Spelljammer Dispatch: Adventuring in the Astral Sea

Teos Abadía

Teos Abadía

I trust this missive finds you well! Last time we reviewed the varied adventurers you may find in Wildspace. Now let’s get to what it’s like to travel the void between planets, and even the Astral Sea itself.

Traveling the Astral Sea

Here’s the big picture – and I mean big! The Astral Sea is a plane where everything from the bodies of forgotten dead gods to floating fortresses can be found. Also accessible throughout the Astral Sea are entire systems of planets, known collectively as Wildspace.

Anyone can move through the astral. You simply will yourself to move! The stronger your intellect, the faster you can move. You can pick a direction, or even a destination, so long as it is in Wildspace or the Astral. If you choose to travel towards Krynnspace, off you go. This is very useful, since locations in the Astral can shift over time. You don’t hunger, you don’t thirst, and you don’t age, so you can travel at a slow speed if you want. We call it a sea, and that’s fitting, because you can even see Astral fish and catch them with a line and some bait. Just watch out for space eels and far worse things you don’t ever want to see on the end of your line!

Once you reach a planetary system, such as Realmspace, you transition into Wildspace. Most systems have planets rotating around a sun (Greyhawk is one of the exceptions, with even the sun rotating around Oerth).

DMs take note: this gives you a lot of room to develop adventures. You can zip through the Astral Sea, or add detail by having travelers encounter any number of wonders as they travel. It is also an elegant way to expand your campaign. From a material plane (such as Toril and Realmspace) you can introduce characters to either the Astral or Wildspace, and then to the other, and then to other planes… all at a pace that works for you!

Traveling Wildspace

Once you leave the Astral, time resumes its relentless march and the rules of Wildspace apply. Let’s discuss the key aspects.

Air Envelopes

The void of Wildspace lacks breathable air. Fortunately, when you leave the Astral Sea or a planet, you take a bubble of air with you. The size depends on how big you are. A spelljamming vessel gets an even bigger air envelope, and everyone inside shares it (you would only form your own air envelope if you left the ship’s envelope).

The size corresponds to the space you take up, so it’s easy to remember. A small or medium creature has a 5-foot-square air envelope, while a large one is 10-feet-square. A spelljammer brings with it an envelope that is the size of the ship’s longest dimension. For example, a nautiloid ship is 180 feet long, so that’s the size of the envelope extending from any of the ship’s surfaces. The bubble tends to smooth itself, so in this case it’s an oval. But, it is possible for a rectangular shape to have a rectangular bubble.

Your air has a quality: fresh, foul, or deadly. Fresh air is what you want, but it degrades after 120 days if the ship has the normal crew capacity. Foul air poisons you, and will degrade in another 120 days to deadly. If you are a fond of breathing, take heed. You will immediately begin to suffocate until you find fresh air. Sometimes the deadliest part of a ghost ship isn’t the ghost!

Air envelopes create all kinds of fun scenarios. If the ship can’t approach an area, say a cave inside an asteroid, the characters have to explore with their personal envelopes. That can create some fun tension, since a personal air bubble only lasts for one minute!

When two objects or creatures have their air envelope overlap, the air combines and immediately becomes the quality of the largest object. This is another interesting way to add tension or pace your campaign by requiring stops at planets or other large bodies with an atmosphere.

Gravity Planes

On a spelljammer, gravity extends from the imaginary horizontal line that would extend through the center of the vessel. Gravity points down from both sides, towards that line. This means that one crew member could stand on the ship’s deck, while another could stand on the bottom of the ship’s hull. Both can move and act normally, as if that side of the horizontal line was the surface of a planet. Anything that leaves the air envelope will no longer experience gravity, and will continue moving in the same direction until it strikes something. So, if you want to try a risky maneuver that might leave you outside the ship’s air envelope, and you want to return, tie a rope around yourself. You can also rely on flight, teleportation, or something similar.

When a spelljammer enters an atmosphere, its gravity plane is suppressed. If two ship-sized objects touch, the gravity plane of the largest ship wins out. I can imagine some of you are thinking tactically, and yes, you can use this to your advantage. Falling in a gravity plane is just like falling anywhere if you strike a surface.

The ship with the most hit points is considered largest. This can lead to some interesting tactics that further reinforce the idea of firing siege weapons from afar and then closing to board. More on that later! Also worth noting that a weightless creature is at disadvantage when making a melee attack with a weapon unless they have a flying or swim speed, or if the weapon deals piercing damage.


