Optional Rules Variant 305-A: BattleMech Combat on Low-Gravity Worlds NOTE: See also BattleMech Combat in Vacuum, in BattleTechnology # 0103. That article discusses vacuum as an insulator, gravity questions, cockpit depressurization rules, and other things which relate directly to conditions on a smaller world. We have included a few of the rules and topics mentioned in this article, and in the Ranged Combat article in the same issue as a jumping-off point for further rules variants. Thank you to William H Keith, Jr, our first editor, who wrote those rules. You may wish also to see the discussion of recoil in freefall in Away Boarders, by Harrison Coulter, BattleTechnology #10. As always, rules variants are not laws. They are for fun, for expanding the simulator game to approximate special conditions. If you differ with a rule or decision here, write in and tell us about it. Include your version. You might just be right, in which case, we'll print it. Be aware that some complex factors have been averaged together for ease of play. Smaller worlds have lesser gravities. You weigh less. Your Mech weighs less. Your bullets and your missiles weigh less. Your mass, though, is the same. Your inertia (your difficulty in changing from rest to motion, turning, or stopping) is the same. Remember: you can move farther or faster, but it's just as hard to slow down. The weight (not mass) of a Mech, man, vehicle, piece of equipment, or object used as a club can be found by multiplying the world's surface gravity by the object's weight. A 75 ton Marauder on a world with a surface gravity of . 10 weighs 7.5 tons. BattleMechs may run faster than normal on lower gravity worlds. For every full .2 Gs under 1 Gravity, a Mech may run one additional hex. A Hunchback on a world with. 12 surface gravity may run 10 Inexes instead of its usual 6. For clarity, we'll be referring to an Extended Run, the difference between your normal running movement and the expanded movement in low- G. The Extended Run of the Hunchback is 4, the difference between its regular run and its possible lowG movement. For ground vehicles and for infantry, the same; add one factor to the movement rate for each .2 G below 1. Piloting Skill Rolls are required for each use of the extended run. A Piloting Skill Roll is also required for each time a Mech attempts to stop without slowing to a walk for one turn first. If he attempts to change facing while running, an additional Piloting Skill Roll is needed. There is a Skill Roll Modifier of +1 added for each two hexes of Extended Run Range. (In this case, you must round up). This is cumulative with the I usual Skill Roll Modifiers for running. A jump-capable Mech may also jump farther. Call this the Extended Jump Range . (A LAM moves farther too.) For every full .1 Gs under 1 G, you may add one hex more to your Extended Jump. A Phoenix Hawk, with its normal Jump MP of 6 could add an Extended Jump of 8 more hexes, for a total of 14 hexes. No Piloting Skill Roll is needed for the first turn in which this is done. If the world's gravity is between .25 G and.6 G, and the margin by which you fail the roll is greater than 5, you will perform a leap as described in Escape Velocity. If the world's gravity is .2 G or under, see Extended Range Failure Chart for further movement. Escape Velocity On very small worlds like moons, planetoids, or asteroids, vehicles and people must face the problem of escape velocity. Simply put: if you go too far too fast, you have a chance of running or jumping off of the planet entirely! On worlds with a surface gravity of .2 G or less, a Mech or vehicle must make an additional Piloting Skill Roll, and a person must make a Dex Skill Roll, for each two turns in a row run or jumped using Extended Range. If the roll is failed by 4 or less on a .2 gravity world, the Mech will spend a turn in mid-air, having leapt up like an inadvertent ballet dancer. It must then make another Piloting Skill Roll to avoid taking fall damage (at the reduced weight mentioned before). While in the air (or suspended above the ground, in the case of a world with no atmosphere), the pilot's attention is assumed to be on his piloting. He may not fire. In the case of a vehicle with a trained gunner, or of a Mech with two men like a Battlemaster, the non-pilot may fire. It is at a Skill Roll Modifier of 4, as the vehicle will be wobbling crazily, so it isn't recommended. Still, it may be done. If the Skill Roll is failed, you have achieved escape velocity. Congratulations, especially if you are not jumpcapable. Jump-capable Mechs and LAMs which have taken no jump jet or conversion equipment damage, make two Piloting Skill Rolls and take two turns to return to the ground, during which you may not fire. If you have taken such damage, or if you manage to have a heat shutdown during this time, continue as follows, but a LAM has six turns before it's out of the game; a jump-capable Mech has four instead of three. These pilots are more likely to be trained in low-G maneuvers. Combining and averaging a number of factors for simplicity of play, the rule is: if a planet has an atmosphere, you now have three turns until you pass beyond it. Infantry have 6 turns. During the last one of these turns, the atmosphere is thinned to half. If you have an ICE engine, or if you're piloting a hovercraft, when you past the atmosphere, you've just lost all power. (If the planet has no atmosphere, of course, you had none to begin with.) For that last turn, you have half power. After that, cockpit hits or any breach of an environment suit can mean instant destruction. You have that