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# Hybrid Railgun Ram Accelerator

 (+1) [vote for, against]

First, let's consider the prior art, the Ram Accelerator.

These are a type of mass accelerator which consist, more or less, of a long tube which is filled with a mixture of fuel and oxidizer, with thin, disposable diaphragms at each end to keep the fuel/air mix contained.

A specially shaped projectile is shot through one of the diaphragms, the gas inside the tube is compressed between the projectile and the tube walls, the compression causes heating, and the heating causes gas to combust. If the projectile is moving faster than the flame propagation speed, most of the combustion occurs immediately behind the projectile.

Since the gas pressure behind the projectile is higher than in front, it continuously accelerates for as long as it's in the tube.

This idea is to choose non electrically conductive materials for the diaphragms, a conductive material for the tube, and string a conductive wire from one diaphragm to the other.

Next, we electrify the wire and tube, supplying a high DC voltage which is slightly less than the breakdown voltage of the fuel/air mix. We make sure that our power supply can supply a nice, high current, once an arc is established.

Finally, we shoot a hollow conductive projectile through the tube, with a high starting velocity. As it pierces the first diaphragm, inertia keeps the wire in place, as the projectile is going to fast to give the wire a chance to fall.

Since the tube is filled with combustible gas, and the projectile is appropriately shaped, the same thing begins to happen as occurs in a ram accelerator.

Since the starting voltage is so high, and the projectile is conductive, electricity arcs from the wire, through the projectile, to the wall of the tube.

The electric arc adds thermal energy to the burning fuel/air mix, and thus increases thrust.

In addition, there's a flow of electricity down the wire, through the projectile, and back up the tube, which creates a magnetic field. There is a current flow through the projectile at 90 degrees through this field. Thus, we have electromagnetic thrust.

How much speed can be achieved by adding together combustion and high current, I do not know, but it would be exciting to find out.

 — goldbb, Mar 21 2016

//How much speed can be achieved by adding together combustion and high current// Well, speed of sound in H2 is about 4,200 ft/sec.
 — FlyingToaster, Mar 22 2016

At least it's not in Other:Gen … Oh, wait …
 — 8th of 7, Mar 22 2016

I did not know one could have so many different kinds of thrusting at once!
 — bungston, Mar 22 2016

 I suggest getting rid of the wire and conductive tube, and just using the standard two conductive rails.

 Three reasons: 1. I'm not sure an arc will improve the propulsion much, and I see no other reason for it beyond reduction of sliding friction. Railgun rails already have low friction. 2. Furthermore, the arc is going to be very difficult to strike against the inside of the tube, which has negative radius of curvature. At least put a sharp ridge on the inside of the tube to strike the arc against. 3. The wire is going to fall against the tube after the projectile has passed, causing a short circuit.

Sure, the rails will split the gas into to separate flows around the projectile, but I don't think that's a problem. It should still ram just fine.
 — notexactly, Mar 27 2016

That reminds me…
 — Ian Tindale, Mar 28 2016

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