In simplified terms the original HYPACC was a giant static air gun that used water pressure to contain and compress air (air is not so good for the job as it is too heavy).

The new version HYPACC 2, is more like a single stroke engine that rises from the seabed and accelerates toward the surface. At a point near the surface its top opens and uses water like a piston to pump hydrogen to a massive pressure (like an air gun).

The hydrogen is not mixed with oxygen so it does not burn. Hydrogen is the fastest, lightest gas and delivers the pumped up energy to the projectile with greatest efficiency. To help get the ‘engine’ moving as fast as possible the same idea as a ‘water-rocket’ is used beneath to accelerate the whole thing upward.

The key to making it work is to have an empty (rarefied) cylinder at the top for the water to rush into. This is done with a mixture of hydrogen and oxygen, which is ignited. Once burned it forms steam, which, in turn, condenses to water, leaving a vacuum cylinder for the water to fill.

In effect this sucks the whole thing upwards, helped along by the water-rocket below. The water rushing down the cylinder is about to have a head-on collision with the device that is shooting up. Hundreds of tonnes of water are crashing towards hundreds of tonnes of steel with a pocket of hydrogen gas standing between them.

The energy from that collision pumps the hydrogen to thousands of atmospheres, firing the projectile out of the barrel.

Hydrogen pump guns are a proven technology, most notably demonstrated by the ‘SHARP’ gun (after Gerald Bull’s HARP project) developed by the Lawrence Livermore laboratory.

HYPACC 2 is an alternative way of achieving the same result. The two main drawbacks to a full-scale version of SHARP are firstly, finding an appropriate site and secondly, constructing a recoil mechanism that will deal with the colossal forces involved. HYPACC 2 eliminates these problems.

It can be sited directly on the equator as with the ‘Sea Launch’ system, far from human habitation. The entire device is free-floating and has no need of mechanical recoil.

The density of the atmosphere at sea level is a disadvantage to a purist orbit gun but I am convinced the role of a super gun is most suited to a hypersonic accelerator for scramjet drones.

Large payloads of tough freight delivered to low-orbit staging would be the key to exploiting the bounty of our near space. 

The upper cylinders in the animated sequence have been adapted for the sake of clarity. The proportions of the device would be far longer relative to diameter than shown. The hydrogen ‘pump cylinder’ in the animation may be rendered unnecessary with a hydrogen rich burn leaving residual gas or liquid hydrogen injected at the appropriate moment via a heat pile. The cylinders may also be arranged to stagger the pump sequence behind the projectile along the barrel length (as with the V3).