Tuesday, March 17, 2015

Building a Spaceship in Dungeons and Dragons

Why? Because we can, that's why.

D&D space travel has been done before, usually with teleportation magic (or Spelljammers). What I'm setting out to do here, though, is to build an actual spaceship, that actually traverses the space it crosses. Specifically, I want to design a spaceship that can be built at the lowest level possible – most of the components are actually fairly cheap since the designers weren't expecting you to apply physics to them. The ship will be designed for a 1-man crew, but should be readily adaptable to larger crews.

In case it isn't obvious, I'm well aware this is deeply silly. For those of you here for the nuclear history, don't worry. This blog is still about history; this is just a momentary diversion. So if you don't like D&D just skip this and come back later.

I'm doing my best to stay within the strict rules-as-written of the D&D ruleset. That said, there are a couple of issues of rules interpretation, which I will point out as I go. Obviously, this is not intended for use in an actual game – even if a DM is willing to allow it, you should probably homebrew your spaceships rather than trying to force the rules through these kinds of contortions.

Also, I'm making heavy use of magic device traps. I'm making some assumptions that are not specifically addressed by the rules, namely: that all traps can only fire once per round, that they can be triggered by the press of a button in a separate chamber or be set to automatic continuous fire, and that they are not vulnerable to damage that is insufficient to disrupt the surface they are placed on.

But Mark, Why Don't We Just Teleport?

Because spaceships are cool and I like messing around with physics. Also, combining orbital mechanics, momentum conservation, and teleport opens up a whole horrible can of worms I'd rather leave firmly nailed shut.

What Isn't Allowed

I will not be using any of the following in this paper:
  • Teleport and related spells and effects (see above)
  • Wish (makes it too easy)
  • Wealth-by-level-breaking tricks (see above)
  • Real-life chemistry (it obviously doesn't work in a world made out of the four classical elements)
Assembling the Team

Project Leader and Astronaut: Wizard-11 with 20 Intelligence, maxed ranks in Craft (Metalworking), Knowledge (Engineering), and Use Magic Device, the Leadership feat, and the Landlord feat (from the Stronghold Builder's Guide). He will do the spacecraft design and fly the vehicle.

Chief Engineer: His cohort, an Artificer-9 with the feats Apprentice (Craftsman), Craft Wondrous Item, Extraordinary Artisan, Favored in Guild (Arcane), and Magical Artisan (Wondrous Item). He'll be doing most of the actual manufacturing, except for some pieces we'll subcontract.

Project Administrator: A Marshal-1 with Motivate Intelligence and an 18 Charisma. We have some skill checks to make and Marshals need the work. Fluffwise, he's in charge of administration, accounting, etc.

The Design Team: Our astronaut has a Leadership score of 19 (11 + 2 Charisma + 2 Great Renown + 1 Fairness and Generosity + 1 Special Power + 2 Base of Operations), giving him 40 level-1 expert followers, all with 13 Intelligence and 4 ranks and Skill Focus in Craft (Metalworking) and Knowledge (Engineering).

The Financial Backers: The three other members of the program leader's adventuring party, who will be contributing to the project budget.

The Mother of All Skill Checks

We want to go to space. First we need to figure out how to do that – or, to be more precise, our characters need to figure out how to do that. The DC is obviously set by the DM, so we need to just buff our rolls until we can pass any plausible DC. We will use:

14 ranks in Knowledge (Engineering): +14
20 Intelligence: +5
Guidance of the Avatar Magic Trap: +20 (3,000 x 0.75 x 0.75 x 0.9 x 0.95 = 1442.81 gp)
Aid Another: +62 (my artificer and all 30 members of the design team use the Aid Another action; with the assistance of the Marshal's aura, they all automatically pass)

We then take 10. This gives us a cumulative roll of 117, which should be enough to invent orbital mechanics, life support systems, engine nozzle design, etc. from scratch. We may need to roll separately for each individual subsystem, but a 117 should beat any DC that isn't just the DM saying “no” in a really passive-aggressive way.

Note that, as a trap, we can charge the cost of the guidance of the avatar trap to our Landlord budget.

Research Program, Phase I: 1442.81 gp (charged to Landlord budget)

Vehicle Assembly Building

The Vehicle Assembly Building will be statted with the Stronghold Builder's Guidebook as an extended dry dock with packed earth internal and external walls. This has a base price of 15,020 gp. We build our base in warm terrain 30 miles from a small city, giving us a -7% modifier on the cost. I will also assume the bravery of our astronaut has inspired the populace to donate their labor, giving us a further 30% discount. Finally, our project leader has ready access to fabricate, giving us a final 5% discount on the cost of the space, for a total facility price of (15,000 x 0.93 x 0.7 x 0.95) + (20 x 0.93 x 0.7) = 9,289.77 gp

As a structure, we can charge this to our Landlord budget.

