Embedded Files
One thing many people complain about in Phase World, Mutants in Orbit, Robotech, Aliens Unlimited, and other palladium space settings, is the 'mach in space' movement system and the absurdly low speeds there of. in robotech i didn't mind much, since my games rarely got into space. ever since getting phase world, i've been trying to devise a more realistic space travel system while maintaining the cinematic feel of the setting. after several failed attempts, i eventually found a method i liked, and i've been refining it since.
Section 1.) The Primer- An explanation of the dynamics behind space travel and combat.
There are a lot of misconceptions about space travel due to the way TV shows and Movies often present it. While there are a few shows that get the basics down right, and a somewhat larger number that present their material in a fashion that can fit how things would really work, most shows fail to make use of the basic rules of space travel. which are more or less as follows;
Ships are not fighter planes:
Without an atmosphere and wings, the atmosphere like 'swooping' maneuvers seen in many films and TV shows are not really efficient. while you could replicate such with thrusters, it is expending a lot of extra energy/fuel for what is in most cases nothing more than theatrics. In general, ships would maneuver more like those seen in shows like Babylon 5, or the new Battlestar Galactica. Spinning, flipping end over end, sliding sidewise or up/down, rotating to face a new direction to make a change of course. These kinds of maneuvers are very energy efficient, but still make for an interesting combat. It is also worth pointing out that g-forces from such maneuvers are slight. thrusters are much weaker than the main drives of a ship, which means that the strongest g-force felt by a crew (at least on a ship without high tech scifi dampening) would be the acceleration of its drive. The crew on a ship with a drive able to reach .5 gravities of thrust will never feel more than .5 gravities of thrust, even if it is firing its thrusters at the same time to alter the course. without dampening and artificial gravity, a ships crew will 'fall' towards the engine, thrusters just shift the exact angle slightly.
Ships are not arrows:
Unlike aircraft in an atmosphere, ships in space do not have to have their nose/bow facing the direction of travel. while the direction of the engine compared to the direction of travel is important, if the engine is shut off, the ship can point any which way, and will still be traveling the same direction. This means that it is very easy to bring weapons to bear on a target. If an enemy gets behind you, you do not have to 'shake them off', you can just flip end over end to point your front towards him and open fire. (For a good example watch the Babylon 5 episode "Midnight on the Firing Line") It also means that a ship can alter course easily, by shutting off its drive, altering the direction it faces, then turning the drive back on to begin accelerating onto the new course.
There is no friction in space:
Here on earth, vehicles and people have to deal with moving through an atmosphere, along the ground or water.. moving through materials that rub against things and slow them down so that constant energy is required to keep moving. In space, there is nothing to create friction and slow things down. Once an object begins moving at a speed, it will continue to move at that speed. This means that once a ship has accelerated up to its desired speed, it can shut off its drive and coast at that speed until it uses its drive to speed up again or to slow down. you can see an example of this in the film 2001: A Space Odyssey, where the ship Discovery is traveling to Jupiter, but its engines were shut down. in the sequel Film 2010: Odyssey Two, you can see that the ship Leonov only activates its drive when it needs to speed up or slow down, and leaves it off for most of the film. The downside of this lack of friction though is that you cannot stop in less time than it took you to get up to speed in the first place. Because your drive has to do the job of slowing you down as well as speeding you up, it will take the same amount of time to slow down as it took to speed up. The upside of the lack of friction however is that discussing the "range" of a ship is effectively pointless. Once up to speed and coasting, a ship can travel any distance, the only limit is how long it will take to get there.
The video below is "The Physics of Starship Battles - Motion and Momentum" by spreading the Muse productions. it gives an excellent introduction to how actual space movement works, or at least its core elements
Section 2.) "Naturalistic Movement"
The main idea is Inertia and thrust. Thrust is the ships ability to alter it's velocity, and inertia keeps a ship moving at a velocity when the drives are off. under this system, ships in combat would accelerate (thrust) to a speed, and then would coast at that velocity while fighting, altering speed only if needed. this set up also allows for some more interesting combat methods, such as kinetic impactors, the use of reaction drives as weapons, and other such interesting methods. in addition, it opens up the option of slower than light interstellar travel, which in turn allows for low-tech star nations and very interesting cosmozoans. i have intentionally designed the system to be directly compatible with palladium's current game mechanics, with minimal modifications needed. first is the unit of measurement. for simplicity, these are in mach, or the speed of sound, although in space this seems kinda silly. to make the math easier, i stuck to metric, although those stuck in the imperial mode can use miles and feet if they want.
1 mach = 1079 kph. (674mph)
1 c (speed of light) = 1,000,000 mach.
now, thrust is measured in how many mach a ship can accelerate by in a set period. for reference i have figured out the acceleration in gravities for each listing, so GM's and players can get an idea of how powerful the ships are. also listed are the kinds of drives that generally make use of which thrust profile.
