Since I have such a thing for mecha, I thought i'd practice my writing by working on a novel of sorts based around giant robots, so I'm posting my notes here just because. The science is probably wrong but eh, I'll work that out later, these are just scratchings anyways. I got a lot of inspiration for this from Tsutomu Nihei's "Knights of Sidonia", among other things like Hiroshi Sakurazaka's "All you need is KILL". Reading those gave me this idea, so time to work it and see what happens.
Mechs are launched from ground level by massive building sized electromagnetic accelerators, which are aligned into an octagonal pattern, every set of eight (which is equal to one octagonal pattern) having its own miniature power plant supplying energy to each. When mooks are present within Earth-atmosphere they are launched at 25% charge at a lower angle to avoid being shot out of the atmosphere. All of the Mechs have a weird cylinder that provides near perfect electromagnetic resistance to avoid equipment damage during launch. This peels off naturally when their velocity reaches a certain point. When fired at a lower angle for an IEAA (In Earth Atmosphere Assault) the pilot must trigger it's release, which can be accomplished by a sharp auditory gesture, such as screaming "RELEASE". Optional phrases can be programmed in to fit pilot specifications (Aka: manly moments of screaming fiery fury)).
The bolts holding the shell around the Mech trigger their detonators and a set of rocket engines situated at key points fire, creating enough thrust to propel each half of the protection cylinder away from the bot within a very short amount of time to prevent the pilot from being caught with his pants down and shot to death. Should direct space action be needed, the Mechs can be loaded into ships and fired off in a similar fashion to an IEAA. The canister they are placed in is designed to burn up in the Earth's atmosphere to prevent possible property damage/injury and loss of life should the halves find themselves aimed towards population centers. Since the launch sites themselves where required to be located at least 20 miles from any populated areas this isn't an issue, the canister halves are recovered and either repaired or recycled for scrap parts for future use.
There are hundreds of these sites on the surface of the planet, most located underground in isolated, and otherwise inhospitable areas such as deserts or large stretches of open Jungle to prevent human casualties should they ever be attacked. Smaller silos for population protection are located several miles from their assigned cities, to act as a temporary countermeasure to mook attack before a larger defence force can supply nessesary
The accelerators launch the pods at increadibly high speeds, depending upon the situation and the electromagnetic charge supplied, the canisters can easily reach speeds high enough to allow them to escape the atmosphere into hard vaccum within a few seconds. During an IEAA this speed is reduced depending upon the distance away the conflict area is.
The railguns themselves are retractable and heavily armored. At their maximum exposal they measure in at two hundred feet, with a diameter of sixty. This isn't really nessesary seeing as it is rather risky exposing the launch rail to such an extent, and in reality there aren't any advantages to doing so other than a faster cool-down rate/easier access to attempt repairs to their internal mechanisms.
To counteract the massive amounts of force applied to the pilots themselves, they are issued special suits that contain an area of a strange electrically charged fluid that emits waves around the wearer that tends to cancel out up to eighty percent of the wearers inertia, while dampening the forces hitting them while being launched into space. These also act as a survival aid should the pilot find himself required to ejects in the middle of a dog-fight, providing extensive protection from the elements, while also allowing one to recycle their bodies waste into a potable water source should they be required to survive until their unit can come and pick them up. It also acts in a similar way to kevlar to provide protection from injuries sustained in combat, and any combat related situations outside the cockpit.
The pilots are all given standard issue .45 caliber side arms for personal protection. Though some pilots where known to replace them with far more exotic weapons.