Haha, no in universe background yet, aside from hints in the rules. :P
Construction Rules:
These protomechs are built almost entirely in the same manner as clan protomechs. The internal structure, engine, cockpit, jump jet, and heat sink mass are all calculated in the same manner.
Inner Sphere protomechs do not have access to clan grade protomech armor, and must instead make use of armor equivalent to that used by support vehicles (Tech Manual Page 134) Armor of any barrier armor rating up to tech level E may be selected, however if Tech Level E BAR 10 armor is chosen, the armor occupies one of the protomech's torso weapon slots.
The typical armor utilized on these protomechs is Tech Level D BAR 10 armor, and weighs 63 kilograms per point.
Inner Sphere protomechs may mount any inner sphere ballistic and energy weapons that normally occupy six or fewer critical slots on a battlemech. As with clan protomechs, ammunition is allocated per shot, and energy weapons must have enough heatsinks (at 250 kg per heatsink) to dissipate all the heat they create.
Inner Sphere missile systems are added on a per-tube basis just like clan missile systems. Inner sphere protomechs may not mount MMLs. Thunderbolt missile launchers may be added in the same manner as standard ballistic weapons.
Missile Launcher weight per tube (IS)
LRM: 400 kg
SRM: 500 kg
Streak SRM: 750 kg
MRM: 300 kg
Rocket Launcher*: 50 kg
ELRM: 900 kg
NLRM: 600 kg
Mech Mortar: 800 kg
*Rocket Launchers are one shot weapons, and thus do not require additional mass for ammunition. The range of the rocket pack is dependent on the number of tubes it includes. 1 to 10 tube packs use the range of the Rocket Launcher-10. 11-15 packs use the range of the Rocket Launcher 15, and packs larger than 15 use the range for the Rocket Launcher 20
Missile Ammunition weight by type (IS)*
LRM: 8.33 kg per missile
SRM: 10 kg per missile
Streak SRM: 10 kg per missile
MRM: 4.17 kg per missile
ELRM: 11.11 kg per missile
NLRM: 8.33 kg per missile
Mortar: 31.25 kg per shell
*Protomechs equipped with improved one shot versions of their missile systems do not need to pay additional mass for the single shot of ammunition.
Other weapon ammunition weight by type (IS)
AC-2/LB-2X/LAC-2/UAC-2/RAC-2: 22.22 kg per shot
AC-5/LB-5X/LAC-5/UAC-5/RAC-5: 50 kg per shot
LB-10X: 100 kg per shot
Light Gauss Rifle: 62.5 kg per shot
Light/Standard Machinegun: 5 kg per shot
Heavy Machinegun: 10 kg per shot
Vehicle Flamer: 50 kg per shot
Plasma Rifle: 100 kg per shot
AMS: 83.33 kg per shot
Narc Beacon: 166.67 kg per shot
Improved Narc Beacon: 250 kg per shot
Sprayer (mech): 100 kg per shot
Fluid Gun: 50 kg per shot
Hyper Velocity AC-2: 33.33 kg per shot
Hyper Velocity AC-5: 66.67 kg per shot
Magshot Gauss Rifle: 20 kg per shot
Light Rifle: 55.56 kg per shot
Medium Rifle: 111.11 kg per shot
Heavy Rifle: 166.67 kg per shot
Battlemech Taser: 200 kg per shot
Thunderbolt-5: 83.33 kg per shot
Thunderbolt-10: 166.67 kg per shot
Thunderbolt-15: 250 kg per shot
Thunderbolt-20: 333 kg per shot
Additional Equipment Available to Inner Sphere Protomechs
While the original clan program was intended to produce cheap, easy to construct combat platforms, the Helenstern program desired a more multi-role special operations platform. As such, a wider array of equipment was adapted for use by the Helenstern protomechs.
A Pods*
B Pods*
Anti Missile System
Narc Beacon
Improved Narc Beacon
Beagle Active Probe
Guardian ECM
TAG
C3 Slave
C3 Command**
C3i
Communications Equipment
Sprayer (mech)
Bloodhound Active Probe
Angel ECM
Chaff Pod
Remote Sensor Dispenser
Vehicular Mine Dispenser
Vehicular Grenade Launcher
M-Pod
Protomech Melee Weapon***
*A-Pods and B-Pods must be torso mounted, and may be detonated during any weapon attack phase, inflicting damage in accordance with standard rules found on Total Warfare page 130.
**The C3 Command Computer may only be mounted on Ultraheavy protomechs
***The Inner Sphere Protomech Melee Weapon is functionally identical to the clan version.
Exotic Equipment
The Helenstern program has also produced a few examples of exotic equipment to augment their experimental protomechs, with at times only questionable results.
Fuel Cell and Electric Engines: Researchers experimented with non-fusion engines not as a way to reduce cost, but as a way to reduce the protomech's sensor signature. Though functional non-nuclear engines were developed, they never managed to meet expectations.
Rules: A fuel cell engine weighs 1.25 times the mass of an equivalent fusion engine, while an electric engine weighs a prohibitive 3 times the mass of a fusion engine. Both types have a short range (100 kilometers) and, because they were custom built for a highly specialized role, offer no cost savings over standard fusion engines
Triple Strength Myomers: Devised as a relatively easy means of boosting protomech performance, there remain a few hurdles to overcome. The high heat required by modern versions of the myomers made them wholly unsuited to use by protomechs. As such, the Helenstern project went back to the original formula, with all its limitations
Rules: These triple strength myomers grant all the bonuses and penalties of prototype triple strength myomers (Interstellar Operations page 104). For absolute clarity, triple strength myomers double the damage of a protomech frenzy attack (as well as doubling the damage bonus of any equipped protomech melee weapon), and double the protomech's lifting capability. They also impose penalties to maintenance and repair, and remain susceptible to green gas munitions, as detailed in Interstellar Operations.
Stealth Armor: Perhaps due to wishful thinking, the Helenstern made a valiant attempt at adapting battlemech stealth armor to a protomech. The result is arguably functional, but the extra mass required to support the armor limits what such stealth mechs can actually do on the field.
Rules: Stealth armor weighs 63 kg per point of protection, requires an ECM of some sort to function, and additionally requires that ten heat sinks (above those already required for weapons) are included in the design. Once you have all of that, it functions exactly like battlemech stealth armor (total warfare page 142)
Full Sized Cockpit: While the first protomech cockpits produced under Helenstern were of the same standard design adapted by the Word of Blake (complete with the need to remove limbs to fit an adult pilot), Director Gutenberg acknowledged the concern that relying on such extreme measures would greatly limit their available pool of potential pilots. Her original solution of employing adolescents was likewise deemed impractical for widespread deployment. As an alternative, engineers adapted the enlarged cockpit developed for ultra-heavy protomechs to the smaller designs.
Rules: This simply allows the use of the ultraheavy protomech cockpit on standard sized cockpits. As a refresher, the ultraheavy cockpit masses 750 kg, includes an ejection system, and can accept a normal sized pilot.
Mixed Tech:
If built as a mixed tech design, the protomech may be equipped with clan weapons, standard protomech armor, or tech level F support vehicle armor up to a barrier rating of 10 (tech F BAR 10 armor occupies a single torso weapon slot, so the only reason to use it over true protomech armor in this case would be fluff related).
Be wary that your mixed tech design doesn't turn into a straight clan protomech. Otherwise, what's the point of all this writing I've done?