Vehicle Assembly Building: 9,289.77 gp (charged to Landlord budget)


I used the Stronghold Builder's Guidebook to design the cockpit. We will receive a 5% discount because our “stronghold” is mobile, as well as the 30% free labor and 5% fabricate discounts on the space itself. The SBG isn't entirely explicit about what gets these bonuses and what doesn't. The labor and mobility discounts definitely apply to the basic walls and components, but it's not clear if it applies to the wall augmentations and the wondrous architecture. The fabricate discount is specified to be for “furniture”, so it probably applies only to the component, not the walls. For the other items we get a steep discount anyway thanks to our artificer's cost-reducing feats.

The cockpit will be the smallest and cheapest component in the book, a Study/Office, Basic, taking up 0.5 ss and costing 200 x 0.95 x 0.7 x 0.95 = 126.35 gp. That's a box 20 ft long, 10 ft wide, and 10 ft tall.

The next step is to figure out our exterior wall percentage. No exterior wall percentage is listed for 0.5 ss (the chart starts at 1 ss), so I'll assume it's 100%. I want to make the hull out of something reasonably sturdy to avoid giving the DM an excuse to poke holes in it, but also light, so I'll use mithral. (Apparently structural mithral is different from the stuff weapons are made out of, because it only costs 3.3 times as much as iron instead of 1,667 times.) This is 3 inches thick and is priced at 20,000 gp per square, so 10,000 x 0.95 x 0.70 = 6,650 gp for us.

A spaceship's no fun if we can't see out of it, so I'll make part of the wall transparent. The price is 3,000 gp to make an 800 square feet section of wall transparent, but we don't need that much. A 10 ft. x 10 ft. viewport is plenty, adding 375 x 0.5 x 0.75 x 0.75 x 0.9 x 0.95 = 90.18 gp to our cost. We could just use a window instead, but again, that seems like giving the DM an invitation to break it.

We need to make this airtight. The airtight augmentation costs 7,500 gp per ss, so that's 3,750 x 0.5 x 0.75 x 0.75 x 0.9 x 0.95 = 901.76 gp for us.

We'll want an airlock as well. I'll add two iron doors at a price of 500 gp each, or 1,000 x 0.95 x 0.7 = 665 gp. The book notes that we get a certain amount of hallways for free, so we don't need to pay for the space in between them. We'll include covered and sealed pinhole openings in the inner and outer doors to allow us to equalize the pressure in the airlock with the cockpit and the vacuum of space.

 According to the text of the Nailed to the Sky epic spell, the heat or cold of space deals 2d6 damage per round. Our mithral walls have 90 hit points, and the iron doors only have 60. However, they have a hardness of 15 and 10, respectively.   Furthermore, heat deals only half damage to objects, and cold deals only quarter damage.   At the maximum roll of 12 damage, that's less then the iron's hardness, so they won't take any damage.   (Hat tip Brian Ballsun-Stanton below.)

Finally, I want this thing to fly so we have some more precise maneuvering capability than is provided by our main thruster. I want a maneuvering capability of at least 5' per round – about 1 ft per second. Five feet per round is equal to a bit more than ½ mile per hour, the very slow speed. That costs us 8,500 gp per space for the speed plus another 15,000 gp per space for the flying, so that costs us a total of 11,750 gp. We can't make this ourselves because it requires the reverse gravity spell and a 17th level caster (we'll be subcontracting that to the famed wizard Bo-Wing the Aeromancer).

So, our cost is:

126.35 gp (Study/Office, Basic)
6,650 gp (Walls)
90.18 gp (Viewport)
901.76 gp (Airtight)
665 gp (Airlock)
11,750 gp (Flight)

All of which we can charge to Landlord.

Cockpit: 20,183.29 gp (charged to Landlord budget)

This gets us a 20 ft x 10 ft x 10 ft metal box that can hover, very slowly.

A quick note on mass, since we'll need it later: our box is 20 ft x 10 ft x 10 ft, giving it a surface area of 1,000 ft2. The walls are three inches thick, giving us a total wall volume of 250 ft3 of mithral, or 7.1 cubic meters. Iron has a mass of 7,874 kg/m3, and mithral is described as weighing half as much as iron, so that gives our box a total mass of 27,952.5 kg. I'll round up to an even 30 metric tons to take account of our passenger and cargo.

Environmental Support and EVA

To keep our brave astronaut alive in the depths of space will require handling the following requirements: air, water, food, waste elimination, and thermal regulation. Also, although we could save some money by having our brave astronaut wear his “space suit” all the time, I want the interior of the cockpit to be a shirt-sleeve environment – among other things, that means we don't have to worry about damage to any possible cargo.

A ring of sustenance (2,500 gp) can fill the need for food and water. We'll have to buy it since Forge Ring is a hair too high for our caster level, but it's not that expensive anyway. (Stored rations and water would be cheaper, but I want to minimize book-keeping, and we might run out of room if we're planning a long flight.) This should also eliminate the need for waste; no food or water in, so nothing comes out. Adding the wondrous architecture chamber of comfort (from SBG) fixes the room's temperature at 70 F and “magically circulates fresh air in and out”, taking care of both our air and temperature problems, at a cost of 7,500 x 0.5 x 0.75 x 0.75 x 0.9 x 0.95 = 1,803.52 gp.