1 mach per melee = 2g's advanced drives (contragravitic drive, torch drive)
1 mach per minute (4 melee's) = .5g's basic drive (fusion drive, orion drive, Photon drive[antimatter drive])*
1 mach per hour (240 melee's) = .0085g's simple drives (ion, plasma, NERVA)
1 mach per day = .00035g's passive drives (light sail, magsail, plasma sail)
although light speed is the absolute speed limit, most drives reach a point where the amount of energy used to accelerate is negated by relativity. most won't have the fuel to reach this max velocity, but there are always ways. (note, i am being generous here. these are general categories, not specifics. GM's feel free to bump these up or down depending on the drive and races tech level.)
advanced drives: .6 c (600,000 mach)
basic drives: .25c (250,000 mach)
weak drives: .10c (100,000 mach)
passive drives: .7c (700,000 mach) (passive drives will need boosting of some sort to reach such speeds before leaving a system)
* when working with mach per minute accelerations, it is helpful to just divide the listed mach by 4 to find how many it can gain in one melee. gaining a mach every 4 melees is helpful when figuring out the "background" info for a long trip, but it is hard to use in a melee by melee fashion during combat, while fractional mach's per melee can be used in combat easily enough.
Section 3.) 'Psuedo-Vector' Movement.
While coasting (not accelerating and letting inertia keep your velocity going, also known as 'cruising' to many star pilots) a craft can alter it's bearing at angles to it's direction of movement, meaning it can point it's bow somewhere other than directly towards where it is traveling. using the main engines, this can allow the craft to rapidly change direction with only a little thrust. a full period of acceleration brings the craft onto the new path, with the normal change of velocity. however, there is a limit to this. first, if the new course is more than 90 degrees from the current direction of travel, the acceleration will become deceleration, reducing the crafts velocity instead of increasing it, and if you change your bearing 180 degrees (placing your engines directly along the path of travel), you will only decelerate, and not change your direction of travel. second, the larger the craft, the longer it will take to swing the craft to a new heading. a fighter can change heading rapidly, in only a few seconds. a cruiser, being larger and more massive, will take longer, up to a whole melee. truly large vessels like battleships and packmaster carriers are more massive still, and will take up to 1 minute to change heading. as a result, large vessels rarely engage in such high-energy maneuvers. This same ability to orient the ship in any direction while coasting makes "traditional" naval and aviation tactics developed for use on planets obsolete. a warship trying to cross it's enemy's bow will usually find it's enemy cut it's drives and maneuvering to bring its broadside facing the direction of travel. a a fighter that has an enemy pull up "in his six", behind him, can flip over and bring its guns to bear on the enemy, all without changing its direction of flight. fans of the old video game Asteroid would be very familiar with this style of sliding combat, as that game replicated realistic space movement and inertia rather well, albeit on a two dimensional confined plane. space battles are usually fought while coasting, with acceleration and deceleration as a means to tactical advantage, speeding up and slowing down to get into or get out of the range of the enemies weapons.
Section 4.) Distances:
one of the important parts of this system is figuring out how fast you will be crossing distances. thankfully, this is easily worked out. in the span of a single melee (15 seconds), you will cross about 4.5 km per mach of velocity. thus to figure out how far your travel each melee, you merely need to multiply your velocity in mach's by 4.5 to find out how many kilometers your cross. the big issue is ultimately that involving relative movement. if an enemy is coming towards you, you will close on each other (cross the distance between you and him), at a rate equal to both your velocity and his velocity combined. if he is moving away from you, you'll close the distance equal to your rate of velocity minus his velocity. if the enemy if moving perpendicular to your course, there is no simple way to calculate the rate, sadly (if any mathematicians read this and can E-mail me a way, please do so.) the best i can suggest is averaging out your relative velocities. since at even 1 mach your crossing 4.5 km a melee, obviously when your moving at orbital velocities (30+ mach), your going to be crossing alot of distance pretty fast. this may not seem like much of an issue, but it is when considering weapons ranges.
(Image Borrowed from Starfleet Battles)
Section 5.) Notes on Ranges and Weapons:
the only other major alteration made is weapon ranges. because ships are much faster, weapons must be much farther ranges to compensate. while it may be tempting to just increase all ranges by 10 or even one hundred times, this does require some minor rewriting of the ship stats, and thus is to be avoided.
instead, treat the listed weapon ranges in space as Range Brackets, each providing a penalty to strike that is higher the farther away the target is. each multiple of the listed range adds a -1 to strike within that bracket, with the listed distance being the distance at which no penalty is applied. thus, for example, the anti-ship laser cannons of a CCW battleship, with a range of 1600km (1000 miles), can fire out to 1600km with no penalty, 3200km for a -1 penalty, 4800km for a -2 penalty, 6400km for a -3 penalty, and so on. depending on the bonuses to strike provided by the crew, on board targeting systems, and situational modifiers, it is possible to fire more than twenty times as far as the listed ranges before it becomes impossible to strike the target (as always, a natural twenty is an automatic hit..at any range)
this mechanic allows for more realistic ranges in space, while encouraging vessels to close to 'point blank range' to increase the chances of striking the target..creating the visual dynamics of ships practically hull to hull exchanging fire that hollywood loves so much.
