The Successor State Houses are locked in an on-going death struggle which demands that territory--above all, territory capable of supporting human life--be taken and held. Most BattleMech combat simulations are set on worlds where atmospheric and surface conditions are more or less similar to those of Terra. There are hundreds of worlds in the Inner Sphere where Man can live without complex or cumbersome artifical aids, worlds where he can walk freely in the open without space suit or respirator, oxygen mask or sealed armor. And yet, for every Earthlike world there are hundreds more where man cannot live without special equipment. They range from planets like Sirius V where cities are sealed domes under frigid, poisonous atmospheres, to airless, cratered moons and utterly barren balls of rock and ice or molten lava. While Earthlike worlds are most often the focal points of struggle between the warring Successor State houses, all too frequently it is an utterly inhospitable planet which, by virtue of its location, or its raw materials, or its abandoned relics of lost Star League technology, becomes yet another battleground in Man's unending wars. Optional Rules Variant 0103-B presents rules and guidelines which can be incorporated by BattleTech and Mech Warrior referees and players. They can be applied to simulate movement and combat on airless, low-G worlds such as Earth's moon, Sol I (Mercury), and on the barren rocks which can be found in virtually every star system across the Galaxy. They should be used in conjunction with BattleTech scenarios such as On the Shores of a Sea on Gordo in this issue. Future issues of BattleTechnology will deal with movement and combat on other types of worlds, including high-gravity planets, and worlds with poisonous or corrosive atmospheres. These rules are divided into sections, each dealing with adifferent aspect of movement or combat on a typical, airless moon. Referees and players may elect to choose only those rules which apply to scenarios of their own devising. GRAVITY Large moons-bodies such as Earth's moon-typically have diameters of two or three thousand kilometers or less, and masses which are only a fraction of that of Earth. Most solar systems have numerous small planetary bodies-such as Sol I and Sol IV-with diameters less than four or five thousand kilometers. Such worlds and wordlets have gravitational fields much weaker than those of Earth-sized worlds. While people and objects may weigh less on such worlds, mass is not changed in a lower gravitational field. This means that a 50-ton Centurion will weigh only 10 tons on a planet or moon with a surface gravity of .2 G... but that Centurion will still have the mass, and the inertia, of a 50-ton BattleMech. It will take as much energy to get the machine moving or to stop it as it would in a standard 1 -G gravity. Since the weight is so much less compared to the size of the power plant, it will be possible for the 'Mech to jump farther or run faster... but its full, 50-ton mass must still be overcome when it is being turned or slowed. The following rules can be used to simulate low planetary surface gravities. The weight(not mass) of a BattleMech (or any other piece of equipment) on a low-gravity world can be determined by multiplying the world's surface gravity by the object's weight. A 60-ton 'Mech on a moon with a surface gravity of .12 Gs weighs 7.2 tons. BattleMechs may run faster than normal on low-G worlds. For every full .2 Gs under 1 G, a'Mech may run 1 additional hex. Thus, a PhoenixHawk (normally with 9 Running MPs), could move 13 hexes in 1 turn on a world with a gravity of .12. Additional piloting Skill Rolls are necessary every time a'Mech attempts to move faster than would normally be allowed, and if the 'Mech stops without first slowing to a walk for one full turn. An extra Piloting Skill Roll is also necessary if the 'Mech attempts to change facing while running. All Piloting Skill Rolls have a Skill Roll Modifier of +1 added for every 2 hexes over the 'Mech's normal top running speed. This is in addition to the usual Skill Roll Modifiers for running. BattleMechs may also jump further on low-G worlds. For every full.1 Gs under 1 G, a'Mech may jump 1 additional hex. Thus, a Phoenix Hawk with a normal 6 Jumping MPs could jump 14 hexes under.12 Gs. No additional Piloting Skill Roll is necessary for this maneuver. BattleMechs which fail these Piloting Skill Rolls fall and skid. The rules for skids are presented in FASA's CityTech, and in the Rules of War BattleTech Manual. Damage for collisions between 'Mechs is calculated using their full 1-G weight, not their weight on a low-G planet. This is because the damage caused by such impacts is related the'Mechs'speed and to their mass, not to their weights. Failing 'Mechs, however, fall more slowly than they would in a 1-G environment and consequently do less damage to themselves and to others when they land. The number of damage