Dr. Fair's Nutty Ideas Project

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How to build railguns and coilguns, continued...
                            
Sunscreen for Hell     

During the mid-70s, the U.S. Army had a project to double the range of the 155 mm howitzer without changing its hardware. Army researchers replaced its standard single base nitrocellulose propellant with a triple base propellant of nitrocellulose, nitroglycerine and nitroguanidine. This gave the howitzer the extra range, but at the cost of raising the temperature of the combustion gasses. This, in turn, caused a phase change in the gun barrel steel. Instead of being good for thousands of rounds, barrels wore out after a few hundred shots. The user community said they couldn’t live with this.

This problem of the propellant softening gun barrel steel was a crisis of sunken money and careers on the line. The inventors of the new propellant brought in Fair and his fellow physicists to save their hides. Dr. Harry Fair's team tested a formulation the Swedes had invented to extend the lives of their guns: titanium oxide (a white powder) mixed with wax, similar to what dedicated surfers wear on their noses, basically a sunscreen for hell.

It worked. Fair and his people were heroes.

One day in 1987, sitting with me in his office at the old DARPA building, Fair told me that this project was what made him realize that they needed to find a radically new propulsion technology. “We used to get together for Reuben sandwiches at the Mt. Hope Inn and talk about this. We came to the conclusion that chemical propulsion had reached its asymptote,” in part because “It’s been under development for a thousand years,” for both guns and rockets.

Newbie note: Asymptote is the part of a graph where a curve that had been going upward pretty much levels out. Basically, an asymptote shows that whatever the graph measures isn't changing much any more.

Fair’s team spent weeks talking about alternatives. The equation for kinetic energy was their talisman, and space their Holy Grail. An object in low Earth orbit moves at 9 km/s (32,400 km per hour or about 19,000 miles per hour) with respect to an object on the surface.  According to the equation for kinetic energy, such an object possesses just 40.5 KJ/kg, or 1 ¼ kilowatt hours per kg worth of kinetic energy. What if it were possible for a gun to apply this kinetic energy with perfect efficiency? With electricity at ~4 cents per kilowatt hour (at the time), perfect efficiency meant –  holy cow! – space launch for a dollar per kilogram.

Newbie note: KJ is short for kilojoule or one thousand joules, a measurement of energy. A joule is equal to 1 watt for one second. A 100 watt incandescent light bulb can run for twelve and a half hours on 1 ¼  kilowatt hours of electricity, the same amount of energy it takes, with perfect efficiency, to put a kilogram into low Earth orbit.

Nutty Ideas

Of course no gun could have perfect efficiency, but Fair and his colleagues enjoyed scheming how to get something nearly this good. “We looked at catapults, storing energy in rubber bands,” Fair says, laughter in his voice. “We called it the ‘Nutty Ideas’ project.”

Eventually, says Fair, two realistic solutions stood out, both based upon electromagnetic forces: railguns and coilguns.

Fair’s team knew that these guns would need magnetic field densities in the range of 3-4 Teslas, but they saw this as solvable. Replace iron with air and increase the number of windings. Just a matter of engineering. However, as it later turned out, while the basic physics is easy, the engineering was way harder than any of us expected.

Why building super powerful magnets is hard to do --->>

The next step for Fair was to find out what, if any, research was being conducted on electromagnetic launch (EML). He soon discovered that back in the early 70s, Princeton physics professor Gerard K. O’Neill had become an EML gun enthusiast. Unlike Fair, O’Neill had confidence that chemical propulsion technology was bound to get exponentially better, but paradoxically this belief led him to become an EML advocate. According to NASA’s 1974 projections, by 1981 the Space Shuttle would be lofting payloads at a marginal cost of only $160/lb ($352/kg), and all this for a total investment of just $5.5 B. For only another $1 B, NASA officials promised that they could modify the shuttle to deliver payload at $70/lb. In 1975, one NASA official promised that if the “large technology movement caused by shuttle continues to be supported,” by 2000 they could loft payloads for $25/lb ($55/kg).

More --->>

 

 
       © 2013 Carolyn Meinel