We'll also want to pick up a necklace of adaptation to allow us to venture outside once we reach our destination. This adds 9,000 x 0.5 x 0.75 x 0.75 x 0.9 x 0.95 = 2,164.22 gp to our cost. I considered using bottle of air and a gas mask instead, which would be a little cheaper, but adaptation wraps us in “a shell of fresh air” so we don't have to worry about keeping the pressure at the right level, which could be an issue with the bottle approach. We'll use the spell resist energy to protect us against the heat and cold – we get 20 points of resistance at level 7, so that should be plenty.

Summing up:

2,500 gp (Ring of Sustenance)
1,803.52 gp (Chamber of Comfort)
2,164.22 gp (Necklace of Adaptation)

We can charge the chamber of comfort to our Landlord budget, but the other two will have to come from our general funds.

Environmental Support and EVA: 6,467.74 gp (1,803.52 gp charged to Landlord budget, 4,664.22 gp charged to general budget)

Navigation and Sensing

Characters in D&D are notoriously near-sighted, due to the -1 penalty to Spot checks for every 10 feet of distance. Even with a nanite swarm, we won't be able to physically see either our destination or any potentially hazardous objects until we're basically right on top of them. Fortunately, divination magic can pick up the slack.

The best option I've found is the find the path spell. We'll install an energy transformation field (from Magic of Faerun) loaded with find the path in the cockpit, which we will power using a level-1 spell trap triggered by a button. Specifically, we'll install the field inside a closet: energy transformation field's area of effect is a 40' radius spread, which would otherwise cover the entire cockpit, absorbing the effects of any other magic we might try to use.   Magic such as, for example, the life support system.

When in flight, every hour we hold down the button for six rounds; the six level-1 spells are absorbed by the field, which then casts find the path on us. Find the path tells you the “shortest, most direct physical route to the specified location... The spell enables the subject to sense the correct direction that will eventually lead it to its destination, indicating at appropriate times the exact path to follow or physical actions to take. For example, the spell enables the subject to sense trip wires or the proper word to bypass a glyph of warding.” This would appear to include rocket firings as needed to dodge asteroids and other hazardous obstacles.

We'll provide the find the path spell from a scroll cast using Use Magic Device; our modifier for that is +5 (Intelligence) + 7 (ranks) + 20 (Guidance of the Avatar spell trap) = +32, which is enough to pass on a roll of 1. A scroll of find the path costs 2,400 gp. We'll have to subcontract the energy transformation field, because we're two levels shy of casting 7th level spells. A 7th-level spell costs 13 x 70 gp to have an NPC cast, plus the cost of its material components, which in this case costs 5,000 gp. The spell trap to charge the field costs 500 gp x 0.75 x 0.75 x 0.9 x 0.95 = 240.47 gp. We can charge the spell to the Landlord budget, but the rest comes out of general funds.

Navigation and Sensing: 8,550.47 gp (240.47 gp charged to Landlord budget, 8,310 gp charged to general budget)


  1. (sorry if this is a dupe. my first comment vanished silently.)

    Have Hardening (spell compendium 109) cast by a 20th level wizard, increases hardness by 10. Mithral's base hardness: 15. Thus, it ignores the first incoming 25 points of damage. "Electricity and fire attacks deal half damage to most objects; divide the damage dealt by 2 before applying the hardness. Cold attacks deal one-quarter damage to most objects; divide the damage dealt by 4 before applying the hardness." Thus, the hull will be hardened to 100 damage per attack from cold, and 50 damage per attack from fire.

    For propulsion, I do hope you'll be going with the decanter of endless water approach. For close in manoeuvring, have you considered spring-loaded weights? The weights can be manipulated by a psion's telekinetic force power, imparting 20 feet of movement to a 250 pound weight. It's also worth emplacing telekinetic spheres (using custom magic item rules in this instance, maybe), since they reduce weight to 1/16th per 5000 pounds. The only downside is its maximum velocity.

    You may also be interested in hauntshift based automation. (I discuss that on my answer on magical surveillance states on the RPG stack exchange.)

    1. Good idea on the hardening! I'd forgotten hardening can block energy damage. I'll update the article accordingly.

      On propulsion, I don't want to say too much yet because I'm not done writing it, but this proves to be a more complicated subject then it appears. For close-in maneuvering, I want to stick with the flight speed, because that way we don't have to keep track of fuel.

      Regarding hauntshift, unfortunately I don't have the book that spell appears in.

  2. I have beheld the true face of Nerdom today, and am not worthy...

  3. Have you liked at Dragonstar ( Fantasy Flight Games ), its D&D in space; though they do use teleport, you need a minor artifact ( read expensive ) and an astronavigation computer to direct the teleport; usually you do it the slow way, or find a nice Portal Ring that flies you to around where you want to be.

    One thing to keep in mind, shadow walk increases speeds by seven...

    1. Sadly, I've never had a chance to read Dragonstar. What I've heard of it sounds really cool, but there's only so much room in the book budget.

      Good idea on shadow walk! I'm away from my books right now so I don't know if there's room in the budget for the baseline version, but I'll look into it!