same number of turns until you escape the planet's gravitational pull. On each of those turns a Mech may make a Piloting Skill Roll, (infantry a Dex Skill Roll), both at a Skill Modifier of 2. If a MechWarrior has space training (Gamemaster discretion), this modifier does not apply to him. A vehicle is at a disadvantage here; it has less variety of movement possible. It has a Skill Modifier of 4. (Skill Modifier: subtract from BattleTech, add to MechWarrior). If the Skill Roll is made, your troubles are still not over. Make another Skill Roll, this time with a favorable modifier of 4 (ADD to BattleTech, SUBTRACT from MechWarrior). It you miss, see the rule on Orbital Velocity. If you make it, see Returning to Ground (LAMS, jump-capable Mechs, and flight-capable vehicles may then maneuver normally) . If the stipulated number of Skill Rolls are all missed, you escape the planet's gravity and continue into space. It will take a long time for you to slow down; there is no atmospheric friction to slow you now. You're out of the game. Gamemaster: if you have a campaign going, you must decide factors like direction of movement and length of time to rescue. Orbital Velocity A moon does not move away from a planet because its outward movement is balanced by the planet's gravitational pull. You too have the chance to become the satellite of an uninspiring piece of rock. Uncorrected: If you rolled this outcome, you will move parallel to the ground in the direction in which you were last headed. If this is uncorrected, you will disappear over the horizon. If planetary radius is over 3 kilometers, this is effectively the end of the game for you. Distance to the horizon d = square root of (r+h) squared - r squared. where d = distance to horizon, r = radius of the planet, and h = height of Mech or observer. If somebody shoots at you during this involuntary retreat, line of sight is important. For simulator purposes, you are out of the game once you have passed a certain limiting distance. Measure the longer dimension of the board you are playing on. Triple it. Keep track on a piece of scratch paper how far you have moved each turn. When you have gone that triple distance, you are beyond return. UNLESS the planetary radius is under 3 kilometers. In that case, you will return, at a velocity double that of your extended range, on the opposite side of the board in a random location, in 5-15 (2 d6 plus 3) turns. Sometimes this is relevant, so keep track. You'll still have to make a two Piloting Skill Rolls, one to slow down, and one to regain control, when you arrive again. Infantry, it's going to take you 10-20 turns (2 d6 plus 8). To Correct: Make your relevant Skill Roll with a Skill Modifier of 2. Wait one turn. Then make another Skill Roll to land without damage. If you miss, remember that your damage is at the low-G weight. You may continue to attempt correction until you have passed that limiting distance. Returning to Ground It takes as long to return to the ground as it did to leave it. You may choose to accelerate toward the ground, if you have jump jets, etc. If you fail your Skill Roll to land and you have not accelerated, you take damage for your low-G weight. If you have accelerated into your Extended Range, you will take damage at your normal weight. (If you have weapons which cause recoil, you may use that recoil to accelerate by firing the weapons. You have a Skill Modifier of 4 on your Gunnery Skill to do this accurately. The exact amount which this affects your movement must be discussed later. So, yes you could if you were really there, but the rules are not yet written as to how to do it, so you can't yet. See contributing suggested rules, above.) Now it gets fun, folks. If something as large as a Mech can achieve orbit, what do you think happens to shells and missiles? How do weapons work in this environment? Several factors apply. Gravity first. Lasers and flamers and PPCs are not attracted by gravity. They go in a straight line. They are simply affected by the line of sight rule to the horizon. You can fire as far as you can see, with lessened effectiveness. Machine guns, autocannon, and missile fire are also given an extended range by the weakened gravity. The Extended Range Table from BattleTechnology 0103, itself a variant rule, is reprinted below. The changes are not in the table itself, but in the fact that with anything but lasers and flamers, the basic to-hit number is 11, not 12. Misses are the problem - for autocannon and missile fire. If on a small planetoid, an orbiting Mech can come around the planet and eventually come upon another Mech's back, so can his missiles. Machine gun bullets will not achieve orbit on anything much bigger than a weather balloon. We have decided, rather than giving you a formula with seventeen or so variables, to condense it all into the following table. If your missile etc achieves orbital velocity, it will continue around the planet in 5-15 turns, and eventually reenter on the opposite side of the board at a random location. Gamemaster, when it reenters, plot its path secretly. Have everyone write down his intended movement. If anyone is passing through the item's path, roll as if it had been fired at him with a gunnery skill of 4, short range. If it hits, do normal damage. Back to BattleTechnology 11 Table of Contents Back to BattleTechnology List of Issues Back to MagWeb Magazine List © Copyright 1989 by Pacific Rim Publishing. This article appears in MagWeb.com (Magazine Web) on the Internet World Wide Web. Other military history articles and gaming articles are available at http://www.magweb.com