This is my take on the classic "Spelljammer Helm" for use in the Cosmic Seas setting. It is more an arcane machine, being used with assorted other devices. Most ships will have these or similar devices in use. As their is no Phlogiston, the dangers of these drives are not as immediate.
AETHON ELEMENTAL ENGINE (Helm)
Cost: 100,000gp (Minor), 250,000gp (Major)
Aethon Helms are a type of Spelljamming Helm that has become the primary type of power source for space-going vessels within the Dragon Empire. The Helm looks like a table, but angled at a 45 degree increase so a seated person can access every part of it with comfort. On top of the helm are attached any number of etched rune plates, each one tied to a function of the ship. Both major and minor Aethon helms are powered by a Fallen Star that is fueled by Stardust Fuel (see below). This power source is always enclosed in a sealed container that resembles a boiler or furnace. While this provides movement, it is primarily used to push the ship forward; maneuvering is primarily accomplished through use of the ship's sails and oars. Because the motive power of the ship comes from a powerful elemental furnace, only spellcasters can pilot ships fitted with an Aethon helm.
For every week of travel, an Aethon Drive consumes one 20 lbs. tank of Stardust Fuel. This consumption rate can be offset by using Stellar Sails (see below), though most ships keep a backup supply of Stardust, just in case. Aethon Engines break down less, but if a space ship with an Aethon engine crashes and the DM can make a DC 24 Constitution check using the Constitution modifier of the pilot. If the check fails, the engine explodes, dealing 10d10 points of fire damage to all objects and creatures within a 60-foot radius of the engine. A DC 17 Dexterity save halves the damage.
Away from planets and other large objects, a ship equipped with an Aethon Drive flies through space at what is called cruising speed. The cruising speed of a ship depends on the Aethon Drive (or Helm) propelling it. A minor helm allows a ship to travel between adjacent planets in 2d6+2 days, while a major helm moves between adjacent planets in 1d6+1 days. (The random element assumes that even adjacent planets may be in different parts of their orbits. In extreme circumstances, you could double or even triple these times.
Stardust is a type cosmic dust composed of particles in space. These "elemental particles" are infused with Transmutation Magic in its purest form and are thus highly prized by magic users and supernatural beings. By itself, a handful of this substance allows a user to cast the reverse gravity spell with a duration of 1d10 minutes. However, the real power of this substance is to power Aethon Drive equipped Spelljamming ships through space.
Stardust Fuel is produced in specialized refineries located in the upper atmosphere of worlds near stars, where the dust is sifted from the solar winds. Different races have different means of doing this, but the basics are the same. The Dragon Empire maintains Stardust Refineries in every system in which it has a presence, maintaining its own stockpiles of the substance.
Stardust is sold in 20 lbs. iron tanks (like a propane tank) that cost 50gp per tank.
Stellar Sails are a remarkable item that allows vessels to travel farther and more efficiently. When paired with an Aethon Drive Helm (see above), Stellar Sails converts ambient magical energy found in Sunlight and Starlight into fuel for the helm. Each Stellar Sail generates enough energy to half a ships consumption of Stardust Fuel. If used without stardust fuel, and Aethon Drive paired with Stellar Sails moves between worlds at double the time