points caused by a 'Mech falling and by collisions brought on through an attack by Death From Above are calculated using the 'Mech's weight in low G, rather than its usual weight. Fractions of damage points are rounded up. VACUUM There is no air in space. Moons and worlds with surface gravities substantially less than Earth's (less than about .4 G) are unlikely to have more than a very thin atmosphere, if, indeed, they have any atmosphere at all. The following guidelines may be applied to 'Mech combat in airless or nearly airless environments: BattleMechs may function more or less normally in vacuum, so long as they are fusion-powered. BattleMechs with internal combustion engines (ICEs) will not operate in vacuum. This applies to other vehicles as well. Vehicles will work in vacuum if they are fusion-powered or run on batteries, chemical engines, or f uel cells. ICEs require atmosphere (and oxygen) to function. Likewise, hovercraft will not work at all on an airless body, no matter how they are powered. Hovercraft depend on thrust provided by jets of air directed by fans in the vehicle's plenum chamber and will not operate in vacuum. Non-Mech vehicles must be wheeled or tracked. MechWarriors may choose to wear lightweight pressure suits inside their 'Mech cockpits. These are form-fitting, open only at wrists and neck, and come with gloves and a helmet which can be quickly sealed in place. A fitting at the warrior's waist allows the cockpit life support system to be connected directly to the suit, providing air and some cooling. These pressure suits are extremely uncomfortable, however, and are not worn as a general unless there is a danger of depressurization. They will support the pilot for as long as the BattleMech has power and he remains attached to the 'Mech's life support. Once the pilot disconnects from the'Mech, he can survive for4 hours off a small, rechargeable life support kit worn on his back or slung on his hip. The suits are intended solely to preserve the pilot's life in case of decompression; they have no armor value and are too lightweight to serve well as standard space suits. The BattleMech cannot be piloted while the pilot is wearing a pressure helmet. Removing the 'Mech's neurohelmet requires a successful roll against the character's Base Saving Target for his DEX. Once he begins removing the neurohelmet, the 'Mech cannot move or fire. Donning the pressure helmet and gloves and sealing up his pressure suit requires a second roll against the character's Base Saving Roll Target for his DEX. One roll can be made for each turn the character attempts to remove or don a helmet. There is a DM of -1 if the atmosphere is too thin to breathe during depressurization (See below.) BattleMechs which take hits to their heads or torsos may suffer damage which causes depressurization. Each turn in which a'Mech suffers at least 1 point of armor damage to its head or 5 points of armor damage to its center torso (front or rear), it will suffer depressurization on a 2D6 roll of 9+. There is a DIVI of +1 to this roll for each additional 1 point of armor damage to the head, or 5 points of armor damage to the torso, which the 'Mech suffers in the same turn. Depressurization may be slow or fast. If depressurization occurs, the player should roll 2D6, with a -1 modifier for each point of head damage or 5 points of center torso damage (front or rear) the'Mech has received so far. The result is the number of 10-second turns it will take for the cockpit to lose all of its air. If the result is 11 or more, roll 2D6 a second time. This new roll will be the number of minutes (rather than turns) the'Mech will continue to hold pressure. If the result of the first roll is 2 or less, then explosive decompression occurs, and the cockpit loses all of its air almost at once (see below.) Whether the result is in turns or minutes, divide this number by 3, rounding fractions up. This is the number of turns (or minutes) the cockpit atmosphere will remain breathable. Once the atmosphere is no longer breathable, there is a -1 DIA to attempts by the pilot to remove his neurohelmet and don his pressure helmet. Example: A Shadow Hawk fighting on an airless moon receives 12points of damage to its center torso. The pilot rolls 2D6, and adds 1 since more than 5 points of armor were damaged beyond the initial 5 points necessary to force the roll. The result is 9, so the ShadowHawk begins losing atmosphere. The pilot rolls again to find out how long it takes to completely depressurize. He rolls 2D6, then subtracts 2 for the amount of damage sustained by the 'Mech so far. The final result is 7. The cockpit will depressurize completely in 7 turns, or about 70 seconds. Had the result been I I or more, he would have had to roll 2D6 again for the number of minutes before depressurization occured. Finally he divides 7 by 3 and rounds the fraction up. He has three turns, or thirty seconds, before he can no longer breathe his