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--- traveller:roll20 [2020/10/24 16:38] – sam
+++ traveller:roll20 [2020/10/25 14:48] (current) – sam
@@ Line 1: / Line 1: @@
+{{ :traveller:traveller-heading.png?nolink&800 |}}
 ====== Roll20 Scripts ======
 ===== Physics [!physics] =====
-The //Physics// scripts are designed to provide aid in calculating basic things such as information on planets, or plotting travel times.
+The //Physics// script is designed to provide aid in calculating basic things such as information on planets, or plotting travel times. It's not specifically tied to //Traveller//, but was written with that game in mind. As with my other scripts, it is available on [[https://github.com/samuelpenn/rpg/blob/master/roll20/traveller/physics.js|GitHub]].
+The ''!physics'' command takes a sub-command and a number of arguments. It can be shortened if desired, down to ''!phy'' to save on typing. There are three sub-commands - ''thrust'', ''rocket'' and ''planet''.
+The sub-commands can be shortened to the shortest unique word, which current is a single letter for all of them.
+==== thrust ====
+The ''thrust'' sub-command uses the equation of motion to calculate how long it takes to travel a given distance under constant acceleration.
+<code>
+!phy thrust 1g 1.2mkm
+</code>
+This will give information on how long to accelerate to the mid-point, then decelerate to the destination. It also gives the time taken for when you don't want to decelerate - for example a missile that will accelerate all the way to the destination.
+If 'g' is not specified on thrust, then acceleration is assumed to be in ms<sup>-2</sup>.
+The distance is assumed to be kilometres unless other units are specified. ''km'', ''mkm'' (millions of kilometres) and ''au'' (astronomical units) are supported units.
+==== rocket ====
+The ''rocket'' sub-command will use the classical rocket equation to calculate the delta-vee for a rocket. This isn't used much in //Traveller//, but it's there in case it's needed.
+<code>
+!phy rocket 1000 200 350
+</code>
+It takes the wet and dry mass of the ship (units aren't important, since it's only the ration that matters), and the Isp (specific impulse) of the drive (in seconds).
 ==== planet ====
@@ Line 18: / Line 49: @@
 Displays statistics on a planet with a radius of 6400km, and a density of 5.5g/cm³. It will display the planet's mass, escape velocity and surface gravity.
-{{ :traveller:earth.png?nolink&200|}}
-{{ :traveller:super-earth.png?nolink&200|}}
 You don't have to specify the full command. You can use !phy instead of !physics. You can also specify the first letters of the command word.
@@ Line 29: / Line 57: @@
 !phy p 6400 5.5
 </code>
+{{ :traveller:earth.png?nolink&200|}}
 You can specify different units, for example you can use 'e' for Earth, 'j' for Jupiter or 'sol' for Sol. You can also specify, m (metres), km (kilometres), mkm (millions of kilometres) or au (astronomical units).
@@ Line 36: / Line 66: @@
 </code>
+=== Orbits ===
+{{ :traveller:earth-orbit.png?nolink&200|}}
+Another option is to specify an orbit. If a third parameter is specified, then it is the distance to an orbit, which by default is from the centre of the planet. To specify a 7,000km orbit around a 6,400km radius planet you would use:
+<code>
+!physics planet 6400km 5.5 7000km
+</code>
+Alternatively, you can specify an orbit as an altitude by using +<altitude>.
+<code>
+!physics planet 6400km 5.5 +400km
+</code>
+=== Solar Orbits ===
+{{ :traveller:solar-orbit.png?nolink&200|}}
+You can also specify solar orbits, simply by using larger numbers.
+<code>
+!physics planet 1sol 1sol 1au
+!physics planet 2sol 1.5sol 3au
+!physics planet 5j 1.5j 1mkm
+</code>