Railgun

Jowan knows Fireball XL5, and that's got the railgun.

It has a loading bay on which factory units are built. The loading bay can merge streams of completed factory units onto a launch rail. The launch rail has many acceleration points which kick each passing unit faster. The departure velocity is sufficient to put each unit into Mercury orbit. The orbit needn't be high, there's no atmospheric drag to consider, just don't graze mountains.

Each kicker is powered by one or more railgun power storage units and direct Surface power collector connections which can be wired rather than broadcast. The power storage augments and smooths the kick. The initial idea is a bank of super-capacitors.

A factory unit of 20 tonnes leaves an 84km rail at 4.1km/s with an acceleration of 100m/s² after 41 seconds. There is no atmosphere to plane on. The kicker could lift the unit from the rail as well as kick

Moving the decimal points, an 8.4km track at 1km/s² after 4.1 seconds sounds extreme but it's the same sum. It's all dependent on the power input. The advantage of the second sum is that the track only has to handle 120 units at any given moment instead of 1200, and everything is lighter.

Either way we may have cold night-only launches to get rid of the heat and maybe use superconductivity.