cabin air. Once the air in the cabin is too thin to breathe, the MechWarrior will take 2D6 damage points against his HTK every turn until he manages to don his pressure helmet. Once the cabin has been completely depressurized, the MechWarrior will take 2D6 x 3 damage points against his HTK every turn until he manages to don his pressure helmet and gloves. The usual rolls must be made each turn to determine whether or not the pilot remains conscious. Obviously, if he becomes unconscious before he successfully dons his pressure helmet and gloves, he will die. If explosive depressurization occurs (a roll of 2 or less in the roll for the length of time in depressurization) the cabin loses all of its air at once. The pilot suffers an immediate 2D6 x 5 damage points against his HTK, then takes 2D6 x 3 damage points every turn thereafter until he can get his helmet and gloves on. The MechWarrior mayattemptto repairthe damage in orderto keepthe BattleMech operational. Finding the source of the leak and repairing it requires a roll against his Base Saving Roll target for his DEX. There is a DIVI of -1 to this roll for each lost point of head armor or each 5 lost points of center torso armor. While he is repairing the damage, his 'Mech cannot move or f ight. The roll may be attempted once each turn. If a roll is successful, the cockpit stops losing atmosphere, and the BattleMech may be operat normally. However, every time the BattleMech takes additional damage its head or center torso, the pilot must roll 2D6 again. On a roll of 10 or higher, his jury-rigged repairs fail, and his cabin begins losing air again at the same rate as before, beginning at the point where the air loss had ceased previously. The pilot may elect to attempt repairing the damage again. Repairs are impossible if explosive decompression occurs. HEAT One of the greatest problems faced by BattleMechs is that of heat build up during combat. It is much more difficult to get rid of heat in a vacuum thar it is when surrounded by atmosphere, since vacuum is a perfect insulator Heat sinks used by 'Mechs in atmosphere generally rely on air currents to carry heat away from the BattleMech, and normal 'Mech heat sinks must 1A modified for them to work in vacuum at all. BattleMechs which have not been painted silver (see below) in ordert reflect sunlight efficiently will pick up 2 additional heat points every turn tho are on level, open ground. They will pick up only 1 extra point of heat evel turn they are on rough terrain-which assumes that they are in shadow least half of the time. BattleMechs which move into rough terrain may have their pilots speciII that they are entering shadow in order to cool off. If there is ever doubt (sud as when a BattleMech falls during combat), the matter can be settled 4 rolling 1 D6: on odd results, the'Mech is in sunlight and will pick up 2 poira of heat per turn, while on even results, the'Mech is in shadow and will pid up no extra heat at all. 'Mechs which run at greater than normal speed (due to the effects d lower gravity) gain one extra heat point. This is in addition to the normal he build-up from running. 'Mechs which attempt to jump gain 2 extra points heat in addition to other heat gains, no matter how far they jump. Though vacuum is an excellent insulator, rock is an excellent conductor of heat. 'Mechs can lose heat rapidly in shadowed areas on vacuum world where waste heat can "soak off" into the cold rock. 'Mechs which enter shadow in rough terrain lose one extra heat poll each turn they remain in shadow, so long as they do not move or fight, 'Mechs which lie down in shadowed areas (thereby exposing more of their surface to cold rock) can lose 3 heat points per turn. Heat losses due tot shadow are in addition to other points lost through heat sinks. OTHER NOTES In a BattleTech or MechWarrior campaign, if it is known in advance that a BattleMech unit is going to be operating on a vacuum world, the unit's Techs should be given the opportunity to ready each 'Mech for vacuum operations. This process includes modifying the vehicle's heat sinks, changing lubricants and hydrolic fluids to substances which will keep working in vacuum, and painting the hull with a highly reflective silver paint. This conversion requires 2D6 hours per'Mech. If it is not performed, the 'Mech will have problems with heat build-up (see above). There is also a chance that the arms or legs will freeze up due to the failure of lubricants or hydrolic fluids in vacuum. Each hour that the 'Mech operates in vacuum, it will receive one internal hit in any arm or leg (rolled randomly). These hits can be repaired only by servicing the 'Mech (in a pressurized workbay or area) for one hour for each hit... and then by performing the maintenance described above. Recoil can cause unforeseen problems in low-gravity fields. While mass is unaffected by gravity, the lower weight of the firer can interfere with his ability to handle the recoil