While it can be fun to ride a dragon through space, most of us lack such friends. We instead need a spelljammer, which is a vessel equipped with a special kind of device known as a spelljamming helm. A helm looks different depending on the maker, but typically appears to be a throne or similar device with various embellishments. Some folks like the ones with sharp menacing angles. I prefer the ones with lots of cushions. Either way, you must be a spellcaster and attune to the helm.

Once attuned, you can pilot the vessel through space, air, or even underwater if the ship is built for that. The spelljammer pilot can see around the ship as if they were standing upon the ship in any location of their choosing.


When in an atmosphere, a ship’s movement speed is tens of feet per six seconds, depending on the vessel. When flying through Wildspace, all spelljammers soar at an incredible 100 million miles in 24 hours.

Seriously! That’s fast, and it lets your campaign get to the cool parts quickly. But, also, there is a built in stopgap that lets you drop in surprises. When a spelljammer would come close to something large enough to have an air envelope, it slows to the movement speed, which tends to range between 25 to 50 feet per round. This speed is also what you use if you travel in an atmosphere, though often converted to miles per hour. A ship that moves at a speed of 30 feet will travel 3.5 miles per hour. To convert other speeds, add or subtract a half mile for every 5 feet of movement speed difference. A ship moving at 45 feet will travel 5 miles per hour.

A ship can maintain its speed (spelljamming or otherwise) as long as it has a rested spelljammer pilot at the helm. A ship can stop to rest, or it can have the pilot transfer attunement immediately by simply touching a willing creature.

Ships and Combat

The ships found in space are as varied as the creatures, worlds, and cultures designing them, from seemingly delicate elven vessels to the stone hive ships of the beholder nations. Most crews know to run from a mind flayer nautiloid or neogi nightspider on sight, and a good smuggler knows the difference between a hammerhead and a scorpion ship and when one is better than the other for a particular situation.

Ships add a huge variety to your campaign. Slowly introducing ships allows your players to experience surprises as they see how many creatures and ship types there are. New ships are also something the party can take over, allowing them to upgrade their ship over time.

You can find a full dossier and even deck plans for all of the spelljammer vessels on the Roll20 compendium, as well as bring them into your game as handouts or to use the maps for exciting Wildspace battles.

Wildspace Combat

There are a few key differences you should learn before you ever leave the dock. First, most ships will aim to fire siege weapons and close to board. This is because reloading siege weapons takes time, and a ship often has creatures who will deal greater damage to the crew with melee, spell, or by other means. Spelljammers are also valuable, so destroying them is seldom the goal.

A DM gets to choose the starting distance, and this will determine how long ships get to use siege weapons and whether other ranged attacks can be used. The rules mention using side initiative (found in the Dungeon Master’s Guide) as an option. In this format, each side takes turns, and that side chooses the order in which all allies act. A ship moves on the pilot’s turn.

Boarding can take place whenever one ship is adjacent (within 5 feet) of another. Creatures usually choose the Ready action to move across as soon as this takes place.

Some situations call for destruction. A spelljammer pilot can decide to ram another, or a creature, resulting in a crash. This can also result in the gravity plane changing for one ship, and creatures falling.

Ramming a ship requires a special attack roll, and typically inflicts damage to both ships (or the ship and a creature) based on the size of what is struck. Repairs take time and cost 20 gp per hit point repaired, though you can use the mending spell.

Spells and Magic Items

Clever spellcasters have devised the second level air bubble spell, which lasts 24 hours. And while ports are filled with high-priced spelljammer helms, the fifth level create spelljamming helm will work just as well.

If you can’t cast spells and want breathable air the next time you enter a derelict ship’s deadly air envelope, a fish suit can provide you with air and a swim speed or flying speed as appropriate.

Being a consummate wanderer, I’m a big fan of orreries. A wildspace orrery magically tracks the position of all suns, planets, moons, and comets in a system. You can even see your location as a glowing spec.

Well, I may have taken on some questionable cargo at the last port, and I hear the splintering of crates, so that will be all for this week. I guess my next dispatch will be on creatures and monsters. See you next time… I hope!

Start your own Spelljammer: Adventures in Space on Roll20!

Teos Abadía

Teos Abadía is a Colombian-American freelance author and developer working with Wizards of the Coast, Penny Arcade, Dwarven Forge, Hasbro, and several organized play programs. Teos was a primary author on the Acquisitions Incorporated D&D book and on the vast Dungeon of Doom and Caverns Deep adventures for Dwarven Forge. Board game work includes the recent HeroQuest game relaunch. Blogging at, Teos shares knowledge and advocates for diversity and better industry pay. Reports that he was created by tinker gnomes in a device powered by space hamsters are incorrect… it leaves out the important role played by flumphs.