The Crown of the Stars - A Spelljammer 5e Tale
Gravity and Vacuum
A helm creates a magical gravity similar to normal gravity on the Earth. This magical effect extends to the edge of the air bubble (300 feet). This magical gravity pulls down in relation to the orientation of the ship. Anyone falling overboard will fall as they would on the Earth until they reach the edge of the air bubble. Ten feet beyond the edge of the magical bubble they will stop falling and simply hover there weightless in the vacuum of space (refer to vacuum exposure below). This will be true for anything dropped. If the ship is moving, anything that falls overboard will simply be left behind once it has left the ships gravity bubble. Anything thrown or fired from the ship will behave normally, as it would on the Earth, until it reaches the edge of the magic bubble. It will then continue in a straight line at its current speed forever, unless it hits something or enters another source of gravity. If two or more ships get close enough to each other that their gravity bubbles touch, they will automatically orient themselves so that “down” on all ships is in the same direction. If the ship is more than double the tonnage the gravity will orientate towards the larger ships “down”. If a ship enters the gravity of a planet, it will orient itself with that planet’s natural gravity. This alignment of gravity fields occurs almost instantly with no adverse effects to anyone aboard the ship. All planets, even small ones or large asteroids, have natural gravity. The effects of a planet’s gravity extend 32,000 feet above its surface. All planets have gravity roughly equivalent to that experienced on the Earth regardless of the size or mass of the planet. Not all planets are ball shaped. Some may be disk shaped. Others may be in the shape of a cube. Regardless of the shape of the planet, natural gravity (in this fictional universe) always pulls down toward each of the primary surfaces. This will be toward the center of spherical planets, or towards each of the major flat surfaces of a planet with flat sides.
Beings exposed to the airless cold of space are not immediately doomed. Contrary to popular belief, characters exposed to vacuum do not immediately freeze or explode, and their blood does not boil in their veins. While space is very cold, heat does not transfer away from a body that quickly. A creature can hold its breath for a number of minutes equal to 1 + its Constitution modifier (minimum of 30 seconds). When a creature runs out of breath, it can survive for a number of rounds equal to its Constitution modifier (minimum 1 round). At the start of its next turn, it drops to 0 hit points and is dying. For example, a creature with a Constitution of 14 can hold its breath for 3 minutes. If it starts suffocating, it has 2 rounds to reach air before it drops to 0 hit points.