The ice gun is a barbell-shaped ramjet flying in a tunnel cut through antarctic ice sheet and filled with hydrogen at about twice the atmospheric pressure. Forward half of the ramjet is the umbrella projectile carrying cargo, while the aft half carries liquid oxygen. Upon leaving the gun, the aft half separates and disintegrates in the atmosphere. To reduce the stress of acceleration force on the cargo, the tunnel is about 1000 km long and the projectile employs hydrogen injection. The ice gun belongs to the transverse gas gun family because the hydrogen flow is transverse to the projectile direction. The maximum velocity is about 8 km/s. There is no bibliography. The minimum mass is only 100 tons not counting the ice.
The ice gun stands out due to its low cost (less than 1% of the cost of chemical rocket launchers) and the ability to carry fragile cargo and people. Its only shortcoming is the reliance on the ice sheets which are melting due to global warming. A short version of the gun also deserves attention. For example, a 100 km long gun accelerating projectiles to 4.4 km/s would expose the cargo to the acceleration of 10 G, and would be one order of magnitude more economical than the chemical rocket launchers.
At launch the ramjet is placed behind the breech of the gun. When the breech valve is opened, hydrogen flows through the ramjet at about 1 km/s; fast enough to generate thrust. To improve ramjet performance at low velocity, the bore of the gun is smaller at the breech. There is no direct contact between the ramjet and the ice. When the ramjet approaches the muzzle, the muzzle valve is opened. Hydrogen flows forward through the valve at about 1 km/s, thereby increasing the maximum velocity of the ramjet.
A small amount of oxygen is added to the hydrogen. There should be too little oxygen in the mixture to sustain combustion, yet enough to eliminate the need for flame holders and to reduce the mass of oxygen carried by the ramjet. Combustion of 1 ton of oxygen is sufficient to heat up 5 tons of hydrogen to 2000 K. If the ramjet flies in pure hydrogen, about 80% of its mass is oxygen. If the ramjet flies in the mixture of hydrogen and oxygen, less than 60% of its mass is oxygen. To reduce the mass of oxygen carried by the ramjet, the temperature of the exhaust gas is high only at the end of acceleration. Hydrogen is difficult to transport, so it has to be produced on site, probably by wind-powered electrolysis.
To prevent melting of the ice, the breech must be lined with steel. Wet, frozen newsprint may be used as the liner in the area exposed to sonic boom. This material is also suitable for downsized models of the ice gun. Having built and tested the models at different hydrogen pressure, we can estimate performance of the real ice gun. The tensile strength of plain ice is about 1.5 MPa. Frozen newsprint is one order of magnitude stronger.
The tunnel consists of a multitude of short adits made with large hole saws. Having cut a cylindrical block of ice, the saw breaks off the block with the so called core dogs, withdraws to the surface, dumps the block, and returns to the adit. A new adit begins at the surface of the antarctic ice sheet. At a depth of about 100 meters the adit turns and continues horizontally until it reaches the tunnel. When the tunnel is finished, the upper ends of the adits are plugged with ice.
Gravity moves the antarctic ice sheet. The fast moving part of the sheet, called ice stream, flows about one kilometer per year. A tunnel excavated perpendicularly to such a fast flowing ice would soon be deformed so much that the cargo would experience excessive perpendicular forces. To avoid this problem, the tunnel is excavated in a nearly stagnant ice, in the direction of the ice flow. Another potential problem is gradual collapse of the tunnel due to stress in the ice.
C. R. Bentley, "Ice Thickness and Physical Characteristics of the Antarctic Ice Sheet," Antarctic Map Folio Series, Folio 2, American Geographical Society, New York, 1964.
C. R. Bentley, "Subglacial Rock Surface Topography," Antarctic Map Folio Series, Folio 16, American Geographical Society, New York, 1972.
L. Crossley, Explore Antarctica, Cambridge University Press, Cambridge, 1995.
N. K. Vasiliev, "On development of fibre-ice-composites," Cold Regions Science and Technology, Vol. 21, No. 2, January 1993, pp. 195-199.
High-resolution topographic maps of Antarctica are available from Radarsat.
Curator: Al Globus
NASA Responsible Official: Dr. Ruth Globus
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