of a weapon he is firing. In BattleMechs, the 'Mech's changed handling characteristics can throw the pilot's aim and reactions off slightly. In gravity fields less than .4 of Earth's, an additional DM of +1 is added to all attempts to fire weapons which cause significant recoil. Lasers cause no recoil at all, while the reocil from machine guns is too low to cause problems for the firer. Autocannons, PPCs, and missiles, however, cause a great deal of recoil, and the DM+1 should be applied to each attempt to hit with these weapons. MechWarriors using the rules for extending personal weapon range (0102-A) may find their accuracy with projectile weapons affected at Extreme or Maximum Range. This is because the sights for such weapons take into accountthe fall of the projectile in a 1 -G gravityfield. On worlds with surface gravities less than.4, attempts to hittargets at Extreme or Maximum Range with single shot fire have a DM of +1 added to each roll against a To Hit target. This is not applied to laser weapons of any kind, or to auto-fire weapons using burst or full-auto fire. (Full-auto fire is not aimed in the conventional sense and is not subject to this restriction.). This effect can be eliminated during MechWarrior campaigns by having the MechWarriors or their Techs re-sight aimed-fire projectile weapons to take the change of gravity into account. Thirty minutes spent with each weapon will allow the sights to be adjusted for the planet in question. However, the sights must be readjusted if the weapon is taken to another world, and yet another surface gravity. Those rules variants applying to heat on airless worlds assume that the moon or planet is within a star's ecosphere; that is, it receives approximately the same heat and light from its star as Earth does from Sol. Worlds closer to the system's sun (such as Mercury in Earth's system) will receive much more heat-and BattleMechs operating on their surface under the light of the local star will overheat and shut down very quickly. Worlds outside the local star's ecosphere will receive less heat and light than Earth does from the Sun, and BattleMechs may have problems from cold rather than heat. The effects of a range of temperature on BattleMechs are too extensive to be dealt with here and will be the subject of a future BattleTechnology optional rules variant. Until those rules are published, players and referees must assume that combat is taking place in an area where local temperatures are between Oo C. and 30' C.-more or less within the range of average temperatures on Earth. Earth's moon, after all, lies at the same mean distance from the Sun as does Earth, but the surface temperature ranges from -170 degrees C. to above the boiling point of water, depending on whether it is day or night. On worlds such as Valdis I (described in this BattleTechnology issue's Worldbook) a narrow band near the world's terminator-the demarkation line between night and day-will have such temperatures, even though it is boiling hot on the dayside, and freezing cold on the nightside. Depending on the planet's rotation, BattleMechs may be able to operate for anywhere from less than an hour to many hours before the temperature rises or falls so much that the 'Mech becomes incapacitated. Chemical flamers require oxygen to produce a flame and will not work in vacuum. BatleMech-mounted fusion flamers will operate in vacuum. However, they cannot be used to set fires in target hexes. These rules are designed to add the flavor of movement and combat in low-G, vacuum environments to BattleTech and MechWarrior simulations. Necessary details about the surface conditions of such worlds-surface gravity, atmosphere composition and pressure, and similar data, are provided in BattleTechnology's continuing Worldbook columns, and in other articles and features in this magazine. These rules would serve well for combat on Fire, the moon of Brimstone described in the Worldbook for BattleTechnology, Issue 0101. They could also be applied to combat on Valdis 1, described in this issue's Worldbook; or to combat on Gordo, the large moon described in this issue's BattleTips column. As with all such rules variants, their use is optional and at the discretion of the players and the referee. They are intended to add realism to simulations set on alien worlds with conditions markedly different from conditions on Earth, but applying these rules should not be allowed to overly complicate play or detract from the excitement of a BattleTech game. Individual referees and players alone can determine that balance of realism versus playability which they best enjoy. Back to BattleTechnology 3 Table of Contents Back to BattleTechnology List of Issues Back to MagWeb Magazine List © Copyright 1988 by Pacific Rim Publishing. This article appears in MagWeb (Magazine Web) on the Internet World Wide Web. Other military history articles and gaming articles are available at http://www.magweb.com