Section 6.) Relative course, and weapons fire
The course of an enemy ship relative to your own has an impact on your ability to shoot at it. if the enemy is moving towards you, it will be easier to shoot them than if they were moving away from you, or if they were moving on a course that crosses yours. this is due to the need to adjust for changes in distance and position when shooting. a ships computers will do this automatically, but it makes shots more difficult. if a ship is moving towards you, there is no modifier to strike. if it is moving away from you, there is a -1 to strike modifier. if it is moving on a course that crosses yours, there is a -2 to strike modifier. these penalties are fairly small, but given the penalties for target size (see Dimension book 3: Phaseworld sourcebook), and the penalties for ranges (see section 5 above), these small penalties can have a large effect on attacks against an enemy ship.
These rules apply to Missiles in space as well as direct fire weapons like energy weapons and rail guns. Because of the small size of missiles (and the need to keep their price down), drive systems with long durations of operation would be rare. most missiles would be ejected out of the launcher, and run their drive for a short time to build up velocity, before shutting down the drive and coasting to the target. such missiles would have a velocity equal to the firing ship's velocity, plus the listed mach # of the missiles speed. if using missiles that can accelerate all the way to the target, ignore the listed ranges, and treat the entire volley as a space craft with an acceleration equal to the missiles listed mach #. this approach, while allowing missiles to be useful in running battles while under acceleration, makes the battle more complex for the gamemaster.
It is also worth noting that the penalties for target movement found in Rifts Ultimate Edition never apply in space. Spacecraft carry more powerful targeting systems, and even with the velocities attainable in space travel, the sheer size of space means it is much easier to calculate firing solutions against moving targets. however, the penalties for Target size, and other modifiers outlined in Dimension book 2 Phase World, Dimension Book 3 Phaseworld Sourcebook, and Phase World: Fleets of the 3 Galaxies, should apply at all times during the use of these rules.
Section 7.) Notes on orbital velocities:
In a misc. note, normal orbital velocity around a 1 gravity planet like earth is between 20-36 mach. anything less falls back to the planet, anything more escapes the planets pull. a ship can reach orbit if it can sustain 1 mach per melee of acceleration long enough to reach orbital speeds. (many less powerful ships have boosters or special drive modes to allow this.) given how powerful most ships are in phase world and others, this really doesn't matter much, but for settings like Aliens Unlimited, Robotech, and Mutants in Orbit this can help define which ships cannot enter an atmosphere.
Section 8.) Game settings and suggested applications of these rules.
Phase World - this is the setting these rules were designed to work with originally. accelerations should be mach per melee unless the GM decides otherwise. Contragravitic drive ships will have inertial dampening, so the g forces of acceleration will effect the crew less. (depending on the GM, it can be no effect, or just a reduced effect, or either depending on the ship or ship type.)
Robotech - This game setting currently has little space combat information, so these rules can be applied as is. since the ships use fusion or plasma rockets, assign thrust points to each ship, using the optional rules presented here. most veritechs will likely have 800 to 1000 thrust points, in my opinion. starships will have tens of thousands, enough that doing record keeping for all but the least advanced (such as the Oberth class) is not worth the effort. i recommend acceleration in the "mach per minute" range, as this prevents veritechs like the Alpha's and Logans from achieving stable orbit on their own, as described in the RPG and seen in the show. most starships will have accelerations of about a third to half a mach per melee (roughly 1/3rd gravities), as this matches the "time to reach % of light" descriptions in the RPG. the listed %'s of the speed of light should be considered that ships maximum velocity limit.
Mutants in orbit - these rules can be applied more or less as is, using the Rules for thrust points on the optional rules page. merely determine the ships thrust points and remember that ships can coast most of the way on interplanetary journeys to save fuel. i would recommend acceleration in the mach per minute range, as none of the drives described are particularly powerful. (just a helpful note, the "extra large fuel tank" you can buy in the ship construction really should mass twice as much as the standard tank. and you should be able to purchase multiple standard fuel tanks on a ship as well.)
Alien Unlimited - much of the basics of this system are already present in this setting, such as acceleration. the main things that need adding are thrust points and a maximum velocity for the various drives. the listed time period for "reaching light speed" should be considered the amount of time it takes to turn on the FTL component of the drive system, not a literal acceleration to the speed of light.
Mechanoids - Currently, Mechanoids would fall under the same category as Robotech or Mutants in Orbit. you merely need to determine the rate of acceleration you desire, and assign thrust points. The long promised Mechanoids Space, a second edition version of the setting, might be different, but it is not yet published
(image borrowed from Palladiumbooks.com)
There are some optional rules which cover certain situations these rules make possible, but they are not required to use these rules and can be ignored if the GM would prefer.
Page updated
Google Sites
Report abuse