a number of engineering references (the least technical of which were GURPS vehicles, Winchell Chung's Project Rho website http://www.projectrho.com/rocketstub.html and a couple of NASA reports) I came up with the following ...

Spaceship Zero masses 40 US tons or 8000lbs.

It can achieve a thrust of 3g for 30 hours (90g-hours of thrust or 240000lbs of thrust for 30 hours)

Using the standard formula for Specific Impulse related to fuel mass and the dry mass of the ship, it works out quite nicely that Spaceship Zero has a fuel to dry mass ratio of 1:2. In other words, 33% of the mass of Spaceship Zero is fuel. This works out that 1% of the mass of a vessel is required as fuel to give 3g-hours of thrust.

Meanwhile. with a bit of fudging between GURPS and real-world data, it works out that Spaceship Zero has a Magnetic Confinement Fusion Motor with 3D vectored thrust options and an exhaust velocity of 1.8 x10e7 miles per hour!!! All of this power is contained within a package that masses just over 4.5 US tons.

Going by this, you require 3.75% of Zero's mass to be devoted to thrusters to achieve 1g thrust.

Allowing for a 25MW fusion reactor at GURPS TL10, 100MW of lead/acid battery storage and a 100DR TL10 hull (polyaluminite should be TL13, but I was trying to work out how much a standard Spacecorp hull would mass), an additional 25% of a ship's mass must be devoted to control, engineering, life support and structure.

So, to sum it up, the technological constants of xenon-powered Spacecorp vessels are that:

1) To achieve 1g of thrust, 3.75% of the ship's mass must be devoted to thrust systems.

2) 1% of a ship's mass (if devoted to xenon fuel) will provide 3g-hours of thrust if the thrusters described above are employed.

3) 25% of a ship's mass must be devoted to engineering, life support, control and structure.


Now, does anyone have an aspirin?

Nicely done - mind if I post this to the SpaceCorp yahoogroup?

Not a problem. I would have posted it there as well myself ...

Now, having worked out the technological bases for the Earth spacecraft in Spaceship Zero, the next step is to work out the bases for the weaponry employed by humans. Instead of delving into the scientific wilderness that is desiging hypitheticla weaponry, I shall instead limit myself to the weaponry listed in the Spaceship Zero rulebook, One day, if I feel bored enough, I may try and work out the physical constants that govern their functions - but my initial explorations convince me that such a project can only lead to SPACE MADNESS!! I'm an engineer, dammit; not a physicist ...

However, back to the job in hand.

The smallest listed spacecraft (the Star Skipper) masses a mere 5 US tons (10,000lbs) and carries a single Atomic Coil Turret (we shall assume that it is the 3" version for the minute). Using the data derived for vessel performance, its 3g thrust, 36g-hours of fuel and other dedicated space comes to a total of 48.25% of the total mass of the craft. Rounding this off to 50%, we find that a 3" Atomic Coil Turret requires 2.5 US tons (5,000lbs) in order to be installed.

The next vessel in terms of complexity is the Space Hopper. This has two Atomic Coil Turrets and an Atomic Star Burster or Cosmatomic Missile (I am assuming they are the same thing as one appears in the spacecraft descriptions and the other appears in the weaponry descriptions). In total, 66.25% of the Space Hopper is spoken for by fuel, thrusters and engineering/control spaces. This leaves 20 US tons from the 60 US tons listed in the book.

Assuming the Atomic Coil Turrets are the 3" versions, this leaves 15 US tons (30,000lbs) for the Atomic Star Burster.

The last weapon remaining is the Rocket Torpedo Launcher. This is found on the Galactic Frigate. In order to achieve its stated performance, 48.5% of its mass must be devoted to the necessary equipment. Subtracting the 5 US tons for the Atomic coil Turrets and the 15 US tons for the Atomic Star Burster leaves 30 US tons for the Rocket Torpedo Launcher.

However, given the stated flexibility of the Galactic Frigate, we cannot assume that it will be mounting 3" Atomic Coil Turrets. If we assume 6" Atomic Coil Turrets (and that they require twice as much mass as a 3" Turret), this reduces the available space for a Rocket Torpedo Launcher to 25 US tons. This should include a magazine space for the torpedoes as well as the launcher mechanism. Given the capabilities of the submarines of the 1950s, we can happily assume that full magazine is about 20 missiles. Allowing 1 US ton per missile, the actual launch and loading mechanisms should only weigh 5 US tons.

So, to summarise our calculations:

3" Atomic Coil Turret = 2.5 tons (5,000lbs)
6" Atomic Coil Turret = 5 tons (10,000lbs)
Atomic Star Burster/Cosmatomic Missile = 15 tons (30,000lbs)
Rocket Torpedo Launcher = 5 tons (10,000lbs)
Rocket Torpedo = 1 ton (2,000lbs)

So far, I have discussed how to determine the thrust for a Spacecorp vessel, how much space fuel takes up and how much tonnage the various weapons need. Now I come to those last, annoying statistics: Handling, Armour, Brawn, Body and Crew.

The easiest to determine are Armour, Brawn and Body. These appear to be related to the weight of a vessel. although there are only stats for four Spacecorp ships in the Spaceship Zero rules, this is enough to derive simple graphs for these values. I used Excel, but any good spreadsheet should do.

By entering the data for the mass of a spacecraft and its Armour, Brawn and Body and constructing grpahs, we can see that there is a logarithmic relationship between the mass of a vessel and these values. Adding a logarithmic trendline provides a "normal" line which can be used to work out what values a vessel should have for its mass.

Of course, there is scope to alter these values, depending on the exact role of the vessel. For example, a cargo vessel does not need as much Armour as the graph would show, but it might need more Brawn. When it comes to Armour, remember that a vessel has less Energy DR than Matter DR. The approximate ratio seems to be 3:2 Matter: Energy, but there is no reason why this should not be changed. However, any massive deviation is likely to lead to a Spaceship Zero vessel that, somehow, seems wrong.

Handling appears to be related to Thrust, but the relationship is not so clear. I assign a Handling value based upon the role of the craft. A nippy fighter will have a Handling of 20, while a large cargo vessel will have a low Handling.

As for Crew, that is up to the designer. However, you should have a number of pilots equal to the number of digits in the mass of a vessel. So, a 10,000 ton vessel will have 5 pilots and a 100 ton vessel will have 3. More advanced vessels will need less pilots, while old clunkers will need more. As for pssengers, I recommend a working value of engineers equal to the number of pilots and at least one passenger per weapon. You will also need to leave space for Marines, Star Skipper pilots and the monkey.