inertia

noun

in·er·tia i-ˈnər-shə 

1 a: a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force b: an analogous property of other physical quantities (such as electricity) 2 : indisposition to motion, exertion, or change : INERTNESS

inertial i-ˈnər-shəl 

-shē-əl  adjective inertially i-ˈnər-sh(ə-)lē 

 adverb

I'm very pleased with how this worked out in actual gameplay. Some adjustments have been made that make it better.

When an object is in motion, any change in momentum or trajectory subjects it to the effects of inertia. While, realistically, inertia will impact a spacefarer's life from moment to moment, in gameplay, it only impacts combat. When in combat, whenever you change direction, reduce speed, or attempt to stay in a space, the player will have to contend with inertia.

MAPS
Inertia is determined by location. If you are in open space, in an asteroid field, or anywhere else where objects will have a minimal impact on gravity; these maps will have a difficulty of (10), which can be challenged with a d20 roll plus your bonus for challenging inertia. If a large body, such as a planet, is on the map, the difficulty increases by (4) per planet. If the planet has a moon, the difficulty increases by (2) per moon (There will be a table for how many planets and moons are recommended per map based on the average level of the party.). Nebulae have the greatest challenge against inertia. If the map you are fighting on is a nebula, this will provide the greatest challenge as the base difficulty for a nebula map is (15). If fighting in a nebula, there may be proto-bodies (infant stars) nearby. The difficulty of a nebula increases by (2) for every proto-body.

SHIP SPEED
Speed in this game is designed so that it can clearly and simply interact with inertia. Your ship has a number of spaces that it can move each round. You may traverse a combat map at six different speeds (the amount of spaces per round that you may move divided by (6), rounded to the nearest whole number). Thus, if you are able to move (24) spaces per round, you may choose to move per round in increments of (4).

EFFECTS
Drift: If you are attempting to remain stationary on your turn (staying in your current space), you will need to roll to determine how much your ship drifts. If you exceed the map's difficulty on your roll, you will be able to remain in your space. Otherwise, you will drift by one space in a random direction (1d6 on a hexagonal grid). You will need to roll this check and determine the direction each time you try to remain stationary. If, on subsequent turns, you choose not to challenge the difficulty of the map when holding position, you simply continue to drift in the direction you drifted in the previous round.

Controlled Drift: You may not simply move two or three spaces at a time due to how ship speed is designed to interact with inertia--unless your maximum spaces per turn are low enough--however, instead of remaining stationary, you may forego the inertia check and deliberately drift in a direction of your choice to move a single space. This may be done freely each round you are stationary and does not require a roll. In this event, you may choose the direction you drift instead of choosing randomly. You may not perform a controlled drift when on a map with a gravity well.

Drag: When turning, on a hexagonal grid, you can choose to turn in six directions, making a maximum turn angle of (3) ((3) being a complete 180-degree reverse.). If, while moving, you attempt to change your direction, you meet the difficulty, you may freely turn to that maximum turn angle of (3). If you fail, you may only turn at an angle of (1). If you critically fail, you may not turn at all. Similarly, if you attempt to stop or reduce speed, you may not reduce speed on a critical failure, may only reduce your speed increment by (1) on a standard failure, and on a success you may completely stop. The direction and speed you are traveling have no effect on the direction your ship is pointed; this is useful since weapons do not have a 360-degree range of attack.

Acceleration: Accelerating in a direction you are able to move and in a straight line is not subject to inertia and requires no roll against the map's difficulty unless you are accelerating away from a gravity well.

GRAVITY WELLS
When drifting, a ship will not drift at random when a planet, moon, or proto-body is near, and will instead always drift towards the gravity well. On a failure against drag, the gravity of the well will force you towards meaning that a standard failure reduces your turn angle to (0) if you are turning away from the well. Your failure is completely negated if you're turning towards the well. If you critically fail, the well will automatically drag you toward it and subsequent consecutive inertia difficulty checks will increase by (2) per failure (to a maximum of a -(6) penalty). After any successful inertia check, all penalties are removed. Critical successes are automatic.

Slingshot: If you find that you are having difficulty escaping a gravity well, you may attempt to use the gravity well to hurl you to safety. If attempting a slingshot, accrued penalties are reduced by (2), and there are no penalties for subsequent failures. On a success, you are removed from combat and the turn order entirely. You do not experience any combat losses.

Orbit: As stated, if you fail the inertia difficulty to escape a gravity well six consecutive times, your character is lost, but you get a single save: you may attempt to fall into orbit around the planet. This is rolled without the accrued penalties. If successful, your character will survive but is essentially removed from combat. Unlike a slingshot, you are considered to have lost the combat and will face the consequences (such as being robbed by your attackers or captured by a bounty hunter.).

Movement: When moving towards a gravity well, you may move at double speed. When moving away from a gravity well, you may move normally on a successful inertia check, unless trapped in the gravity well.

Getting trapped in a Gravity Well: This occurs when you have failed (3) consecutive inertia checks on a map with a gravity well. On the second failed check, you get a penalty of -(2), and on the third, -(4). On a further (3) consecutive failed inertia checks, your character is lost (on the first of these three final checks, your penalty increases by another -(2) to the maximum of -(6).). When trapped in a gravity well, you may not move away from it. You are trapped in whichever gravity well you are closest to (I am aware that it's different for actual physics. Inertia isn't in this game for realism. It's in this game because it's one of the elements I'm using to make space combat in an RPG truly different from combat in the typical fantasy RPG.).